OBRABOTKAMETALLOV TECHNOLOGY Vol. 24 No. 3 2022 on the assigned objectives there are the following types of grinding: preventive (prophylactic), maintaining (corrective) and reconstructive (profi ling) grinding. Each of these approaches determines the technology of its implementation [5]. Thus, reconstructive grinding is characterized by the need for a large metal removal from the rail using rail grinding trains (RGT) operating at relatively low speeds, and in turn, preventive grinding should be performed with the RGT running at maximum speed but with a relatively small removal of metal from the rail (Table). It is impossible to effectively implement such a range of operating modes on one type of process equipment [6–8]. Rail grinding trains, such as RR-48, RShP-48 and RShP-48K models are limited to the following grinding modes: RGTs with an operating speed of 4 to 8 km/h; average metal removal speeds from 0.05 to 0.3 mm per pass. During each pass, the “active” grinding process, which consists in fl at face grinding with rotating abrasive wheels running with a rotation speed of 3600 rpm with wheels being rotated using electric motors. With grinding work being carried out at speeds not exceeding 8 km/h and with only minimal metal removal, the use of these types of rail grinding trains for preventive purposes is extremely ineffi cient. Technological impacts of rail grinding Technological impact The purpose of the impact Machining technology Preventive (prophylactic) Preventing the formation of surface defects in rails Insignifi cant metal removal ( up to 0.1 mm) at high speeds (up to 90 km/h) Repair (corrective) Removal of surface defects of rails, elimination of wave-like wear, correction of the cross profi le of the rail Heavy metal removal (up to 1.5 mm) in certain sections of the rail head at medium speeds (up to 15 km/h) Restorative (profi ling) Restoration of the transverse (repair) profi le of rails, reprofi ling of old-year rails and when relaying rails in curved track sections Heavy metal removal (up to 3.5 mm) along the entire transverse profi le of the rail at low speeds (up to 6 km/h) Another factor that has a signifi cant impact on the effi ciency of the rail grinding process is the necessity to organize periods when sections of track are “temporarily closed for maintenance” while the work is carried out. The existing speeds of the RGT (up to 8 km/h) do not allow it to be used within the schedule of passenger and freight trains. This leads to the need to close entire hauls for traffi c – the organization of technological windows, – and as a result, to the occurrence of large fi nancial costs caused by a decrease in the capacity of sections of the railway track [9]. In view of the above limitations, the current problem facing the maintenance of railway tracks is the need for the expansion of the rail grinding trains technological capacities. The key task in solving this problem is to increase the operating speed of rail grinding trains everywhere in order to eliminate or at least reduce the duration of closures for maintenance. The most promising solution lies in increasing the operating speeds of the RGT when performing work on preventive and corrective grinding with insignifi cant removals of the rail metal [10, 11]. Since its inception, rail grinding technology has been focused primarily on preventing the formation of wave-like rail wear, wheelspin and surface defects in the most loaded sections of the track, i.e. it was of a preventive nature. For this purpose, the technology of rails passive grinding has been used since 1960s [12]. The term “passive”, in this case, characterizes the absence of additional movements in an abrasive tool (usually rotating or reciprocating) due to special drive mechanisms. Grinding occurs only as a result of the pressing and longitudinal movement of the tool. This technology on local railways was implemented with the help of the so-called rail-grinding carriages (RGC), which also lubricate the rails. These carriages were driven by a locomotive. During this process (Fig. 1, a) abrasive bars were pressed against the rail with a constant force. These bars were located on the
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