GB2343137A

GB2343137A - Curing the rubber of an article by heat transfer

Info

Publication number: GB2343137A
Application number: GB9820284A
Authority: GB
Inventors: Andrew Duncan Peacock; Robert John Ellis
Original assignee: Avon Vibration Management Systems Ltd
Current assignee: Avon Vibration Management Systems Ltd
Priority date: 1998-09-17
Filing date: 1998-09-17
Publication date: 2000-05-03
Anticipated expiration: 2018-09-17
Also published as: GB2343137B; GB9820284D0

Abstract

In order to manufacture an article such as a hydraulically damped mounting device, which includes a part (5) of rubber material and a part made of polyamide or coated with polyamide, the article is partially enclosed in a mould so that at least a part (1,2) of the article made of polyamide or coated with polyamide is exposed. RF power is applied between the exposed part (1,2) of the article and a part (63) of the surrounding mould. The RF power is absorbed and heat is conducted to the part (5) of rubber material thereby to cure it. This enables the part (5) of rubber material to be enclosed within the mould and yet for heat to be conducted to it. The use of RF power, rather than other ambient heating, avoids problems caused by the low thermal conductivity of the polyamide during manufacture, but permits the polyamide to resist heat transfer to the article when it is in use.

Description

MANUFACTURE OF MOULDED ARTICLES The present invention relates to the manufacture of rubber articles which are produced by curing material (e. g rubber) in a suitably shapes mould.

It is particularly, but not exclusively, concerned with the manufacture of a hydraulically damped mounting device. One type of known hydraulic mounting device has a pair of chambers for hydraulic fluid, connected by suitable passageway, and damping is achieved due to the flow of fluid through that passageway.

An example of such a hydraulic mounting device is shown in EP-A-0115417, which discussed a hydraulically damped mounting device for damping vibration between two parts of a piece of machinery, e. g. a car engine and a chassis. It disclosed various"cup and boss"type of mounting devices, in which a"boss", forming one anchor part to which one of the pieces of machinery was connected, was itself connected via a deformable (normally resilient) wall to the mouth of a"cup", which was attached to the other piece of machinery and formed another anchor part. The cup and the resilient wall then defined a working chamber for hydraulic fluid, which was connected to a compensation chamber by a passageway (usually elongate) which provided the damping orifice.

The compensation chamber was separated from the working chamber by a rigid partition, and a flexible diaphragm was in direct contact with the liquid and, together with the partition formed a gas pocket.

In the hydraulically damped mounting devices disclosed in the specification discussed above, there was a single passageway. It is also known, from other hydraulically damped mounting devices, to provide a plurality of independent passageways linking the chambers for hydraulic fluid.

Fig. l ouf the accompanying drawings shows one example of a"cup and boss"type of mounting device, and has been disclosed in our UK patent application No.

2282430. The mounting device is for damping vibration between two parts of a structure (not shown), and has a boss 1 connected via a fixing bolt 2 to one of the parts of the structure, and the other part of the structure is connected to a generally U-shaped cup 4. A resilient spring 5 of e. g. rubber interconnects the boss 1 and the cup 4. A partition 7 is also attached to the cup 4 adjacent the ring 6, and extends across the mouth of the cup 4. Thus, a working chamber 8 is defined within the mount, bounded by the resilient spring 5 and the partition 7.

The interior of the partition 7 defines a convoluted passageway 9 which is connected to the working chamber 8 via an opening 10 and is also connected via an opening 11 to a compensation chamber 12. Thus, when the boss 1 vibrates relative to the cup 4 (in the vertical direction in Fig. 1), the volume of the working chamber 8 will change, and hydraulic fluid in that working chamber 8 will be forced through the passageway 9 into, or out of, the compensation chamber 12. This fluid movement causes damping. The volume of the compensation chamber 12 needs to change in response to such fluid movement, and therefore the compensation chamber 12 is bounded by a flexible wall 13.

In use, the force received by the mounting device is principally parallel to the fixing bolt 1, and this direction defines an axis of the boss 1.

The above structure is generally similar to that described in EP-A-0115417, and the manner of operation is similar. In EP-A-0115417, the partition supported a diaphragm which acted as a boundary between fluid in the working chamber and a gas pocket. In the arrangement shown in Fig. 1, there is an annular diaphragm 50 which is convoluted. That diaphragm 50 is held on the partition 7 by an upper snubber plate 22, that snubber plate 22 is held in pace by a ring 40, which is clamped to the partition 7 and to the cup 4, by a clamping ring 41. The resilient spring 5 is also connected to the ring 40. The upper snubber plate 22 has openings 21 which permits fluid in the working chamber 8 to contact the diaphragm 50.

In the arrangement shown in Fig. 1, the passageway 9 is in the form of a spiral, and the internal dimensions of that spiral are uniform.

