WO1996004126A2

WO1996004126A2 - Membrane press

Info

Publication number: WO1996004126A2
Application number: PCT/GB1995/001777
Authority: WO
Inventors: Jeffrey Allen Field
Original assignee: Jeffrey Allen Field
Priority date: 1994-07-29
Filing date: 1995-07-28
Publication date: 1996-02-15
Also published as: WO1996004126A3; AU3118895A

Abstract

A membrane press comprises a first part including a pressure chamber closed by a flexible membrane, and a second part comprising a bed for receiving a workpiece, the first and second parts being relatively movable between an operative position, wherein the membrane is in contact with the bed and/or with a workpiece thereon, and an inoperative position, wherein the membrane is spaced from the bed, releasable locking means being provided to lock the first and second parts together in the operative position while pressure is applied to the membrane.

Description

MEMBRANE PRESS Field of the Invention

This invention relates to a membrane press. Background to the Invention In the application of veneers to contoured substrates, it is necessary to ap¬ ply an even pressure to the whole of the surface while the adhesive used to attach it cures or sets, depending on the type used. This is conventionally carried out us¬ ing a membrane press, in which at least one press surface comprises a rubber mem¬ brane which is pressed against the veneer by means of high pressure air, usually heated to activate or cure the adhesive.

It will be understood that the term "veneer" encompasses plastics and other foils as well as natural wood veneers.

In conventional membrane presses, the rubber membrane is secured over a rigid steel frame, and the escape of compressed air is prevented, in use, by urging one frame against the other with the membrane edges compressed between them. This is done by hydraulic rams, typically mounted beneath the vertically-slidable lower frame to urge it upwardly into contact with the fixed upper frame. A sub¬ stantial force is required to be exerted by the rams, not to influence the pressing of the veneer on to the substrate, but simply to ensure that the seal is maintained. This arrangement has a number of disadvantages. Firstly, in order to con¬ tain the force exerted by the rams, to maintain the seal, the machine requires a very substantial framework. This is costly, heavy and space-consuming. Secondly, it is necessary to close the press and apply air pressure to the membrane in stages in order to seat the membranes between the frames and to avoid the risk of "guillo- tining" them. Thirdly, the high sealing pressures experienced between the frames, in conjunction with the operating temperatures required for the adhesives used, tend to cause silicone rubber membranes to become brittle relatively quickly, lead¬ ing to their failure at the edge regions. This means that natural rubber membranes are more generally used, even though silicone rubber has the advantages of being a much better conductor of heat and more flexible, and therefore quicker to heat up the adhesive and better able to follow the contours of the substrate closely to en¬ sure accurate and flaw-free lamination of the veneer. Silicone rubber has been found to be of especial benefit when using plastics veneers. A further advantage of silicone rubber is that the adhesives used do not stick to it, so that the time- consuming job of removing excess adhesive bonded to the membrane, experienced with natural rubber, is substantially or completely avoided. In practice, some of the advantages of silicone rubber can be gained by overlaying the natural rubber mem¬ brane with a membrane of silicone rubber, or a relatively thick membrane of sili¬ cone rubber can be used on its own. However, this reduces the benefits of increased thermal conductivity as compared with natural rubber, and is very costly, with silicone rubber costing up to three times that of natural rubber. Summary of the Invention

According to the invention, there is provided a membrane press comprising a first part including a pressure chamber closed by a flexible membrane, and a sec¬ ond part comprising a bed for receiving a workpiece, the first and second parts be- ing relatively movable between an operative position, wherein the membrane is in contact with the bed and/or with a workpiece thereon, and an inoperative posi¬ tion, wherein the membrane is spaced from the bed, releasable locking means be¬ ing provided to lock the first and second parts together in the operative position while pressure is applied to the membrane. In one preferred embodiment of the invention, the first part comprises a frame within which the pressure chamber is mounted, the second part has sides extending generally normally to the bed, and the frame is dimensioned and ar¬ ranged so as to fit, in the operative position, over the sides of the second part, the locking means comprising bolts extendible outwardly through the sides of the sec¬ ond part and into engagement with the frame. More preferably, the sides of the second part are each formed with an additional wall outwardly thereof, the frame being received between the sides and the additional walls, with the bolts being ex¬ tendible through the walls as well. The walls are suitably formed with cylindrical members into which the bolts are engaged, the cylindrical members being closed at their outer ends. The pressure chamber may be mounted in the frame by means of slidable supports so that, as the first and second parts are moved together, the membrane is brought into contact with the bed, and with any workpiece thereon, before the frame reaches the locking position in which the bolts may be engaged.

