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1 现象大修柴油机时,在气缸盖上有时常会发现两气阀座口之间(俗称鼻梁区)最易发生裂纹故障。这是由于这一部位受热负荷和爆发压力的影响较大,因此往往会因强度不足而发生龟裂。以4125型柴油机为例,根据有关实际测量方面的科研资料得知,气缸盖底面的温度分布是不均匀的,在每缸活塞凹槽对应的气缸盖底面处温度较高,缸与缸之间的出砂孔和水孔边缘的温度较低。由于温差的存在,相应产生热应力及残余应力,最后必然导致裂纹的出现。浅裂纹能够引起气阀座锥面变形,影响气阀的密封性和导热性。深裂纹如同冷却水套穿通,则就
1 phenomenon overhaul diesel engine, sometimes found on the cylinder head between the two valve seat openings (commonly known as the bridge of the nose) the most prone to crack failure. This is because this part of the thermal load and the impact of the outbreak of a greater impact, it is often due to lack of strength and cracking occurs. Taking 4125 diesel engine as an example, according to the scientific research data about the actual measurement, it is known that the temperature distribution on the bottom surface of the cylinder head is not uniform, and the temperature at the bottom surface of the cylinder head corresponding to the piston groove of each cylinder is higher. The sand and water holes at the edge of the lower temperature. Due to the existence of temperature difference, the corresponding thermal stress and residual stress, the final will inevitably lead to the emergence of cracks. Shallow cracks can cause deformation of the valve seat cone, affecting the valve sealing and thermal conductivity. Deep cracks as the cooling water jacket through, then