Experimental Investigation on Friction Performance of O-ring Used in Compensatory Configuration of Mechanical Seal
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Experimental results of O-ring frictional force under dry friction and water lubrication were obtained using INSTRON,based on knowing the principle of dry friction and water lubrication.The relationship of frictional coefficient with load and sliding speed was analyzed.The results indicated that water film could be developed between contacting surfaces under water lubrication,which led to less frictional force and stability of performance.Keywords:
Dry friction
Coefficient of friction
Static friction
Frictional coefficient
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Friction torque
Silicon rubber
Static friction
Contact area
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Static friction
Dynamical friction
Galling
Normal force
Contact area
Contact force
Dry friction
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The fretting characteristics of the nitrile rubber O-ring for a mechanical seal were successfully simulated by axisymmetric finite element analysis,using the Mooney-Rivlin model with high-order terms.The effects of the displacement amplitude,medium pressure,precompression ratio and friction coefficient were investigated.The results show that three contact states for the fretting characteristics of rubber Oring can be determined,i.e.stick state,mixed stick-slip state and slip state with the increase of the displacement amplitude.The fretting running behavior of rubber O-ring was strongly dependent upon the medium pressure,precompression ratio and friction coefficient.In mixed stick-slip state,the strong fluctuations of frictional force on the sealing interface would weaken the floatability of floating ring.In slip state,the high Von Mises stress may lead to shear failure and severe surface wear.However,O-ring possessed the optimum comprehensive performance when working in stick condition.In a word,to mitigate shear failure and surface wear of O-ring and meet the floatability and tracking property of the seal ring,the mixed stick-slip state should be avoided and a compression of appoximately 10% and a lower coefficient would be preferred.
Frictional coefficient
Coefficient of friction
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Previous research into the friction behaviour of elastomers has typically focused on the effects of velocity, contact pressure, counter surface and lubrication on the coefficient of friction. O-ring type elastomer seals are common in many different industries. Friction plays a critical role during the setting and in service of these components. An experimental O-ring friction testing rig has been developed that can measure the effects of sliding speed and hydrostatic pressure on elastomer friction. Finite element analysis (FEA) packages can adopt fixed friction coefficients or ones that are pressure dependent. For the latter case, the dependence of the frictional behaviour is typically obtained from the instantaneous stress response at any given pressure and then related to the normal force response. The friction rig described in this paper uses industry standard dimensions for the O-ring gland, the pre-compression levels, extrusion gap size and pressure rating. The coefficient of friction is derived by dividing the measured friction force by the normal force, which was determined using an FEA modelling approach, as it could not be measured directly. Finally, a relationship between the frictional velocity and surface roughness is obtained in order to provide a frequency dependent Coefficient of Friction (CoF) that is easily translatable between surfaces.
Hydrostatic equilibrium
Hydrostatic pressure
Frictional coefficient
Hydrostatic stress
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Reciprocating motion
Hysteresis
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Dry friction
Silicone oil
Linear relationship
Linear motion
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Static friction
Reciprocal
Friction torque
Dynamical friction
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For stable frictional torque transfer, wet clutch pads have the functional requirements of a high traction and a low wear rate with positive μ-V frictional characteristics. However, because of the intrinsic negative μ-V frictional characteristics of a friction material that has a static friction coefficient greater than its kinetic friction coefficient, the frictional torque transfer has unstable vibrations during the clutch-pad engagement. To reduce the vibration mode during the engagement of wet clutch pads, the kinetic friction coefficient should be made greater than the static friction coefficient through modifications in the design parameters as well as in the characteristics of the friction materials. To obtain positive μ-V frictional characteristics, it is important to manipulate the static-friction coefficient, which largely develops in the boundary lubrication stage during the clutch-pad engagement. The formation of the boundary film is described by slip boundary conditions and hydrodynamic lubrication films. It also includes the elastic deformation of the wet pad material due to the contact pressure. The wet clutch pad material is made of a porous structure through which the lubricant can easily spread when the applied load and sliding speed are imposed. The lubrication and the direct contact of the surfaces are simultaneously considered for a frictional torque transfer that lasts for less than one second, depending on the working conditions. In this study, some of the computational results with a measured μ-V friction coefficient covering both the static and kinetic friction during the wet-clutch engagement are obtained for the lubrication and the direct-contact pressures.
Friction torque
Normal force
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To determine the friction forces and friction coefficient in dry and lubricated conditions between steel and a triol crosslinked polyurethane, the authors developed a new experimental method consist in sliding of a steel cylinder on a plate polymer sample in the direction of the cylinder axis. By using this method the experiments were realized on a deformed path in the polymer sample by maintaining the same pressure distribution between the contact elements during the experiments. The experiments were realized with normal load between 1 N and 8 N and a cyclic linear speed having values between 1mm/s and 10 mm/s. Were determined the friction forces and friction coefficients in dry and lubricated contacts. An analytical model to evaluate the friction force in the cylinder – polymer contact surface has been developed and a good correlation with the experiments was obtained.
Normal force
Dry friction
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