Aug 14, 2017

What are the stresses in the Product Filtering System during heating and cooling?

In the continuous hot galvanizing line, the Product Filtering System undergoes the process of heating, cooling, galvanizing, post-plating cooling - series of organizational changes and performance changes, and there are various tensile and bending stresses. Experienced a series of changes in thermal stress, phase transition stress and mechanical stress. The original cold plate deformation and stress will change, on this basis will produce new deformation and stress. In contrast, the thermal stress has the greatest effect on the shape of the plate, followed by the mechanical stress, the phase transition occurs at high temperature, the effect of phase change stress is not too great.

For Product Filtering Systems, if the same temperature is maintained throughout the width direction during heating or cooling, i.e., heating or cooling at the same time, no new stress is generated. But in fact, the product filter system and the central part of the two parts of the heating or cooling is always uneven, the temperature difference. This phenomenon, although no actual measurement of the data, but can be learned from the analysis, but also from the furnace annealing of the Product Filtering System confirmed the form. The main reasons include the unevenness of the gas temperature in the furnace and the thermal effects of the edge of the Product Filtering System during heating or cooling.

In general, there are thermal stresses and residual stresses (collectively referred to as secondary stresses) in heated pressure vessels. Since the j integral of Rice is no longer independent of the integral path in the presence of secondary stress, and the size and analysis of the welding residual stress are quite difficult, the secondary stress is the self-equilibrium force and the elastic-plastic fracture in the presence of secondary stress Analysis is also quite difficult.

In recent years, considering the existence of secondary stress fracture analysis technology has been greatly developed, and the method of failure assessment method for the simultaneous application of secondary stress load situation. For example, the new R6 used in considering the secondary stress of the engineering method. It is in the A reference stress method of the expression of the introduction of the impact of secondary stress, and from the use of engineering considerations, even if there is secondary stress, still use no secondary stress when the failure of the assessment curve, no longer engage in another A set of failure assessment curve, and the introduction of a plastic correction factor ρ to compensate for the engineering method, according to the results of the derivation and the appropriate simplified given by the secondary stress intensity factor and the mechanical load stress intensity factor ratio and mechanical load close The degree of plastic yield load L determines the graph of ρ.

At present, the engineering regulations for fracture assessment, such as the new PD6493, the new IIW file, and the Swedish specification, have adopted the new R6 method to consider the secondary stress method, which has been used in the 1970s. (Eg 60%) of the secondary stress as the equivalent stress, and then the stress treatment of the secondary stress treatment.

The nonuniformity of the Product Filtering System in the thickness direction will result in bending and bending stresses in the Product Filtering System. The Product Filtering System can be divided into two parts of the upper and lower layers. If the length of the upper part of the Product Filtering System is larger than the length of the next, the upper compressive stress and the lower layer are subjected to tensile stress when the stress is large enough to deform the Product Filtering System , The Product Filtering System is raised upwards, and we call it a positive bend. On the other hand, if the length of the upper layer of the Product Filtering System is greater than the length of the lower layer, the upper layer is subjected to tensile stress and the lower compressive stress, and when the stresses are large enough to deform the Product Filtering System, the Product Filtering System is recessed down Negative bending.