Experimental and Analytical Assessment of the Power Parameters of the Combined Rolling-Extruding Process Using a Round Billet from Alloy 01417 Obtained Using an Electromagnetic Mold

Analytical and experimental studies have been carried out, which made it possible to propose new technological modes of combined rolling-extruding for the production of rods from alloy 01417 for the further drawing of wire for electrical purposes. The force parameters on the rolls and the die are calculated when extruding a rod with a diameter of 5 mm on the laboratory unit CRE-200 and the industrial unit CRE-400. The obtained values of the forces on the rolls and the die do not exceed the permissible values of the power load of the units. Therefore the selected parameters are suitable for conducting experiments on the manufacture of prototypes of rods. To verify the conclusions made, experimental studies were carried out on the CRE-200 unit at a temperature of 320 oC and a drawing coefficient μ = 12.1. The results of experimental studies in comparison with the calculated data showed that the deviation of the calculated data does not exceed 15%.

MANUFACTURE OF ROUGH AXLES PRE-MACHINED BY THE ROUNDING PROCESS

The article deals with the definition of the term “rough axle” (profile billet). Among other things, data on the manufacturing process of axle billets, as well as manufacturing methods for rough axles in Ukraine are presented. Rough axles in our country are manufactured using three different methods of hot-forming process: free forging, screw rolling and radial-rotation profile forming. New method of manufacturing a pre-machined rough axle is described. References to the paper, i.e., determination of comparative characteristics of internal defects of different types of rough axles produced by several domestic manufacturers using various methods and technological processes are made. These characteristics were determined by the Testing Center for railcar-building products of DP "UkrNDIV" during different types of testing rough axles manufactured in the period from 2002 to 2017. The testing is described and the parameters of the test objects which were determined, namely, geometrical dimensions, surface integrity, marking, testing of sound permeability and internal defects of the axles, chemical composition and mechanical characteristics of the axle structure, macrostructure cleanliness, nonmetallic inclusions in the steel, micrographic cleanliness are indicated. Also, the testing results of pre-machined rough axles, manufactured by the method of turning the round billet, carried out by the Testing Center of DP "UkrNDIV" in the period from 2018 to 2021 are presented. Findings based on the tests results are set forth, that is, the tested parameters of test objects meet the requirements of regulatory documentation, steel-melting and manufacturing technological processes for rough axles manufactured by PJSC "INTERPIPE NTRP" comply with DSTU HOST 31334:2009, DSTU HOST 4728:2014 and TU U 30.2-23365425-701:2018. The list of literature sources including state standards and technical specification used while writing the paper and the article itself are given. Key words: rough axle, continuously steel-casting method, round billet.

Influence mechanism of large inclusion on wheel fatigue crack

In this paper, the formation mechanism of wheel rim crack and control technique was investigated. Feature of wheel rim crack and aggregated attachments on the inner wall of nozzle were examined through scanning electron microscope and energy dispersive spectrometer. Metal rheological test of round billet rolling was conducted to investigate the corresponding location of large inclusions in the round billet and in the wheel. It was found that the rim crack of wheels during service is caused by large inclusions that originated from the aggregated inclusions on the inner wall of the nozzle. According to Murakami’s modelling, the critical size of the inclusions that initiate cracks relates to the depth from the tread. The critical sizes of the inclusions for cracks initiation at 10 mm, 14 mm, 16 mm and 20 mm below the tread are about 0.1 mm, 0.2 mm, 0.5 mm and 1.5 mm, respectively. Process optimization was made with combination of a series methods. Dispersed annular venting stopper was adopted to block the aggregation and attachment of inclusions on the inner wall of nozzle. Current and frequency of electromagnetic stirring in mold were increased to restrain the impact depth of molten steel flow and inclusions. Cooling intensity of the secondary cooling was decreased to reduce the probability of inclusions captured at the solidification front. After optimization, the number of large inclusions was greatly reduced by more than 80%, and the number of inclusions larger than 1 mm is greatly reduced from 35% to 8%. The risk of wheel rim cracks occurrence could be reduced greatly.