IL27645A - Production of cellular bodies of low specific weight - Google Patents

Description

niuii inn 3ini"T m PATENTS AND DESIGNS ORDINANCE SPECIFICATION Production of Cellular Bodies of I*ow Speci ic Weight Vp©a * ya ο» »κη o*si* "ns*» COKDRAVES A.S. incorporated under the laws of Switzerland, of Schaffhauserstrasee 580, 8052 Zurich, Switzerland do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement :- The present invention relates to bodies of low specific gravity and to a new method of producing the same, for example in the form of a loose mass of spheroid granules which, for instance, may be usable as aggregate for concrete or gypsum slurry and other casting masses for the purpose of reducing the specific weight or heat conductivity and/or of increasing the mechanical etrength or of reducing costs, and which for instance may be used in place of the known spheroid and porous granules of swelled clay. Such swelled clay granules are inexpensive and possess considerable strength and form-stability however, in view of their specific weight of 0.9 - 1#5 they are still relatively heavy and possess also a corresponding considerable thermal conductivity.

Furthermore, they absorb water like a sponge. Thus, it takes frequently a very long time until building walls formed of concrete including such aggregate material are dry, and under unfavourable climatic conditions they might become humid again. Furthermore, in humid conditions they have the same thermal conductivity and heat capacity as concrete free of this type of aggregate. If, for instance, such granules "of swelled clay are used as aggregate for cellular plastic materials, for instance polystyrene or hardenable urethane foam to reduce costs or to increase strength or to improve sound insulation, the specific weight and the heat conductivity of these materials is increased to such a considerable extent that the advantage of the use of such light weight building materials is almost offset.

A further possible utilisation of a loose mass of a filler material for the filling of cavities for the purpose of heat insulation in place of cork or "brick scraps* First of all, these materials are still relatively heavy and fully absorb water, so that cork scrap or other granules of material of vegetable origin tend to rot.

In view of these disadvantages^ at present frequently rock wool or spun glass fibres are used, which, however, tend to felting and sticking together and thereby lose their good heat insulating properties. Furthermore, it is frequently not possible to introduce such fibrous material into the cavities in a simple manner.

For all of, the described applications of a loose granular material of low specific gravity, there exists a substantial need of loose spheroid granules of e:rre ely low weight and correspondingly low heat conductivity, which granules take up as little water as possible, will not be decomposed and will not rot even under unfavourable climatic conditions, which, however, at the same time possess relatively high mechanical strength and form-stability so that they will not be squashed under relatively low pressure or completely destroyed by certain solvents such as acetone, as would be the case with laminated mica or swelled polystyrene granules.

An economically and technically even more important field of application of bodies of low specific weight of the type according to the present invention are formed bodies or plates or other building elements with a specific weight within the order of magnitude 1 insulation effect and also a relatively high strength and form-stability even at elevated temperatures. The strength characteristics of such bodies should correspond substantially to those of compressed bodies of mixtures of fibres with synthetic resin, and concrete or brick walls or bodies.

It is known that such requirements basically can be best fulfilled by hollow cellular structures or composite structural bodies including firm and tight outer shells and one or more interior fillings of hollow cellular structure, if desired with reinforcing inserts.

Known composite bodies or structural members of hollow cellular structure include for instance an internal honeycomb structure consisting of prefolded and stripwise connected cardboard, synthetic material or metal foils for the forming of inter-connected hexagonal hollow tubes, the initially open end faces of which are glued together with outer shells or some kind of intermediate layers.

Apart from the fact that such honeycomb structures are resistant to tension and compression only in the direction of the cell axes but have considerably less resistance to deformation forces in a direction transverse thereto, the thermal insulation effect of such structures is not particularly good because within the cells of the honeycomb unimpeded air convection is possible from one to the other of the end faces. If a good insulation effect is required, the expedient is used of cladding the honeycomb structure at both end faces with plates of plastic foam or fibrous material, or by filling the honeycomb cells prior to closing with foam masses. The production of structure, however, is generally economically feasible only in the case of planar plates with parallel faces and of comparatively small standardised thicknesses, because the plane end faces of the honeycomb arrangements must be cut in advance exactly to the desired shape and dimensions of the composite building element to be produced. In most cases it is attempted to achieve the desired thermal insulating properties and low specific weight of a light weight building element by filling a mould cavity for a cast or pressed body, which may be produced in any desired manner, with a foamable mass or swellable material which is foamed or caused to swell in the closed mould and is, thereafter, somewhat stiffened. As example for an initially liquid synthetic mass, v/hic may be foamed in the mould, polyurethane may be named and as an example for a granular mass of synthetic material, which may be subjected to an extreme degree of swelling by application of heat, polystyrene may be named* The use of polyurethane will result in a cellular structure with small cells of relatively stable shape and good load-carrying characteristics provided the temperature does never, rise substantially above 50° C.

