CN1304351A - Apparatus and method for twin sheet thermoforming - Google Patents

Abstract

Apparatus for twin sheet thermoforming has each mould half incorporating a sheet support means which can hold a sheet by its edge and support the sheet during heating and wherein at least one of the sheet support means can retract during thermoforming. The sheets are supported clear of each mould half by the supports but are heated from between. A movable heater may carry sheets while simultaneously heating and transfer heated sheets to the mould halves of the thermoforming apparatus.

Description

Apparatus and method for thermoforming of twin sheets

Background of the invention

field of invention

This invention relates to apparatus and methods for thermoforming of twin sheets, and more particularly to an improved method and apparatus which does not require a sheet support frame.

Overview of prior art

Twin-sheet thermoforming is becoming more common in the forming of large items. Some applications have been made, such as refrigerator cabinets and other large appliance cabinets, see for example US Patent No. 5,374,118. The specification describes a process in which two extruded panels are conveyed directly between opposed mold halves before they are combined to form a cabinet front. Since the material is continuously extruded, whereas the molding process is a discontinuous process, this method creates serious material handling problems and material waste problems. Therefore, cooling a malleable sheet that can be heated immediately before molding is considered more appropriate in the art.

An example of this approach is described in PCT Publication WO 96/25287, which shows a typical thermoforming process in which a pair of sheets are held and separated by a frame. The sheet is heated on the outside of the mould, the frame carrying the sheet is inserted between the two half-moulds, and the half-molds and the frame in between which supports the sheet are combined. The process involves many time-consuming steps in a product cycle, which in turn adds additional complexity to the machinery, would require redundant factory space and include significant additional equipment if the process were to be operated in an automated fashion.

It is therefore an object of the present invention to provide an apparatus and/or method for twin-sheet thermoforming which aims to overcome the above-mentioned disadvantages or which will at least provide the public with a useful choice.

Summary of the invention

A first aspect of the invention consists in proposing a device for thermoforming of twin sheets comprising:

a pair of opposed mold halves movable during thermoforming between an open position and a closed position,

sheet support means associated with each of said half-molds, each sheet support means being connected to their respective half-molds and configured to hold a thermoplastic sheet around its periphery, the sheet support means being configured to holding the sheets separately from each other in their open position, each said half-mold, its respective support means and the sheet held by said support means together defining a pressurized volume,

Means associated with each of said mold halves, capable of producing a controlled pressure differential between each defined volume and its exterior.

Another aspect of the present invention is to propose a method for thermoforming of twin sheets comprising:

Retaining a heated thermoplastic sheet on each of a pair of mold halves to provide a sealed volume between the sheet and the mold halves while controlling the spaces enclosed between the sheets and the respective mold halves air pressure difference between to prevent either of the sheets from sagging,

varying said pressure differential to ensure that the narrowest spacing between the sheets occurs at, and only at, the parts that will contact each other and form a seam between them,

moving said half-moulds closer to each other while increasing the pressure differential effect and seating each said sheet itself against an annular weld zone, and

The mold halves continue to be brought closer together to bring the welded areas together and form a seam between the welded areas.

A further aspect of the present invention is to provide an apparatus for thermoforming of two sheets, wherein each half-mould comprises a sheet support means capable of holding a sheet by its edge and supporting said sheet during heating, and At least one of said sheet support devices is retracted during thermoforming.

To those skilled in the art, the invention will admit of many structural changes and broadly different embodiments without departing from the scope defined by the appended claims. The disclosure and description herein are purely illustrative and not intended to be limiting in any sense.

Brief description of the drawings

Figure 1 is a cross-sectional view of a two-sheet thermoforming apparatus according to an embodiment of the present invention, wherein the sheets and heaters are in place and the edges of the sheets are held apart, held apart,

Figure 2 is a perspective view of a portion of the thermoforming apparatus shown in Figure 1, showing the sheet support, an adjoining element and a portion of the mold cavity,

Figure 3 is a cross-sectional view of a portion of the thermoforming apparatus shown in Figure 1, with the heater removed and a portion of the thermoforming process in progress,

Figure 4 is a cross-sectional view similar to Figure 3, where the thermoforming process continues,

Figure 5 is a cross-sectional view similar to Figure 4, wherein the thermoforming operation is substantially complete and the two sheets are joined together,

