How to achieve a good surface finish in sand casting

Published - 9th Oct 2018

Sand casting processes allow us to produce components with an excellent surface finish, making them suitable for a range of industrial applications, from automotive parts through to aircraft impeller blades.

In this blog, we will be looking at the factors that contribute to a good surface finish.

The integrity of the pattern

The quality of the pattern is critically important. As we’ve explained previously, top-class patterns help to create top-class castings.

Our patterns are created by specialist pattern makers using paper designs, 3D models or software drawings supplied by our customers.

The patterns are manufactured using a high-quality resin to reduce the impact of wear and tear and increase the life expectancy of the equipment.

The choice of sand

The type of sand is also important. Any breakdown in the sand mould will lead to roughness on the casting.

At Haworth Castings, we use a high-quality silica sand. This sand is chosen carefully as the size and the shape of the sand particles influence the surface finish. Finer particles achieve a better surface finish.

This sand is mixed with a cold-set binder (to bond the sand particles together) and a catalyst. This helps to create a strong, durable sand mould which, in turn, helps to create an excellent surface texture on the casting.

Effective ramming of the moulds

Ramming is the process by which the sand is compacted into the moulds. This process is carried out manually by our highly skilled foundry team. The moulds must be rammed correctly to ensure that all the apertures are filled so that the sand does not break away during the casting process.

High-integrity sand cores

The choice of core manufacturing process is another important consideration.

As we’ve explored previously, cores are added to the sand moulds to create cavities and intricate features. In the foundry, we use three main techniques: shell core-making, the cold-box process and hand-ramming techniques.

Shell core-making produces the best surface finish, but it is also the most expensive technique. It is used when high-precision is a priority – such as safety-critical components for aircraft impellers.

Machining and finishing

Of course, we use a wide range of machining and finishing techniques to enhance the surface finish of our castings. These include turning, surface grinding and shot blasting. In fact, our castings all go through shot blasting for this reason and it is often carried out after heat treatment to improve the surface finish.

Our skilled foundry team advises customers on the best approach for their casting project.

To find out more about our high-precision castings, please call us today on 01794 512685 or email us: sales@haworthcastings.co.uk