GB2156012A - Making gaskets from expanded graphite - Google Patents

Abstract

In a method of making a gasket comprising graphite foils with an apertured reinforcement plate 1 between them, a bed 3 of particles of expanded graphite which encloses the apertured plate 1 is brought obliquely into engagement with a pressing tool 6 which has apertures 7 conforming with those 2 in the plate 1, to bring about compaction of the graphite above and below the plate into foils which adhere thereto but leave substantially uncompacted the expanded graphite particles which fill the plate apertures. The uncompacted graphite falls into a chute 8. The pressing tool may be in the fornm of an apertured, rotatable cylinder, the uncompacted graphite being extracted through the apertures in the cylinder under vacuum (Figs. 3 to 5). <IMAGE>

Description

SPECIFICATION Method of making a gasket This invention relates to a method of making a gasket, more particularly a gasket of the kind comprising graphite foils with a reinforcement plate between.

In UK patent application 2 088 491A there is described a method of making such a gasket for automotive and petrochemical applications which entails (among other things) pressing particles of expanded graphite in a mould onto the opposed faces of an apertured reinforcement plate to compact the particles and unite them into foils which adhere to the plate. The method as described in the citation avoids the excessive waste of graphite that results when cutting foils from sheets of compressed expanded graphite, but does not give good results when applied to the manufacture of gaskets which have a relatively narrow area bridging adjacent apertures, as in a gasket for the cylinder head of an internal combustion engine. What happens is that the bridging portion becomes formed with too low a density to have adequate strength or sealing capacity.

In the method according to the invention of making a gasket comprising graphite foils with an apertured reinforcement plate between them, a bed of particles of expanded graphite which encloses the apertured plate is brought obliquely into engagement with a pressing tool which has apertures conforming with those in the plate, to bring about compacting of the graphite above and below the plate into foils which adhere thereto but leave substantially uncompacted the expanded graphite particles which fill the plate apertures. The graphite left substantially uncompacted can then be collected for re-use.

The angle of engagement between the bed of expanded graphite particles and the pressing tool is preferably less than 30 > , and it is particularly preferred to employ an angle less than 15 . The bed is suitably brought into engagement with the pressing tool by moving it on a conveyor belt which is run at a velocity substantially equal to that of the pressing tool.

Preferably, the bed is formed by depositing a layer of expanded graphite particles onto the moving conveyor belt, laying apertured reinforcement plates on the layer of expanded graphite particles, and covering the plates with a further layer of expanded graphite particles.

According to one procedure the bed of particles of expanded graphite enclosing the apertured plate is bought into engagement with a series of pressing tools which are secured to a conveyor belt moving above and obliquely to the bed.

According to another procedure, the bed of particles of expanded graphite enclosing the apertured plate is brought into engagement with a rotating cylinder whose curved surface is so apertured as to constitute the apertured pressing tool or a series of such tools, for gradual compacting of the graphite.

The expanded graphite particles employed suitably have a density in the range 4-40 kg/m3. The graphite foils forming part of the finished gasket will usually have a density which is in the range 800-1600 kg/m3. The finished density need not be achieved wholly by compaction in the bed of graphite particles, that compaction being primarily to expel air smoothly from the expanded graphite while (a) producing a composite whose graphite foils are of uniform density and are firm enough to withstand handling during and after removal from the bed and (b) leaving the uncompacted graphite particles easily removable, as by allowing them to fall under gravity or by sweeping them away in a current of air.

Ordinarily, compaction of the graphite particles in the bed to a density of at least 400 kg/m3 is aimed at.

With a reinforcement plate that is smoothfaced, as distinct say from perforated or tanged, it will usually be necessary to precoat the plate with adhesive before enclosing it in the bed of expanded graphite particles.

The invention will now be further described with reference to the accompanying drawings, in which: Figure 1 is a schematic drawing of plant for making a gasket; Figure 2 is a view in perspective of part of the plant of Fig. 1, including pressing tools; Figure 3 is a perspective view of a form of pressing tool alternative to those shown in Fig. 2; Figure 4 is a perspective view of the pressing tool of Fig. 3 in association with a chain of reinforced plates; and Figure 5 is a vertical section through the parts shown in Fig. 4.

