A study has been made of the influence of minor casting defects on the fatigue properties of cast steel throws for large crankshafts. The rotating-beam fatigue strength of both smooth and notched specimens having diameter of 70 to 100 mm were investigated using a 5, 500 kg-M large-sized fatigue testing machine. The test specimens are cut out from the pin, in the direction parallel with the pin center-line, from two actual size crank throws having more than 650 mm in pin diameter. The cast steel crank throws are made from vacuum degassed steel and heat-treated to the strength level of 50 kg/mm sq. by double normalizing and tempering. It was found that the fatigue strength varied between 16kg/mm sq. and 13 kg/mm sq. according to the number and distribution of pin-holes and shrinkage porosity on the surface of the machined test specimens. The former figure corresponds to a casting having defects of less than 1 mm in dimension, and less than 2 mm in dia. as revealed by the liquid penetration test, the latter figure of fatigue strength namely 13 kg/mm sq. corresponds with the largest defect of 3 mm in dimension by visual test. The corresponding figure for a sound casting was found to be 17 kg/mm sq. to 18 kg/mm sq. using test specimens taken from keel blocks poured from the same melt and, having surface defects of less than 1 mm as indicated by the liquid penetration test. The above figures obtained by us have been used for comparison with those of estimated values of working stress in the fillet area of crankpin and web.
This paper describes experimental investigations about the noise generation and the induced vibration of exhaust gas economizers. Various experiments on actual economizers and models have been carried out, and the following results are obtained. In the economizer a resonance phenomenon of acoustic vibration is induced by vortex streets formed behind each circular tube in the gas stream. Noise or vibration problems in economizers may be encountered in those instances when a natural acoustic frequency of the economizer in the direction normal to both the flow direction and tube length is close to the vortex shedding frequency which is mainly determined from the Strouhal number. Therefore in a rectangular duct such as economizers, the acoustic mode of vibration is transverse across the width of the duct, and the acoustic vibration of the lowest frequency has a wave length equal to twice the duct width. The use of properly spaced baffles between the tube rows at pressure nodes (velocity antinodes) eliminates the vibration almost perfectly. Experiments simulated in a water circulating tank show that the Strouhal number is strongly affected by configurations of multiple tube arrangement. Moreover, several evidences that the vortex shedding from each tube should be definitely related to those from other tubes are obtained.