Sheet shaping method

• US 4,191,039 A
• Filed: 01/18/1978
• Issued: 03/04/1980
• Est. Priority Date: 01/18/1978
• Status: Expired due to Term

• Current Assignee: John Brown Industries Limited
• Original Assignee: Leesona Corp.
• Inventors: Bradbury, Christopher G.
• Primary Examiner(s): Silbaugh, Jan J.
• Application Number:
  US05/870,925
• Time in Patent Office: 776 Days
• Field of Search: 264/89, 264/93, 264/237, 264/348, 264/28, 425/384, 29/421 R, 72/56,60, 65/94,106
• US Class Current: 72/60
• CPC Class Codes: B29C 49/66 Cooling by refrigerant introduced into the blown article
• CPC Class Codes: B29C 51/10 Forming by pressure difference, e.g. vacuum
• CPC Class Codes: B29C 51/42 Heating or cooling

Abstract

An improved method and apparatus for shaping sheets of thermoplastic material is disclosed in which sheets are pressure molded against a mold member by the direct application of a liquid coolant under pressure thereto. The coolant contacts the surface of the sheet and upon pressure reduction vaporizes and accordingly, due to the heat of vaporization effect, rapidly absorbs a large amount of heat from the sheet so as to form a solidified skin on the outer surface of the sheet after or simultaneously with the shaping of said sheet. The sheet thus remains in the mold for a shorter dwell time inasmuch as the sheet becomes more quickly shape retentive because of the rapid cooling. This accordingly permits smaller and less bulky equipment to be utilized in sheet shaping processes. The attendant reduction in equipment size can result in substantial cost savings for such equipment.

Claims

1. A method of shaping a sheet of thermoplastic material, comprising providing a sheet at a temperature sufficient to enable it to be shaped by the application of pressure thereto, placing the heated sheet material into an at least partially enclosed mold and disposed in proximity to a shaping member thereof and therafter directing liquid coolant under a pressure sufficient to maintain said coolant in a liquid state and to enable shaping of said sheet into said mold by the direct contact of said coolant with said sheet so as to force said sheet into contact with said member and thereafter depressurizing said mold so as to permit the vaporizing of at least a part of the same said coolant contacting said sheet material, thus quickly removing heat from the surface thereof by means of the heat of vaporization effect so as to form at least a solidified skin of cooled material on said sheet material surface opposite to that surface contacting said mold member and thereafter removing said sheet from said mold.

2. The method of claim 1, wherein said coolant is sequentially admitted to said mold at a first pressure, at least partially removed from said mold at a substantially lower second pressure and thereafter the sheet material removed from said mold.

3. The method of claim 2, including substantially closing said mold about said sheet material.

4. The method of claim 2, wherein said second pressure is above that required to shape said sheet.

5. The method of claim 1, wherein said pressure vaporizing and removal steps are sequential in operation, said mold member being at least partially vented after said coolant contacts said sheet so as to lower the pressure of said mold below a point at which ebullition of the coolant occurs.