Surface Finishes for Permanent Mold Castings
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Surface Finishes and Treatments
As a premium permanent mold casting provider, ChinaSavvy offers various surface finishes, treatments and secondary operations for aluminum gravity die casted parts, including, but not limited to:
Anodizing
Done on aluminum permanent mold casted parts, anodizing involves the creation of an anodic film, which aids in increasing the part’s resistance to corrosion and abrasion. Furthermore, this process delivers an aesthetically pleasing appearance that will not fade (as paints do). Learn more about this process by visiting our Anodized Aluminum Fabrication page.
Plating
Zinc, chrome and nickel plating is performed on aluminum gravity die casted parts. Zinc plating is the most inexpensive and provides resistance to corrosion.
Impregnation
A treatment process applying a sealing medium in order to deal with porosity issues.
Machining
ChinaSavvy offers a wide range CNC machining services including turning, drilling and milling.
Heat Treatment
The main heat treatment types used in gravity die casting secondary operations for aluminum includes T5 and T6 heat treatments. T5 is a stress release by thermal heat treatment while T6 is solution heat treated and artificially aged.
Powder Coating
Yielding a higher uniform thickness and better color, powder coating is capable of hiding minor flaws on the surface, has a highly durable gloss, is hard and has a better resistance (than paints) against dings and scratches.
Painting
A common and economical surface finish or treatment, painting is divided into wet spray painting (left to dry normally), lacquering and stove varnishing (both requiring baking). While stove varnishing is capable of achieving different colors and art textures, lacquering can achieve one unique color at a time.
Polishing
A common surface treatment, some aluminum casts can also achieve mirror surface finishes.
Cast Coatings
Cast coatings in permanent mold casting is vital for three reasons. Firstly, coatings provide a protective barrier between the casting and the mold – this is necessary in order to avoid mold wear and erosion.
Secondly, castings offer manufacturers a certain degree of control over the solidification step (in terms of rate of solidification and direction of solidification) in the permanent mold casting process.
Thirdly, coatings provide a barrier between the mold and cast. This enables the cast to be released from the mold in the final steps of the casting process.
Control over Thermal Gradients
If cast coatings are properly used, it can provide manufacturers with a control of thermal gradients, including the direction of solidification. In turn, this allows a pathway for molten metal to flow into the solidifying structure, helping top compensate for normal metal shrinkage that normally occurs during solidification.
This control over thermal gradients become a very important aspect in cases where wall thicknesses are vital.
Insulation Coatings
In cases where casts require thin walled sections (which need addition insulation in order to prolong the solidification process) in parts of the mold where release is difficult, one of two options are available to manufacturers (as release coatings are, by nature, not insulative):
- Either a combination coating allowing for some insulation and some release is used, or
- An insulative base coat is used with a release top coat.
Different insulation coatings have varied insulating qualities as well as as what surface finish it will impart on the casted part.
The qualities of the coating is determined by the function of the type of refractory filler used, this filler’s heat capacity and its thermal conductivity. Another contributing factor to mold coatings insulative capability, as well as the surface finish imparted, is the amount of binder used and the dilution rate.
Commonly, binders are a sodium silicate with refractory materials including:
- Alumina
- Bentonite
- Graphite
- Olivine
- Talc
- Titanium Oxide
- Vermiculite
Chill and release cast coatings act as a protective barrier to prevent mold wear as well as act as heat conductors to allow for a rapid solidification process. In release coatings, graphite is commonly used as the lubricant.
Back to Main Page: Permanent Mold (Gravity) Casting.
Further Suggested Reading:
- Permanent Mold Casting Process
- Permanent Mold Casting Tolerances
- Metals that can be Permanent Mold Casted
- The Limitations of Casting Using Permanent Mold Processes
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