Method of welding plastics

Abstract

Abstract 891,909. Heating plastics by electric resistances. KARL MAGERLE. Aug. 10, 1959 [Aug. 9, 1958], No. 27243/59. Class 39(3) In apparatus for welding plastic sheet along a predetermined welding line, especially along curved lines such as circles, rectangles or ovals in which pressing members are provided with an electrically heated conductor energized by current pulses, the energization circuits are so connected that the electrical conductor is energized in portions between two sets of spaced points which overlap in space at consecutive time intervals so that the whole of the conductor is heated. In this way welding of the plastic sheeting in the welding press is more uniform along the length of the curved line which may be the circular bottom of a cylindrical container. Preferably the heater element 1, Fig. 1, is circular and is supplied at points 6, 7, 9, 10 by respective secondary halves of a transformer, 5 and 8 being switching devices such as relays. The heating element 1 may be preheated by a short duration low amplitude pulse. Switching control unit 12 is controlled automatically or manually. There may be more than one current pulse in each energization interval. Welding may be along other shaped lines, closed, Fig. 4, (not shown) or open Fig. 5, (not shown) to compensate for the thermal expansion of the heater the frame 35, Fig. 6 is a support which applies pressure and 37 is the current connection to heating element 38 which 'floats' on 'elastic' support 39. A protective covering 40 of heat resisting 'elastic' material is held by a clamp 41. A similar arrangement in which the heating element has two leads secured together at their lower ends is described with reference to Fig. 7 (not shown).

Inventors

• 👤 Imhof Waltraud

Bibliographic Details