CH637097A5 - Method for producing foam glass and then made foam glass. - Google Patents

Abstract

The known technique for manufacturing porous glass with closed pores, wherein the glass foam is rapidly cooled and nearly frozen, gives a relatively thin pore glass. Nevertheless, in order to improve the thermal insulation characteristics of the porous glass, which are essential when it is used as construction and insulating material, a relatively coarse porous structure is desired. To obtain such a structure, the glass foam is submitted to inflation until most part of the lamillar walls situated between the different bubbles of the foam are tom and a plurality of neighbouring bubbles merge into a single cavity. During inflation, the influence of heat on the glass foam is maintained after its formation and/or the ratio between the average gas pressure in the foam bubbles and the pressure acting from outside on the foam is raised to a value higher than the value of this ratio obtained with the formation of the foam and/or the surface tension of the glass forming the lamellar walls, opposing to the gas being in the bubbles of the foam as well as the resistance to the glass pressure are brought down to values lower than those obtained with the formation of the foam.

Description

       

  
 

** WARNING ** beginning of DESC field could overlap end of CLMS **. 

 



   12.  Method according to one of the claims 1 to 11, characterized in that the raw mixture is heated in a mold, preferably in a mold made of dried or fired clay or other ceramics or in a suitably separable one, in order to avoid the raw mixture cake from spreading apart during the expansion or post-expansion process Metal mold made of scale-free steel or another metal. 



   13.  A method according to claim 12, characterized in that for the production of an at least partially encased foam glass molded body, a mold forming the shell of the produced molded body, preferably a thin-walled mold made of pre-fired or dried clay or ceramic, is used after the manufacturing process. 



   14.  Method according to one of claims 1 to 11, characterized in that a core or carrier body, preferably made of ceramic, is introduced into the raw mixture to produce a cellular glass body with a solid core or carrier at least partially covered by cellular glass. 



   15.  Method according to one of claims 1 to 14, characterized in that the raw mixture in the dry or dried state in a preheated oven, its oven temperature below the enclosing temperature, at which the blowing agent granules are enclosed in a gas-tight manner by the mass forming the raw mixture cake and preferably between 400 "C and 700" C, or placed in an oven zone of appropriate temperature and in the oven or 

   the furnace zone is first heated to approximately the temperature prevailing there and the raw mixture cake that forms subsequently, preferably within 20 to 60 minutes, by increasing the furnace temperature or shifting it to a higher temperature in the furnace zone to the temperature range required for the formation of the glass foam Enclosure temperature and the transition temperature of the raw mixture cake to a thin, flowing mass, which causes the forming bubbles to rise to the surface, of the raw mixture cake, and preferably falling in the range from 700 ° C. to 9000 ° C., is then further heated and then the post-expansion process is carried out and that foam glass formed thereafter, preferably within less than 30 minutes,

   by reducing the furnace temperature or moving it to a lower temperature furnace zone at least to a temperature near the upper limit of the transformation range of the glass forming the foam glass, preferably to a temperature falling in the lower part of the transformation range, and then, preferably with the interposition of a to influence the material properties of the finished aftertreatment process serving for foam glass, is allowed to cool to room temperature. 



   16.  Method according to one of the claims 1 to 15, characterized in that the foam glass formed is deformed in the warm plastic state at a temperature above the transformation range of the glass forming the foam glass. 



   17th  A method according to claim 16, characterized in that the foam glass is squeezed together to increase the thermal insulation in a predetermined heat flow direction in the direction parallel to this heat flow direction and thereby the cavities formed in the post-expansion process by combining a plurality of adjacent foam bubbles are flattened lenticular. 



   18th  A method according to claim 16, characterized in that the foam glass is pulled apart or extruded to increase the stiffness in a predetermined loading direction in the direction parallel to this loading direction and thereby the cavities formed in the post-expansion process by combining a plurality of adjacent foam bubbles in a spindle-shaped length will. 



   19th  A method according to claim 16, characterized in that the foam glass is deformed into a foam glass molded body of a predetermined shape. 



   20th  Method according to one of the claims 1 to 19, characterized in that for the production of foam glass with partially coarse-pored and partially fine-pored foam structure in the glass foam during the post-expansion process, an inhomogeneous temperature distribution with areas of substantially higher temperature than the areas prevailing during the formation of the glass foam of the same or only a slightly higher temperature than the temperature prevailing during the formation of the glass foam is generated in the areas provided for fine-pored foam structure. 



   21.  Method according to one of claims 1 to 20, characterized in that to increase the breaking strength, in particular the brittle fracture strength, of the foam glass on the inner walls of the cavities formed in the post-blowing process by combining a plurality of adjacent foam bubbles, essentially homogeneous over the wall surface, in the finished Foam glass surface layers leading to compressive stresses along the wall surfaces are generated. 



   22.  Foam glass produced by the method according to one of Claims 1 to 21, characterized in that the major part of the total cavity volume of the foam glass is formed by cavities, each of which has a cross-sectional area of at least 0.5 cm 2 in at least one cross-sectional plane running through the cavity . 



   The invention relates to a process for the production of closed-pore foam glass, in which a raw mixture containing at least glass powder and blowing agent is heated to temperatures above the transformation range of the glass forming the glass powder until the blowing agent by chemical reactions and / or thermal dissociation proceeding above this transformation range and / or evaporation, a blowing gas develops which initially forms spherical bubbles within the raw mixture cake that has been baked together by softening the glass powder grains, which bubbles continue to grow with the further development of gas while the cake is inflated,

   until the adjacent bubbles collide and then, as they continue to grow, form a polyhedral shape with the formation of lamella-like walls between the individual bubbles, and the cake thus changes into a glass foam formed by the lamella-like walls between mutually adjacent, approximately polyhedral foam bubbles.  The invention further relates to foam glass produced by this method. 



   Methods of the aforementioned type have been known for a long time, for. B.  from US-PS 2 233 608 and 3 811 851, CH-PS 426 601 and 473 741, DT-PS 2 028 666 and the book Silicate from W.  Hinz, VEB Verlag Berlin 1971, volume 2, pages 267, 268 and 283, 284.  With these known methods, however, it was only possible to produce foam glass with relatively small pore sizes, the maximum being of the order of millimeters



  will.  For example, in the aforementioned CH-PS pore sizes in the range from 0.2 to 2 mm and in the mentioned DT-PS pore sizes in the range from 0.1 to 1 mm are given as realizable values of the pore size.  The reason for this lies in the process technology used in the known processes, after the aforementioned transition of the cake into a glass foam formed by the lamellar walls between mutually adjacent, approximately polyhedral foam bubbles, i. H. 



  when the so-called optimal foaming is reached, the heating of the glass foam abruptly abruptly terminated, in practice referred to as a temperature shock, to temperatures within or just a little above the transformation range mentioned, because with this quenching the polyhedron glass foam formed is frozen, so to speak, so that a further one Development of the foam is no longer possible, and in the state referred to as optimal foaming, polyhedron glass foams can at least reach pore sizes of the order of millimeters in the case of the raw mixtures of waste glass powder and a few percent blowing agents that are usually used. 



  According to the prevailing view in the professional world, e.g.  in terms of how optimal foaming is expressed - further development of the foam was not desirable for manufacturing reasons, on the contrary, such a development should be prevented by the deterrent and instead the state of optimal foaming should be maintained and frozen, so to speak. This is because, due to bad experimental experience, it was feared that the polyhedron foam would collapse in further development beyond the state of the so-called optimal foaming. 

  In addition, there was also the opinion in the professional world that a more favorable foam glass structure than that of the so-called real polyhedron foam would not be possible and that improvements could only be achieved with regard to the fine structure, e.g. B.  - As described in the above-mentioned CH-PS - with regard to the internal structure of the lamellar walls mentioned or - as described in the above-mentioned DT-PS - with regard to the uniformity of the foaming at all points within the foam glass produced. 



   In fact, however, the foam glass with the structure of a real polyhedron foam produced by the previously known methods is by no means optimal with regard to the requirements to be placed on foam glass in practice.  In practice, foam glass - as can be seen in almost all relevant publications and publications - is mainly used as a building and insulating material, and it is primarily the thermal insulation properties of the foam glass that are important. 

  Of course, the strength properties of the foam glass also play an important role in this area of application, but in this respect there are usually so large reserves that a reduction in strength within these reserves can be readily accepted in order to improve the thermal insulation properties, and from that it follows that a foam glass structure is to be regarded as optimal with regard to the requirements in practice if it has the best thermal insulation properties of all foam glass structures that are possible. 



  The thermal insulation properties of a foam glass structure are now essentially determined by the shape and cross section of the aforementioned lamellar walls forming the foam glass, or in other words, the heat conduction of foam glass essentially results from the heat flow flowing over the lamellar walls in the direction of the temperature gradient, while that of the cavities enclosed by the lamellar walls practically do not contribute at all or only to a very small extent to the heat conduction. 

  As a result, the ratio of the volume of the lamellar walls to the total volume of the foam glass or  the density of the foam glass, which is proportional to this ratio with the density of the foam-glass material forming the lamella-like walls as a proportionality factor, is of crucial importance for heat conduction, because it should be clear that the heat conduction becomes greater, the greater the percentage of the volume of the heat-conducting lamella-like elements Walls or  the smaller the percentage of the volume of the non-heat-conducting cavities in the total volume of the foam glass becomes. 

