Volume 34, N. 3, September-December 2011 | PDF(9 downloads)
The energy efficiency in SPT is generally evaluated based on the nominal drop height. Measurements of the drop height in systems different from those used in Brazil have shown that the drop height values can be significantly different from the nominal ones, inclusively in those systems where lifting-releasing operations are automatically performed. Measurements of the drop height have been carried out in a manual lifting-releasing pinweight hammer system regularly used in Brazil. The average value of the drop height was 0.79 m, with a standard deviation of 0.03 m and a coefficient of variation of 4%. Only 6 out of the 129 measured values provided drop height values smaller than 0.75 m, which is an indication of the tendency the operator has to lift the hammer above the standard height. The average potential energy error was only 5.1%. The obtained results may be attributed to the crew experience and cannot be considered typical values of Brazilian practice. However, they do represent a condition that can be achieved in practice, provided a proper operation is undertaken. Thus, it must be seen as a goal. The impact velocity of the hammer has also been evaluated from the instrumentation. The average ratio between kinetic energy and potential nominal energy (or e1 value) was 0.74, and 0.70 if the measured potential energy is used instead of the nominal energy. An average value of 0.99 has been obtained for the energy below the anvil and kinetic energy ratio (or e2 value).