GB2111896A

GB2111896A - Process for producing a gasket element

Info

Publication number: GB2111896A
Application number: GB08234527A
Authority: GB
Inventors: Roland Schaefer
Original assignee: LECHLER ELRING DICHTUNGSWERKE; Elring Dichtungswerke GmbH
Current assignee: LECHLER ELRING DICHTUNGSWERKE; Elring Dichtungswerke GmbH
Priority date: 1981-12-15
Filing date: 1982-12-03
Publication date: 1983-07-13
Also published as: DE3149541A1; ES8308759A1; ES518171A0; FR2518013A1

Abstract

To form a gasket sealing element with curved edges an elastomeric material blank 20 is compressed in the cutting region by a ram 23 causing the material to deform as shown by dotted lines 24. The cutter 30 is then driven though the material, cutting the blank 20 along lines 26, and on the relief of the pressure the element obtained has a cut edge which is concave and enables a locating fit in a gasket. <IMAGE>

Description

SPECIFICATION Process for producing a gasket element In the production of flat gaskets which, like cylinder head gaskets in modern engines, for example, are subject to stringent requirements, there is an increasing tendency to incorporate sealing elements of elastomeric material in openings in the gasket board which forms the body of the flat gasket, since the available sealing forces are frequently limited and there is therefore a need for sealing areas which provide a tight seal even under relative low compression.However, until now, the mounting of gasket elements of this kind in metallic gasket boards or composite gasket boards such as, for example, the traditional metal/asbestos gasket boards, has presented technical manufacturing problems, if, as is the case in engine assembly, for example, the flat gasket must be provided as a single unit and must not consist of a number of parts.

It is known to fit the gasket elements in question into the gasket board by adhesive bonding or vulcanising or, if the abutment surfaces are suitably formed, by snap-fitting, but it has also been known to resort two such complicated procedures as injection-moulding a gasket element onto the edge of an opening in a gasket board orvulcanising a gasket element onto a metal binding ring which is then inserted in the opening in the gasket board and flanged so as to engage over the edge of the opening. Obviously, all these solutions have technical disadvantages from the point of view of production, since they require either complex and timeconsuming production methods or expensive equipment.This is also true of the annular gasket elements with a concave outer contour which are intended to be snap-fitted into openings in a gasket board; these gasket elements have hitherto been produced by injection moulding, for example, which not only necessitates expensive equipment but also leads to a high percentage of waste of the elastomeric material used, which is a major drawback particularly in the case of expensive materials such as the otherwise advantageous fluorinated elastomers.

The aim ofthe invention was to provide a simple and inexpensive process for producing gasket elements from an elastomeric material, these elements having an area of contact which is concave or convex in cross section, at least in certain areas, so that an annular gasket element of this kind, for example, with an outer peripheral surface which is concave in cross section can readily be snap-fitted into an opening in a gasket board.

Starting from a process for producing a gasket element from a blank consisting of elastomeric material wherein at least one area of contact of the gasket element is produced by cutting at right angles to one surface of the blank, particularly by punching, this aim is achieved according to the invention by the fact that pressure is exerted on the blank adjacent to the area of contact, of convex or concave cross section, which is to be produced and approximately perpendicular to the surface thereof, in such a way that elastomeric material is displaced at right angles to the imaginary cutting surface and through this surface, and in that the cutting is carried out whilst this pressure is maintained.The basic concept of the invention is thus that it should be possible to cut or punch through the blank in a straight line but obtain an area of contact which is curved in cross section, if the elastomeric material is displaced through the imaginary cutting surface before the cutting operation and then the cutting or punching operation is carried out whilst this state is maintained, so that when the elastomeric material is released the cutting surface is deformed to give the required area of contact with the desired contour.

The explanations given above show that, if pressure is exerted on both sides of the imaginary cutting surface, it is only the pressure difference over the cutting point which matters, since it is this pressure difference which determines the displacement of the preferably incompressible elastomeric material through the imaginary cutting surface.

With the process according to the invention, it is readily possible to produce gasket elements of any desired shape, e.g. in the form of circular discs or circles or ovals or rectangles, in plan view, and also linear gasket elements, and any materials which are predominantly elastic and substantially incompressible may be used.

The pressure to be applied before and during the cutting or punching may be generated mechanically, hydraulically or pneumatically, and the loading or deformation of the blank which subsequently results in the desired contour of the area of contact may be fixed either by means of the load applied to the blank or, better, by means of the strain path of a pressure ram or the like (the latter alternative is more favourable since then a pressure ram can be advanced up to an abutment without taking account of the degree of force required to do this). Since the cutting surface is rectilinear in cross section when the blank is under load, this cutting surface may be produced by means of any desired cutting or punching tool, e.g. a tubular stamping gauge, a belt knife or the like.

In order to stamp a disc-shaped gasket element, for example, from a sheet of elastomeric material, the peripheral surface of this sealing element having a concave or convex contour symmetrical to the central plane of the sheet in cross section, the elastomeric material must be prevented from migrating at the two main surfaces when the pressure is applied. This can be achieved by creating correspondingly high friction between the blank, the pressure ram and the support surface opposite this ram. It is therefore advisable for the elastomeric material on at least one of the surfaces of the blank through which the imaginary cutting surface passes to be held in place at least on one side of the cutting surface so that the process of displacement of the elastomeric material through the imaginary cutting surface is restricted to the interior of the blank.The preceding remarks show, however, that the process according to the invention makes it possible, for example, to stamp out gasket elements which are in the form of truncated cones on the outside, by holding the elastomeric material of the blank in place on one main surface and aliowing the elastomeric material to migrate at the opposite main surface of the blank.

