Detailed introduction of permanent mold casting process -2
Selection of casting parting surface
There are three types of parting surface: vertical, horizontal, and comprehensive (vertical, horizontal mixed parting, or curved surface parting). The principles for selecting the parting surface are as follows:
1. In order to simplify the structure of the Metal Mould and improve the accuracy of the manuscript, it is better to arrange the castings with simple shape in half mould, or most of them in half mould
2. The number of parting surfaces should be as little as possible to ensure the appearance of castings and the convenience of casting out and down the core
3. The selected parting surface should ensure the convenience of pouring and riser, the steady flow of metal filling, and the gas in the cavity can be discharged
4. The parting surface shall not be chosen on the machining datum plane;
5, try to avoid surface parting, reduce the number of disassembly parts, and live.
Design of casting system
According to some characteristics of metal mold casting, the following points should be paid attention to when designing the gating system: The casting speed of metal is high, which is more than about 20% of the sand mold. Secondly, when the liquid metal is filled, the gas in the mold cavity should be removed smoothly, the flow direction should be as far as possible consistent with the direction of the liquid flow, and the gas should be smoothly squeezed to the riser or outlet, no Swirl, no impact on the wall or core, and no spatter.
The gating system of metal mould is generally divided into three types: top-pouring, bottom-pouring, and side-pouring.
1) top injection type, its heat distribution is more reasonable, is advantageous to the sequence solidification, may reduce the metal liquid consumption, but the metal liquid flow is not stable, easy to enter the method when the casting is high, easy to impact the bottom of the mold glue or the mold core. If used for casting aluminum alloy, generally only suitable for casting height less than 100 mm of simple pieces;
2) bottom injection type, the flow of liquid metal is more stable, which is favorable to exhaust gas, but the temperature distribution is unreasonable, which is unfavorable to the smooth solidification of the casting;
3) side injection type, both the advantages of the above two, metal liquid flow smooth, easy to slag collection, exhaust, but metal liquid consumption, gate cleaning workload.
The structure of Metal Mould pouring system is similar to that of sand mould casting, but because the metal mould wall is not permeable and has strong heat conductivity, the structure of Metal Mould pouring system is required to reduce the velocity of liquid metal flow, smooth flow and reduce the erosion of mould wall. In addition to ensuring that there is sufficient time to remove the gas cavity, but also to ensure that in the filling process shall not produce a spray.
When a metal mold is used for pouring the Ferrous, because of the high cooling rate of the casting and the sharp increase of the viscosity of the liquid flow, the closed gate is usually used, and the sectional area ratio of each part is: F inside: F Transverse: F straight = 1:1.15:1.25