  Therefore, in order to compare the thermal insulation properties of different foam glass structures to comparable ratios, one has to start from the same density of the foam glasses to be compared with each other and of course from the same foam glass material for the lamellar walls of the foam glasses to be compared. 

  Because now with a given density of a foam glass or  predetermined ratio k of the volume Vw of the lamellar walls to the total volume Vges of the foam glass, provided that the foam glass structure is essentially the same at all locations on the foam glass, each wafer-thin foam glass pane cut out in any cross-sectional plane of the foam glass has a ratio AVw / corresponding to the predetermined volume ratio Vw / Vges = k lSVges = Vw / Vge, = k of the volume AVw = d corresponding to the product of the total cross-sectional area Fw of the lamella-like walls and the pane thickness d. 

  Fw of the lamellar walls in the foam glass pane to the product of the total area Fges of the foam glass pane and the pane thickness d corresponding total volume AVge, = d.  Fges of the foam glass pane, the ratio Fw / Fges = d in a foam glass of predetermined density with essentially the same foam glass structure at all points of the foam glass in any cross-sectional plane.  Fw / d. 

  Fges = AVw / AVges = Vw / Vges = k of the total cross-section F ", the lamellar walls to the total cross-sectional area Fges at the interface equal to the constant k and thus the percentage of the total cross-section Fw of the lamellar walls in the cross-sectional area Fges of the same size in each cross-sectional plane, regardless of the special foam glass structure of the foam glass in question.  With the same density and the same foam glass material and even structure distribution, foam glass blocks of the same dimensions in mutually corresponding cross-sectional levels therefore have the same overall cross sections of the lamellar walls even with different foam glass structures.  

  Furthermore, if the cross-sectional areas in all of the cross-sectional planes perpendicular to the temperature gradient direction are the same size in these foam glass blocks, then, according to the above, the overall cross-sections of the lamellar walls in all of these cross-sectional planes are also the same size, and again also with different foam glass structures of the individual foam glass blocks. 

  The thermal resistance represented by such a foam glass block is in this case proportional to the ratio of the average length of the current paths of the heat flow flowing through the foam glass block in the direction of the temperature gradient to the overall cross section of the lamellar walls, which is the same size in all cross-sectional planes perpendicular to the temperature gradient direction, and because this overall cross section the slat-like walls are the same size under the aforementioned conditions, which apply to comparable conditions, even with foam glass blocks with different foam glass structures, there are differences in thermal resistance with different foam glass structures only

   if different average lengths of the current paths of the heat flows flowing through these foam glass blocks with different foam glass structures result from the different foam glass structure.  The specific thermal resistance of a foam glass structure therefore becomes a maximum or, in other words, the thermal insulation properties of a foam glass structure are optimal if this structure results in the greatest possible mean length of the current paths of the heat flow flowing through the foam glass structure.  The ratio of the effective mean current path length to the thickness of the foam glass block or  regarding the fictitious current path length resulting in the straight-line passage of the heat flow through the foam glass structure in the temperature gradient direction. 

  This ratio of the effective to the fictitious current path length is greater the further the heat flow has to run back and forth across the foam glass structure as it passes through the foam glass structure or 



  the greater the proportion of the path sections running transversely to the temperature gradient direction in the total current path length.  Since the current paths, as already mentioned above, run almost exclusively within the lamella-like walls, a foam glass structure is optimal with regard to its heat insulation properties if the greatest possible proportion of the lamella-like walls is transverse to the temperature gradient direction or  the smallest possible proportion runs in the temperature gradient direction, or in other words, if the shape of the cavities enclosed by the lamellar walls causes the greatest possible lateral deviations of the effective current paths from the associated fictitious current paths running directly in the temperature gradient direction through the foam glass structure. 

  However, this is not the case with the foam glass manufactured according to the previously known methods with the structure of a real polyhedron foam, because with a real polyhedron foam the shape of the cavities is roughly spherical, and in this case the effective mean current path length is only approx.  20% greater than the length of a fictitious current path leading straight through the foam glass structure, while other foam glass structures such as e.g. B.  Structures with lenticular flattened cavities to a ratio of the effective to the fictitious current path length of 2 and more or  on approx 



  twice as good thermal insulation properties as those of the foam glass produced by the known methods can come. 



   The invention was therefore based on the object of providing a process of the type mentioned at the outset for producing a foam glass which, owing to its structure, has overall more favorable properties and, in particular, better thermal insulation properties than that according to the known processes with regard to the requirements to be placed on foam glass in practice manufactured foam glass with the structure of real polyhedron foam. 



   According to the invention, this is achieved in a method of the type mentioned at the outset by subjecting the glass foam to a post-expansion process in order to achieve a coarse-pore foam structure until the predominant part of the lamellar walls coalesces between the individual foam bubbles and a large number of adjacent foam bubbles in each case form a single one Have united cavity and that for this purpose the heat on the glass foam is further maintained after its formation and / or the ratio of the average gas pressure in the foam bubbles to the pressure acting on the glass foam from the outside to a value above the value achieved with the formation of the glass foam Ratio and / or the surface tension of the glass forming the lamellar walls compared to the gas in the foam bubbles and the toughness

   of the glass forming the lamellar walls to values below the values of the surface tension or  of toughness. 



   The present method has advantages in two respects in terms of improvements in the thermal insulation properties of the foam glass produced.  First of all, by further inflating the glass foam in the post-inflation process with the volume of the lamellar walls remaining the same, the total volume of the foam glass is increased and thus the density of the foam glass is reduced, which, according to the above statements, leads to a reduction in the percentage of the total cross section of the lamella-like walls at the cut surface of a Cross section through the foam glass and thus to an increase in the specific heat resistance of the foam glass produced, which is inversely proportional to this percentage, or  leads to an improvement in the thermal insulation properties of the foam glass. 

  Furthermore, there is a significant improvement in the thermal insulation properties of the foam glass produced from the combination of a plurality of adjacent foam bubbles, achieved with the present method, into a single cavity.  This is because the cavities that form in this combination, which are relatively large compared to the pore size of the foam bubbles, in contrast to the roughly spherical foam bubbles in the horizontal direction generally have considerably larger dimensions than in the vertical direction and, due to the resulting coarse-pore foam glass structure, result in im essentially lenticular flattened cavities to relatively large lateral deviations of the effective current paths of the heat flow from the assigned,

   Fictitious heat flow paths running directly in the vertical direction through the foam glass structure and accordingly to a relatively large ratio of the effective to the fictional current path length, which, according to the above statements, significantly increases the specific thermal resistance of the foam glass, which is proportional to this ratio, or 



  a corresponding improvement in the thermal insulation properties of the foam glass results.  Overall, the increase in the ratio of effective to fictitious current path length, which can be achieved with the present method, in conjunction with the mentioned reduction in density, enables improvements in the thermal insulation properties of foam glass up to a factor of 2 and above. 

 

   In a preferred embodiment of the present method, the glass foam is heated in the post-expansion process to a temperature which is above the temperature prevailing when the glass foam is formed, and thereby both the gas pressure in the foam bubbles to a value above the pressure value achieved with the formation of the glass foam as well as the surface tension and toughness of the glass to values below the values of surface tension and toughness achieved with the formation of the glass foam.  In this preferred embodiment of the present method, the glass foam is preferably heated in the post-expansion process to a temperature which is 500 ° C. to 100 ° C. above the temperature prevailing when the glass foam is formed. 



   Advantageously, proportions of a substance can be added to the blowing agent which enter into a gas-developing chemical reaction with one of the substances contained in the glass foam only in the region of the temperature prevailing when the glass foam is formed or above it.  If the reaction temperature of this reaction is in the range of the temperature prevailing when the glass foam is formed, then this gas-evolving reaction alone can bring the gas pressure in the foam bubbles to a value above the pressure value achieved with the formation of the glass foam, i.e. H.  in this case, only a further heat effect on the glass foam after its formation is required to carry out the post-expansion process, but no increase in temperature thereof is required. 

  Nevertheless, the glass foam can of course also be heated in this case beyond the temperature prevailing during its formation, e.g. B.  to accelerate the course of the gas-evolving reaction and / or to further increase the gas pressure in the foam bubbles and to reduce the surface tension and toughness of the glass. 

  If, on the other hand, the reaction temperature of the gas-evolving reaction is above the temperature prevailing when the glass foam is formed, then further heating of the glass foam in the post-expansion process is absolutely necessary to initiate the reaction, at least to the reaction temperature. H.  under these circumstances, the temperature increase to the reaction temperature or  the resulting increase in gas pressure in the foam bubbles and the resulting reduction in surface tension and toughness of the glass are effective before the effect of the gas-evolving chemical reaction begins with a further increase in the gas pressure in the foam bubbles. 

  The reaction temperature should therefore expediently be not insignificantly above the temperature prevailing when the glass foam is formed if the post-expansion process is to be based primarily on the gas-evolving chemical reaction. 



   Instead of such proportions of a substance that enters into a gas-developing chemical reaction with one of the substances contained in the glass foam, or also in addition to this, the blowing agent can also advantageously have proportions of a substance that is evaporable in the post-expansion process and that is inert compared to the substances contained in the glass foam with a substance above that in the Formation of the glass foam prevailing temperature lying evaporation temperature. 