Figure 6 is a cross-sectional view of a twin-sheet thermoforming apparatus according to another embodiment of the present invention wherein the seam-forming die edges are incorporated in the sheet support means and in-mold trimming of finished products is possible,

Figure 7 is a cross-sectional view of a portion of the apparatus shown in Figure 6 in which a portion of the thermoforming operation has been performed,

Figure 8 is a cross-sectional view similar to Figure 7, where the thermoforming operation continues and the sheets have just been joined,

Figure 9 is a cross-sectional view similar to Figure 8 with the thermoforming operation substantially complete,

Figure 10 is a cross-sectional view similar to Figure 9 in which the thermoforming operation has been completed and in-molding trimming has been performed by the shearing action between the upper sheet support means and the lower mold half,

Figure 11 is a cross-sectional view through a panel support device according to an embodiment of the present invention,

Figure 12 is a cross-sectional view through a double sheet forming apparatus according to another embodiment of the present invention,

Figure 13 is a cross-sectional view through the twin sheet forming apparatus of Figure 1 and one sheet with heating means according to another aspect of the invention,

Figure 14 is a cross-sectional view through a region of the twin sheet forming apparatus and the associated sheet with heating means, depicting the grippers used in the transfer of the sheet and including some concealed parts shown in dashed lines,

Figure 15 is a perspective view of an embodiment of a heating device adapted to accommodate panels of different sizes,

Figure 16 is a perspective view of another embodiment of a heating device adapted to accommodate panels of different sizes.

Detailed description

Referring to FIG. 1 , an apparatus for thermoforming of twin sheets is shown in section, having a lower mold half 1 and an upper mold half 2 . The thermoforming device is shown with a pair of thermoplastic sheets 5, 6 held in place. Each panel 5 or 6 is supported on its respective half-mould 1 or 2 by a panel supporting device 11 which is movably connected to the body 10 of the half-mould. The preferred form of sheet support means is an annular support member 11 fitted in an annular groove 12 which surrounds the mold cavity 16 of the mold half.

The sheet support element 11 holds the sheet along its edge 51 (for example by using an annular vacuum seal 20). Other ways of retaining the sheet around its edges can also be used. For example, a series of hinged and lock-down clamps that can be operated manually or automatically, for example by solenoid valves or pneumatics, may be used. Figures 11, 12 and 14 illustrate means for securing such panels and will be described in further detail.

The support element 11 is shown in a preferably substantially fully extended position, which may for example be defined by a series of pins and sockets or any other suitable means, and which can be pressed into the groove 12 so that the half The mold bodies 10 may be brought together until the opposing seam regions 17 of the mold halves abut. A series of springs 13 are provided in the groove 12 between the bottom surface 13 of the support element 11 and the bottom 15 of the groove 12 to provide progressively increasing resistance to the pressing of the support element 11 . Obviously, means other than springs could be provided, such as finely controlled mechanical actuators, hydraulic or pneumatic actuators or any other suitable device, springs being just the least complicated option.

When the half-mold bodies 10 come together during thermoforming (eg by abutment of the support elements 11 ), the sheet support 11 will automatically enter the groove 12 . In order to produce a sheet separation similar to existing clamp frame arrangements, abutment elements 19 may be provided which extend from opposite surfaces 18 of the support element 11 to provide an abutment 28 therebetween. This abutment element 19 also allows to provide a reasonable passage between the sheets, for example for inserting a radiant heater 9 for heating the thermoplastic sheets 5 , 6 . In the case of inserting heaters, an additional separation may be required, for example, by controlling the template separation or by making one or more adjoining elements 19 proportionally elongated and elastically pressed in by an amount having their length get. As can be seen in Figure 2, this abutment, given the precise position of the mold halves and complete rigidity in typical thermoforming operations, still allows access to the free space inside the mold cavity. Also, it is desirable that such abutment elements/means are provided only below the sides of the mold halves so that their ends remain completely open and the sheets 5,6 can be easily inserted between the mold halves to be picked up and held by the fixture 20 .

A preferred method of sheet loading and heating will be described later with reference to FIGS. 13 to 16 .

Referring now to FIGS. 1 to 5, a method of thermoforming by the apparatus of FIG. 1 is shown. In FIG. 1 , plates are shown with heaters 9 interposed therebetween. The heater 9 may for example comprise a simple electric heater and is used to raise the temperature of the thermoplastic sheets 5, 6 to a suitable thermoforming temperature prior to processing. The heater 9 is then withdrawn.

