Inventor named by the Applicant: J.P. van

Dongeren, Bergeπthei .

The invention relates to a method for manufac¬ turing,, by injection molding, a composite seal, in particular suitable for reception in an internal groove recess of a pipe part provided with a coupling, a retaining annular element being formed from a less elastic material and said retain ng annular element being provided w th one or more sealing parts of a more elastic material, use being made of a mold. Such a method for manufacturing a composite seal is known per se.

According to said known method, the retaining element and the selaiπg part of the composite seal are formed from polymers having a different modulus of elasticity.

Because in this case the sealing part is formed in its entirety by in ecting the relevant polymer in a ho -plastic state into a su table molding cavity of a mold, the molding cavity being immediately completely injected in its entirety, intimate mixing with the already formed retaining element takes place in the surface region thereof, as a result of which the

properties of the sealing part also vary as a result of the varying composition. In addition, said known compo¬ site seal is consequently not capable of being manufactured completely reproducibly, inter alia, as a consequence of the pressures used during the injection molding.

Although mixing of the elastic and non-elastic plastics can be eliminated by appl ing the non-elastic plast c to the surface of the previously formed sealing parts with a low injection molding pressure, this results in a reduced adhesion of the sealing parts, a longer production time and additional costs.

The object of the invention is to eliminate the disadvantages of the known composite seal to be received in a pipe part.

The invention therefore relates to a method of the type mentioned in the introduction which is character sed in that one or more sealing parts are first formed from a more elastic plastic which is compatible with the less elastic plast c, in a manner such that the retaining element is gradually formed and is joined physically and/or chemically to the sealing parts, at least one portion of the free surface of the retaining element can be provided with a film of the more elastic plastic, and the face s de of the reta ning element has at least one projection of the less elastic plastic in the vicinity of the insertion opening of a pipe part to be received.

Because the elastic sealing parts are situated

at a distance from one another of at least the wall thickness of the retaining annular element and this is virtually the same over the entire length thereof, the rigidity of the retaining annular element is mainta ned because no elastic plastic of the sealing parts is p esent therein, while, owing to their homogeneity, the seal ing parts, together with the retaining annular element, provide an optimum sealing function. In addition, a good joint is ensured between all the parts' of the sealing ring. It is pointed out that a composite seal is known per se which comprises a retaining annular element com¬ posed of a less elastic material which is joined, at least on the face end, with a sealing part which, on the one hand, can interact th the inside of the groove recess and, on the other hand, with the outside of an inserted pipe part. The retaining annular element and the sealing part of said known seal are manufactured from rubber having a different hardness and can be joined to each other by vulcanising. As a result of this, however, deformation takes place both of the retaining annular element and the sealing part, w ile the joint of the two parts is not uni orm.

A composite seal is furthermore known in which the first sealing part rests against the inside of the groove recess and has the form of a shoulder which is pressed in when the seal is introduced into the groove recess. With the exception of the lip-shaped part against which the inserted pipe part rests, the second sealing part is completely surrounded by non-elastic

p l a s t i c .

Because said known seal is composed largely of a non-elastic plastic, the entity is fairly rigid, as a result of which a good sealing action cannot readily be obtained. To improve the sealing action, it is there¬ fore preferable in said known seal to bring about the oint with the sealing chamber by welding or by applying an adhesive.

Apart from this, a composite seal is known in which the less elastic retaining body is completely received in the more elastic sealing part. The retaining body therefore acts as a seal. Such a con¬ struction has the result that, when p pe parts are pushed into each other and the deformation of the elastic material takes place to a greater or lesser extent, the seal will then have the tendency of emerging from the sealing chamber, as a result of which the sealing action is lost.

In order to eliminate such problems, a composite seal of the above type is also known in which the less elastic reta ning body is provided on a face end thereof with a U-shaped end part which completely clasps the sealing part n the vic nity of said face end.

Such a seal is, however, not suitable for recep- tioπ in an internal groove recess of a receiving pipe part.

Finally, a composite seal for joining a receiving and an inserted pipe part is known which is situated in a sealing recess of the recei ing pipe part and is com-

posed of an elastic body which, at the seal ing chamber side, is provided with a groove for receiving not yet completely cured plastic. To obtain a good oint between the material of the elastic body and that with which the groove is filled, rubber is preferably used as elastic material and polyurethane as not completely cured plastic.

