Carlos Henrique da Silva

The influence of contact stress distribution and specific film thickness on the wear of spur gears during pitting tests

One of the main gear damage mechanisms is the formation of pitting and spalling on the tooth flank. Several factors have significant influence on the damage formation, such as: contact stress level; tooth profile type; relative contact speed; surface finish and lubrication conditions. This work comprehends the global observation of all such parameters and was carried out to explain the phenomena related to this wear mechanism. The wear test equipment uses the power recirculation principle and is commonly known as FZG test rig. The gears were made from AISI 8620 steel and had two types of surface finishing (by shaving or by milling). The wear experiments were performed with two torque stages: 135 N.m (running-in) and 302 N.m (steady-state), and two test temperatures: 60°C (running-in) and 90°C (steady-state). The wear level was determined by using image analysis. In order to calculate the specific film thickness and friction coefficient, the roughness of tooth flank was measured at each test stop. After the experiments were completed, it was possible to confirm that, for both manufacturing processes, the boundary lubrication regime was adopted at the tooth flank and the specific film thickness presents a different behavior when compared to addendum, pitch diameter and deddendum regions. The wear on the gear flanks depended on the lubricant film thickness and it was higher for the milled gears. Keywords: contact fatigue, gears, pitting, shaving, contact stress, specific film thickness

Austempered Ductile Iron for Gears

It is discussed the use of ADI (Austempered Ductile Iron) for gears. The gears were produced from continuous cast iron bars, heat treated for grade 3 of ASTM ADI Standard A897M06 (UTS >1200 MPa), and compared to carburized steel AISI 8620 and to induction hardened steel AISI 4140. Tests on gears were made using equipment developed at UTFPR, measuring the time for pitting and spalling on the surface of the gears. The results show very good potential of using ADI for gears, replacing induction hardened steels. The results show too that the nodule size affects the life of gears, independently of the mechanical properties of the matrix. The ADI with smallest nodules show higher life for pitting formation. It is discussed additionally the mechanisms of crack propagation under the surface of the gears, for all tested materials.

Surface Characterization of Three-Layer Organic Coating Applied on AISI 4130 Steel

Resin-bonded molybdenum disulfide (MoS2) is widely applied as a solid lubricant. However, multiple coatings are usually required to meet other requirements in mechanical systems. In this study, a quenched and tempered AISI 4130 steel was used as the substrate, being shot blasted. Furthermore, three layers were successively deposited: a zinc phosphate layer, a phenolic resin (basecoat), and a topcoat based on MoS2. The thicknesses of different layers were obtained by scanning electron microscope and by the ball-cratering method. 3D surface roughness parameters were determined for each step of manufacturing, following three approaches: average values, isotropy level, and distribution of heights. The ball-cratering method was successfully applied for determining the thickness of the zinc phosphate but presented a relative deviation for the others layers. The phosphating step was decisive for the final surface topography of resin-bonded coating in terms of distribution of heights. On the other hand, the isotropy level imposed by the shot blasting of steel was practically unaltered by all manufacturing processes.

Assessment of tribological behavior and physicochemical properties alterations of polytetrafluoroethylene imposed by wear test

Purpose The purpose of this article is to discuss the tribological behavior of polytetrafluoroethylene (PTFE) and property changes imposed by wear tests. Design/methodology/approach Long-duration dry wear tests were carried out in a sliding bearing on shaft tribometer. Differential Scanning Calorimetry (DSC) and Fourier Transformed Infrared Spectroscopy (FTIR) analyses were performed in the PTFE in its original condition and after the tests. Findings The wear products merged in multilayer films and were expelled out of the test sequence. Through DSC and FTIR analyses in the polymeric material, before and after tests, it was possible to verify an increase of the crystallinity degree of PTFE, as well as absence of crystalline fusion of the material. The wear products presented changes in the infrared spectra, which suggests the occurrence of some bonds of hydrogen and oxygen. Originality/value It was verified on correlation that fibril mechanism, which occurred during PTFE wear, and its crystallinity degree increase. Also, analysis of PTFE wear products showed CO and CH bonds, which were imposed by wear test.