Effects of re-pressing under high hydrostatic pressure upon the shrinkage and density of sintered VK6 hard alloy blanks
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Hydrostatic re-pressing of preformed blanks can be employed as a means of producing parts of the required shape and size only in those cases where the density of the blanks is evenly distributed through-out their volume. When the distribution of density in the starting blanks is uneven, re-pressing will alter their relative dimensions and change their shape. To obtain parts of the required shape and size from blanks with an uneven distribution of starting porosity, recourse must be had after re-pressing, as in the case of parts produced by ordinary hydrostatic pressing, to machining.
The chief advantages of re-pressing under high hydrostatic pressure are a low value of coefficient of shrinkage after final sintering and reduced distortion of parts.
The density of alloy specimens, as determined by hydrostatic weighing, is virtually unaffected by re-pressing.
The number of large pores substantially decreases as a result of repressing only in specimens presintered at 650°C; with other types of pretreatment, the effect of pre-pressing on the number of large pores is less marked. The least number of pores is found in specimens produced by hydrostatic pressing without a plasticizer.
KeywordsPorosity Shrinkage Hydrostatic Pressure Relative Dimension Uneven Distribution
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