As soon as this is the case, softening of the material and a potentially dangerous gas expansion takes place. Polystyrene is sufficiently stable up to temperatures of about 110° 0; however, its mechanical strength and form- stability even at low temperatures is much too small for use of this material for load-carrying structures of for plates to be exposed to mechanical stresses. Only in cases were such material is clad on all sides with solid also cannot be overcome by embedding in the foam material bodies of greater strength such as granules of swelled clay.

Furthermore, it has already been proposed to produce hollow cellular structures in such a manner that a mixture of hollow spheres with rigid-walls and liquid hardenable binder material are introduced into the cavity of a mould which for instance is lined at least partly with a foil designed to form the shell of the cellular building element, and that the aforesaid mass of hollow spheres is exposed in the mould cavity to pressure which, is maintained until the binder agent is set. It has been found that it is not easy to mass-produce stable hollow spheres at tolerable costs and furthermorei by using smooth-walled and substantially form-stable hollow spheres, upon pressing these hollow spheres against each other, the liquid binder agent tends to escape from the spheres exposed to pressure into the remaining free cavities so that the connection between these spheres is of insufficient strength.

The invention proceeds along new paths to create bodies of low specific weight which possess the desired favourable properties of strength and form-stability as well as resistance to chemical and atmospheric influences.

According to the present invention, the method of producing bodies of low specific weight based on foari material is characterised in that a loose mass of spheroid swelled granules is mixed with a liquid, hardenable binder until substantially complete wetting of the surfaces of all granules is achieved, and subsequently this mass complete covering of the binder agent layers coating all the granules, in such a manner that a dry, loose mass of spheroid swelled granules is formed, each granule havin a coating shell of hardenable binder agent, and outwardly adhering thereto, a solid pulverulent material, which is at least partially embedded in the binder layers For producing a loose mass of spheroid, extremely light granules with hard shells usable as aggregate for casting masses or as filler material for the filling of cavities in the manner described above and also, for instance, as a packing material for air filters or air humidifiers in air conditioning installations, the dry and loose mass of coated swelled granules produced in accordance with the present invention is preferably e:cposed in a loose and movable condition to the influence of heat, for instant in a stream of warm air, for hardening the shells of binder agent. In this manner, spheroid bodies are obtained, each having a closed shell of hardened binder agent with solid pulverulent material embedded therein. It is advantageous if inside the shells the original swelled granules are maintained because the latter will additionally- support the thin shells from inside and protect the same against destruction by local pressure or impact stresses. However, even when, for instance under the influence of elevated temperatures or certain chemicals, the swelled granules within a greater or smaller proportion of the shells are destroyed, the remaining hollow shells of the granules are still capable of fulfilling the function assigned to the same.

The present invention also encompasses a loose τ all of the above mentioned requirements and which is characterised in that it consists of round foam bodies , preferably spheroid polystyrene granules, which have been subjected to maximum swelling and wherein each granule is provided with a thin-walled, closed round shell of hardened synthetic resin material with solid particles embedded therein or adhering externally thereto. The following characteristics may be combined in such a granular mass:- (a Low weight per unit of volume, of the magnitude of a max. of 300 kg/m^ preferably max. 100 kg/m^. . (b) Considerable resistance to pressure and form- stability of the individual granules for the purpose of preventing destruction of the same under compression of the mass and upon transporting and mixing the same with other materials, for instance with a concrete nass. (c) Resistance to unfavourable climatic conditions such as moisture, wide temperature variations and air pollution. (d) Low susceptibility to' microbes, insects and other biological pests.

