Classification and Methods of Shrinkage Defect Control
# 05, May 2016
1 Bauman Moscow State Technical University, Moscow, Russia
The objective is to put forward a proposal to divide the internal shrinkage defects into the dimensional levels according to defects of certain size and shape.References
The paper presents the terminology used to describe the internal shrinkage defects in the casting and shows its flaws. These include the lack of well-defined threshold size values and shape of defects. It is shown that in describing defects their sizes and shape are defined qualitatively rather than quantitatively. And it is noted that division of defects into pores and shells is based on the morphological characters.
The paper notes that a distinct difference between defects is necessary because of different methods of their elimination from the casting body.
The paper presents an overview of control methods to determine the defects of the shrinkage nature in castings. These are methods of destructive and non-destructive testing, such as X-rays, tomography, and metallography. The paper also shows advantages and disadvantages of the considered methods of control. Based on the control method capacities it offers to divide the shrinkage defects into the three dimensional levels.
To estimate the shape of defects the paper suggests a new option, that is a shape criterion. By the example of the typical defects of each dimensional level are defined the threshold values of the shape criterion.
The paper discusses the basic techniques to estimate the porosity and offers a relationship between the defects of different dimensional levels and a porosity score and percent. It shows that the transition from a dimensional level to another one is in line with not only increasing pore size, but also with a significant deterioration of the mechanical properties of castings.
The main conclusions are as follows:
1. At present, there is no single unambiguous classification of casting shrinkage defects in the technical literature.
2. As follows from the analysis of the classifications of shrinkage defects, their control and estimation methods that there are three dimensional levels proposed, with each one corresponding to defects of a certain size and shape and methods of their control.
3. A common approach proposed to estimate the castings porosity for various control methods is to define a percent of porosity.
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