Introduction to Machine Tool Castings

Machine tool castings can also be called large castings.

I. Machine tool bed standard: GB9439-88

II. Characteristics of the bed:

(1) Good wear resistance and shock absorption. Since graphite in cast iron is conducive to lubrication and oil storage, it has good wear resistance. Similarly, due to the presence of graphite, the shock absorption is better than steel.

(2) Good process performance. Since gray cast iron has a high carbon content and is close to the eutectic composition, it has a relatively low melting point, good fluidity, and a small shrinkage rate, so it is suitable for casting complex structures or thin-walled castings. In addition, since graphite makes it easy to form chip breakage during cutting, the machinability of gray cast iron is better than that of steel.

3. Relationship between hardness and tensile strength: There is a certain corresponding relationship between the hardness and tensile strength of gray cast iron, and its empirical relationship is:

1. When O≥196N/mm㎡

HB=RH(飞00+0 4380b)(B1)

2. When 0≥796N/mm㎡

HB=RH (44+O 7240b) (B2)

The relative hardness (RH) value is mainly determined by the raw materials, melting process, treatment process and cooling rate of the casting.

4. Advantages of using resin sand mold to cast machine tool bed castings

1 The resin sand mold has good rigidity and high strength in the initial casting stage. This makes it possible to use the graphitization expansion of cast iron during solidification to effectively eliminate shrinkage cavities and shrinkage defects, and realize the casting of gray cast iron and ductile iron parts with few or no risers.

2 In the production of solid casting, polystyrene foam molds are used to apply furan resin self-hardening sand molding. When the molten metal is poured into the mold, the foam plastic pattern is rapidly vaporized and burned by the high-temperature molten metal, and the molten metal replaces the original position occupied by the foam plastic, cools and solidifies into a solid casting with the same shape as the pattern.

3 Relatively speaking, lost foam casting has great advantages over traditional sand molds for the production of single or small batches of automobile covers, machine tool beds and other large molds. It not only saves the expensive wooden mold costs, but also is easy to operate, shortens the production cycle, improves production efficiency, and has the advantages of high dimensional accuracy, small processing allowance, and good surface quality.