Effects of the radial force on frictional characteristics of polyurethane rotary shaft seals

Sealing is the control of fluid interchange between two regions which share a common boundary. In order to control this fluid interchange, leakage components are used in mechanical engineering. Leakage components play a crucial role in the proper functioning of machines and tools. Although, the sealing mechanism of the leakage components is studied for many years, the subject is still an unsolved problem. Rotary lip seals are most used widely the machine industry in order to prevent leakage and exclude contamination since they have many advantages. There are many parameters which affect the performance of radial lip seal performance. The radial force is one of those factors and is related to the leakage and wear. It is therefore important to investigate the radial force effect on sealing performance in order to improve seal design. The radial force is generated by two different factors. Those factors are garter spring and elastomer component of the seal. The half of the total radial force is produced by garter spring and the other half is produced by elastomer deformation which occurs because of the interference between the elastomer ring and the shaft. In this thesis firstly, the sealing problem is defined. The basics of seal design are explained. Later on, leakage components are introduced and rotary lip seals are mentioned in details. Steel frame, garter spring and elastomeric component of radial lip seals are examined. Different rotary lip seal designs are introduced for different applications. In addition, the sealing mechanism of radial lip seals is explained. Micro and macro sealing mechanisms are examined. Especially, micropumping is explained in details. Moreover, the parameters which affect sealing performance of rotary lip seals, are referred. Beside of explaining the effect of radial force, interference effect is also explained in details. In the end, experimental set up which is developed in order to investigate interference effect is introduced. Test conditions are explained. Results are mentioned and analyzed. The purpose of this study is to investigate the effect of radial force produced by interference on the static contact properties and frictional characteristics of a radial lip seal by experiments. For this reason, a test system has been developed. In this test system a cylinder is placed on four load cells in order to monitor the moment generated between seal and counterface. Thermoplastic polyurethane and its two different versions; hydrolisis resistant thermoplastic polyurethane and self-lubricated thermoplastic polyurethane are selected as the seal material. Instead of standard inner diameters, custom-made radial lip seal samples are ordered. Therefor three different inner diameters (40, 39,80, 39,60 mm) are selected for each elastomeric material. Two groups of experiments are made and 27 samples are tested under room temperature. The test conditions are determined for the first group of experiments as follows: • The speeds are chosen as 1, 3 and 5 m/s. • The seals are tested under 0,5 and 0,3 bar for a short period. During the second group of experiments, the frictional torque is measured compared for different inner diameters. The effect of speed, pressure, material and interference are investigated. For the second group of experiments, test conditions are determined as follows: • The seals were tested for 10.000 meter rotating distance • The system pressure is selected to be 0,3 bar during tests. During the second group of experiments, oil leakage observation and torque measurement was made. The effect material and interference for long rotating distances are investigated.