MOULD FOR THE PRODUCTION OF VACUUM-FORMED, TRIM-COVERED ARTICLES

Abstract: A vacuum-forming mould comprising a moulding portion (10) and a vacuum chamber (20). The moulding portion has a laminar structure including one or more layers of a plastics or resinous material containing electrically-conducting fibres, thus providing means to heat the moulding portion. The vacuum chamber contains a heat-insulating material.

Description: This invention relates to a mould for the production of vacuum-formed, trim-covered articles and to articles made therein. By the term "trim-covered articles" herein, there is to be understood, particularly but not exclusively, articles comprising a resilient core having an integral cover of a fabric or other sheet material. A commonly-­ encountered example of such an article is a seat component (e.g. a cushion or a squab) for a motor vehicle, the component comprising a foam core with an integral cover of fabric or plastics material. A mould and moulding process such as has commonly been used hitherto for the production of such articles will be illustrated in the following description and with reference to the accompanying drawings PRIOR ART I and PRIOR ART II. In these drawings, PRIOR ART I is a schemtaic cross-­ sectional view of a conventional vacuum-forming mould and PRIOR ART II is a perspective view of a moulded product. Referring to the drawings, a moulding portion C is supported above a vacuum chamber D, to which it is linked by means of a plurality of small-bore holes G. A layer of air-impermeable fabric A is laid over the mouth of the mould and sealed around the mould periphery at position J. A vacuum is applied to the underside of fabric A via port F and holes G. Depending upon its constitution and elastic properties, the fabric A, in response to the vacuum, either stretches or slides through the seal at position J and is drawn against the mould walls B. The mould is filled with a foam-forming mixture and closed by means of lid E. After curing the foam and removing the moulding, a moulded product H is obtained having an integral cover K. Moulds of the aforementioned type, in which the moulding portions are generally made of a plastics or resinous material, are difficult to heat in the controlled and uniform manner which is essential for the production of acceptable mouldings. It is also difficult, when using such known moulds, to ensure that the trim material is uniformly and reproducibly applied to the inside of the mould and especially to ensure that the trim material (particularly if it is a non-stretchable fabric) is not "bunched" or creased on the one hand or excessively stretched or torn on the other. We have found that these and other disadvantages can be overcome by providing the mould with a laminar structure which includes at least one heating element and a peripheral annular clamp which permits controlled and reproducible lining of the mould with the trim material. Accordingly, the present invention provides a mould for use in a vacuum-forming process, said mould comprising a moulding portion and a vacuum chamber, in which the moulding portion has a laminar structure including at least one heating element and the vacuum chamber contains a heat-insulating material. The present invention also provides a mould as described in the immediately-preceding paragraph, said mould additionally including a peripheral annular clamp to permit controlled and uniform lining of the mould with a trim material. The present invention further provides a vacuum-­ forming process for the production of trim-covered articles and a vacuum-formed, trim-covered article made thereby. Suitably, the laminar moulding portion of the mould in cludes at least one layer of a plastics or resinous material containing electrically-conducting fibres. The said layer can be, for example, a polyurethane, a polyester, an epoxy resin or a phenolic resin. Examples of electrically-conducting fibres can include fibres of carbon, metallised carbon, stainless steel or one of the nickel/chromium alloys available under the Registered Trade Mark NICHROME. The moulding portion may additionally include one or more layers of a plastics or resinous material rein­ forced with fibres of, e.g., carbon, glass, aramid (such as KEVLAR) or polyamide (such as NYLON). (The words KEVLAR and NYLON are Registered Trade Marks). The heat-insulating material contained in the vacuum chamber can be any porous material capable of withstanding compressive loads, e.g. hollow or solid plastics beads (such as polystyrene), ceramics (including glass), open-celled rigid foams (such as those available under the Registered Trade Mark OASIS), coarsely-ground talc, compressed wood-wool or horsehair. Preferably, the peripheral annular clamp comprises two flange elements which define between them an opening for the passage of a trim material into the mould, together with means to adjust the depth of said opening. The present invention will be illustrated, merely by way of example, in the following description and with reference to the accompanying drawings, in which: Figure l is a schematic cross-sectional view of a mould according to the present invention; Figure 2 is an enlarged view, again in cross-­ section, of a portion of the mould of Figure l; Figure 3 is schematic plan view of a heating element as used in the mould of Figure l; Figure 4 is a schematic side view of a mould according to the present invention and including a peripheral annular clamp; Figure 5 is a plan view of the mould shown in Figure 4; Figure 6 is a section on line VI-VI of Figure 5; Figures 7 to lO are schematic views of alternative embodiments of the peripheral annular clamp shown in Figures 4 to 6. Referring to Figure l, the moulding portion lO is sealed at ll around its periphery to vacuum chamber 20. The seal ll can be removable. Alternatively, the seal ll can be permanent, in which case the base 2l of the vacuum chamber 20 must be removable. The cavity 22, defined by the moulding portion and the vacuum chamber is capable of evacuation (by means known per se ) through port 23. Item l2 represents an electrical connection for a heating element forming part of the moulding portion lO (see Figure 2). The cavity 22 is filled with heat-­ insulating material (not shown in Figure l). In Figure 2, the moulding portion lO of the mould of Figure l is of laminar construction. The layer to be adjacent the moulding cavity (layer 30) comprises a resin-­ rich material which preferably includes one or more pigments capable of reversible colour-changes in response to variation in temperature. This enables an observer to see whether the mould is at the correct temperature and/or whether a fault has occurred. Layer 3l is of a fibre-reinforced plastics or resinous material, the fibres being of glass, carbon, aramid or polyamide. This layer is suficiently thin and rigid to ensure good heat transfer to layer 3O. Layer 32 comprises a plurality of undirectional electrically-conducting wires which are bonded in place with a resin. These wires carry a heating current. Layer 33 is of plastics or resinous material and can incorporate temperature detection and control means, e.g. probes, thermistors and thermocouples. This facilitates accurate monitoring and control of the moulding temperature. Layer 33 can, if desired, additionally contain reinforcing fibres (as for layer 3l). Layer 34 is a further heating layer (similar to layer 32) in which the unidirectional wires extend substantially at right angles to those of layer 32. This ensures that when vacuum holes or bolt holes are made in the mould there is no significant loss of heating or "cold spots". Finally, layer 35 is of a thermally-insulating material. In Figure 3, a pair of undirectional heating elements (cp items 32 and 34 in Figure 2) are shown super­ imposed one upon the other. The elements are provided respectively with contacts 40 and 4l. The wires constituting each of the two layers 32 and 34 are preferably closely-spaced, for example from l to 4O wires per centimetre width in each layer. Item 42 is a hole (such as may be drilled through the laminar mould portion to serve as a vacuum hole) and it will be seen that the close spacing of the wires in layers 32 and 34 limits the area of heat loss to the cross-hatched area surrounding hole 42. In Figures 4, 5 and 6 (wherein like numerals denote like parts) the mould comprises a moulding portion 50, a lid portion 5l hinged at 52, and a peripheral annular clamp 53 having a hinge 54 and a locking device 55. Between the clamp 53 and the moulding portion 50 there is an opening60 for the passage of a trim material (item 6l in Figure 6) into the mould. The depth of the opening 60 is adjustable so as to optimise the frictional resistance between the trim material and the clamp on the one hand and between the trim material and the moulding portion on the other hand. Alternative embodiments of the peripheral annular clamp are illustrated in Figures 7 to lO. In Figure 7, the clamp consists of two flange elements 70 and 7l which define between them an opening 72 for the passage of the trim fabric 73 into the mould (part of which is indicated at 74). The position of flange elements 7O and 7l relative to each other can be varied to adjust the depth of opening 72. In Figure 8, the clamp comprises a plate 8O having threaded adjustment means 8l. The plate 80 and a peripheral flange 82 provided on the mould define between them an opening 83 for the passage of a trim material 84 into the mould. The surfaces 80 and 82 to be in contact with the trim material are smooth and, as indicated generally at 85, all curves are radiussed. In Figure 9, the clamp comprises a pair of plates 9O and 92 defining between them an opening 92 for the passage of a trim material 93 into the mould. In this embodiment, the clamp is provided with a hinge 94 and adjusting means 95. In Figure lO, the mould is provided with a stepped portion lOO around its periphery and the clamp is constituted by a ring member l0l of complementary shape, members lOO and lOl defining between them an opening lO2 for the passage of a trim material lO3 into the mould. As described herein, the moulding portion will be of low-cost and light-weight construction. The moulds of the present invention can be repaired and replaced quickly and can be drilled to provide vacuum holes or to take mould-inserts without deleterious effects on the moulded products. The use of a vacuum ensures rapid and efficient heating of the mould and the insulating material in the vacuum chamber prevents heat loss. Furthermore, the insulating material can be used to withstand the high compressive forces exerted on the mould during the moulding process. Alternatively, fibre-reinforced ribs can be fitted to the underside of the mould to assist support.

