Jai Enterprises is the Leading Designer of Casting Process in Coimbatore

THE CHOICE OF FINISH

MECHANICAL FINISHING

There are a variety of mechanical finishing processes which can enhance the aesthetic quality of castings, and in several cases, these processes will also be used as a pre-treatment if the casting requires subsequent painting. For Sand Casting, Shotblasting is often used to remove sand, and to provide an even surface finish whilst giving a good key for painting. In the case of Gravity and Pressure Die-castings, Vibratory Finishing is the most efficient method for cleaning the castings, removing burrs and smoothing the surface. This provides a more pleasing casting finish and again is good preparation for subsequent painting. To achieve a polished casting finish, a cheap and effective method is Ball Burnishing, which is often used on aluminium cookware and window furniture. Polishing provides an attractive finish for castings, but care must be taken in selecting alloys which have corrosion resistance appropriate to their destination environment.

POWDER COATING, PAINTING

Powder Coating is a low-cost process for items requiring a high degree of impact and abrasion resistance. It is an electrostatic process where powdered pigment is sprayed from a gun and is electrically attracted to the component. The powder is then fused by heat in an oven. The resulting finish is tough and durable and is available in varying levels of gloss and texture. It should, however, be borne in mind that masking on items to be powder coated is difficult and time-consuming (hence costly), and should be avoided if possible. Small surface blemishes which are not easily detectable on raw castings become much more noticeable after powder coating. Specialist powders are available for particular applications, including anti-bacterial coatings for medical applications, and anti-graffiti coatings for street furniture etc. For higher levels of surface finish, Wet Sprayed Coatings should be considered. Wet painting involves spraying a pigment suspended in a solvent onto a component, which must be rotated to give complete coverage. Proper surface pre-treatment and the application of a suitable primer such as Zinc Chromate is essential if the final paint coating is to be truly protective. Stove Enamelling temperatures are not usually high enough or of sufficient duration to influence the properties of Aluminium castings but should be taken into account with fully heat-treated castings. Where it is necessary to add lettering or other artwork to painted castings, this can often be achieved by Silk Screen Printing.