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A white paper, authored by William Liu of SGS Industrial Services, SGS New Zealand Ltd. in Auckland, was recently published in the internationally recognized 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.

Publisher Elsevier of Amsterdam

The leading provider of science and health publications, Elsevier currently serves more than 30 million scientists, students and health and information professionals worldwide. The Elsevier global network of 7,000 journal editors, 70,000 editorial board members, 300,000 reviewers and 600,000 authors provide the world-class information and innovative tools necessary to advance science and health, assist in critical decision-making, enhance productivity and improve results.

Elsevier roots lie in the publishing of journals and books and the company has fostered the peer-review process for over 130 years.

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.

The Featured SGS Paper

William Liu's paper, "The Microscopic Features of Cavitation Erosion and the Solution in the Plastic Injection Moulding Machines" focussed on cavitation problems occurring specifically in the plastic injection moulding machine nozzle unit. Cavitation erosion, a type of surface failure caused by shock waves or micro-projects resulting from vapor 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 aluminum alloy include three, differently-sized types of erosion pits; a large 1-2 mm round pit with a smooth surface, a smaller 100μm consisting of round, overlapping pits in parallel lines and 5μm 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 vapor pressures caused by dosing chemicals in the coolant. The paper concluded with the successful solution of replacing the aluminum alloy with stainless steel.

The Microscopic Features of Cavitation Erosion and the Solution in the Plastic Injection Moulding Machines:

  1. Introduction
  2. The failure scenario of the injection moulding machine
  3. The galvanic corrosion test
  4. The microscopic features of the cavitation erosion
    4.1  The cavitation erosion on the non-anodized aluminum alloy
    4.2  The cavitation erosion on the anodized aluminum alloy
  5. The rectifications
  6. The root causes of the bubble formation
  7. Conclusions
    References

SGS Coating Inspection & Failure Analysis

SGS coating inspection and failure analysis is ensuring continued protection at construction sites, factories, laboratories, shipyards and power plant facilities around the world. SGS specialists assess coatings on ferrous steel, stainless steel, aluminum, concrete, brick and plastic to determine conformity, compatibility and performance. Inspection and analysis conducted by SGS experts prevent costly repairs and downtime due to coating failures such as concrete decay, corrosion and loosening adhesive coats by determining causes of coating failures in order to avoid similar occurrences in the future.

SGS congratulates William Liu on being selected for this prestigious distinction and wishes him continued success.

For further information, please contact:

SGS Industrial Services
William Liu
Metallurgy and Tribology Specialist
SGS New Zealand Limited
17 Maurice Road, Penrose 1061
PO Box 13-518, Onehunga 1643
Auckland
New Zealand
t: +64 9 635 0303
f: +64 9 636 6054
www.sgs.com/ndt

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