During the complete curing of the polyurethane present in the groove, the polyurethane will be mixed to some extent with the rubber and thus ensure a good joint. The less elastic retaining body is in this case, however, completely surrounded by more elastic material, with the exception of the side facing the groove recess, and said retain ng body is situated in the centre of the groove recess. The sides facing the insertion opening and facing away therefrom are therefore composed com¬ pletely of elastic material.

According to the invention, the sealing parts are preferably formed from a thermoplastic elastomer, in particular an elastomer based on polyalkene or a rubber. Such a material ensures a good seal as a result of the flexibility or defor ability thereof. A material which has proved particularly suitable is a thermo¬ plastic rubber such as that which is marketed by Monsanto under the name Santoprene.

The additional rigidity required for the seal is obtained by the non-elastic plastic body.

The film of the more elastic plastic optionally formed on the retaining body is formed more

particularly by entraining the more elastic plastic of the already formed sealing parts.

As has already been stated above, the formation of the retaining annular element takes place gradually. This is achieved, in particular, by carrying out the injection molding thereof in a manner such that the molding cavity present for the retaining annular element in the mold is gradually filled by controlled displace¬ ment of one of the wall parts. By gradually making the molding cavity free, it is in fact prevented that inhomogeπe ities are produced by mixing of the thermoplastic materials used. The temperature of the plastic material used for the retaining element is, however, still so high that a physical and/or chemical bonding with the sealing parts already formed is ensured.

The invention furthermore relates to a pipe part provided with a coupling having an internal groove recess wherein a composite seal is received, compris ng a reta ning annular element of a less elastic material which is joined to one or more sealing parts of a more elastic material, comprising sealing elements which are able, on the one hand, to interact with the inside of the groove recess and, on the other hand, with the outside of an inserted pipe part, characterised n that the retaining element is a monolithic part which is gradually formed from a less elastic plastic which is physically and/or chemically joined to one or more sealing parts formed from a more elastic plas ic which

is compatible with the less elastic plas ic and the face side of the retaining element has at least one projec¬ tion of the less elastic plastic in the vicinity of the insertion opening of a pipe part to be received. Furthermore, at least a portion of the surface layer of the retaining element portion that is free of sealing parts is preferably pro ided with a film composed of the more elastic plastic.

The invention also relates to a pipe joint co - posed of a pipe part provided with a coupling having an internal groove recess, a retaining annular element composed of less elastic material and provided with one or more sealing parts of more elastic mater al, and also an inserted pipe part, which is characterised in that a pipe part is present wherein the retaining element is a monolithic part which is gradually formed from a less elastic plastic, which is joined physically and/or chem¬ ically to one or more sealing parts, formed from a more elastic plastic, which is compatible with the less elastic plastic, and preferably formed from a thermoplastic elastomer or a rubber, a portion of the surface layer of the retaining element portion that is free of sealing parts can be provided with a film composed of less elastic plastic and the face side of the retaining element has at least one projection of the less elast c plastic in the vicinity of the insertion opening of a pipe part to be received.

The invention will be explained in more detail by reference to the following exemplary embodiments with

the aid of the dra ing, wherein:

Figure 1 shows a cross section of a first embodiment of a pipe part provided with a composite seal according to the invention; Figure 2 shows a cross section of another embodiment of a pipe part provided with a composite seal according to the invention; Figure 3 shows a finished pipe joint with a composite seal according to Figure 2 and Figure 4 shows a stage during the manufacture of a com¬ posite seal according to the invention. Figure 1 shows a pipe part provided with a composite seal composed of a retaining annular element of a less elastic plastic. The retaining annular element is provided with a sealing part 2 on the inside of the sealing recess. The retain ng element is pre¬ ferably formed from a thermoplastic material based on a polyalkeπe, such as polypropeπe.

The sealing part 2 is preferably composed of a thermoplastic elastomer such as a polystyrene- prolyalkeπe-polystyrene rubber, the polyalkeπe section being an etheπe-propene polymer, but obviously an ethene polymer or a propeπe polymer is also suitable. Such a thermoplastic rubber is manufactured by Monsanto and marketed under the name Saπtopreπe.

