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Aluminum profile processing annealing is divided into sheet annealing and foil annealing. The purpose of annealing: eliminate cold work hardening in order to continue rolling or deep processing; control the status and performance of the product; remove the rolling oil and improve the surface quality.
According to the production capacity and scale, the aluminum annealing furnace is divided into single annealing and annealing furnaces. The annealing line is generally composed of several annealing furnaces, compound loading and unloading vehicles, furnace material tables and cooling chambers. The furnace adopts a large fan to heat the aluminum material. The guiding device in the furnace can effectively ensure that the airflow passes through the aluminum evenly, making it evenly heated. The heater adopts a top-mounted monolithic structure for easy disassembly and maintenance. The door opening and closing adopts pneumatic pressure-type or mechanical transmission-elevation type, with stable operation and good sealing performance. The fume extraction system of the furnace can effectively remove the oil film on the surface of aluminum and regulate the pressure in the furnace. The furnace charge is generally 10 to 50 tons.
Aluminum annealing furnace is the most widely used equipment in aluminum heat treatment. With the development of technology and the product quality, there higher requirements have been put on the aluminum annealing, such as the consistency of the appearance quality and performance indicators of the annealed products. The appearance quality includes peeling, air bubbles, oil spots, oxidation corrosion and surface finish. Intrinsic quality includes mechanical properties, grain size, anisotropy and other aspects. Except the annealing process and equipment, the before processing of annealing, such as ingredient composition, casting process and cold working rate, also has an important effect on the intrinsic quality of the annealed product.
In order to improve the quality of the annealed product, improvement measures need to be taken in furnace atmosphere, furnace temperature control, furnace type, etc.
1) For some special requirements of the annealed products, oxygen and moisture content of the protective gas can be used as the annealing furnace atmosphere to prevent the oil molecules from cracking during the volatilization process, resulting in hydrocarbons and free carbon particles, oil spots on the surface of the product. At the same time, the thickness of the surface oxide film can be reduced, so that after the annealed, the product original metallic luster is basically protected.
When using protective gas, the furnace first heated to about 150℃, filled with protective gas and then heated. During the heating period, the oil film on the surface of the product volatilizes and is discharged from the exhaust outlet, at the same time, the protective gas is added to maintain the positive pressure of the furnace. After all the oil film is volatilized, high-temperature heating and heat preservation are performed to recrystallize the product in a relatively short period of time and then the temperature is released from the furnace.
2) Vacuum annealing is a relatively new modular aluminium profile processing and annealing technology, which can prevent the cracking, oxidation and polymerization of rolling oil molecules. In vacuum annealing, the furnace is first pumped to a certain degree of vacuum, then heated, and needs to be filled in during the heating process. Protective gas is used to drive out oil and gas, reduce the load on the vacuum pump, and accelerate the convection of heat. At the beginning of cooling, more protective gas is needed to keep the furnace slightly under negative pressure or positive pressure, and the furnace is quickly cooled by convection fans and coolers. Vacuum annealing furnace sealing requires vacuum pump capacity, high requirements for equipment, generally used for electrolytic capacitors, high purity aluminum foil annealing.