Dimensional changes in dental plaster during the setting process.
The authors, using an NIN apparatus, examined the dimensional changes occurring in dental plaster during the setting process from its slurry state immediately after being mixed to its solid state, and the following results were obtained : 1) Linear shrinkage that can be seen in the initial stage of the setting process shows a tendency to become larger when the water/powder ratio is increased, and the length of the specimen is shorter. 2) Expansion initiation time shows a tendency to be quickened when the water/powder ratio is reduced, but little difference due to the length of the specimen is recognizable. 3) The apparent linear expansion shows a tendency to become larger when the water/powder ratio is smaller, and when the length of the specimen is shorter. 4) Velocity (time constant) from the beginning of expansion to the maximum expansion is almost constant, being little influenced by the water/powder ratio and the length of the specimen.
Development of measurement apparatus for expansion and shrinkage during setting, using a non-contact micro displacement meter.
Dental plaster and investment are used after being mixed with water or another liquid. Therefore, when they start setting, their condition changes from fluid to non-fluid. In other words, for some time after they are mixed with water or liquid, they look slurry, but as soon as setting begins they cease to be slurry and become solid, while at the same time they start expanding. In order to measure the dimensional change of this kind of material at the time of setting, it is preferable to measure it automatically under a loadless, non-contact condition immediately after it is mixed with water until the time when it has become solid. The conventional apparatus used for this purpose includes the following: comparator [1-4], micrometer microscope [5-8], dialgauge micrometer [1,2,7-20], straingauge extensometer [21,22], cathetometer & photographing [23], electromicrometer [24-28], micro-displacement meter [29-31], optomicrometer [32], etc. However, none of these seem to satisfy, in the strictest sense, the exact measuring condition stated above. Therefore we, the authors of this report, thought of pursuing and examining the actual dimensional change occurring in the mixture of plaster and investment from its slurry to solid condition at the time of setting. First of all, we tried to develop a kind of measuring apparatus which would fit the purpose of our research. We test-developed and examined the automatic measuring apparatus with a built-in, non-contact micro-displacement meter, which we named "NIN Setting Expansion and Shrinkage Apparatus" (which hereinafter we shall call "NIN Apparatus" for short). We actually used this test-developed NIN Apparatus by using for material the
Turbine blade temperature calculation and life estimation - a sensitivity analysis
Abstract The overall operating cost of the modern gas turbines is greatly influenced by the durability of hot section components operating at high temperatures. In turbine operating conditions, some defects may occur which can decrease hot section life. In the present paper, methods used for calculating blade temperature and life are demonstrated and validated. Using these methods, a set of sensitivity analyses on the parameters affecting temperature and life of a high pressure, high temperature turbine first stage blade is carried out. Investigated uncertainties are: (1) blade coating thickness, (2) coolant inlet pressure and temperature (as a result of secondary air system), and (3) gas turbine load variation. Results show that increasing thermal barrier coating thickness by 3 times, leads to rise in the blade life by 9 times. In addition, considering inlet cooling temperature and pressure, deviation in temperature has greater effect on blade life. One of the interesting points that can be realized from the results is that 300 hours operation at 70% load can be equal to one hour operation at base load.