Investigation of the wear behaviour of PA 66 mixed MoS2 bearing pulley against coated AISI 1050 work steel

Polymer materials are widely used in the industry along with pairs of polymer and metal parts rubbing against each other to work. Polymer materials and composites, are commonly used in slipping/rolling parts as gears, cams, bearings, power transmission belts that have self-lubricating properties to avoid the lubrication requirement that has problems related to pollution. Plastics are the materials which is cheap, easy to obtain and used in the all field of industry. On the other hand, they become useless by sloughing through wear since they have low strenght. When the contact happens between the reciprocating material pair, friction and wear problems occur. There are three mechanism having a role in polymer wear. These are adhesive, abrasive and fatigue wear. Increasing of the wear resistance and decreasing of the friction coefficient depend on selection of the right material pairs. Wear is defined as the damage on the solid surface with the material displacement or removal by the mechanical effect of the solid, liquid or gas contact. The damage include mostly material removal. Even though there are many wear type and categories defined as a result of studies on wear problem, a certain standard could not be established. The varying from material type, enviroment conditions to operating conditions of the wear mechanisms lie behind failing to create this standard. Corrosion may also be in the factors which is responsible for effecting the wear. Because of the synergistic relations among them, they appear as the factors effecting each other. While corrosion which occurs in the triangle of enviroment, inter surface and material, participate in returning of the materials into their first form in nature as a driving power, the corrosion products composed after the process accumulate on the material surface, dissolve and cause changes in the internal structure of material. That situation generate corrosion damage as the changes of the material surface feature, weight loss and structural discontinuity formation. Breakups on the material surface also pose a problem for the encounterer material surface. In this case, not only the surface corroded but also the encounterer surface is effected by the corrosion damage. That why it is needed to take precautions against corrosion to control the wear. One of the method for precaution against the corrosion is making coating on the surface which has potential to corrosion. In the study, it is aimed to investigate the wear behaviour of Pa 66 mixed MoS2 bearing pulley which is working against to steel coated with different coatings in the elevator door mechanism. Polyamides developed in order to take the place of natural cotton by W.carothers in 1934 is one of today's most widely used engineering plastics. Poylamide applications are desirable for the good sliding friction properties (low friction coefficient), high thermal resistance, good electrical properties, impact resistance, elasticity resistance and dimensional stability against chemicals. MoS2 is a solid lubricant is used to reduce the wear rate and increase the pv limits in nylons and composites. The mission of bearing pulleys in the mechanism is to open and close the elevator door by making both sliding and rolling motion on the lineer rail and simultaneously carry the elevator door panel weight. A double disk test device which had been designed by considering working these functions, was used in this study. The test device was designed to be able to test four specimens simultaneously. The bearing pulleys which was positioned around the 400 mm diameter disc with such an angel 90° among them and contacted to the disc using pneumatic pistons with adjustable pressure settings are able to make both sliding and rolling motion by rotating disc velocity. Sliding distance can be measured using a fixed magnet on the disc with a magnetic sensor showing the number of cylcle in the test device. Several test can be carried out by changing sliding velocity, pressure, pulley material, rail material or geometry. In the study, four different tests carried out with four different coating by keeping pulley material, geometry, rail geometry, sliding velocity and pressure constant. Cataphoresis coating, powder paint coating, galvanized coating and chrome coating were choosen as coating type because of commonly used in industry. The weight loss was measured with a precision scales frequently from the begining to the end of the test to investigate the behaviour of wear and the interface temperature on the contact area was measured using an infrared thermometer. The changing of wear amount and interface temperature with calculating sliding distance using the data taken from the magnetic sensor was shown in graphics. Every test was carried out with constant value of velocity 1,256 m/s and pressure 3 MPa. At the end of the all four test, bearing pulleys reached to 1500 km as sliding distance. The resulting wear rates are 1,69 𝑥 10−9𝑔𝑟/𝑁𝑚, 1,35 𝑥 10−9𝑔𝑟/𝑁𝑚, 0,67 𝑥 10−9𝑔𝑟/𝑁𝑚, 2,38 𝑥 10−9𝑔𝑟/𝑁𝑚 for powder coating, cataphoresis coating, galvanized coating and chrome coating, respectively. The first experiment was performed against powder paint coated disk. Shortly after the experiment began, the powder paint coating started to wear by the bearing pulleys which had harder surface comparing to itself. This situation reflected to the bearing pulleys as abrasive wear effect since it disrupted the powder paint surface sturcture. During the test, the number three bearing pulley had to be canceled by getting damaged in a short time because of the positioning error of the pneumatic arm. At the same time, it was observed several wear mechanisms which effected the bearing surface negatively by reason of disk oscillation in vertical direction and it cauesed to cancel the number four bearing pulley as well. Because of the oscillation gouging wear type was observed in the begining of the test and during the ongoing process galling wear showed up on the bearing pulleys surface. The number one and two bearing pulleys reached up to 1500 km without losing their functionality after all. The second experiment was performed against cataphoresis coated disk by repairing the disk balance. During the test which was observed uniform wear, there were not any gauging wear damage, cracking, pitting wear damage depending on surface fatigue. Instead of these wear damages, cuting and polishing wear damage which caused weight loss was observed in the direction of pulley and disk contact point. All four bearing pulleys reached up to 1500 km without losing their functionality. In the third experiment, the bearing pulleys worked against to the galvanized coated disk. Even though it gave the minimun wear rate comparing to the other coating types, it had the worst wear damage. Even the four bearing pulley reached to the 1500 km, at the end of the test it was concluded that this type of coating was not practical for the system. The fourth experiment was performed against to the chrome coated disk. The maximum wear rate was observed in this test but we have not any information on what type of wear damage occured during the test since it's test data has taken from the previous study. We just can say that it gave the worst wear rate value with respet to the other coating types. As a result, even though chrome coating gave the maximum value after calculating the wear rate, it was observed the cataphoresis coating caused the lightest wear damage on the bearing pulleys.