Permanent mold casting is a metal casting process using reusable molds (so-called "permanent molds", usually made of metal).
1) metal type has high thermal conductivity and thermal capacity, fast cooling rate, compact casting structure, and about 15% higher mechanical properties than sand type castings.
2) castings with higher dimensional accuracy and lower surface roughness can be obtained and have good quality stability.
3) improve the environment, reduce dust and harmful gas, and reduce labor intensity due to the use of sand cores.
1) the metal mold itself has no permeability, so the air in the mold cavity and the gas produced by the sand core must be derived by certain measures.
2) the metal type is non-yielding, and it is easy to crack when casting solidifies
3) longer metal mold manufacturing cycle and higher cost. Therefore, it is only when mass production is conducted that the economic effect can be shown.
As the metal mold itself is airtight, the exhaust problem of the cavity must be paid enough attention to, otherwise it will cause defects such as pores, cold insulation and undercast.
(1) vent: general in the final filled in the cavity diameter of 1-5 mm circular vent.
(2) exhaust groove: the exhaust groove is also called ventilation groove, ventilation groove, etc. For gas tank depth h, general 0.25 mm for cast iron and bronze, for aluminum alloy is commonly 0.5 mm, width is generally 10 to 15 mm
(3) exhaust plug: the exhaust plug, also known as a vent plug, is generally made of 45 steel or copper bar.
Measures to extend the life of metal forms
1) choose metal materials correctly
2) properly design the metal wall thickness
3) properly design the metal structure to avoid sharp changes in Angle and wall thickness as much as possible.
4) the pouring system should be designed to make the metal liquid enter the mold cavity as smooth as possible to avoid the strong flushing of the cavity working face. As far as possible, the casting system should be designed in the sand core.
5) heat treatment of metal moulds shall be carried out to eliminate casting stress.
6) suitable coatings and correct spraying process should be selected to avoid "thermal shock" as much as possible. Properly preheat and cool the metal mold. Correct timing of casting release.
7) the metal type shall be cleaned carefully and properly kept after use. In order to improve the service life of metal type, some protective measures such as partial siliconizing, chromizing, aluminum infiltrating, anodizing and plasma spraying can be taken.