Chilled iron refers to setting up chillers in the cavity, cavity surface, and inside the mold to speed up the local cooling rate of the casting. The cold iron is used in conjunction with the gating system and the riser system to control the solidification sequence of the castings to obtain qualified castings.

Cold iron is divided into inner cold iron and outer cold iron. The chilled iron placed on the surface of the profile during modeling is called external chilled hard iron. External cooling is used on the side of the casting, which can be divided into two categories: direct external cooling (open cooling) and indirect external cooling (dark cooling or sand separation cooling).

External chill iron is used in a variety of casting materials and casting methods, such as iron castings, steel castings and non-ferrous alloy parts, green sand casting, resin sand casting, shell casting, investment casting, lost foam casting, and V method casting and reverse casting Gravity casting, etc.

1 green sand assembly line modeling nodular cast iron elevator rotor ()

The shaft hole core of the ductile iron elevator rotor (formed by green sand assembly line) is changed from resin sand core to nodular cast iron core (Figure 1), which effectively prevents shrinkage cavity, shrinkage cavity, slag inclusion, water seepage, and other phenomena after casting the shaft hole. Sulfur has achieved good technical and economic benefits.

Figure 1 Ductile Iron Elevator Rotor Shaft Hole Iron Core

2 Resin sand molding servo cylinder ()

The resin sand molding steering machine cylinder () used to be fed by a heating standpipe, but after cooling by cold iron (Fig. 2), the defect of the shrinkage cavity in the seat was solved.

Figure 2 Steering gear cylinder lapped cold iron

When the main body is used to heat the riser, the heat is concentrated at the part where the riser is connected to the casting body, and the solidification is delayed, resulting in low hardness of the casting, poor shape of graphite, and other quality problems. In the past, the main heating riser was used to eliminate the shrinkage defect, and then the cold iron was used to achieve the same effect, and the quality was more stable, so the use of cold iron achieved the purpose of reducing the riser and improving the process yield.

3 Housing Cast heat-resistant steel (1.4837) Turbine housing runner

The heat-resistant steel (1.4837) shell cast heat-resistant steel (1.4837) turbine casing runner is first chilled with end-face chilled iron, and the lap shaft hole after processing has serious shrinkage defects. Subsequent improvements adopted the split type and forming surface type chilled iron process (Figure 3), which solved the shrinkage cavity and porosity problems during the machining of the shaft hole of the grinding tool. However, chilled iron cannot completely solve the shrinkage porosity problem of castings, it can only reduce shrinkage porosity defects, and cannot play a feeding role.

Figure 3 Surface-type chilled iron for lap joint forming of shell casting turbine shell

The principle of solving shrinkage cavity and shrinkage cavity defect is to cool the hot spot rapidly. Generally, cold iron can only replace defects, that is, move defects to non-critical parts, but cannot eliminate defects. Unless there are enough feed channels to achieve sequential solidification, defects can move to the last solidified riser. Most of the split surface chill iron is in contact with the casting belt, and most of the belt is covered by chilled iron, which greatly improves the cooling effect of the casting and speeds up the cooling speed of the belt. After dissection and PT examination, the loose defect of the ratchet wheel had become a small central shaft <Φ0.5 mm. After machining, loose defects have been eliminated.

4 Using the new technology of "casting cold iron" to solve the problem of investment precision casting

The new technology of "casting cold iron" solves the problems of thin-walled and complex castings (steel castings) in precision casting with large hot spots, difficult feeding and forming, and prone to shrinkage cavities and shrinkage defects. The key to this process technology is to place a "casting cold iron" at the hot spot of investment casting to ensure that the cold iron will not be oxidized in a high-temperature roasting environment and will not contact molten metal during processing. pouring.

Process plan and precautions: choose the appropriate cold iron, so that it will not produce scale during high-temperature roasting, and it will be easy to process after casting; it will be oxidized in the environment, and the molten steel will be separated from the cold iron to prevent the cold iron from the molten metal Direct contact prevents cold iron from causing other side effects while cooling and preventing shrinkage cavities. The "cast chill iron" special heat-resistant paint is used to protect the chill iron and prevent the chill iron from oxidation.

The technical characteristics of this process: ①The basic process and characteristics of traditional investment casting are retained; ②A cold iron is set at the hot joint of investment casting to make the molten metal filled in the shell crystallize and solidify in a chilled state, which simplifies Production Process. The gating system of traditional investment casting improves the process yield and casting qualification rate.

This process can be applied to investment casting precision casting of medium and large thin-walled complex castings with hot spots, and the forming effect is very good. Can be used widely.

5 Applied to hanging sand cold iron to produce grinding machine bridge plate castings ()

Tests have proved that the use of sand-hanging cold iron can increase the hardness of the guide rail, and will not produce cemented carbide to affect processing. At the same time, the tendency of the guide rail to loosen is reduced. The sand-hanging cold iron and its manufacture that cause defects such as white holes, pores, adhesion, and short service life are shown in Figure 4.

Figure 4 Hanging sand cold iron and its production

Hanging sand cold perm not only has the effect of cold perm but also eliminates the negative effects of ordinary cold perm. It is economical, affordable, and feasible to produce machine tool castings with large wall thicknesses by using chilled iron with hanging sand. Considering the structure and hardness requirements of the guide rail surface, the thickness of the hanging sand layer is selected to be 8-10mm. Resin sand is used for curing, coated sand is heated and cured, and sand is molded to make cold iron.