Distribution of Temperature along Axis of the Steel Sample at Sliding under Electric Current against Steel Counterbody

Introduction. Knowledge of the temperature field in the vicinity of a piecework/tool contact can be useful in optimizing the metalworking process. Infrared thermography is a convenient way to obtain the temperature distribution. This method is widely used in a heat control. It seems reasonable to find out the applicability of the method of infrared thermography to determine the temperature distribution character in the piecework/tool contact. It is of scientific interest to compare the temperature distribution obtained using a thermal imager and thermocouples in the model piecework/tool contact. It has been suggested that the sliding of a steel rod against a steel ring can serve as approximation of a sliding of a steel ball smoothing the surfaces of metal parts. The contact temperature can be changed using electric current. The purpose of the work is to study the features of temperature distribution along the axis of a steel rod, sliding against steel counterbody under the influence of electric current using infrared thermography and using thermocouples. Experimental details. The hardened steel of the St3 grade (AISI steel 1020; Fe - 0.2% C) with the hardness HB274 served as a model counterbody. The sliding electrical contact was carried out without lubricants according to the pin-on-ring slip scheme at a pressure of p = 0.13 MPa and a sliding speed of v = 5 m/s. Steel 45 (50 HRC) served as a counterbody. The temperatures were measured with thermocouples attached to the rod by spot welding and with FLIR A655 sc thermal imager. Results and discussion. It was shown that the temperature distribution along the rod axis was non-linear with relatively high (up to 600 K/cm) temperature gradients in the contact zone under sliding electrical contact if the temperatures were measured with a thermal imager. Measurement of temperatures on the rod axis with thermocouples under the same conditions showed a linear temperature distribution with low (about 100 K/cm) temperature gradients in the contact zone. Current passing through the rod in the absence of slip was also accompanied by a linear temperature distribution. It was assumed that the nonlinearity of the temperature field during its imaging with a thermal imager was due to the difficulty of setting the correct value of the emissivity. This coefficient depends on the presence of oxides, roughness and other state parameters of the radiating surface. The lateral surface of the sample with a high temperature in the area of the sliding contact had a state different from that of the same lateral surface in the zone of attachment of the sample to its holder. Therefore the emissivity set for the state of the surface in the slip zone of the sample did not correspond to the state of the surface in the zone of the sample holder. Possible values of the emissivity (about 0.7) corresponding to a contact temperature of about 400 degrees C were obtained by experimentally estimating of convective and radiative heat-transfer coefficients. It was noted that the exact temperature field can be determined using a thermal imager only after time-consuming calibration of the emissivity and preparation of the sample surface. It was concluded on the limited possibility to apply infrared thermography under piecework/tool sliding contact and it was offered to carry out the thermal control of the same contact using thermocouples.