Published - 25th Jul 2017
Shot blasting is a finishing process used to clean castings and prepare them for further treatment. It is widely used in many industrial areas, such as the automotive, aviation, rail and shipbuilding sectors. At Haworth Castings, we use this technique in all our sand casting work.
Shot blasting is the first process carried out after the casting has been removed from the sand mould. It is also sometimes carried out a second time after heat treatment to improve the surface finish.
Firstly, the casting is placed in an enclosed cabinet on a rotating turntable. As the casting is rotated, small steel balls (shots) are accelerated towards the workpiece at high speed and at varying angles through a pressurised nozzle.
Various shot media can be used in shot blasting, with different shapes, sizes, densities and materials (such as ceramic, glass and steel). The choice of material and size is dependent on the surface treatment required. At Haworth Castings, we use stainless steel shots.
There is a common misconception that shot blasting and shot peening are similar processes. In fact, the techniques differ considerably.
It’s true that both processes involve accelerating shot media at a casting at high speed in an enclosed area but this is carried out for entirely different reasons.
Shot blasting is primarily used for cosmetic purposes to enhance the surface texture of the casting and to remove any small particles of sand or other materials from the surface. It also provides an excellent preparation for painting and brings out the natural colour of the metal, which can sometimes ‘dull’ during the production process.
Importantly, shot blasting also highlights any surface defects or small imperfections, such as porosity.
Shot blasting is an abrasive procedure that enhances the surface finish whereas shot peening does not alter the surface texture of the casting. In fact, shot peening, as we discovered in our last blog, is designed to increase the strength of the casting to extend its fatigue life. So, it is not a cosmetic procedure. Instead, shot peening alters the physical properties of the metal to add strength.
Whichever technique is used, our experienced foundry engineers work closely with customers at every stage to ensure that our castings are finished to meet exacting requirements.
Want to find out more about our finishing techniques? Give us a call today to find out how we can support your needs. Please call us on +44 (0)1794 512685 or email us: sales@haworthcastings.co.uk
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