GB2248579A - A vacuum forming machine in which vacuum is automatically initiated upon delivery of the sheet to the machine - Google Patents

Abstract

A vacuum forming machine (2) comprising holder means (4) for holding a sheet (6) of plastics material, heater means (8) for heating the sheet (4) of plastics material whilst the sheet (6) of plastics material is held by the holder means (4), a work area (10) for receiving a forming device (12) over which the sheet (6) of plastics material is to be moulded, a vacuum pump (16) for providing a vacuum, and valve means (18) for connecting the work area (10) to the vacuum pump (16), the holder means (4) being such that it is movable by hand from a first position in which the heater means (8) is operable to heat and soften the sheet (6) of plastics material to a second position in which the sheet (6) of plastics material is positioned above the forming device (12) in the work area (10), and the valve means (18) being such that it is automatically operated by the movement of the holder means (4) to the second position. <IMAGE>

Description

A VACUUM FORMING MACHINE This invention relates to a vacuum forming machine.

Vacuum forming machines are well known. They are used to vacuum form sheets of plastics material.

Usually, a sheet of plastics material is held in a frame and it is then placed adjacent a source of heat which heats the sheet of plastics material and causes the plastics material to become soft. The softened plastics material in its frame is then brought into close association with a forming device over which the sheet of plastics material is to be moulded. The forming device is in the required shape of the product to be formed. After the softened sheet of plastics material is brought into the close association with the forming device, the air between the sheet of plastics material and the forming device is evacuated. This causes the softened sheet of plastics material to deform until it is in intimate contact with the surface of the forming device. The deformed sheet of plastics material is allowed to cool, whereupon it retains its deformed shape.

The known vacuum forming machines vary in size from large and complex automatic vacuum forming machines to small manually-operated vacuum forming machines which are designed for low quantity production or demonstration purposes.

The known small manually-operated vacuum forming machines may contain a bank of heating elements, the temperature of which can be zone controlled. These heating elements can be moved away from the sheet of plastics material once the sheet of plastics material has reached a desired softened state. The heating elements are moved away by rotating a container in which they are held, or by sliding the container on runners. In other known small manually-operated vacuum forming machines, the softened sheet of plastics material in its frame is pivoted or slid away from the bank of heating elements.

The known small manually-operated vacuum forming machines may also employ pivoting or sliding actions to bring the sheet of plastics material into contact with the forming device. Alternatively, the forming device may be lifted up from a cavity beneath the framed sheet of plastics material, which framed sheet of plastics material is then held stationary.

In the known small manually-operated machines, once the sheet of plastics material or the forming device have been placed in position, a valve is manually operated to connect the space between the forming device and the sheet of plastics material to a vacuum pump or an evacuated tank, whereupon air between the sheet of plastics material and the forming device is sucked away and the plastics material is caused to deform to the shape of the forming device. Rubber seals are usually employed between the holding frame and a holder of the forming device in order to prevent leakage of outside air into the evacuated area.

It is an aim of the present invention to provide a vacuum forming machine which is of the above mentioned small manually-operated type and which is of a simpler construction and which is simpler to operate than the above mentioned known small manually-operated vacuum forming machines.

Accordingly, the present invention provides a vacuum forming machine comprising holder means for holding a sheet of plastics material, heater means for heating the sheet of plastics material whilst the sheet of plastics material is held by the holder means, a work area for receiving a forming device over which the sheet of plastics material is to be moulded, a vacuum pump for providing a vacuum, and valve means for connecting the work area to the vacuum pump, the holder means being such that it is movable by hand from a first position in which the heater means is operable to heat and soften the sheet of plastics material to a second position in which the sheet of plastics material is positioned above the forming device in the work area, the valve means being such that it is automatically operated by movement of the holder means to its second position, and the vacuum forming machine being such that the automatic operation of the valve means enables a vacuum to be formed in the work area thereby to cause the sheet of plastics material to be vacuum formed over the forming device.

The vacuum forming machine of the present invention may be cheaply produced and it may be ideally suited for experimental work, occasional production and for teaching purposes.

Preferably, the holder means comprises first and second open frame devices. Other types of holder means may however be employed.

The work area is preferably a work tray. Other types of work areas may however be employed.

When the holder means comprises the first and the second open frame devices and when the work area is a work tray, then the first and the second open frame devices may co-operate with the work tray to seal that part of the work area beneath the sheet of plastics material.

The vacuum forming machine may include a vacuum tank for receiving air from the work area. Usually, the vacuum tank will be positioned beneath the work area. The vacuum tank can be provided at other positions in the vacuum forming machine if desired. The vacuum tank may be of cylindrical or circular construction.

The vacuum pump may be any suitable and appropriate known vacuum pump.

