The Operation And Precautions Of Flame Heating Surface Quenching

Preparation before quenching

• 1. The workpiece must undergo pre-heat treatment such as quenching and tempering, normalizing, etc.
• 2. The surface of the workpiece is not allowed to have oxide scale, dirt, oil stains, etc.
• 3. The workpiece with severe decarburization, cracks, blisters and pores on the surface cannot be flame quenched

Flame preheating

Cast steel, cast iron, alloy steel can be slowly heated to about 300~500ºC with a quenching nozzle with a small flame to prevent cracking.

The quenching temperature of steel parts is Ac3+(80~100ºC), and the quenching temperature of iron castings is 730ºC+28×ωSi ºC -25×ωMnºC.

Flame intensity:

• 1. Commonly used fuel gas is acetylene and oxygen, and the ratio of acetylene to oxidation is 1:1.5~1:1.25.
• 2. The oxygen pressure is 0.2~0.5MPa, and the acetylene pressure is 0.003~0.007MPa (the pressure of the float-type acetylene generator is 0.006MPa). Generally, it is better for the flame to be blue and neutral.
• 3. The working pressure of coal gas is 0.003MPa, and the power of propane gas is 0.005~0.01Mpa.

Distance between flame and workpiece:

• 1. Shaft workpieces are generally 8~15mm, the lower limit for large pieces is closer, and the upper limit for small pieces with complex shapes is farther.
• 2. When the gear with modulus less than 8 is heated and quenched at the same time, the distance between the nozzle flame center and the tooth tip is preferably 18mm, and the circular linear velocity of the gear is less than 6m/min.
• 3. When the single tooth of the gear is quenched sequentially, the distance between the flame center and the tooth surface is 2~4mm.

Nozzle or workpiece moving speed:

• 1. Rotation method: linear speed is 50~200mm/min
• 2. Advance method: linear speed is 100~180mm/min

Distance between flame center and spray hole:

• 1. Continuous quenching: 10~20mm, too close, water is easy to splash and fire. Too far, insufficient or too deep hardened layer.
• 2. The water spray column should be inclined backward by 10º~30º, and there should be a partition between the water spray hole and the fire hole.

Quenching medium:

• 1. Tap water, the water pressure is 200~300kPa.
• 2. For alloy steel parts with complex shapes, use 30~40ºC for 1.5~2h, and large workpieces can be tempered by themselves (cold to about 300ºC).

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