An overview of sand core making in casting

Published - 11th Jun 2019

Cores are used in our foundry casting process to create cavities as well as internal and external features which cannot be generated by our patterns. These cores are made from sand and, at HaworthCastings, we use three main techniques:

• shell core making
• the cold box process
• hand-rammed core making

In this blog, we will take a look at the benefits of each process in turn.

Shell core making

Using this process, fine AFS graded sand is coated with a resin and blown into a pre-heated core box, ideally made from cast iron, which contains the desired shape. The surface is heated to 210-250°C, depending on the required core. This allows the chemical components in the sand to bond together and form the shape within the core box.

The benefits of shell cores include high strength, good dimensional accuracy and excellent surface texture. The surplus sand is also easier to remove, through heat treatment and other knockout processes, so that it can be recycled.

The cold box process

With this technique, a 50 AFS grade of sand is mixed with resin binders before being blown into the core box. This box is sealed and the triethylamine gas setting resin (TEA) is purged with air. The air passes through the sand and it is expelled from the core box through strategically placed vents. The core box is purged for a set time to allow the core to harden. The duration depends on the shape and size of the core.

The main advantage of this technique is that no heating is required and the sand is evenly distributed into the core box, allowing it to fill hard-to-reach corners and cavities.

Hand-rammed core making

The third process involves manually ramming the cores, using a 75 AFS sand, from which the moulds are manufactured. This process is carried out on our foundry bench, which means that multiple core boxes can be rammed up at the same time. This is by far the quickest way to produce cores of different shapes and sizes but it is not suitable for highly complex core shapes.

At Haworth Castings, we can advise you on the best and most cost-effective coring technique for your casting requirements. Contact us today at: sales@haworthcastings.co.uk or call +44 (0)1794 512685 to find out more.