Raw Materials
- Sand: The raw material is high quality silica sand. The regular shape in the sand is supposed to be, high in purity, as well as thermal stability in order to produce a high quality cast.
- Resin: The material coating is predominantly a compound obtained from phenolic resin. It achieves a satisfactory adhesion on grains, supports a firm, stable castings' formation in a shell shape, as well as improves surface quality as well as castings' overall toughness.
Production Procedure
Pre - coating of Sand
- The pre - heating is done with a specified temperature in the beginning, which is generally 120 - 150°C.
- Then, heat is transferred from hot sand into a mixer. The surface of grains is painted smoothly with a layer of phenolic resin in a continuous mixing. A curing agent can also be added in the process in order to accelerate the process of hardening of the resin.
Molding
- The pre-coat resin sand is charged into a mould cavity. The mould is either wood, metal, or plastic, as a function of castings complexity and quantity.
- The mould is charged with sand in a manner that not only provides a shape but also a density. The mould is heat-cured at a curing temperature (approx. 200 - 250°C) in order to fix the resin-coated sand as also form a firm mould.
Casting
- Molten metal, either hardened resin-coated pre-coated ductile iron or stainless steel, is cast into pre-coated hardened resin mould. The metal is selected as a matter of application requirement, i.e., heat resistance, toughness, as well as resistance to corrosion.
- During pouring, care is taken not to trap air as also not to let a free flowing of molten metal into each section mould.
Cooling and Shakeout
- After casting, cool down moulding at a relaxed rate in order to remove internal stresses.
- Once cooled at a desirable level, cast is taken out from its mould in a process known as shakeout.
Finishing
- The castings are subjected to a series of finishes that involve surface treatment, as well as machining and grinding. Burr as well as excess material is removed with grinding. The castings are machined with turning, drilling, as well as with milling in order to attain specified dimensions as in the case with the valve parts. The castings can be treated with surface treatments such as painting or galvanizing in order to boost its resistance towards corrosion.
Quality Control
- Dimensional Testing: The castings are evaluated with high accuracy instruments like micrometers, calipers, as well as coordinate-measuring machines (CMM) in a bid to establish whether castings are in specified dimensional tolerances.
- Non - destructive Testing (NDT): Ultrasonics, magnetic particles, and penetrants are also used in order to inspect internal as well as surface defects in castings, i. e., inclusions, porosities, as well as cracking.
- Mechanical Property Testing: Mechanical impact, hardness, and tensile testing is conducted in order to analyze castings' acceptable mechanical properties that can be tolerated by them in terms of operation.
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