  In this case, too, for the same reasons as explained above for the reaction temperature of a gas-evolving reaction, the evaporation temperature should expediently not be substantially above the temperature prevailing when the glass foam is formed, if the post-expansion process is based primarily on the evaporation of said inert substance should, however, the evaporation temperature must in any case be higher than the temperature prevailing when the glass foam is formed, since otherwise there is a risk that the foam glass to be produced collapses during the post-expansion process. 



   Finally, in addition to the chemically reacting substance and / or the vaporizable substance mentioned, or instead of the same, portions of a substance which can be decomposed in the post-expansion process and which releases gas at a decomposition temperature above the temperature at which the glass foam is formed can also be added to the blowing agent will.  Here, too, the decomposition temperature should expediently not be substantially above the temperature prevailing when the glass foam is formed, if the post-expansion process is to be based primarily on the elimination of gas during the decomposition. 



   When using substances which evolve and / or evaporate and / or decompose and thereby release gas in the post-expansion process as a blowing agent, the reaction or  Evaporation or decomposition temperature is not significantly higher than the temperature prevailing when the glass foam is formed, the further inflation of the glass foam until a plurality of adjacent foam bubbles are combined to form a single cavity, mainly due to an increase in gas pressure in the foam bubbles above the pressure value achieved with the formation of the glass foam in addition, while one carried out in the blowing agent without such substances,

   solely on further heating of the glass foam beyond the post-expansion process based on the temperature at which it is formed, the further expansion of the glass foam is primarily based on reductions in the surface tension and the toughness of the glass. 



   In the present process, the glass foam is expediently formed in the temperature range between 7500 ° C. and 900 ° C., and the post-expansion process is advantageously carried out at temperatures in the temperature range from 8000 ° C. to 1000 ° C. or when fillers are added up to 1150 ° C. 



   For procedural reasons and with regard to the technical effort and in particular the energy required for the production of foam glass according to the present method, it is expedient to subject the glass foam to the post-expansion process immediately after its formation.  But it is also generally possible and in certain cases such as B.  When using glass powder with an exceptionally sharply falling surface tension and toughness of the glass above the temperature prevailing during the formation of the glass foam, it is also advantageous to subject the glass foam to the post-expansion process only after interposing a cooling phase and then to reheat it. 

  The glass foam can expediently be cooled to room temperature in the cooling phase and then heated again to a temperature above the temperature prevailing when the glass foam is formed in order to carry out the post-expansion process. 



   The invention further relates to foam glass produced according to the present method, which is characterized in that the major part of the total cavity volume of the foam glass is formed by cavities, each of which has a cross-sectional area of at least 0.5 cm 2 in at least one cross-sectional plane running through the cavity . 

 

   In a preferred embodiment of the foam glass produced according to the present method, in the majority of the cavities with at least 0.5 cm 2 cross sectional area, the cross section with the largest cross sectional area of the respective cavity has at least one, preferably two, intersecting at right angles, the or .  which are larger than the dimension of the cavity in the normal direction to this cross section.  With particular advantage for the thermal insulation properties of the foam glass, the majority of the cavities with at least 0.5 cm 2 cross-sectional area can be flattened roughly approximately in a lenticular manner in at least approximately the same flattening direction, which essentially corresponds to the normal direction mentioned.   



   Furthermore, in the foam glass produced by the present method, a metallic coating can advantageously be deposited on the cavity inner walls, at least in the majority of the cavities with at least 0.5 cm 2 cross-sectional area.  Foam glasses with such a metallic coating on the cavity walls have u. a.  usually have a relatively high resistance to brittle fracture. 



   The invention is explained in more detail below on the basis of general manufacturing technology and some exemplary embodiments of the present method. 



   A 50 to 99.5% by weight is expediently used for the production of foam glass by the present process. -%, preferably 80 to 99 wt. -%, raw mixture containing glass powder used. 



   Preferably, in the present method, glass is used for the glass powder, at least for the most part, with a transformation range that is at least partially within the temperature range from 500 ° C. to 6000 ° C. 



   In the present process, in particular when the foam glass produced is used as construction and insulating material, it is advantageously possible to use at least partially pulverized waste glass as glass powder for the raw mixture.  For the production of foam glass for the building industry, waste glass consisting of utility glasses, preferably bottle glass and other container glass, as well as pane glass, is expediently used. 



  For the production of foam glass for technical devices, in particular for thermal insulation and high temperature stresses, waste glass consisting of device glasses, preferably borosilicate glass and / or low-melting lead glass and / or high-melting silica glass, is expediently used. 



   The waste glass is expediently broken into glass fragments of less than 5 mm in size in a jaw crusher, and the splinters are then ground in a disk vibrating mill or a ball mill to give glass powder with grain sizes of up to 1 mm at most.  As a rule, the glass powder obtained in this way is used directly for the raw mixture in the present process, that is to say without being divided into grain fractions. 

  In particular in the production of foam glass for the building industry using the present method, it is recommended for cost reasons that the upper limit of the size range of the glass powder particles resulting from the grinding of the glass fragments is as high as possible or  just as permissible for a correct execution of the present method, since of course with a given disk vibrating or ball mill the duration and thus the costs of the grinding process become greater the finer the glass fragments have to be ground or  the lower the maximum grain size that forms the upper limit of the grain size range of the glass powder grains. 

  In this context, it should be mentioned that in the present process, even with a maximum grain size of 1 mm, a flawless process flow and good quality of the foam glass produced can be expected if the raw mixture in addition to glass powder and blowing agent certain fine-grained additives such as. B.  Clay contains, whereas in the known processes for the production of foam glass usually only glass powder with maximum grain sizes in the order of a tenth of a millimeter can be processed. 



   Of course, it is also possible with the present method and for certain uses of the foam glass produced is advantageous to grind the glass splinters more finely, e.g. B.  up to a maximum grain size of 0.5 mm or in special cases even up to a maximum grain size of 0.25 mm.  This is mainly possible if the aforementioned fine-grained additives are undesirable due to the intended use or for other reasons.  In this case, the raw mixture should expediently contain a proportion of very fine-grained glass powder, preferably with grain sizes below 50>, and for this purpose it is generally necessary to grind the glass splinters more finely than up to a maximum grain size of 1 mm. 

  If the glass powder resulting from the grinding process is used directly for the raw mixture, one can either proceed so that the glass splinters are ground to such a small maximum grain size that the proportion of very fine glass grains in the glass powder obtained increases as the maximum grain size decreases corresponds to the required proportion of very fine-grained glass powder in the raw mixture, or you can part of the glass splinters up to a first predetermined maximum grain size of z. B.  0.5 mm, in which the proportion of very fine-grained glass powder is still below the required value, and the other part of the glass splinters up to a second predetermined maximum grain size of z. B. 

   Grind 0.25 mm, in which the proportion of very fine-grained glass powder is already above the required value, and select the ratio of the one part to the other so that the mixture of the glass powder resulting from the two parts contains the required proportion of very fine-grained glass powder .  Another possibility, which comes into consideration in particular in the production of foam glass for technical devices and other special purposes, is to subsequently add the glass powder resulting from the grinding process, e.g. B.  with the help of a vibrating sieve machine to divide into several grain fractions and then to assemble the glass powder to be used for the raw mixture from certain fractions of the different grain fractions corresponding to the requirements in the production of the foam glass concerned. 

  The glass powder can advantageously be made from glass grains of a first grain fraction with medium-sized grains, e.g. B.  with a grain size between 125 and 250, a second grain fraction with fine grains, e.g. B.  with grain sizes between 50 and 125 pt, and a third grain fraction with very fine grains, e.g. B. 

   be composed with grain sizes below 50, u, and the proportions of the individual grain fractions can be appropriately chosen in order to achieve a grain packing that is as dense as possible such that the spaces between grains of the second grain fraction and which remain in a uniform mixture of the grain fractions between the grains of the first grain fraction and the gaps remaining between the grains of the first and second grain fractions are then filled with grains of the third grain fraction.  

  However, since the latter possibility requires several additional process steps in the production of the glass powder, namely the division of the glass grains resulting from the grinding process into grain fractions, the dimensioning of the parts of the different grain fractions required for the composition of the glass powder and finally the mixing of these parts, is necessary Application mainly limited to the cases where the use of glass powder with a very specific grain size distribution is essential for a smooth process in the production of the foam glass or for the quality of the foam glass produced. 



   In the present process, a fine-grained material is expediently used as blowing agent, which is obtained by chemical reaction with a substance contained in the raw mixture or which forms when heated, and / or by thermal dissociation and / or by evaporation or  Sublimation develops a blowing gas which only reaches a partial pressure which corresponds to the external pressure acting on the raw mixture cake at a temperature above the bonding temperature of the glass grains forming the glass powder, which marks the transition of the raw mixture to a viscous mass, preferably at a temperature above 600 ° C. and already at a temperature below the transition of the raw mixture cake to a thin,

   the flowing temperature of the raw mixture cake, which allows the forming bubbles to rise to the surface, preferably at a temperature below 9000C, the bubble formation required, the sum of the external pressure acting on the raw mixture cake and the surface tension ô on the inner wall of a blowing agent Size d-forming bubble generated bubble pressure Ap = 48 / d corresponding partial pressure reached. 



   To avoid unnecessary additional consumption of blowing agents which do not participate in the formation of bubbles and also to avoid unfavorable influences of the blowing agent on the consistency of the glass forming the glass foam, in the present process it is advisable to use only less than 1% by weight of the raw mixture cake. % of the mass of soluble, preferably mass-insoluble blowing agent can be used. 



