Why does the crusher frame crack?

The Shenyang crusher is primarily used for crushing large materials. Therefore, during construction, the equipment frame is susceptible to damage, and cracking may occur over time. What are the main causes?

1. Low ambient temperature

Because the welding was performed in winter, the ring temperature was below 0°C. Welding at low temperatures increases the tendency for cracks due to the rapid cooling of the weld metal. Q345, in particular, has a higher alloying element content than low-carbon steel and a greater tendency to harden, making it more prone to cracking during low-temperature welding.

2. Crusher electrode drying

The crusher frame was welded using manual arc welding, using low-hydrogen E5016 electrodes. Before welding, the electrodes must be dried at 350°C to 400°C for two hours and then held in a cool, dry place before use. However, tracking the welding process revealed that the electrodes were often dried at a temperature of only around 200°C. This prevented the removal of moisture adsorbed in the electrode coating and the crystallized water within the coating components, increasing the tendency for moisture-induced pores and cracks.

3. Weldment Cleaning

Because the E5016 electrode is sensitive to water, scale, rust, and oil on the weld surface, rigorous surface cleaning is required to prevent pores. However, lax adherence to the process during actual welding can exacerbate the tendency for pores and cracks.

4. Restraint Stress

The main weld seam of the frame is a closed weld, and the welding sequence uses straight-through welding, resulting in high weld stress and restraint stress.

5. No post-heating or hydrogen removal measures

Hydrogen in the weld is the primary culprit for cold cracking in low-alloy, high-strength steel. Preheating and post-heating can reduce the cooling rate and extend the cooling time after welding, allowing hydrogen to be released more fully, thereby reducing the hydrogen content in the weld and minimizing cold cracking and material hardening. Prompt post-heating after welding not only allows hydrogen to escape fully, but also reduces residual stress and the hardenability of the material to a certain extent. Choosing an appropriate post-heating temperature can compensate for the preheating temperature.

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