Quenching of investment precision castings

Quenching of investment precision castings

In the process of investment casting precision casting, sometimes it is not enough to rely solely on the gate for cooling, and additional measures need to be taken to help the gate form a certain solidification sequence, which is called casting quenching.

Casting quenching, as the name suggests, refers to intense cooling. Compared with ordinary air cooling (natural cooling in air), the cooling speed is relatively high. The alloy liquid in contact with the quenched material can quickly solidify, thereby improving the filling capacity (range) of the gate. So, what are the ways of quenching investment castings?

1、 The most common method of quenching is cold iron, which is usually added to thicker parts of the casting. Due to the large heat storage capacity of cold iron, it can quickly form a large undercooling on the surface of the casting, promote the rapid solidification of the casting towards the gate, shorten the distance that needs to be filled by the gate, and form a dense casting to reduce or reduce shrinkage or porosity.

2、 Adding cobalt oxide material to the surface coating of the casting, cobalt oxide decomposes when it comes into contact with the molten metal, resulting in an endothermic reaction and the formation of a cooling layer on the surface of the casting.

3、 Air cooling is used to forcefully cool the parts on the surface of the casting that require quenching with compressed air, forcing the surface of the casting to form a high degree of undercooling to improve the solidification sequence of the casting.

4、 Water cooling refers to placing the parts on the surface of the casting that require quenching in water after pouring. Utilize water to form chilling.

5、 Furthermore, steel sand, silica sand, and other materials are used to bury the parts of the mold shell that have poor heat dissipation (including thick and deep grooves) for pouring. Insert the same material into the interior of the casting, and machine it off after the casting solidifies. The principle is consistent, using high heat storage capacity to enhance subcooling.

Of course, solving the fundamental problem of castings requires effort from the design of the casting structure. Only with a reasonable structure of the casting can casting technicians design a reasonable gating system and thus produce qualified products. As an auxiliary method, quenching can have some effect, but it cannot solve all problems.

Precision machining