   In particular, a substance from the alkaline earth carbonates, silicon carbides and talc and the oxides of manganese, cobalt, copper, nickel and iron or a mixture of several of these substances can advantageously be used as blowing agent in the present process.  With particular advantage, the blowing agent can consist at least partially of silicon monocarbide.  In addition to pure silicon monocarbide, mixtures of the same with at least one oxide of the metals manganese, cobalt, copper, nickel and iron can also be used. 



  The use of silicon monocarbide as an essential component of the blowing agent has, as will be explained in more detail below with the aid of an exemplary embodiment, in particular considerable advantages for the course of the post-blowing process.  In the present method, favorable results are also achieved with a blowing agent consisting at least partly of talc.  A mixture of talc and calcite or of talc and calcite and brown stone or of talc and at least one oxide of the metals manganese, cobalt, copper, nickel and iron is preferably used as blowing agent.  Furthermore, very good results could be achieved with the present process even with blowing agents consisting at least partly of calcite. 



   With regard to the external nature of the blowing agent in the present process, it should be noted that a granular material with an average particle size preferably in the range between 5 and 20% of the intended average bubble size of the glass foam is expediently used as the blowing agent.  A fine-grained material with grain sizes below 100 Il, preferably below 20 y, can advantageously be used as blowing agent. 

  If a granular material developing the expanding gas mainly by thermal dissociation and / or evaporation above the transformation region of the glass is used as blowing agent, the grain sizes of the blowing agent grains should expediently be substantially greater than 10>, preferably above, to achieve a glass foam with larger foam bubbles around the individual grains 20>, because in the case of thermally dissociating or evaporating blowing agents, a foam bubble forms around each blowing agent, the final size of which is primarily determined by the gas volume resulting from complete dissociation or evaporation of the blowing agent in question, and usually below 10 yi for particle sizes 0.2 mm,

   and with a glass foam consisting of such fine foam bubbles, the Naohpäh process is relatively difficult, because then z. B.  have to combine over 100,000 foam bubbles to form a 1 cm cavity.  If, on the other hand, a granular material developing the expanding gas mainly through chemical reactions occurring above the transformation area of the glass is used as the blowing agent, then the grain sizes of the blowing agent grains should be used to achieve the largest possible ratio of reaction surface to amount of reactant or 

   from grain surface to grain volume are expediently substantially below 10 p, because experience has shown that chemically reacting blowing agents result in larger foam bubbles than would be expected based on the grain size of the blowing agent granules and the resulting volume of the gaseous reaction product, and then, of course, the point of view comes as close as possible rapid reaction process and thus the largest possible ratio of grain surface to grain volume in the foreground. 



   In the foam glass produced by the present process, the individual cavities within the foam glass formed by combining a plurality of adjacent foam bubbles should be approximately the same size - which is generally sought in view of the best possible heat insulation properties of the foam glass, then it is advantageous, if already the foam bubbles of the glass foam from which the post-inflation process is based are approximately the same size, and in order to achieve this, a granular material is expediently used as the blowing agent, which essentially achieves glass foam with foam bubbles of approximately uniform size around the individual grains Grains of uniform size with a size tolerance below 20% compared to a nominal value of the grain size. 



   With regard to the required amount of blowing agent, the principle of the present process7 is that the percentage by weight of the blowing agent in the total weight of the raw mixture is greater than 1.2 times the ratio of the sum of the molecular weight numbers of the molecules of the blowing agent required to form a molecule of the blowing gas to the product of the the intended density of the foam glass corresponding to the density number and the temperature value in "K should be the absolute temperature prevailing when the glass foam is formed.  As a guideline, one can assume that this percentage should be at least three times the said ratio.  

  There is no mandatory maximum value for the proportion by weight of the blowing agent in the total weight of the raw mixture, but practice has shown that this proportion by weight should expediently be below 10%. 



   The following guidelines apply to the measurement of the weight fraction of the blowing agent in the total weight of the raw mixture:
If a granular material is used as blowing agent, it is only at temperatures above the enclosing temperature, at which the blowing agent granules are essentially gas-tightly enclosed by the mass forming the raw mixture cake and which in the temperature range between the transition temperature of the raw mixture to a viscous mass that is still open-pored the glass grains forming the glass powder and the flow temperature of the raw mixture cake which marks the transition of the raw mixture cake to a thin, flowing mass of the forming bubbles causing the surface to develop, a blowing gas develops with a partial pressure above the external pressure acting on the raw mixture cake,

   then the weight fraction of the blowing agent in the total weight of the raw mixture should expediently be less than 2.5% and preferably be between 1% and 2%.  These low proportions by weight are quite sufficient in this case, because a loss of blowing gas due to the gas-tight encapsulation of the blowing agent granules practically does not occur before gas formation. 

  If, on the other hand, a granular material is used as the blowing agent, which develops a blowing gas with a partial pressure above the external pressure acting on the raw mixture cake, even at temperatures below the aforementioned sealing temperature, the weight fraction of the blowing agent in the total weight of the raw mixture should in any case be greater than 1% and are preferably between 2% and 5%, because in this case there is a not inconsiderable loss of expansion gas due to the raw mixture cake which is still open-pore below the enclosure temperature, which loss must be compensated for by a correspondingly higher proportion by weight of the expansion agent in the total weight of the raw mixture. 



   If, in addition, a material is used as blowing agent which contains soluble constituents in the mass forming the raw mixture cake, the proportion by weight of each of these constituents in the total weight of the raw mixture should expediently be greater than the proportion by weight of the constituent in question in the raw mixture cake and preferably at least twice as large this soluble percentage by weight. 



   With particular advantage, a material can be used as blowing agent in the present process which contains constituents which react chemically with one another at a reaction temperature above the transformation range of the glass forming the glass powder and produce at least part of the blowing gas as a reaction product, and which preferably compared to the the mass forming the raw mixture cake is inert and insoluble in it.  The reaction temperature should expediently be in the range between the above-mentioned enclosure temperature and the above-mentioned flow temperature of the raw mixture cake. 

  With such expanding agents, a precise control of both the expanding and the post-expanding process can be achieved by a suitable choice of the reacting blowing agent components in relation to the reaction temperature in connection with a suitable choice of the weight proportions of these reacting blowing agent components in the total weight of the raw mixture. 



   In order to achieve certain properties of the foam glass produced by the present process and / or to influence the course of the process during its manufacture, the raw mixture can contain certain additives such as, for example, glass powder and blowing agent in addition to the two basic components. B.  Fillers, fluxes, coloring additives, mixing liquids etc.  be added. 

  In particular, the following guidelines apply to the addition of such additives to the raw mixture:
To increase the mass marking the transition of the raw mixture cake to a thin liquid that forms the bubbles that rise to the surface
Flow temperature of the raw mixture cake and / or
Enclosure temperature at which the blowing agent granules are essentially gas-tightly enclosed by the mass forming the raw mixture cake, the raw mixture can expediently be an inert or with or contained in the raw mixture  when the resulting substances are heated, reactive filler is added.  With such fillers, the viscosity of the viscous mass forming the raw mixture cake is generally increased. 

  In the present process, this can be of particular importance for the post-expansion process, since the post-expansion process is in most cases carried out at temperatures above the so-called expansion temperature prevailing when the glass foam is formed and, on the other hand, should be carried out below the flow temperature mentioned to avoid difficulties in its course are so that increasing the toughness and thus the flow temperature can be of considerable advantage at relatively high blowing temperatures.  The filler used in the present process is primarily a substance from the group of substances comprising quartz powder, chamotte powder, kaolin, corundum powder and clay, or a mixture of several of these substances. 

  In general, the filler used should expediently be as fine-grained as possible and have average grain sizes of less than 100 .mu.m, preferably less than 10 .mu.m, which is usually the case with the aforementioned substances or  is feasible.  The weight fraction of the filler in the total weight of the raw mixture should expediently be below 50% and preferably in the range between 10% and 30%. 



   To reduce the bonding temperature of the glass forming the glass powder, which marks the transition of the raw mixture to a still open-pore viscous mass, and / or the temperature at which the blowing agent granules are essentially gas-tightly enclosed by the mass forming the raw mixture cake, and / or the transition of the raw mixture cake to form a thin, flowing mass of the raw mixture cake, which marks the forming bubbles and rise to the surface, the raw mixture can advantageously be added with the flux reducing the viscosity of the raw mixture cake. 

  The addition of fluxes is particularly considered when the gas evolution of the blowing agent to be used starts at relatively low temperatures and the above-mentioned ambient temperature would be above the temperature at which gas evolution begins without the addition of fluxes to the raw mixture.  In this case, the enclosure temperature is expediently reduced by adding a flux to a value which is below the temperature at which the gas development of the blowing agent begins.  Boric acid or lithium carbonate can advantageously be used as the flux. 



  In this case, the weight fraction of the flux in the total weight of the raw mixture should preferably be between 0.2% and 1%. 