The interface 5 between the retaining annular element 1 and the sealing part 2 is composed of thermo¬ plastic material of the sealing part 2 and thermo¬ plas ic elastomer of the retaining annular element 1

fused with each other. These parts are thus physico- chemically joined to each other.

In Figure 1, the seal ing part 2 is located centrally on the retaining annular element 1 and there- fore also centrally in the sealing recess 4. Such a location of the two components is, however, not required to obtain a good seal of a receiving and an inserted pipe part.

As is shown in Figure 1, the seal ing part 2 is provided with ribs 6 and 7.

The sealing part 3 is also provided with one or more ribs 8. Said sealing part 3 is manufactured from the same material as is used for the sealing part 2.

Figure 2 shows an exemplary embodiment of a com- posite seal for joining a receiving and inserted pipe part. The sealing part 2 is in this case constructed with two lips 2a and 2b. This embodiment differs, however, in particular from the embodiment shown in Figure 1 in that the sealing part 2 and the sealing part 3 are joined to each other via a joining part 9.

This joining part 9 is therefore located on one of the two face sides of the retaining annular element. Since only one feed point is required to manufacture the sealing lips, this embodi ent can be manufactured by a cheaper production method.

The shape of the composite seal according to the invention is not limited to the embodi ents described above. Thus, within the scope of the invention, the shape and also the number of ribs on the elastic parts

may be changed.

Figure 3 shows a finished pipe joint which is provided i h a composite seal according to Figure 2. As is evident from Figure 3, the introduction of the nserted pipe part 10 both presses the lips 2a and 2b against the inside of the groove recess and the sealing part 3 against the retaining annular element 1. Because the sealing part 3, l e the sealing part 2, is composed of a thermoplastic elastomer, such as the thermoplastic rubber marketed under the name Santoprene, these parts can easily be deformed on introducing the inserted pipe part and a particularly good sealing action can be ensured.

Figure 4 shows a stage of the injection molding of the retaining annular element 1. The sealing parts have in this case already been formed by completely injecting the corresponding mold cavities with a thermo¬ plastic elastomer. Preferably, use is made of the thermoplast c elastomer marketed under the name Santoprene.

Another thermoplastic rubber may, however, also be used. In view of the application, a rubber is to be preferred in this case which has a Shore hardness of appro imately 55A and which can be used at tempera- tures of approximately -50°C to approximately 100°C. After the sealing parts have been formed, the retaining annular element 1 is formed in the same mold. During the injection molding of the retaining annular element of, preferably, polypropene, a s ill just liquid

"plug" is first formed starting from the feed point 15. Then the tubular slider 12 is moved in a controlled manner to the right so that the initially formed "plug" moves to the right as a result of the movement of the slider and the feed point thereof builds up to form the retaining element. The formation o this polypropene "plug" is fairly essential because, dur ng the controlled movement of the slider to the right, the polypropene plug slides over the material of the prev ously formed sealing parts 2 and 3. This prevents the material of the sealing parts being forced into the molding cavity between the polypropene plug and the slider and inhomogeneities being able to occur. In Figure 4, the portion past the broken line 11 corresponds to the polypropene plug initially formed at the feed point. This por ion is the distance over which the tubular slider is moved to the right. It is pointed out that the polypropene plug remains liquid during the controlled withdrawal of the slider. During the forma¬ tion of the retaining element, this plug of liquid polypropene entrains parts of the already formed sealing parts 2 and 3, but without affecting the sealing proper¬ ties of the sealing elements.

By thus carrying out the injection molding gradually, one or more injection molding channels 13 (see Figures 2 and 3) are produced in the joining sec¬ tion 9 of the two sealing parts, while these channels ap¬ pear at the other face side of the retaining element as channel-like openings 14. In the embodi ent according to Figure 1, only one (or more than one) pro ec t i on (s ) such

as 15 will be produced by the injection moulding.

Although the sealing parts in the above embodi¬ ments are formed from a thermoplastic elastomer such as the thermoplastic rubber marketed as Santoprene, other rubbers may obviously be used provided they have a favourable Shore hardness in addition to a service temperature range w ich is sufficiently wide.