For rectangular aluminum melting furnaces, preheating the furnace chamber before startup is a crucial step to ensure production safety and quality.

Preheating the furnace chamber has several important implications. Firstly, the furnace lining material absorbs a certain amount of moisture during manufacturing and storage. If the furnace is heated to high temperatures directly without preheating, the moisture will rapidly vaporize, causing a dramatic increase in volume and generating immense pressure within the furnace lining. This can lead to cracking and spalling of the refractory material, severely affecting the furnace's lifespan and potentially causing safety accidents. Secondly, preheating allows the furnace temperature to rise gradually, preventing uneven heating of different parts of the furnace chamber due to rapid heating, reducing thermal stress concentration, and lowering the risk of refractory material damage. Furthermore, a preheated furnace chamber has a relatively uniform temperature, preventing the molten aluminum from solidifying rapidly due to localized low temperatures, thus ensuring the continuity and stability of production.

Controlling the preheating temperature requires a scientific approach. The preheating process should involve a slow temperature increase.  Too rapid a temperature increase will create a large temperature gradient within the furnace chamber, subjecting the refractory material to significant thermal stress and increasing the likelihood of damage. During preheating, temperature monitoring equipment, such as thermocouples, should be used to monitor the furnace temperature in real time. The thermocouples should be installed in representative locations within the furnace chamber to ensure that the measured data accurately reflects the overall temperature of the furnace. When the furnace temperature reaches 300-500℃, it indicates that most of the moisture has been removed from the furnace chamber, and the refractory material has adapted to a certain temperature change. At this point, the charging operation can begin.

In summary, preheating the furnace chamber before starting a rectangular aluminum melting furnace is an important measure to ensure production safety, extend the furnace's lifespan, and guarantee the quality of the molten aluminum.  Scientifically controlling the preheating temperature is key to achieving these goals.