 

   For the production of colored foam glass according to the present process, a color-imparting additive can also advantageously be added to the raw mixture, preferably a substance from which the transition metal oxides and chromates as well as nickel monoxide, manganese dioxide, cobalt (III) oxide, iron (III) oxide, chromium ( III) -oxid and vanadium (V) -oxid group of substances or a mixture of several of these substances.  It should be noted that various of these substances and in particular the specified metal oxides can also act as blowing agents at the same time, which must be taken into account when selecting the blowing agent to be used and when measuring the proportion by weight of the total weight of the raw mixture.  In special cases, the coloring additive can also form the blowing agent alone at the same time. 

  The proportion by weight of the coloring additive in the total weight of the raw mixture should generally be kept as low as possible and preferably between 0.5% and 10%. 



   It may also be advantageous for the process sequence of the present method to simplify the achievement of a uniform distribution of its constituents in the mixture and / or to improve the blowing process and an associated increase in the strength of the foam glass produced with a mixing liquid, preferably with water to mix into a dough and then stir in dough form until a substantially homogeneous mixture is formed and then to dry the dough at an elevated temperature, preferably in the temperature range between 100 ° C. and 1300 ° C. 



  If, in addition to such a mixing liquid, a flux is also to be added to the raw mixture, then a substance which is soluble in the mixing liquid, preferably boric acid in the case of water as the mixing liquid, should be used as the flux and the flux must be dissolved in the mixing liquid before the mixing liquid is mixed with the raw mixture. 



   Such mixing of the raw mixture with water or another liquid is not absolutely necessary in the present process.  Rather, in many cases there is also the possibility of heating the raw mixture in the dry state for carrying out the expanding process, and this of course has the advantage that the process step of drying the raw mixture dough mentioned can be saved.  In these z. B.  If silicon monocarbide is used as the main constituent of the blowing agent, the raw mixture is mixed, preferably stirred, in order to achieve an even distribution of its constituents in the mixture until a substantially homogeneous mixture is formed, and then heated to carry out the blowing process in the dry state. 



   For the production of foam glass moldings: according to the present process, the crude mixture can expediently be heated in appropriate forms.  The use of molds in which the raw mixture is heated also prevents the raw mixture cake from running apart during the expansion or post-expansion process.  Forman made of ceramic or metal, preferably scale-free steel, can advantageously be used for this purpose, which should expediently be able to be dismantled from the mold in order to simplify the removal of the foam glass molded body produced.  In order to prevent the foam glass from sticking or adhering to the inner walls of the molds, it is furthermore expedient to provide the molds with a coating of a slurry of gypsum-sand or koalin-graphite mixture on their inner walls before the raw mixture is introduced. 

  This applies in particular to metal molds because there is a relatively high risk of such adherence.  If, as explained above, the raw mixture is mixed with a mixing liquid to form a raw mixture dough, then when using molds for heating the raw mixture it is generally advantageous if the raw mixture dough is only dried after it has been introduced into the mold, because the dough fills the lower part of the mold completely and evenly, which is usually not possible with already dried chunks of raw mix. 

  In addition, the raw mixture dough, after being introduced into the mold, can in any case be dried in the same oven or the pre-zone in which the raw mixture is heated when the mold is passed through the oven in which the raw mixture is subsequently heated when the mold is heated the inflatable  Post expansion temperatures take place. 



   In the present process for producing a molded foam glass body, an essentially closed, separable mold with a cavity adapted to the dimensions of the molded foam glass body can advantageously be used, and a weight quantity of the raw mixture corresponding to the product of the volume of the cavity and the intended density of the molded glass body can be introduced into the mold will.  In this case, the raw mixture is expediently mixed in the dry state and introduced into the mold, since in closed molds the removal of the vapor of the mixing liquid which arises when drying the moist mixed raw mixture causes certain difficulties. 

  However, it is of course also possible to introduce the raw mixture in a moist state, only then either the mold should only be closed after the raw mixture has dried or small openings should be provided on the top of the mold through which the steam can flow off.  When introducing the raw mixture in the moist state, it must also be taken into account that the amount by weight of the introduced moist raw mixture must be greater by the weight of the mixing liquid contained in it than when introducing it in the dry state. 

  In general, the production of foam glass moldings with such closed molds has the advantage of a high dimensional accuracy of the foam glass bodies produced, provided that appropriate process management and a suitable composition of the raw mixture ensure that the glass foam which forms in the blowing process and continues to expand in the post-blowing process is surrounded by the mold Completely fills the cavity at the end of the post-expansion process, and this can usually be achieved if the glass foam in the final phase of the post-expansion process has sufficient toughness to be able to adapt seamlessly to the shape of the cavity walls. 

  However, the effort for the production of foam glass moldings when using molds and in particular closed molds is relatively high, because in addition to the investment required for the molds, there is also a considerable amount of work for the preparation (assembly and elutriation) of the molds before the start of the process and the disassembly thereof after the completion of the procedure. 

  This manufacturing effort can be done with simple shapes of the foam glass moldings to be manufactured such as. B.  Reduce cuboid blocks by using a shaft furnace with the cross-section of the moldings to be produced instead of individual molds running through a continuous furnace, to which raw mixture is continuously fed on the input side and which continuously releases a foam glass rod with the cross-section of the moldings to be produced on the output side, but firstly requires it such shaft furnaces, because of the complicated conveying device, require a considerably higher investment than the conventional continuous furnaces and secondly, each individual molded body must be cut off from the foam glass rod produced,

   so that even using such a shaft furnace, a really considerable reduction in production costs cannot be achieved. 



   In contrast, can be achieved in the present method, a substantial reduction in the production costs for molded foam glass body if either for the production of molds such. B.  thin-walled individual molds made of pre-fired or dried clay are used, which after completion of the manufacturing process an integrated component such. B.  form a casing of the molded body produced or if high dimensional accuracy can be dispensed with or  if rounded shapes can be accepted at the corners and edges of the moldings to be produced. 

  In the latter case, the use of molds can be dispensed with entirely if the raw mixture to avoid the raw mixture cake or  of the Giass foam during the expansion or post-expansion process, the toughness of the raw mixture cure or  of the glass foam increasing substance is added.  As such substances, other clay and kaolin are very suitable.  When dispensing with molds, however, it is necessary that the raw mixture already as an intrinsically stable molded body, whose weight (in the dry or dried state) corresponds approximately to the weight of the foam glass molded body to be produced and whose dimensions are proportional to the dimensions of the molded body to be produced, in the for heating the Raw mixture serving furnace is introduced. 

  This can be achieved when using clay as a toughness-increasing substance in that the raw mixture is mixed with the clay and relatively little water, thus producing a plastically deformable mass which is then brought into the shape of the intrinsically stable molded body and in this state the introduction is dried in the oven used to heat the raw mixture.  Other possibilities for the formation of said intrinsically stable molded body consist in a dry pressing of the raw mixture or in the use of adhesive additives to the raw mixture, however the formation from a plastically deformable mass made with clay has proven to be the simplest and cheapest method. 

  In general, when not using molds, it should be noted that the intended temperature values and heating times during the expansion and post-expansion process are strictly observed, that the temperature increase during the expansion process is kept as low as possible compared to the expansion process. B.  can be achieved by blowing agents with components that react with one another, and that unnecessary blowing agent surpluses that are not intended to cover any losses are avoided.  If these conditions are met, a relatively good dimensional accuracy of the foam glass moldings produced can still be achieved despite the absence of molds. 



   The following guidelines generally apply to the conduct of the procedure in this case:
The raw mixture is in the dry or dried state in a preheated oven, the oven temperature of which is below the enclosure temperature at which the blowing agent granules are essentially gas-tightly enclosed by the composition forming the cake mixture, and which is preferably between 400 "C and 700" C, or in a furnace zone of appropriate temperature is introduced and in the furnace or  the furnace zone is initially heated to approximately the temperature prevailing there. 

  Subsequently, the raw mixture cake that forms, preferably within 20 to 60 minutes, by increasing the oven temperature or moving it to a higher temperature in the oven zone to the temperature required to form the glass foam, in the temperature range between the surrounding temperature and the transition of the raw mixture cake to a thin liquid bubbles forming to the surface allow the mass-marking flow temperature of the raw mixture cake, which preferably falls in the range from 700 ° C. to 900 ° C., to be heated further. 

  The post-expansion process is then carried out and the foam glass formed thereafter, preferably within less than 30 minutes, by reducing the furnace temperature or moving to a lower temperature furnace zone, at least to a temperature close to the upper limit of the transformation range of the glass forming the foam glass, preferably cooled to a temperature falling in the lower part of the transformation range, and then allowed to cool to room temperature, preferably with the interposition of an aftertreatment process serving to influence the material properties of the finished foam glass. 

  The foam glass formed is advantageously cooled only briefly after the post-expansion process to a temperature falling in the transformation region of the glass forming the foam glass, preferably in the lower part of the same, and then again in a tempering process which serves to achieve minimal residual stresses in the foam structure Temperature heated above the transformation range and then gradually cooled to a temperature below the transformation range in a cooling process lasting for several hours and then allowed to cool to room temperature, preferably in an ambient temperature environment. 

  When producing foam glass according to the present method on a larger scale, such as. B.  In the production of blocks made of foam glass, it is advantageous in terms of rational production if the heating of the raw mixture to the formation of foam glass and the subsequent cooling of the foam glass formed is carried out in a tunnel or pusher furnace and differently by gradually or continuously moving the workpiece into furnace zones Temperature and control of the speed of the workpieces through the furnace or  the individual furnace zones a predetermined temporal temperature profile of the heating and cooling processes is maintained. 



