The invention relates to a seal and is particularly, but not exclusively, concerned with a seal for use with a hydraulic piston and cylinder assembly.

In a typical application for a seal in a hydraulic piston and cylinder assembly the seal is annular and includes radially inner and outer sealing surfaces which sealingly engage respective inner and outer concentric cylinders of the assembly.

Certain seals are known as four point or quad seals. Such a seal has a generally rectangular configuration and defines annular sealing surfaces at each of its four corners.

In a typical application, the pair of concentric annular sealing surfaces at one annular side face of the seal typically constitute a pressure seal to maintain a pressure condition in the associated piston and cylinder assembly and the two concentric sealing surface at the other annular side face of the seal function to keep contaminates out of the sealing interface.

Seals of this general type are especially effective

in piston and cylinder environments where the first set of sealing surfaces acts to maintain the pressure in the pressure chamber of the piston cylinder and the second set of sealing surfaces preserves the sealing effectiveness of the first set of sealing surfaces by preventing the entry of contaminates into the sealing environment.

However, seals used in hydraulic piston and cylinder arrangements including those of the quad or four- point type include a relatively large volume of rubber and this large volume of rubber can detract from the travel efficiency and the load efficiency of the associated piston and cylinder assembly. Specifically, the problem of axial compression or squishing occurring in the large rubber volume of such seals increases the lost motion or travel of the associated cylinder assembly with a consequent derogation in the travel efficiency of the cylinder assembly. Further, the squishing of the rubber generates high friction losses which derogate the load efficiency of the cylinder assembly in the sense of reducing the load output of the assembly as compared to the load input.

It has been proposed hitherto to reinforce seals by means of relatively rigid elements. Examples of such proposals can be seen in British Patents Nos

1069556 and 1437358. However, such seals require the assembly together of separate sealing members and reinforcing elements. Such assembly can be tedious and time consuming and an object of the present invention is to provide a seal which is relatively easy to produce and which will provide a relatively high travel efficiency and load efficiency of an associated cylinder assembly.

According to the invention there is provided a seal comprising an annular seal member moulded on to an annular insert of relatively rigid material to provide sealing surfaces.

By moulding the sealing member directly on to the insert, it is unnecessary to assembly the insert and sealing member together as separate components and the seal of the invention is advantageous in that respect.

In one arrangement, the annular insert is arranged on one end of a cylindrical piston.

Preferably the insert includes or extends from an enlargement or flange on said one end of the piston and the seal member is secured to said flange. The enlargement or flange may project radially outwardly from the cylindrical member and/or radially inwardly

from the cylindrical member. The seal member may extend around the entire flange. In such a case, the seal member may be moulded partly on to the remainder of the cylindrical piston adjacent the f1 nge.

The flange may be formed with an axially extending rib around which rib the material of the seal member flows during the moulding process. The rib increases the bond between the seal member and the insert. The rib may be of annular form e.g., coaxial with the piston. The rib may either extend from the radially outer periphery or circumferenti l edge of the flange or may be spaced radially inwards of that edge.

If desired, the annular flange can be formed with an axially extending rib around which rib the material of the seal member flows during the mould process. Such a second rib may be annular and e.g., concentric with the first rib. The second rib may extend radially inwardly from the radially inner periphery of the annular end edge or may be spaced inboard of the radially inner periphery of the annul r end edge.

In one embodiment, the seal member has an outer circumferenti l surface which is flush with the

radially outer periphery of the annular flange.

The seal member may have one sealing surface radially outboard of the insert and one sealing surface radially inboard of the insert or may be in the form of a four point or quad seal with two axially spaced apart sealing surfaces radially outboard of the insert and two axially spaced apart sealing surfaces radially inboard of the insert.

The seal is preferably arranged in sealing engagement with coaxial inner and outer cylindrical surfaces of a housing of a fluid-operable piston and cylinder assembly, the cylindrical piston extending into and being slidable along an annular chamber defined between the inner and outer cylindrical surfaces. The annular chamber may have a closed inboard end and an open outboard end with the piston extending into the open outboard end of the annular chamber so that the opposite end of the piston on to which the sealing member is moulded is disposed within said annular chamber. The piston may include a main body portion having a wall thickness less than the radial distance between said cylindrical surfaces and positioned centrally in said chamber in concentric relation to said cylindrical surfaces to define spaced concentric annular spaces on either radial side of said main body portion. Where the

piston has a flange or enlargement thereon, an end edge of the flange or enlargement preferably faces a closed end of the chamber.

