The invention relates to a vacuum mounting press.

Vacuum mounting presses are known. For example, European Patent EP 0 360 450 discloses a heated vacuum mounting press comprising a flexible diaphragm and an electrically heated glass platen. Sheet workpiece material is placed into the press between the diaphragm and the glass platen, air is evacuated from the press, and the material is heated by the glass platen. The combination of pressure and heat is used to adhere layers of a laminate material, such as in dry mounting, heat sealing, or canvas bonding. The electrically heated glass platen comprises a glass platen with a coating of a conductive material; current passing through the conductive coating generates heat, which is used in turn to heat the workpiece. The use of a conductive coating as an electrical heating element ensures that the heat is generated uniformly across the surface of the glass platen.

However, such devices can be inefficient. In particular, much of the generated heat is wasted without raising the temperature of the workpiece. In addition, problems can arise due to uneven temperature distribution in the platen. Certain areas of the workpiece (such as multiple samples, or materials of different density) can act as local heatsinks, cooling adjacent regions of the platen, whilst others are unaffected, leading to localised 'cold spots'.

There is therefore a need for an improved vacuum mounting press. According to the invention there is provided a heated vacuum mounting press comprising:

an electrically heated first platen,

a flexible first diaphragm moveable between open and closed positions relative to a first side of the first platen, and

an air evacuating means for evacuating air from between the first platen and the first diaphragm when the first diaphragm is in its closed position relative to the first platen, whereby the first diaphragm is able to be flexed against sheet workpiece material positioned between the first diaphragm and the first platen in use to provide substantially even pressure over the surface of the sheet workpiece material whilst heat is applied to the sheet workpiece material from the electrically heated first platen, the press being characterised in that it further comprises an additional heat source located on a second (opposite) side of the first platen, and that at least the first platen is partially transparent to allow a user to view the workpiece material during operation of the mounting press.

In use, one or more various layers of sheet workpiece material are assembled as appropriate and inserted into the press between the first diaphragm and first platen. Air is then evacuated from between the first platen and the first diaphragm to cause the sheet workpiece material to be squeezed between the first platen and the first diaphragm. When the first platen is heated, the required processing (such as for example bonding of the various layers of the sheet workpiece material) can be effected.

For the avoidance of doubt, it will be understood that the arrangement of the components of the mounting press during operation is therefore first diaphragm -> workpiece -> first platen -> additional heat source.

The abililty to view the workpiece during operation of the vacuum mounting press allows a user to monitor the lamination (or other) process taking place, and hence to guard against creases or misalignment of the workpiece components, and more accurately control the heat and timing used. For the avoidance of doubt, it will be understood that it is essential for the user to be able to look through any region of the first platen, and hence to view any part of a workpiece placed in contact with that region of the first platen. In some embodiments, the user is able to view the whole work surface during operation of the vacuum mounting press. The inventor has surprisingly found that the provision of an additional heat source on the second side of the first platen results in improved operation of the vacuum mounting press. Without wishing to be bound by theory, it is believed that, even where the heat supply of the first platen is uniformly distributed (such as is the case where the first platen has a conductive coating through which an electrical current is passed), localised differences in the workpiece material can result in variations in heat absorption from the platen, and hence variations in the workpiece material temperature. Furthermore, radiative and other heat losses from the second, non- working side of the first platen (i.e. that facing away from the workpiece material and first diaphragm) decrease the efficiency of the vacuum mounting press. The provision of an additional heat source is believed to help to reduce such heat losses, and to promote uniformity of temperature distribution in the first platen. It is also believed that the use of an additional heat source can enable the vacuum mounting press to achieve higher temperatures and a more even temperature distribution across the sheet workpiece material. Higher temperatures may be useful for applications such as transfer printing, ink transfusing, or ink or dye sublimations. The additional heat source may also be used to supply heat, instead of the first electrically-heated platen, in the case where the sheet workpiece material is heat- sensitive, in order to limit the possibility of damage from direct contact with a heated first platen. Furthermore, an additional heat source may be useful where the heat output of the first platen is insufficient. This may be particularly the case where the first platen operates at (relatively) low voltages for safety reasons (such as where the device is intended for use by a domestic consumer). In such situations, the additional heat source allows satisfactory overall heat output without the need for unsafe voltages. In some embodiments, the additional heat source is embedded in, or located on the surface of, a second platen. Suitable heat sources include water-filled tubes, linear electrical heating elements (such as tape or wire), and electrically-conductive coatings (such as those described in EP 0 360450 B1). It will be understood that, in order for a user to view the workpiece material during operation of the mounting press some embodiments, the second platen should be at least partially transparent. In particular, at least some of the transparent areas of the first and second platens should align so as to allow a user to view the sheet workpiece material during use of the vacuum mounting press.

