EP1202942A1

EP1202942A1 - Polymerceramic materials with thermal expansion characteristics similar to those of metals

Info

Publication number: EP1202942A1
Application number: EP00962296A
Authority: EP
Inventors: Peter Greil; Andreas Basteck; Steffen Walter
Original assignee: Rauschert Paul KG Firma
Current assignee: Rauschert Paul KG Firma
Priority date: 1999-08-10
Filing date: 2000-08-05
Publication date: 2002-05-08
Also published as: WO2001010791A1; US6783866B1; DE19937322C2; DE19937322A1

Abstract

The invention relates to polymerceramic composite materials with almost zero contraction compared to the mould after final partial pyrolysis and with comparable thermal expansion characteristics (preferably within an application range of 400 °C or below) to metal construction materials, especially gray cast iron or steel, obtained according to the method described below. The invention also relates to corresponding composite structures and moulded parts and to methods for producing and using the inventive materials, composite structures and moulded parts. These polymerceramic composite materials can be used e.g. instead of or in contact with steel or gray cast iron as temperature-resistant moulded parts, predominantly in mechanical engineering, without finishing after the moulding process.

Description

Polymer-ceramic materials with metal-like thermal expansion behavior

SUMMARY OF THE INVENTION The invention relates to polymer-ceramic composite materials with an approximate shrinkage compared to the original shape after final partial pyrolysis and with a comparable thermal expansion behavior (preferably in an application range of 400 ° C. or below) such as metallic construction materials, in particular gray cast iron or steel. which are obtainable by the processes described below; corresponding molded parts and composite structures comprising these composite materials; Processes for the production and use of these composite materials, molded parts and composite structures. The polymer-ceramic composite materials can be used, for example, instead of steel or cast iron in temperature-resistant composite structures or molded parts, primarily in mechanical engineering without post-processing using the master molding process. BACKGROUND OF THE INVENTION Ceramic materials are used increasingly as a construction material for thermally and mechanically stressed functional elements in machines, apparatus and devices due to their high wear resistance and good temperature resistance as well as corrosion resistance. The requirements to be met for the geometric precision of the functional elements can, however, only be met by ceramic materials by complex post-processing or by a complex molding process (iterative process), which complicates cost-effective production, in particular of components of complex shape or that require high precision. Furthermore, the mechanical post-processing can cause damage to otherwise closed surfaces, for example, and thus lead to reduced stability. In addition, the difference in thermal expansion between ceramics (silicon and silicon carbide, for example 3 - 4.5 x 10 ^"6 K ^_1 , aluminum oxide and zirconium oxide approx. 8 - 9 x 10 ^{" 6} K ^q ), and gray cast iron

(9 - 10 x 10 ^"6 K ^{" 1} ) or steel (10 - 13 x 10 ⁶ K ^" ) (temperature range Room temperature up to approx. 500 ° C) with temperature stress to different expansions between metal and ceramic, which in the association of ceramic and metallic parts cause mechanical overloading of the ceramic part as well as internal stresses on joining and connecting surfaces as well as gap increases on sealing surfaces and thus the functional ability of the relevant part, for example Limit the machine or system.

Plastic products have the advantage of being inexpensive to manufacture, but these parts have low dimensional accuracy and low long-term service temperature resistance of less than 1,50 ° C, rarely less than 200 ° C.

So-called Polymer ceramics, in the production of which a polymer partially or completely decomposes by pyrolysis and thus completely or partly converts it into an inorganic composite material, which, however, still contains organic components after temperature treatment. In addition, the polymer ceramic fillers, e.g. B. ceramic powder.

DE 412 08 describes the reaction of ceramic fillers with reactive groups such as OH groups on their surface with crosslinkable functional groups in a polymer matrix (isocyanates, siliconates and their salts and esters) between 100 ° C and 180 ° C 35 described. Free-flowing masses were used for the compression molding of polymer ceramics. In addition to the principle of curing through surface condensation reactions, DE 442 84 65 describes the production of polymer ceramics from an organosilicon matrix between 200 and 800 ° C. The formation of primary chemical bonds between ceramic filler and polymer is regarded as a prerequisite for the formation of a dimensionally and temperature-stable network in the heating process, which allows relatively small volume changes to be achieved with less than 1% linear shrinkage. The shape of such polysiloxane / filler compositions with surface-active groups on the ceramic powder is by pressing and, as stated in DE 195 23 655, alternatively also by casting; Injection molding and extrusion possible. In order to increase the mechanical strength, fiber fillers which, for example, have ammo groups on their surface, can also be incorporated (DE 196 45 634). DE 198 14 697 describes piezoelectric actuators, in the production of which ceramic and metallic parts or precursors thereof are extruded simultaneously. Neither the desired constancy of shape compared to the original shape nor the metal-like expansion coefficients of the present invention are suggested or sought therein, nor are the composite materials according to the invention, in particular individual parts consisting of polymer ceramic component and metal part in the composite.

There are plenty of uses for temperature resistant

Materials and components, for example in automotive engineering

(Connection parts, housing or brake parts that come into contact with a higher ambient temperature, exhaust manifold or components thereof), in machine tool construction, in robot technology (for example for guiding and sliding elements), in the area of metallurgy or also in the area of pressure and vacuum pump technology, or other areas. It is also particularly important here to minimize costs and to use substitutes for metals, in particular cast iron and steel, to reduce the risk of corrosion and / or in the interest of a lightweight construction.

