Annealing muffle furnace gear annealing

The annealing muffle furnace plays a key role in gear annealing. By precisely controlling the heating temperature, holding time, and cooling method, it can effectively eliminate internal stress, refine grain size, and achieve uniform composition in gears, thereby improving their processing and mechanical properties. The following are specific application and process points:

1. The role of annealing muffle furnace in gear annealing
Eliminating internal stress: Gears will generate internal stress during forging and cutting processes, leading to deformation or cracking. The annealing muffle furnace releases internal stress and reduces the risk of deformation by slowly heating to an appropriate temperature and keeping it warm. For example, after annealing, the deformation of large workpieces such as machine tool beds and mold blanks can be significantly reduced.
Grain refinement: During annealing, the grains of gear materials (such as steel) will rearrange to form equiaxed structures, enhancing the toughness and plasticity of the material. For example, after annealing, the elongation of cold-rolled steel plates can be increased, but the hardness may decrease, which is more conducive to subsequent deep drawing processing.
Uniform composition: Annealing can eliminate component segregation in gear materials (such as carbide segregation in steel), make alloy elements evenly distributed, and improve material performance consistency.

2. Gear Annealing Process Flow
Taking the gear rolling cutter made of general high-speed steel (such as M2 steel) as an example, its annealing heat treatment process is as follows:
preheat:
Select a specialized quenching fixture and first dry it in a well type air furnace at around 500 ℃ to remove surface moisture.
Preheat in a medium temperature salt bath furnace at 850-870 ℃ for twice the heating time to reduce thermal stress.
Heating:
The heating temperature is 1225-1230 ℃, and the grain size is controlled at 9.5-10 levels. Overheating of 1-2 levels is allowed to ensure uniformity of austenite.
Cooling:
Pre cool in the air for a few seconds after being fired at high temperature, and then quench.
Gear cutters with a modulus<5 are generally quenched twice at 580-620 ℃ and 450 ℃; Gear cutters with a modulus ≥ 5 are subjected to graded isothermal quenching, which involves first graded in a neutral salt bath at 580-620 ℃ for 2 minutes, and then transferred to a nitrate bath at 260-280 ℃ for 1.5 hours.
Tempering:
Tempering at 550 ℃ for 1 hour for 4 times, isothermal quenching requires 4 tempering times to eliminate quenching stress and improve toughness.

3. Key points for selecting annealing muffle furnace
Temperature range: Select the appropriate annealing temperature based on the gear material. For example, the annealing temperature for carbon steel gears is about 780-820 ℃, for cast iron gears it is about 500-700 ℃, and for high-speed steel gears it can reach 1280 ℃.
Furnace size: The furnace volume should be greater than three times the total volume of the gears to ensure uniform heating of the gears.
Heating element:
Annealing below 1000 ℃: Optional resistance wire heating.
1000-1300 ℃ annealing: commonly used silicon carbide rod heating, fast heating and high temperature resistance.
Annealing above 1300 ℃: requires heating with a silicon molybdenum rod for better stability.
Temperature control accuracy: Choose an intelligent temperature control system with a temperature control accuracy of ± 1 ℃ to ensure stable annealing temperature.
Safety: Equipped with safety devices such as over temperature alarm and power-off protection to prevent accidents caused by operational errors.

4. Application Cases
Automotive gearbox gears:
Material: 40Cr steel.
Process: After carbonitriding, the material is kept at 800 ℃ in an annealed muffle furnace, then quenched and tempered to a depth of 0.25-0.4mm, resulting in an increase in surface hardness and wear resistance.
High precision gears:
Process: Firstly, spheroidization annealing is carried out to improve machinability, and after quenching, the hardness of the tooth surface is increased. Then, the size is stabilized by low-temperature tempering at 260 ℃, and the fatigue life is improved.