Preferably, the second part comprises a floor-mounted stand with the bed extending horizontally uppermost thereof, and the first part is slidably mounted above the second part, with pneumatic rams or the like being used to raise and lower the second part. Thus, supporting columns may extend upwardly from the stand, with the first part being provided with bearings which run over the columns. The pressure chamber preferably contains heating elements, for example electrically-heated, and the bed may also be provided with heating means to ensure that the workpiece may be heated on both sides. This is important for some appli¬ cations using thermoplastic or thermosetting adhesives.

In an alternative embodiment of the invention, there is provided a mem- brane press having a pressure chamber comprising a rigid pan having one face thereof open, and a membrane moulded so as to fit into the pan to close the said one face thereof, the membrane being provided with a peripheral rim dimensioned and arranged such that the pressure within the chamber urges the rim into airtight sealing contact with the wall of the chamber.

The rim is preferably provided with a rigid reinforcing frame therein. In one embodiment, the rim is substantially channel-shaped in cross-section, with the frame being formed by frame components bolted to the walls of the pan with the outermost wall of the rim between the frame and the wall of the pan. The outer¬ most wall of the rim preferably has a spaced pair of continuous beads or ribs thereon, directed inwardly, the frame components being provided with correspond- ing outwardly-directed grooves. The grooves preferably have a slightly smaller depth than the thickness of the ribs, such that, with the resilience of the material, which is most suitably silicone rubber, the sealing of the external face of the outer¬ most wall with the wall of the pan is enhanced along the lines of the ribs, above and below the lines of the fixing bolts. In an alternative embodiment, the rim of the membrane incorporates a moulded-in rigid reinforcing frame, suitably of extruded aluminium or an alloy thereof.

In the membrane press of the invention, it is no longer necessary to provide hydraulic rams to effect a seal, and it is simply necessary to lock the movable pan and its associated mountings into position adjacent to the fixed pan. This is pref¬ erably achieved by means of slidable bolts, actuated by pneumatic rams, for exam¬ ple, engaging in latching blocks positioned on the vertical supports for the machine. Upper blocks can be used to lock the movable pan at an inoperative po¬ sition spaced above the fixed pan to facilitate loading and unloading of the work- pieces, as well as maintenance work on the machine. The movable pan and its associated mountings are preferably raised and lowered by means of vertical pneumatic rams, and the upper locking positions ensure that there is no risk of the movable pan dropping accidentally during the loading and unloading and other operations.

It has been found that, with the press of the invention, the laminating of components can be carried out more quickly and with more consistent high qual¬ ity than with conventional presses. The capital cost of the press is less, and the running costs are substantially lower, since hydraulic rams are no longer used, and the amount of heat consumed is reduced. Throughput is increased, with less la¬ bour being required. Brief Description of the Drawings

In the drawings, which illustrate different exemplary embodiments of the invention:

Figure 1 is a side elevation of a membrane press according to a first embodiment; Figure 2 is an enlarged sectional side elevation of the lower membrane mounting pan of the press;

Figure 3 is a plan view of the locking arrangement for the slidable upper membrane mounting;

Figures 4, 5 and 6 are sectional views of the edge of the membrane illustrat- ing an alternative method of construction of the membrane;

Figure 7 is an end elevation of a press according to another embodiment of the invention;

Figures 8 and 9 are simplified sectional views of the press of Figure 7 in the loading and operative positions respectively; Figure 10 is an enlarged sectional view of one of the locking bolts of the press of Figures 7 to 9; Figure 11 is a sectional view through the pressure chamber; and Figure 12 is an enlarged sectional view of the edge of the pressure chamber, viewed at right angles to the view of Figure 11. Detailed Description of the Illustrated Embodiments Referring to Figure 1 , the membrane press consists of a rectangular support¬ ing structure 1, formed of vertical and horizontal steel beams, and carrying at each corner a supporting slide 2 on which is slidably mounted the movable mount 3 for the upper membrane 4, which is shown in its normal rest configuration bowing downwardly under its own weight, and thus keeping itself clear of the heating ele- ment, as described hereinafter. The upper movable mount 3 is supplied with elec¬ trical power for the heating element therein, and with compressed air to pressurise the membrane in use. These supplies are omitted from the drawing for the sake of clarity. The upper mount 3 is capable of being locked into the rest position as illus¬ trated, or alternatively in the operative position adjacent to the lower membrane, by means of locking bolts described hereinafter with reference to Figure 3. Pneu¬ matic rams (not shown) are used to raise and lower the upper mount 3, and these are arranged to hold the mount 3 at any intermediate position if the control is re¬ leased or the electrical power fails, thus ensuring safety of operation. The lower membrane mount 5 is fixed in the frame, and is again supplied with electrical power and selectively with compressed air in operation.

