Published - 21st Jan 2016
In this blog, we take a look at the important role played by risers and runners in sand casting.
These are vertical channels that provide a continuous flow of molten metal to eliminate shrinkage as solidification occurs during the casting process.
As we discussed previously in our blog on shrinkage, metals are generally less dense as liquids than solids and so castings shrink on cooling. This can result in cavities in the casting. Risers prevent this by feeding molten metal to the casting as it solidifies.
The design of the risers, including the size and the number, is determined entirely by the casting requirements. The risers must have sufficient capacity to supply the volume of molten metal needed to compensate for shrinkage. The design must also promote directional solidification. This can, in part, be achieved by placing the riser(s) near the thickest and largest part of the casting as this will cool and solidify last.[1]
At Haworth Castings, we typically use Kalmin insulating riser sleeves. The insulating properties help to keep the metal at a higher temperature and in a molten state for longer periods of time than traditional products. This means that smaller insulated risers can replace larger conventional sand-filled risers[2]. One of the key characteristics of the sleeves is that they do not burn – which reduces the fumes and smoke in the foundry.
Once the casting process has been completed, the risers and sleeves can be sawn off. The metal can then be recycled to make further sand castings.
Runners are connected channels that convey the molten metal to different parts of the mould.
A well-designed running system can regulate the speed of the molten metal, avoid shrinkage and minimise turbulence. It is vital that the running system does not have any sharp corners or edges which could restrict the flow of metal and reduce its effectiveness.
Generally, we use Kalpur insulating feeder sleeves and filters. Again, the insulating properties optimise feed performance.
The filters assist in the removal of any impurities that enter the channels and also control the speed of the molten metal flow.
Once the casting process has been completed, the runners are sawn off and, again, the material is recycled.
The running system and risers are designed in house by our experienced team of foundry engineers for each individual job – to match our customers’ specific requirements.
If you would like further information about sand casting, please email us today at: sales@haworthcastings.co.uk or call +44 (0)1794 512685.
[1] Degarmo 2003
[2] Foseco
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