In particular, there is a lack of materials which, even at higher temperatures, have a thermal expansion (thermal expansion, thermal expansion coefficient = TAK) comparable, in particular the same, that of steel or gray cast iron, and which can also withstand high temperatures in the temperature range of interest, even after prolonged exposure. Such materials and parts and components made from them should be able to be produced in the master molding process by press molding or in particular by casting, injection molding or extrusion. An important goal is to enable the production of (especially larger) molded parts or composite structures from larger parts with high dimensional accuracy in the original molding process without post-processing and thus the risks for components resulting from their brittleness, possible material damage due to abrasive shaping and other post-treatment methods Adaptation to the required shapes and dimensions with a high degree of dimensional accuracy are required, particularly in the case of polymer ceramic components, to reduce or eliminate them. For this, the pyrolysis following the shaping at a temperature that practically enables zero shrinkage in the primary molding process is a prerequisite.

There is in particular an urgent need to be able to manufacture molded parts, in particular larger molded parts, or composite structures from larger components (such as molded parts) cost-effectively with high dimensional accuracy, which provide thermal expansion in the area of the mainly used metallic construction materials, in particular steel or gray cast iron, as well as sufficient Strength, temperature resistance especially at elevated temperatures and corrosion resistance.

The invention has for its object to provide polymer ceramic materials, the thermal expansion of the finished product compared to known polymer ceramic materials is matched to the thermal expansion of steel and gray cast iron and at the same time to achieve a high degree of dimensional stability during production in the primary molding process, so that in particular molded parts or composite structures complicated geometry or larger dimensions, for example with a minimum outer diameter of more than 20 mm, preferably more than 50 mm. These and the other objects mentioned are surprisingly achieved by the polymer ceramics described in the present disclosure, composite structures comprising polymer ceramic components and molded polymer ceramic parts. In the state of the art there is no indication of the solution to this task, and the task itself is not considered there either. General description of the invention

Some, several, or in particular all of the above-mentioned objects are defined by one (1) a preceramic polymer (ceramic binder, hereinafter referred to as polymer or more precisely, which term can also include mixtures of polymers), (n) its pyrolysis-related degradation products and (m ) If necessary, fillers (ceramic powder, ceramic filler) comprising polymer ceramic or also synonymously polymer ceramic composite material, in particular a polymer ceramic material, which is characterized by a coefficient of thermal expansion that that of a metal (this term encompasses alloys in the broader sense), in particular of Steel or cast iron, comparable, in particular the same, is and is preferably obtainable by heat treatment under theoretically or preferably empirically determined conditions (in terms of duration and, above all, temperature and temperature profile), which enables the material l or a molded body produced therefrom after the final heat treatment within a tolerance of less than 0.1%, preferably less than 0.05%, has the same linear dimensions as the original shape (zero shrinkage in the primary molding process).

The invention relates in particular to a molded part which consists of such a material and / or a composite construction which comprises such a material.

The molded parts, composite structures or materials as well as processes according to the invention make it possible, in particular, that the required dimensional accuracy (essentially zero shrinkage compared to the shape) of the polymer ceramic component can be achieved directly (by appropriate heat treatment and / or composition of the polymer ceramic material) in the primary molding process. This enables enormous cost reductions by a factor of 2 or more, since there is no need for post-processing. The associated adaptation of the thermal expansion behavior to that of metals, in particular steel or gray cast iron, enables the application, for example, in the areas mentioned at the beginning. Thus, the urgent practical needs are surprisingly taken into account. In particular, the polymer-ceramic materials according to the invention also have the advantage of a certain residual elasticity which, for example, can cushion and reduce surface tensions induced from the outside and / or reduce losses due to friction in connection with other parts.

Description of the drawings:

Fig. 1 shows the dimensional changes in partial pyrolysis of polymer-ceramic masses. (1) = thermal expansion, (2) = pyrolysis shrinkage, (3) = polymer, (4) = ceramic.

2 shows an example of the coefficient of expansion of polymethylsiloxane m as a function of the pyrolysis temperature m argon.

3 shows a three-dimensional matrix to illustrate the methods described below, on the basis of which e.g. empirically the optimization problem of simultaneously obtaining zero shrinkage and a metal expansion comparable to that of metals can be solved.

FIG. 4 shows the expansion and subsequent shrinkage of a polymer ceramic material described in more detail in exemplary embodiment 2 at different pyrolysis temperatures.

Detailed description of the invention

The invention relates to a polymer-ceramic composite material or, in particular, a molded part made of a polymer-ceramic material or a composite construction comprising at least one component made of a polymer-ceramic material (for example a molded part according to the invention), the underlying polymer-ceramic material being a thermal expansion behavior comparable to metallic construction materials and shrinkage compared to the original shape after final partial pyrolysis, obtainable by a process which comprises that one mixes at least one polymer material and one or more ceramic fillers (and, if necessary, further additives) with one another, then subjects them to crosslinking - in the case of the molded part with the production of a corresponding green body, in the case of a composite construction directly in the presence of further components (parts), provided that the composite construction is to be produced in the master molding process (alternatively, it can also be produced by subsequently connecting other components with one or more molded parts according to the invention) - and finally subjecting the resulting material, the resulting preliminary stage of the composite construction or the resulting green body of the molded part to a partial pyrolysis, the weight ratios of the components used and the Type of heat treatment based on theoretically or (preferably) empirically determined values so that the resulting polymer-ceramic composite material, the resulting molded part or the resulting composite construction - hereinafter collectively referred to as the "product" - has the thermal expansion behavior comparable to that of a metal and, after partial pyrolysis, has the same linear dimensions as the original shape within a tolerance of less than or equal to 0.1%.

The invention preferably relates to a polymer-ceramic composite, a molded part or a composite construction according to the preceding paragraph, obtainable by partial pyrolysis of a mixture comprising a ceramic filler in a proportion of 10 to 80 percent by volume and a polymer in a proportion of 20 to 90 percent by volume, the partial pyrolysis in the range between 200 and 800 ° C., preferably in the range from 500 to 750 ° C., so that a shrinkage of 0.1% or less, preferably 0.05% or less, is achieved compared to the original shape.