Figure 2 shows only an edge portion of the lower membrane 6 and its pan 7. The pan 7 is formed of steel and has side walls 8 formed with an upper retaining lip 9. The membrane 6 is moulded from silicone rubber and has a peripheral rim 10 of a channel shape in cross section, with the outermost wall 11 of the rim 10 formed with two spaced internal ribs or beads 12. A metal frame 13, for example of aluminium, is formed in sections with radiused corner blocks conforming with the internally radiused rim corners to avoid the presence of sharp corners which could provide a source of weakness in the membrane. The metal frame 13 has two spaced grooves 14 therearound corresponding to, but slightly shallower than, the beads 12, and occupies the channel shape in the rim 10. At intervals along its length, the frame has fixing bolts 15 which pass through the outermost wall 11 of the rim 10 and the side wall 8 of the pan 7 to pass through a welded external tube 16 contain¬ ing an O-ring seal 17 engaged by the fixing nut 18 to provide a hermetic seal. It will be seen that, when the pan is internally pressurised by the compressed air, the rim 10 is compressed by the pressure acting outwardly, thus ensuring that, the higher the pressure, the greater the sealing effect.

Also within the pan 7, a heating plate 19 is mounted horizontally, spaced from the floor of the pan by spaced mounting blocks 20, through which fixing screws 21 pass to engage closed sockets 22 in the base of the pan. The heating plate 19 is suitably formed of aluminium, with a silicone mat heater 23 attached to its underside. The floor of the pan 7 is provided with an insulating layer 24 of ceramic paper. A guard 25 of 50 mm eldmesh (Trade Mark) material is mounted on legs 26 located on the blocks 20 to prevent the membrane 6 from sagging on to the heating plate 19 when the compressed air pressure is released. It also serves to sup¬ port the workpiece during loading and unloading. The upper membrane mount 3, while generally the same as described for the lower mount, does not require this guard, as the membrane sags downwardly away from the heating plate.

In use, the workpiece, typically in the form of a contoured particle board substrate with a layer of adhesive thereon (in separate film form, or coated on to the substrate, for example), and with the veneer located over this. The upper mem- brane mount 3 is released from its rest position and lowered by the pneumatic rams on to the workpiece, being locked into its operative position adjacent to the lower membrane by means of the locking bolts as hereinafter described. The mem¬ branes are then both pressurised by introducing compressed air into the pans, where it becomes heated by the heating plates, in turn heating the membranes and causing the adhesive to cure or otherwise activate. The pressure is maintained for the desired length of time and then released, permitting the upper mount to be un¬ locked, raised by the pneumatic rams to its rest position, and then locked in that position by the bolts.

Figure 3 shows one end of the top of the upper membrane mount, with two of the four locking bolts. The bolts 30 slide in tubular guides 35, and each com- prise a 50 mm EN32 carbon steel pin pivotally mounted to a carriage 31 which slides between upper and lower rails (not shown), and which carries two pairs of adjustable guiding wheels 32 arranged bear against the side walls 33 of the upper framework members. A horizontal double-acting pneumatic ram 34 is mounted on the framework centrally of the carriage to move it forwards and backwards to en- gage and withdraw the bolts from holes in adjustable locking blocks (not shown) mounted on the vertical members of the framework. An identical mechanism to that illustrated is mounted back-to-back therewith to operate bolts at the other side of the framework.

Figures 4 to 6 show an alternative mounting system for the membrane in the pan. An extruded aluminium strip 40 having a longitudinal slot 41 therein is initially filled with some of the silicone compound used to form the membrane, the casting of this being done in such a way as to leave a fillet 42 extending from the slot 41 by a short distance, for example of the order of 4-5 mm. This stage is shown in Figure 4. The strip 40, with its silicone filling bonded thereto, is then formed into a frame with radiused corners, and the membrane 43 is then cast with the strip embedded therein, as shown in Figure 5. The completed membrane can then be fit¬ ted into the pan 7, as shown in Figure 6, using solid clamping bars 44 with threaded rods projecting through hermetically sealed sockets in the wall of the pan 7, or with sprung retaining bars (not shown) located within the pan in place of the clamping bars.