During heating, the plates 5, 6 will be softened to a point where they can no longer support their own weight. This usually becomes especially important once the sheet has reached its glass transition temperature. For ABS plastic sheets, this will occur around 90°C. In order to mitigate any sagging consequences, the pressure in each cavity 24, 25 defined by each sheet 5, 6 and their respective mold halves 1, 2 can be appropriately controlled to support the sheet.

Not shown are the details of the individual mold halves and their cavities for thermoforming, which include small passage slots and air holes that provide air into the cavity 16, which are used to control the pressure in the cavity during thermoforming . These holes can be used to support the board to prevent sagging or sagging. In order to prevent sagging during heating, the pressure in chamber 25 will be kept below the ambient pressure and the pressure in chamber 24 will be kept above the ambient pressure.

Various types of pressure-based sheet support systems are known in thermoforming technology. An example of a current application is the use of a beam sensor on one side of the sheet to detect if "bubbles" of the sheet interfere with the beam. Depending on whether the panel is supported from above or below and on which side of the panel the sensor is located, the controller controls the pressure in the support chamber to bring the panel into a favorable condition. In a modified form, a controlled leak is introduced between the bearing cavity and the surrounding space, and a minimum pressure (positive or negative) application time is imposed, thus causing the "bubble" to oscillate continuously according to the hysteresis effect of the system through the border of the beam.

This control over sheet sag is maintained until the sheet reaches thermoforming temperature. For ABS plastic this is usually above 140°C. Considerations such as the complexity of the molded shape may dictate a higher molding temperature.

The total heating time of the sheet will depend on the material, thickness and heater power. When using 2-3mm thick ABS sheet and heating at a rate that gives efficient throughput without sacrificing sheet quality, the typical total time for the heating process would be 120 seconds with the sheet at least half of the total time Benefit from effective support.

Referring now to Figure 3, the heater 9 has been withdrawn and the mold halves have been brought somewhat closer together. The abutment 28 between the abutment elements 19 of the support elements 11 has caused the compression of the spring 13 between the surface 14 of the support element 11 and the surface 15 of the groove 12 of the mold body 10, so that each support element 11 has been slightly to compress. Also the pressures in chambers 24 and 25 have now been adjusted so the positive pressure in chamber 24 is decreasing and perhaps even a vacuum is being applied and this vacuum and chamber 25 have been increased. The result is that the softened thermoplastic sheets 5, 6 are pulled apart, which together with the closing of the molds has brought a portion 52 of each thermoplastic sheet into contact with a seam region 17 of their respective mold halves.

Referring now to FIG. 4 , the mold halves continue to be brought together, the abutment 28 causing further compression of the spring 13 and further pressing in of the support element 11 . Simultaneously the vacuum in cavities 25 and 24 is increased to continue to draw the thermoplastic sheet into cavity 16 and thus begin to form the final shape, eg portion 53 of the sheet now contacting the inner surface of the cavity. The fixing of the side 51 is now less important, however it is still recommended that the side be fixed tightly.

Referring now to FIG. 5 , the mold halves 1 and 2 have been fully brought together, at which point the spring 13 is fully compressed, so that the support elements 11 are now fully pressed into their respective cavities 12 . Continued application of vacuum in the mold cavity 16 causes the individual sheets 5, 6 to be drawn completely into the cavity, conforming to the shape of the cavity. The seam areas 17 of the mold halves 1 and 2 have completely abutted so that a seam 55 is formed between the two sheets 5, 6 of thermoplastic material. Preferably the mold halves 1 and 2 have been brought together so that it is closer to the thickness of the two panels in the seam forming area 17, so that the material is forced away from the seam 55 so that the inside of the thermoformed part For example, a reinforcing bead 56 is formed.

The thermoforming process is thus essentially complete. Now that the part is allowed to cool, the foam can be sprayed and the part can be removed and trimmed in due course. Since it is also possible to pull the part out of the mold before trimming, it is possible to provide an in-molding trimming device, such as a knife or cutting blade, or for example a shear as will be described with reference to FIGS. In the mould, it is located at the seam area 17 as shown in FIG. 12 .

