Rotary thermoforming process and apparatus

• US 4,244,915 A
• Filed: 12/29/1978
• Issued: 01/13/1981
• Est. Priority Date: 12/29/1978
• Status: Expired due to Term

• Current Assignee: Rexam Plastic Packaging Company Limited (Ball Corporation)
• Original Assignee: Hercules Incorporated (Ashland Global Holdings, Inc.)
• Inventors: Boardman, Bruce B.
• Primary Examiner(s): Silbaugh, Jan H.
• Application Number:
  US05/974,453
• Time in Patent Office: 746 Days
• Field of Search: 264/544, 264/547, 264/549, 264/550, 264/551, 264/553, 264/555, 425/326.1, 425/342.1, 425/387.1, 425/388, 425/292, 425/296, 425/302.1
• US Class Current: 264/551
• CPC Class Codes: B29C 51/22 rotatable about an axis

Abstract

The invention is a process and apparatus for continuously thermoforming plastic containers wherein opposed co-rotating discs process a molten sheet of thermoplastic material having a wedge-shaped cross-section, said discs transporting said thermoplastic material through a plug-assisted pressure and/or vacuum forming station, a shear station and a part removal station.

Claims

1. A process for thermoforming plastic containers comprising:

extruding a sheet of thermoplastic material having a wedge-shaped cross-section vertically downwardly adjacent to the surface of at least one rotating disc and normal to its axis of rotation wherein the planar surface of said sheet is substantially parallel to the surface of said rotating disc;

contacting said sheet, without utilization of any clamping means, with the surface of said disc wherein said disc is rotating in a vertical plane about a horizonal axis, said wedge-shaped cross-section of said sheet accommodating stretching caused by the arcuate movement of said sheet and the accompanying differential in tangential velocity across the radius of said disc and across the width of said sheet, said sheet being progressively thicker across its width toward the outer edge of said disc to provide additional material across the width of said sheet for presentation of a substantially uniform thickness of said sheet along the surface of said disc immediately prior to the step of;

plugging portions of said sheet into mold cavities contained within said disc;

thereafter applying a pressure differential across said plugged portion of said sheet forcing said plugged portion of said sheet into intimate contact with said mold cavities;

cooling said sheet;

shearing said sheet at the periphery of said mold cavities to form a finished container; and

stripping said sheet in its sheared condition and ejecting said finished containers from said disc.

2. Apparatus for thermoforming plastic containers comprising:

an extruder die to extrude a sheet of thermoplastic material having a wedge-shaped cross-section vertically downwardly;

co-rotating first and second coaxial discs positioned below said extruder die to receive said sheet adjacent to the interior surfaces of said discs wherein the planer surface of said sheet is substantially parallel to the surfaces of said disc;

said wedge-shaped cross-section of thermoplastic material thereby eliminating the need for clamping means by accommodating stretching caused by the arcuate movement of said sheet and the accompanying differential in tangential velocity across the radius of said disc and across the width of said sheet;

mold cavities contained within said first disc;

plug means connected to said second disc, said plug means being complimentary with said mold cavities to plug portions of said sheet into said cavities as said disc rotate;

pressure differential means connected to said discs to force said sheet further into intimate contact with said mold cavities after said sheet is plugged into said cavities;

cooling means connected to said mold cavities to harden said sheet while such sheet is in contact with said mold cavities;

shear means concentrically mounted with respect to said plug means for shearing said sheet at the periphery of said mold cavities after said sheet is cooled to form finished containers; and

removal means connected to said discs to knock out said finished containers and to strip away said sheet, said plug means, said pressure differential means, said cooling means, said shear means and said removal means each being operated sequentially as said discs rotate through 360°

to continuously form containers.

3. A process for thermoforming plastic containers comprising:

extruding a sheet of thermoplastic material, having a wedge-shaped cross-section, vertically and downwardly between and adjacent to the surfaces of a first and a second rotating disc, said rotating discs being parallel, opposed and rotating in unison on a common horizontal axis, wherein the planar surface of said sheet is substantially parallel to the interior surfaces of said first and said second rotating discs, wherein said first rotating disc contains mold cavities spaced around its periphery and said second rotating disc contains plug means complimentary to said mold cavities of said first rotating disc, said plug means spaced around the periphery of said second rotating disc;

contacting said sheet, without utilization of any clamping means, with the surface of said first disc, said wedge-shaped cross-section of said sheet accommodating stretching caused by the arcuate movement of said sheet and the accompanying differential in tangential velocity across the radius of said first disc and across the width of said sheet, said sheet being progressively thicker across its width toward the outer edge of said first disc to provide additional material across the width of said sheet for presentation of a substantially uniform thickness of said sheet along the surface of said first disc immediately prior to the step of;

plugging portions of said sheet, utilizing plug means of said second disc, into mold cavities contained within said first disc;

thereafter applying a pressure differential across said plugged portion of said sheet forcing said plugged portion of said sheet into intimate contact with said mold cavities;

cooling said sheet;

shearing said sheet at the periphery of said mold cavities to form a finished container; and

stripping said sheet in its sheared condition and ejecting said finished containers from said first disc.