Referring now to Figure 7, the membrane press comprises a movable first part 70 containing the pressure chamber and membrane as hereinafter described, and a fixed second part 71 comprising a flat metal bed 72 carried by a floor mounted stand 73. The bed 72 is carried on a double walled supporting frame 74 while a guiding and supporting structure 75 extends upwardly from the stand 73 to guide the first pan 70. The structure 75 includes four tubular guide columns 76 one at each corner, on each of which runs a guide bearing 77 for the first part. Three vertical pneumatic rams 78 at each end of the apparatus lift and lower the first part, while a latching mechanism 79 adjacent to each corner holds the first part in its inoperative position, as illustrated in Figure 7, until the first part is lifted off the latches and the latches are withdrawn by means of pneumatic cylinders 80.

The stand 71 includes a series of horizontal pneumatic cylinders along each side driving steel bolts through aligned holes 81 in the stand and through corre¬ sponding holes 82 in the first part of the press. The holes 82 are adjustable as here- inafter described with reference to Figure 10.

Figures 8 and 9 are sectional views showing the two stages in the operation of the press. The pressure chamber 83, described hereinafter in more detail with reference to Figures 11 and 12, has a membrane 84 at its lowermost part and is car¬ ried by a supporting grid 85 of steel beams, the grid being suspended within the frame structure of the first part 70 by means of four rods 86 each of which is freely slidable relative to the upper part 87 of the frame and has an adjustable suspension nut 88 by which the load is transferred to the frame 87 when the pressure chamber is suspended as shown in Figure 8. In this position, the bolts 89 are held retracted by their respective pneumatic cylinders 90.

In use, the workpiece is placed on the bed 72 and the first part is lowered until the membrane is pressed against the workpiece. In this configuration air is al¬ lowed to exhaust from the pressure chamber and may be forcibly exhausted if re¬ quired by means of a venturi air mover operated by the pneumatic system.

With the membrane 84 resting on the workpiece, the frame of the first part continues its downward movement with the sliding rods 86 permitting relative movement between the floating pressure chamber and the frame. As shown in Fig¬ ure 9, the side members 91 of the frame locate between the sides of the stand. In the rest position as shown in Figure 9, the holes through the sides and the outer wall members align with the holes in the side members 91 so that the bolts 89 may be extended by means of the rams 90 to lock the first part securely to the second part. Air is then admitted to the pressure chamber under pressure, being heated in the process by the heating element as hereinafter described with reference to Fig¬ ures 11 and 12, so as to press and heat the workpiece for the desired time interval, at the end of which the inlet valve closes simultaneously with the opening of the outlets, and the pan is exhausted. The air mover is boosted by an increase in the control air volume to speed up evacuation, until the pan internal pressure is re¬ duced to a safe level (10-15 p.s.i.), determined by the setting of a pressure switch monitoring the pan inlet pressure. Only when the pressure is at a safe level can the sequence continue, with the bolts 89 being withdrawn and the rams 78 (Figure 7) extended to lift the first part clear of the second part to permit the workpiece to be withdrawn. Figure 10 shows the locking mechanism in more detail. The side 92 of the support for the bed, and the outer wall 74 have short sections of tube mounted therein with the bores of the tubes aligned. The tube 93 on the wall 74 has a clo¬ sure cap 94 securable thereon. The side member 91 of the first part of the press also has a short section of tube 95 mounted therein, but this is arranged so as to float and to be adjustable in position to ensure that it is accurately aligned with the fixed tubes 93. Vertical adjustment of this tube 95 is achieved by means of a screw 96, accessible from beneath, provided with a locking nut 97. This is adjusted to permit the bolt 89 to pass through without interruption. The bolt is driven as hereinbefore explained by means of a pneumatic ram 90 by way of a pivoting yoke 98.