Preferably, the valve means is a valve plate which is spring biased to a closed position and which is rotatable to an open position as the holder means is moved to its second position.

The vacuum forming machine may include an arm which is connected to the valve means and which is caused to rotate when the holder means is moved to its second position, rotation of the arm being such as to cause rotation of the valve means to its open position.

The heater means may be a row of electrically heated elements. Other types of heater means may be employed.

Preferably, the vacuum forming machine is one in which the first position of the holder means is adjacent and below the heater means. Alternatively, the first position of the holder means may be adjacent and above the heater means.

The vacuum forming machine may include guide means for helping to guide the holder means from its first position to its second position. Preferably, the guide means comprises a pair of spaced apart side walls which are each provided with a slot for retaining the holder means in its first position, and which are each provided with a curved end guide portion which is formed as an extension of a lower surface of the slot.

The vacuum forming machine may include switch means for automatically switching the heater means to an ON condition consequent upon the holder means being moved to its first position, and for automatically switching the heater means to an OFF condition consequent upon the holder means being moved away from its first position.

The vacuum forming machine may include reflector means for reflecting heat from the heater means towards the holder means for holding the sheet of plastics material.

The vacuum forming machine may include handle means for facilitating carrying of the vacuum forming machine.

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 is a perspective view of a vacuum forming machine; Figure 2 shows holder means forming part of the vacuum forming machine shown in Figure 1; Figure 3 is a vertical cross section through the vacuum forming machine shown in Figure 1; Figure 4 is a cross section through a work area and valve means forming part of the vacuum forming machine shown in Figure 1; and Figure 5 is a cross section which is similar to Figure 4 but which shows the valve means in an open position and which shows the presence of a forming device in the work area.

Referring to the drawings, there is shown a vacuum forming machine 2 comprising holder means 4 for holding a sheet 6 of plastics material, and heater means in the form of a row of heating elements 8 for heating the sheet 6 of plastics material whilst the sheet 6 of plastics material is held by the holder means. The vacuum forming machine 2 further comprises a work area 10 for receiving a forming device 12 over which the sheet 6 of plastics material is to be moulded.

The vacuum forming machine 2 further comprises a vacuum tank 14 and a vacuum pump 16 for providing a vacuum in the vacuum tank 14. Valve means 18 is provided for connecting the work area 10 to the vacuum tank 14.

The holder means 4 is such that it is movable by hand from a first position in which the heating elements are operable to heat and soften the sheet 6 of plastics material to a second position in which the sheet 6 of plastics material is positioned above the forming device 12 in the work area 10.

The valve means 18 is such that it is automatically operated by movement of the holder means 4 to its second position. The vacuum forming machine 2 is such that the automatic operation of the valve means 18 causes air from the work area 10 to pass to the vacuum tank 14 and a vacuum to be formed in the work area 10 thereby to cause the sheet 6 of plastics material to be vacuum formed over the forming device 12.

As can best be seen from Figure 2, the holder means 4 comprises first and second open frame devices 20, 22 respectively. As can best be seen from Figure 1, the work area 10 is formed by a work tray 24 having upstanding side walls 26. As can best be seen from Figure 5, the first and the second open frame devices 20, 22 co-operate with the work tray 24 to seal that part of the work tray 24 beneath the sheet 6 of the plastics material.

As shown in Figure 3, the vacuum tank 14 is positioned beneath the work area 10. The vacuum pump 16 is connected to the vacuum tank 14 by a short pipe 28.

Referring especially to Figures 1, 4 and 5, it will be seen that the valve means 18 comprises a valve plate 30 which is spring biased to a closed position. The valve plate 30 is mounted on a rod 32. The rod 32 is mounted for rotation in a bracket 34 at one end and in a bearing 36 at the other end. Rotation of the rod 32 causes the valve plate 30 to move between its closed position as shown in Figure 4 and its open position as shown in Figure 5.

Rotation of the rod 32 is effected by rotational movement of an arm 36 which is connected to the rod 32. The arm 36 is caused to rotate in an anticlockwise manner as the holder means 4 is placed in its second position in the work area 10.

The vacuum forming machine 2 includes guide means 38 for helping to guide the holder means 4 from its first position to its second position. The guide means 38 comprises a pair of spaced apart side walls 40, 42. Each side wall 40, 42 is provided with a slot 44.

The side walls 40, 42 form part of a housing 46 of the vacuum forming machine 2.

When the holder means 4 is in the slots 44, then the holder means 4 is in its first position. The side walls 40, 42 are each provided with a curved end guide portion 48 which is formed as an extension of a lower surface 50 of the slots 44. As the holder means 4 is pulled out of the slots 44, the holder means 4 is able to follow the guide portion 48 down in order to facilitate positioning of the holder means 4 in its second position in the work area 10.