The moulding process preferably includes applying an intermediate layer of material to the insert before moulding the material of the sealing member thereon. The intermediate layer may be a bonding agent.

In a different seal arrangement, the insert is an annular ring member. In such a case the seal member may be formed on the insert so as to cover the majority of the surface area of the insert. Considering the seal in transverse cross-sec ion, the seal member may extend around at least 270 degrees of the ring member or may extend totally around the ring member.

The ring member may include a main body annular portion of constant axial and radial dimensions; and protrusions on said main body portion at circumferentially spaced locations therearound. Preferably at each of said circumferentially spaced locations, a first protrusion extends axially in one direction from said main body portion and a second protrusion may extend axially in the other direction from said main body portion.

The axially outer surface of each protrusion may be exposed.

Preferably at each of said circumferential ly spaced locations, a third protrusion extends radially outwardly from said main body portion and a fourth protrusion may extend radially inwardly from said main body portion.

The radially inner and outer surfaces of the third and fourth protrusions respectively may be exposed.

Preferably the insert is formed with at least one axially extending bore through which the material of the sealing member flows during the moulding process.

Preferably the seal member has one sealing surface radially outboard of the insert and one sealing surface radially inboard of the insert.

The seal member may have two axially spaced apart sealing members radially outboard of the insert and two axially spaced apart sealing surfaces radially inboard of the insert after the fashion, e.g., of a four point or quad seal.

As with the seal in said one arrangement the seal

may seal the piston may have an enlarged end engages the seal between coaxial inner and outer cylindrical surfaces of a housing of a fluid operable piston and cylinder assembly, the piston extending into and being slidable along an annular chamber defined between the inner and outer cylindrical surfaces, the seal being engageable with an end surface of the piston. The moulding process for said different seal arrangement may also include applying an intermediate layer of, e.g., a bonding material, to the insert before moulding the material of the seal member thereon.

A seal in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which:-

Fig.1 is a fragmentary view of a piston and cylinder assembly incorporating a seal in accordance with the invention;

Fig.2 is a fragmentary view on an enlarged scale showing a portion of the piston and cylinder assembly of Fig.1;

Fig.3 is a fragmentary view on a still further enlarged scale showing a portion of the piston and cylinder assembly of Fig.2 removed from the

cyl inder;

Fig.4 is a fragmentary view of a modified piston and cylinder incorpora ing a seal in accordance with the invention;

Fig.5 is a fragmentary view on an enlarged scale of a portion of the piston and cylinder assembly of Fig. ;

Fig.6 is a fragmentary end edge view of the piston seen in Fig.5; and

Fig.7 is a fragmentary view similar to Fig.3 showing a modified form of seal in accordance with the invention;

Fig.8 is a fragmentary view of a piston and cylinder assembly employing a seal according to the invention, the seal and piston being separate elements;

Fig.9 is a fragmentary view of an annular insert member employed in the seal of Fig.8;

Fig.10 is a fragmentary perspective view of the annular insert member of Fig.9;

Fig.11 is a fragmentary view of the seal of Fig.8;

Fig.12 is a fragmentary plan view of the seal of Fig.11;

Figs.13 and 14 are cross-sectional views taken respectively on lines XIII-XIII and XIV-XIV of Fig.11 ;

Fig.15 is a fragmentary cross-sectional view of a modified form of seal in accordance with the invention where the seal and piston are separate elements.

Fig.16 is a fragmentary cross sectional view taken on line XVI-XVI of Fig.15; and

Figs.17 and 18 are cross-sectional views of flashless moulds for producing the seals shown in Figs.1 to 7 and Figs.8 to 16 respectively.