In FIG. 12 , the seam area of the lower mold half is provided with a separating element 109 which retracts back into the groove 110 when sufficient pressure is applied to the pre-compression spring 111 . As the mold halves continue to close, the edges 112 and 113 of the upper and lower mold halves, respectively, cooperate to trim the resulting edge from that part. This will be further described below with reference to FIGS. 6 to 10 .

Referring now to Figure 6, another embodiment is described which achieves the same purpose of eliminating the support frame and allowing heating of the thermoplastic sheet with a single heater interposed therebetween, while at the same time achieving the same goal of utilizing a cut-off method for in-molding For trimming purposes, the method uses a depressible support element during cutting. It should be noted that in both the present embodiment and the embodiment shown in FIGS. 1 to 5 , only one depressible supporting element can be provided and the same overall effect can be achieved. For example, in Figures 6 to 10, the support element 41 of the upper panel can be fixed substantially without altering the operation of the machine.

Referring now to Figure 6, the two mold halves are no longer substantially identical. The upper mold half 4 has an annular sheet support member 41 which can be pressed into a recess 42, and a spring 45 is arranged between opposing faces 44 and 43 to provide a spring force and resist such pressing. A sheet 8 is held by a vacuum groove seal 48, which is evacuated through a pipe 47, see in particular the embodiment of Figs. 1 to 5 . In the embodiment shown in Figure 6, the inner surface of the press-in element 41 itself forms part of the mold cavity. As noted above, element 41 in Figure 6 can be formed integrally and as an integral part of the immovable portion of mold body 40 without significantly affecting the performance of the thermoforming device. The sheet support member 41 has a small seam forming area 49 protruding from its lower surface adjacent to the vacuum seal 48 holding the edge 80 of the sheet 8 . The effect of this protruding edge is described in the following figures.

The lower mold half 3 has a mold half body 30 in which a sheet metal support element 31 is held in a groove 32 . A first spring 35 is arranged in this groove 32 to act between the face 34 of the support element 31 and the face 33 of the main body 30 . Another spring 36 is arranged at the bottom of the groove 32, which acts between the faces 34 and 33 only when the support element 31 is pressed sufficiently into the groove. The depth of the groove and the height of the support element 31 are set such that it will contact the other spring 36 when the support element 31 is pressed in sufficiently so that the seam forming region of the upper surface is in the plane of the mold surface 26 . The reason for this will be given with reference to FIGS. 7 to 10 . The edge 70 of the sheet 7 is secured by a vacuum seal 38 , which is evacuated through the tube 37 . For obvious reasons, the tube 37 extends to the outside of the support element 31 , and a half-groove is provided in the mold body 30 to allow the depression of the support element 31 .

As in the previous embodiments, the use of springs is a choice based on simplicity. Many other methods of allowing the press-in of the sheet metal support elements can be foreseen, such as precise mechanical actuation, pneumatic or hydraulic bearings. These various options do not depart from the scope of the present invention.

In use, a heater can be inserted between the thermoplastic sheets and used to heat the thermoplastic sheets to a thermoforming temperature in much the same manner as shown in Figure 1 . Still further preferred methods of loading and heating panels will be described below with reference to FIGS. 13 to 16 . Once the heaters are removed, the mold halves 3, 4 are slowly brought closer to each other while the cavities 22, 23 previously used to support the panels 7, 8 and prevent sagging are evacuated to pass through areas 71 and 23 of the panels as in Fig. 7 The plates are separated in the manner shown at 81 . At this stage, neither element 31 or 41 has started to press into its respective cavity since the support elements have not yet abutted to cause the respective spring 35, 45 to compress.

Referring now to FIG. 8 , showing that the thermoforming process continues, the mold halves 3, 4 have come together to such an extent that the sheet support members 31 and 41 now abut the edges 70, 80 of the respective sheets 7, 8 in contact therebetween, and The seam regions 39 , 49 of the carrier elements 31 , 41 are now contacted. The continued evacuation of the cavities 22 , 23 has resulted in further shaping of the individual sheets, for example the portion 72 of the lower thermoplastic sheet is now in contact with the mold surface 26 .

