SGS non-destructive testing white paper featured in Engineering Failure Analysis
20/02/2014
A white paper, authored by William Liu of SGS Industrial Services, SGS New Zealand Ltd in Auckland, was recently published in the internationally recognised and respected academic journal Engineering Failure Analysis.Entitled: ‘The microscopic features of cavitation erosion and the solution in the plastic injection moulding machines’, the paper addressed cavitation erosion, corrosion, bubble implosion and failure analysis in nozzle units of plastic injection moulding machines.
Cavitation erosion, a type of surface failure caused by shock waves or micro-projects resulting from vapour bubble implosion in fluids, has often been misinterpreted as flow-accelerated corrosion (FAC). There is, however, a clear distinction between cavitation erosion and FAC. Cavitation erosion is a mechanical process whereby bubble implosion erodes material, while FAC is a corrosion process in which fluid flow dissolves the protective oxide film.
In the paper, premature failure of the nozzle unit in plastic injection moulding machines was discovered to be the result of cavitation erosion, not corrosion. Distinct characteristics of the cavitation erosion found on the soft aluminium alloy include three differently-sized types of erosion pits: a large 1-2 mm round pit with a smooth surface, a smaller 100 µm consisting of round, overlapping pits in parallel lines and 5 µm micro erosion pits. It was suggested that the varied sizes of erosion pits may well be associated with the different sizes of bubbles imploding. Bubble formation was due to the change in surface tension and vapour pressures caused by dosing chemicals in the coolant. The paper concluded with the successful solution of replacing the aluminium alloy with stainless steel.
The Elsevier-issued journal Engineering Failure Analysis features original, high-quality research papers, communications and review articles concerning the analysis of engineering failures and related studies.
Elsevier’s roots lie in the publishing of journals and books and the company has fostered the peer-review process for over 130 years.
www.sgs.com/ndt
