GB1449670A - Commutators - Google Patents

Abstract

1449670 Making commutators AIRSCREW HOWDEN Ltd 3 Oct 1974 [5 Oct 1973] 46716/73 Heading B3A [Also in Division H2] A method of making a commutator comprises embedding a number of conductive bars 1 in insulating plastics material 3 to form a moulded commutator having at least one annular seat 6 and placing a ring of high tensile material 10 on the or each seat so as to stress the ring in tension and apply a radially inward load on each bar which is greater than the centrifugal force on the bar at maximum running speed. The bars 1 have deep recesses 4 at either end and they may be spaced apart by thin insulating shims, e.g. of mica. Phenolic or other plastics material is moulded in the end recesses 4 to form an annular groove 5. The rings 10, which are of high tensile steel, are heated prior to insertion in the grooves so as to exert a compressive force on cooling. The grooves 5 are subsequently filled by the addition of more insulating material. Preferably the commutator is built around a central steel tube 2. In an alternative embodiment a single ring (10) is located in a recess which extends to about the axial centre of the bars (1), Fig. 2 (not shown). A further alternative embodiment includes a ring (10) embedded in plastics material on ledges (21) of radially extending bars (1), Fig. 3 (not shown). The preload applied by the steel rings to the copper bars is preferably greater than three times the maximum centrifugal load.