Production process of casting defects in nodular cast iron roller

The basic structure of roller casting includes barrel and shaft head, which is in the shape of revolving body. The barrel is mostly of double wall structure, as shown in Figure 1. Material grade QT500-7, overall dimension φ 420 mm × 2 500 mm, wall thickness of cylinder body 20 ~ 40 mm, shaft head φ 140~ φ 190 mm steps.

Technical requirements:

(1) The wall thickness should be accurately controlled, and the shaft heads at both ends should be concentric with the cylinder body, otherwise the rotation balance of the drum will be affected;

(2) The shaft head is not allowed to have shrinkage defects, otherwise the strength performance of the drum will be affected;

(3) Inclusion and porosity are not allowed in castings.

Using furan resin sand manual molding core making process, the tensile strength of molding sand and core sand 8-shaped test block is 0.8 ~ 0.9 MPa and 0.9 ~ 1.0 MPa respectively, the width of sandbox belt is 100 mm, the width of reinforcing rib around sandbox is 80 mm, and the spacing is about 600 mm. The single weight of the roller is mostly 400 ~ 900 kg. In order to reduce the sand iron ratio and improve the process yield, the molding process of one box of 2 pieces is adopted, the transverse runner is in the middle, the two castings are symmetrically distributed, and 120 mm is placed on the ceramic tube of the inner runner × 120 mm filter screen, the layout of plate is shown in Fig. 2.

(a) Upper type
(b) Hypo type

The semi open and bottom pouring system is adopted, and the runner ratio is 0 Σ F straight: Σ F horizontal: Σ Fner = 1.3:1:1.5, the section area of the sprue is 5024 mm2, the section area of the transverse sprue is 3850 mm2, and the section area of the inner sprue is 5880 mm2.

The end faces of shaft heads at both ends are respectively made of φ 100 mm × 300 mm heat insulation riser, riser neck 80 mm × 20 mm × 40 mm. There is no chill on the cylinder body, and special shaped cast iron chill is placed on the shaft heads at both ends and the joint part of the shaft head and the cylinder body. The casting process is shown in Fig. 3.

Pouring temperature is 1 350 ~ 1 370 ℃, pouring time is 55 ~ 65 s, furnace temperature is 1 500 ~ 1 520 ℃, adding amount of spheroidizing agent with 5% w (mg) is 1.3%, and the spheroidizing process of injection method is optimized.