The vacuum forming machine 2 includes switch means in the form of a switch 52 for automatically switching the heating elements 8 to an ON condition consequent upon the holder means 4 being moved to its first position in the slots 44. The switch means is such that it automatically switches the heating elements 8 to an OFF condition consequent upon the holder means 4 being moved away from its first position and out of the slots 44.

The vacuum forming machine 2 includes reflector means in the form of a reflector 54 for reflecting heat from the heating elements 8 towards the holder means 4 when it is in the slots 44.

Referring to Figures 3, 4 and 5, it will be seen that the valve plate 30 closes an orifice 56 which connects the work area 10 to the vacuum tank 14.

Referring to Figure 2, it will be seen that the first open frame device 20 has a pair of handles 58, and that the second open frame device 22 has a pair of handles 60. The handles 58, 60 can be gripped to cause flat mating surfaces 62, 64 on the first and second open frame devices 20, 22 respectively to clamp between them the sheet 6 of plastics material, see Figure 5.

The row of heating elements 8 are provided in an upper part of the housing 46 as shown and they are positioned to radiate heat downwards. The reflector 54 facilitates the even downward distribution of heat from the heating elements 8. The reflector 54 is secured in the upper part of the housing 46 as shown in Figure 3.

As shown in Figure 1, the bearing 36 is mounted in one of the side walls 26 of the work tray 24. An "0" ring seal (not shown) is provided within the bearing 36 to seal the exit for the rod 32 whilst allowing the rod 32 to rotate.

As shown in Figure 5, the forming device 12 is mounted on a rigid base 66. The rigid base 66 rests on strip members 68, 70 which are mounted as shown in Figures 4 and 5 on the inside surfaces of side walls 26.

A space 72 is then left between the rigid base 66 and the bottom of the work tray 24. This space 72 enables the valve plate 30 to pivot between its open and closed positions as shown in Figures 4 and 5. As shown in Figure 5, the side walls 26 of the work tray 24 extend above the upper surface of the rigid base 66 by a small amount which is typically lmm.

As shown in Figure 5, the first and second open frame devices 20, 22 have different dimensions such that the second open frame device 22 slides easily over and around the outside of the work tray 24. In contrast, the first open frame device 20 is smaller and it rests on top of the side walls 26 of the work tray 24.

During a vacuum forming operation, the vacuum pump 16 is first switched on via switch 74, see Figure 1.

Whilst the vacuum pump 16 is evacuating the vacuum tank 14, a sheet 6 of plastics material is placed between the first and the second open frame devices 20, 22, and an appropriately shaped forming device 12 is placed in the work tray 24.

When the pressure in the vacuum tank 14 has been reduced sufficiently, for example to -25 inches of mercury, the first and the second devices 20, 22 with the sheet 6 of plastics material are slid into the slots 44, whereupon the heating elements 8 are automatically switched on. The sheet 6 of plastics material thus becomes heated and when it has been sufficiently heated and softened, the first and the second open frame devices 20, 22 are removed from the slots 44, the first and the second open frame devices 20, 22 being gripped by the handles 58, 60. As the first and the second open frame devices 20, 22 are removed from the slots 44, the switch 52 is automatically triggered to an OFF condition in which the heating elements 8 are turned off.

The removed first and second opened frame devices 20, 22 are simply and easily able to follow the guide portions 48 down to the work area 10. This operation is effected as quickly as possible. As the first and the second open frame devices 20, 22 reach their final position, the second open frame device 22 contacts the arm 36, thus causing the valve plate 30 to pivot from the closed position shown in Figure 4 to the open position shown in Figure 5.

Air in the base 72 is thus permitted to pass through the orifice 56 and into the vacuum tank 14. The communication of the work area 10 with the vacuum tank 14 causes the softened sheet 6 of plastics material to be pushed hard against the smooth flat edges of the side walls 26 of the work tray 24 to effect a seal and to prevent entry of air from the outside, see Figure 5. The sheet 6 of plastics material is deformed to the shape of the forming device 12 as shown in Figure 5. The deformed sheet 6 of plastics material is then allowed to cool, whereupon the first and the second open frame devices 20, 22 can be removed from the work area 10, and separated to allow the removal of the moulded sheet 4 of plastics material.

It is to be appreciated that the embodiment of the invention described above with reference to the accompanying drawings has been given by way of example only and that modifications may be effected. Thus, for example, the vacuum pump 16 may be arranged to evacuate the air directly from the work area 10 without employing the intermediate vacuum tank 14. The guide portions 48 may be replaced by a pivoting arms connected between the upper part of the housing 46 and the first and second open frame devices 20, 22 in order to guide the first and the second open frame devices 20, 22 to the work tray 24.

