When powders are compressed statically by piston compression the porosity decreases. The process of powder compression indicates various forms as shown in Fig. 1.
As the author maintained in his previous reports15∼20) the relationship between the ratio of the compressed volume C=(V0-V)/V0 and the pressure P is represented in the following equation
C=(V0-V)/V0=abP/(1+bP)
where V0=initial volume of powder, V=volume of powder under static load P, a and b are the characteristic constants of powder.
The a corresponds to the maximum ratio of compressed volume C∞, that is the initial porosity. The b corresponds to the coefficient of compression and has the meaning related to the rheological behavior of the powders. In the case of ordinary powders the a indicates the value 30 to 80%.
From the above equation we get
P/C=1/ab+1/a×P
The plot of P/C against P from this equation will give a straight line of positive slope 1/a, with an intercept 1/ab as is shown in Fig. 3. The applicability of this equation is a very wide range of compression process.
It has been proved that the above equation is applicable to a wide variety of powders and compreses the equation put forward by Athy4). Moreover this equation is better applicable than the equations given by Balshin and Nutting as is shown in Fig. 5.
In the case of tapping compression, if we take the tapping number instead of P, we can find the good applicability of its process as shown in Fig. 6.