Advantageously, the blank is subjected to a pressure such that it decreases in thickness by 30 to 70%, since the cutting pressure exerted by a stamping gauge is then negligible, i.e. the cutting pressure does not affect the contour of the area of contact to be produced, which is predetermined by the pressure applied before the cutting or punching.

Further features, advantages and details of the invention will become apparent from the accompanying claims and/or from the description which follows and from the accompanying drawings of two preferred embodiments of the process according to the invention; in the drawings: Figure 1 is a cross section through part of a flat gasket, the gasket board of which comprises openings, into which circular gasket elements prepared according to the invention have been snap-fitted; Figure 2 shows the forming pressure being applied to the blank, in the form of a sheet, before a gasket element in the form of a circular disc is stamped out; Figure 3 shows the parts shown in Figure 2, but after completion of the stamping operation, but with the gasket element still kept under pressure;; Figure 4shows the parts shown in Figure 3 after the gasket element has been released from the pressure, and this gasket element can subsequently have a central, circular-cylindrical opening stamped into it in the usual way; Figure 5 shows a view corresponding to Figure 2, showing the production of a circular gasket element with concave outer and inner circumferential surfaces, and Figure 6shows a section through the gasket element produced according to Figure 5.

Figure 1 shows a gasket board 10 containing, for example, two circular openings 12 and 14. A circular gasket element 16 or 18 is snap-fitted into these openings, the outer circumferential surface 16a or 18a of the gasket element having a contour which is concave in cross section so that the gasket element in question automatically stays in place in the associated opening 12 or 14 once it has been pressed in.

Figures 2 to 4 are intended to illustrate the production of the gasket element 16. It is assumed that this gasket element consists of a substantially elastic and incompressible material.

First, a sheet 20 of the selected elastomeric material, which serves as the blank, is placed on a support 22 and is then subjected to load by means of a ram 23 so that elastomeric material is displaced outwardly through the imaginary cutting surface 26 which is to be produced, as indicated by the dotted lines 24. The displacement pattern denoted by the lines 24 is obtained when the elastomeric material cannot migrate at the two main surfaces 20a and 20b of the sheet 20, and this is most easily achieved if a ram 23 and a support 22 are used, the surfaces of which have a very high coefficient of friction relative to the elastomeric material of the sheet 20.

While the pressure exerted by the ram 23 is maintained, the cutting surface 26 which is rectilinear in cross section is produced by means of a stamping gauge 30 in the form of a circularcylindrical tube (see Figure 3). After the pressure has been released and the gasket element 32 thus produced has been pressed out of the sheet 20, the cutting surface 26 forms the outer circumferential surface 16a, which is concave in cross section, as a result of the gasket element returning to its former shape, so that only a central, circular-cylindrical opening need be stamped out to convert the gasket element 32 into the gasket element 16.

Figure 6 shows a circular gasket element 50 having an outer circumferential surface 50a which is concave in cross section and a similar inner circumferential surface 50b. A gasket element of this kind may also be produced extremely easily by means of the process according to the invention, as will be explained with reference to Figure 5.

First, a sheet 60 of elastomeric material is subjected to loading by means of a circular ram 62 and, whilst this loading is maintained, the two circumferential surfaces 50a and 50b, which are initially rectilinear in cross section, are produced by means of an outer and inner circular stamping gauge 64 and 66, respectively. After the pressure has been released and the gasket element 50 has been pressed out of the sheet 60, it assumes the shape shown in Figure 6.

The process according to the invention is also suitable for the production of gasket elements with a partly cylindrical, partly concave or convex area of contract, if the ram or rams are constructed so that pressure is exerted on the blank only along one or more parts of the imaginary cutting surface, on that side of the cutting surface towards which the area of contact which isto be produced is curved.

Claims

1. A method of forming a gasket element from a blank consisting of elastomeric material, wherein at least one area of contact of the gasket element is produced by cutting at right angles to one surface of the blank, including exerting pressure on the blank adjacent to the area of contact which is to be produced and substantially perpendicular to the surface thereof in such a way that elastomeric material is displaced at right angles to the imaginary cutting surface and through this surface, and carrying out the cutting while this pressure is maintained.

2. A method as claimed in claim 1, wherein the pressure is produced by a ram which is separate from a cutting or punching tool.

3. Process as claimed in claim 1 or 2, wherein the pressure is exerted on the blank along the entire imaginary cutting surface and on one side thereof.

4. A method as claimed in claim 1 or 2, wherein, in order to produce a partly cylindrical, partly concave or convex area of contact, the pressure is exerted on the blank along only part of the imaginary cutting surface and on that side of the cutting surface towards which the area of contact is intended to curve outwardly.

5. A method as claimed in one or more of claims 1 to 4, wherein the elastomeric material on at least one of the surfaces of the blank through which the imaginary cutting surface passes is held in place at least on one side of the cutting surface.

6. A method as claimed in claim 5, wherein at least one of the surfaces of the blank through which the imaginary cutting surface passes is pressed against a surface with a high coefficient of friction relative to the elastomeric material.

7. A method as claimed in any of the preceding claims, wherein the pressure which is exerted on the blank is such that its thickness decreases by 30 to 70%.

8. A method as claimed in any of the preceding claims, wherein the elastomeric material is substantially incompressible.

9. A method of forming a gasket element substantially as herein described with reference to the accompanying drawings.