   In addition to the thermal aftertreatment mentioned above, the foam glass produced by the present process can also be subjected to a mechanical aftertreatment to improve its material properties, namely by deforming the foam glass formed in the hot-plastic state at a temperature above the transformation range of the glass forming the foam glass.  In order to increase the rigidity in a predetermined loading direction, the foam glass can expediently be squeezed together in the direction transverse to this loading direction, the cavities formed in the post-expansion process being flattened in a lenticular manner by combining a plurality of adjacent foam bubbles. 

  Likewise, the foam glass can also be squeezed together in order to increase the thermal insulation in a predetermined heat flow direction in the direction parallel to this heat flow direction, the cavities formed in the post-expansion process also being flattened like a lens.  Furthermore, the foam glass can be pulled apart or extruded in order to increase the rigidity in a predetermined loading direction in the direction parallel to this loading direction, the cavities formed in the post-expansion process being extended in a spindle-shaped manner, and finally the foam glass can be increased in all to increase the thermal insulation directions perpendicular to an axis direction are pulled apart or extruded in the direction parallel to this axis direction, the cavities formed in the post-expansion process also being drawn out in a spindle-shaped manner.  

  Of the abovementioned possibilities of improving the material properties of the foam glass, the achievable increase in thermal insulation in a predetermined heat flow direction by squeezing the foam glass in the direction parallel to the heat flow direction is of particular importance, because this increases the possibility of a further improvement in the heat insulation properties of the present method produced foam glass results. 

  In this context it should be mentioned again that the cavities created in the post-inflation process by combining a plurality of adjacent foam bubbles in any case generally have considerably larger dimensions in the horizontal direction than in the vertical direction and are accordingly essentially lenticularly flattened anyway in the vertical direction ( the horizontal and vertical directions refer to the position of the foam glass during the manufacturing process).  You can already squeeze the foam glass together in the vertical direction.  reinforce existing lenticular flattening and thus achieve a further improvement in the thermal insulation properties of the foam glass in this vertical direction. 



   The deformability of the foam glass in the warm plastic state can also be used to deform the foam glass produced as part of a mechanical aftertreatment into a foam glass molded body of a predetermined shape.  This possibility is particularly important for the above-mentioned case that the use of molds in the production of foam glass moldings is completely dispensed with and the foam glass moldings produced therefore do not have a high degree of dimensional accuracy, because here the foam glass moldings can now be reshaped as part of a mechanical aftertreatment required or  achieve the desired shape accuracy. 



   In general, the present method assumes that the raw mixture or  of the glass foam formed in the blowing process to at least approximately the same temperatures over the entire volume of the raw mixture or  Glass foam - as is the case with the commonly used ovens in any case with a suitable procedure or  sufficient residence times are generally achieved - to a substantially uniform foam glass structure of the foam glass produced over the entire foam glass volume.  In special cases.  However, it may also be desirable to produce foam glass with a partly coarse-pored and partly fine-pored foam glass structure. 

  This can be achieved in the present method in that in the glass foam during the post-expansion process an inhomogeneous temperature distribution with areas of substantially higher temperature than the temperature prevailing during the formation of the glass foam in the areas provided for coarse-pore foam glass structure and areas of the same or only slightly higher Temperature is generated as the temperature prevailing during the formation of the glass foam in the areas provided for fine-pored foam glass structure.  The inhomogeneous temperature distribution can advantageously be generated by heat radiation with different intensities in the different radiation directions. 

  For example, in that the glass foam is heated during the post-expansion process by a heat source radiating onto the glass foam in a predetermined direction, foam glass with a foam glass structure which gradually changes from coarse to fine pores in the predetermined direction can be produced. 



   The strength of the foam glass produced by the present process is in general, despite its coarse-pored structure due to the cavities created in the post-expansion process by combining a large number of adjacent foam bubbles, and despite the resulting reduction in strength compared to foam glass with fine-pored structure, due to this coarse porosity Practice, e.g. B.  when using the foam glass as a building material, required strengths.  However, as with all other glass products and also with foam glass with a fine-pored structure, the reserves in breaking strength are only small due to the brittleness of glass.  An increase in the breaking strength and in particular the brittleness of the foam glass is therefore essential. 

  Such an increase can be achieved in the present method by producing homogeneous surface layers on the inner walls of the cavities formed in the post-expansion process by combining a plurality of adjacent foam bubbles essentially above the wall surface, which in the finished foam glass lead to compressive stresses along the wall surfaces.  These surface layers can advantageously be produced by superficial chemical reaction of the material forming the cavity walls with at least one substance located in the cavities to form a reaction product with a lower thermal expansion than that of the wall material. 

  Another advantageous possibility is to produce the surface layers by means of a substance which adheres from the atmosphere within the cavities to the cavity inner wall and forms a self-contained coating over the wall surfaces with a lower thermal expansion than that of the wall material.  The surface layers can also advantageously be produced by a substance which deposits on the interior walls of the cavity from the atmosphere within the cavities and then dissolves superficially in the wall material and which forms a solution with the wall material of less thermal expansion than that of the pure wall material. 

  Finally, with appropriate compositions of the material forming the cavity walls, one can also proceed expediently in such a way that the surface layers are produced by a substance contained in the wall material and diffusing to the wall surfaces by heat treatment.  The surface layers are preferably produced under the conditions of the post-expansion process during the same.  To form the surface layers, a substance from the group of substances comprising the silicides, nitrides, titanates, zirconates and the rare earths or a mixture of several of these substances can expediently be added to the raw mixture.  Instead of or in addition to this, a metal oxide, preferably an oxide of the metals nickel, copper and iron, or a mixture of several metal oxides can advantageously be added to the raw mixture to form the surface layers. 

  Another advantageous possibility is to add clay to the raw mixture to form the surface layers. 



   In the following, some special exemplary embodiments of the present method are described in more detail with all the details that are important for the process control:
example 1
A mixture of 98 wt. -% glass powder with a maximum grain size of 125 p and 2 wt. -% powdered silicon monocarbide with a maximum grain size of 10 p used.  The raw mixture was mixed well and then shaken dry into a mold.  

  The open mold filled with the raw mixture up to about 30% of its height was then in an oven within a period of 3 hours to the temperature of 6500 ° C. above the transformation range of the waste glass used for the glass powder, which range from 500 ° C. to 600 ° C. heated up.  With this still below the enclosure temperature of approx.  At 680 720 ° C., at which the silicon carbide grains are essentially gas-tightly enclosed by the mass forming the raw mixture cake, the silicon carbide used as blowing agent does not develop any expanding gas, as could be determined by an examination of the atmosphere in the furnace. 

  After heating to 650 "C, the mold with the still open-pore raw mixture cake made of glass grains glued together and silicon carbide grains distributed in the spaces between the glass grains is within approx. 



  25 minutes to the blowing temperature of approx.    880 "C heated.  During this heating process, the raw mixture cake initially changes into a viscous mass in the temperature range from 6800C to 7200C, from which the silicon carbide grains distributed therein are enclosed gas-tight, and from about 750 "C a chemical reaction of the silicon carbide with the silicon dioxide contained in the raw mixture then begins, in which carbon monoxide and carbon dioxide are formed and which are likely according to the following reaction equations 2 SiO2 + SiC <3 SiO + CO and 3 SiO2 + SiC <4 SiO + CO2 expires. The resulting carbon oxides form the expanding gas, which initially causes a small bubble to form around each silicon carbide grain.

  With the formation of these bubbles, the reaction between the silicon carbide and the silicon dioxide slows down considerably, because the carbon oxide gases contained in the bubbles largely isolate the surface of the silicon carbide grain contained in the bubble from the viscous mass surrounding the bubble and thus from the silicon dioxide. However, the gas pressure in the bubbles is relatively high because of the still relatively high toughness at these temperatures and the large surface tension of the viscous mass forming the raw mixture cake. With further heating to the blowing temperature, however, both the toughness and the surface tension of the mass forming the raw mixture cake decrease sharply, so that the bubbles standing under high gas pressure can now gradually increase with this decrease.

  As a result, the mass forming the raw mixture cake is gradually foamed and begins to rise in shape. After the blowing temperature of approx. 8800C has been reached in the oven, the temperature increase is stopped and the blowing temperature is maintained for about 2 to 5 minutes. During this time, the mass in the mold continues to increase until the raw mixture cake has passed into a glass foam formed by lamellar walls between mutually adjacent, approximately polyhedral foam bubbles.



  The end of this transition phase can be seen from the fact that the initially rapid increase in mass in the form slows down more and more. At this point, the post-expansion process is initiated and the temperature in the furnace is raised to 950 ° C. in about 10 minutes. This causes the increase in the mass of the mold to accelerate again and then stops almost completely after 10 minutes.

  Simultaneously with this further increase in the mass in the form during the post-inflation process, the previously almost smooth surface of the mass is becoming increasingly uneven, which is obviously due to the fact that relatively large cavities are created within the mass by combining a large number of adjacent foam bubbles and the immediately below Cavities arising on the surface of the mass due to expansion cause the surface of the mass to rise in its central areas. At the latest when one of these cavities bursting directly beneath the surface of the mass bursts, the post-expansion process is stopped.