The piston cylinder assembly 10 as seen in Fig.1 in the form of an annular hydraulic cylinder and piston assembly such for example as a slave cylinder assembly for operating the release bearing of a mechanical clutch wherein the assembly is disposed concentrically around the drive shaft coupling a clutch disc to the drive shaft of a gearbox of a

motor vehicle. Such a slave cylinder arrangement is shown for example in U.S. Patent Nos. 4,585,106; 4,585,107; 4,585,108; 4,585,109; 4,624,290? 4,660694; 4,684,003 and 4,687,084.

The cylinder assembly 10 includes a housing 12 provided with concentric tubular members 14 and 16 preferably cast integrally with housing 12. Members 14 and 16 coact to define an annular cylindrical housing chamber 18 and a cylindrical or annular piston 20 is slidably positioned in chamber 18.

Piston 20 includes a cylindrical main body portion 20a extending into an open outboard end 18a of chamber 18 to dispose an inboard end portion 20b of the piston within chamber 18. The main body portion 20a of the piston has a wall thickness substantially less than the radial distance between the inner cylindrical surface 16a of tubular member 16 and the outer cylindrical surface 14a of tubular member 14 and the piston is positioned centrally within housing chamber 18 in concentric relation to the central axis of the piston and cylinder assembly to define spaced concentric annular spaces 22 and 24 on both radial sides of the main body portion 20a of the piston.

Ar. annular seal S is provided at the inboard end 20b

of the piston so that hydraulic fluid introduced into the annular chamber 18- through a passageway 28 in housing 12 displaces the piston and seal assembly to the left, as seen in Fig.1 thereby displacing to the left a release bearing (not shown) mounted on the outboard end of the piston. The release bearing engages release fingers of the clutch of the vehicle in known manner to disengage the clutch. When hydraulic fluid is withdrawn from chamber 18 through passageway 9, piston 20 is allowed to be displaced to the right under the action of the clutch spring fingers and the clutch is re-engaged in known manner.

Inboard end portion 20b of the piston 20 is in the form of an annular flange 20c whch projects radially inwardly and radially outwardly of the main body portion 20a of the piston 20. The flange 20c has an outer annular rib 20d which projects axially from the flange and an inner annular rib 20e which also projects axially from the flange. The ribs 20d, 20e are concentric and coaxial with the piston 20. The outer rib 20d extends radially inwardly from the outer periphery 20f of the flange 20c and the inner rib 20e extends radially outwardly from the inner periphery 20g of the flange 20c. The flange 20b faces closed end 18b of the chamber 18.

Seal S includes a seal member 26a of elastomeric material encapsulating flang-e 20c and protrusions 20d, 20e. Elastomeric seal member 26 defines annular sealing surfaces 26a, 26b,26c and 26d at the four corners of the generally rectangular cross- sectional configuration of the elastomeric seal.

Seal member 26 is moulded on to piston 20 to form a seal as described below with reference to Fig.17.

The concentric slave cylinder assembly of Figs.1-3 further includes an outer wiper seal assembly 128 and an inner seal assembly 30. Outer wiper seal assembly 28 includes an annular steel stamping 32 press fitted on the free annular end of outer annular housing member 16 and an elastomeric wiper seal 34 bonded on to stamping 32 and including an inner annular lip portion 34a wipingly engaging the outer periphery of annular piston 20. Inner wiper seal assembly 30 includes an annular steel stamping 36 press fitted on the free annular end of inner annular housing member 14 and an elastomeric wiper seal 38 bonded to stamping 36 and including an annular lip portion 38a wipingly engaging the inner periphery of annular piston 20.

When the piston and cylinder assembly of Figs.1-3 is utilized in a typical piston and cylinder assembly,

