Thermoforming machine with controlled cooling station

• US 5,620,715 A
• Filed: 02/10/1994
• Issued: 04/15/1997
• Est. Priority Date: 02/10/1994
• Status: Expired due to Term

• Current Assignee: Penda Corporation (Kruger Family Industries, LLC)
• Original Assignee: Penda Corporation (Kruger Family Industries, LLC)
• Inventors: Geurts, Charles G., Roberts, Wesley W., Hart, James P.
• Primary Examiner(s): Timm, Catherine
• Application Number:
  US08/195,299
• Time in Patent Office: 1,160 Days
• Field of Search: 425/387.1, 425/134, 425/135, 425/445, 425/388, 425/383, 425/384, 425/812, 425/342, 425/143, 264/237, 264/348, 264/288.4, 264/44, 264/143, 264/328.14, 264/547, 264/550, 264/551, 264/544, 264/549, 264/291
• US Class Current: 425/143
• CPC Class Codes: B29C 51/22 rotatable about an axis
• CPC Class Codes: B29C 51/427 Cooling of the material with a fluid blast

Abstract

A four-station rotary thermoformer has a rotary carriage which transports a sheet of thermoplastic material clamped on a subframe through a load/unload station; a heating station; a forming station where the sheet is molded; and a cooling station removed from the mold where the part is cooled on the subframe. The molded sheet is cooled in a cavity which has a lower portion mounted on a lift which travels vertically to engage against an upper portion and enclose the sheet for cooling. A multiplicity of air vents discharge cooling air into the cavity. Cooling air leaves the cavity through recirculation duct. The supply of air within the cooling cavity results in a uniform current of air against the article'"'"'s surface, thus providing uniform cooling. A programmable controller controls the supply of cooling air and receives input from an infrared sensor which detects the temperature of the thermoformed article and also receives information from a sensor of the cooling air temperature. The programmable controller is programmed to provide a cooling cycle consisting of a three-parts. In the first part, the air is recirculated using the heat capacity of the recirculating air in the air supply system to start cooling at a low rate. During the second part, the flow of cooling air temperature is lowered until a pre-determined maximum cooling rate is reached and held for a selected time. During the third part, the cooling air is again recirculated.

Claims

1. A machine for thermoforming a thick gauge thermoplastic sheet against a rigid mold, the machine comprising:

a) a frame;

b) a carriage mounted for movement on the frame;

c) at least one subframe connected to the carriage, wherein the subframe is engageable with a sheet;

d) a heating station mounted to the frame, wherein the subframe is movable through the heating station for heating of the sheet;

e) a forming station mounted to the frame, wherein the forming station has a thermoforming mold positioned to engage a heated sheet on the subframe which has traversed the heating station, and the mold being operable to mold the heated sheet to a desired shape; and

f) a controlled cooling station mounted to the frame, the controlled cooling station including an upper portion, a lower portion, the upper and lower portions being relatively movable between a closed position wherein the upper and lower portions define a cavity which is adapted to surround the molded sheet to receive the molded sheet on the subframe after the forming station, and an opened position, a multiplicity of first ducts for introducing cooling air into the cavity to cool the molded sheet held in the subframe, each of the first ducts extending from one of the upper and lower portions to direct cooling air uniformly around the formed thermoplastic sheet, and at least one second duct extending from one of the upper and lower portions for removing heated air from the cavity, wherein the second duct is in fluid communication with the first ducts so recirculation of the cooling air can be effected.

2. The apparatus of claim 1 further comprising a load/unload station positioned after the controlled cooling station, wherein the molded and cooled sheet is accessible at the load/unload station from the apparatus exterior to remove the molded and cooled sheet from the subframe and to position an unprocessed sheet in the subframe for operation thereon by the apparatus.

3. The apparatus or claim 1 wherein the carriage is a carousel rotatably mounted to the frame and the sheet on the subframe describes a circular path as it moves through the apparatus.

4. The apparatus of claim 1 further comprising:

a) a cool air supply duct in fluid communication with a supply of cool air and connected in fluid communication to the first ducts;

b) an intake fan positioned in the cool air

supply duct for blowing cooling air through the first ducts onto the molded sheet;

c) at least one damper positioned in the cool air supply duct to selectably control the amount of recirculated and cool air introduced into the cooling cavity; and

d) a programmable controller which controls the temperature of the cooling air which is directed through the first ducts by adjusting the damper.

5. The apparatus of claim 4 further comprising a sensor for detecting the temperature of the molded sheet within the controlled cooling station, wherein the programmable controller controls the temperature of the cooling air to achieve a selected end temperature of the molded sheet as detected by the sensor.