A polymer-ceramic composite, a molded part or a composite construction according to one of the two is more preferred The preceding paragraphs, which in addition to a ceramic filler and a polymer contains other additives up to 10 percent by volume.

A polymer-ceramic composite, a molded part or a composite construction according to one of the last three paragraphs is more preferred, characterized in that its thermal expansion is the same as that of steel or gray cast iron.

A polymer-ceramic composite, a molded part or a composite construction according to one of the last four paragraphs is more preferred, characterized in that its thermal expansion in the range from -50 ° C to 500 ° C is the same as that of steel or gray cast iron.

A polymer-ceramic composite, a molded part or a composite construction according to one of the last five paragraphs is more preferred, characterized in that its thermal expansion in the range from room temperature to 400 ° C. is the same as that of steel or gray cast iron.

A polymer-ceramic composite, a molded part or a composite construction according to one of the last six paragraphs is more preferred, characterized in that ceramic fillers with a grain size of 1 to 50 μm are used in its manufacture.

The invention also relates to a composite construction, in particular a single part, consisting of a polymer-ceramic molded part according to one of the last seven paragraphs in combination with metal parts.

An individual part according to the directly preceding paragraph is preferred, in which the metal parts are steel or cast iron parts.

The invention also relates to a production method for a polymer-ceramic composite material, a molded part or a composite construction according to one of the last 9 paragraphs, comprising as a process step that at least one polymer material and one or more ceramic fillers (and, if necessary, further additives) are mixed with one another, then subjected to crosslinking - in the case of the molded part to produce one Corresponding green body, in the case of a composite construction directly in the presence of other components (parts, especially made of other materials), provided that the composite construction is to be produced using the original molding process (alternatively, it can also be produced by subsequently connecting other components with one or more molded parts according to the invention ) - and finally subjecting the resulting material, the resulting preliminary stage of the composite construction or the resulting green body of the molded part to a partial pyrolysis, the weight ratios of the com components and the type of heat treatment on the basis of theoretically or (preferably) empirically determined values so that the resulting product has the thermal expansion behavior comparable to that of a metal and, after partial pyrolysis, within a tolerance of equal to or less than 0, 1% has the same linear dimensions as the original form.

The invention relates in particular to a method according to the immediately preceding paragraph, the weight ratios of the components used being selected such that the resulting product has a thermal expansion behavior comparable to that of steel or cast iron and, after partial pyrolysis, within a tolerance of equal to or less than 0 , 05% has the same linear dimensions as the original form.

A method according to the penultimate paragraph is preferred, the weight ratios of the components used and the type of partial pyrolysis being selected on the basis of empirically determined values, characterized in that the empirical determination comprises the following steps: (A) first empirical determination for a material or molded part made of a polymer or a polymer-ceramic material or a component of the composite construction made of a polymer or a polymer-ceramic material of the exact pyrolysis temperature for zero shrinkage compared to the original form in the primary molding process and determination of the thermal expansion coefficient of the material thus obtained;

(B) by adding ceramic fillers (whereby further variables have to be kept constant at first) adapting the expansion coefficient to that of steel or cast iron; and

(C) subsequent determination of the exact pyrolysis temperature for zero shrinkage in the primary molding process and simultaneous setting of a coefficient of thermal expansion in the range of that of the desired metal, step (B), if the necessary pyrolysis temperature lies between the grid points used, being repeated once more with fine reduction and it it may be necessary to repeat steps (B) and / or (C) again or iteratively several times.

Also preferred is a method according to the penultimate paragraph, wherein the weight ratios of the components used and the type of partial pyrolysis are selected on the basis of empirically determined values, characterized in that the empirical determination comprises the following steps: (A *) pyrolysis of a polymer or Polykeramikwerkstoffes a known composition at various pyrolysis temperatures to determine the thermal expansion coefficient of the ceramic material in each case _j polymer available or -formteils or Komponetente of the composite structure and determination of the shrinkage or expansion of the material so obtained available;

(B *) admixing ceramic fillers to adapt the thermal expansion coefficient to that of steel or cast iron; and (C *) determination of the pyrolysis temperature with zero shrinkage; whereby, since in step (B *) only one grid is built, the necessary for this necessary pyrolysis temperature can lie between the grid steps, so that iteratively the range of the pyrolysis temperature and the suitable composition can be obtained by repeating steps (B *) and / or (C *) one or more times.

The invention also relates to the use of a polymer-ceramic material, a composite construction comprising the same, or a molded part thereof, as described above under "Detailed Description of the Invention", preferably in machines, devices or systems in which they come into contact with metallic materials or parts a temperature range from -50 ° C to 400 ° C, especially from room temperature to 350 ° C, especially from 25 to 300 ° C.

Unless otherwise stated, the general terms mentioned above and below have the following meanings within the scope of the present disclosure:

"Comprehensive" means that in addition to the components mentioned, other components or additives may also be present, preferably in the range from 10 or less, in particular from 7 or less volume percent (vol%) (synonymous with "at least containing"), or, in the case of processes that further process steps and / or materials are possible. Instead of comprising, it can preferably be “containing”.

Instead of the term "partial pyrolysis", the terms "heat treatment" or "pyrolysis" are used above and below. The heat treatment is preferably carried out in a controlled manner, for example by relatively long heating rates and relatively long cooling rates, for example cooling rates in the range from 0.2 to 10 ° C / mm, so as to prevent the occurrence of stresses in the resulting materials or molded parts. The heat treatment is preferably carried out with the exclusion of air and oxygen, in particular under inert gas such as argon. "Theoretically or empirically determined" in connection with the heat treatment refers to literature approaches or in particular to variants of the mixing rule with empirical measurements, for example dilatometry (expansion dependence of temperature and expansion coefficient and comparable variables) and the shrinkage. Preferred methods for the theoretical or empirical determination of the parameters for the heat treatment, in particular the maximum pyrolysis temperature, but also also the holding time (which can be variable in particular in the range below 400 ° C., on the other hand can be used relatively constant above this temperature) and / or the rate of warming up and cooling down are mentioned below.

