Research into the lubrication of a rotary lip seal using ferrofluid

The paper presents the results of research into a hybrid seal which is a combination of standard rotary lip seals and a magnetic fluid seal. To maintain the magnetic fluid in the friction zone region, either a specially shaped pole piece was used or the shaft was modified accordingly. The research study concerns the allowable operating pressure and lubrication conditions in short-term and durability tests after which shaft wear was also assessed. Magnetic fluids with different rheological and magnetic properties were considered. The test results showed that the long-term operation of a hybrid seal is possible. The requirements, however, are the appropriate value of the magnetic field and dynamic viscosity of the magnetic fluid.

How to measure the radial load of radial lip seals

The radial load of a radial lip seal indicates how strongly the sealing lip is pressed on the shaft. The radial load significantly affects the function of the seal. The German standard DIN 3761-9 describes the measurement of the radial load according to the split-shaft method but leaves room for interpretation. During the revision of the standard, a parameter study was conducted at the University of Stuttgart. This study analyses the influence of the measurement device, the mandrels and the measuring procedure on the results. Based on the study results, recommendations are derived and summarized in a best-practice guideline, which should enable an appropriate and reproducible measurement of the radial load.

Numerical Simulation and Experimental Study on Sealing Performance and Frictional Property of Rotary Lip Seal

The hydrodynamic theoretical lubrication model of the friction pair between the rotary shaft and the lip seal under the state of full film lubrication was established in this paper. The Reynolds equation was solved by using the finite difference method, and the influence of the viscosity-temperature characteristics of the lubricant was taken into account in the solution process. The distribution of the film thickness and the hydrodynamic pressure in the sealing area was obtained. At the same time, the bench test was carried out and the correctness of the model was verified by comparing the simulation results and test results of reverse pumping rate and friction torque under different rotational speed of the shaft. The microasperity of the lip surface is a necessary condition for achieving the sealing effect. Therefore, the influences of the contact load of the seal and the root mean square deviation of the lip surface on the sealing performance and frictional property were analyzed by using the theoretical model. The analysis results show that the sealing performance and frictional property can be changed by changing the contact load and surface roughness of the lip, but a single increase in the influence of a certain factor cannot achieve good results, and comprehensive consideration is required in product design.

STUDY OF HERMETIC ABILITY OF A COMBINED FERROFLUIDIC SEALED OF BEARING ASSEMBLIES

The purpose of the research is to increase the efficiency of hermetic ability of bearing assemblies by using com-bined ferrofluidic sealed. The research objective is theoretic justification of the maximum concentration of ferro-magnetic particles in fluid, investigation of hermatic ability of a combined ferrofluidic seal under conditions of tem-perature changing and speed of a shaft rotation of packing bearing assembly. The study of hermetic ability of lip and ferro-fluidic sealed was carried out on a test bench, allowing to determine the packing ability of seals both in static and dynamic mode. On the basis of theoretical data, formulas were determined to find the maximum concen-tration of hard and magnetic phases in a ferrofluid, and its composition based on a polyethylsiloxane liquid PES-5 with a 40 kA/m saturation magnetization and a 1.2 Pas dynamic viscosity coefficient was developed. A mixture of magnetite with powdered iron was used as the ferromagnetic phase. Oleic acid was used as a surfactant. Studies to determine hermetic capacity have shown a higher efficiency of the combined ferrofluidic seal compared to the lip one. During static test within the temperature range between 20 to 600C, the critical pressure difference of the com-bined seal was 4-16% higher than that of the lip seal. Temperature increase of the bearing assembly from 20 to 1200C causes a decrease in critical pressure difference of up to 50%. This is due to a decrease in the sedimentative stability of the magnetic fluid as a result of an increase in temperature. Studies show that the combined ferrofluidic seal has a higher hermetic tightness at the starting torque than the standard lip seal. In contrast to the lip seal (which tends to lose its tightness at the starting torque), no leakage of pressure fluid from the sealed unit was observed of the com-bined ferrofluidic one with a pressure drop of 0.094 MPa. The results obtained allow reasonably select the concen-tration of magnetic particles in the ferrofluid, and also prove the prospects of replacing standard lip seals with com-bined ferrofluidic ones.

Mixed elastohydrodynamic lubrication model of rotary lip seal with non-Gaussian surfaces: experimentation verification and numerical analysis on effects of sealed pressure

Many published models can be used to analyse the sealing performance of rotary lip seal. The surfaces are normally assumed to be periodic variation. However, the quasi-randomness of surface height distribution should be considered, especially the non-Gaussian distribution. Hence, a mixed elastohydrodynamic lubrication model with non-Gaussian surfaces is proposed and used to analyse the effects of sealed fluid pressure on the seal performance in this paper. Based on digital filter and Johnson’s translator system, a rough surface simulation method is introduced to simulate non-Gaussian rough surface. Based on this method the mixed lubrication model with non-Gaussian surfaces is built. The proposed model is verified by comparing the simulation results to experimental observations. Furthermore, it is hardly to find the research focused on the effects of sealed pressure. Hence, the effects of sealed fluid pressure on the seal performance is focused.