Contents of Journal of Mechanical Engineering 60, 1 (2009)

CHOWDHURY, M. A., HELALI, M.: Tribological behaviour of PTFE and rubber 
under longitudinal horizontal vibration                                        1

KUMAR, B. R., RAMANA, K. V., RAO, K. M.: Condition based maintenance and 
fault diagnosis of a booster pump unit                                        19

OTHMAN, A. M.: Economical investigation of pump's regulation field by 
analytical-numerical method                                                   33

TÖKÖLY, P., BOŠANSKÝ, M., MEDZIHRADSKÝ, J.: Usage possibilities of chosen
software for strength analysis of gear teeth                                  49

The paper presents the tribological behaviour of PTFE and rubber under external longitudinal horizontal vibration. Variation of friction coefficient is investigated experimentally when mild steel pin slides on PTFE and rubber. To do so, a pin-on-disc apparatus having facility of vibrating the test samples at horizontal direction was designed and fabricated. Horizontal vibration is created along the direction of sliding (longitudinal direction).
The experimental set-up has the facility to vary the amplitudes and frequencies of vibration while velocity of vibration is kept constant. Studies have shown that the friction coefficient increases with the increase of amplitude and frequency of vibration for above said materials. During the experiment, the effects of duration of rubbing, sliding velocity and normal load are also investigated. The rates of increase of friction coefficient are different for PTFE and rubber. The experimental results are compared with those available in the literature and simple physical explanations are provided.

Condition based maintenance of rotating equipment plays an important role in enhancing the machinery availability, reducing down-time and avoiding catastrophic failure. With the advent of user friendly vibration monitoring instruments available at affordable prices, more and more industries across the globe are adopting to this scientific route to diagnose vibration problems and implement remedial measures in a reasonably short period of time. The present work highlights an experimental investigation to monitor the vibration condition of booster pump unit, which is a part of boiler feed pump train of a large utility thermal power plant. The booster pump is driven by a 3500 kW, 1440 rpm motor. Motor along with booster pump is supported by 4 bearings. Tri-axial measurements have been made at the bearing supports for 12 months. Displacement and velocity are measured along horizontal, vertical and axial directions. The experimental data is plotted on time domain for graphical analysis to ease viewing of vibration signals. Based on the experimental data, faults are diagnosed using ISO standards and causes are predicted. It is observed that the front and rear bearings of booster pump are experiencing excess vibration. The work is concluded by way of suggesting remedial measures to ensure vibration intensity at the said points within safe limits.

Pumps are widely used and they consume about 25 – 35% of the volume power produced. If they operate outside the designed region extra energy is consumed. The pumping system parameters P, Q, H_ST for a given regulation field are investigated and presented in order to predict the most economical running conditions within a certain period of time. The consumed and input power in the economical performance criterion is solved by integration on the basis of static head and flow rate differentiation in order to apply the method to the cases where time changes of static head are dominant and the time changes of flow rate are very small and vice-versa. The input power relation, in economical performance criterion, is also solved by determining the equation of input power curves in the regulation field in three-dimensional form, where P = f(Q, H). The results show that the accuracy of this equation is within ±2.35%. Computer program is developed to calculate the resulting equations for both input and output power. The method is tested and applied to several regulation fields of pumps with variable speed drive. The results show that the calculated values are close to the measured efficiency values within ±2% difference.

In the article, the usage possibilities of chosen software for gear teeth stress analysis by FEM are discussed. The possibilities of convenient usage of CATIA V5 and ANSYS are tested on the basis of chosen gear teeth computer graphics model. Conclusions and recommendations for their use in stress analysis of gear teeth are made according to the obtained results.