Referring now to Figure 9, the molding process is shown further by continuing to move the mold halves. The spring 45 between the surface 44 of the upper sheet support element 41 and the surface 43 of its corresponding groove 42 is now fully compressed. The spring 45 between the surface 34 of the lower sheet support element 31 and the surface 33 of its corresponding groove 32 is now compressed to such an extent that the support element 31 comes into contact with another spring 36 arranged in the groove. However, unlike the upper support element 41, the lower support element 31 still has some available depression freedom. The thermoformed part is now more fully formed, the lower plate 72 is now fully formed and rests against the mold surface 26, the upper plate 82 is almost fully formed, and the vacuum continues to be maintained in the small remainder of the cavity 23 to complete the process. Task. A seam 74 is initially formed in a region between the abutment of the support elements 31 and 41 .

The final stage of the process is depicted in Figure 10. The mold halves have been further brought together. The upper bearing element 41 has been completely pressed into its corresponding groove. The lower bearing element 31 is pressed further into its groove by the further compression of springs 35 and 36 which are located between the surface 34 of the bearing element 31 and the surface 33 of its corresponding groove 32 . The elasticity of the springs 35 and 36 means that a great pressure has been applied to the abutment between the seam areas 39 and 49 to expel the plastic material from the seam area 76 and to form a Bead 75, which will provide actual reinforcement to the weld. This continued movement has depressed the welded area 39 of the support element 31 below the edge 27 of the mold body 30 so that the welded area 49 of the support element 41 overlaps the edge 27 of the mold body 30 with a sufficient close tolerance therebetween. , a cutting action has cut away the seam and support area 77 .

From the description and description of the apparatus and process, it is quite clear that the present invention provides a method by which panels can be supported together with each half-form without using a separate support frame, Also the thermoforming process can be carried out in a simple operation by bringing the mold halves together. Also in the system described with reference to Figures 6 to 10, an in-molding trimming operation is achieved that does not require additional tools and parts, and which completes the beading in the final element.

FIG. 11 depicts another arrangement for securing a thermoplastic sheet 90 to a support element 91 . In this arrangement, a clamping toggle 92 is mounted which is rotatable about a pivot 93 . This may include supporting the toggle plate 92 away from a protrusion 94 extending from the support member. The toggle plate 92 includes a clamping arm 95 having a clamping face 96 adapted to bear against the surface of the sheet 90 . An actuator 98 is connected to the clamp toggle 92 to manipulate it for a rotational movement, usually at least 90 degrees. The actuator 98 may comprise a solenoid valve, which has the advantage of controllable bearing pressure. An elastic strip seal 99 is arranged in a groove 100 in the surface of the support element 91 . The elastic strip can be made, for example, of silicone rubber and has a sealing edge 101 which rises from the surface 102 of the carrier element. In use, the clamping face 96 presses the sheet material against the resilient strip seal 99 . Preferably there are many such clamps located in sufficient space to ensure adequate sealing of the panels by the seal 99 around the entire edge of the panels. A typical setup for a 3mm ABS sheet is to use 45mm wide brackets spaced 50mm apart.

Referring to Figure 12, spaced clamps can be interspersed at points with the abutment 103, and brackets 107, 108 can be placed in alternating positions on the upper (105) and lower (106) mold halves, respectively, so that each The movement of the brackets of the mold halves is not hindered by the brackets of the other mold halves.

Referring now to Figures 13 to 16, a preferred method and apparatus for loading and heating panels is shown. FIG. 13 depicts the basic method applied to a molding device such as that described in FIG. 1 . A movable heater box 115 is provided which can be moved to a position between the upper and lower mold halves. The heater box includes upper and lower heater supports 117, 118 which support each of the panels mounted on the mold halves 119, 120, respectively. A heater 121 is arranged between the plates 122,123. It is preferable to arrange upper and lower heaters so that the heating of the upper and lower sheets can be independently controlled according to the influence of sheet thickness. This setup allows the panels to be preheated on the heater box before being introduced into the mold halves. The heater box acts as both a heater and a sheet carrier, so the time required to heat the sheet and the time that would be spent on sheet transport effectively overlap.

In one approach, the sheet is preheated in the heater box to a temperature that is guaranteed to be below the glass transition temperature (eg, 70°C). This preheating can be carried out more slowly than when the sheet has been held in place, which is preferably used as it ensures an even heat distribution and penetration for further heating at a later date. The heater box moves with the sheet substantially to a position between the mold halves. By this time, the mold half may have completed an earlier thermoforming sequence or cycle. The panels are then transferred onto the panel support elements of the corresponding mold halves. Once transferred to the corresponding mold half, said support of the sheet by means of a controlled pressure system is initiated and maintained. This heater provides further heating to raise the sheet to thermoforming temperature before being removed from between the mold halves. In a typical example using a 3mm thick ABS sheet, this further heating may take 60 seconds. The heater is then removed and the thermoforming process already described begins.

