Cause Analysis Of Piston Damage
Regarding the hydraulic breaker, as we all know, the impact piston is indispensable in the list of the most core components. As for the failure of the piston, it is often the most, and generally causes serious failures, and the types of failures emerge in endlessly.Therefore, HMB has summarized several causes of piston failure.
1.Scratches on the working surface,Piston strain crack
The reason:
● low surface hardness
Use a hardness tester to measure the hardness of the core (35 ≥ 45 is the acceptable hardness interval value). If it is lower than 35 degrees or even only more than 20 degrees, large pistons, especially hydraulic breakers with relatively large impact energy, are particularly prone to surface cracks. After cracks appear, the tolerance on one side will expand in tens of wires, thereby destroying the normal gap between the piston and the cylinder, causing serious strain.
● Impurities mixed in hydraulic oil
● The gap between the drill rod guide sleeve (upper and lower bushes) is too large, and the guide sleeve fails.
When the drill rod is working, the axis is inclined. When the piston hits the drill rod, it receives an inclined reaction force, which can decompose an axial force and a radial force, and the radial force can push the piston to one side , the original gap disappears, the oil film is destroyed, dry friction is formed between the cylinder and the piston surface, and the piston surface is scratched as result.
2.piston breakage
The reason:
a. Material problem
The carburized low-alloy steel piston is the internal cause of the impact end face depression and crack cracking.
The hardness difference between the piston striking part and the drill rod’s striking part hardness should be appropriate
b. Heat treatment problem
During forging or heat treatment, the piston material produces cracks, which expand the cracks until they are broken under the action of alternating stress.
3.The piston has a deep pit, and the cylinder body has a point-to-point symmetrical longitudinal strain;
The reason：
a. Entering impurities, causing the piston to lose balance front and rear, with the concept of tilting the head, causing strain
b. Cavitation, cavitation generally occurs in the cylinder, not on the piston. Cavitation will cause a deep black hole, and the excess material in it will be decomposed in the rapid impact of the hydraulic oil, and the entire cylinder will be strained.
c. Rust pits, as shown in the picture are not rust pits. Rust pits are generally caused by the piston material (for example, some manufacturers use 42CRMO or simply use 40CR and other materials due to market pressure) or when storing, they did not pay attention to pushing the piston into the cylinder. In rainy days, Corrosion is caused for a long time, and the yellow rust turns into black rust and finally becomes a pit. Generally, this phenomenon is common for small and micro breakers that start to leak oil before the maintenance period.
original source: https://www.hmbhydraulicbreaker.com/news/cause-analysis-of-piston-damage/
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