6.4. Process Variables

The most important factors involved during sintering process are temperature, time and furnace atmosphere. The influence of these factors on the sintering process is described below:5

Sintering Temperature: Increasing the sintering temperature greatly increases the rate and magnitude of any changes occurring during sintering. Figure 6.2 illustrates the effect of increasing temperature for a constant green density.

Figure 6.2: Sintered density time curves illustrating effects of increasing green density and sintering temperature on densification.

Sintering Time: Although the degree of sintering increases with increasing time the effect is small in comparison to the temperature dependence. The loss of driving force with increasing time at any temperature is one of the reasons why it is so very difficult to remove all porosity by sintering. An attempt should be made to achieve the desired properties of the sintered parts by shorter sintering times and correspondingly higher temperatures. However, the maintenance costs and energy consumption of a furnace increase when its operating temperature is raised.

Sintering Atmosphere: The proper production, use and control of sintering atmospheres which are essential for the optimum use of the powder metallurgy process are described in a later section.