METHOD AND MOULD FOR MOULDING A SEALING ASSEMBLY COMPRISING A SEALING RING AND A RETAINING RING

Abstract: In moulding a sealing assembly which is to be placed inside a socket end of a pipe joint and which comprises a sealing ring made of an elastomeric material and a retaining ring (5) made of relatively stiff thermoplastic material, the retaining ring (5) is first moulded in a first mould cavity of a mould. The sealing ring (4) is then moulded in a second mould cavity (10) which is partly bounded by a portion of the retaining ring (5). In this connection, the second mould cavity (10) is sealed at the position of the junction between the retaining ring (5) and the other inside wall parts of the second mould cavity (10) as a result of the retaining ring (5) being clamped on the inside onto a core part (12) of the mould, which core part (12) projects into the retaining ring (5) and moulds the inside of the sealing ring (4), and of an outer part (13) of the mould, which outer part (13) forms the outside of the sealing ring (4), being clamped against the outside of the retaining ring (5).

Description: Method and mould for moulding a sealing assembly comprising a sealing ring and a retaining ring. The invention relates to a method and a mould for moulding a sealing assembly which is to be placed essentially inside a socket end of a pipe joint and which comprises a sealing ring made of an elastomeric material and a retaining ring made of a relatively stiff, thermoplastic material, the sealing ring and the retaining ring being firmly joined to one another and generally being disposed coaxially in line with one another. Such a sealing assembly is described in the non- prepublished Dutch Patent Application 1 000 584. The sealing assembly concerned was found not to be capable of being satisfactorily moulded by known techniques. The object of the invention is therefore to provide a method and a mould with which a sealing assembly of the type described can expediently be moulded, which sealing assembly can satisfy all the requirements imposed thereon. This object is achieved according to the invention by a method for moulding a sealing assembly which is to be placed essentially inside a socket end of a pipe joint and which comprises a sealing ring made of an elastomeric material and a retaining ring made of relatively stiff thermoplastic material, the sealing ring and the retaining ring being firmly joined to one another and generally being disposed coaxially in line with one another, which method comprises the steps of moulding the retaining ring in a first mould cavity of a mould, then moulding the sealing ring in a second mould cavity which is partly bounded by a portion of the retaining ring, the second mould cavity being sealed at the position of the junction between the retaining ring and the other inside wall parts of the second mould cavity as a result of the retaining ring being clamped on the inside onto a core part of the mould, which core part projects into the retaining ring and moulds the inside of the sealing ring, and of an outer part of the mould, which outer part forms the outside of the sealing ring, being clamped against the outside of the sealing ring. This object is also achieved by a mould for moulding a sealing assembly which is to be placed essentially within a socket end of a pipe joint and which comprises a sealing ring made of an elastomeric material and a retaining ring made of relatively stiff thermoplastic material, the sealing ring and the retaining ring being firmly joined to one another and generally being disposed coaxially in line with one another, which mould comprises a first core part which determines the inside shape of a part of the retaining ring, and also a second core part, an annular outer part to be placed around the second core part and a fourth mould part to be placed around the outer part, wherein, in the condition of the mould in which the sealing ring is moulded, the sealing ring placed on the first core part, the second core part, the outer part and the fourth mould part are positioned with respect to one another in such a way that they bound a second mould cavity for moulding the sealing ring which extends essentially in the axial elongation of the retaining ring, the second core part adjoining the inside of the retaining ring so as to form a seal, the outside part adjoining the outside of the retaining ring so as to form a seal and the fourth mould part retaining the retaining ring on the first core part . The invention is explained in greater detail in the following description of preferred embodiments of the method and the mould according to the invention with reference to the drawings, in which: Figure 1 is an axial section of a portion of a socket end of a pipe joint in which a sealing assembly moulded according to the invention is provided, and Figure 2 shows, in an axial section, a portion of a mould according to the invention with sealing assembly moulded therein. Figure 1 shows a portion of a socket end 1 of a pipe part . The socket end 1 is provided on the inside with a separate sealing assembly 2. A spigot 3 of another pipe part can be inserted into the socket end in order to form a joint between said two pipe parts. In particular, the pipe parts are moulded from plastics material, such as polyvinyl chloride (PVC) or polypropylene (PP) or from another material suitable for pipes . The sealing assembly 2 comprises a sealing ring 4 made of an elastomeric material and a retaining ring 5 joined thereto and made of a stiff material. With spigot 3 inserted into the socket end 1, the sealing ring 4 is intended to provide the seal between the socket end 1 and the spigot end 3. The retaining ring is preferably made of a stiff plastics material, for example polypropylene. The sealing assembly 2 is preferably made by coinjection, the sealing ring 4 and the retaining ring 5 being firmly joined to one another during the moulding process. The sealing ring 4 