The microscopic features of cavitation erosion and the solution in the plastic injection moulding machines

The premature failure mode of the nozzle unit in the plastic injection moulding machines was discovered to be cavitation erosion, rather than corrosion. The microscopic features of the cavitation erosion on the soft aluminium alloy have its own distinct characteristics. Three types of erosion pits in different size order have been discovered: a large round pit with very smooth surface are in the size range of 1–2 mm, small round overlapping pits in the pattern of parallel line are approximately 100 μm, and micro erosion pits are about 5 μm. These different size order erosion pits might be associated with the different size order of bubbles imploding. The root cause of the bubble formation was the alteration in surface tension and the vapour pressures due to the dosing chemicals in the coolant. The solution to the cavitation erosion with substituting stainless steel to aluminium alloy has been successful.