The following details m (percent by weight or) volume percent always refer to the starting materials (before the heat treatment, which generally leads to the partial degradation of the polymer used).

A metallic, in particular gray cast iron or steel, comparable or, in particular, the same thermal expansion behavior (or thermal expansion behavior) is understood in particular to mean a corresponding thermal expansion coefficient, ie the corresponding thermal expansion coefficients (thermal expansion coefficient, TAK) are preferably in the range from 9 to 13 x 10 ^"6 K behave ^_1. This thermal expansion can be found according to the invention is preferably in the range of -50 to 500 ° C, especially from room temperature to 400 ° C.

The parameter "thermal expansion coefficient comparable or in particular the same to a metal (or a metallic construction material)" (or corresponding thermal expansion behavior or heat (expansion) behavior) also enables the material differentiation from other polymer-ceramic materials, components of composite constructions and molded parts, because this result an appropriate structure and composition is required. By "comparable" it is meant in particular that the coefficient of thermal expansion of the corresponding product are up to and including 20%, in particular 10%, preferably up to and including 3%, below the lower or above the upper coefficient of thermal expansion of the corresponding metal, such as in particular steel or gray cast iron. With a "same" coefficient of thermal expansion, this differs from that of the corresponding metal by 1 percent or less, in particular by 0.1% or less.

Even if this is not specifically stated, the upper and lower limit values mentioned are always included when specifying ranges, such as% or temperature ranges or the like.

A preceramic polymer is to be understood in particular as a polymer whose pyrolysis does not result in a virtually complete conversion to carbon or other inorganic substances (as would be the case, for example, with polyesters, polyethers or epoxides). Preferred examples are mentioned below without being intended to limit the range of possible polymers.

If a polymer is mentioned above and below, unless otherwise stated or evident, a preceramic polymer is always meant.

"Zero shrinkage" means a linear shrinkage of 0.1% or less, especially 0.05% or less.

The process according to the invention for producing the polymer-ceramic materials and moldings mentioned at the outset is particularly characterized in that, via the degree of conversion of the polymer into the polymer-ceramic binding phase, determined by the heat treatment temperature, and in connection with the incorporation of ceramic fillers with matched thermal expansion of the molded part, components of composite structures or composite constructions are produced which, in terms of their thermal expansion behavior, largely match those of metals, in particular steel or Gray cast iron, which are comparable or the same, ie the corresponding thermal expansion coefficients (thermal expansion coefficients, TAK), are preferably in the range from 9 to 13 x 10 ^"6 K" ¹ .

A composite construction within the meaning of the invention is to be understood in particular as a combination of one or more parts (components) made of polymer-ceramic material, which is connected to one or more parts (components) made of other materials, in particular metal, especially steel or gray cast iron , Composite structures can be invented either directly by introducing their components ("components of the / a composite structure" - in the case of the polymer ceramic component as a preliminary stage, together with the part or parts from other materials, together the "preliminary stage of the composite structure") in the master molding process with heat treatment or alternatively by Connecting one or more molded parts made of a polymer ceramic material according to the invention with the other components (parts made of other materials), in particular metal parts, or by any conceivable combination of these steps.

The polymer ceramic materials and molded parts according to the invention are particularly suitable for use in combination with metallic components (for example if the polymer ceramic parts are in contact with metal, in particular gray cast iron or steel parts, be it by material bonding (for example by gluing) or in particular positive locking (e.g. by introducing molded parts in the primary molding process or during or after heat treatment) or frictional locking (e.g. by wrapping under press tension or the like), m temperature-stressed assemblies such as m brakes, motors or other machines, devices or systems resulting products also fall under the composite structures according to the invention.

Which are preferably made of a polymer, in particular a crosslinked organosilicon polymer, and if necessary one or Several ceramic fillers and, if desired, further additives, compounded starting material, in particular after shaping and crosslinking, for example at temperatures between 0 and 200 ° C, in particular between 100 and 200 ° C, a controlled heat treatment in the temperature range between 200 and 800 ° C, preferably 400 and 750 ° C, in particular between 500 and 750 ° C, especially in the temperature range between 500 and 680 ° C, whereby an amorphous polymer-ceramic binder phase between the filler particles is produced from the polymer, in particular a polysiloxane resin. The decisive factor here is that the thermal expansion of the starting mass is compensated by partial pyrolysis of the polymer component to the extent that the initial dimensions of the master part are retained after cooling and thermal contraction. Dimensional stability can be ensured by simple control of the heat treatment temperature within narrow limits (0.1% linear or below), whereby in particular manufacturing tolerances of less than or equal to 0.05% are achieved under constant manufacturing conditions. 1 shows the dimensional changes that occur during the heat treatment. In particular, moldings or (in the presence of other components made of other materials, in particular metals) composite structures according to the invention can be produced using the original molding processes customary in ceramics, such as pressing, casting, injection molding or extruding.

