Effect of electrocontact surfacing on the wear resistance of high-strength cast iron

Abstract

In connection with the use of high-strength cast irons for the fabrication of crank and distributing shafts, connecting rods, wheel hubs, etc., the regeneration of these parts is a timely problem [i, 2]. An analysis of the working surfaces of parts arriving for repair shows that their main defect is increased wear. Worn parts can be regenerated by surfacing or by galvanic coatings. However, the surfacing methods and the kinds of galvanic coatings used at the present time do not ensure a high quality of the repair of the parts. It is well known that [3] with electrocontact surfacing, joints of different alloys with high physicomechanical characteristics can be obtained. To determine the possibility of using this method for the regeneration of parts made of high-strength cast iron VChS0-2, a unit was built for electrocontact surfacing. The welding material with surfacing was a spring wire of class II All-Union State Standard (GOST) 9389-60. Comparative investigations of the wear resistance were made on samples subjected to electrocontact surfacing, unsurfaced samples, and samples surfaced by vibrating-arc surfacing. The tests for wear were made in an MI friction machine, in accordance with a rotating sample-- fixed block scheme. The lubricant was standard oil AS-8 for automobile engines. The duration of experiments was ii h. Abrasion of the samples was carried out for a period of i h with a specific pressure of 6.25 kgf/cm 2. The subsequent investigations were made with a pressure on the sample of 12.5 kgf/cm 2, close to the loads arising at the necks of the crankshaft during the work of ZMZ-53 engines. In each series 8 samples were tested with recording of the following parameters: the friction path, the work of friction, the friction moment, and the temperature in the contact zone. The value of the wear of the samples and the blocks was evaluated from the weight loss. Before a test, after abrasion, and after each 2 h of friction, the samples were washed in benzene, dried, and after cooling to a temperature of 18~ were weighed on an analytical balance with an accuracy of 0.0001 g. The parameters of the friction conditions were recorded every i0 min. The temperature in the contact zone of the friction were measured with a Chromel--Alumel thermocouple and an ~PP-09 electronic semiautomatic potentiometer. The junction of the thermocouple was inserted into an opening in the block, drilled at a distance of i r~n from the friction surface. The results of the tests (Table i) showed that unsurfaced samples have the best wear resistance. The wear resistance of samples surfaced by electrocontact surfacing was found to be higher than the wear resistance of samples surfaced by vibrating-arc surfacing, used at the present time in automobile repair plants for surfacing the necks of the crankshafts of ZMZ21A and GAZ-24D engines. Judging from the change in the moment of friction and the temperature in the contact zone of the wearing surfaces (Fig. i), these parameters for samples surfaced by the electrocontact method are lower than for samples surfaced by vibrating-arc surfacing. This is evidence that the friction conditions of samples surfaced by the electrocontact method are far more favorable than for samples surfaced by vibrating-arc surfacing, which is confirmed by the presence of an oil film of relatively great thickness between the wearing surfaces. The thickness of the oil film was determined by measurement of the friction at the contact, which