  The processes during the post-expansion process within the glass foam formed in the previous expansion process are essentially as follows: At the expansion temperature of approx. 8800C, the glass foam is still relatively fine-pored, i.e. The individual foam bubbles of the glass foam have dimensions in the range between about 0.5 and 2 mm, which can be easily determined by cooling and cutting open the glass foam immediately after the blowing process.

  With the further heating of the glass foam during the post-expansion process, firstly, the toughness and surface tension of the glass forming the glass foam continue to drop sharply, and secondly, the pressure within the individual foam bubbles increases both due to the temperature increase and due to a chemical reaction between the carbon dioxide contained in the foam bubbles and the Remaining of the silicon carbide grain still remaining in the foam bubble, in which the carbon dioxide is reduced by the silicon carbide to form silicon to carbon monoxide.



  The free silicon formed during this reaction is deposited as a firmly adhering, essentially self-contained coating on the inner walls of the cavities formed in the post-expansion process by combining adjacent foam bubbles. The silicon coatings on the cavity walls can be easily determined on the finished foam glass. The pressure increase due to the chemical reaction results from the fact that one molecule of carbon dioxide produces two molecules of carbon monoxide in the reaction. The reaction probably only starts at temperatures above 900 "C.

  Possibly the tearing of the walls between the individual foam bubbles leading to the union of adjacent foam bubbles and thus to the formation of the relatively large voids is initiated or promoted by the reaction, because the processes of the reaction in the individual foam bubbles are not completely identical, so that two So during the course of the reaction there are pressure differences between the individual foam bubbles which, if the height is sufficient, could lead to the walls tearing open between the individual foam bubbles.

  In addition, the amount of silicon carbide still present in the individual foam bubbles is also of different sizes, so that pressure differences between the individual foam bubbles could also result from the fact that in the foam bubbles, where the silicon carbide has been used up, the reaction and thus the increase in pressure stops while the reaction and the pressure increase in the other foam bubbles continues. In any case, there is reason to believe that all of the silicon carbide is used up; no residues of silicon carbide grains could be found in the finished foam glass.

  In addition to this possibility that the tearing of the walls between the individual foam bubbles is caused by pressure differences between the foam bubbles, there is of course also the possibility that the tearing of the walls mainly due to the sharp drop in surface tension and toughness of the glass forming the walls with the further rising temperature as well as the decrease in the wall thickness of the walls associated with the further expansion of the foam bubbles with a simultaneous increase in the tensile stresses acting on the walls.

 

  In any case, the cavities formed during the post-expansion process by combining foam bubbles have dimensions in the order of magnitude of centimeters, which can also be readily determined by cutting the finished, cooled foam glass. Following the post-expansion process, the resulting foam glass is cooled within 20 minutes to the temperature of 5100C falling in the lower part of the transformation area of the glass forming the foam glass, and this rapid cooling, so to speak, freezes the foam glass structure achieved at the end of the post-expansion process. The thermal stresses resulting from this rapid cooling in the foam glass are then removed in a tempering process to achieve minimal residual stresses in the foam structure.

  For this purpose, the foam glass is heated again to 6200C within 15 minutes and then gradually cooled in a 5-hour cooling process to the temperature of 480 ° C below the transformation range of the glass forming the foam glass. Because of the extraordinarily slow cooling when passing through the transformation range After this cooling process, the mold is then removed from the oven and allowed to cool to room temperature in an ambient temperature environment. Since the foam glass is already completely solidified below the transformation area, this relatively rapid cooling can occur Room temperature no longer creates internal stresses in the foam glass.

  The finished foam glass is then removed from the mold. The resulting foam glass has a density of 0.143 g / cm3 and a foam structure with essentially regularly distributed, slightly lenticularly flattened cavities that have a diameter in the horizontal direction (in relation to the position of the foam glass during the manufacturing process) between 1 and 2 cm and in the vertical direction Have dimensions between 0.8 and 1.4 cm and are coated on their inner walls with a thin silicon layer. The lenticular flattening of the cavities probably arises in part only during the cooling process mentioned, because it was observed that the foam glass sagged somewhat in the mold during the cooling process.



   Example 2
The process explained in Example 1 was carried out using a raw mixture of 82% by weight of glass powder with a maximum grain size of 1 mm and 3% by weight of powdered silicon monocarbide with a maximum grain size of 50 p and 15% by weight of clay with a maximum grain size of 20, pt repeated, but no mold was used to heat the raw mixture, but the raw mixture was mixed with water and shaped into a cuboid and then dried at 1200C for about 3 hours and then in this cuboid form in the serving for heating the raw mixture Oven was introduced. The temperatures and heating or

  Cooling times for the heating of the raw mixture, the blowing process, the post-blowing process, the rapid cooling of the foam glass formed after the post-blowing process, the tempering process and the subsequent slow cooling of the foam glass were essentially the same as in Example 1, but in the over- During the initial phase from the tempering process to the subsequent slow cooling at the temperature of 6200C, the foam glass body formed is reshaped in a tough-plastic state for final shaping and for further flattening of the slightly lenticularly flattened cavities within the foam glass body.

  The finished cuboid foam glass body had a density of 0.161 g / cm3 and, compared to Example 1, was distributed in a similar but somewhat smaller way with a somewhat stronger flattening.



   Example 3
In this and all the following examples, the process sequence is qualitatively the same as in Example 1, as are the heating and cooling times and the heating temperature of the raw mixture of approx. 6500C and the final temperatures of the subsequent cooling of approx. 5100C following the post-expansion process The tempering process of approx. 6200C and the subsequent hourly cooling process of approx. 4800C are essentially the same as in example 1, because the waste glass used for the glass powder is the same in all cases and the temperatures and times mentioned above differ the properties of that used for the glass powder. Result in glass.

  Furthermore, this and the following examples have in common with example 2 that the raw mixture is mixed with water and formed into a cuboid, which is then subjected to a 3-hour drying process at approx. 1200C and then introduced without a mold into the oven used to heat the raw mixture . Different from Examples 1 and 2 in this and the following examples are only the compositions of the raw mixture, in particular with regard to the blowing agents used and other additives to the raw mixture as well as with respect to the grain sizes of the glass powder, the blowing agent used or the type and sequence resulting therefrom final temperatures of the blowing and blowing process which are dependent on the blowing and blowing process and the properties of the foam glasses produced.

  For this and all other examples, only these different features are therefore given in tabular form below.



  Composition of the 97.3% by weight glass powder with the raw mixture: max. Grain size of 0.25 mm,
2% by weight calcite, 0.7% by weight
Boric acid (dissolved in the mixing water) final temperature expansion process: 800 C final temperature expansion process: 850au
Density of manufactured
Foam glasses: 0.126 g / cm3 average Diameter of the cavities: 1.1 cm average height of
Cavities: 0.8 cm
Example 4 Composition 94% by weight of glass powder with the raw mixture: max. Grain size of 0.4 mm,
3% by weight calcite, 3% by weight
Talc final temperature inflation process: 7800C final temperature expansion process: 840po density of the manuf.



  Foam glass: 0.153 g / cm3 average Diameter of the cavities: 1.25 cm average Height of the cavities: 0.9 cm
Example 5 Composition 93.7% by weight of glass powder with the raw mixture: max. Grain size of 0.25 mm,
2% by weight calcite, 2% by weight
Talc, 2% by weight manganese dioxide,
0.3% by weight boric acid (dissolved in the mixing water) final temperature expansion process: 780 C final temperature post expansion process: 830 C density of the



  Foam glass: 0.137 g / cm3 average Diameter of the cavities: 1.35 cm average Height of the cavities: 1.05 cm
Example 6 Composition 93.5% by weight of glass powder with the raw mixture: max. Grain size of 0.3 mm,
3% by weight silicon monocar bid, 3% by weight manganese dioxide,
0.5% by weight boric acid (dissolved in the mixing water) final temperature expansion process: 860 C final temperature post expansion process: 920 C density of the manuf.

 

  Foam glass: 0.132 g / cm3 average Diameter of the cavities: 1.6 cm average Height of the cavities: 1.1 cm
Example 7 Composition 86% by weight of glass powder with the raw mixture: max. Grain size of 0.5 mm,
3 wt .-% silicon monocarbide, 3 wt .-% manganese dioxide, 8 wt .-% clay final temperature expansion process: 890 C final temperature post-expansion process: 960 C density of the manuf.