such as a concentric slave cylinder for operating the clutch of a motor vehicle, annular sealing surfaces 26c and 26d function to maintain pressure in an expansible pressure chamber 40 defined between the inboard end of seal member 26 and the closed end 18b of housing chamber 18, and annular sealing surfaces 26a and 26b function to preclude the entry of contaminants into the sealing interface. Seal S and seal 30 function to further preclude the entry of contaminants into the sealing interface. Elastomeric seal S also functions to maintain annular piston 20 in concentric, spaced relation to cylindrical housing surfaces 14a and 16a with a consequent reduction in sliding friction as between the several annular reciprocating members 14, 16 and 20. The flange 20c and ribs 20d, 20e of the annular piston serve to substantially reduce the total volume of rubber in the seal assembly, thereby reducing seal squish and increasing travel efficiency and load efficiency of the piston and cyli der assembly. The surfaces of protrusions 20d, 20e serve to maximise the bonding interface area between the seal member 26 and the piston and thereby provide a secure bonding as between the seal member and the piston. Specifically, the flange 20c of the piston and the ribs 20d, 20e coact to provide an insert giving firm backing for the seal member 26, to maximise extrusion of the elastomeric

material of the seal member, and to preclude twisting of the seal membe relative to the piston. The positive bonding of the seal to the piston as a result of moulding is further augmented by the provision of a concentric annular groove 20h between the ribs 20d, 20e which causes a concentric annular rib portion 26i to be formed during moulding of the seal member 26. The sealing surfaces 26a, 26c lie radially outboard of the insert and the surfaces 26b, 26d lie radially inboard of the insert formed by the flange 20c and ribs 20d, 20e.

In the piston and cylinder assembly seen in Figs.4 and 5, like reference numerals have been employed for those parts which correspond to the parts of the assembly of Figs.1 through 4. Thus the assembly of Figs.4 and 5 includes a housing 12 provided with concentric tubular members 14 and 16 cast integrally with housing 12; members 14 and 16 coact to define an annular cylindrical housing chamber 18; the pressure fluid is introduced into chamber 18 through a passageway 28 in the housing; and inner and outer wiper seal assemblies 28 and 30 are provided at the outboard end 18a of the chamber 18 for wiping engagement with the inner and outer cylindrical surfaces of the piston.

The piston 40 and the annular elastomeric seal 41

attached thereto differ from the piston and seal of the Figs.1-3 embodiment.

Specifically, piston 40 includes an annular main body portion 40a extending into the open outboard end 18a of the housing chamber 18 and an inboard end portion disposed within the chamber 18.

Inboard end portion is radially enlarged with respect to main body portion 40a to form a flange 40b and, specifically, flares radially outwardly at 40c and 40d. A pair of concentric annular ribs 40f and 40g project axially inboard from an annular end 40e edge of flange 40b with outer rib 40f spaced radially inwardly from the radially outer periphery of annular end edge 40e and inner rib 40g spaced outwardly from the radially inner periphery edge of annular end edge 4Qe.

Seal 41 includes an elastomeric seal member 42 moulded on to the edge 40e and ribs 40f and 40g and defines annular sealing surfaces 42a and 42b respec ively sealingly engaging the inner cylindrical surface 16a of outer tubular member 16 and the outer cylindrical surface 14a of inner tubular member 14 to define an expansible pressure chamber 40 between the seal and closed-end 18b of housing chamber 18. Seal member 42 includes a main

body annular portion 42c secured to the enlarged annular end edge 40e of the- piston, and a pair of annular lip portions 42d and 42e extending radially outwardly and axially inboard from the main body portion 42c to respectively define annular sealing surfaces 42a and 42b radially outboard and radially inboard of the flange 40b. An annular groove 42f in the inboard face of the seal serves to define the radially inner surfaces of the lip portions so as to provide flexibility for the lip portions and so as to minimize the elastomeric volume of the seal.

The outer circumferential surface of the seal main body portion 42c is flush with the peripheral outer edge of the flange 40b of the piston so as to provide a smooth, continuous profile for the piston and cylinder assembly.

As with the piston and cylinder assembly of Figs.1- 3, seal 41 is formed by moulding as described below with reference to Fig.Ϊ7.