The actual sheet transfer involves either bringing the mold halves together so that the individual mold halves approach their respective sheet, or moving the heater box (or its upper plate or its lower plate) into contact with the respective mold halves.

In the alternative, there is an additional reduction in the time each cycle uses the mold halves, but it complicates the processing of different panels through the same heater box which itself contains a controlled upforce Chamber 124 and lower pressure chamber 125 each contain a peripheral sheet seal 126, 127 and support means sufficient to hold the sheet in a sealed position. Thus, the heaters can provide support for the upper and lower sheets prior to transfer, and the sheets can be brought up to thermoforming temperature before the heater cartridge enters position between the molds for transfer. This reduces the time required to set up the mold for each cycle and allows for increased cycle times for a given production time. During the transfer, there is a transition time where the support of the sheet is switched from the pressure chamber of the heater box to the pressure chamber of the mold half.

There is no major difficulty in maintaining the panels in a sealed condition in terms of panel dimensioning, and the peripheral suction seal and support described in Figure 13 is suitable. However, there are some indications that conducted heat can soften the edges of the sheet more than desired and then the seal may be lost due to deformation at the edge of the sheet.

Figure 14 depicts a clamping bracket based support and transport system that is well suited for the heating or transport methods described above. This arrangement makes extensive use of the actuator controlled toggle 130 as described with reference to FIG. 11 . These brackets 130 preferably fasten the sheet not directly to the sealing element 131, but slightly to the outside thereof. This allows toggle plate 130 to work in cavities 132 , 133 formed in the support elements of mold half 134 and heater box 135 , respectively, without conflicting with sheet 136 or seal 131 . If higher thermoforming temperatures are used, auxiliary clamps (not shown) may be provided which disengage prior to the transfer process for auxiliary fixation, which will reduce the integrity of the sheet in the peripheral region. A further cavity 137 may be provided for any adjoining of the mold halves. It will also be appreciated that this clamping arrangement can be applied to the sheet support elements of the mold halves in the thermoforming process of Figure 6, as it overcomes conflict problems that may be associated with the use of a mechanical sheet clamping arrangement.

If different board sizes are catered for and the boards are brought up to full thermoforming temperature, heating of the boards prior to transfer presents great difficulties due to the need to accommodate perimeter sealing arrangements. But if the method is limited to heating only below the glass transition temperature prior to transfer, then the heater cartridge can be provided with supports that accommodate different sheet sizes, but which do not provide a perimeter seal. Examples of such arrangements are shown in FIGS. 15 and 16 .

In FIG. 15, heater box 140 includes a plurality of suction support columns 141 uniformly spaced throughout the heater box to support a panel at numerous locations on its lower surface, regardless of the size and shape of the panel. The number and spacing of these support columns will need to be set according to the strength properties of the sheet material at the predetermined transition temperature.

In FIG. 16, a heater box 145 includes a plurality of automatically movable toggle clamps 142 adapted to be automatically repositioned along a series of tracks 143 on a wall 144 extending inwardly through the heater box. . Movement of the toggle can be achieved by known means of linear actuation, and the toggle can be arranged substantially as shown in FIG. 14 .

In a heater box adapted to carry sheets of different sizes, if the heaters were segmentally controllable so that only the area of the heater directly adjacent to the sheet that had been placed on it was actuated, then this would be very favorable. This reduces wasted energy and in turn ensures that the free edges of the plate being secured are not heated by additional radiation from heater elements not directly beneath the plate. Where the heater is intended to be used with a wide variety of sheet shapes and sizes, the heater may be formed from any number of arbitrary areas, such as a grid of rectangular areas, which can be independently controlled, the shape and configuration of which can be specifically Suitable for the range of panels to be used.

In one form, the present invention eliminates the need for adjustable or different stationary jig assemblies that are required in conventional molding processes and are necessary throughout the molding process. The present invention allows molds to be changed rapidly and components produced, thereby introducing considerable flexibility in the vacuum forming process over a wide range of products.

