TWIN SHEET THERMOFORMER

• US 3,787,158 A
• Filed: 07/03/1972
• Issued: 01/22/1974
• Est. Priority Date: 07/03/1972
• Status: Expired due to Term

• Current Assignee: John Brown Industries Limited
• Original Assignee: Gaylord W. Brown, George L. Pickard
• Inventors: Brown, Gaylord W., Pickard, George L.
• Primary Examiner(s): Spicer, Jr., Robert L.
• Application Number:
  US05/268,883
• Time in Patent Office: 568 Days
• Field of Search: 425/384,388,397,451,413,437,156,813,DIG.48,109
• US Class Current: 425/156
• CPC Class Codes: B29C 51/12 of articles having inserts or reinforcements
• CPC Class Codes: B29C 51/18 Thermoforming apparatus
• CPC Class Codes: B29C 51/261 Handling means, e.g. transfer means, feeding means B29C51/44 takes precedence
• CPC Class Codes: B29C 51/267 Two sheets being thermoformed in separate mould parts and joined together while still in the mould B29C49/0691 takes precedence
• CPC Class Codes: B29C 51/46 Measuring, controlling or regulating
• CPC Class Codes: Y10S 425/048 Sheet clamping

Abstract

Thermoforming apparatus having a pair of plastic sheet heating stations, each including upper and lower heaters, on opposite sides of a differential pressure forming station, upper and lower plastic sheet supporting carriages for supporting upper and lower pairs of plastic sheets of differing thicknesses; transfer apparatus for shuttling the upper carriages to alternate ones of the heating stations while concurrently moving alternate ones of the lower sheets to opposite ones of the heating stations so that two of the upper and lower sheets are simultaneously heated, one in each heating station, while the other two upper and lower sheets are concurrently superposed at the forming station where they are formed into a hollow article by differential pressure forming apparatus at the forming station, and control apparatus for alternately operating the upper and lower heaters at each heating station for longer and shorter periods of time while the upper and lower heaters at the other station are being operated for shorter and longer periods of time respectively to subject the plastic sheets which are alternately moved to the heating stations to different amounts of heat.

Claims

1. Apparatus for forming a hollow object in sheets of deformable thermoplastic material comprising:

a central forming station;

a pair of sheet heating stations on opposite sides of said central forming station at which sheets of deformable thermoplastic material are heated;

upper and lower carriage means for supporting upper and lower pairs of said sheets of thermoplastic material;

means mounting said upper and lower carriage means for movement between said sheet heating and forming stations;

means for concurrently moving said upper and lower sheet supporting carriage means in opposite directions to move said lower sheet supporting means in a to-and-fro path between a first position in which one of said lower sheets is at one of said heating stations and the other of said lower sheets is at said forming station and a second position in which said other lower sheet is at the other heating station and said one sheet is at said forming station and to concurrently move said upper sheet supporting means in an opposite to-and-fro path between a first position in which one of said upper sheets is at said other heating station and the other of said upper sheet is at said forming station superposed with said other lower sheet and a second position in which said other of said upper sheets is at said one heating station and said one upper sheet is at said forming station superposed with said one lower sheet;

upper and lower molding means including differential pressure applying means at said forming station movable toward and away from each other between removed positions and adjacent positions for forming a shape in at least one of the upper and lower superposed sheets and fusing the sheets together;

energizable and deenergizable upper and lower sheet heating means at each of said heating stations; and

means for selectively, individually operating each of said heating means at each station including control means for operating one of the heating means at one station for a longer time than any of the other heating means are operated and for operating one of the heating means at the other heating station for a shorter time than any of the other heating means are operated when said upper and lower sheet supporting means are in said first positions and for operating said one heating means at said one station for a shorter time than any of the other heating means and for operating said one heating means at the other heating station for a longer time than any of the other heating means when said upper and lower sheet supporting means are in said second positions.

2. The apparatus of claim 1 wherein said operating means comprises timer means for initiating operation of the one heating means at said one station a predetermined time before operation of the other heating means at said one station is initiated when said sheet supporting means are in said first positions;

and additional timing means for initiating operation of said one heating means at said other station a predetermined time after operation of the other heating means at said one station is initiated when said sheet supporting means are in said first positions.