is therefore preferably composed of a thermoplastic elastomer which readily adheres to the material of the retaining ring 5. In the embodiment shown, the sealing assembly is provided on the outside with a circumferential, outwardly projecting rib 6. Said rib 6 falls, preferably as a fit, into a groove 7 provided on the inside of the socket end 1. This achieves the object that the sealing assembly 2 is very well positioned in the axial direction with respect to the socket end 1. The retaining ring 5 is provided, on the side remote from the sealing ring 4, with an outwardly projecting rim 8. Said rim 8 is disposed against the head end 9 of the socket end 1 on it or at a short distance from it when the seal assembly 2 is provided in the socket end 1. The rim 8 serves to camouflage the gap 10 between the retaining ring 5 and the socket end 1. The rim 8 is not necessary for positioning the seal assembly 2 in the socket end 1. In the non-prepublished Dutch Patent Application 1 000 584, a number of other possible embodiments of a seal assembly of the abovementioned type are described in greater detail, which embodiments can be moulded with the method described below. The method for moulding the sealing assembly 2 described above is described with reference to Figure 2, in which a portion of a mould with sealing assembly 2 moulded therein is shown in axial section. First of all, the retaining ring 5 is formed by injection moulding in a first mould cavity of a mould (not shown) . The mould is then opened, the retaining ring 5 remaining firmly seated on a first core 11, and the first core 11 is conveyed along with the retaining ring 5 to a position in which the sealing ring 4 is moulded by injection moulding in a second mould cavity 10. This situation is shown in Figure 2. The second mould cavity 10 is bounded by a second core 12 and an annular outer part 13 of the mould and a portion of the retaining ring 5 already moulded. At the position of the junction between the retaining ring 5 and the sealing ring 4 to be moulded in the second mould cavity 10, the retaining ring 5 is clamped against the core 12 which projects into the retaining ring 5 and tapers slightly, and seals off the second mould cavity 10 at that position. The conical shape of the core 12 is desirable in order that, when the mould is closed, in which operation the core 12 and the outer part move in the axial direction with respect to the core 11 with the retaining ring 5 thereon, there is sufficient play between the front of the core 12 and the retaining ring 5 for the core 12 to pass readily over the retaining ring 5 and, in case of a closed mould, the retaining ring 5 is disposed in a clamping fashion on the core 12 in order to form a good seal with respect thereto. The entry of the core 12 into the retaining ring 5 is simplified still further by also providing a rounding-off 15 at the unsupported end of the retaining ring 5. The outer part 13 is annular in order to prevent seams from being produced on the sealing ring 4, which seams could be the cause of leakage. The portion of the outer part 13 which is in contact with the retaining ring 5 is also conically constructed in order to bring about a firm clamping on the retaining ring 5 and, consequently, a good seal at that position. During the injection of the material of the sealing ring 4 into the second mould cavity 10 via a sprue part 16, the seal between the retaining ring 5 and the core 12 is reinforced still further by the flow and the pressure of the injected material. To guide the flow of the injected material, the retaining ring has a special shape on the side directed towards the sprue part 16, as can be seen in Figure 2. A space 17 is present between the retaining ring 5 and the core 12. Said space 17 is provided in order to prevent a rim being produced on the inside of the retaining ring 5 after the injection of the sealing ring 4, which rim could present problems during the fitting of a spigot end 3 (not bevelled or deburred) into the socket end 1 with sealing assembly 2. The minimum rim which now remains presents no assembly problems during the insertion of the spigot end 3 since said rim does not give rise to interference in the direction of movement of the spigot end 3. In the mould, the retaining ring 5 and the second mould cavity 10 are disposed in the axial direction virtually in line with one another in order to make possible the demoulding of the moulded sealing assembly, in particular the sealing ring 4 thereof, without damage occurring. After cooling, the sealing ring 4 acquires its desired conical shape. During the demoulding of the sealing assembly 2, the core 12 is first pulled out, which can be done with a linear movement since the moulded sealing ring 4 extends essentially in the axial direction in the mould. Therefore, the sprue part 16 (hot runner) can also be of a known design. In this situation, there is sufficient space between the outer part 13 and the core 12 to keep the sealing ring 4 undamaged. This is further promoted by a rounding-off 18 on the outer part 13 and consequently on the sealing ring 4, which rounding-off prevents the sealing ring 4 from being cut into or damaged when the core is pulled out . The outer part 13 is then moved in the axial direction, while a mould part 14 still does not move and firmly holds the retaining ring 5 on the core 11. This ensures that the sealing assembly 2 does not remain stuck in the outer part 13. During the further opening of the mould, in which operation the mould part 14 is also moved, the sealing assembly 2 can be pulled off the core 11. The core 12 and the outer part 13 are made up of a number of plates. At the position of the separating planes between the plates, vents 21, 21a, 21b, 21c etc. are provided. As a result of the position of said vents, any marks which remain behind on the sealing ring 4 as a consequence will not result in the risk of leakage because the marks are not disposed at critical positions.

