Finishing – an overview
Published - 25th Aug 2015
Finishing is the last critical stage in the aluminium sand casting and gravity-die casting process. It is designed to:
- give the component the desired surface texture
- remove excess material or surface contaminants
- enhance the aesthetic qualities
- act as a pre-treatment for other finishing processes (such as painting)
The following provides a quick summary of the main processes.
Finishing techniques
Linishing and fettling are the first stages in any aluminium sand casting and gravity-die casting finishing process. Fettling involves the removal of the risers and any excess material while linishing involves grinding or sanding the component to improve the surface flatness. These techniques can be carried out using manual cutting, grinding or automated tools.
Castings require different levels of finishing depending on the type of metal used and the end application. We offer a variety of more specialised finishing techniques to meet specific customer requirements.
Paint finishes
Painting can increase the component’s resistance to corrosion, wear and erosion and enhance the aesthetic qualities. One such technique is powder coating. A powdered pigment is sprayed onto the component and fused on the surface in a curing oven. Other similar techniques include wet spray coating, nylon coating and infrared reflective painting.
Anodising
Anodising uses electrolysis to produce a hard transparent oxide coating that increases corrosion resistance and protects the surface of the casting. Sulphuric acid and chromic acid anodising are the two most popular techniques.
Pressure testing
Hydraulic, pneumatic and air decay testing are used to check the pressure test resistance of castings and ensure that there are no leaks. If any leaks are identified, the castings can be injected with vacuum impregnation sealants to fill any cavities or inclusions.
Shot blasting and peening
In shot blasting, the casting is placed on a spinning wheel in an enclosed cabinet. Stainless steel shots (or ball bearings) are propelled at high speed at the surface of the casting. This helps to create a uniform finish and remove any sand or other surface contaminants. Shot peening is a similar, gentler process that uses finer ball bearings to avoid cracks on the surface.
Polishing
Polishing gives the casting a shiny surface appearance once the other processes have been completed.
The level of finishing is entirely guided by our customers’ requirements. If you would like further information about our sand casting, gravity-die casting or finishing processes, please email us today at: sales@haworthcastings.co.uk or call +44 (0)1794 512685.