A preferred example of suitable polymers are organosilicon polymers, in particular polysiloxane resins which are easy to process, but also polysilane, polycarbosilane, polysilazane, polyborosilazane or mixtures thereof can be used. Where polymer and polymer material, highly crosslinked organosilicon polymer or the like are mentioned above and below, mixtures of several of these components can also be present. Taken together, these then give the volume percentages mentioned as preferred. By building ceramic fillers in volume contents of 10 to 80% by volume, preferably for the production of molded parts or composite structures which can be obtained in the pressing, casting, injection molding or further extrusion processes, of about 20 to 80% by volume, in particular 30 to 80% by volume -%, preferably from 30 to 70%, primarily from 30 to 60% by volume, especially between 30 and 50% by volume, which have a thermal expansion adapted to the thermal expansion of the polymer-ceramic binder phase, moldings or To produce composite structures whose thermal expansion behavior between room temperature and 500 ° C is largely comparable to that of steel (10 - 13 x 10 ^ K ^"1 ) or gray cast iron (9 - 11 x 10 ^{" 6} K), in particular the same. For example, the pyrolysis temperature with zero shrinkage is first determined for a given polymer. Then the coefficient of thermal expansion is determined and, if necessary, compensated for by suitable fillers. The installation of ceramic fillers (= ceramic fillers) then enables dimensional stability and a further adapted thermal expansion to be achieved at the same time. The reverse procedure (first determination of composition and pyrolysis temperature, then, if necessary, iterative, variation of these parameters until a reversal is achieved is also possible. Below are preferred methods. FIG. 3 illustrates how this optimization problem is solved by means of a three-dimensional matrix.

Preferred ceramic fillers are listed in Table 1, but other non-reactive ceramic compounds with a correspondingly high thermal expansion can also be used.

Table 1

CSZ: Cubic Stabilized Zirconia; PSZ: Partially Stabilized Zirconia; ** Sikron SH 300 (Quarzwerke Frechen)

Silicates, such as sodium, magnesium, calcium or lithium aluminum silicates, or calcium fluoride can also be used as fillers, especially if the thermal expansion coefficient of the polymer ceramic is higher after a certain pyrolysis temperature than that of the corresponding metal, especially steel or gray cast iron.

Where a ceramic filler, ceramic filler, ceramic filler, filler or the like (all with the same meaning) is mentioned above and below, mixtures of several of these components may also be present. Taken together, these then give the volume percentages mentioned as preferred.

In addition to the polymer and the filler, other additives may also be present, preferably in the range below 10% by volume, especially below 7% by volume, which can increase the strength, for example glass frits, or in particular wax-like substances such as wax, and / or catalysts such as aluminum acetylacetonate.

Products according to the invention are preferred in which the polymers and / or the additives do not form any chemical (in particular no covalent) bonds to the fillers during pyrolysis.

The preferred process according to the invention also differs fundamentally from the polymer pyrolysis process with reactive fillers which either completely at temperatures above 800 ° C. (DE-PS 392 60 77) or at lower temperatures react via reactive groups on the surface (DE 442 84 65) with the polymer phase to form primary chemical bonds. The ceramic fillers can be partially or completely replaced by a so-called own filler, which can be produced by heat treatment of the preceramic polymer and subsequent processing into a powder. Eigenfuller have the advantage of being able to adjust the thermal expansion through the pyrolysis temperature.

Products according to the invention which are produced without the addition of float glass frits are particularly preferred. Products according to the invention are also preferred in which the polymer component does not comprise phenylmethylsiloxane resins. Products according to the invention are also preferred in which the polymer component does not comprise siloxanes with unsaturated groups. Products according to the invention are also preferred in which the polymer component does not comprise any polyesters, epoxides or polyethers. Also preferred are products according to the invention, in the production of which no solvents are used, except in the case of the use of casting, injection molding and extrusion processes, where this is possible. Kaolin is preferably excluded as filling material.

Depending on the flow properties of the polymer component used (solid or liquid at room temperature) and the filler content (= ceramic filler content), the polymer / filler masses are shaped using shaping processes customary in ceramics, e.g. Pressing, casting or injection molding in closed molds or extruding. The polymer binder phase is then crosslinked under pressure at preferred temperatures of 0 to 200 ° C., in particular between 100 to 200 ° C., preferably under an inert gas. After removal from the mold, the molded part has a high green strength and can be machined if desired.

The porosity typical of polymer-ceramic materials, which occurs in particular in the temperature range from 200 ° C to 800 ° C The decomposition of the polymer phase and the removal of gaseous organic fission products reaches their maximum, is retained inside the molded part, but can largely be converted or broken down into a closed pore structure on the molded part surface.

A preferred embodiment of the invention is the use of carbon-containing release or demolding coatings on the mold surfaces, which remain on the product surface, in particular the molded part surface, after demolding and heat treatment and lead to a seal. This also enables, for example, the use of products, in particular molded parts for applications in which pressure or vacuum is generated (pumps).

The polymer ceramic composite material according to the invention is particularly suitable for dimensionally accurate manufacturing processes and composite structures or molded parts with narrow tolerances, as well as a thermal expansion comparable to the metallic carrier material (in particular steel or gray cast iron), which is used for applications as temperature-stressed functional elements in a wide variety of assemblies such as machines, motors or systems are of particular importance.

In the following, two alternatives for theoretical or empirical determination are described in detail, in which way the suitable main parameters (pyrolysis temperature and composition, with a small shrinkage of 0.1% or less, preferably 0.05% or less, and a coefficient of thermal expansion comparable or preferably equal to that of gray cast iron or steel) for the products according to the invention, in particular polymer ceramic materials and moldings, can be specifically determined in order to arrive at products according to the invention, in particular polymer ceramic materials (cf. also FIG. 3):

Alternative (I) (preferred) Step (A): First, for one of a polymer or one polymer-ceramic material of known composition or a corresponding molded part or a component of a composite construction made of the material empirically determines the exact pyrolysis temperature for zero shrinkage compared to the original form in the original molding process and the thermal expansion coefficient (TAK) of the material with zero shrinkage.

Step B: The addition of ceramic fillers (taking into account other variables such as the material, degree of filling and binder layer of the filler, i.e. initially keeping them constant) adjusts the expansion coefficient to that of steel or cast iron.

