EP0752978A1

EP0752978A1 - Heat insulating mouldings

Info

Publication number: EP0752978A1
Application number: EP95908284A
Authority: EP
Inventors: Wilhelm Kullen; Olaf Schmenkel
Original assignee: ElringKlinger AG
Current assignee: ElringKlinger AG
Priority date: 1994-03-31
Filing date: 1995-02-16
Publication date: 1997-01-15
Also published as: DE4411436A1; WO1995026938A1

Abstract

For the simpler and more economical production of heat insulating mouldings for motor vehicles with internal combustion engines which can be used in particular for the thermal insulation of components conveying exhaust gases in the engine compartment and in the region of the exhaust system, it is proposed that they be made using a hardenable moulding compound comprising a high-temperature-resistant binder, a particulate component constituted of a porous material and a fibrous or needle-shaped reinforcing component.

Description

Insulated molded parts

The invention relates to thermal insulation molded parts for motor vehicles with internal combustion engines, in particular for the thermal insulation of exhaust gas-carrying components in the engine compartment and in the area of the exhaust system.

Previously known thermal insulation molded parts for motor vehicles with internal combustion engines are based on sheet metal parts made of steel or aluminum, which serve as carrier material and give the molded part the necessary strength. To achieve the necessary thermal insulation values, the sheet metal parts are glued or clamped with glass fiber fabric, steel wool, aluminum wool etc. In addition to their function as a carrier material, the sheet metal parts also function as a fastening part.

The sheet metal parts are generally produced by means of a forming or deep-drawing process, which is more complex the more complicated the shape of the sheet metal parts or the heat-insulating molded parts themselves is.

The object of the invention is to propose a new type of heat-insulating molded parts which can be manufactured more easily and more cost-effectively.

This object is achieved by heat-insulating molded parts which are produced using a curable molding compound which comprises a high-temperature-resistant binder, a particulate component of a pore-containing material and a fibrous or needle-shaped reinforcing component.

These thermal insulation molded parts can be produced without problems as self-supporting molded parts. The heat-insulating molded parts according to the invention are preferably at most less compressible, more preferably essentially incompressible. The binder will preferably comprise an inorganic reaction mixture forming a ceramic matrix, since moldings of this type can later be easily disposed of with household waste or - as will be described further below - can be recycled in the course of the production of new heat insulation molded parts. The use of a purely inorganic formulation also ensures very environmentally friendly production.

Inorganic reaction mixtures which are cold-curing are preferably used, since the tools for such molding compositions can be produced from plastic or wood. This means that expensive production of metal casting molds can be avoided.

In view of the desired high temperature strength of the molded parts, they are preferably produced essentially free of organic components.

Particularly suitable binder systems are described in DE 40 40 180 AI. The molding compositions described there - with or without foaming agents - are not suitable as molding compositions for the present invention, since the molded parts produced in this way do not withstand the mechanical stresses in the motor vehicle, but it has surprisingly been found that the molding compositions according to DE 40 40 180 are good are suitable as a binder system for the present invention.

A preferred inorganic reaction mixture contains water glass, potassium hydroxide solution and furnace filter dust from the production of corundum. This dust arises when bauxite is melted in large furnaces. At temperatures of approx. 2,200 ° C, fine particles as well as evaporated and condensed material are whirled up due to the resulting thermals. This dust is then collected in the suction filters. The chemical composition, depending on the raw material (bauxite) used, is approximately

50-70% A1 ₂ 0 ₂

20-50% Si0 ₂ and additions of T ± 0 ₂

Fe ₂ 0 ₃

CaO

MgO

Na ₂ 0 κ ₂ o

and possibly other trace elements. The grain size varies in large ranges from about 0.1 μm to 200 μm. The curing time can be set in wide ranges, for example between 5 seconds and 1 hour, by metering in the potassium hydroxide solution. This creates the possibility of optimally adapting the curing time to the existing manufacturing options.

Sodium water glass is preferably used as the water glass, since this is not only cheaper than potassium water glass, but also offers the advantage that the ceramic matrix formed has a higher mechanical strength and greater temperature resistance.