When the piston and cylinder assembly of Figs.4 and 5 is utilized in a typical piston and cylinder assembly, such as a concentric slave cylinder for operating the clutch of a motor vehicle, annular sealing surfaces 42a and 42b function to maintain pressure in the expansible pressure chamber 40

defined between the inboard end of the seal and the closed end 18b of the housing chamber 18, and wiper seal assemblies 28 and 30 function to preclude the entry of contaminates into the sealing interface. Elastomeric seal 42 also functions to maintain annular piston 40 in concentric, spaced relation to cylindrical housing surfaces 14a and 16a with a consequent reduction in sliding friction as between the several annular reciprocating members 14, 16 and 40. The flange 40b of the annular piston serves to substantially reduce the total volume of rubber required to mould the seal member 42 thereby reducing seal squish and increasing travel efficiency and load efficiency of the piston and cylinder assembly. Enlarged annular end edge 40e and ribs 40f, 40g maximize the bonding interface area between the seal member and the piston and thereby provide a secure bonding as between the seal member and the piston. Specifically, the large end edge 40e provides a firm backing for the seal member and the ribs 40f, 40g form inserts to minimize extrusion of the elastomeric material of the seal member, and preclude twisting of the seal member relative to the piston.

The piston and seal of Fig.7 is generally similar to the piston and seal of the Figs.1-3 embodiment with the exception that the annular seal 44 includes four

lip portions 44a, 44b, 44c and 44d respectively defining four annular sealing surfaces 44e, 44f, 44g and 44n.

When the piston and seal seen in Fig.7 is utilized in a typical piston and cylinder assembly, such as a concentric slave cylinder for operating the clutch or a motor vehicle, annular sealing surfaces 44e and 44f function to maintain pressure in the pressure chamber of the piston and cylinder assembly and annular sealing surfaces 44g and 44h function to preclude the entry of contaminants into the sealing interface.

In each of the various disclosed embodiments of the invention piston and cylinder assembly, it will be seen that the enlarged inboard end portion of the piston defines a convoluted enlarged inboard annular end edge which bonds with the material of annular seal member to provide a firm backing and a firm attachment and insert for the seal to minimize extrusion of the seal during operation of the piston and cylinder assembly and to preclude twisting of the seal relative to the piston during operation of the piston and cylinder assembly. The described piston and seal also serve to ensure that the main body of the piston is positively spaced from the confronting inner and outer cylindrical surfaces of

the housing so as to maximise the travel efficiency of the piston and cylinder assembly.

Reference is now made to Figs.8 to 14 where, unlike the seal arrangement of Figs.1 to 7, the seal and piston are separate elements.

r

In Fig.8, a seal 110 is arranged in the annular cylindrical chamber of 18 of a piston and cylinder assembly 100 of a kind similar to that in Fig.1. Seal assembly 110 is disposed on one side of annular piston 20 so that hydraulic fluid introduced into the annular chamber 18 through a passageway 9 in a housing 12 displaces the seal 10 and piston 20 to the left, as seen in Fig.8 thereby displacing to the left a release bearing mounted on the end of the annular piston. the throwout bearing engages the release fingers of the clutch of the vehicle in known manner to disengage the clutch. When the hydraulic fluid is withdrawn from chamber 18, piston 20 is allowed to be displaced to the right under the action of the clutch spring fingers and the clutch is re-engaged in known manner. A slave cylinder assembly of the type seen in Fig.8 is disclosed for- example in U.S. Patent No.4,577,549.

Seal assembly 110 includes an annular insert member 124 and an annular elastomeric seal member 126.

Annular insert member 124 is formed in a suitable injection moulding process and is formed of a suitable plastic material such as glass reinforced plastic or a mineral filled plastic. Insert member 124 is in the form of a ring member and includes a main body annular portion 124a of constant axial and radial dimensions, axial protrusions 124b, and radial protrusions 124c.

Axial protrusions 124b and radial protrusions 124c are provided at circumferentially spaced locations around main body portion 124a. At each circumferential location, a protrusion 124b extends in one axial direction from main body portion 124a, a second protrusion 124b extends in the other axial direction from main body portion 124a, a radial protrusion 124c extends radially outwardly from main body portion 124a, and a further radial protrusion 124c extends radially inwardly from main body portion 124a. Protrusions 124b extend for the full vertical height of annular main body portion 124a whereas radial protrusions 124c have a thickness that is only a fraction of the thickness of main body portion 124a and are centred with respect to the thickness of the main body portion. A throughbore or hole 124d is provided in main body portion 124a between each set of protrusions.