Explanation: According to the example in Fig. 2 and Fig. 3, the expansion coefficient changes with increasing pyrolysis temperature. For polysiloxane, for example, the TAK up to 400 ° C pyrolysis temperature is approximately 90 x 10 ^"6 K ^{" 1} , while for pyrolysis above 800 ° C it is below 1 x 1 O ^ K ^"1. This means that the TAK decreases with increasing pyrolysis temperature between 200 and 800 ° C. However, at 650 ° C it is still not small enough to have the same expansion coefficient (TAK) as steel or gray cast iron, so step (B) must be carried out.

A theoretical rough estimate (without taking the grain size into account) can be carried out according to Turner and Kerner: From the modeling of the thermal expansion preservation of the filled polymer masses according to Turner's approaches

i-Ki-Pi ₊ ^a ₂ K ₂ ^F 2

(α) =

K ₁ F ₁ K ₂ F ₂

P ₅

or taking into account shear effects at the phase boundaries according to Kerner K _x (3K ₂ + 4G ₁ ) ² + (K ₂ -K _x ) (I6G ₁ + 120 ^ ₂ )

(α) = _λ + V ₂ (α ₂ -α ₁ )

(4G ₁ + 3tf ₂ ) [4V ₂ G ₁ (K ₂ -K _l ) + 3J ₁ JT ₂ + 4G ₁ 1 ₁ ]

From the knowledge of, for example, the tabular form (e.g. in the Handbook of Chemistry and Physics), temperature-dependent thermal expansion coefficients _x of phases 1 (1: polymer; 2: filler), the compression and shear modules K _x and G ₁ as well as the mass or Volume fractions F ₁ and V _x and the densities r _x expected values for the average expansion of the composite materials can be derived.

Subsequently or independently of such an estimate, an empirical determination is carried out by means of a matrix examination of different fillers with different expansion coefficients, for example according to the following example (e.g. with cylindrical bodies as a sample):

Example matrix for determining mixing ratios and pyrolysis temperatures in order to achieve certain desired coefficients of thermal expansion: filler polymer 1 polymer 1 polymer 1 polymer 1

Conc. TAK1 TAK2 TAK3 TAK4 (% by weight) 0 30 50

65 70 75 80 83

85 90 TAK 1 = thermal expansion coefficient for pyrolysis at e.g. 500 ° C TAK 2 = thermal expansion coefficient for pyrolysis at e.g. 550 ° C

TAK 3 = thermal expansion coefficient in pyrolysis e.g. 600 ° C

TAK 4 = thermal expansion coefficient in pyrolysis e.g. 650 ° C

The TAK are given in m 10 ^"6 K ^{" 1} .

In this way, the range is found in which the polymer ceramic mixtures each have TAK values in the range of, for example, gray cast iron or steel.

Step (C): Then the exact pyrolysis temperature for zero shrinkage in the primary molding process and simultaneous setting of a coefficient of thermal expansion in the range of that of the desired metal, e.g. of steel or gray cast iron, determined: Since only one grid is built up in the first step (B), the pyrolysis temperature required for this can lie between the grid points, so that step (B) may have to be repeated again with fine reduction (for example, by using a narrower one Temperature range for pyrolysis, for example at pyrolysis temperatures of 510, 530 and 540 ° C and filler quantities of, for example, 50, 55 and 65%). It may be necessary to repeat this process (steps (B) and / or (C)) again or iteratively several times.

Alternative (II)

Step (A *): First, by pyrolysis of a polymer or a polymer-ceramic material of known composition (material or molded part or component of a composite construction made from the material) at different pyrolysis temperatures, the linear thermal expansion coefficients (TAK) of the respective products available, in particular the underlying polymer ceramic materials or the the resulting molded parts are determined and at the same time the loss or expansion. Step (B *): The addition of ceramic fillers (taking into account other variables such as material, degree of filling, grain size and binder layer of the filler, ie they must be kept constant at first) adjusts the expansion coefficient to that of steel or cast iron. Here, a matrix analogous to that shown above for step (B) can be used, and / or a prediction of suitable ranges can be determined according to the methods mentioned there for the rough estimation. In this way, the range is found in which the polymer ceramic mixtures each have TAK values in the range of, for example, gray cast iron or steel.

Step (C *): The exact pyrolysis temperature for zero shrinkage compared to the shape obtained after the thermal pretreatment and in the case of molded parts or components of composite structures (compared to the shape in the primary molding process) is then determined. Since only one grid is built up in the first step (B *), the pyrolysis temperature required for this can lie between the grid points, so that step (B *) may have to be repeated in fine reduction (for example through a narrower temperature range for the pyrolysis, for example at pyrolysis temperatures of 510, 530 and 540 ° C and filler quantities of, for example, 50, 55 and 65%). It may be necessary to repeat this process (B * and / or C *) again or iteratively several times

As soon as the above-mentioned parameters, in particular filler content, polymer content, temperature of thermal crosslinking and (partial) pyrolysis temperature, optionally content of further additives and also further parameters such as size of the filler grains and the like, are known, m can now be maintained under constant conditions a simple production can also be carried out in large numbers or quantities of molded parts or materials according to the invention. It is immediately apparent that at high pyrolysis temperatures the fillers should have higher expansion coefficients than steel or gray cast iron to compensate for the very low polymer TAKs here (e.g. in the case of polysiloxanes) (here in particular come silicates or CaF ₂ , especially as mentioned above, m Consideration that can be used alone or together with other filler materials, or MgO), while at lower pyrolysis temperatures (where the polymer ceramic still has a high TAK) the fillers must have a low TAK to compensate for the TAK in the direction of that of cast iron or steel (Here, for example, silicon nitride or silicon carbide come into consideration).

The preferred temperatures for pyrolysis (actually partial pyrolysis) are 200 to 800 ° C, in particular 400 to 750 ° C, preferably 500 to 750 ° C, especially between 500 and 680 ° C inclusive.

Granular fillers whose preferred grain size is in the range from 1 to 50 μm are preferably used as fillers.