The self-curing inorganic reaction mixture, which forms a ceramic material, is particularly preferred because it forms a matrix which has a comparable strength to sintered ceramic.

In order to accelerate the hardening process of the inorganic reaction mixture forming the ceramic matrix, a warm hardening can be carried out at approximately 70-80 ° C. No particular requirements are to be made of the particulate component made of porous material, except that it has the lowest possible thermal conductivity. In particular, the particulate component need not have any particular mechanical strength, in particular no great compressive strength, and the particulate component also does not require high thermal stability. In the event that there is a change in the particulate component at the high temperatures prevailing in the engine compartment, this essentially leaves the function of the heat-insulating molded part unaffected, since the matrix surrounding the individual particles from the high-temperature-resistant binder forms the mold shark - Ensures the activity of the thermal insulation molded parts and also prevents any imperfections that may form within the matrix from forming larger cavities, so that even in the worst case when the particle-shaped component is destroyed as a result of the effect of temperature, the molded parts always have a structure in which a large number of cavities that serve for thermal insulation are preserved.

However, preference is given to using particulate, pore-containing materials which can also withstand the high-temperature conditions in the engine compartment or along the exhaust system, hollow glass spheres, expanded glass, Ver ikulite and / or pearlite being preferred here. The use of expanded glass instead of hollow glass spheres poses no problems, since the closed-pore structure of the hollow glass spheres is not necessary for the particulate, pore-containing component and the open-pore structure of the expanded glass particles does not have a disruptive effect in view of the normally set toughness of the molding composition . Expanded glass is also much cheaper than glass hollow spheres. Vermiculite and pearlite particles are preferred materials because of their very low density, with vermiculite due to its layer structure also from the point of view of a improved acoustic insulation effect can be selected as a particulate component.

In addition to the thermal insulation properties of the particulate, pore-containing material, the possibility is used as a side effect to produce the molded parts with a relatively low specific density, which is preferably <2 g / cm ^, more preferably <1.5 g / cm3 . Moldings with such a low specific density can be used for thermal insulation on a large scale without causing weight problems in automobile construction.

A wide range of reinforcing materials is also available for the reinforcing component, with fibrous reinforcing components not only meaning individual fibers, but also non-woven fabrics, fiber fabrics, knitted fabrics or the like. The needle-shaped reinforcement components are also to be understood as needle fleece or the like.

However, the needle-shaped or fibrous reinforcing component is preferably mixed into the molding composition in the form of individual fibers or individual needles. Needle-shaped wollastonite, glass fibers, mineral fibers, mineral wool and / or metal fibers have proven to be particularly suitable.

The needles or fibers of the reinforcing component should preferably have a length in the range from approximately 50 to approximately 200 μm. The lower limit of approx. 50 μm results from the fact that no reinforcing effect is achieved with significantly shorter fibers, while mixing of the molding compound becomes problematic with fibers with a significantly greater length than 200 μm and breakage of the long fibers the production of the molding compound is to be feared. An exception here are glass and metal fibers, which can be up to approx. 15 mm long. In addition to the previously described indispensable components of the molding composition according to the present invention, the molding composition may optionally contain, for example, a filler which can either be used to improve the properties of the molded parts or simply to reduce the cost of the molding composition material.

Talcum powder is a preferred filler, for example, because its platelet structure improves the elasticity of the hardened molding material.

Mica can also be used as a filler and is valued for its high heat resistance.

A particularly cheap filler is lime, which is used in particular as a substitute for stretching the molding compound.

However, hardened and comminuted molding material itself is also suitable as fillers for newly manufactured molded parts. In this way, used molded parts can be completely reused and do not have to be disposed of with the waste.

In the case of the fillers, care is preferably taken to ensure that the particle size of the filler particles ranges from approximately 0 to approximately 200 μm, with the largest possible particle size distribution. This means that a very narrow distribution within the range 0 to 200 μm grain size is preferably avoided.

The molding composition may also contain inorganic pigments, in particular in the form of metal oxides, such as Iron oxides, chromium oxides, etc.

