6.10.1 Batch-Type Furnaces

Batch-type furnaces are used for sintering in protective atmospheres when the quantities produced do not warrant installing continuous furnaces. A typical box-type sintering furnace is shown in Fig. 6.15, which is similar to pusher-type continuous furnaces except that the boats are stoked through the furnace by hand rather than with a mechanical stoker.

Figure 6.15: Box-type, manually operated sintering furnace.3

Small pilot plant or laboratory muffle furnaces are similar to box furnaces. Heating through a muffle is less efficient than having the electric heating element exposed to the furnace atmosphere and furnace chamber. Full muffle furnace reduces the need for the flow of atmosphere purging gas, particularly while using expensive gases like hydrogen or dissociated ammonia.

In addition to box-type furnaces, bell-type furnaces are also used for batch-type sintering of metal powder compacts, particularly in cases when very good atmosphere control is required. Figure 6.16 shows a typical bell-type furnace. The compacts are arranged on a load supporting base with a removable sealed retort over the load to contain the protective atmosphere. A portable heating bell is lowered over load and retort for the heating cycle.

Figure 6.16: Bell-type sintering furnace showing stationary bases, retorts and heating bell.3

6.10.2 Continuous Sintering Furnace

Most sintering furnaces are used for large volume production work and are of the continuous type, that is...