Other additions are possible. If necessary, these components must be taken into account in steps (A), (B) and / or (C) or A *, B * and / or C *, so that, for example, multidimensional matrices are created under (B) or B * , or they are simply kept constant and only the filler content varies (see Fig. 3).

The invention also relates to moldings made from the abovementioned, in particular the preferred, starting materials; Composite constructions which comprise e or more components (in particular molded parts) made from a polymer ceramic according to the invention and one or more components made from other materials, in particular metal, especially steel or gray cast iron; the above-mentioned, particularly preferred, production processes for the products, in particular the polymer-ceramic materials according to the invention; e Method, in particular as described above, for the theoretical or, preferably, empirical determination of the pyrolysis temperature and the ratio of polymer to ceramic filler, and, if appropriate, the proportion of other additives and / or other parameters, such as the particle size of the ceramic filler used, around a polymer-ceramic material or to obtain a molding according to the invention; the use of a product according to the invention, in particular a polymer-ceramic material or, above all, a molded part in machines, devices or systems in which they come into contact (in particular solid or loose, for example sliding) with metallic materials or parts, in particular at temperatures in the range from room temperature to 400 ° C, such as at 25 to 300 ° C, preferably at 50 to 300 ° C; as well as corresponding machines, devices or systems.

The invention particularly relates to methods, materials and moldings according to the examples.

Examples

The following examples serve to illustrate the invention, but are not intended to restrict it.

Example 1: To produce a full cylinder measuring 1.5 x 4 cm, which is to serve as a spacer, the solid polymethyl silicone resin NH 2100 (Chemische Werke Nünchritz) and a mixture of A1 ₂ 0 ₃ (average grain size <3 μm; TAK 8.3 x 10 ^"6 K ^_1 ) and Sι0 ₂ (average grain size 11 μm, Sikron SH 300, Frechen Quartz Works, TAK 14 x 10 ^{" 6} K ^"1 ) in a volume ratio of 50 vol% polysiloxane resin, 40 vol% A1 ₂ 0 ₃ and 10 vol.% Sι0 ₂ m a 2000 ml grinding pot, which is filled with 0.6 kg ceramic grinding balls, mixed dry for 12 hours at a speed of 30 mm ^1. The mix is in a heated stirred tank a low-viscosity suspension was transferred at 140 ° C. (melting point of NH 2100 approx. 50 ° C.) with constant stirring as a plasticizing aid 3.5 mass% wax are added (composition m mass%: 3.45 mass% wax, 28.85 mass% NH 2100 and 67.7 mass% filler).

The cylinders are manufactured with a low-pressure injection molding system at 150 ° C with a pressure of 5 MPa m using a cylinder injection mold made of steel preheated to 180 ° C and with an outside diameter of 25 mm. After curing while maintaining the pressure, the mold is removed and stored in a heating cabinet for complete crosslinking at 260 ° C. for 12 h. After removal from the mold, the molded part is subjected to a heat treatment in an argon atmosphere. Passive cooling follows with heating to 580 ° C with a heating rate of 2 ° C / m and a holding time of 4 h.

The cylinders produced in this way have a flexural strength of 50 MPa and, compared to the dimensions of the hot-pressed base body, have an average longitudinal shrinkage in the longitudinal direction of <1%. The linear thermal expansion in the temperature range from room temperature to 500 ° C is 13.6 x 10- ⁶ K ^"1 .

Example 2

To produce a molded part of a compressor, 73.8% by mass (corresponds to 47.5% by volume) of Al ₂ O ₃ (average grain size <15 μm; TAK = 8.3 x 10 ^ K ^"1 ), 4.6% by mass -% MgO (corresponds to 3.3% by volume; TAK = 14 x 10 ^"6 K ^{" 1} ) (average grain size <10 μm), 21.2% by mass (corresponds to 49.2% by volume) silicone resin (NH 2100 ) and 0.4% by mass of aluminum acetylacetonate as catalyst mixed as in embodiment 1. 520 g of the sieved (160 μm mesh size) powder are introduced into a preheated and graphite-coated steel press mold. The hot pressing is carried out in a heatable hydraulic press with a movable upper punch with a constant pressure of 10 MPa, whereas the temperature is increased in steps of 10 ° C after a holding time of 30 mm each from 80 ° C to finally 130 ° C. At this temperature 24 Held for hours to ensure the curing of the molding compound.

After removal from the mold, internal bores are made by turning with hard metal tools. The heat treatment then takes place in a graphite-heated resistance furnace in an argon atmosphere, the green body being supported on a porous Al ₂ O ₃ support. With a constant heating rate of 2 ° C / min it is heated to 580 ° C and kept at this temperature for 5 h. The cooling takes place again with a constant cooling rate of

2 ° C / mm.

The linear thermal expansion of the molded body obtained in the temperature range from room temperature to 500 ° C. is 11.3 × 10 ^“6 K ^{” 1} . The shaped body has a high degree of dimensional accuracy: Compared to the initial length of 115.25 mm (perpendicular to the pressing direction) of the hardened shaped body, a shrinkage of <50 μm can be determined, which corresponds to a linear dimensional change of <0.05%. The molded body can therefore be used directly for installation without further surface treatment. The bending strength σ _B is 51 N / mm ² , the material remains stable up to a temperature of 405 ° C.

Embodiment 3 In order to determine the thermal expansion behavior, test sticks with a rectangular cross section of 5 x 5 mm ² and a length of 38 mm are produced by hot pressing according to embodiment 2. The compositions of the sample sticks examined in a dilatometer are shown in Table 2:

Table 2: Sample compositions for the investigation of thermal expansion with approximate zero shrinkage. The data are given in% by mass

TAK = linear thermal expansion, T _pyr = pyrolysis temperature * amount m parts by mass (or g)

In a differential dilatometer (Netzsch Gerätebau), the test strips are measured against an Al ₂ 0 ₃ standard in the temperature range from room temperature to 500 ° C. The heating rate is 5 ° C / mm. As can be seen in Table 2, heat treatment in the temperature range from 570 to 671 ° C enables the examined specimens to expand very well to the values of ferritic steels (10 - 14 x 10 ^ K ^'1 ) or gray cast iron (9 - 11 x 10 ^ K ^"1 ). The shrinkage is less than 0.1%.