6. The apparatus of claim 4 wherein heat is removed from the cooling air by a heat exchanger.

7. The apparatus of claim 4 wherein heat is removed from the cooling air by the addition of cool ambient air to the cooling air.

8. A rotary thermoforming apparatus for molding at least one thick gauge sheet of thermoplastic material, the apparatus comprising:

a) a frame;

b) a carriage mounted to the frame for rotary motion;

c) at least one subframe mounted to the carriage which releasably engages a sheet;

d) heaters mounted on the frame and positioned to heat the sheet when the carriage is rotated to bring the subframe into proximity thereto;

e) a thermoforming mold mounted on the frame and spaced from the heaters, wherein the heated sheet is rotatable on the carriage away from the heaters to be formed by the mold into a desired shape; and

f) a cooling cavity mounted on the frame and spaced from the thermoforming mold, the cooling cavity having at least one duct mounted therein to discharge cooling air onto a molded sheet engaged by the subframe which has been displaced from the thermoforming mold by the carriage, and at least one duct opening into the cavity for removing heated cooling air.

9. The apparatus of claim 8 further comprising a controller and a first sensor for detecting the temperature of the molded sheet within the cooling cavity, wherein the controller receives temperature data from the first sensor and controls the temperature of the cooling air to achieve a selected end temperature of the molded sheet.

10. The apparatus of claim 8 wherein the cooling cavity comprises:

a) an upper portion having at least one duct which discharges cooling air above the molded sheet engaged on the subframe; and

b) a lower portion having at least one duct below the molded sheet, wherein the lower portion is movable vertically with respect to the upper portion to at least partially enclose the molded sheet to facilitate cooling thereof.

11. The apparatus of claim 10 wherein the lower portion has a lower surface and an upwardly extending peripheral wall, and wherein the lower portion is movable between an opened position in which the subframe is free to pass between the upper portion and the lower portion into the cooling cavity, and a closed position in which the lower portion engages against the upper portion so that the upper and lower portions are adapted to enclose the molded sheet for cooling.

12. The apparatus of claim 8 further comprising a load/unload station positioned after the cooling cavity, wherein the molded and cooled sheet is accessible from the apparatus exterior to remove a molded sheet from the subframe and to position an unprocessed sheet in the frame for operation thereon by the apparatus.

13. A rotary thermoforming apparatus for molding at least one thick gauge sheet of thermoplastic material, the apparatus comprising:

a) a frame;

b) a carriage mounted to the frame for rotary motion;

c) at least one subframe mounted to the carriage which releasably engages a sheet;

d) a load/unload station on the frame which is accessible from the apparatus exterior to allow the mounting of a sheet of thermoplastic material on the subframe and to permit the removal of a molded sheet therefrom;

e) heaters positioned on the frame after the load/unload station for heating the sheet when the carriage is rotated to bring the subframe into proximity thereto;

f) a thermoforming mold on the frame and spaced from the heaters, wherein the heated sheet is rotatable on the carriage away from the heaters to be formed by the mold into a desired shape; and

g) a cooling cavity on the frame and spaced from the thermoforming mold, the cooling cavity having an upper portion and a lower portion each having ducts which discharge cooling air into the cavity onto a molded sheet engaged by the subframe which has been displaced from the mold by the carriage, wherein the upper and lower portions are moveable vertically with respect to one another to alternatively enclose the molded sheet for cooling and to open to permit the cooled molded sheet to pass to the load/unload station.

14. A rotary thermoforming apparatus for molding at least one thick gauge sheet of thermoplastic material, the apparatus comprising:

a) a frame;

b) a carriage mounted to the frame for rotary motion;

c) at least one subframe mounted to the carriage which releasably engages a sheet;

d) heaters positioned on the frame to heat the sheet when the carriage is rotated to bring the subframe into proximity thereto;

e) a thermoforming mold on the frame and spaced from the heaters, wherein the heated sheet is rotatable on the carriage away from the heaters to be formed by the mold into a desired shape; and

f) a controlled cooling station mounted to the frame, wherein the controlled cooling station has a cavity which is adapted to surround the molded sheet to receive the molded sheet on the subframe, at least one first duct in fluid communication with the cavity for introducing cooling air into the cavity to cool the molded sheet held in the subframe, and at least one second duct in fluid communication with the cavity for removing heated air from the cavity and wherein the second duct is in fluid communication with the first duct;

g) a fan disposed in the first duct for moving cooling air to the cavity;

h) an air intake in fluid communication with the first duct for intaking ambient air for cooling;

i) a valve disposed between the first duct and the second duct, the valve controlling the mixture of the ambient air and heated air from the second duct, the mixture of the ambient air and heated air being supplied as the cooling air to the cavity.

