| 摘要 |
815,989. Heating resistors for plastics. PFAFF A.G., G. M. Dec. 13, 1955 [Dec. 16, 1954], No. 35677/55. Addition to 754,936. Class 39(3) [Also in Group VIII] The plastic seamwelding apparatus of the parent Specification is modified by the provision of heating bands, one of which is shown at 24 -having a resistance continuously increasing towards their looped ends. As shown, band 24 is fixed to an insulating carrier 20 pivotable about a feed roller (see Group VIII). Band 24 is fed by current supply members 22 and is made of resistance material in the form of a flat loop; the cross section of the loop steadily diminishes towards the free end which is bent at an angle so as to extend parallel to the material to be welded; also the end of band 24 carries one or more bridge pieces 40, the overall resistance of which is greater than that of the band in front of the bridge pieces so that the highest point of the temperature gradient along the band coincides with the band end. |