Because the sheets are supported circumferentially away from the mold surface, and because the seams of the sheets only contact the seam areas of the mold immediately prior to fusion, the sheets remain sufficiently softened in the seam areas to provide good fusion. This advantage is evident in the disclosed embodiment of the present invention in which both sheet support means can be retracted.

Variations on the described schemes will be evident, and not all of them have been mentioned or described above. A special example is the fixing of one of the sheet metal support elements in either forming method. These modifications do not depart from the scope of the present invention.

Claims (25)

1. be used for the device of twin sheet thermoforming, comprise:

A pair of opposed half module, it can move between an open position and a closed position in the thermoforming process,

The sheet material supporting arrangement relevant with each described half module, each sheet material supporting arrangement links to each other with their half modules separately, and be configured to and keep a thermoplastic sheet around its periphery, this sheet material supporting arrangement is formed at and keeps each sheet material when described half module is positioned at its open position separated from one anotherly, each described half module, its separately supporting arrangement and the sheet material that keeps by described supporting arrangement define a pressurized volume together, and

The device relevant with each described half module, it can produce a controlled pressure reduction between each defined volume and outside thereof.

2. the device that is used for two plate formings as claimed in claim 1, it is characterized in that: one or more described sheet material supporting arrangements are movably with respect to half module separately, thereby, can described supporting arrangement be depressed with respect to described half module separately under the pressure of an adjacency section between described supporting arrangement and another supporting arrangement or the half module.

3. the device that is used for two plate formings as claimed in claim 2, it is characterized in that: described sheet material supporting arrangement can move with being adjacent to each other, and be provided with abutment means, this abutment means makes and keeps between the described sheet material separating, described sheet material supporting arrangement is adjacent to each other, when described half module moves to its closed position, described sheet material supporting arrangement is depressed with respect to their half modules separately, thereby make in use, each sheet material will with its separately a seam of half module form the zone and contact, and along with of the further motion of described half module to described closed position, forming the regional described zone that contacts with the seam of described half module in the sheet material will contact with each other, and be pressed in together by closing of described half module, to form a seam.

4. the device that is used for two plate formings as claimed in claim 1, it is characterized in that: described sheet material supporting arrangement comprises the welding zone of a fusion, under the enough vacuum of described enclosed volume, by it described sheet material is contacted, and by described half module closing to described closed position, it is adjacent to each other, thereby the seam region of described sheet material can be lumped together, to form a seam.

5. as any one described device that is used for two plate formings in the claim 1 to 4, it is characterized in that: it comprises the device that is used for from a moulding section automatic dressing seam region, in the described seam region one can be depressed under the plane of respective mold half of the described seam region of next-door neighbour, so that another described seam region and described half module are cooperated mutually, described seam region is pared off to cut off in the operation at one.

6. as any one described device that is used for two plate formings in the claim 1 to 5, it is characterized in that: described sheet material supporting arrangement comprises one from a surface of described supporting arrangement outstanding elastic strip and many isolated clamping elements, each described clamping element can rotate with respect to a surface of described clamping element, so that described sheet material is pressed on the described elastic strip, the interval of described clamping element is enough near, to form a continuous periphery sealing between sheet material and described elastic strip.

7. as any one described device in the claim 1 to 6, it is characterized in that: it comprises a heater assembly and a heater mobile device, to move described heater assembly between described half module when described half module separates, described heater assembly is suitable between a pair of sheet material this sheet material being heated.

8. device as claimed in claim 7, it is characterized in that: described heater assembly comprises the sheet material supporting arrangement that is located at its upper and lower side, in order to thereon, downside keeps a sheet material, when moving into place position between half module with box lunch, described sheet material can be sent on the described sheet material supporting arrangement of described each half module.

9. device as claimed in claim 8, it is characterized in that: described heater assembly comprises a upper and lower pressure chamber and a pressure feed passage, with allow will independent control pressure be applied in the described upper and lower chamber each, and the described heater sheet material supporting arrangement on each is suitable for carrying out the periphery sealing with a described sheet material in the described upper and lower side, seals each described chamber with each described sheet material in use.

10. install as claimed in claim 8 or 9, it is characterized in that: the described sheet material supporting arrangement of described heater assembly comprises many clamping elements that separate and relevant cooperation clamping surface, and the clamping element of described heater assembly is round the periphery setting of the described sheet material between each position of the clamping element of described half module sheet material supporting arrangement.

