What are inclusions?

Inclusions are a common problem in metal casting. In this blog, we look at this issue and the measures that are taken to prevent them.

Inclusions – a definition

According to the Oxford English Dictionary, an inclusion is a ‘body or participle of distinct composition embedded in a rock or other material’. In the metal casting industry, the term has a specific meaning – referring to unwanted particles of dross, refractory materials, sand or deoxidation products trapped in metal castings.

Inclusions can be caused by various factors, including impurities from the metal ingot or interaction of the metal with the mould surfaces or the outside atmosphere.

Inclusions are problematic because they can affect the mechanical properties of the metal casting. They are usually identified through x-ray detection.

What is the difference between porosity and inclusions?

These two issues are separate. Inclusions are solid particles entrapped in the casting whereas porosity is the result of gas entrapment in the solidifying metal.

On an X-ray, inclusions show as dark, jagged asymmetric shapes whereas porosity takes the form of dark spots or specks.

Reducing the risk of inclusions in sand casting

In the casting industry, many different techniques are used to manage and reduce the incidence of inclusions, such as adding chemicals during the metal pour to allow the dross to float to the top – where it can be skimmed off.

At Haworth Castings, we install special ceramic filters or Kalpur technology (an all-in-one pouring cup, filter and sleeve) in the running system. These devices filter out the unwanted dross or slag during the metal pour.

Inclusions are much less of a problem nowadays, with the advent of improved process design and running systems. Generally, inclusions only occur in the event of a rare breakdown in the running system.

Our highly experienced foundry team manages this sand casting process with the utmost care to ensure the integrity of every component.

Haworth Castings is one of the UK’s leading suppliers of high-precision aluminium castings. To find out more about our capabilities, please call us today on +44 (0)1794 512685 or email us: sales@haworthcastings.co.uk