Investment casting mold materials
As a profession manufacturer investment casting manufacturer in China, we offer high quality and low cost lost wax parts according to drawing or samples. Based on our many years experiences, we hereby wish to introduce the feature of Investment casting mold materials.
(1) Melting point
The melting point and solidification temperature range of the mold material should be moderate, with the melting point generally ranging from 50 to 80°C, and the solidification temperature of the mold material generally selected to be between 5 and 10°C, in order to facilitate the preparation of the mold material, molding, and dewaxing processes.
(2) Thermal stability
Thermal stability refers to the ability of mold materials to resist softening and deformation when the temperature rises. The thermal stability of wax-based mold materials is often expressed by the softening point, which is the temperature at which the deformation (deflection) of a standard cantilever specimen reaches 2mm after heating and holding for 2 hours. The softening point of mold materials should generally be higher than the temperature of the mold workshop by more than 10℃.
(3) Shrinkage
In order to ensure that the investment mold reaches the desired dimensional accuracy, it is required that the shrinkage rate of the mold material be small, generally less than 1%. The linear shrinkage rate of high-quality mold materials can be as low as 0.5% or less. A small shrinkage rate also results in a small expansion coefficient, which is beneficial for preventing the shell from bursting during dewaxing.
(4) Strength
The mold material should have sufficient strength at room temperature to ensure that the mold will not break or fracture during the production process such as molding and shelling. Usually, when used for small castings, the tensile strength of the mold material should be greater than 1.4 MPa (14 kgf/cm2), and for large castings, it should not be lower than 2.5 MPa. If the mold material is tested for bending strength, it should be greater than 2.0 MPa, preferably 5.0~8.0 MPa.
(5) Hardness
The surface of the mold material should have a certain hardness to prevent damage or friction during production. The hardness of the mold material is usually expressed by penetration (penetration: 1 degree = 1/10mm). The surface hardness of high-quality mold materials can reach 4 to 6 degrees. Of course, if the hardness of the mold material is too high, the finishing property will be poor and it is prone to brittleness.
(6) Liquidity
The mold material should have good fluidity to facilitate filling the molding cavity, obtaining a molded part with clear edges, accurate dimensions, and smooth and clean surface. It is also convenient for the mold material to flow out of the mold shell during the dewaxing process.
(7) Coating property
The mold material should be well wetted by the refractory material and form a uniform coating. The coating property of the mold material can be measured by determining the wetting angle between the mold and the binder.
(8) Ash content
The residue of the mold material after burning is called ash. After the shell is baked, the residual mold material ash remaining in the cavity should be minimized, generally below 0.05% (mass fraction), to avoid affecting the surface quality of the casting.
(9) Weldability
Most investment casting assemblies use welding methods, so the mold material should have good welding performance to prevent the mold assembly from breaking during transportation and shelling processes.
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