HK1044311B - Process and apparatus for manufacturing a thermoplastic part with an injected elastomer seal - Google Patents

Description

The present invention relates to a manufacturing process for a thermoplastic part with an injected elastomer seal and an injection moulding device to perform the process.

Thermoplastic parts with elastomer seals are used, for example, in the engine compartment of cars or as housings of all kinds in the electrical industry. Often it is necessary that these parts maintain their watertight function reliably even after several disassemblies. The same applies to extreme temperature loads. Because of their great elasticity over long periods and even at high temperatures (150 - 200 °C), seals are very often made of interlocking plastics (e.g. rubber or LSR (liquid silicon rubber)).However, if the manufacture of seals from interlocking plastics requires tools heated to temperatures of about 170-200°C, it is difficult to produce both in one tool or in a fully automatic process. In addition, interlocking plastics are very fluid when processed in the tool, so that the sealing methods common to thermoplastic tools are not sufficient.The Commission has also been involved in the preparation of the draft budget for the European Council in Brussels.

Unlike interlocking plastics, seals made of thermoplastic elastomers can be injected into the nuts of thermoplastic parts without any major problems. However, a disadvantage of thermoplastic elastomer seals is that they have a low or very low resistivity.

Another problem with seals made of thermoplastic elastomers is that the seal can fall out when handling the thermoplastic part if it does not have sufficient adhesion to the thermoplastic part.

The purpose of the invention is therefore to provide a method for the manufacture of a thermoplastic part which has an injected seal, which is reliably held in the thermoplastic part and preferably maintains its sealing properties even in the case of repeated disassembly and assembly of the thermoplastic part and in the presence of high temperatures, suitable for automation.

It is another task of the invention to create a device for carrying out this process.

The first problem is solved by a method according to claim 1.

Subclaims 2 to 7 contain further versions of the process of the invention.

The second problem is solved by a device according to claim 8.

Subclaims 9 to 14 contain further design elements of the device.

The general terms of claim 1 and claim 8 are described in US-A-5246065, US-A-5160474, JP-A-02179741 and JP-A-03140220.

The following figures describe the embodiments of the invention in detail. Figures 1 to 4 show various thermoplastic parts produced by the inventive process.In each case, cross-sections are shown through the area of the nut and seal for an intermediate product (1b, 2b, 3b, 4b) and the final product (1a, 2a, 3a, 4a).Figure 5 shows the manufacturing steps for the intermediate product and the final product and the schematic structure of the injection moulding tools.

Figures 1b, 2b, 3b, 4b show cross-sections of a thermoplastic part 1 produced by the inventive process in the area of seal 3 in various embodiments. Seal 3 consisting of a connecting plastic (e.g. rubber or LSR) is located in and completely fills the nut 2 of the thermoplastic part 1 and the seal 3 has on the open side of the nut a seal flip 5 protruding over the face 4 of the thermoplastic part and two seals flip 5 running parallel to the face 4 and notching 7. In the examples of Figures 1a, 2a and 4a, the edges of the 2 rear seals 6 are moved in the direction of the inner seal 2 by means of a deep seal.

Figures 1a-4a and 1b-4b now describe different embodiments of the manufacturing process for a thermoplastic part according to the invention. Figures 1b, 2b, 3b and 4b each show an intermediate step of the process, namely the thermoplastic part 1 before the injection of the seal 3 into the nut 2. The thermoplastic part 1 is produced by a conventional injection molding process. A use 2 is reserved for the inclusion of the seal 3. In order to be able to inject the rubber or LSR seal on one side without over-spraying in a further step of the process according to the invention, the first embodiment of the invention of the sprayblast process involves a rubber profile corresponding to the shape of the seal 1 in Figure 2. The two profiles are designed to be used in parallel when the inside of the rubber are injected. For example, the use profiles 10 and 12 (LSR 2 and LSR 2), the two profiles are designed to be used on the inside of the same profile.

In another embodiment of the method of the invention for the manufacture of a thermoplastic part 1 with a seal 3 from a mesh plastic, the sealing of the nut 2 is not done by the thermoplastic part 1 itself but by the injection tool when the rubber or LSR is injected, and the tool is fitted with a seal-head, adapted to the course of the surfaces next to the nut 2, which seals the nut 2 when the rubber or LSR is injected. Preferably, these seal-heads deform the edges of the nut 2 when the tool is closed before the rubber or LSR is injected into the inner part of the tool to form the back cuts 6 (see Fig. 4).

To inject the interlocking plastic to form the seal 2, the tool is partially heated at the second core, the temperature of this area being between 170°C and 230°C. Preferably, heating of the tool is limited to an area adapted to the course of the nut 2 and this area is thermal insulated from the rest of the tool in order not to expose the whole thermoplastic part 1 to the high temperature in the second stroke.

Figure 5 shows an example of a device for the manufacture of a thermoplastic part with an injected seal from a reticle plastic.