If desired, the first and second open frame devices 20, 22 may be pulled together with clamps rather than being manually operated. The vacuum pump 16 may be connected to the work tray 24 via a rotary valve or a poppet valve. The housing 46 may be provided with handles to facilitate carrying of the vacuum forming machine 2.

The vacuum forming machine 2 may be especially useful for laboratories, schools and colleges, pattern shops, design studios, prototype shops, do-it-yourself or hobby enthusiasts, packaging development areas and medical laboratories.

The vacuum forming machine 2 may enable small experiemental vacuum formings to be made without interrupting production on larger automatic machines, The vacuum forming machines may be provided with a residual current cut out device. The heating elements 8 may be radiant infra-red heaters which are advantageously sheathed. A manual reset thermal overload switch may be provided.

A separate outlet may be provided for auxiliary use of the internal vacuum pump 16.

A heater guard and/or a viewing light may be provided if desired. The vacuum forming machine 2 is able to operate simply by plugging it in to a 13 amp socket.

Full earth bonding will normally be employed. The vacuum forming machine 2 may be able to operate with a wide range of plastics materials including acrylic plastics materials, polyvinylchloride plastics materials, polycarbonate plastics materials and acrylonitrile butadiene styrene materials.

Any suitable and appropriate type of forming device 12 may be employed. The forming device 12 may be made from fine grained hardwood, epoxy resin, aluminium, plaster of paris or any other suitable and appropriate materials. Suitable release agents can be employed in order to facilitate separation of the formed sheet 6 of plastics material from the forming device 12. The forming device 12 may be provided with radiused corners and tapered sides as may be suitable and appropriate. The forming device 12 may also be provided with a plurality of vent holes as may be suitable and appropriate. The vent holes may be 0.5 - 0.75mm in diameter. The forming device 12 may give male and female patterns as required. Other plastics materials that may be used are cellulose acetate butyrate and polyethylene.

The present invention also extends to the various separate features described above taken singly or in any combination.

Claims (16)

1. A vacuum forming machine comprising holder means for holding a sheet of plastics material, heater means for heating the sheet of plastics material whilst the sheet of plastics material is held by the holder means, a work area for receiving a forming device over which the sheet of plastics material is to be moulded, a vacuum pump for providing a vacuum, and valve means for connecting the work area to the vacuum pump, the holder means being such that it is movable by hand from a first position in which the heater means is operable to heat and soften the sheet of plastics material to a second position in which the sheet of plastics material is positioned above the forming device in the work area, the valve means being such that it is automatically operated by movement of the holder means to its second position, and the vacuum forming machine being such that the automatic operation of the valve means enables a vacuum to be formed in the work area thereby to cause the sheet of plastics material to be vacuum formed over the forming device.

2. A vacuum forming machine according to claim 1 in which the holder means comprises first and second open frame devices.

3. A vacuum forming machine according to claim 1 or claim 2 in which the work area is a work tray.

4. A vacuum forming machine according to claim 2 and claim 3 in which the first and the second open frame devices co-operate with the work tray to seal that part of the work area beneath the sheet of plastics material.

5. A vacuum forming machine according to any one of the preceding claims and including a vacuum tank for receiving air from the work area.

6. A vacuum forming machine according to claim 5 in which the vacuum tank is positioned beneath the work area.

7. A vacuum forming machine according to any one of the preceding claims in which the valve means is a valve plate which is spring biased to a closed position and which is rotatable to an open position as the holder means is moved to its second position.

8. A vacuum forming machine according to claim 7 and including an arm which is connected to the valve means and which is caused to rotate when the holder means is moved to its second position, rotation of the arm being such as to cause rotation of the valve means to its open position.

9. A vacuum forming machine according to any one of the preceding claims in which the heater means is a row of electrically heated elements.

10. A vacuum forming machine according to any one of the preceding claims in which the first position of the holder means is adjacent and below the heater means.

11. A vacuum forming machine according to any one of the preceding claims and including guide means for helping to guide the holder means from its first position to its second position.

12. A vacuum forming machine according to claim 11 in which the guide means comprises a pair of spaced apart side walls which are each provided with a slot for retaining the holder means in its first position, and which are each provided with a curved end guide portion which is formed as an extension of a lower surface of the slot.

13. A vacuum forming machine according to any one of the preceding claims and including switch means for automatically switching the heater means to an ON condition consequent upon the holder means being moved to its first position, and for automatically switching the heater means to an OFF condition consequent upon the holder means being moved away from its first position.

14. A vacuum forming machine according to any one of the preceding claims and including reflector means for reflecting heat from the heater means towards the holder means for holding the sheet of plastics material.

15. A vacuum forming machine according to any one of the preceding claims and including handle means for facilitating carrying the vacuum forming machine.

16. A vacuum forming machine substantially as herein described with reference to the accompanying drawings.