Meaning
Mechanical and chemical erosion of the internal cylinder walls of a moulding press occurs over extended production cycles as a result of abrasive resins and corrosive additives. Severe injection barrel wear reduces melt pressure control and alters the shot size consistency. This physical deterioration governs the maintenance schedule and the process capability index of the moulding cell.
The process is continuous and stops only when the worn barrel is replaced or sleeved with a harder alloy.
Particle Friction
Glass fibers and mineral fillers added to polymer resins act as abrasive agents that grind down the steel flights of the screw and the inner surface of the barrel. This injection barrel wear is accelerated when high-pressure injection cycles force these hard particles against the metal surfaces. As the clearance between the screw flights and the barrel wall increases, molten polymer flows backward during the holding phase.
This backflow leads to inconsistent part weight and variable cushion sizes.
Screw Bypass
Halogenated flame retardants and fluoropolymer additives release corrosive acids when they are held at high temperatures for too long. These acidic compounds attack the protective nitrided layer of the steel, accelerating the progress of injection barrel wear. This chemical attack creates a pitted surface where degraded polymer can accumulate, burn, and then break free into the melt stream.
The resulting black specks and brown streaks ruin the cosmetic appearance of light-coloured or transparent moulded parts.
Clearance Audit
Periodic internal bore measurements using a dial bore gauge are necessary to track the progression of the clearance increase. When injection barrel wear exceeds the maximum tolerance specified by the machinery manufacturer, the screw cannot generate the pressure needed to pack out thin-walled parts. Moulders must monitor this wear to plan maintenance shut downs before the quality of the moulded parts falls below the customer’s limits.