15. The apparatus of claim 14 wherein the cooling station has an upper portion which is fixed, and a positionable lower portion which has a lower surface with an upwardly extending peripheral wall, and a lower duct which extends from the lower surface to direct cooling air uniformly around the molded sheet.

16. The apparatus of claim 14 further comprising a load/unload station positioned on the frame and after the controlled cooling station, wherein the molded and cooled sheet is accessible at the load/unload station from the apparatus exterior to remove a molded sheet from the subframe and to position an unprocessed sheet in the frame for operation thereon by the apparatus.

17. The apparatus of claim 14 further comprising at least one heat exchanger mounted within the first duct for cooling the cooling air.

18. The apparatus of claim 14 further comprising a heated air dump connected to the second duct for dumping excess heated air which is not recirculated.

19. The apparatus of claim 14 further comprising:

a programmable controller which controls the temperature of the cooling air which is directed through the first duct by adjusting the valve.

20. The apparatus of claim 19 further comprising a sensor for detecting the temperature of the molded sheet within the controlled cooling station, wherein the programmable controller is operably connected to the sensor to receive input therefrom and controls the temperature of the cooling air to achieve a selected end temperature of the molded sheet as detected by the sensor.

21. A thermoforming machine comprising:

a frame,

a carriage supported on the frame for movement relative thereto, the carriage including a subframe, the subframe being engageable with a thermoplastic sheet to be molded in the thermoforming machine,

a heating station mounted on the frame, the subframe being positionable in the heating station to heat the thermoplastic sheet,

a forming station mounted on the frame, the forming station including a mold, the mold being engageable with the thermoplastic sheet to form the sheet into a molded article, and

a cooling station mounted on the frame and separate from the forming station, the cooling station being movable between an opened position so that the molded article can be received at the cooling station, and a closed position, the cooling station, when in the closed position, defining a cavity adapted to enclose the molded article, and the cooling station including an inlet for introducing cooling air into the cavity for circulation around a molded article received in the cavity, and an outlet for discharging cooling air from the cavity.

22. A thermoforming machine as set forth in claim 21 wherein the cooling station includes upper and lower plenums, the upper and lower plenums being movable relative to each other to open and close the cooling station, and wherein the inlet includes a plurality of cooling air vents, the vents being spaced about the cavity when the cooling station is closed, and each of the vents being positioned on one of the upper and lower plenums.

23. A thermoforming machine as set forth in claim 22 wherein the cooling station includes means between the upper and lower plenums for sealing the cavity when the cooling station is closed.

24. A thermoforming machine as set forth in claim 22 wherein the cooling station includes means for supporting the molded article as it is cooled to prevent distortion of the molded article during cooling.

25. A thermoforming machine as set forth in claim 22 wherein the lower plenum includes a support rack for supporting the molded article as it is cooled to prevent distortion of the molded article during cooling.

26. A thermoforming machine as set forth in claim 22 wherein at least some of the vents include means for preventing direct impingement of cooling air on a molded part received in the cavity to prevent localized areas of cooling on the molded part.

27. A thermoforming machine as set forth in claim 21 wherein the cooling station includes means for circulating cooling air around a molded article received in the cavity, the means for circulating cooling air including the inlet and the outlet.

28. A thermoforming machine as set forth in claim 21 wherein the cooling station includes an upper portion, a lower portion, the upper and lower portions being movable relative to one another between a first position wherein the cooling station is in the closed position and the upper and lower portions define the cavity, and a second position wherein the cooling station is in the opened position, and an air supply system including a supply duct connected to one of the upper and lower portions for supplying cooling air to the cavity, the supply duct being in fluid communication with the inlet, and a return duct connected to one of the upper and lower portions for removing cooling air from the cavity, the return duct being in fluid communication with the outlet.

29. A thermoforming machine as set forth in claim 28 wherein each of the upper and lower portions includes a plurality of air vents all in fluid communication with the supply duct for introducing cooling air into the cavity, the air vents forming the inlet.

30. A thermoforming machine as set forth in claim 29 wherein the return duct is connected to the supply duct so recirculation of the cooling air can be effected, and wherein the air supply system includes means for controlling air flow into the cavity and for controlling cooling air temperature, the means for controlling air flow and air temperature including a first damper positioned in the supply duct for regulating air entry into the cavity, and a valve at the juncture of the supply and return ducts for regulating the amount of recirculated air that is recycled as cooling air.

31. A thermoforming machine as set forth in claim 30 wherein the means for controlling air flow and air temperature includes a temperature sensor positioned in the supply duct, and a programmable controller operably connected to the temperature sensor and the dampers.