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What are the key to improving the quality of casting?
Currently most of the gray iron casting machines for quality gray iron castings, from the chemical composition, quality of raw materials, ingredients, alloying, melting temperature, thermal aging inoculation until environmental strictly controlled.
1, melting link
1) carbon equivalent. Should adopt a higher carbon equivalent, HT250, to 3.95 as well; HT300, with 3.82 as well; HT350, with 3.76 as well.
2) silicon-carbon ratio. Suggest the best control in the silicon-carbon ratio 0.55-0.62.
3) alloying control. Alloying elements beneficial to improve casting performance, generally w (Cu) 0.4-0.6% or w (Cr) 0.2-0.4%.
The amount of iron to be added is less than 10%, while high scrap, high carburizing, graphite such good quality.
3, the temperature of molten iron
High temperature of molten iron can be refined graphite, is the basis of equivalent carbon, high strength gray cast iron. Molten iron temperature 1500-1550 ℃, the liquid iron oxide will be reduced significantly reduce SiO2 ash.
The method is more important than the birth of inoculant efficient, according to the actual situation, and strive to adopt stream inoculation, pouring cup bred, floating silicon gestation, birth and other endo instantaneous birth methods to ensure the quality of birth. Triangle specimens should be used, thermal analysis curves, cooling degree than before and after birth to test the inoculation effect, both to prevent cold graphite shortage caused by birth, but also to prevent pregnant casting caused by excessive shrinkage.
5, performance testing
Strengthen the attached performance testing and test bars cast microstructure, while in particular to strengthen the metallurgical cold graphite, carbides and pearlite test, improve casting metallurgical quality to maturity> 1, hardening <1, Quality factor> 1.
6, thermal aging
1) heating rate should be slow, generally (30-50) ℃ / h is appropriate.
2) the annealing temperature should be 500-550 ℃, holding time to burn through 25mm per hour is calculated.
3) furnace temperature control maintained at ± 20 ℃.
4) order after thermal aging should prevent roughing to eliminate processing stress.