In some embodiments, at least one or both of the first and second platens comprises a glass platen.

It will be appreciated by the skilled man that electrical heating offers fine control of the heat output, ensuring that any undesired changes in temperature can be rapidly corrected. Unlike the first platen, the additional heat source is not in direct contact with the sheet workpiece material, and therefore such fine control of the heating is not always essential (as it is in the first platen).

Nevertheless, in some embodiments, it may be beneficial for the heat output of the additional heat source to be uniform and/or to be finely controlled. Thus, in some embodiments, the heat source comprises an electrically conductive coating on the platen. A preferred metal oxide coating is fluorine-doped tin oxide. It is believed that the use of an electrically-conductive coating as the heater element results in a uniform supply of heat across the surface of the platen. It will be understood that, where the heat source comprises an electrically conductive coating, it should be provided with appropriate connections to an electrical supply. Such connections may take the form of, for example, bus bars. The electrical supply may be any suitable electrical supply, as will be readily apparent to the skilled addressee, including (but not limited to) a transformer for connecting to a supply of alternating current (such as a domestic electricity supply) or a supply of direct current (such as a battery pack). In some further embodiments, the vacuum mounting press further comprises control means for controlling the supply of electricity to the first and second electrically-heated platens. In some still further embodiments, the control means may provide a supply of electricity to the second platen only when the first platen has reached its operating temperature and the supply to the first platen is reduced or disconnected. The heating effect of the second platen helps to maintain the first platen at this temperature as described above. Only when the temperature of the first platen drops outside its operating range is the electrical supply to the first platen resumed, and the supply to the second platen disconnected. In this way, fluctuations in the power requirements of the vacuum mounting press are reduced, compared to a similar device in which both platens operate at the same time (giving a high power requirement) and are then shut off on reaching operating temperature (giving a low power requirement). The reduction in fluctuation of the power requirements also ensures that the maximum current draw of the vacuum mounting press from its electrical supply is reduced. In some cases, this can ensure that the current draw remains within the limits of (for example) a domestic power supply, without compromising the ability of the vacuum mounting press to operate at the required temperature levels. For example, an embodiment of the vacuum mounting press may have a current draw of 11 A at 240V AC, allowing it to be connected to a UK domestic wiring circuit through a 13A fuse. In some embodiments, the second platen is spaced apart from the first platen so as to define a gap therebetween. In some further embodiments, the gap contains a fluid. For example, the fluid may be air. In particular, the air may be in fluid communication with the atmosphere. Alternatively, the gap may be sealed to the atmosphere. In some still further embodiments, the vacuum mounting press comprises means for circulating fluid within the gap. Such means may comprise for example a fan or other mechanical device. Without wishing to be bound by theory, it is believed that the fluid also enables heat transfer from warmer regions to colder regions of the first platen, thereby promoting uniformity of temperature. It will be understood that, where the fluid is a gas, it will be necessary to account for significant thermal expansion as the first platen (or, where appropriate, at least one of the first and second platens) is heated. In such embodiments, it may be desirable to allow the gas to exit the gap between the first and second platens, such as for example by having the gap open to the atmosphere. Alternatively, and depending on the operating temperature of the device, it may be sufficient to choose materials for the first and second platens which are able to withstand the appropriate pressures. Suitable materials are well known in the art.

In some embodiments, the vacuum mounting press comprises more than one second platen. It will be understood that, in such cases, the second platens may be identical or different, provided that each second platen has the features required by the invention.

In some embodiments, the additional heat source on the second side of the first platen comprises a layer having at least two regions, such that at least one of the regions can be heated independently of at least one other such region. In some embodiments, both (or all) of the regions may be heated independently of each other. The use of selective heating in certain regions is thought to allow additional control of temperature in the first platen, by supplying heat only to cooler regions of the first platen. For example, such regions may be created through the use of separate heating elements. Where the heat source comprises an electrically conductive coating on a platen, regions may be created by selectively applying one or more separate regions of an electically-conductive coating over part of the platen surface (such as by screen printing), or by removing parts of a continuous coating (such as by chemical etching or sandblasting) to leave one or more separate regions of coating on the platen surface.