The device is an injection moulding tool in an injection moulding machine, preferably a two-component machine, with a locking unit comprising at least one matrix 13 and two cores 15, 17. The core 15 together with the core 13 forms the workpiece for injection moulding the thermoplastic part. Together with the core 17, the matrix 13 forms the tool for injection of the seal 3. An automatic device for transporting the thermoplastic parts from the cavity for the first stroke to the cavity for the second stroke may be provided. Such devices include, for example, rotary tables, robots and sliding matrices.

The first core 15 is designed to save the nut 2 when the thermoplastic part is injected (see Fig. 5a). It can also be designed to inject the seal profiles 10 when the thermoplastic part is injected. The core 17 for injecting the seal from a mesh plastic has a thermal insulated area 19 in the area of the nut 2 (Fig. 5b). The insulation can be achieved, for example, via an insulation slit 18. In the insulated area 19 there are heating agents 20. These can be, for example, an electric heater or a heating channel for hot oil. The insulated area 19 can be either formed with the second one or formed by a pre-formed partition, which can be formed in a corresponding form for the second partition. The insulated core 19 can also be formed in the form of a partial oil or oil-based partition.

The device for the manufacture of the thermoplastic part with an injected seal from a mesh plastic need not consist of a single injection moulding machine. Rather, the two steps of moulding the thermoplastic part and injecting the seal may be carried out by two separate machines. Nor does it need to be that the first core 15 is suitable for the moulding of tight profiles 10. The tight profiles may instead also be formed on the second core 17. In particular, it is possible that the insulated area 19 or the insert may have tight protrusions preferably with a point profile.

The device and process described are not limited to a seal made of interlocking plastics, but can also be used with thermoplastic plastics.

Claims (14)

1. Method for producing thermoplastic parts with an injected seal consisting of an elastomer with the following steps:

   Moulding a thermoplastic part (1) with a groove (2) and injecting an elastomer into the groove (2), wherein prior to or during injection at least one undercut (6) or a plurality of separate undercuts (6) are formed on one or both groove edges, owing to which the seal is held in the groove, characterised in that the mould core (17) in the region (19) covering the groove (2) is heated to a temperature of 170°C to 230°C during injection of the elastomer, and in that the remaining regions of the mould core (17) are kept at a low temperature compared to the region (19).
2. Method according to claim 1, characterised in that during moulding of the thermoplastic part (1) sealing profiles (10) are integrally moulded with the thermoplastic part (1) near the groove (2), the sealing profiles sealing the groove (2) from overpackings during injection of the elastomer and being formed prior to or during injection of the elastomer in such a way that they form undercuts (6).
3. Method according to claim 2, characterised in that sealing profiles (10) are moulded as pointed profiles with relatively pointed cross-section.
4. Method according to claim 3, characterised in that the sealing profiles (10) are moulded with a leg (12) perpendicular toward the groove (2), the leg passing into the side wall (9) of the groove (2).
5. Method according to any one of claims 2 to 4, characterised in that the remaining forming of the sealing profiles (10) or the edges (11) of the groove (2) is simplified owing to the temperature in the vicinity of the groove or in the region of the sealing profiles (10).
6. Method according to any one of claims 1 to 5, characterised in that a cross-linking plastics material, in particular rubber of LSR is injected as elastomer.
7. Method according to any one of claims 1 to 5, characterised in that a thermoplastic elastomer is injected.
8. Injection moulding device for producing thermoplastic parts with injected elastomer seal with at least one female mould (13) and at least two cores (15, 17), the female mould (13) and the first core (15) forming a mould for injection moulding a thermoplastic part (1) with a groove (2) for receiving the seal (3) and the female die (13) together with the second core (17) forming a mould for injection moulding the elastomer seal (3) in the groove of the thermoplastic part and for forming undercuts (6) on the groove edges which keep the injected elastomer seal in the groove (2), characterised in that the second core (17) comprises a region (19) which can be heated to 170°C to 230°C and is adapted to the course of the groove (2) and thermally insulated against the remaining regions of the core.
9. Injection moulding device according to claim 8, characterised in that the heatable region (19) consists of an insert or a plurality of partial inserts.
10. Device according to claim 8 or 9, characterised in that the first core (15) is formed in such a way that sealing profiles (10) are integrally moulded with the thermoplastic part (1) in the vicinity of the groove (2) during injection moulding of the thermoplastic part (1), the sealing profiles sealing the groove (2) against overpacking during injection of the elastomer and in that the second core (17) is formed in such a way that these sealing profiles (10) are formed prior to or during injection of the elastomer into the undercuts (6).
11. Device according to claim 8 or 9, characterised in that the second core (17) has sealing projections which seal the groove (2) against overpacking during injection of the elastomer and which form the groove edge prior to or during injection of the elastomer into the undercuts (6).
12. Injection moulding device according to any one of claims 8 to 11, characterised in that it comprises a two-component mould and a two-component machine.
13. Injection moulding device according to any one of claims 8 to 12, characterised in that a mechanism is provided for automatically transferring the thermoplastic parts from a first cavity for a first cycle to a second cavity for a second cycle.
14. Injection moulding device according to claim 13, characterised in that the mechanism for automatically conveying the thermoplastic parts comprises a rotary table, a robot or a sliding female mould.