| Selective transfer is defined as a special effect of a metal with selected composition transferring from a copper alloy to steel during the friction of copper alloy / steel pairs lubricated by a boundary lubricant in which copper is not oxidized. Studies of selective transfer in the past dealt mostly with copper / steel or steel /steel pairs rubbing under the condition of boundary lubrication with various selective transfer mediums, such as glycerine, triethanolamine or lubricants with selective transfer additives. However, it is seldom to report polymer compounds with self-selective transferring effect without lubrication of any applied selective transfer medium.The principle of selective transfer was applied to modify polymers in this dissertation. A tribological design for the material composition of a polymer compound was carried out according to the key elements of selective transfer. The aim of the tribological design of the polymer compound was that the new polymer compound designed is endowed with an ability to build a system of selective transfer during the rubbing of which against steel under the condition of dry friction and to bring about the self-selective transferring effect without lubrication of any applied selective transfer medium. Therefore, the ultra high molecular weight polyethylene (UHMWPE), which is a kind of excellent thermoplastic tribological material, was chosen as the base of the polymer compound designed. The Schiff base copper complex and the glycerine microcapsules with polyethylene wall were chosen as the additives of the polymer compound designed. So a new kind of modified UHMWPE with 15%wt. of Schiff base copper complex and 5%wt. of glycerine microcapsules with polyethylene wall was developed by means of so-called mixing and compounding process in this dissertation. This modified UHMWPE was called "SCG-UHMWPE" for short in the abstract. A series of tribological tests have demonstrated the self-selective transferring effect of the SCG-UHMWPE.The pin-disk and ring-block friction and wear tests showed that the rubbing pairs composed of SCG-UHMWPE playing a role of static piece (pin or block) and GCr15 steel playing a role of moving piece (disk or ring) could run normally under the condition of dry friction with light loading and relative high sliding velocity (1.3m/s, 2.6m/s,3.9m/s and 4.4m/s). On the one hand, the anti-friction and anti-wear properties of SCG-UHMWPE / GCr15 steel rubbing pair were a great improvement on that of pure UHMWPE / GCr15 steel and UHMWPE modified by Cu powder / GCr15 steel rubbing pairs when the sliding velocity was high enough (such as 2.6m/s, 3.9m/s and 4.4m/s). When the relative sliding velocity was higher, i.e. reached 3.9m/s during the ring-block friction and wear tests, the SCG-UHMWPE / GCr15 steel rubbing pair could run normally but the pure UHMWPE / GCr15 steel and the UHMWPE modified by Cu powder / GCr15 steel rubbing pairs could not. On the other hand, if the SCG-UHMWPE was in the service of a material for rubbing pairs at relative low sliding velocity (1.3m/s), its anti-friction and anti-wear performance was not poorer than that of the pure UHMWPE on the whole. This means that the SCG-UHMWPE must be praiseworthy for its excellent performance and behavior.The tribological property of the SCG-UHMWPE / GCr15 steel rubbing pair was different from that of pure UHMWPE / GCr15 steel rubbing pair under the condition of dry frication. The general theory of plastic tribology can explain the tribological behavior of the pure UHMWPE / GCr15 steel rubbing pair but not explain that of the SCG-UHMWPE / GCr15 steel rubbing pair. The tribological behavior of the SCG-UHMWPE / GCr15 steel rubbing pair is only explained rationally by the mechanism of selective transfer: the friction heat produced by the sliding velocity which was high enough could make the glycerine microcapsules' wall from common polyethylene with a low molecular weight added in the SCG-UHMWPE melt preferentially, whose melting point is lower than that of the UHMWPE, and then the glycerine medium in thecapsules be thus set free. At the same time, deformation of the surface of the SCG-UHMWPE caused by friction processes could make the Schiff base copper complex added in the SCG-UHMWPE decompose and the copper atoms in the complex be thus set free. Therefore, a system of selective transfer could be built because of completing the key elements of selective transfer through a combination of two key elements above mentioned, i.e. glycerine medium and free copper atoms, with the third key element, i.e. a steel pairing. So SCG-UHMWPE / GCr15 steel rubbing pairs could produce the effect of selective transferring which improved their anti-friction and anti-wear properties without lubrication of any applied selective transfer medium.In this dissertation phenomena of selective transfer produced by SCG-UHMWPE / GCr15 steel rubbing pairs were observed and analyzed through a scanning electron microscope, an energy spectrum analyzer and an optical microscope. The analyses demonstrated the self-selective transferring characteristic of the modified UHMWPE with 15%wt. of Schiff base copper complex and 5%wt. of glycerine microcapsules with polyethylene wall.In this dissertation a series of comparison tests for pure UHMWPE / GCr15 steel, UHMWPE modified by Cu powder / GCrl5 steel and SCG-UHMWPE / GCr15 steel rubbing pairs were carried out under conditions of boundary lubrication with glycerine, which is a classical selective transfer medium, and a traditional mineral oil respectively. These tests further demonstrated that the modified UHMWPE with 15%wt. of Schiff base copper complex and 5%wt. of glycerine microcapsules with polyethylene wall is a new type of UHMWPE compound which could form a selective transfer system during the rubbing of which against a steel under the condition of dry friction and bring about the self-selective transferring effect without lubrication of any applied selective transfer medium.The modified UHMWPE with 15%wt. of Schiff base copper complex and 5%wt. of glycerine microcapsules with polyethylene wall had also other... |
PDF Full Text Request