Claims: 1. A mould for use in a vacuum-forming process, said mould comprising a moulding portion and a vacuum chamber, characterised in that the moulding portion (10;50) has a laminar structure including at least one heating element (32; 34) and in that the vacuum chamber (20) contains a heat-insulating material. 2. A mould according to Claim 1, characterised in that the moulding portion (10;50) includes one or more layers (32; 34) of a plastics or resinous material (e.g. a polyurethane, a polyester, an epoxy resin or a phenolic resin) containing electrically-conducting fibres (e.g. carbon or metallised carbon fibres, stainless steel fibres or fibres of a nickel/chromium alloy). 3. A mould according to Claim 1 or 2, characterised in that the moulding portion (10;50) additionally includes one or more layers (30; 31; 33) of a plastics or resinous material reinforced with fibres (e.g. carbon, glass, aramid or polyamide fibres). 4. A mould according to any preceding claim, characterised in that the heat-insulating material in the vacuum chamber (20) is a porous material capable of withstanding compressive loads (e.g. hollow or solid plastics beads, ceramics, open-celled rigid foams, compressed wood-wool, coarsely-ground talc or horsehair. 5. A mould according to any preceding claim, characterised in that it includes a peripheral annular clamp (53; 70, 71;80; 90, 91; 101) to permit controlled and uniform lining of the mould with a trim material (61; 73; 84; 93; 103). 6. A mould according to Claim 5, characterised in that the annular clamp comprises two flange elements (70, 71; 90, 91) which define between them an opening (72; 92) for the passage of the trim material (73; 93) together with means to adjust the depth of said opening.

Inventors: ATKIN, HOWARD STUART, GIBSON, NEIL SKEEN, GRIFFITHS, PHILLIP MARTIN
Applicants: DUNLOP LIMITED
Application year: 1986
Main classification: B29C51
IPC codes: B29C51, B29C35, B29C33