Permanent molds use cast iron or steel machined molds t […]
Permanent molds use cast iron or steel machined molds to produce large quantities of repeatable parts. In contrast, the casting and casting molds are destroyed during the parts removal and die-casting process, and the molten metal is injected into the mold at very high pressure. Thus, the mold must be designed to withstand these pressures, which significantly increase the cost compared to the gravity-filled permanent mold.
Permanent castings can be made to have uniform nonporous microstructures, but these qualities are highly dependent on the cure rate and casting tool design. Mold must be carefully designed, gates, vents and risers are working together, so the metal in the smooth flow of complete filling mold.
The design and placement of gates and gates is essential to help ensure that metal-controlled laminar flow into the mold as well as sufficient feed to all parts of the casting. The laminar flow also minimizes the amount of gas entering the melt. Excessive dissolved gases in the melt create voids in the casting.
The riser serves as a metal reservoir, providing a constant flow to a portion of a portion that may become isolated. The thicker part of the sheet is frozen faster. Therefore, the riser needs to be carefully placed to continuously feed the cavity during the cooling of the metal, otherwise the area of the casting may not have enough metal to fill the back of the shrinkage metal. The voids formed by this phenomenon are the casting defects known as shrinkage porosity, which are the main enemies in the casting world. Ideally, the riser and gate are finally cured, resulting in the so-called "directional solidification".
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