The so called casting size tolerance is that casting size exceeds the specified tolerance range. This is an important investment casting defects, which will cause casting scrap.
Lost wax precision casting dimensional accuracy has a great influence on. Some information on long-term investment casting and casting size measurement results show that the length of the casting direction,especially length 25mm size on it, lost wax casting bias accounted for over 50% of the total variation; when casting size increases, the relative impact of melting mold reduce the length of 250mm, lost wax casting bias accounted for about 40% of the total variation.Melting mold size deviation was mainly due to the instability caused by the molding process, such as locking force size, pressure wax temperature, die pressure fluctuations caused by factors such as investment casting size deviation.And Shell thermal expansion,shell temperature when pouring the molten, metal pouring temperature, and casting in the type of position etc will affect casting size.
Investment castings can be produced in all alloys from a fraction of an ounce, for dental braces, to more than 1,000 lbs. (453.6 kg) for complex aircraft engine parts. Smaller components can be cast at hundreds per tree, while heavier castings often are produced with an individual tree. The weight limit of an investment casting depends on the mold handling equipment at the casting plant. The majority of U.S. facilities cast parts up to 20 lbs. (9.07 kg). However, many domestic facilities are increasing their capability to pour larger parts, and components in the 20-120-lb. (9.07-54.43-kg) range are becoming common.
A ratio often used in designing for investment casting is 3:1—for every 1-lb. (0.45-kg) of casting, there should be 3 lbs. (1.36 kg) to the tree, depending on the necessary yield and the size of the component. The tree always should be significantly larger than the component, and the ratio ensures that during the casting and solidification processes, the gas and shrink will end up in the tree, not the casting.
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