Estudo da leitura do sinal de runout utilizando sensores do tipo eddy current em eixos de aço revestidos pelo processo de laser cladding

Abstract

The continuous vibration monitoring in rotary machines is a common practice at the automation engineering and predictive maintenance fields. Specially for gearboxes speed increasers and reducers, the radial and axial vibration of the rotary shafts is measured by vibration system analysis sets that use eddy current (EC) sensors for data collecting of relative displacement. When using proximity sensors, the surface conditions of the measured part directly influence the collected signal. In order to increase the reliability of the measurement, geometrical deviations in the runout track must be known. Therefore, the runout test is a crucial step in rotary sets manufacturing processes to ensure the integrity of these regions. The output results with EC sensors test is the Total Indicated Runout (TIR), which is a composition of geometric deviations of the surface (mechanical runout) and a noise in the collected signal known as electrical runout (ERO) that arises due to oscillations in the electrical and metallurgical properties of the target material, and this disturbances in signal are captured as variations in the distance betwen sensor and object. This test is widely practiced in industry for shafts manufactured from forged steel parts. Due to most diverse manufacturing deviations of these shafts, there are situations in which it is possible to carry out a process of adding material for dimensional recovery by addictive manufacturing (AM). One option is the material deposition technology through laser cladding process (LC). However, not much is known about how material properties of these coated layers applied over shafts influence the reading of EC sensors. This work explores the readings captured by an EC sensor during TIR tests on two rotating shafts made of steel alloys 18CrNiMo7-6 and 42CrMo4, each one of them coated with two metallic powder alloys - HGMET and X-402 - deposited by LC process. Considering the defects of the clads inherent to the coating process and the alterations caused in the microstructure of the substrate, it was concluded under the pre-established conditions and through the presented results that the ERO signal behaves randomly and presents values from 150 up to 400% above the values recorded on the uncoated substrate material. In practical terms for the industry, also considering the costs of the process for recovering shaft collars, the study does not recommend the use of this solution neither over vibration reading tracks nor their surroundings.