11. device as claimed in claim 10, it is characterized in that: each in the described clamping element of some of described at least heater assembly can move automatically, with in a plurality of position operation, thereby can be used for fixing the sheet material of different size with other clamping element.

12. device as claimed in claim 8, it is characterized in that: described sheet material supporting arrangement comprises the absorption supporting arrangement, its sting and and described sheet material is fixed on its non-molded surface, and they stride across described heater assembly and distribute, so that they can clamp the sheet material of different size.

13. as claim 11 or 12 described devices, it is characterized in that: described heater assembly comprises many heating element heaters, described element is provided with by the zone, and the described zone of described element links to each other with control device, is used for according to which zone of heated board dimension being controlled described heater assembly activateding.

14. a method that is used for twin sheet thermoforming comprises:

On each of a pair of half module, keep a heated thermoplastic sheet, so that the volume of a sealing to be provided between described sheet material and described half module, draught head between each space that is controlled at each sheet material simultaneously and seals between the half module separately, sagging to prevent arbitrary described sheet material

Change described pressure reduction, occur in, and only take place to contact with each other and form the part place of seam betwixt to guarantee the thin space between sheet material,

Move described half module close to each otherly, increase the pressure reduction effect simultaneously, and make the welding zone of each described sheet material seat itself by an annular, and

Continue to make described half module close to each other, being joined together in described welding zone, and between described welding zone, form a seam.

15. method as claimed in claim 14 is characterized in that it comprises the steps:

At the described sheet material of either side preheating of heater box movably,

Described sheet material is sent on the described half module,

Described heater cartridges is removed between described half module.

16. method as claimed in claim 15, it is characterized in that, the described preheating of described sheet material is limited in this underheat and is elevated to its glass transition temperature with the temperature with described sheet material, and described method also comprises the steps, promptly after described sheet material is sent on the described half module and before removing described heater cartridges further the described sheet material of heating to forming temperature.

17. method as claimed in claim 16 is characterized in that, the described preheating of described sheet material is enough to the temperature of described sheet material is elevated to their forming temperature, and described method also comprises the steps:

On a quilt, keep a malleation in the chamber of sheet material and heater cartridges sealing, keeping a negative pressure in the chamber between sheet material and the heater cartridges down at one.

18., it is characterized in that the step of the described sheet material of described transmission comprises as any one described method in the claim 14 to 17:

Described heater cartridges is placed between the described half module,

With each described half module and described heater assembly corresponding half put together, contact each sheet material up to a supporting arrangement that is arranged on each half module, and

Grasp each described sheet material with individual described supporting arrangement.

19. method as claimed in claim 18 is characterized in that, comprises described half module corresponding half step that puts together of each described half module and described heater assembly close to each other.

20. method as claimed in claim 18 is characterized in that, corresponding half step that puts together of each described half module and described heater assembly is comprised the upper and lower sheet material supporting of removing described heater assembly.

21., it is characterized in that the step that transmits described sheet material may further comprise the steps as any one described method in the claim 18 to 20:

Keep a controlled pressure in the space between each described sheet material and heater cartridges, being enough to can prevent to support floppily each described sheet material,

In case described each supporting arrangement grasps described sheet material, little by little introduce a controlled pressure in the space between each described sheet material and each described half module, and compensate the pressure that keeps in the space between each described sheet material and the heater cartridges, be positioned at the described pressure support in the described space between described sheet material and the described half module separately fully and prevent sagging up to each described sheet material

From described heater cartridges, discharge each described sheet material.

22. as any one described method in the claim 14 to 19, it is characterized in that, it further may further comprise the steps: described half module is further close to each other, one of them described seam region is suitable for being depressed with respect to its corresponding half module, this corresponding described half module and another described seam region cooperation cut off described seam region to cut off operation by one from moulding section.

23. device that is used for twin sheet thermoforming, wherein each half module comprises a sheet material supporting arrangement, this device can keep a sheet material by its edge, and during heating supports described sheet material, and wherein at least one described sheet material supporting arrangement can be recalled during thermoforming.

24. one kind basically with reference to accompanying drawing 1 described device.

25. one kind basically with reference to the described method that is used for twin sheet thermoforming of accompanying drawing.

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