Selecting Finishing Techniques for Castings

Mechanical Finishing Techniques There are several mechanical finishing processes available to enhance the visual appeal of castings. In many instances, these methods also serve as pre-treatments before applying paint. For sand castings, Shotblasting effectively eliminates sand and establishes an even surface texture while providing a suitable base for painting. Gravity and Pressure Die castings benefit from Vibratory Finishing, a highly efficient method to cleanse the castings, remove burrs, and create a smoother surface. This results in an improved casting finish and prepares the surface for subsequent painting. For achieving a polished finish, Ball Burnishing proves to be a cost-effective technique, often utilized in aluminum cookware and window furniture. While polishing enhances the aesthetics of castings, it's essential to select alloys with corrosion resistance suited to their intended environment.

Alochroming: Enhancing Aluminum Alloy Castings Alochroming, also known as Chromating, involves chemical treatment for aluminum alloy castings. This process entails immersion in chemical baths, spray application, or brushing with a solution that chemically reacts with the aluminum, leading to an etched surface or the formation of a chemically converted protective film. Alochroming serves as a pre-treatment for painting and yields decorative, corrosion-resistant finishes. However, these finishes are often too susceptible to abrasion for standalone use. Our offerings include Alocrom 1200, providing an iridescent gold color, and Alocrom 1000, which imparts a light green hue. These finishes are electrically conductive and cost-effective, making them suitable for high-volume production. Given the RoHS Directive's introduction, we advocate transitioning to Trivalent Chromate alternatives, such as Alocrom 407/47, which complies with RoHS standards and offers comparable protection.

Electroplating for Various Alloys Electroplating finds extensive use on Zinc and Copper alloy castings, with more limited applications on Aluminum castings, primarily for decorative purposes. Coatings like Copper, Nickel, Zinc, Chromium, Silver, and Gold are employed. A high level of surface integrity is a prerequisite for this process.

Coating and Painting Techniques Powder Coating presents a cost-effective solution for items requiring excellent impact and abrasion resistance. This electrostatic process involves spraying powdered pigment onto the component, followed by heat fusion in an oven. The resulting finish is robust, durable, and available in varying levels of gloss and texture. Nonetheless, careful consideration is required to avoid masking difficulties and enhance the appearance of the final product. Wet Sprayed Coatings are recommended for superior surface finish. Wet painting entails spraying a pigment suspended in a solvent onto a rotating component, necessitating proper surface pre-treatment and primer application for effective protection. Stove Enamelling should be accounted for with fully heat-treated castings. Silk Screen Printing can be employed for adding artwork or lettering to painted castings.

Anodizing for Aluminum Castings Anodising, an electrolytic process, produces a substantial oxide coating on Aluminum. By thickening the naturally occurring oxide film on Aluminum, anodising enhances corrosion resistance and protects various surface finishes. Sulphuric Acid Anodising offers film thickness ranging from 3 to 25 microns, suitable for decorative applications with options for dyeing, etching, and brightening. Thicker films are better suited for external applications, prioritizing durability, corrosion resistance, and wear. Chromic Acid Anodising produces films of 3 to 7 microns, offering good ductility and a suitable surface for paint and bonding. This finish has an opaque appearance.