Increasing the post-repair resource of the wheels attachment bolts of transport machinery
Authors: Doshchechkina Irina 
Published: December 2024

Abstract. Problem. The state of war in our country and a significant reduction in the production of new vehicles exacerbated the problem of increasing their operational resource due to repairs. Improving the quality and increasing the efficiency of transport vehicles involves, first of all, the fight against wear and tear, because the reason for their premature failure (from 75 to 90%) is significant wear and tear of parts. A significant number of parts of the main structural units of vehicles are exposed to cyclic loads, so it is quite reasonable to pay attention to the issue of increasing the fatigue strength of products. Considering the significant shortage and high cost of spare parts, an expedient and economically beneficial solution to these problems is the restoration and strengthening of the surface layers of products during repair The parts that mostly fail prematurely and require repair using rational methods of recovery include the bolts of fastening the wheels of buses - a very common vehicle that is intensively operated in very difficult conditions. The development of effective technological processes for the restoration of bolts with a simultaneous increase in the post-repair resource at the lowest costs is definitely an urgent issue, because it will prevent another possible premature failure in operation Goal. The purpose of the work is to restore and increase the post-repair resource of the bolts for fastening the disks of the rear wheels of the bus. Methodology. The subject of the study were the serial bolts for fastening the discs of the rear wheels of the bus made of 40X steel after quenching and tempering at 500-550º C with a trostite-bainite structure and a hardness of 35-37 НРС. For vibro-arc surfacing, electrode wire Нп-30ХГСА with a diameter of 1.2 mm was used. Food carbon dioxide was used as a protective gas, and a 5% solution of soda ash in water was used as an accelerating coolant. After surfacing, the surface was subjected to bombardment with low-energy (up to 3 keV) titanium ions in an argon environment at the Bulat - 3t installation. After the specified methods of bolt processing, the roughness and surface profile were evaluated, the microstructure was studied, and the mechanical properties were determined. The strength limit of the slotted part of the bolt was determined using special samples on the CD10 universal machine (made in Germany). Cyclic tests of welded samples were carried out according to the scheme "tension during rotation of the cantilever-loaded sample" on the UMP-02 machine. Tensile tests were performed according to standard methods. Originality. To increase the cyclic durability and wear resistance of bolts, a modern method of surface modification was used - ion bombardment with low-energy ions (without coating), which made it possible to strengthen the surface layer without losing plasticity. An increase in the resource was achieved due to a change in the state of the surface (obtaining ultrafine crystalline nano-sized grain, healing of surface stress concentrators), and a change in the mechanism of plastic deformation - from dislocation to rotational with grain-boundary sliding of ultra-fine grains. Practical value. The recommended mode of vibro-arc surfacing provides surface hardness for the possibility of further mechanical processing without additional thermal weakening, which increases the cost-effectiveness of the process of compensation of the worn surface layer. Modification of the surface by ion brombarbing after surfacing made it possible to increase the cyclic durability by 2 times, significantly increase the static strength without loss of plasticity, and increase the hardness to ensure wear resistance.