For producing monolithic bodies of cellular structure of low specific weight with relatively high pressure resistance and form-stability as well as high resistance to climatic and chemical influences, advantageously the dry and loose mass of coated foam material granules is compressed, while the binder agent is setting, so as to form a structure of hollow cells with r of any of said hollow cells being any originally formed foam granule preferably of a compressed but otherwise unchanged foam granule.

Preferably, a body of cellular structure thus produced has cell walls which are integrand with each other into a monolithic structure, or which make transition into each other and form practically closed cells, and which consist of a hardened binder agent, preferably a synthetic resin, for instance on an epoxy basis, and solid pulverulent material embedded therein, preferably mineral material, for instance quartz or chalk powder, the particle dimensions of which are mainly only slightly below the minimum thickness of 0.05 mm of the cell walls. The walls surround polyhedral cells, the three co-ordinate dimensions of which are substantially equal to one another and preferably are between 2 and 8 mm It will be readily understood that a body of such cellular structure has excellent strength and a form-stability in all directions of stress, comparable with that of concrete and bricks, a very low weight per unit of volume and a correspondingly low heat conductivity . and, provided a high quality· binder resistant to temperatures up to 200 - 300°C is used for producing the cell walls, the same will retain their strength and shape even at higher than normal ambient temperatures and upon exposure to intensive sun radiation. Furthermore, such a cellular structure is not sensitive to moisture, does not form a nutrient medium for microorganisms and will not be eaten by animals, particularly insects, for instance termites.

Advantageously loose, more or less strongly pre- of 2 - 3 nm are used as the spheroid swelled granules.

Swellable polystyrene is commercially available for instance in the form of a granular mass under the registered trade name " tyropor" and can be swelled in hot water or with super-heated steam to a weight per litre of less than 0.01 kg. If the polystyrene granulate is swelled in an unlimited space, individual swelled granules are formed having approximately spheroid or oval shape and quite a smooth surface. Thus, swelled polystyrene granules form excellent heat insulators and are hydrophobic, i.e., they take up practically no water and are in general ver resistant to solvents except specific solvents such as acetone, and are particularly resistant to water or biological-organic decomposition conditions, as long as the temperature does not rise beyond 100° C. At higher temperatures or under the effect of specific solvents they collapse to a small size of residual material. In addition, polystyrene granules are not very inflammable, i.e., when ignited they generally do not sustain burning.

This inherent lack of form-stability or mechanical strength of the swelled -polystyrene bodies is favourable to or even a prerequisite for the realisation of the above defined principle of the invention: When wetted on their surfaces with a liquid binder agent and subsequently coated by the admixture of dry solid sand or powder forming a dry shell of solid pulverulent material, and then exposed to pressure, the initially round-shaped polystyrene granules are deformed into polyhedral bodies which contact each other along relatively large areas. the resiliently yielding surface of the polystyrene granules so that the binder agent cannot be pushed aside but will be squeezed outwardly between the solid particles. Thereby a mixture of binder agent and solid particles is formed and this mixture is hardened under the influence of heat to a monolithic structure of hollow polyhedral cells which is of considerable mechanical strength.

Quartz sand having a partiple size corresponding to a diameter of between 0.1 and 0,2 nun is particularly suitable as the fine-grained solid material. However, also other mineral powders of corresponding particle size, for instance impregnated chalk powder or the products obtained .by gr nding ceramic fragments may be used.

Particularly suitable as a binder agent is epoxy resin which is utilised in liquid form with a hardener admixed and which sets more or less quickly under the influence of elevated temperatures. It is essential that the binder agent used combines intimately with the solid powder and with the shell-forming material, and is capable of forming thin but mechanically highly stable hard layers. It is also advantageous to utilise as the finegrained solid material V metal powder, for instance aluminium powder, particularly if a somewhat higher degree of heat transmission through the complete cellular structural element is desired or, for instance a higher specific weight is desired for better acoustic insulatio With a grain size of the solid powder corresponding to a diameter of 0.1 mm, even by using relatively little binder agent, an average wall thickness of the hardened hollow cellular structure of about the same magnitude and attained.. By using the very finest powder of solid material and even less of the liquid binder, a correspondingly lighter but also less resistant hollow cellular structure is obtained. On the other hand the use of a coarse grained solid material, for instance of 0.2 - 0. ram grain size and of a somewhat more viscous binder agent in larger quantities will lead to a correspondingly more thickly walled and stronger but heavier hollow cellular structure. The heat required for the hardening of the foam mass which in the mould cavity is exposed to pressure, may be produced in a furnace or for instance by diathermic heating in a high frequency electric alternating field.

