Rolling contact fatigue life of AISI 52100 steel balls with mineral and synthetic polyester lubricants with PTFE nanoparticle powder as an additive

This work evaluates the rolling contact fatigue life of AISI 52100 steel bearing balls with mineral and synthetic oil, with and without additive, using a four-ball tester. IP 300/87 was applied with a total load of 600 kg (corresponding to a maximum Hertz stress of 8.709 MPa). SN-350 (a neutral mineral solvent) and TMP-05 (an environment friendly synthetic polyester) of the same viscosity were additivated with PTFE nanoparticle powder in different percentages. The total test time for each specimen was recorded and processed on Weibull probability plots. L₁₀ and L₅₀ are given for pure base oils and oils additivated with 1, 3 and 5 wt.% of PTFE powder. The results point to an increase in the fatigue life when additive-containing oils were used. In order to provide some understanding of the protection mechanism of the additive, the contact angle and the influence of the surface wettability on the lubricant unctuosity were analysed. Scanning electron microscopy and LINK techniques were used to study pitting, crack propagation, the chemical influence of additive and fluorine content.     

Tribological behaviour of polyalphaolefins: Wear and rolling‐contact fatigue tests

Polyalphaolefin (PAO) fluids have become widely accepted as high‐performance lubricants and functional fluids due to certain inherent, and highly desirable, characteristics. One of these characteristics is their low toxicity, which, combined with excellent viscometrics and lubricity, have made low‐viscosity PAO fluids an important component in lubricant formulations. Typical data found in product specifications for lubricants are the kinematic viscosity and the viscosity index. These values do not give enough information with which to choose the optimum lubricant for a lubricated contact. In mechanical systems, rolling, sliding, and rolling/sliding contacts occur, and lubricants have to work optimally under these operating conditions. In this study the rolling‐contact fatigue lives (L₅₀ and L₁₀) of PAOs of different viscosities were experimentally determined. The tests were carried out using a four‐ball machine. Wear tests were also carried out using another four‐ball tester in order to measure the wear‐scar diameter and the flash temperature parameter. The lubricants were characterised by infrared spectroscopy, and the pitting of the balls was observed using scanning electron microscopy.     

Rolling fatigue tests of three polyglycol lubricants

In this work, the rolling fatigue lives of three polyglycols (PAG-9, PAG-12 and BREOX-B-135X) are determined using IP-300 standard. A four-ball test machine was used and 10% life (L₁₀) and 50% life (L₅₀) were obtained. In addition, the stress-time curves for L₁₀ and L₅₀ were also determined. This work showed that: firstly, all polyglycols were tested under boundary lubrication regime (λ < 1) where in rolling contacts the surface mode of failures prevails; secondly, in oils of the same family, the pressure-viscosity coefficient is relatively constant, therefore an increase in viscosity improve the minimum film thickness with the consequent increase of the λ ratio; and finally, differences in λ ratio for the three polyglycols resulted in different asperity interactions and rolling contact fatigue lives.     

Laser scan planning based on visibility analysis and space partitioning techniques

This paper presents a methodology to develop an automatic process planning system applied for scanning parts with free-form surfaces by using a laser stripe system mounted on a coordinate measuring machine (CMM). The part has been modelled using a STL format that permits the automatic recognition of any part surface. The valid orientations of the scanning device are obtained in order to guarantee the visibility of the zone to be scanned and also to be compatible with the constraints imposed by the process. With the aim to speed up the calculation of valid orientations, we apply different methods like space partitioning techniques base on kd-tree as well as back-face culling algorithms. Once the space occupied by the part is partitioned in regions, recursive ray traversal algorithms are used in order to exclusively check for intersection the part triangles of the STL model that can potentially be traversed by each laser beam direction. In order to reduce the scanning time related to laser orientation changes, part triangles must be classified into a set of clusters based on their common visibility orientations. Finally, the scanning paths for each cluster are generated as well as the joining paths between them by taking into consideration depth of field and laser beam width.