Insects use lubricants to minimize friction and wear in leg joints

A protein-based lubricating substance is discovered in the femoro-tibial joint of the darkling beetle Zophobas morio (Insecta). The substance extrudes to the contacting areas within the joint and appears in a form of filiform flows and short cylindrical fragments. The extruded lubricating substance effectively reduces the coefficient of sliding friction to the value of 0.13 in the tribosystem glass/lubricant/glass . This value is significantly lower than 0.35 in the control tribosystem glass/glass and comparable to the value of 0.14 for the tribosystem glass/dry PTFE (polytetrafluoroethylene or Teflon). The study shows for the first time that the friction-reducing mechanism found in Z. morio femoro-tibial joints is based on the lubricant spreading over the contacting surfaces rolling or moving at low loads and deforming at higher loads, preventing direct contact of joint counterparts. Besides Z. morio , the lubricant has been found in the leg joints of the Argentinian wood roach Blaptica dubia .

Lubrication in Hot Forging with Pulsed Ram Motion

The effect of pulsed (oscillating) ram motion control on lubrication was investigated in hot forging of stainless steel workpiece with oxide glass lubricant. During the retreat in the pulsed ram motion, the workpiece was re-lubricated by flow of lubricant through the gap between the workpiece and the die. A hot spike-type forging test on a servo press with pulsed ram motions was carried out to investigate the lubrication performance of the oxide glass. In the test, the workpiece with a temperature of 1223 K was extruded into the hollow part of the upper die together with oxide glass in a manner that combined pulsed and stepwise ram operations. The re-lubrication of the workpiece with oxide glass was confirmed by the test results showing 5–10% reduction in the forging load and 5% longer length of the backward extruded part of the workpiece under an appropriate pulsed ram motion.

Experimental Study on Heat Transfer Boundary Conditions for Steel Hot Extrusion Process

Heat transfer boundary conditions have significant influence on the FEM analysis of the steel hot extrusion process using glass lubricant. However, the determination of heat transfer coefficient between billet and tooling lacked experimental basis. In order to obtain rational values of the coefficient, experimental study was conducted to measure it on thermal contact between P92 steel and H13 steel separated by glass lubricant. The influence of contact temperature, contact pressure and lubricant thickness was investigated. The obtained results can provide experimental basis for the determination of heat transfer boundary conditions for steel hot extrusion.

The Effects of Friction and Lubrication on Multipass Hot Deformation

Plane strain compression tests have been carried out to investigate the variation of friction coefficient for the ferritic stainless steel, AISI 430, during single and multi pass hit deformation using glass lubricant and BN. A graphical method has been employed to evaluate the friction coefficient. It is found that the friction coefficient declines as strain increases under slip friction conditions with glass lubricant. On the contrary, under partial sticking friction condition with BN, the friction coefficient increases as strain increases. Furthermore, the variation of the friction coefficient on multipass hit is almost identical with single hit until the second pass, but the value of the friction coefficient on the third pass is slightly higher than that observed following single pass deformation.