How to control heat input to reduce stress cracks when welding the NGW31-3.15 planetary reducer frame made of cast iron

Control the welding heat input and reduce stress cracks of the cast iron NGW31-3.15 planetary reducer base, with the core of small heat input+preheating and slow cooling+segmented intermittent+hammering to remove stress+multi-layer and multi pass temperature control, controlling heat and stress throughout the entire process before, during, and after welding.

1、 Before welding: Control heat foundation (reduce temperature difference and rigidity)

1. Selection of welding materials (reducing cracking from the source)

Priority should be given to nickel based cast iron welding rods (ENi CI, such as Z308) or high vanadium cast iron welding rods (Z116), which have good weld plasticity, strong crack resistance, and are suitable for cold welding/low heat input.

Welding rod diameter: 2.5~3.2mm, fine welding rods are easier to control heat input.

Welding rod drying: 150 ℃ for 1 hour, to remove moisture and prevent porosity.

2. Preheating and stress reduction (core temperature difference control)

Hot welding (high requirement/thick wall): Preheat the entire body to 600-700 ℃, maintain the welding process at * * ≥ 400 ℃ * *, and significantly reduce temperature difference and stress.

Semi hot welding (universal): Preheat locally to 200-400 ℃, use oxyacetylene or heating strip, monitor with thermometer, temperature difference ≤ 50 ℃.

Cold welding (repair/no heating conditions): No preheating, but minimal heat input+strict segmentation+hammering is required.

Heating stress reduction zone: Heat the rigid areas on both sides of the weld (300-400 ℃) to allow the weld to contract freely and reduce restraining stress.

3. Groove and cleaning (reducing fusion ratio and impurities)

Create a U-shaped/large angle V-shaped groove (60-70 °) with a thin blunt edge to reduce the depth of fusion (fusion ratio) of the base material and reduce the tendency for white casting and quenching hardening.

Thoroughly polish the groove to a metallic luster, remove oil, rust, paint, and sand holes to avoid cracking caused by impurities.

2、 During welding: precise control of heat input (core operation)

1. Welding parameters (low current, low voltage, fast speed)

Welding rod arc welding (core):

Current: φ 2.5 → 70~90A; φ 3.2 → 90~120A (20-30% lower than carbon steel).

Voltage: 16-19V, short arc (arc length ≤ electrode diameter), heat concentration, small heat affected zone.

Welding speed: 8~12cm/min, fast welding with less heat accumulation.

Heat input control: ≤ 15kJ/cm, formula: Q=(UI × 60)/(v × 1000) (U: V, I: A, v: cm/min).

Gas shielded welding (optional): Use ERNi-CI welding wire, current 80~110A, voltage 18~21V, gas flow rate 10~15L/min, short-circuit transition, low heat input.