In Fig. 1, a line of reinforcement plates 1 having apertures 2 is enclosed in a bed 3 of particles of expanded graphite, the bed being moved in the direction of the arrow A by a conveyor belt 4 on which the bed rests.

Above the bed 3 and at an angle of about 5" to it is mounted a second conveyor belt 5 in the form of a chain to which are secured a series of pressing tools 6 each of which has apertures as at 7 conforming with those (2) in the reinforcer plates 1. At the end of conveyor belts 4 and 5 is a chute 8 for collection of expanded graphite particles left uncompressed by the tools 6.

With belts 4 and 5 moving at substantially the same speed, the bed 3 is brought obliquely into engagement with pressing tools 6, and the graphite above and below the plates 1 is thus gradually compacted into foils which adhere to the plates, while the graphite filling the plate apertures, as at 11 in the drawing, with the graphite above and below those apertures and the graphite between successive plates 1, is left uncompacted and therefore capable of flow. The gradual compaction facilitates smooth expulsion of the large amount of air occluded in the expanded graphite. As the plates with their adherent graphite foils 1 2 move over chute 8, the uncompacted graphite falls freely under gravity into the chute and can be collected for re-use.

In Fig. 5, a bed 31 of exfoliated graphite on a moving conveyor belt 32 encloses apertured reinforcement plates 33 which are connected to form a chain 34 (see Fig. 4). The bed of graphite and the chain move at the same linear speed, and are transferred to a second belt 35 for compaction of the graphite.

The bed of exfoliated graphite is brought into engagement with a rotating cylinder 36 whose surface moves at the same linear speed as the bed. The cylinder is provided with a pattern of apertures 37 which correspond to the apertures 37a in the plates 33 and are in register therewith. Perfect registration is of course not possible at all points around the circumference of the cylinder 36 but 'best registration' is provided for at the position of maximum compression 39.

Compression of the graphite occurs in the gap between the cylinder and the opposing conveyor belt which gradually reduces over -+ of the circumference of the cylinder. This gradual compression gives time for the air to escape from the graphite without disturbing the graphite layer or causing air to be trapped as blisters.

Only those regions of the graphite layers lying opposite solid (unapertured) regions of the cylinder will be compressed to a compact form.

Graphite in regions corresponding to apertures 37 in the cylinder and apertures 37a in the plates 33 will not be compressed but will pass through the apertures in the cylinder and plates. This graphite, as at 41, will be largely uncompressed and suitable for re-cycling. It may be collected for this purpose by sucking it through a tube 42 connected to a vacuum system.

Claims (10)

1. A method of making a gasket comprising graphite foils with an apertured reinforcement plate between them, in which a bed of particles of expanded graphite which encloses the apertured plate is brought obliquely into engagement with a pressing tool which has apertures conforming with those in the plate, to bring about compaction of the graphite above and below the plate into foils which adhere thereto but leave substantially uncompacted the expanded graphite particles which fill the plate apertures.

2. A method according to claim 1, in which the bed of particles of expanded graphite enclosing the apertured plate is brought into said engagement by a moving conveyor belt.

3. A method according to claim 2, in which the bed is formed by depositing a layer of expanded graphite particles onto the moving conveyor belt, laying apertured reinforcement plates on the layer of expanded graphite particles, and covering the plates with a further layer of expanded graphite particles.

4. A method according to claim 1, 2 or 3, in which the bed of particles of expanded graphite enclosing the apertured plate is brought into engagement with a series of pressing tools which are secured to a conveyor belt moving above and obliquely to the bed.

5. A method according to any one of claims 1 to 4, in which the graphite left substantially uncompacted is allowed to fall and is collected for re-use.

6. A method according to claim 1, 2 or 3, in which the bed of particles of expanded graphite enclosing the apertured plate is brought into engagement with a rotating cylinder whose curved surface is so apertured as to constitute the apertured pressing tool, or a series of such tools, for gradual compaction of the graphite.

7. A method according to claim 6, in which the graphite left substantially uncompacted is sucked away and collected for reuse.

8. A method according to claim 1, substantially as hereinbefore described with reference to Figs. 1 and 2 of the drawings.

9. A method according to claim 1, substantially as hereinbefore described with reference to Figs. 3, 4 and 5 of the drawings.

10. A gasket made according to any preceding claim.