In the manufacture of such a mount, the rubber or other material for forming the spring is shaped in a mould. Heat must be applied to the material of the spring to cure it. However, it is common to coat the fixing bolt, and possibly some or all of the boss with polyamide. This is done to reduce heat transfer from the surrounding of the mounting device to the spring when the mount is in use. Polyamide has a low thermal conductivity and thus, when the mounting device is used as an engine mount, heat transfer from the engine to the spring is minimised, thereby prolonging durability of the mount.

However, the polyamide coating means that, when manufacturing the mount, ambient heat is not readily transferred to the bolt, and hence to the spring. This increased the cure time of the spring, and thus can reduce the quality of the spring, once cured, thereby impairing the durability of the mount.

A similar problem can arise in moulding of other articles, e. g when moulding an article, a component of which is made of or coated with a polyamide. Again, in that situation, transfer of heat to the article may insufficient to achieve adequate curing. This arising particularly when the polyamide-coated part is a separate component from the rubber itself, as in hydraulically damped mounting device discussed above, since the polyamide component may prevent adequate curing of the rubber around itself, thereby weakening the bonding between the rubber and that component.

It has been realised that polyamide material is rapidly heated by RF power. Thus, at its most general, the present invention proposes that, in the heat-curing of an article, at least a part of which is made of polyamide or coated with polyamide, RF power is applied to heat at least that part of the article.

Thus, in the hydraulically damped mounting device previously described, where the fixing bolt and possibly at least part of boss, is coated with a polyamide, to components are arranged to that at least the bolt projects the mould. Thus, it is available for receiving RF power, which heats the polyamide, and the heat thus generated is transferred to the material of the spring.

Where the part of the article coated with polyamide is of metal, it is then preferable to use that part as one electrode, and surrounding parts of the mould is another electrode, with the RF power then being applied between those electrodes. In this way, satisfactory curing of the material of the spring, can be achieved, and satisfactory hydraulically mounting device produced.

An embodiment of the present invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which; Fig. 1 is a cross-sectional view through a hydraulically damped mounting device in accordance with GB 2282430, and has already been discussed; Fig. 2 shows a mould for manufacturing hydraulically damped mounting devices in accordance with the present invention.

Fig. 2 shows a mould for forming part of two hydraulically damped mounting devices. Using the same numbering of components as in Fig. 1, the boss 1 of each mount is supported in a respective mould part 60. Each such mould part 60 has a recess 61 therein, so that the bolt 2 which projects from the corresponding boss 1 is exposed within a respective recess 61. The springs 5 of eg rubber then projects from the mould part 60 towards respective mould parts 62 which define the inner surfaces of the spring 5, and thus will form the shape of the working chambers 8 of each mount once the mounts are completed. Fig. 2 also shows the clamping ring 41 which extends around the sides of the spring 5, and also extends downwardly over the mould parts 62. Note that the ring 40 is not shown in Fig. 2, but may be present between the springs 5 and the clamping ring 41. Outer mould clamps 63,64 then hold the resulting structures in place whilst the rubber material of the spring 5 is cured.

Although not visible in Fig. 2, the bolts 2 and possibly parts of the bosses 1 which will be exposed in the final mount are coated with a polyamide such as nylon. The polyamide coating reduces heat transfer from the surrounding structures, such as eg an engine to the rest of the mount when the mount is in use.

With the mould in the position shown in Fig. 2, RF power is applied between the bolts 2 and a part of the surrounding mould, such as the mould clamp 63. The polyamide coating of the bolt 2 readily absorbs such RF power, and the power is transferred as heat by conduction through the respective bosses 1 to the springs 5. The heating of the springs 5 thus generated cures the rubber material of the springs 5. The fact that the bolts 2 are exposed in the recesses 61 means that the RF power can readily be applied during the moulding cycle. Thus, satisfactory heating can be achieved despite the low thermal conductivity of the polyamide coating on the bolts 2.

Although the embodiment described above is concerned with the manufacture of a hydraulically damped mounting device, it can be seen that it is readily applicable to other articles at partially formed by a material which is cured by heat, part or all of which is made of polyamide or is polyamide-coated.

Claims

CLAIMS 1. A method of processing an article including at least one part of rubber material comprising coating a second part of the article with polyamide, and applying RF power to at least said second part of the article, whereby said second part is heated and the heat causes heating of said at least one part, thereby to cure said rubber material.
2. A method according to claim 1, wherein said second part of the article is of metal, and acts as an electrode for the application of the RF power.
3. A method of processing an article including at least one part of rubber material, at least a second part of which article is of polyamide, comprising applying RF power to at least said second part of the article, whereby said second part is heated and the heat causes heating of said at least one part, thereby to cure said rubber material.
4. A method according to any one of the preceding claims, wherein the article is at least partially enclosed in a mould when the RF power is applied, a part of the mould acting as an electrode for the applications of the RF power.
5. A method according to any one of the preceding claims wherein the article is a hydraulically damped mounting device.