Figure 11 is a sectional view of the pressure chamber from one end, while Figure 12 shows an enlarged view from 90° to the view of Figure 11. The mem¬ brane 84 is a plain sheet of a silicone rubber which is simply clamped around edges -jetwec... a -pmg frame 101 and 'licon? πasket 102 bedd? ^*

103 of the pressure chamber. The chamb /hich is lined with a layer 104 of a ce¬ ramic fibre insulating material, is supplied with compressed air via-an inlet 105 at each end thereof, Figure 12 showing the view at one end adjacent to the air inlet. Mounted within the chamber is a parallel pair of aluminium plates 106 and 107 spaced apart by a series of discontinuous blocks 108. On the underside of the lower plate 107 are mounted a series of parallel silicone matt heaters 109 supplied with power from a series of electric junction boxes 110 mounted down one side of the chamber. Where the air inlet 105 enters the chamber, a deflection plate 111 is mounted therebeneath to deflect the incoming air around the plates 106 and 107. The blocks 108 being discontinuous and the air being admitted from each end of the chamber, turbulence is generated, ensuring efficient heat transfer from the plates to the air, which then discharges all around the edges of the plates and in due contact with the membrane, rapidly heating this to the desired working tem¬ perature, as well as pressing the membrane into firm contact with the workpiece.

The operation of the device is controlled by a programmable logic control- ler (PLC) which ensured the correct sequencing of all the operations and, for safety, ensures that compressed air cannot be admitted to the pressure chamber until all the locking bolts are firmly located in position. Micro-switches on each pneumatic ram controlling the position of the bolts signal the position to the PLC. The venturi air mover ensures that the air may be rapidly exhausted from the pres- sure chamber, thus ensuring that very precise control may be obtained over the duration of the pressing operation, ensuring that consistent results are yielded.

Claims

1. A membrane press comprising a first part including a pressure cham¬ ber closed by a flexible membrane, and a second part comprising a bed for receiv¬ ing a workpiece, the first and second parts being relatively movable between an operative position, wherein the membrane is in contact with the bed and/or with a workpiece thereon, and an inoperative position, wherein the membrane is spaced from the bed, releasable locking means being provided to lock the first and second parts together in the operative position while pressure is applied to the membrane.

2. A membrane press according to Claim 1 , wherein the first part com- prises a frame within which the pressure chamber is mounted, the second part has sides extending generally normally to the bed, and the frame is dimensioned and arranged so as to fit, in the operative position, over the sides of the second part, the locking means comprising bolts extendible outwardly through the sides of the second part and into engagement with the frame.

3. A membrane press according to Claim 2, wherein the sides of the sec¬ ond part are each formed with an additional wall outwardly thereof, the frame be¬ ing received between the sides and the additional walls, with the bolts being extendible through the walls as well.

4. A membrane press according to Claim 2 or 3, wherein the walls are formed with cylindrical members into which the bolts are engaged, the cylindrical members being closed at their outer ends.

5. A membrane press according to any preceding claim, wherein the pressure chamber is mounted in the frame by means of slidable supports so that, as the first and second parts are moved together, the membrane is brought into con- tact with the bed, and with any workpiece thereon, before the frame reaches the locking position in which the bolts may be engaged.

6. A membrane press according to Claim 5, wherein supporting columns extend upwardly from the stand, with the first part being provided with bearings which run on the columns.

7. A membrane press according to any preceding claim, wherein the pressure chamber contains heating elements.

8. A membrane press according to Claim 7, wherein the heating ele¬ ments are electrically-heated.

9. A membrane press according to any preceding claim, wherein the bed is provided with heating means.

10. A membrane press according to Claim 1, wherein the pressure cham¬ ber comprises a rigid pan having one face thereof open, and wherein the mem¬ brane is moulded so as to fit into the pan to close the said one face thereof, the membrane being provided with a peripheral rim dimensioned and arranged such that the pressure within the chamber urges the rim into airtight sealing contact with the wall of the chamber.

11. A membrane press according to Claim 10, wherein the rim is pro¬ vided with a rigid reinforcing frame therein.

12. A membrane press according to Claim 11, wherein the rim is substan¬ tially channel-shaped in cross-section, with the frame being formed by frame com- ponents bolted to the walls of the pan with the outermost wall of the rim between the frame and the wall of the pan.

13. A membrane press according to Claim 12, wherein the outermost wall of the rim has a spaced pair of continuous beads or ribs thereon, directed inwardly, the frame components being provided with corresponding outwardly-directed grooves.

14. A membrane press according to Claim 13, wherein the grooves have a slightly smaller depth than the thickness of the ribs, and the resilience of the mem¬ brane material is such that the sealing of the external face of the outermost wall with the wall of the pan is enhanced along the lines of the ribs, above and below the lines of the fixing bolts.

15. A membrane press according to any preceding claim, wherein the membrane is formed of a silicone rubber material.

16. A membrane press according to Claim 10, wherein the rim of the membrane incorporates a moulded-in rigid reinforcing frame.