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Method for forming double-walled units
| Details |
Inventors: Greer, Kent Reaney; Hampson, William Rodney; Smith, Benjamin James;
Assignee: Imperial Chemical Industries Limited (London, EN)
Primary Examiner: Powell; William A.
Assistant Examiner: Kittle; John E.
Attorney, Agent or Firm: Cushman; Darby & Cushman
A method of forming a double-walled unit from thermoplastic materials, preferably polymethyl methacrylate, in which two sheets, one of which is provided with an aperture to allow the passage of air between the sheets, are stretched apart under thermoforming conditions by imposed pressure differences, the desired spatial relationship between the sheets being obtained by adjustment of the pressure differences, and in which the sheets are simultaneously bonded about their perimeters. |
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DETAILED DESCRIPTION We claim: 1.
A method of forming a double-walled unit comprising the steps of (1) selecting two sheets of an organic thermoplastic material, a first sheet having a perimeter fitting wholly within or matching the perimeter of the second sheet, (2) providing one of the sheets with at least one aperture to allow the passage of air into the space between the sheets so that each sheet can be shaped independently of the other after they have been bonded together about their perimeter, (3) providing means for bonding the two sheets together about their perimeters and heating at least the unapertured sheet to a temperature above the softening point of the thermoplastic, (4) stretching the unapertured sheet relative to the other bonded sheet by means of different pressures acting on each of the sheets to give a desired shape, the control of the shape being effected by the different pressures applied so that the use of moulds is avoided, and (5) allowing the unit to cool below the softening point of the thermoplastic material.
2.
A method of forming a double-walled unit comprising the steps of (1) selecting two sheets of an organic thermoplastic material, a first sheet having a perimeter fitting wholly within or matching the perimeter of the second sheet, (2) providing one of the sheets with at least one aperture to allow the passage of air into the space between the sheets so that each of the sheets can be shaped independently of the other after they have been bonded together about their perimeter, (3) heating at least the unapertured sheet to a temperature above the softening point of the thermoplastic, (4) applying a clamping means to the perimeter of the sheets thereby bonding them together by the application of pressure over the area of the sheets contacted by the clamping means, (5) stretching the unapertured sheet relative to the other sheet by means of different pressures acting on each of the sheets to give a desired shape, the control of the shape being effected by the different pressures applied so that the use of moulds is avoided, and (6) allowing the unit to cool below the softening point of the thermoplastic material
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