Mechanism analysis and process optimization of transverse cracking of hydraulic crushing hammer piston
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摘要:
针对破碎锤中的活塞横裂现象，分析了活塞产生横裂的机理，并提出了一种新的活塞热处理制造工艺。采用硬度计和金相组织显微镜对活塞材料进行分析，得出发生活塞横裂故障部位的材料成分和金相组织符合设计要求，而硬度和硬化层深度低于设计要求。利用ANSYS求解活塞 “卡死”情况下的最大应力为1 229.8 MPa，超出材料的屈服极限850 MPa，最大应力的位置在活塞横裂处；利用Fluent求解活塞所受的径向不平衡力，在活塞的回油槽中受到的最大径向力为3 408 N，最小径向力为10 N，在活塞的进油槽中，最大径向力为15 675 N，最小径向力为73 N。结果表明，活塞在径向不平衡力作用下形成的“卡死”现象是活塞发生横裂的主要原因。提出延长活塞的渗碳时间、增加活塞在热处理过程中的校直次数等热处理新工艺，经耐久实验验证，所提工艺可以有效解决活塞横裂问题。
Abstract:In view of the phenomenon of piston transverse crack in crushing hammer, the paper analyzes the transverse crack of piston, and puts forward a new heat treatment process of piston. The piston material was analyzed by using a hardness tester and a metallographic microscope. It is found that the material composition and metallographic structure at the location of the piston transverse crack failure are in line with the design requirements, while the hardness and hardened layer depth are lower than the design. Using Ansys, the maximum stress of the piston is
1229.8 MPa, which exceeds the yield limit of the material by 850 MPa, and the maximum stress is located at the transverse crack of the piston. Fluent was used to solve the radial unbalance force on the piston. The maximum radial force and the minimum radial force in the oil return groove of the piston were3408 N and 10 N. In the oil inlet groove of the piston, the maximum radial force is15675 N and the minimum radial force is 73 N. The results show that the "stuck" phenomenon formed by the radial unbalanced force is the main reason for the transverse crack of the piston. A new heat treatment process such as extending the carburizing time of piston and increasing the number of times of piston straightening during heat treatment is proposed. The durability test shows that the proposed process can effectively solve the problem of piston transverse cracking.-
Key words:
- hydraulic crushing hammer /
- pistons /
- transverse cracking /
- jamming /
- radial unbalance force
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图 1 活塞与缸体组件的装配三维剖视图
1. 前壳；2. 钎杆；3. 活塞；4. 缸体；5. 油封固定器；6. 后壳。
Figure 1. 3D sectional view of assembly of piston and block assembly
图 5 活塞硬度梯度取样位置示意图
Figure 5. Schematic diagram of the sampling location of the piston hardness gradient
图 7 50倍放大后活塞金相组织图
Figure 7. Piston metallographic structure diagram of 50 times piston
图 8 500倍放大后活塞金相组织形貌图
Figure 8. Metallographic structure and morphology of 500 times piston
图 14 回油槽和进油槽局部放大图
Figure 14. Partial enlarged view of oil return groove and oil inlet groove
图 17 回油槽和进油槽压力云图
Figure 17. Pressure cloud chart of oil return groove and oil inlet groove
表 1 活塞合格金属材质元素质量分数范围
Table 1. Piston qualified metal material element mass fraction range
元素 质量分数 Ni 0.028～0.033 Si 0.0015 ～0.003Mn 0.008～0.012 P ≤ 0.00015 S ≤ 0.0001 Cr 0.014～0.018 Mo 0.004～0.006 
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表 2 活塞正常区域金属材质光谱分析
Table 2. Spectral Analysis of metal material spectrum in the normal area of piston
元素 质量分数 Ni 0.0324 Si 0.0019 Mn 0.0116 P 0.00007 S 0.00006 Cr 0.0173 Mo 0.00587
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表 3 活塞横裂区域金属材质光谱分析
Table 3. Piston cross-crack area metal material spectrum analysis
元素 质量分数 Ni 0.0318 Si 0.0021 Mn 0.0108 P 0.00009 S 0.00008 Cr 0.0175 Mo 0.00584
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表 4 破碎锤参数
Table 4. Crushing hammer parameters
参数 数值 活塞上端直径D2/mm 185 活塞中部直径D/mm 208 活塞下端直径D1/mm 190 钎杆尾部直径D3/mm 125 破碎锤工作压力P1/MPa 28 氮气室的初始容积V/L 24 氮气室的初始压力P/MPa 3.0 活塞质量Mp/kg 284 活塞材料弹性模量E/（N·m2） 2.12×1011 活塞材料密度$ \rho $/（kg·m−3） 7850 活塞打击头直径D4/mm 146
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表 5 网格无关性验证结果
Table 5. Grid independence verification results
网格单元数量 应力值/MPa 2 893 229 457.62 3 170 064 514.68 3 674 387 510.92 4 460 354 356.35 4 699 218 364.33 4 976 105 355.11
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