Following the injection moulding of ring member 124, the ring member is coated with a suitable adhesive or bonding agent and placed in a suitable mould whereafter, in a flashless moulding process as described below with respect to Fig.18 elastomeric member 26 is moulded around the insert member. In the final seal as seen in. Figs.11, 12, 13 and 14, elastomeric seal member 126 substantially totally encapsulates ring member 124 with the exception that the axially outer surfaces 124e of protrusions 124b are exposed in the final seal assembly and the radially upper and radially lower surfaces 124f of the radial protrusions 124c are exposed in the final seal assembly.

As best seen in Figs.13 and 14, elastomeric seal member 126 has a generally rectangular transverse cross section and defines separate annular sealing surfaces 126a, 126b, 126c and 126d at its four corners. In the final moulded seal, elastomeric seal member 126 is firmly and interlockingly joined to ring member 124 by the interlocking relationship of the elastomeric member with the protrusions 124b and 124c and by the interlocking passage of the material of the elastomeric member 126 through axial bores 124d in the ring member.

In use, as seen for example in the concentric slave cylinder arrangement of Fig.8, the sealing surfaces 126c and 126d operate to provide a pressure seal in the pressure chamber 18 and the sealing surfaces 126a and 126b operate to preclude the entry of contaminants into the sealing interface. The ring 124 minimizes the volume of rubber in the seal assembly and thereby minimizes seal squish, with consequent improvements in travel efficiency and load efficiency of the associated cylinder assembly. further, the ring serves as a positive locating device for the material of the seal member 126 and restricts the range of movement of the seal member by providing an overall stiffness or rigidity for the seal member while yet allowing the elastomeric material to continue to effectively perform its sealing functions.

The modified seal seen in Figs.15 and 16 includes an insert member or ring member 128 and a coactiήg elastomeric seal member 130.

Ring member 128 is of constant radial and axial dimensions throughout its circumferential extend and includes a main body portion 128a of polygonal cross-sectional configura ion and a rib portion 128b extending totally around the main body portion 128a and projecting centrally from the side face 128c of

main body portion 128a.

An elastomeric seal member 130 substanti lly totally encapsulates ring member 1 8 with the exception of the axially outer annular surface 128d of rib portion 128b. Elastomeric member 130 is generally rectangular in transverse cross-section and defines four annular sealing surfaces 130a, 130b 130c, and 130d at the four corners of the member.

As with the seal assembly of the Figs.8-14 embodiment, the seal of the Figs.15 and 16 embodiment is formed by flashless moulding as described below with reference to Fig.18.

The seal of the Figs.15 and 16 embodiment functions in an environment such as the slave cylinder environment of Fig.8 to provide a pair of annular sealing surfaces 130c and 130d respectively radially outboard and inboard of the insert to maintain the pressure seal in chamber 18 and further functions to provide annular sealing surfaces 130a and 130b respectively radially outboard and inboard of the insert to preclude the entry of contaminates into the sealing interface, while insert 128 functions to reduce the volume of the rubber employed in the seal member, and thereby the seal squish, and further functions to provide locating rigidity for the seal

member without derogating the sealing function of the elastomeric material.

Reference is now made to Fig.17 which illustrates a mould for flashless moulding used in producing a seal of the kind shown in Figs.1 to 3. Flashless moulding is described in British Patent No.1397968 to which the reader is directed.

A movable lower heating platen 200 comprises a first section 201 formed with a bore 203, and a second section 204 comprising a base part 205 bolted to the first section 201 and cylindrical projection 206 which lies coaxially within the bore 203. An annular space is defined between the bore 203 and projection 206 which, in use, slidably receives the piston 20. The first and second sections 201, 204 are formed with heating channels 207 for receiving heating medium such as steam.

Heat insulating plates 208 are mounted on the upper surfaces of the platen sections 201, 204 and a three-plate mould is arranged on top of the insulating plates 208. The three plate mould comprises a base plate 209, a central plate 210 and an upper plate 212.