In some embodiments, the additional heat source on the second side of the first platen comprises a reflective surface for reflecting towards the sheet workpiece material radiation emitted by the first platen. For example, the additional heat source may comprise a platen having a reflective coating on one surface thereof. It will be understood that, in some embodiments, a single electrically conductive coating on the platen forms both the heat source, and the reflective surface. The inventor has surprisingly found that the provision of a second platen comprising a reflective surface for reflecting towards the sheet workpiece material radiation emitted by the first platen results in improved operation of the vacuum mounting press. Without wishing to be bound by theory, it is believed that, even where the heat supply of the first platen is uniformly distributed (such as is the case where the first platen has a conductive coating through which an electrical current is passed), localised differences in the workpiece material can result in variations in heat absorption from the platen, and hence variations in the workpiece material temperature. Furthermore, radiative and other heat losses from the second, non-working side of the first platen (i.e. that facing away from the workpiece material and first diaphragm) decrease the efficiency of the vacuum mounting press. The provision of a second platen comprising a reflective surface for reflecting towards the sheet workpiece material radiation emitted by the first platen is believed to help to reduce such heat losses, and to promote uniformity of temperature distribution in the first platen.

In some embodiments, the heated vacuum mounting press further comprises an additional heat source located on the first side of the first platen. The additional heat source may be embedded in or located on the surface of the first diaphragm, or located between the first diaphragm and the first platen, provided that the first diaphragm is able to form a seal against the first platen such that air can be evacuated from between the first platen and first diaphragm, and that the first diaphragm is able to be flexed against sheet workpiece material positioned between the first platen and first diaphragm to provide substantially even pressure to the workpiece material, as set out above. Alternatively, the additional heat source located on the first side of the first platen may be located such that the first diaphragm lies between the first platen and the additional heat source. It will be understood that the additional heat source on the first side of the first platen is located such that, in use, the sheet workpiece material on which the press operates is placed between the first platen and the additional heat source.

The inventor has surprisingly found that the provision of an additional heat source on the first side of the first platen results in improved operation of the vacuum mounting press. Without wishing to be bound by theory, it is believed that, especially where the sheet workpiece material is relatively thick, delays in transmission of heat through the workpiece material can lead to incomplete processing, or poor efficiency. The provision of an additional heat source is believed to help to ensure that heat is evenly transmitted through the sheet workpiece material, whilst maintaining efficiency. In some further embodiments, the additional heat source on the first side of the first platen is in thermal contact with the sheet workpiece material during operation of the heated vacuum mounting press. It will be understood that the term 'thermal contact' is intended to mean that heat can be transferred from the additional heat source to the sheet workpiece material by thermal conduction. This may as a result of direct contact, or through one or more intervening layers (such as the first diaphragm). The additional heat source on the first side of the first platen may be provided with means to urge it towards the sheet workpiece material during operation of the heated vacuum mounting press, in order to ensure that thermal contact is maintained.

In some still further embodiments, the additional heat source is moveable between a first position in which the additional heat source is in thermal contact with the sheet workpiece material during operation of the heated vacuum mounting press, and a second position in which the additional heat source is not in thermal contact with the sheet workpiece material. In some still further embodiments, the additional heat source is located such that the first diaphragm lies between the first platen and the additional heat source, and the additional heat source is connected to (such as for example embedded in, or attached to the surface of) a second diaphragm, such that evacuation of air from between the first diaphragm and the second diaphragm causes the additional heat source to move into thermal contact with the first diaphragm, and hence with the sheet workpiece material. Evacuation of air from between the first diaphragm and the second diaphragm may be achieved by the air evacuation means responsible for removing air from between the first diaphragm and the first platen, or by a separate air evacuation means.

In some embodiments, the additional heat source on the first side of the first platen is embedded in, or located on the surface of, a third platen. Suitable heat sources include water-filled tubes, linear electrical heating elements (such as tape or wire), and electrically-conductive coatings (such as those described in EP 0 360 450 B1). It should be understood that the use of the term 'third' platen does not necessarily imply the presence of a 'second' platen.