  Foam glass: 0.154 g / cm3 average Diameter of the cavities: 1.3 cm average Height of the cavities: 0.9 cm


    

Claims (22)

 PATENT CLAIMS 1. A process for the production of closed-pore foam glass, in which a raw mixture containing at least glass powder and blowing agent is heated to temperatures above the transformation range of the glass forming the glass powder until the blowing agent is caused by chemical reactions and / or thermal dissociation and / or evaporation occurring above this transformation range develops a blowing gas which initially forms spherical bubbles within the raw mixture cake, which has been baked together by softening the glass powder grains, and which continues to grow with the further development of gas while the cake is inflated,  until the adjacent bubbles collide and then, when they continue to grow, form a polyhedral shape with the formation of lamellar walls between the individual bubbles, and the cake thus changes into a glass foam formed by the lamellar walls between mutually adjacent, approximately polyhedral foam bubbles, characterized in that the Glass foam is subjected to a post-expansion process to achieve a coarse-pored foam structure, polyhedron bubbles continue to grow due to coalescence and at the expense of the smaller bubbles and form larger cavities,  and that for this purpose the heat effect on the glass foam is further maintained after its formation and / or the ratio of the average gas pressure in the foam bubbles to the pressure acting on the glass foam from the outside to a value above the value of this ratio achieved with the formation of the glass foam and / or the surface tension of the glass forming the lamellar walls compared to the gas in the foam bubbles and the toughness of the glass forming the lamellar walls are brought to values below the values of the surface tension or toughness achieved with the formation of the glass foam.  2. The method according to claim 1, characterized in that portions of a substance are added to the blowing agent, which enters into a gas-developing chemical reaction with one of the substances contained in the glass foam only in the region of the temperature prevailing in the formation of the glass foam or above it, and thereby the gas pressure in the foam bubbles according to pV = RT and is brought to a value above the pressure value achieved with the formation of the glass foam by further reaction.  3. The method according to claim 1 or 2, characterized in that the glass foam is subjected to the post-expansion process only after the interposition of a cooling phase and is heated again for this purpose.  4. The method according to any one of claims 1 to 3, characterized in that at least partially pulverized waste glass is used as glass powder for the raw mixture.  5. The method according to any one of claims 1 to 4, characterized in that a fine-grained material is used as blowing agent, which by chemical reaction with a substance contained in the raw mixture or formed during heating thereof and / or by thermal dissociation and / or by Evaporation or Sublimation develops a blowing gas that only at a temperature above the transition temperature of the raw mixture to a viscous mass bonding temperature of the glass grains forming the glass powder, preferably at a temperature above 6000C, reaches a partial pressure that corresponds to the external pressure acting on the raw mixture cake, and that Already at a temperature below the flow temperature of the raw mixture cake, which marks the transition of the raw mixture cake to a thin, flowing mass, which causes the forming bubbles to rise to the surface, preferably at a temperature below 900 ° C., the temperature required for the formation of bubbles,  the sum of the external pressure acting on the raw mixture cake and the partial pressure Ap = 48 / d corresponding to the bubble pressure generated by the surface tension 8 on the inner wall of a bubble of size d of size d.  6. The method according to any one of claims 1 to 5, characterized in that a substance from which the alkaline earth carbonates, silicon carbides and talc and the oxides of manganese, cobalt, copper, nickel and iron or a mixture of several of these substances is used as blowing agent .  7. The method according to any one of claims 1 to 6, characterized in that the raw mixture to increase the transition temperature of the raw mixture cake to a low-viscosity, the resulting bubbles rising to the surface mass marking flow temperature of the raw mixture cake and / or the surrounding temperature at which the Blowing agent granules are enclosed in a substantially gas-tight manner by the mass forming the raw mixture cake, an inert filler or a filler which is contained in the raw mixture or reacts with the substances formed when it is heated is added.  8. The method according to any one of claims 1 to 7, characterized in that the raw mixture to reduce the transition temperature of the raw mixture to a still open-pore viscous mass marking the bonding temperature of the glass forming the glass powder and / or the temperature at which the blowing agent granules from the The mixture forming the raw mixture cake is enclosed essentially gas-tight, and / or the flux reducing the viscosity of the raw mixture cake is added to the transition temperature of the raw mixture cake to a thin, flowing mass of the raw mixture cake that causes the bubbles to rise to the surface.  9. The method according to any one of claims 1 to 8, characterized in that the raw mixture for the production of colored foam glass, a coloring additive, preferably a substance from which the transition metal oxides and chromates and nickel monoxide, manganese dioxide, cobalt (III) oxide, iron (III) oxide, chromium (III) oxide and vanadium (V) oxide comprising a group of substances or a mixture of several of these substances, and the proportion by weight of the coloring additive in the total weight of the raw mixture is preferably between 0.5% and 10 % lies.  10. The method according to any one of claims 1 to 9, characterized in that the raw mixture to simplify the achievement of a uniform distribution of its components in the mixture and / or to improve the blowing process and an associated increase in the strength of the foam glass produced with a stirring liquid, preferably with water, mixed into a dough and then stirred in dough form until a substantially homogeneous mixture is formed and the dough is then dried at an elevated temperature, preferably in the temperature range between 1000C and 1300C.    11. The method according to any one of claims 1 to 9, characterized in that the raw mixture is mixed to achieve a uniform distribution of its constituents in the mixture in the dry state until a substantially homogeneous mixture is formed, preferably stirred, and then to carry out the swelling process in dry state is heated.  12. The method according to any one of the claims 1 to 11, characterized in that the raw mixture is heated in a mold, preferably in a mold made of dried or fired clay or other ceramics or in one, to prevent the raw mixture cake from diverging during the expansion or post-expansion process expediently dismantled metal mold made of scale-free steel or another metal.  13. The method according to claim 12, characterized in that for the production of an at least partially encased foam glass molded body after the completion of the manufacturing process forming the shell of the molded body, preferably a thin-walled shape made of pre-fired or dried clay or ceramic, is used.  14. The method according to any one of claims 1 to 11, characterized in that for the production of a foam glass body with at least partially covered by foam glass solid core or carrier in the raw mixture before its heating, a core or carrier body, preferably made of ceramic, is introduced.  15. The method according to any one of claims 1 to 14, characterized in that the raw mixture in the dry or dried state in a preheated oven, its oven temperature below the enclosing temperature, at which the blowing agent granules are enclosed in a gas-tight manner by the mass forming the raw mixture cake and preferably is between 400 "C and 700" C, or is placed in a furnace zone of appropriate temperature and in the furnace or  the furnace zone is first heated to approximately the temperature prevailing there and the raw mixture cake that forms subsequently, preferably within 20 to 60 minutes, by increasing the furnace temperature or shifting it to a higher temperature in the furnace zone to the temperature range required for the formation of the glass foam Enclosure temperature and the transition temperature of the raw mixture cake to a thin, flowing mass, which causes the forming bubbles to rise to the surface, of the raw mixture cake, and preferably falling in the range from 700 ° C. to 9000 ° C., is then further heated and then the post-expansion process is carried out and that foam glass formed thereafter, preferably within less than 30 minutes,  by reducing the furnace temperature or moving it to a lower temperature furnace zone at least to a temperature near the upper limit of the transformation range of the glass forming the foam glass, preferably to a temperature falling in the lower part of the transformation range, and then, preferably with the interposition of a to influence the material properties of the finished aftertreatment process serving for foam glass, is allowed to cool to room temperature.  16. The method according to any one of claims 1 to 15, characterized in that the foam glass formed is deformed in the warm plastic state at a temperature above the transformation range of the glass forming the foam glass.  17. The method according to claim 16, characterized in that the foam glass is squeezed to increase the thermal insulation in a predetermined heat flow direction in the direction parallel to this heat flow direction and thereby the cavities formed in the post-expansion process by combining a plurality of adjacent foam bubbles are flattened lenticular.  18. The method according to claim 16, characterized in that the foam glass is pulled apart or extruded to increase the rigidity in a predetermined loading direction in the direction parallel to this loading direction and thereby the cavities formed in the post-blowing process by combining a plurality of adjacent foam bubbles in a spindle shape in the Length.  19. The method according to claim 16, characterized in that the foam glass is deformed into a foam glass molded body of a predetermined shape.  20. The method according to any one of claims 1 to 19, characterized in that for the production of foam glass with partially coarse-pored and partially fine-pored foam structure in the glass foam during the post-expansion process, an inhomogeneous temperature distribution with areas of substantially higher temperature than the areas prevailing when the glass foam is formed of the same or only slightly higher temperature than the temperature prevailing during the formation of the glass foam in the areas provided for fine-pored foam structure.  21. The method according to any one of claims 1 to 20, characterized in that to increase the breaking strength, in particular the brittle fracture resistance, of the foam glass on the inner walls of the cavities formed in the post-blowing process by combining a plurality of adjacent foam bubbles, essentially homogeneous over the wall surface, surface layers leading to compressive stresses along the wall surfaces are produced in the finished foam glass.  22. Foam glass produced by the method according to one of claims 1 to 21, characterized in that the major part of the total cavity volume of the foam glass is formed by cavities, each of which has a cross-sectional area of at least 0.5 in at least one cross-sectional plane running through the cavity cm2.  The invention relates to a process for the production of closed-pore foam glass, in which a raw mixture containing at least glass powder and blowing agent is heated to temperatures above the transformation range of the glass forming the glass powder until the blowing agent by chemical reactions and / or thermal dissociation proceeding above this transformation range and / or evaporation, a blowing gas develops which initially forms spherical bubbles within the raw mixture cake that has been baked together by softening the glass powder grains, which bubbles continue to grow with the further development of gas while the cake is inflated,  until the adjacent bubbles collide and then, as they continue to grow, form a polyhedral shape with the formation of lamella-like walls between the individual bubbles, and the cake thus changes into a glass foam formed by the lamella-like walls between mutually adjacent, approximately polyhedral foam bubbles. The invention further relates to foam glass produced by this method.    Methods of the aforementioned type have been known for some time, e.g. from US Pat. Nos. 2,333,608 and 3,811,851, CH Pat. Nos. 426,601 and 473,741, DT Pat. No. 2,028,666 and the book Silicates by W. Hinz, VEB Verlag Berlin 1971, Volume 2, pages 267, 268 and 283, 284. However, with these known processes it was only possible to produce foam glass with relatively small pore sizes, the maximum being on the order of millimeters ** WARNING ** End of CLMS field could overlap beginning of DESC **.