The base plate 209 is formed with a circular recess

213 coaxial with bore 203 and receives an annular insert 214 having an inner diameter identical to the diameter of bore 203 and an annular groove 211 at its inner and upper periphery for forming part of the seal member 26. The recess 213 also receives a central circular insert 2 5 which has an outer diameter complementary to the inside diameter of piston 20 and which is formed with an annular groove 216 at its upper periphery for forming another part of the seal member 26.

The central plate 210 is formed with a central recess 217 identical in diameter to recess 213 and coaxial therewith and receives an annular insert 218. The insert 218 has an inner periphery 219 shaped to form further parts of the seal member 26. The recess 217 also receives a central circular insert 220 which may locate by means of dowels (now shown) on the insert 215 so as to ensure that both plates are coaxial. The insert 220 has an outer periphery 222 shaped to form further parts of the seal member 26.

The upper plate 212 is formed with ^" a circular recess 223 identical in diameter to recesses 213 and 217 and coaxial therewith. The recess 223 receives an annular insert 224 formed with a groove 225 and a contoured inner surface 226 for forming the

remaining parts of the seal member 26.

A cylinder plate 227 is movably mounted on a stationary support (not shown). The cylinder plate is formed with passages 221 for steam or other heating medium and an insulation plate 228 is bolted thereto. The insulation plate 228 is formed with a circle of bores 229 and the bores 229 and the lower surface of the insulation plate 228 are lined with a layer or coating 230 of low friction material such as P.T.F.E. A cover plate 232 is bolted to the insulation plate 228 and in the position shown the lower peripheral edge of the cover plate 232 and the radially inner edge 233 of the insert 223 define a constriction 234 therebetween through which moulding material can pass as described below. A piston 235 is arranged in the cylinder plate 227. The cylinder plate is normally biassed downwards towards the lower platen 200 by springs (not shown).

In use, the lower platen 200, together with plates 209, 210 and 212, is first moved downwards by a distance sufficient to enable a piston 20 to be placed between the cylindrical wall 203 and the projection 206. Elastomeric stock 236 in suitable solid form is placed beneath the piston 235 and changes to a flowable form by application of heat from the upper platen. However the heat is

insufficient to cure the stock. The lower platen is then raised to close the mould whereby the various components approach the position shown in Fig.17 with the cylinder plate 227 biassed downwards by its springs. The loading of the springs causes some of the flowable elastomeric medium to flow towards the constriction 234. Continued upward movement of the lower platen 200 causes the cylinder plate 227 to rise relative to the piston 235 causing the elastomeric stock to be forced through the constriction 234 and into the mould cavity defined between the inserts so as to flow around the flange 20c and its annular ribs at the upper end of piston 20 to form the seal member 26. The stock material is also partly moulded around the piston adjacent the flange. The heat provided by the heating medium within the heating passages 207 in the lower platen 200 is sufficient to cure the stock forming the seal member 26 but the cylinder plate 227 is in contact with the lower platen 200 through the intermediary of the insulation plate 228. Therefore the insulation plate 228 serves to prevent curing of the stock within the cylinder plate. As described in U.K. No.1397968 the various mould inserts deflect relative to one another where necessary to seal any gaps between their respective parting lines and thereby prevent formation of flash.

After curing, the lower platen 200 is dropped downwardly and stock in the low-friction bores 229 separates to leave the cured seal member i-n the mould cavity moulded on to the piston. The piston 20 is then removed from the mould and cured material above the constriction (which forms a tear-line on the seal member) is torn away.

To improve the bond between the flange 20c and the stock, the insert end of the piston may be dipped in a bonding agent prior to being located in the mould.

The mould shown in Fig.18 is very similar to that shown in Fig.17 except that provision does not have to be made for the piston 20. In view of the similarities the mould is not described in detail and corresponding parts carry corresponding reference numerals.

It will be seen that the lower platen 200 is a one- piece unit and that the various inserts in the plates 209,210, 212 are this time shaped to suit the quad seal 110 shown. Prior to moulding, the insert 124 is placed in the mould cavity so that the stock will flow around it to form the seal member. The insert 124 is preferably dipped in a bonding agent prior to being located in the mould. The operation of the mould is the same as that described with

respect to F i g . 1 .