It will be appreciated by the skilled man that electrical heating offers fine control of the heat output, ensuring that any undesired changes in temperature can be rapidly corrected. Thus, in some embodiments, the heat source comprises an electrically conductive coating on the platen. A preferred metal oxide coating is fluorine-doped tin oxide. It is believed that the use of an electrically-conductive coating as the heater element results in a uniform supply of heat across the surface of the platen. It will be understood that, where the heat source comprises an electrically conductive coating, it should be provided with appropriate connections to an electrical supply. Such connections may take the form of, for example, bus bars. The electrical supply may be any suitable electrical supply, as will be readily apparent to the skilled addressee, including (but not limited to) a transformer for connecting to a supply of alternating current (such as a domestic electricity supply) or a supply of direct current (such as a battery pack). Other comments and optional features described above in relation to the additional heat source on the second side of the first platen apply equally to the additional heat source on the first side of the platen.

In some embodiments, the vacuum mounting press comprises a first frame part in which the first platen is mounted, and a second frame part in which the first diaphragm is mounted. The first platen and the first diaphragm may each be permanently mounted within their respective frame parts, or they may be removably mounted, such as for example by being mounted to a removable sub-frame. It will be understood that, in some embodiments, each of the first platen and the first diaphragm may have different mounting methods. The first and second frame parts may be moveable with respect to one another between open and closed configurations, in order to move the first diaphragm between open and closed positions with respect to the first platen. Other components of the heated vacuum mounting press may be mounted in the first and second frame parts as appropriate.

Suitable materials for the first diaphragm include polymeric materials, such as a rubber material, and metals (such as in the form of flexible sheets). Other suitable materials will be readily apparent to the skilled addressee. In some embodiments, the first diaphragm may comprise fibres having a negative axial coefficient of thermal expansion. An example of such a material is a para-aramid, such as poly(paraphenyleneterephthalamide), sold as KEVLAR by E. I. du Pont de Nemours and Company. Such materials offer the advantage that they contract under elevated temperatures, in contrast to the majority of materials which expand. The use of fibres with a negative axial coefficient of thermal expansion thereby ensures that there is no loss of definition in the workpiece resulting from sagging of the diaphragm at high temperatures. The fibres may be in the form of a woven cloth. The cloth itself will usually be air-permeable. Thus, in order to ensure that the diaphragm as a whole is impermeable to air (and is therefore able to form an airtight seal against the first platen), the cloth is generally coated with a suitable membrane. An example of a suitable material for such a membrane is silicone.

Where present, the second diaphragm may be formed from the same material as the first diaphragm, or an alternative suitable material.

Where the diaphragm is a rubber material, it may be mounted in the vacuum mounting press (such as for example in the second frame part) by a vulcanising and hot bonding process. A vacuum bag moulding technique may be used in addition to the vulcanising and hot bonding to give a better finish.

The air evacuating means will usually be a vacuum pump.

In some embodiments, the air evacuating means is connected to the first diaphragm, and air is evacuated from between the first diaphragm and the first platen through one or more apertures in the first diaphragm. For example, the air evacuating means may be connected to one corner of a rectangular first diaphragm. In alternative embodiments, the air evacuating means is connected to the first platen, and air is evacuated from between the first diaphragm and first platen through one or more apertures in the first platen. Further alternative constructions will be readily apparent to the skilled addressee. Similarly, where a second diaphragm is present as described above, air may be evacuated from between the first and second diaphragms through one or more apertures in either or both of the first and second diaphragms.

It will be appreciated that the vacuum mounting press may further comprise additional features intended to protect the user, and/or any electronic equipment within the mounting press, from (inter alia) the high temperatures used in operation of the press. Thus, for example, the vacuum mounting press may comprise thermally insulating material between the operating parts of the press (i.e. including the first diaphragm and first platen) and the exterior surface of the mounting press, or between the operating parts of the press and any electronic control equipment. The mounting press may additionally or alternatively comprise one or more thermally insulated handles to allow a user to open the press following use, without the risk of burning from any hot surfaces.

An embodiment of the invention will now be described solely by way of example and with reference to the accompanying drawings in which:

Figure 1 shows one embodiment of a vacuum mounting press according to the present invention;

Figure 2 shows an exploded view of the vacuum mounting press of Figure 1 ;

Figure 3 shows a schematic version of the view of Figure 2;

Figure 4 shows a representation of a circuit for use in controlling the heating elements of the vacuum mounting press of Figures 1 and 2; and

Figure 5 shows one embodiment of a fabric for use in a diaphragm of a vacuum mounting press according to the present invention.

