柴油机气门座圈的抗脱落选材和设计研究

Falling-off Resistant Material Selection and Design of Diesel Engine Valve Seats

针对某型强化柴油机中出现的排气门座圈松脱掉落的现象,分析了导致故障发生的原因,并从选材和设计两方面对该问题进行了深入的研究。通过对预选材料——钴基合金、镍基合金和粉末冶金进行材料强度、热膨胀特性、摩擦特性和体积稳定性等方面的试验研究,对各材料气门座圈的抗脱落特性进行了评价;通过有限元计算方法确定了合适的座圈装配过盈量,在保证结构安全系数的前提下提升防松效果;并通过整机试验,对新材料气门座圈的工作可靠性进行了验证。研究结果表明：镍基合金与气门材料亲和力过强,磨损严重;粉末冶金能在较大的装配过盈量下保持较小的最大内应力,但体积稳定性不如钴基合金;钴基合金具有优越且稳定的高温抗压特性和耐磨特性,并表现出很好的体积稳定性和抵御不正常工况的能力。由于新材料抗压特性的提高,可将装配过盈量提高到0.081~0.113 mm,此过盈量能满足缸盖的使用要求,并能保证1.4以上的安全系数。

The falling-off cause of exhaust valve seats in a strengthened diesel engine is analyzed in terms of material selection and design. Three materials,cobalt,nickel and powder based alloy,are tested on their strengths,thermal expansion properties,friction properties and volume stabilities. The assembly interference is considered through FEM simulation,and the engine test is carried out to validate the reliability of the new material valve seat. The results show that nickel-based alloy has the lowest friction property. The volume stability of powder-based alloy is lower than that of cobalt-based alloy. Cobalt- based alloy has the highest temperature compressive and friction properties,and presents a good ability to defend the abnormal operations. Moreover,with the increase in the material strength,the assembly interference could be enhanced to 0. 081 ~ 0. 113 mm,with a safe coefficient of 1. 4 for both cylinder head and valve seats.