/Expectations

Claims

claims

1. molded part made of a polymer-ceramic material or composite construction comprising at least one component made of a polymer-ceramic material, the polymer-ceramic material having a thermal expansion behavior comparable to that of metallic construction materials and shrinkage compared to the original form after final partial pyrolysis, obtainable by a process in which at least em Mixes polymer material and one or more ceramic fillers with one another, then subjects them to crosslinking - in the case of the molded part to produce a corresponding green body, in the case of a composite construction directly in the presence of further components, provided that

Composite construction in the primary molding process or a polymer-ceramic material of known composition is to be produced - and finally the resulting preliminary stage of the composite construction or the resulting green body of the molded part is subjected to partial pyrolysis, the weight ratios of the components used and the type of heat treatment based on theoretically or empirically determined values be chosen so that the resulting product has the thermal expansion behavior comparable to that of a metal and, after partial pyrolysis, has the same linear dimensions as the original form within a tolerance of less than or equal to 0.1%.

2. Molding or composite construction according to claim 1, obtained by partial pyrolysis of a mixture comprising a ceramic filler in a proportion of 10 to 80 volume percent and em polymer in a proportion of 20 to 90 volume percent, the partial pyrolysis in the range between 200 and 800 ° C , preferably in the range from 500 to 750 ° C., is selected such that a shrinkage of

0.1% or less, preferably 0.05% or less, is achieved.

3. Molding or composite construction according to one of claims 1 or 2, which contains, in addition to a ceramic filler and a polymer, further additives up to 10 percent by volume.

4. Molding or composite construction according to one of claims 1 to 3, characterized in that its thermal expansion is the same as that of steel or cast iron.

5. molded part or composite construction according to one of claims 1 to 4, characterized in that its thermal expansion in the range of -50 ° C to 500 ° C is the same as that of steel or cast iron.

6. molded part or composite construction according to one of claims 1 to 4, characterized in that its thermal expansion in the range from room temperature to 400 ° C is the same as that of steel or cast iron.

7. molded part or composite construction according to one of claims 1 to 6, characterized in that ceramic fillers with a grain size of 1 to 50 microns are used in its manufacture.

8. Composite construction consisting of a polymer-ceramic molded part according to one of claims 1 to 7 in combination with metal parts.

9. Composite construction according to claim 8, wherein the metal parts are steel or cast iron parts.

1 0. Manufacturing process for a molded part according to one of claims 1 to 7 or a composite construction according to one of claims 1 to 9, comprising as process steps that at least one polymer material and one or more ceramic fillers are mixed together, then subjected to crosslinking - in the case of the molded part with the production of a corresponding green body, in the case of a composite construction directly in the presence of further parts - and finally the resulting material, the resulting preliminary stage of the composite construction or subject the resulting green body of the molded part to partial pyrolysis, the weight ratios of the components used and the type of heat treatment being selected on the basis of theoretically or empirically determined values so that the resulting product has a thermal expansion behavior comparable to that of a metal and after partial pyrolysis has the same linear dimensions as the original form within a tolerance of less than or equal to 0.1%.

11. The method according to claim 10, wherein the weight ratios of the components used are selected such that the resulting composite structure or the resulting molded part has a thermal expansion behavior comparable to that of steel or gray cast iron and after the partial pyrolysis within a tolerance of equal to or less than 0, 05% has the same linear dimensions as the original form.

1 2. Method according to claim 1 0, wherein the weight ratios of the components used and the type of partial pyrolysis are selected on the basis of empirically determined values, characterized in that the empirical determination comprises the following steps:

(A) first empirical determination for e molded part made of a polymer or a polymer-ceramic material or a component of the composite construction made of a polymer or a polymer-ceramic material of the exact pyrolysis temperature for ull - shrinkage compared to the original shape in the primary molding process and determination of the thermal Expansion coefficient of the material thus obtained;

(B) by adding ceramic fillers (with other variables initially being kept constant) adapting the coefficient of expansion to that of steel or cast iron; and

(C) subsequent determination of the exact pyrolysis temperature for zero shrinkage in the primary molding process and simultaneous setting of a coefficient of thermal expansion in the range of that of the target metal, step (B) if the necessary pyrolysis temperature between the used

Halftone dots, fine reduction is repeated again and it may be necessary to repeat steps (B) and / or (C) again or iteratively several times.

13. The method according to claim 10, wherein the weight ratios of the components used and the type of partial pyrolysis are selected on the basis of empirically determined values, characterized in that the empirical determination comprises the following steps: (A *) pyrolysis of a polymer or a polymer-ceramic

Material of known composition at different pyrolysis temperatures for determining the thermal expansion coefficient of the polymer ceramic material or molded part available in each case or the available component of the composite construction and determining the

Shrinkage or expansion of the material so obtained; (B *) admixing ceramic fillers to adapt the thermal expansion coefficient to that of steel or cast iron; and (C *) determination of the pyrolysis temperature with zero shrinkage; whereby, in step (B *) only a grid is built up, the pyrolysis temperature required for this can lie between the grid steps, so that iteratively the range of the pyrolysis temperature and the suitable composition can be repeated by repeating steps (B *) and / or or (C *) can be obtained.

4. Use of a molded part according to one of claims 1 to 7 or a composite structure according to one of claims 1 to 9 m machines, devices or systems in which they come into contact with metallic materials or parts.

/Summary