Page 151 - Module DMV20173

8.0 POWDER PROCESSING

9.2.3 SINTERING

1. The last process is sintering, the process after pressing, the purpose of this process

in improve strength and hardness of green compact.
2. This green compact is easily crumbled under low stress.
3. Sintering is a hear treatment operation performed on the compact to bond its metallic
particles, thereby increasing strength and hardness.

4. Since powder metallurgy application is usually involve medium to high production,
most sintering furnace are designed with mechanized flow-through capability for the
work part.
5. The process of heat treatment consists of three steps where the furnace is
segregated into three chambers according to respective process:

a. Preheat, in which the lubricants and binders are burned off.
b. Sinter.
c. Cool down.

Typical sintering temperatures and times are given for the selected metals in Table 8.1.

Table 8.1 Typical sintering temperature and times for selected powder metals.
Metal °C Time (min)

Brass 850 25
Bronze 820 15
Copper 850 25

Iron 1100 30
Stainless steel 1200 45
Tungsten 2300 480

6. In modern sintering process, the atmosphere in the furnace is controlled. The
purposes of requiring controlled atmosphere:
a. Protection from oxidation.
b. Providing a reducing atmosphere to remove existing oxides.

c. Providing a carburizing atmosphere.
d. Assisting in removing lubricants and binders used is pressing.

7. Common sintering atmosphere are inert gas, nitrogen-based, dissociated ammonia,
hydrogen, and natural gas based.

8. Vacuum atmosphere are used for certain metals, such as stainless steel and
tungsten.

BPLK 183 DMV 20173