1. Melting, spheroidizing and inoculation treatment
1000kW medium frequency induction furnace is adopted for smelting, and the charge is 90% Benxi pig iron (silicon content is 1.3%) + 10% scrap. The composition of raw molten iron and final composition of nodular iron refer to the actual production of nodular iron parts, and the analysis results are shown in Table 1; The composition of spheroidizing agent is: 10.5% Mg, 1.2% RE, 33% Si, 35% Cu, with the addition amount of 1.5%. It is treated by impulse method, the discharge temperature of molten iron is 1450 ℃, and the inoculant is 75 ferrosilicon.
The chemical composition of raw molten iron and the final composition of nodular iron are shown in the table:
| Ingredients | C(%) | Si(%) | Mn(%) | P(%) | S(%) | RE(%) | Mg(%) | Cu(%) |
| Molten iron | 3.78 | 1.21 | 0.42 | 0.050 | 0.028 | — | — | — |
| Final component | — | 2.31 | 0.44 | 0.052 | 0.020 | 0.020 | 0.056 | 0.51 |
2. Shell (core) making equipment
The first mock exam is made of the K9407EK shell sand casting machine. The left and right two working centers are respectively manufactured for the left and right shell of the crankshaft, the middle is fixed die, and the 2 crankshafts in the first shell type (including risers). When the left and right die shells of the crankshaft are hot, the two half die shells are thermally bonded with a pneumatic bonding machine. The first mock exam is made of six oil plug holes in a mold, and the K9405E core sand machine is used in a domestic factory. The coated sand adopts bagged finished coated sand with high strength and low gas generation.
3. Molding and pouring
Annular closed iron shot molding line. One pouring sand box is placed in each section, and the size of the sand box is 800 × five hundred × 950mm. The process of one box of four crankshafts (two pairs of formwork) is considered in the sand box. The vibrating station is a vibrating platform with vertical amplitude. There are four pouring stations. The ladle capacity is 300kg, and each ladle casts the shell crankshaft in two sand boxes. It is inoculated in the bag. The cooling time of castings in the sand box is 20-30min. The iron shot is used after separation and cooling. Iron shot diameter Φ 5.5、 Φ 4、 Φ 3. The mixing proportion of iron shot particle size is 40%, 30% and 30%.
4. Ductile iron testing
For the inspection of triangular test piece in front of the furnace, in addition to the conventional inspection phenomena such as blunt sharp angle and slight concave on the upper surface, the waist and core shrinkage shall be inspected at the same time, and the rapid metallographic inspection in front of the furnace shall be conducted at the same time. Crankshaft castings are measured by ultrasonic. When the microstructure of cast iron is measured by ultrasonic, the sound velocity of flake graphite is 4500m / s, that of vermicular cast iron is 5400m / s and that of nodular cast iron is 5600m / s. In addition, the type of cast iron can also be judged according to the change of medium and high frequency attenuation rate of cast iron. The central frequency of nodular cast iron is 5MHz and that of flake cast iron is only 1.5MHz.