Vacuum Impregnation: What It Is, and When to Perform It

Q: What is vacuum impregnation?

A: Vacuum impregnation is an effective way of addressing potential issues caused by porosity in metal castings – in other words, any voids found in the part, whether they’re blind, through or fully enclosed.

Die castings are made for a wide range of applications, some of which require the parts to hold pressurized fluids or gasses. In these cases, internal porosity could cause leaks and attendant corrosion or defects. Vacuum impregnation is a process that seals internal porosity without affecting any of the part’s other physical or functional  features.


Q: When should vacuum impregnation be carried out?

A: Companies often struggle to understand at which stage vacuum impregnation should be carried out – before or after the die casting has been machined?

The answer really depends on the types of porosity that occur in different castings. Blind porosity is open in just one surface, and therefore doesn’t form a continuous passage for liquid, whereas through porosity stretches from one side of a casting to another. These can cause immediate problems such as leak paths, internal corrosion and surface defects on the part. Fully enclosed porosity, meanwhile, is as the name suggests completely enclosed inside the casting, with no passages to the surface.

Vacuum impregnating castings after final machining is the gold standard here, and the single best way to ensure completely leak-free castings. That said, final leak tests carried out on individual parts and followed by vacuum impregnation of only the non-confirming parts (‘fix on fail’) is a thoroughly acceptable alternative.

Some manufacturers vacuum impregnate all parts after pre-machining, which seals both blind and through porosity. In this scenario, only fully conforming parts sent through to production where they’re fully machined.


About Us

Impregnation Services Ltd. (ISL), a family-run business specializing in vacuum impregnation, was founded in 1964. Following a management ‘buy-in’ in 2008 led by husband-and-wife team Justin and Rachael Benson, ISL has seen a major re-investment across people, plant and machinery, resulting in an outstanding vacuum impregnation service for our customers.

With over half a century’s experience in this very specialist field, ISL offers both in-house and on-site porosity sealing services to clients all over the UK and overseas, across industries including automotive, aerospace, process, energy, defence, marine, restoration and valves, pumps and bearings.

Contact us to find out more!