GB933415A - Improvements relating to means for coiling sheath wire heating elements - Google Patents

Abstract

933,415. Making electric heating elements; coiling. ASSOCIATED ELECTRICAL INDUSTRIES Ltd., and WESTMINSTER ENGINEERING CO. June 1, 1962 [June 8, 1961], No. 20768/61. Classes 83 (2) and 83 (4). A method of manufacturing a convoluted sheathed wire electric heating element ineludes winding a sheathed wire heating element of linear form on to a former, having a profile arranged to impart the required shape to the element, at least the surface of the former being of electrically insulating material, and while the element is on the former passing an electric current through the sheath to raise the temperature thereof to a degree and for a period sufficient to remove resilience from the sheath, and if necessary anneal the material thereof, whereby, on cooling and removal of the element from the former, the convoluted element retains the shape which has been imparted to it. The end of a linear sheathed wire heating element is bent out of alignment with the rest of the element and inserted into a slot in the apex of a former 1 having a frustoconical metal bore the profile of which is provided by a spiral ledge formed thereon and covered with electrically insulating material. A pneumatic device 17 then urges a roller 15 to press the element against the spiral ledge while the former 1 is rotated and moved axially, to wrap the element therearound, by an electric motor rotating a shaft 4 threaded in a fixed nut 6. When the winding is completed a clamp 21 is lowered to hold the coiled element in the former 1. The clamp may be in the form of an open inverted V or as shown comprise a flat plate urged down by pneumatic means and having spring mounted plungers 26 thereon one of which engages the outer turn of the coiled element. An electrode 33 is then moved by a pneumatic device 36 to engage the end of the outer convolution of the coiled element and an electrode 47 is moved by a pneumatic device 51 to engage the end of the element which projects down through the slot in the former 1. The electrodes are conveniently secured to the secondary windings of a transformer and a current is passed through the sheath of the element to raise it to red heat to remove the resilience therefrom. The apparatus may be operated automatically under control of a timing circuit including a shaft with cams thereon. The former 1 may be collapsible axially by the clamp 21 before the heating takes place.