Almost all the foundries will encounter casting defects, the common defects include pores, shrinkage holes, slag inclusions and poor spheroidization. What are the causes and solutions of poor spheroidization? Below we will focus on introducing it for you.
Generally, poor spheroidization refers to over-spheroidization or spheroidization recession and gestational recession. There are the causes of poor spheroidization as followings:
(1)The charge is unqualified or quantity large, chemical composition does not meet the require of grade, and there are many impurities and anti-spheroidizing elements.
(2)Improper selection of nodulizer, exit the problem of poor quality or expired or oxidized, small particle size or pulverization, improper dosage etc.
(3)Improper section of inoculant, exit the problems of poor quality and single variety, improper inoculation method, insufficient or excessive inoculum.
(4)Spheroidization temperature is less than 1420℃ or greater than 1520℃.
(5)After spheroidization, the waiting or pouring time is more than ten minutes, resulting in spheroidization decline and gestation decline.
There are two common types of solutions for the poor spheroidization, one is to prevent, and the other is to cure the disease.
The prevent is adopt high standard and correct process method to ensure that the spheroidization is intact and prevent decline. Firstly, choose high quality dedicated high quality pig iron which with high carbon and low silicon, low sulfur and low phosphorus, and less interference spheroidizing elements. Secondly,control the amount of recharge to less than 30% to prevent heredity. Thirdly, select high quality and correct nodulizer and high effective compound inoculant. Fourthly, adopt pretreatment and cover bag treatment. The pretreatment agent always adopt silicon barium, silicon carbide etc, and the amount is 0.3% more or less.
As for cure the disease is taking salvage measures for metal liquids that have been poor spheroidization. There are two ways for the salvage measures.
(1)To connect the high temperature metal liquid, which accounts for half of the ladle capacity. Pour the molten metal into the spare ladle, and add nodulizer and inoculant at the same time.
(2)Add proper amount of nodulizer and inoculant to the first ladle, and then take the high temperature molten metal in the furnace. At this time, quickly poured the two ladle in a short time, but it should be noticed that the temperature of the molten metal in the first ladle should not be lower than 1380℃, and the particle size of the nodulizer and inoculant added in the seconded time is about 5mm.
(3)Finally, test the spheroidization effect observe the triangle test piece and the flame to judge the pros and cons, the flame is better as a candle.
There are many reasons for defects in casting. To solve the casting problems requires rich theoretical base and practical experience. Anyang Huatuo Metallurgy has more than 20 years experience in casting materials, welcome to consult, we will share more experience for everyone.