A creep tempering is done in production process of a spring designed for a fuel-injection nozzle of diesel engine. It is because that creep deformation occurs during use at high temperature and mechanical properties may change. But, conditions (temperature, time) in the creep tempering depend on empirical data that are not necessarily reasonable. In this study, effects of creep tempering on mechanical properties and residual stress of spring are investigated experimentally and theoretically. It is found that shear residual stress increases and spring constant does not so change after creep tempering process. Calculation methods of both shear residual stress and shear creep constitutive expressions of spring are proposed.

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We present a basic idea for the prediction of burner minimum loads for different coal-fired furnaces. Our idea is using the equation expressed by heat loss ratio and radiation intensities. We measured radiation intensities near the burner exit and studied the radiation profiles with decreasing burner load at 25MJ/h single burner test furnace. Radiation intensity decreases with decreasing load and the intensity at the burner minimum load is approximately 150kW/m^2. To get the equation for the prediction, quantities of heat transferred to the flame stabilization region at full and minimum loads are studied theoretically. We compared the decreasing radiation profile with the predicted profile by the equation at 25MJ/h test furnace and got good agreement. Next, we predicted the minimum loads for different types of coal at 150MJ/h test furnace. The assessment using data shows that our equation can be used to predict burner minimum load for the low-stabilized condition from the high-stabilized condition with an error of about 12%.

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