GB2047298A

GB2047298A - Gasket Material

Info

Publication number: GB2047298A
Application number: GB8011203A
Authority: GB
Original assignee: Goetze GmbH
Current assignee: Goetze GmbH
Priority date: 1979-04-07
Filing date: 1980-04-03
Publication date: 1980-11-26
Also published as: DE2914173C2; GB2047298B; DE2914173A1

Abstract

For cylinder head gaskets and similar flat seals the conventional asbestos mat is replaced by a non- woven fibre mat in which the fibres are a mixture of sheet forming natural organic fibres such as cotton and cellulose fibres and non-sheet-forming synthetic inorganic fibres such as rock wool or glass fibres or synthetic organic fibres such as polyamides. The sheet-forming fibres are preferably between 25 and 75% of the mixture and the non-sheet-forming fibres between 75 and 25%. The mat can be formed on a papermaking machine using binders to hold the fibres together and can be made with 30% to 60% by volume of free pores which may subsequently be impregnated to improve the sealing quality and thermal resistance of the sheet.

Description

SPECIFICATION Gasket Material The invention relates to a sheet material suitable for use in flat seals, for example cylinder head gaskets for internal combustion engines.

Cylinder head gaskets, which must have a suitable degree of compressibility to enable them to produce a good seal, are commonly made from a non-woven mat of asbestos fibres. Such a mat can be produced on a normal paper-making machine or by means of rolls from aqueous mixtures of asbestos fibres with a little rubber as a binder. The gasket may incorporate a metal sheet as a reinforcement, the metal sheet commonly being sandwiched between two sheets of asbestos mat. In addition, as described and claimed in British Patent No. 1,447,143 the finished gasket may be additionally impregnated with an organic substance which is cross-linked so that it is plastic or elastic in its final state.

Asbestos is the ideal fibre material for making such cylinder head gaskets. On the one hand, asbestos has the necessary high resistance to changes of temperature and, on the other hand, the asbestos fibres are sufficiently soft, so that the fibre nonwoven formed is given paper-like properties with sufficient strength, deformability and porosity.

At the same time, however, asbestos is markedly harmful to health, since above all the fine asbestos dust forming during the processing thereof may cause serious lung diseases. The use of asbestos should therefore be restricted as far as possible and it is even to be expected that the use of asbestos will be prohibited entirely. In addition, asbestos is constantly becoming more costly by reason of the increasing shortage of raw material. In the future, the use of asbestos could therefore become uneconomic.

As a remedy, it has therefore already been attempted in practice to use other fibre materials for nonwovens for making cylinder head gaskets. Available for use are natural fibres, such as for example cellulose fibres, organic synthetic fibres resistant to changes of temperature, such as for example polyamide fibres, or else inorganic fibres, such as for example rock wool or glass wool. Fibres of this kind, however, mostly do not have all the ideal properties of asbestos fibres at the same time, that is they are either not sufficiently resistant to changes of temperature, or they are also harmful to health, or they are so brittle that the production of a paper-like fibre nonwoven on a paper-making machine is not possible.

The problem of the present invention, therefore, is to discover, without employing asbestos, a soft-material sealing material with paper-like properties with which flat soft-material seals or packings, and in fact in particular cylinder head gaskets, of sufficient strength, deformability, resistance to changes of temperature and porosity can be produced. In particular, it should be possible to impregnate the sealing plate with a substance which is cross-linked so that it is plastic or elastic in its final state.

According to the invention, this problem is solved by means of a soft-material sealing-plate material which is produced from a mixture of fibres capable of forming sheets of paper and fibres not capable of forming sheets of papers. The fibres suitable for such sheet formation which are preferably used are cotton fibres, cellulose fibres or other fibres obtained from natural organic raw materials. The fibres not suitable for such sheet formation which are preferably used are rock wool fibres, glass fibres, slag fibres, ceramic fibres or synthetic organic fibres, preferably based on polyamides.

