| 摘要 |
An apparatus for butt jointing opposite edges of a sheet of plastics material to form a tubular sleeve for use as a printing forme comprises two opposed elongate platens (1 and 2) and clamp means (3), Figure 1 (not shown), to clamp the platens together to sandwich the edges of the plastics material to be joined between them. At least one of the platens includes a strip heater 15, Figure 2, extending along it with thermally insulating material 18 extending along both sides thereof. Preferably, the heater 15 has embedded therein two low power electrical heating elements 16 and a single high power element 17. The thermally insulating material 18 ensures that portions of the plastics material adjacent the opposite edges of the sheet are held firmly in place throughout the heat welding operation to ensure that the completed joint is substantially void free and stress free. The heater 15 and the insulating material 18 are enclosed in a polytetrafluoroethylene sleeve 19. The apparatus may also include nip bars 4 to enable opposite edges of the sheet of plastics material to be clamped into position before the platens are brought together. Adjustable springs 13 or an inflatable hose (24), Figure 6 (not shown), apply pressure at the nip between the platens. The platen 2 may have thereon a polytetrafluoroethylene coating 6, Figure 2, or a curved polytetrafluorethylene strip (21), Figure 4 (not shown). <IMAGE> |