Since during the hardening of epoxy resins exothermal heat is set free and is only very slowly absorbed by the foam granules and thereby fast temperature rises are effected, owing to the small thermal capacity of the granules it frequently suffices to heat a compressed mass of the covered foam granules from the outside in order to cause the thermal hardening of the resin to spread into the interior of the mass.

Generally provision is to be made that upon the pressing of the loose mass of foam granules with double shells of non-hardened binder agent and solid powder adhering thereto, the volume of the granular mass is reduced by the effect of a pressure of at least one atmosphere gauge to 755^ at most, preferably to 50 - 60 , of the initial value.

It is possible without difficulties, prior to having dimensions larger than the granules, for instance swelled clay bodies, of a material of higher specific weight, and upon compression to form an integral "body of the sane and of the hollow cellular structure formed.

It may, however, be even more advantageous to integrate the mass of coated foam granules during compression in the mould with a planar coating material in the form of plates, sheets, foils, mats which is resistant, smooth and pleasantly coloured for instance with synthetic resin-impregnated fibre glass or asbestos mats, for which purpose it may be advantageous to wet these elements, prior to. their introduction into the mould, with a liquid synthetic resin. Similarly, it is also possible fully or at least partially to embed and thereby to integrate connecting elements with the mass during the compression of the same, for instance parts of door fittings, screw or bolt members, supporting or reinforcing bodies. On the other hand, planar covering material in the form of plates, sheets, foils, mats and the like may be adhesively attached to a hollow cellular structure of the described type after completion of the pressing of the same.

Mould members or inserts such as tubular cores, which during compressing are not to become integral with the hollow cellular structure formed, are to be treated with suitable protective substances on a basis of silicone or Teflon (registered trade mark). Thus, it is possible, for instance, to insert into the mould cavity tubes to serve as cores, through which warm air or warm liquids may be passed for hardening the binder agent in the hollow cellular structure. Generally, within the scope of the pressure moulding may be employed.

The invention relates also to a pressed "body of cellular structure produced in accordance with the method . of the invention, which body is characterised by polyhedral and practically closed cells, the walls of which are firmly connected vrith each other and consist of a hardened binder agent with solid powder embedded therein, each cell containing either a swelled granule or at least the remainder thereof, whether there are contained in the cell chambers the original polyhedral foam granules or only the material thereof, which remains after collapse due to over-heating or exposure to. solvents, is unimportant sinoe the strength of the material is primarily determined by that of the cell walls.

The compressed body of cellular structure of the present invention may be adhesively connected, durin or after its compression, with planar covering material such as aluminium or steel sheet, or with asbestos cement or any other kind of fibrous plate material impregnated with synthetic resin, or any type of covering layers or foils, or may also be adhesively attached to shells of such materials* Thus, for instance, aluminium and steel sheet or asbestos cement layers, and also glass fibre-reinforced foils of synthetic resins act as reinforcements, inasmuch as these materials do not only endow the entire composite structural element with a substantially invulnerable surface but also, essentially improve the tensile strength and bending strength of the hollow cellular structure.

Similarl it is ib anchor therein connecting or supporting elements, for instance door fittings, jointing member and the like.

It is also possible to use to a certain advantage corrugated or angularly ribbed profiled plates. The mechanical strength, thermal insulation properties and acoustic insulation properties, the resistance to moisture and other corrosive influences can be adjusted as desired in so many different ways that the buildin element of cellular structure according to the present invention appears usable for self-supporting wall members, window sills, doors and door frames, thresholds, floor elements, ceiling elements, table plates, a substitute for furniture-board but also as, roofing plates. The building elements of cellular structure in accordance with the present invention, thanks to their high strength and low weight, t can also be used in the machine and apparatus building industry.

The method of the present invention and an example of a building element produced in accordance with this method are illustrated in the accompanying drawings, wherein:- Fig. 1 illustrates in diagrammatic elevation an example of carrying out the first step of the method, namely the wetting of polystyrene granules with hardenable epoxy resin liquid, some of the granules being shown on a larger .scale.