The sheet-forming fibres are generally soft and flexible and swell when soaked in water whereas the non-sheet-forming synthetic fibres are relatively hard and stiff with smooth surfaces and-do not swell in water. Fibres with an average length of 0.5 to about 3 mm are preferably employed for both types and the fibre mixture preferably consists of 25 to 75 per cent of the sheet-forming fibres and 75 to 25 percent of the non-sheet-forming fibres. In addition, synthetic resins or rubbers may be present as binders in the soft-material sealing material.

The soft-material sealing material according to the invention is preferably produced on the screen of a paper-making machine from an aqueous suspension of fibre mixture and, if necessary, binder. With a proportion of less than 25% of sheet-forming fibre, a paper-like product is not formed. Proportions of more than 75 per cent of organic sheet-forming fibre, however, have a detrimental effect on the resistance to changes of temperature.

Moreover, a sealing plate for installation between the parts to be sealed should have good compressibility and at the same time spring-back resilience. This is achieved by means of a relatively highly porous soft-material plate material. To this end, in the case of cylinder head gaskets, the free pore volume should be approximately between 30 and 60%. According to the invention, there is the possibility of so choosing the type of fibre and the mixing proportions of the fibres that the desired free pore volume is obtained. In addition, the plate material can be after-compressed to the desired volume by subsequent rolling. Equally, however, in accordance with the invention, the material according to the invention consisting of soft material may also be produced from the moist mixture of fibres and, if necessary, binders in calenders.

The soft-material sealing-plate material according to the invention is preferably subsequently impregnated in accordance with German Laid-open Patent Specification 23 04 558 with a synthetic, organic, completely polymerizable liquid to give a pore filling of between 60 and 90% and this liquid is then heat-hardened to an elastic consistency under the action of the cross-linking agents. In the process, the resistance of the sealing-plate materials to changes of temperature increases to a multiple, since the cross-linked impregnating medium evidently acts as an insulating layer for the organic sheet-forming fibre.

The impregnated sealing plates obtained in this way show under test a deformation behaviour, a slump or subsidence behaviour and an imperviousness to water and oil like those of sealing plates made from conventional asbestos fibre sheets. Consequently, as a result of the invention, an asbestosfree sealing or gasket material has been produced which is at the same time simple and cost-saving to produce. In particular, the sealing plates according to the invention are suitable for producing cylinder head gaskets impregnated in accordance with German Laid-open Patent Specification 23 04 558 and the equivalent British Patent No. 1,447,143.

The following three fibre mixtures are preferably used in the production of cylinder head gaskets in accordance with the invention:- 1. 50 parts of rock wool (fibre length 1.4 mm) 50 parts of cotton (fibre length 2.8 mm) 2. 60 parts of rock wool (fibre length 1.4 mm) 40 parts of cellulose fibre (fibre length 2.8 mm) 3. 25 parts of polyamide fibres (aramide) (fibre length 2 mm) 75 parts of cellulose fibres (fibre length 2.8 mm)

Claims

1. A sheet material for seals such as cylinder head gaskets comprising a non-woven fibre mat in which the fibres are a mixture of sheet-forming natural organic fibres and non-sheet-forming synthetic inorganic or synthetic organic fibres.

2. A sheet material as claimed in claim 1 in which the fibre mixture consists of 25 to 75 per cent of natural organic fibre and 75 to 25 per cent of synthetic fibre.

3. A sheet material as claimed in claim 1 or 2 in which the length of the fibres is between 0.5 and 3 mm.

4. A sheet material as claimed in any of claims 1 to 3 which is porous with the pores forming 30 to 60% by volume of the sheet.

5. A sheet material as claimed in any of the preceding claims including binders holding the fibres together.

6. A process of making cylinder head gaskets in which the sheet material of any one of the preceding claims is used on the sealing material.

7. A process as claimed in claim 6 in which the sheet material is porous and the pores are at least partially filled with a curable synthetic resin impregnating material.

8. Cylinder head gaskets produced by the process of claim 6 or 7.