STUDYING PARAMETERS OF ELECTROLYTIC FLOW TINNING FOR CRANKSHAFT RESTORATION

This study was conducted on the technology for restoring automotive and tractor engine crankshaft journals using electrolytic flow tinning. A laboratory setup was developed, including a sealed housing, process equipment, an electrolyte circulation system and power supply from a VU-4270B rectifier. Metal deposition was carried out at the cathode - the journal using an anode made of grade 3 steel according to GOST 380-2005. The electrolyte was prepared with distilled water; it contained FeCl2 – 250-300 g/l, KCl – 40-50 g/l, H3BO3 – 15-30 g/l, NaH2PO2 – 15-30 g/l, ascorbic acid – 0.5-2 g/l. The tests were carried out at an electrolyte temperature of 30-70°C, a current of 2-20 A and a feed rate of 10-60 ml/s. Conditions: pH = 1, voltage 3-12 V, metal current efficiency 85-96%. Coating properties were evaluated using TKM-459C hardness tester, 77MT-1 friction machine and AND HR-200 scale were used. The experiment was carried out according to a second-order central-composite design, a total of 17 tests were performed. The maximum metal deposition rate reached >1200 μm/h (under base conditions <700 μm/h), wear resistance was 0.021 (N m)/mm3 and hardness was up to 59 HRC. Optimum parameters were established at temperatures above 60°C, a current of 18 A, and an electrolyte flow rate of 55 ml/s. The constructed second-order regression models demonstrated high adequacy: the determination coefficients were R2 = 0.9858 (deposition rate), R2 = 0.9006 (wear resistance), and R2 = 0.9321 (hardness). Significance was confirmed by Fisher criterion. The obtained dependencies make it possible to predict coating characteristics and optimize crankshaft journal restoration modes. The developed technology is recommended for implementation in repair departments of agricultural enterprises, as it ensures an increase in the service life of components and a reduction in costs.