Surface Treatment

Normally, if there is no special requirements on the surface, products after investment casting are just anti-oil rust painted for rust protection. However, there may also have special purposes like improve appearance, protect the surface from external influences, meet special brand requirement, change material properties, ect. In this case, some surface treatments will be applied to investment castings.

The most applied surface treatments are:

• Color painting: Can be operated according to sample or color number. Secondly used surface treatment method for castings. Mainly used as the surface treatment for steel castings and iron castings.
• Powder coating: Better surface coating way than color paiting, which is good at environment protection and harmless to workers.
• Zinc plating: Suitable for small type of investment castings for its high cost.
• Pickling and passivation: Used to protect castings from corrosion and add a protective layer. Specialized for stainless steel castings.
• Black oxide: More cost-effective way to prevent investment castings from rusting than painting.
• Phosphating treatment: A kind of chemical layer converting process, using used pretreatment technology.

Our surface treatments allow us to offer our customers high quality investment castings with surface finish better than 3.2 micron after lost wax precision casting process. We can offer all kinds of surface treatmens either finished in-house or from our partner. More and more customers benefit from our wide range of surface treatments service. Together with our machining and heat treatment capabilities, our surface treatment capabilities enable us become your “One Stop Shop” investment casting supplier.

stainless steel electric polishing

Stainless steel electropolishing tends to be the most frequent material polishing process compared to other alloys because it enhances its corrosion resistance properties. Electropolishing stainless steel is a reverse plating process that uses a combination of rectified electrical current and a blended chemical electrolyte bath to remove imperfections from the surface. This creates a much cleaner and shinier surface for the   stainless-steel part.

STAINLESS STEEL ELECTROPOLISHING PROCESS

The electropolishing process of stainless steel begins with placing the treated parts in a temperature-controlled electrolyte bath connected to a positive DC voltage charge. The bath components act as electrical anodes (positive terminals), while inside the tank the cathodes (negative terminals) draw current from the components through the conductive electrolyte liquid. As the current travels from the parts to the cathodes, through the electrolyte, it draws metal ions from the surface of the parts and during this process, the electrolyte dissolves the metal surface area of the part.

ADVANTAGES OF STAINLESS STEEL ELECTROPOLISHING

All stainless steels are iron-based alloys with a minimum chromium content of 10.5%. The chromium amount contributes to the basic corrosion resistance of stainless steel. The chromium spontaneously forms a passive oxide layer when exposed to oxygen. This passive oxide layer is very thin but prevents additional oxygen diffusion into the base material and prevents corrosion. Electropolishing in stainless steel enhances the passive oxide layer by making it thicker and thus more resistant to harsh environments.

Enhancing corrosion resistance is not the only benefit when electropolishing stainless steel, below are a few other benefits.

1.Makes the material easier to clean

2.Gives the material an astatically pleasing finish

3.Repairs the surface finish

4.And more

COMMON STAINLESS STEEL ALLOYS

304 Stainless Steel

316 and 316 L Stainless Steel

400 Series Stainless Steels

17-4 pH

MP35N

Nitronic 60

Elgiloy

2205 Duplex Stainless Steel

Other Duplex Stainless Steel

Electropolishing of stainless-steel removes imperfections, impurities, and burrs from the surface of the processed metal objects. Electropolishing is an effective replacement for more traditional techniques of mechanical finishing such as friction, buffing, blasting and grinding. Electropolished parts retain a clean and polished surface with a uniform shine after processing, without the fine directional lines associated with abrasive polishing.

THE ELECTROPOLISHING PROCESS PROVIDES:

Better Physical Appearance

No fine directional lines from abrasive polishing.

Excellent light reflection and depth of clarity.

Bright, smooth polish; uniform luster of shaped parts.

Enhanced Mechanical Properties

Less friction and surface drag.

Increased production and duty cycles in process equipment. Electropolishing greatly reduces fouling, plugging, scaling and product build-up.

Surface retains the true grain structure and properties of the bulk metal.

Fatigue strength is not reduced. Electropolishing allows the true fatigue strength of a part to be accurately determined.

Higher fatigue strength can be promoted by particle-blasting the surface to reintroduce compressive stress without losing electropolishing's advantages.

Stress-relieving of the surface.

Reduces galling of threads on stainless and carbon steel and other alloys.

Better Corrosion Protection

The Benefits of Electropolishing come from producing maximum tarnish and corrosion resistance in many metals and alloys. Stainless steel contains metallic and non-metallic inclusions, which are unavoidably included during manufacture. Mechanical polishing not only fails to remove inclusions, but also tends to push them further into the surface and even increase them by further pick-up of abrasive materials. These inclusions eventually can become points of corrosion.

Ease of Cleaning

Substantially reduces product contamination and adhesion due to the microscopic smoothness of an electropolished surface (much like a glass surface).

Decreases cleaning time. Electropolished surfaces can be effectively hydroblasted in less time and with less pressure. Some companies report that electropolished process equipment surfaces have reduced cleaning time by more than 50 percent.

Improves sterilization and maintenance of hygienically clean surfaces for food, drug, beverage and chemical processing equipment.

Provides best passivation of stainless steel. Unipotentializes stainless steel with the oxygen absorbed by the surface, creating a monomolecular oxide film.

Decarburizes metals.

Removes cold-worked metal oxides.

For Special Effects

Simultaneously deburrs as it polishes.

Radiuses or sharpens edges, depending on racking position.

Polishes areas inaccessible by other methods.

Reveals flaws in metal surfaces undetectable by other means. Electropolishing is one of the most effective inspection tools for judging metal surfaces.

Provides a correct and reproducible microhardness on the metal surface.

Increases magnetism of parts by approximately 20 percent.

Allows micromachining of metal and alloy surfaces.

Processes large numbers of parts simultaneously.

Enables metal to be formed with fewer passes and annealing steps.