Thermal efficiency of heating equipment

There are many heating methods for metal heat treatment. The earliest was to use charcoal and coal as heat sources, and then to use liquid and gas fuels. The application of electricity makes heating easy to control without environmental pollution. These heat sources can be used for direct heating, or indirect heating by molten salt or metal, or even floating particles. The heating temperature is one of the important process parameters of the heat treatment process. The selection and control of the heating temperature is the main issue to ensure the quality of the heat treatment.

In the aluminum strip and aluminum profile production process, the ingot can be hot rolled and extruded to obtain the blank aluminum coil and aluminum profile. In the casting process, although a small amount of grain refiner (Al-Ti-B) can be added to the molten aluminum to achieve the purpose of refining the grain of the ingot, the crystal structure of the ingot is still uneven. This is because the solidification of molten aluminum starts from the inner wall of the mold and expands into the molten aluminum in a direction perpendicular to the cooling surface, so the cast structure has obvious directivity.

The heating temperature varies with the metal material being processed and the purpose of the heat treatment, but it is generally heated above the phase transition temperature to obtain a high-temperature structure. In addition, the transformation takes a certain time. Therefore, when the surface of the metal workpiece reaches the required heating temperature, it must be maintained at this temperature for a certain period of time to make the internal and external temperatures consistent and complete the microstructure transformation. This time is called the holding time. When high-energy density heating and surface heat treatment are used, the heating speed is extremely fast and there is generally no holding time, while the holding time of chemical heat treatment is often longer.

The main heat treatment methods of medium and thick steel plates include normalizing, quenching and tempering (quenching + high temperature tempering), normalizing + controlled cooling, normalizing + tempering, tempering, annealing, direct quenching (DQ), direct quenching + tempering, etc. . Among them, the largest processing capacity is normalizing board, including normalizing + tempering, which accounts for about 70% of all heat-treated products; followed by quenched and tempered board, accounting for about 15%; others such as tempering account for 15%.

There is a huge potential for effective utilization, economical use, and reuse of heat treatment fuel, electricity, water, oil and other resources. The energy of heat treatment heating equipment must be selected reasonably according to local and time conditions. The thermal efficiency of heating equipment has great room for improvement. The waste heat of fuel products must be fully utilized. A large amount of cooling water must be recycled and cleaned from the surface of the workpiece. Grease should be recovered separately, and the failed quenching oil should be collected and refined for reuse or used for other purposes.