Referring to Figure 1, there is shown a rectangular heated vacuum mounting press 2 comprising an upper first frame part 4 and a lower second frame part 6. The lower surface of the upper first frame part 4 is formed by a transparent electrically heated first platen 8, and the upper surface of the lower second frame part 6 is formed by a first diaphragm 10. The electrically heated first platen 8 is formed by a 6 mm thick sheet of glass coated on at least one surface with a conductive metal oxide coating. Opposite edges of the conductive coating on the platen are equipped with bus bars (not shown) to connect the platen to an electrical supply (not shown). Thus, electric current may be passed through the metal oxide coating by means of the electrical supply and the bus bars, to generate heat evenly across the surface of the first platen. The first diaphragm 10 is formed from a sheet of woven KEVLAR fabric coated with silicone.

The first 4 and second 6 frame parts are connected by means of a hinge at the rear (not shown) and are shown held in an open configuration by two gas struts 12. The upper first frame part 4 is therefore held at an angle to the lower second frame part 6, allowing one or more items of sheet workpiece material to be placed on the surface of the first diaphragm 10.

Closing the vacuum mounting press, by bringing the front of the upper first frame part 4 downwards towards the second lower frame part 6, brings the first platen 8 into contact with items of sheet workpiece material placed on the first diaphragm 10. Two catches 12 are provided at the front edge of the lower second frame part 6, which engage with corresponding clips 14 on the upper first frame part 4 when the first and second frame parts are in a closed configuration, to prevent opening of the press. By retaining the first and second frame parts in the closed configuration, the catches 12 and clips 14 assist in creating the required seal between the first diaphragm 10 and first platen 8. An insulated plastic handle 16 is provided on the front edge of the upper first frame part to allow the press to be opened and closed by the user, without risk of contact with hot surfaces.

Controls 18 are also provided on the front edge of the lower second frame part 6, to allow the user to set the required temperature, pressure and duration of operation, and to monitor temperature and pressure during use.

Referring to Figures 2 and 3, the component elements of the vacuum mounting press 2 are shown.

Within the upper first frame part 4, an electrically heated second platen 22 is located above the first platen 8. Again, the second platen 22 is formed by a 6 mm thick sheet of glass coated on at least one surface with a conductive metal oxide coating. Opposite edges of the platen coating are equipped with bus bars (not shown) to connect the platen to an electrical supply (not shown). The metal oxide coating forms a surface reflective to infrared radiation. The second platen 22 can supply additional heat to supplement that supplied by the first platen 8. This enables greater workpiece temperatures to be achieved, and allows faster recovery of temperature fluctuations. In addition the reflective surface of the second platen 22 reduces heat losses from the mounting press, and so improves efficiency.

A sheet of toughened glass 24 is located at the top of the upper first frame part 4. This toughened glass protects the second platen 22 from damage (such as scratches in the metal oxide coating), and also protects the user from contact with hot surfaces within the apparatus. The sheet also helps to retain heat within the device, thereby improving the thermal efficiency.

Within lower second frame part 6, a third platen 20 and second diaphragm 26 are provided between the first diaphragm 10 and the electronic components responsible for controlling the heat and vacuum application (not shown in detail). Again, the third platen 20 is formed from a 6mm thick glass sheet coated on at least one surface with a conductive metal oxide coating. Opposite edges of the platen coating are equipped with bus bars (not shown) to connect the platen to an electrical supply (not shown). The second diaphragm 26 is formed from a rubber sheet, and is identical in construction to the first diaphragm. The third platen 20 supplies heat to the sheet workpiece material through the first diaphragm 10. Thus, whilst the first platen 8 heats one face of the sheet workpiece material, the third platen 20 heats the other face, thereby ensuring that the sheet workpiece material is evenly heated. As a result, the heat output from the first platen 8 can be reduced, increasing efficiency.

An air evacuation means in the form of a vacuum pump (not shown) is also located within the lower second frame part 6, and is connected to an aperture in one corner of the rectangular first diaphragm 10 by means of a flexible low pressure hose (not shown). The pump is therefore able to evacuate air from between the first diaphragm 10 and the first platen 8 when the press 2 is in the closed configuration. The evacuation of the air enables the first diaphragm 10 to be flexed against the sheet workpiece material to provide substantially even pressure over the surface of the sheet workpiece material whilst heat is applied from the first platen 8. The air evacuation means is similarly connected to an aperture in one corner of the second diaphragm 26 by means of a low pressure flexible hose (not shown). The pump is therefore able to evacuate air from between the first diaphragm 10 and the second diaphragm 26. The second diaphragm 26 therefore urges the third platen 20 towards the first diaphragm 10 (against the action of gravity), ensuring that good thermal contact is made between the third platen 20 and the first diaphragm 10. Thus, heat from the third platen 20 passes into the first diaphragm 10, and hence into the sheet workpiece material.

