Why is high quality sand so important in sand casting

Published - 14th May 2019

The sand mould plays a crucial role in the manufacture of a sand casting. The composition and quality of the sand directly influences the final shape, dimensional accuracy and surface finish of the finished casting.

There are also environmental and cost benefits to using high quality sand, all of which will be explored further in this blog.

Sand mixture and surface finish benefits

Today a very high-grade silica 80 AFS ‘dry’ sand is used which is mixed with cold-set binders to connect the sand particles together, producing a very firm mould and consequently an excellent surface finish and definition.

The high-grade sand is very resistant to the high temperatures involved in metal casting and carefully selected as the size and shape of the grains have a critical impact on the surface finish of the casting.

The binder-sand mixture is important to get right as it needs to have enough strength to withstand the force of the molten metal as it fills the mould.

Whilst resins are required to harden the sand to prepare the mould, an over concentration can lead to poor surface appearance and quality. At Haworth Castings 100% of the sand is recycled with all residual chemicals removed from the sand during the reclaim process. This means the sand only ever has one layer of chemical on it at a time which is crucial for dimensional accuracy and surface finish.

The sand mixture plays a crucial role in ensuring a high-quality casting by:

1. Ensuring the mould can cope with the high temperatures and holds its shape
2. Not reacting chemically with the metal in the sand mould
3. Rapidly curing to speed up the pouring and reclamation process
4. Allowing gasses to escape during the pour
5. Enabling the sand to flow smoothly through the running system to all areas of the mould.
6. Making it easy to separate the sand from the casting at the end of the sand-casting process

Health & safety benefits

When dry sand was first introduced, it was purged with carbon dioxide to make the moulds firmer. But, carbon dioxide presented some health and safety risks due to its combustibility. These days we use poliset cold-set binders to bind the sand particles together and these materials do not present the same health and safety risks.

Environmental and quality benefits

Prior to sand reclamation Haworth Castings had to send over 2,000 tonnes of sand to landfill per annum. Recycling means we not only have a much-reduced impact on the environment but it also means that we are able to control the properties and ingredients of the sand.

The chemical binding additives enable us to remove the sand from the moulds very easily with the sand then passed through a thermal cleaning area where the heat removes all the residual chemicals. The result is pristine high-grade sand that give our castings an excellent definition.

Cost benefits

High quality reclaimed sand not only means a better finished casting for our customers but has also taken significant cost out of the business as we are no longer purchasing significant quantities of sand and are unaffected by the fluctuations of sand and waste disposal prices.

For further information about our sand castings capabilities please contact us at: sales@haworthcastings.co.uk or call +44 (0)1794 512685.