The viscosity of the molding compound is - regardless of the type of used binder - preferably adjusted to a viscosity of <150 Pas. This not only permits good processing of the molding compound, but also permits gentle mixing of the fibrous or needle-shaped reinforcing materials.

The advantages of the thermal insulation molded parts according to the invention are, on the one hand, that they do not have a supporting structure, e.g. Sheet metal parts, need and can be produced in almost any configuration using easily produced shapes. Compared to the previous thermal insulation parts based on sheet metal parts, a much better, i.e. achieved in particular a smoother surface, and all design options are available to enhance the visual appearance. Since the car manufacturers place increasing value on an appealing design of the engine compartment, there is an essential advantage of the thermal insulation molded parts according to the invention over those known from the prior art. It is also very easy to make the molded part surface acoustically favorable, for example by means of a waffle or honeycomb structure.

Overall, the material that can be used for the production of the thermal insulation molded parts according to the invention is less expensive than for the molded parts according to the prior art, and since the complicated manufacture of formed or deep-drawn sheet metal parts is eliminated, there is also a much more economical manufacture, in particular also because of this, because easily producible plastic and wooden tools are suitable for producing the molded parts.

Only when using corundum furnace filter dust in connection with a special recipe (see below) is curing so rapid that large series production is possible (example 160,000 parts / year). Besides, only guarantees this special recipe and the use of precisely matched fillers and fibers are so strong and tough that they can be used in motor vehicles (vibrations!).

Finally, an exemplary formulation of a molding compound for the production of thermal insulation molded parts according to the invention may be mentioned:

1 part Si0 ₂ as a reference 1.4 to 2.7 parts H ₂ 0 binder

0.25 to 0.5 parts Na ₂ 0

12 to 20 parts of corundum furnace filter dust

2 to 8 parts of reinforcing fibers 0.5 parts of hollow glass spheres

It is important that the binding agent, together with the reinforcing component, forms a sufficiently firm and fast-curing matrix that can withstand the sometimes violent shocks that occur in motor vehicles during normal operation. The particulate, pore-containing material essentially serves only to improve the thermal insulation, and in many cases it may already be sufficient if the particulate, pore-containing material forms cavities in the matrix during the solidification and curing of the molding compound and keeps it free while the fate of the particulate, pore-containing material when the thermal insulation molded parts are used in the motor vehicle during the operating period is of lesser importance, since due to the strength of the matrix, the cavities necessary for the thermal insulation are also retained when the particulate , porous material changes over time or should even burn out from the molded parts. This means that instead of the particulate, pore-containing materials already mentioned, any other pore-containing material can be used which remains stable until the molding compound has cured and thus ensures the formation of pore-shaped cavities in the molding compound matrix.

The heat-insulating molded parts can contain molded-in or embedded fastening means which serve to fasten the heat-insulating part as a shield in the engine area or exhaust gas area of the motor vehicle. Fastening parts can in particular be metal parts with an incorporated thread.

In addition, depending on the application, the thermal insulation parts can have a coating that can be formed by a metallic material or by lacquers. In particular, the coating has the function of improving the radiation reflection on the inside in order to lead to even better thermal insulation by the thermal insulation part.

Particularly preferred molded thermal insulation parts comprise the reinforcing component in the form of a fiber mat. The fiber mat is impregnated with a residual molding compound and, if necessary, shaped before curing. The residual molding compound does not necessarily contain more reinforcing fibers or needles, but it does contain the remaining constituents defined at the outset, such as binders and the pore-containing material.

Some aspects of the invention are explained in more detail with the aid of the drawing, which shows a particularly preferred molded part according to the invention in a sectional view.

The figure shows a detail of a sectional view of a thermal insulation component 10 according to the invention, which consists of a with a molding compound impregnated fiber mat 12 according to the invention.

A high-temperature-resistant fiber mat (temperature-resistant up to approx. 800 to 1,000 ° C.) made of mineral wool was used as the fiber mat 12, which was briefly immersed in a very low-viscosity formulation for the molding composition. Alternatively, the binder could be applied on one or both sides in a viscous formulation.