3. Apparatus for forming a hollow object from sheets of deformable thermoplastic material comprising:

a central forming station;

a pair of sheet heating stations on opposite sides of said central forming station for heating said sheets of thermoplastic material;

upper and lower carriage means for supporting upper and lower pairs of said sheets of thermoplastic material;

means for concurrently moving said upper and lower sheet supporting carriage means in opposite directions to move said lower sheet supporting means in a to-and-fro path between a first position in which one of said lower sheets is at one of said heating stations and the other of said lower sheets is at said forming station and a second position in which said other lower sheet is at the other heating station and said one lower sheet is at said forming station and to concurrently move said upper sheet supporting means in an opposite to-and-fro path between a first position in which one of said upper sheets is at said other heating station and the other of said upper sheets is at said forming station superposed with said other lower sheet and a second position in which said other of said upper sheets is at said one heating station and said one upper sheet is at said forming station superposed with said one lower sheet;

upper and lower molding means including differential pressure applying means at said forming station movable toward and away from each other between removed positions and adjacent positions for forming a shape in at least one of the upper and lower superposed sheets and fusing the upper and lower superposed sheets together to form a hollow article; and

heating means at each of said heating stations;

said moving means including means for converting linear motion to rotary motion including;

fluid responsive reciprocal means alternately movable in a to-and-fro path of travel between a first position in which said upper and lower sheet supporting means are in said first positions and a second position in which said upper and lower sheet supporting means are in said second positions; and

fluid control means for directing fluid to said reciprocal means to move said reciprocal means between sAid first and second positions including means for moving said reciprocal means at a first predetermined speed during the initial portion of its travel from one of said first and second positions to the other and for moving said reciprocal means at a lesser predetermined speed during the final portion of its travel from said one to said other position.

4. The apparatus set forth in claim 3 wherein said fluid control means includes variable flow valve means connected in fluid circuit relation with said reciprocal means, means in parallel with said variable flow means for permitting said fluid to flow freely to and from said reciprocal means during said initial portion of travel and for interrupting said flow of fluid in said parallel path to force said fluid through said variable flow valve means to restrict the flow of fluid to and from said reciprocal means during said final portion of said travel.

5. The apparatus of claim 3 wherein said moving means comprise a fluid operated cylinder having a reciprocable piston comprising said reciprocable means, said fluid control means includes a pair of fluid circuits for coupling a source of fluid to opposite ends of said cylinder, each of said circuits comprises a first circuit line including a valve operable in a first position to permit the free flow of fluid to and from said cylinder and a second position interrupting the flow of fluid in said first circuit line and a second circuit in parallel with said first circuit including a pair of oppositely poled check valves connected in series and a pair of variable orifice valves in parallel with said check valves permitting limited fluid to pass to and from said cylinder.

6. Apparatus for forming a hollow object in sheets of deformable thermoplastic material comprising:

differential pressure forming apparatus at a forming station;

sheet heating apparatus at a pair of sheet heating stations on opposite sides of said forming apparatus;

upper and lower pairs of sheet supporting carriage means for supporting upper and lower pairs of plastic sheets;

means for moving said carriage means in to-and-fro paths of travel between positions at opposite one of said heating stations and superposed positions at said forming stations;

said forming apparatus comprising upper and lower differential pressure molds movable toward and away from each other between removed positions and adjacent molding position into engagement with said upper and lower sheets to form shapes and fuse the sheets together to form said hollow object;

means for moving said molds between said removed and molding position; and

stop means overriding said moving means for temporarily interrrupting the upward movement of the lower mold toward the upper mold after the lower mold engages the lower sheet and before the sheets are fused together.

7. The apparatus of claim 6 wherein said stop means comprises a fluid circuit including a fluid containing vessel having port means therein for permitting the escape of fluid from said vessel, means coupled to said mold and movable in the vessel for displacing fluid through said port means in response to upward movement of said lower mold means and means responsive to said lower mold being moved upwardly into engagement with said lower sheet for temporarily interrupting the flow of fluid through said port means to interrupt upward movement of said displacing means and said lower mold.

8. The apparatus of claim 7 wherein said fluid interrupting means comprises a valve movable between fluid blocking and fluid passing position for selectively interrupting and not interrupting the flow of fluid through said port means, and means operable a predetermined time after said lower mold engages said lower sheet for moving said valve to said fluid passing position permitting fluid to flow through said port means.