Fig. 2 illustrates in diagrammatic elevation an example of carrying out the second step of the method, namely the coating of polystyrene granules wetted with the binder agent by a pulverulent solid material, one Fig, 3 shows in sectional elevation the producing of a building element of cellular structure in a pressure mould.

Fig. 4- is an enlarged section of a detail of the wall structure formed.

According to Fig. 1, swelled polystyrene granules 20 of spheroid shape and of a weight per litre of about 5 - 10 g are introduced from a vessel 2 into a mixing container 1 equipped with a stirrer. The average grain diameter is 3 - 6 mm. From a vessel 3 an amount of about 250 - 3OO g epoxy resin liquid, for instance Araldit (registered trade mark) , with the required hardener addition is mixed to about 10 - 15 litres of such polystyrene granules, and the entire mass is intimately mixed until all polystyrene granules are evenly wetted with a layer 30 of the binder agent. Depending on the amount of the added liquid binder agent and on the viscosity thereof, thinner or thicker binder agent layers are produced on the polystyrene granules. As an average the thickness of the binder agent layer should be about 0.08 - Ο.25 mm. According to Fig. 2, subsequently an amount of fine-grain quartz sand 4-0 or any other mineral sand, for instance impregnated chalk powder or even metal powder, for instance aluminium powder having a grain size of O.05 - Ο.25 mm, i.e., which is about equal to the thickness of binder agent layer 30, is admixed into the mixing container 1 from a bag 4·. The amount of powder must be sufficient for completely covering the polystyrene granules 20 wetted with liquid binder agent, with an outwardly dry fine-grained sand layer 4-0, the individual ■ If the polystyrene granules thus doubly coated, are e:cposed to ,a stream of warm air for the purpose of hardening the binding agent layer with the adhering, or partially embedded solid particles, extremely light round cellular granules with thin hard shells are obtained and the same may be used as aggregate for casting masses, as filler material for the filling of cavities, or as cellular material for air purification or air humidification, A loose mass of polystyrene granules wetted with a binder agent and coated with a layer of solid powder thus obtained is, however, primarily suitable as a filler material for producing a sandwich building plate according to Fig. 3.

Into a mould cavity formed by the mould portions 51, 52 fitted together there had been introduced, superimposed upon each other, a lower metal sheet 61, tubular cores 62, filler material 60 in the form of swelled polystyrene spheres wetted with binder agent and covered with granular solid powder as well as an upper metal sheet 63. The cover sheets 61, 63 have to be previously wetted with the binder agent. The entire · contents of the mould are compressed to less than half their original volume, for which purpose a pressure of about 1 - 5 kg/cm suffices for producing a building plate of a thickness of about 6 cm. The resiliently yielding polystyrene granules are deformed thereby into polyhedrons with contacting plane surfaces. Thereby, the liquid plastic binder agent.30 (Fig. 4·) is squeezed between the solid granules 40 so that the solid grains 0 are completely embedded in the binder agent 30. On the other hand, the sand grains 40 partially penetrating of the hinder agent. While maintaining the pressure, the mould 51» 52 as well as the tubular cores 62, if any, are heated so that the content of the mould is warmod, for instance to 50 - 90°C, whereby the binder agent is sete In this manner, a monolithic, polyhedral cellular structure is formed, which is also integrally adhesively attached to the metal plates 61, 63. The surfaces of the mould parts 51, 52, which are directly adjacent to the filler mass, and also tubular cores 62, if any, were treated with lubricants, for instance silicone grease or the like so that these parts can be easily separated. Provision may be. made for heating the contents of the mould after the setting of the binder agent for a short period of time to a higher temperature of, for instance, 130°C, whereby the polystyrene granules which up to then had filled the cells will collapse and lose their elasticity.

Claims (1)

1. lana A monolithic cellular structure produced by according to any of 1 wherein the polyhedral of the practically closed cello o hardened binder with particles embedded A monolithic cellular structure according to Claim each cell contains a pressed foam A monolithic cellular structure according to Claims 5 or wherein thickness of the cell is mm or leas and the three dimensions of the cells are stantially equal and amount each to abou 2 A monolithic structure according to Claims 5 integrated outer inner coating or intermediate layers in a composite monolithic structure according to formed as a load water building for assemblage in building with different or building insufficientOCRQuality