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高负荷发动机中,由于热交变负荷较大,气缸盖承受的应力,已进入疲劳强度范围。因此,事前必须估计到,气缸盖使用一定时间后,就会断裂而损坏,故而采用球铁或铸钢已属必要。但铸钢成本太高,且不能保证铸件的气密性,而球铁由于传热性能较差,也不理想;只有蠕墨铸铁较好,它和球铁和片墨合金铸铁相比,铸件缩松倾向较小。蠕铁的石墨介于片状和球状之间。按德国钢铁检验标准,蠕铁石墨应属P型,或相当于德国铸造协会(VDG)441号标准中订定的Ⅲ型。目前较保险的生产方法,可按Leoben/Breman-ger铸造所的专利法进行。该法的先决条件是采用低磷、低锰、低硫的生铁,加入的废铁量不得超过20％。生产球铁的孕育方法对蠕铁也能适用。铁水的处理(去
High-load engines, due to the larger heat exchange load, the cylinder head to withstand the stress, has entered the fatigue strength range. Therefore, it must be estimated in advance, the cylinder head after a certain period of time, it will be broken and damaged, so the use of ductile iron or cast steel is necessary. However, the cost of the cast steel is too high, and the gas tightness of the castings can not be guaranteed. However, the ductile iron is also not satisfactory due to the poor heat transfer performance. Comparing with the ductile iron and the flaky graphite alloy cast iron, Less tendency to shrink. The graphite of vermicular iron is between flake and sphere. According to the German steel inspection standards, graphite iron oxide should be P type, or equivalent to the German Foundry Association (VDG) 441 standard set in Type Ⅲ. The currently more insured production methods can be carried out according to the patent law of Leoben / Breman-ger foundry. The prerequisite for the law is the use of low phosphorus, low manganese, low sulfur pig iron, iron scrap added to the amount of not more than 20%. The method of producing ductile iron can also be applied to vermicular iron. Hot metal treatment (go