National Water supplier call on Cranfields expertise
In producing a miniature valve housing for a product that would be used in the national water supply, a number of criteria must be considered. The housing must be able to bear the moving components of the valve, they must continue to seal and remain watertight throughout a long service life, they must keep the water supply safe and conform to standards set out by WRAS (the Water Regulations Advisory Scheme).
Among other things, the moulding forms a cylinder for a sealed piston to run in. Cranfield Solutions were consulted in the design of the part. We were able to advise the use of a POM material (Polyoxymethylene or Acetal). Properties of the material that suit this application are that it is strong and stiff, remains dimensionally stable and does not absorb water. Significantly for this application POM also has very low-friction properties.
To ensure the product could be used in the water system we were able to supply a WRAS approved POM material to conform to the required standard.
The choice of material alone did not resolve all the requirements. POM naturally holds heat and takes time to cool. If areas within the part cool at different rates, this will easily result in uneven surfaces. Not good when a consistent cylinder bore is an essential requirement. To tackle this, we consulted with the client to add cored sections in strategic areas of the component. This enabled us to maintain the structural integrity whilst keeping wall thicknesses relatively similar and therefore heat dissipation consistent throughout. To further aid removal of heat from the key area of the cylinder as rapidly and consistently as possible, water cooled copper-beryllium alloy cores were used in the production of the tool.