A baking furnace is an indispensable device for a process which involves the baking of electrodes of plasma displays or semiconductors or the baking of paste for dielectrics. The construction of a conventional baking furnace will now be described using a sectional view in FIG. 5.
A conventional baking furnace 4 comprises transfer rollers 5, a muffle 6 made of heat resistant glass, a heater 7, a cover, an air feed pipe system 10, an exhaust pipe 11, and an inlet conveyor 15, an outlet conveyor 20.
The muffle 6 is in the form of a flat box rectangular in cross section, extending from the inlet 31 to the outlet 32 of the baking furnace 4. The heater 7 is disposed on the outer periphery of the muffle 6. The air feed pipe system 10 is connected to the muffle 6 to feed air 9 into the latter. The exhaust pipe 11 is a pipe for discharging combustion gases in the muffle 6 to the outside of the baking furnace 4. The muffle 6 and heater 7 are covered by a cover 8. An inlet conveyor 15 is disposed at the inlet 31 of the baking furnace 4 and an outlet conveyor 20 at the outlet 32. Boards 21 supported on support plates 22 enter the baking furnace 4 from the inlet conveyor 15 and are baked as they are transferred in the muffle 6 by the transfer rollers 5 until they are taken out onto the outlet conveyor 20.
The inlet 31 of the conventional baking furnace 4 is positioned on the side associated with a clean room 1. The outlet 32 of the baking furnace 4 is positioned on the side associated with a normal pressure room 2. The clean room 1 and the normal pressure room 2 are separated by a wall 3. The clean room 1 is about 5-10 Pa higher in pressure than the normal pressure room 2.
In such conventional baking furnace 4, since the inlet 31 is disposed on the side associated with the clean room 1 which is higher in pressure than the outlet 32, the difference in pressure between the inlet 31 and outlet 32 of the baking furnace 4 causes the air in the clean room 1 to flow in the muffle 6 from the inlet 31 to the outlet 32 of the baking furnace 4. In the case where the difference in pressure between the clean room 1 and the normal pressure room 2 is 10 Pa, the flow rate of the air flowing in the muffle 6 is 4 m/sec, and in the case of 5 Pa, it is 3 m/sec. Since the cool air in the clean room 1 flows into the baking furnace 4 at said flow rate, the temperature distribution in the muffle 6 varies, presenting a problem that the baking conditions vary to the extent that a baked product of predetermined baking quality cannot be obtained.
For example, in the baking of electrodes for plasma displays or the baking of paste for dielectrics, there arises a problem that the yield of electrodes or dielectrics themselves decreases owing to temperature variations in the muffle 6.
The present invention is intended to solve said problems and provide a baking furnace and a control method therefor, by which a baked product of predetermined baking quality can be obtained.