Research On The Wear Performances Of POM Conveyor Chains Based On Test

Conveyor chains made of POM are commonly used in Tetra Pak automatic packaging line, but showed unexpectedly severe wear in practice. This issue of accelerated wear on conveyor chains became an important problem and needed to find out the root cause. From previous orthogonal tests of UC24 and PC23 on a linear reciprocating sliding test rig, the results demonstrates that water is the most dominant factor on wear of POM rubbing against PP and PC slide strips counterface. After referring to literatures on water affecting wear of polymers, confirmation tests of sliding time up to 500 h for PC23 and PC23 0-gap are performed using the same test rig after improvements, under dry sliding and water lubrication divided into tap water with Cl and purified water without CI. Then multiple wear tests of 450 h for four kinds of UC24 with different additions are simultaneously conducted under dry sliding and tap water lubrication. The main contents of this thesis are as follows:1. The test rig and measurement methods are improved. The height of sliding plane is adjusted for additive conveyor chains and the width of sliding plane is enlarged for accommodating more wear tests. The measuring bracket is used to keep positions of measured points unchanged. The measuring probe is held on surfaces by a bar. Ultrasonic thickness meter is calibrated by screw micrometer at the beginning of measurement to obtain accurate thickness values.2. Water as an important factor is verified. In confirmation tests wear values of both conveyor chains are higher under water conditions than that under dry conditions, especially for PC23. Water is verified to have a great impact on the wear performance of POM conveyor chains. C1 has a certain effect on wear of PC23 while for PC23 0-gap it has almost no effect, and thus C1 in water is not a major factor.3. Wear trend curves are obtained and wear limits of specimens are established in different cases, dry and water. In terms of wear limits, the sliding wear performances of PC23, PC23 0-gap and UC24 in water are sorted in the following sequence:DM UC24>H1 UC24> DL UC24> HX UC24> PC23 0-gap>PC23.4. Graphs of POM specimens are got and wear morphologies are examined with the help of optical photograph, optical microscope and scanning electron microscope (SEM). The results demonstrate that water results in wear of POM full of parallel deep grooves, compared with slight wear with smooth region and few scratches under dry conditions.5. Wear mechanisms take place on the contact surfaces under dry sliding and water conditions are discussed. The transfer film itself from loss of the specimens materials can resistant wear effectively as solid lubricant on contacting zone between wear pairs under dry sliding. Hence grind and little scratch are wear mechanism of POM conveyor chains under dry sliding. The presence of water tends to hinder the formation of transfer film on counterface. Besides, plasticization of the surface by water enables polymer particles and fibrils to be detached more easily from specimens'materials causing it to be less wear resistant.6. Some suggestions are made to improve wear resistance of conveyor chains in water. Potassium titanate whiskers (PTW), Carbon fibre (CF) and glass fibre (GF) could be reinforced on polymers to improve wear resistance of the composite. It needs further research whether these additions improve the wear performance of POM. Plasticizer could be used less in the production of conveyor chains.7. There are some deficiencies in this thesis and it needs future research. Grooved surface of the specimen has been seen from plane view, and morphology of specimens'cross section needs to be observed so as to get the depth and the width of grooves. Particles from specimens under water conditions need to be examined by TEM to compare with that powder under dry sliding. X-ray photoelectron spectroscopy (XPS) of specimens needs to be performed. Whether the transfer film forms under dry sliding and under water lubrication could be examined by XPS which is usually used for analyzing typical elements on the worn surface. It is still confused why the colors of chain and powder from it are different for DM UC24 and HX UC24. These efforts will help prove reliability of the proposed wear mechanism.