It can be seen from Figure 1 that all of the first platen 8, the second platen 22 and the toughened glass 24 are transparent. Thus, the user is able to view the sheet workpiece material during operation of the vacuum mounting press 2, and thereby check that the treatment of the sheet workpiece material is progressing correctly and that the sheet workpiece material remains correctly positioned. A press 2 of the type shown in Figure 1 can be employed for board-mounting, laminating and canvas bonding. The press 2 is simply constructed and is easy to use by operators. In addition, the combination of the first 8 and second 22 platens ensures that the temperature of the workpiece is at the required level, whilst at the same time reducing heat losses from the press 2.

The press 2 may be made in various sizes, for example 29 * 36 inches (73.66 ^χ 91.44 cm) or 50 * 40 inches (127.00 ^χ 101.60 cm). The upper first frame part 4 and lower second frame part 6 may be made from a variety of materials. Where heavy section steel is used, this may be welded for strength and then painted. If desired, aluminium hinges with built-in adjustment features may be employed to enable the upper first frame part 4 to pivot open and closed with respect to the lower second frame part 6. Other materials and types of hinges may however be employed. The rubber material for the diaphragm 10 may be a nitrile material, but other materials may be employed.

Insulation and/or cooling fans may be provided within the upper first frame part 4 and lower second frame part 6 as necessary, in order to prevent excessive temperatures at the exterior of the frame.

It will be appreciated that one of the second 22 and third platens 20 could be omitted from the device, whilst still retaining many of the advantages discussed above. Further, in some situations it may be desirable to operate the device without any heat output from the second platen 22. In such cases, the reflective surface of the second platen 22 will still offer advantages as discussed above, compared to a device lacking the second platen 22. Similarly, second diaphragm 26 could be omitted from some embodiments. Although second 22 and third platens 20 are described as having continuous coatings of conductive metal oxide, in order to generate heat, other heating elements could be used in addition or alternatively.

Although the device is shown with the first 8 and second 22 platens mounted in the upper frame part 4, and the diaphragm 10 mounted in the lower frame part 6, it will be appreciated that in some devices this orientation could be reversed. Thus, the device could be assembled such that the diaphragm 10 is mounted in an upper frame part 4, and the first 8 and second platens 22 are mounted in a lower frame part 6. In such an orientation, the sheet workpiece material would not generally be visible to a user looking downward at the device during operation, unless the diaphragm was made from a suitable transparent material. The vacuum mounting press shown is controlled so that power is supplied to either the first 8 or second 22 platens, but not to both at the same time. The circuit shown in Figure 4 controls the electrical supply to the platens, according to their temperatures, with priority being given to the first platen 8. Thus for example, the first platen might be set to 92 °C and the second platen to 99 °C.

As shown in Figure 4, the first platen (labelled as Element 1) is controlled by means of a temperature controller LTW15K1RD and a thermocouple. When the first platen reaches its operating temperature, DPCO relay 1 is activated, which disconnects the supply to the first platen, and connects the electrical supply to the second platen (labelled as Element 2) by means of solid-state relay 2. The supply to the second platen is controlled by a temperature controller AC1-5JS2MW-A and a second thermocouple, also acting through relay 2. When the temperature of the first platen drops outside its operating range, DPCO relay 1 disconnects the second platen and returns the electrical supply to the first platen.

Referring to Figure 5, a woven sheet of KEVLAR fabric (in a 2/1 twill) is shown. Such a fabric can be used to form a diaphragm suitable for use in a vacuum mounting press. The KEVLAR sheet is coated with silicone (EVERFLEX HEAT MATE sold by Everbuild Building Products Ltd of Leeds, UK) to provide a barrier against air transmission, and is then cut to size and mounted in an appropriate frame. This composition allows evacuation of the air from the workpiece during operation of the vacuum mounting press, without any need for the usual additional materials for this purpose (typically a foam sheet or a sheet of cloth). As can be seen from Figure 4, the fabric incorporates threads of carbon fibre (seen as dark threads) in both the warp and weft directions. These threads are electrically conductive, and can be connected to an electrical supply (such as for example by means of busbars) in order to provide resistive heating within the diaphragm, if required.