Triacetin as Lubricant Additive: Slipping Friction between Metal Pairs under Boundary Lubrication

Friction between rubbing pairs plays a key role in operating machines in an efficient approach. In some intended works or occasional circumstances, slipping friction may occur during dry or boundary lubrication. Lubricating mechanical equipment using proper and efficient lubricant agents is tremendously necessary. This work explores the synthesized triacetin as an additive for lubricant under slipping friction between steel rollers and aluminum, brass, copper, and stainless-steel rods under boundary lubrication. The metal surface morphology under the lubricant with 10% triacetin additive covering roughness periphery is investigated by Field Emission Scanning Electron Microscope imaging. In the dry slipping condition, the friction coefficient is lower for the copper-steel pair compared to the aluminum-steel combination. Compared to the absence of triacetin additive, the steel roller combinations with the rod metal specimens undergoing boundary lubrication with 10% triacetin additive in the lubricant can reduce the slipping friction coefficient by up to 49.2% in the case of steel roller and brass rod pair. The quantitative influences of triacetin additive on metal rubbing pair friction coefficients under boundary lubrication are inversely exponential correlated to triacetin additive, varying in the range of 0 to 10% v/v.

Preliminary Study of the Superlubricity Behavior of Polyimide-Induced Liquid Crystal Alignment

We have studied the friction behavior based on liquid crystal (LC) alignment of a unique tribological system composed of a nematic LC and polyimide (PI). The LC was used as a lubricant and a tribological factor with molecular alignment ability. PI was used as both a rubbing pair part and a LC alignment agent. The LCs used as lubricants included the single LC 5CB and the mixed LCs 5CB–2UTPP3 and 3PEP5–3UTPP4. The PI used as the friction pair was 6FDA-ODA PI, and its counterpart was GCr15 steel. For this system, it was found that under the premise that the nematic phase temperature range of the selected LC meets the operating temperature of the friction test at a suitable ambient temperature, the operating speed and load are controlled to maintain a stable lubricating film thickness between the friction pairs during operation of the system. Moreover, by avoiding excessive or insufficient friction heat generated by the running speed being too high or too low to change the phase state of the LC, with the anchoring energy between the PI and the LC, the LC molecules will align in the rubbing direction, that is, they will arrange parallel to each other along the grooves, which can contribute to achieve superlubricity behavior.

The Wavelet Transform in the AE Signal Feature Research of the Rubbing Fault Caused by the Different Pairs

Combine wavelet function “db10”with MATLAB band energy scale decomposition method, studied the characteristics of acoustic signals on different rubbing pair at low speed situations. The results indicate that acoustic signal generated by rubbing fault has obvious sudden; In general, the characteristics of acoustic signals induced by different rubbing pair is basically similar, so the characteristics of rubbing fault affected by rubbing pair of material is very small; The fault charac-teristic frequency is 328-420KHZ , 223-300KHZ at low speed.

Wear Mechanisms of PTFE in Humidified Hydrogen Gas

PTFE is used as sealing material of machine elements in hydrogen utilizing machine systems, such as fuel cell vehicles and related infrastructures. It is necessary to know the tribological property of sealing materials in hydrogen gas to realize safety and reliability of machine elements operated in hydrogen environment. In this study, humidity in gases was focused on and its effects on the friction and wear of rubbing pair of PTFE pin and AISI 316L disk was investigated in pin-on-disk wear apparatus. The result indicated that the humidity in hydrogen gas had little effect on the friction coefficient between PTFE and AISI 316L. However, the specific wear rate of unfilled PTFE was clearly affected by the humidity. The amount of PTFE transfer film formed on the stainless surface gradually decreased with decreasing the humidity in hydrogen gas. The similar results could be obtained in inert argon gas as well. Water molecules remained in gaseous environments would be included in the formation process of PTFE transfer film affect on formation of PTFE transfer film. The humidity in hydrogen gas should be regulated to ensure the tribological behavior of the PTFE/stainless sliding pair being used in the hydrogen environment.

Effects of Nanostructured Additives on Boundary Lubrication for Potential Artificial Joint Applications

Water-based fluids containing nanostructured fullerene C60 and 18-crown ether-6 were investigated. The effects of those nanostructured additives on the tribological performance of titanium and its alloys as potential biomaterials were analyzed. Experimentally, tribology tests were conducted using a Ti–6Al–4V ball against a disk made of pure titanium as a simplified model of the material rubbing pair. Lubrication mechanisms were studied by comparing the nanostructures, viscosities, and frictions. Results showed that the fullerene C60 in deionized water provided the lowest viscosity and friction. Crown ether, on the other hand, provided high friction and shear. Our analysis indicated that the fullerene was weakly interacted with water compared with the crown ether, resulting in an extended low friction in the boundary lubrication regime. The crown ether required extra energy in order to slide or roll. This led to a high friction. This finding opens the possibilities for lubrication design and optimization for biological and engineering applications in general.

Low Friction Cobalt-Based Coatings for Titanium Alloys

Protective coatings adapted for titanium alloys which come into frictional contact with one another are described. Among the many coatings investigated, the best ones are cobalt based. The coatings are sprayed only on one of the rubbing surfaces. During rubbing, a small part of the coating transfers to the unprotected titanium alloy surface. The rubbing pair is thus essentially composed of two cobalt alloy-based surfaces. This leads to low coefficient of friction and little or no damage to the rubbing surfaces. The coatings find particular application in the protection from adhesive and fretting wear, galling and seizure of gas turbine and jet engine parts or the like made from titanium alloys.