Iron Castings

Iron Castings Specifications

All our castings are produced to a current ISO specification, ISO 185 2005, along with any further certification which a customer may require. Our diverse customer base has given us experience in a wide range of applications for iron castings across many market sectors including pumps and valves, forges, foundries and rolling mills, automotive and aerospace, a wide range of OEMs, quarries and mines, railways and rolling stock, local authorities and artists and sculptors.

We also have long term trading relationships with local pattern makers, machine shops and surface finishers which enable us to quote for the complete supply of machined and painted castings.
Iron Castings Quantities

Iron castings of the size and quantity that Durham Foundry produces are traditionally made in sand moulds. The earliest type of sand system was Greensand, which is a combination of silica sand, clay and water, a naturally occurring sand which contains clay being used as the basis for the system.

This sand is usually red in colour, although after use in a foundry the sand takes on a dark grey/brown colour. This can cause confusion when foundrymen talk about “green” sand. The term green is used to denote that the sand is wet, having about 2% water in it. If greensand is compacted around a pattern, the sand will retain its shape after the pattern is removed, which occurs because the clay in the sand provides an electrostatic bond between the clay and the sand grains.

The more the sand is worked or rammed the greater the electrostatic charge that builds up and the stronger the final mould will be.
One area of potential confusion is the spelling of the word ‘grey’. This can be spelt either as ‘grey’ or as ‘gray’ although gray tends to be an American usage.

Iron Casting Additions

Small additions of dextrose can be added to improve the bond and similar additions of powdered graphite or flour can be used to improve the permeability of the mould. Greensand moulding is a highly skilled job and requires long periods of training to become proficient.

Because of this and other cost considerations, sand systems that were simpler to use were developed in the late 50’s and early 60’s which were based around dry silica sand without any clay addition. The bond was achieved by the addition of a resin and a method of hardening the resin.

Iron Casting Systems

There are two basic systems. Firstly a resin can be mixed into the sand that can be set off, or cured, by passing a gas through the sand. An example of this is the Sodium Silicate system. Sodium Silicate is mixed with the sand, the mould is made and CO2 gas is then passed through the sand around the pattern.

The CO2 causes the silicate to harden through a combined action of dehydration and gelling of the silicate, which results in a stable mould from which the pattern can be removed. The second system is based on a resin and a catalyst. These are mixed into the sand in metered amounts and the sand hardens by a chemical reaction between the resin and the catalyst.

One draw back to this system is that once the sand is mixed, there is a finite time that the sand can be used for. Greensand does not have that problem.

Please browse our website for more information about Durham Foundry and our ability to manufacture Iron Castings then contact us on 0114 249 4977 or e-mail us on castings@durhamfoundry.com or visit our dedicated website castironcastings.com for more information.