Joining thermoplastic cases and covers by fusion

摘要

A method of joining the two thermoplastic parts (10, 20) uses an electric heating element wire (30) which is seated in a channel (21) of the bottom casing (20). The casing cover (10) has a rim (11) which presses the wire (30) into the channel (21) when the parts are assembled. Electric current is applied to the element wire (30) using electrodes (not shown) which are inserted through apertures to heat the wire and fuse the plastic parts together at the joint after which the electrodes are withdrawn. The fusion strength is enhanced and the bond made more reliable if the diameter of heating element (30) is defined as (D), and:- (a) the distance L between the opposed walls of the channel is defined by 1.3D≤L≤1.6D; (b) the wall thickness T of the rim is defined by 1.1 D≤T≤1.2D; (c) the height A of outside wall of the channel is defined by A≥2D; (d) the height B of inside wall of the channel is defined by B≥2D; (e) the height H of the rim is defined by H≥A. <IMAGE>