Nanjing foundry 530 mm mill used in cast steel casing of clubs and easy to damage the rolls and the plum blossom shaft head and make the scrap, and even in extreme cold steel make roll twist off overload situation.
Based on the characteristics of the ductile iron itself decided to use ductile iron instead of cast steel production plum casing.
There are many factors affecting the stability of as-cast ductile iron production, to stable production of nodular cast iron, must grasp well in the production of the following: the stability of the chemical composition and temperature of molten irons, accurate amount of iron liquid, suitable spheroidization and inoculation methods, and reliable in front of the furnace control.
1 equipment selection 1.
1 melting equipment selection melting equipment selection of first is on the premise of meet the needs of the production, follow the principle of high efficiency, low consumption.
The advantage of induction furnace is: fast heating, higher thermal efficiency of the furnace, the oxidation burning loss is lighter, less absorbing gas.
With intermediate frequency electric furnace smelting, therefore, can avoid increasing sulfur, phosphorus, P in the molten iron is not greater than zero.
07%, S no greater than 0.
2 the determination of spheroidizing package in order to improve the absorption rate of nodularizer, increase the balling effect, spheroidizing bag should than ordinary iron liquid bag.
Spheroidizing package as 2:1 ratio of height to diameter.
Option 2 2 raw materials.
1 choose ductile iron burden of nodularizer to join effect on condition that: high carbon and low silicon, inoculation amount.
To stabilize the chemical composition and controlled effectively promote white elements and anti-spheroidizing elements, and guarantee the quality of melting molten iron, choose zhang gang Z14 pig iron, its chemical composition: C>
25% ~ 1.
2 the selection of the choice of nodularizer nodularizer should according to the different of smelting equipment, namely the tapping temperature and the purity of iron liquid (
Such as sulfur content, degree of oxidation, etc. )
The most commonly used in our country is rare earth magnesium ferrosilicon nodularizer, adopt the nodularizer processing, due to higher silicon content in the alloy, can significantly reduce the intensity of magnesium processing.
At the same time can also be due to the increasing silicon some role.
Electric furnace production, due to the relatively high temperature, the chemical composition of the ball, agents are shown in table 1.
Table 1 nodularizer FeSiMg8Re7 chemical project the tapping temperature / ℃ S % % composition of nodularizer/Mg Re Si electric furnace of 1420 ~ 1480 & le;
0 ~ 9.
0 to 8.
03 furnace control before 3.
1 chemical composition choice ductile iron liquid iron should be high carbon, low silicon, low sulfur, low phosphorus.
Good control of sulfur content, is an important condition for the production of ductile iron.
The chemical composition of several grades of ductile iron are shown in table 2.
2 spheroidization and inoculation should be according to the iron liquid composition for the amount of nodularizer, casting
wall thickness and composition of nodularizer and spheroidized absorption rate and other factors in the process of analysis and comparison.
The general is 1.
6% ~ 2.
0%, if the nodularizer placed for a long time, should be a little more.
Ball reaction control is the key to the magnesium absorption rate, high temperature, the violent reaction, time is short, magnesium loss, spheroidizing effect is poor;
Temperature is low, steady, long time, magnesium absorption rate.
Therefore, generally on the premise of guarantee enough pouring temperature, should as far as possible reduce the spheroidizing temperature, control in 1420 ~ 1450 ℃.
Nodularizer to hit into small pieces and granularity in 5 ~ 25 mm, commonly in the bottom of the bag, then in the above plus silicon and iron.
Inoculation treatment is an important part of the process of ductile cast iron production, which not only promote the graphitization, prevent free cementite and white, but also help the ball, and make graphite becomes smaller, more rounded, uniform distribution, so as to improve the mechanical properties of nodular cast iron.
Inoculant using FeSi75 more commonly, its addition amount according to the requirements on the mechanical property of casting, general is 0.
8% ~ 1.
Inoculant granularity according to how much quantity of iron liquid, usually to smash into 5 ~ 25 mm small pieces.
Inoculant should maintain clean, dry.
Nodularizer and inoculant to iron out before joining package, in the continuous production, just after the previous furnace iron, bag is very hot, too early to join will make its bond to the bottom of the bag and weaken the spheroidization and inoculation effect.
To spheroidization response delay time, strengthen the spheroidization and inoculation effect, inoculants in nodularizer and covered with a layer of iron filings.
Spheroidizing method is more, more commonly used simple operation into the method and treatment of ductile iron.
3 before furnace spheroidizing effect inspection before furnace inoculation, spheroidizing effect is good or bad, generally USES triangle sample.
Pouring triangle sample, cold and dark red, quenching water cooling, at the final observation of fracture.
Fracture silvery white, white tip, the center has a loose, concave on both sides, you have calcium carbide smell crushed, at the same time, the tapping and steel are similar, the spheroidizing is good, or bad nodulizing.
4 casting due to the ductile iron liquid prone to spheroidizing recession, as a result, liquid iron as soon as possible after spheroidizing pouring, pouring completed within 15 min after processing, spheroidizing recession there will be no problem.
4 knot in production, using # Z14 pig iron as raw materials, intermediate frequency induction furnace hot metal melting, chemical composition control is: the C3.
5% ~ 3.
2% ~ 1.
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