Claims: CLAIMS 1. Method for moulding a sealing assembly (2) which is to be placed essentially inside a socket end (1) of a pipe joint and which comprises a sealing ring (4) made of an elastomeric material and a retaining ring (5) made of relatively stiff thermoplastic material, the sealing ring (4) and the retaining ring (5) being firmly joined to one another and generally being disposed coaxially in line with one another, which method comprises the steps of moulding the retaining ring (5) in a first mould cavity of a mould, then moulding the sealing ring (4) in a second mould cavity (10) which is partly bounded by a portion of the retaining ring (5) , the second mould cavity (10) being sealed at the position of the junction between the retaining ring (5) and the other inside wall parts of the second mould cavity (10) as a result of the retaining ring (5) being clamped on the inside onto a core part (12) of the mould, which core part (12) projects into the retaining ring (5) and moulds the inside of the sealing ring (4) , and of an outer part (13) of the mould, which outer part (13) forms the outside of the sealing ring (4) , being clamped against the outside of the sealing ring (5) . 2. Method according to claim 1, wherein, during the moulding of the retaining ring (5) , the rim of the retaining ring (5) is provided with a rounding-off (15) on the inside at the position of the junction with the sealing ring (4) to be moulded. 3. Method according to claim 1 or 2 , wherein, during the moulding of the retaining ring (5) , the internal diameter of a portion, adjoining the junction with the sealing ring (4) to be moulded, of the retaining ring (5) is made somewhat larger than the internal diameter of the remainder of the retaining ring (5) . 4. Method according to one of claims 1 - 3, wherein the moulded seal assembly (2) is demoulded by first demoulding the sealing ring (4) , the seal assembly (2) being retained in the mould, and then ejecting the seal assembly (2) out of the mould. 5. Method according to one of claims 1 - 4, wherein, during the demoulding of the sealing ring (4) , the inside is first demoulded by pulling out the core part (12) and the outside is then demoulded by pulling away the outer part (13) in the axial direction. 6. Mould for moulding a sealing assembly (2) which is to be placed essentially within a socket end (1) of a pipe joint and which comprises a sealing ring (4) made of an elastomeric material and a retaining ring (5) made of relatively stiff thermoplastic material, the sealing ring (4) and the retaining ring (5) being firmly joined to one another and generally being disposed coaxially in line with one another, which mould comprises a first core part (11) which determines the inside shape of a part of the retaining ring (5) , and also a second core part (12) , an annular outer part (13) to be placed around the second core part (12) and a fourth mould part (14) to be placed around the outer part (13) , wherein, in the condition of the mould in which the sealing ring (4) is moulded, the sealing ring (5) placed on the first core part (11) , the second core part (12) , the outer part (13) and the fourth mould part (14) are positioned with respect to one another in such a way that they bound a second mould cavity (10) for moulding the sealing ring (4) which extends essentially in the axial elongation of the retaining ring (5) , the second core part (12) adjoining the inside of the retaining ring (5) so as to form a seal, the outside part (13) adjoining the outside of the retaining ring (5) so as to form a seal and the fourth mould part (14) retaining the retaining ring on the first core part (11) . 7. Mould according to claim 6, in which that part of the second core part (12) which adjoins the inside of the retaining ring (5) is of tapering design. 8. Mould according to claim 6, in which that part of the outside part (13) which adjoins the outside of the retaining ring (5) is of conical design. 9. Mould according to one of claims 6 - 8 , in which the outside part (13) is provided with a rounding-off (18) at the position of the junction with the second core part (12) .

Inventors: DE GREEF PETER EVERT JACOBUS, KANTERS ARNOLDUS FRANCISCUS CO, DE GREEF, PETER, EVERT, JACOBUS, KANTERS, ARNOLDUS, FRANCISCUS, CORNELIS
Applicants: GREEF PETER EVERT JACOBUS DE, KANTERS ARNOLDUS FRANCISCUS CO, WAVIN BV, DE GREEF, PETER, EVERT, JACOBUS, KANTERS, ARNOLDUS, FRANCISCUS, CORNELIS, WAVIN B.V.
Application year: 1997
Main classification: B29C45
IPC codes: B29C45