Method for forming double-walled units
AssigneeImperial Chemical Industries PLC
InventorsKent Reaney Greer, William Rodney Hampson, Benjamin James Smith
Life of this patent
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Abstract
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.
Claims9
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.
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.
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 away the unapertured sheet from the other sheet by means of the application of different pressures to the two sheets until the stretched sheet makes contact with a supporting rim spaced apart from the organic thermoplastic sheet and enclosing a major proportion of the area of the stretched sheet, (5) rapidly equalizing the atmospheric pressure on either side of the stretched sheet contained within the rim to bring the spaced apart sheets into substantially parallel relationship while maintaining contact between the rim and the stretched sheet, and (6) allowing the unit to cool below the softening point of the thermoplastic material.
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 away from the other sheet by means of the application of different pressures to the two sheets until the stretched sheet makes contact with a supporting rim spaced apart from the organic thermplastic sheet and enclosing a major proportion of the area of the strecthed sheet, (6) rapidly equalizing the atmospheric pressure on either side of the stretched sheet contained within the rim to bring the spaced apart sheets into substantially parallel relationship while maintaining contact between the rim and the stretched sheet, and (7) allowing the unit to cool below the softening point of the thermoplastic material.
An apparatus for forming a double-walled unit from a pair of thermoplastic sheets comprising:
- means for clamping the pair of sheets together at their peripheries, means for heating at least one of the sheets to above the softening point of the thermoplastic, means for applying different fluid pressures to each of the sheets to stretch a heat-softened sheet relative to the other sheet, to give a desired separation of sheets, and upstanding rim for receiving a first stretched sheet, and means for independently varying the pressures acting on the areas of the stretched sheet inside and outside the contacted rim.
Dependencies are inferred from the claim text.