The "wet" fiber mat produced in this way was pressed into a desired contour using a mold. Since the mat is very flexible due to the impregnation with the molding compound, the simplest shapes and the lowest pressures are sufficient. The ceramic binder hardens in a few minutes at ambient temperature, and the finished molded part can be removed from the mold.

In the thermal insulation component shown in the figure, a molding compound gradient was generated over the cross section of the molded part, i.e. the proportions of the molding compound in the total mass of the insulating component are greater on the surfaces 14 and 15 of the insulating component 10 than in the central region 16. This distribution of the molding compound over the cross-section of the component not only enables the molding compound to be saved in the production of the insulating components, but also improves on the one hand the thermal insulation properties and surprisingly also the acoustic insulation properties and of course results in a lower weight.

In addition, if the molding material is used sparingly, this leads to an optically acceptable surface and to a very low absorption of water and oil by the component 10.

If necessary, the surface can be refined to improve radiation shielding. The advantages of the invention in general lie in particular in the freedom of design in the shaping of the insulation components, in their extremely high strength, their low weight, in particular when using fiber mats as reinforcement and / or carrier material for the molding composition to be used, and high temperature resistance, good thermal insulation properties and good acoustic insulation properties.

In particular, it should be emphasized that a molding material which is suitable for impregnating fiber mats has been proposed for the first time and which is extremely temperature-resistant, i.e. remains temperature-resistant up to 1,000 ° C and which can also be cured in a few minutes at ambient temperature and therefore allows large-scale production of the insulation components.

Claims

P A T E N T A N S P R Ü C H E

Thermal insulation molded parts for motor vehicles with internal combustion engines, in particular for the thermal insulation of exhaust gas-carrying components, the molded parts being produced using a molding compound which can be hardened very quickly and which comprises a high-temperature-resistant binder, a particulate component of a pore-containing material and a fibrous or needle-shaped component Reinforcing component comprises.

2. Shaped parts according to claim 1, characterized in that the binder comprises an inorganic reaction mixture forming a ceramic matrix.

3. Molded parts according to claim 2, characterized in that the inorganic reaction mixture is self-curing, temperatures of up to 80 ° C being generated by an exothermic reaction.

4. Molded parts according to claim 2, characterized in that the inorganic reaction mixture comprises water glass, KOH and furnace filter dust from the production of corundum.

5. Molded parts according to claim 4, characterized in that the water glass consists essentially of sodium water glass be¬.

Shaped parts according to one of claims 1 to 5, characterized ge indicates that the particulate component comprises material containing pores, hollow glass spheres, expanded glass, vermiculite and / or pearlite.

Shaped parts according to one of claims 1 to 6, characterized in that their specific density is <2 g / cm ^, preferably <1.5 g / cm ^.

Molded parts according to one of claims 1 to 7, characterized in that the reinforcing component comprises nadeiform wollastonite, glass fibers, mineral fibers, mineral wool and / or metal fibers.

9. Molded parts according to claim 8, characterized in that the needles or fibers of the reinforcing component have a length in the range from about 50 to about 200 microns, in the case of glass and metal fibers to about 15 mm.

10. Molded parts according to one of the preceding claims, characterized in that the molding composition further contains a filler.

11. Moldings according to claim 10, characterized in that the filler comprises talc, mica, lime and / or recycled molding material in powder form.

12. Shaped parts according to claim 10 or 11, characterized gekennzeich¬ net that the grain size of the filler ranges from 0 to about 200 microns with a wide grain size distribution.

13. Molded parts according to one of claims 1 to 12, characterized in that the molding composition comprises inorganic pigments, in particular based on metal oxides.

14. Molded parts according to one of claims 1 to 13, characterized in that the viscosity of the molding compound is <150 Pas.

15. Shaped parts according to one of claims 1 to 14, characterized ge indicates that the shaped part comprises the fibrous or nadeiform reinforcing component as a high-temperature-resistant fiber mat, which is impregnated with the very quickly hardenable residual molding compound and before the molding compound hardens was modeled.

16. Molded parts according to claim 15, characterized in that the regions of the molded parts near the surface comprise a higher proportion of molding material than those lying distant from the surface.