SCREWS AND BARRELS | MACHINERY
Repairing and refurbishing screws and barrels – while running a good maintenance regime – helps to ensure production efficiency and delay the need to invest in replacement parts
Flight risk: latest in screws and barrels
Running molten plastics through a pressurised container at high speed is a recipe for wear – and screws and barrels bear the brunt of this. It can have many effects on plastics production – includ- ing lower product quality, higher energy consump- tion and production delays. Mike Becker area sales manager at UK-based Magog Industries, says a multitude of factors can lead to problems. “High pressure, polymer viscosity, screw speed,
barrel alignment to the gearbox, and screw/barrel alignment can all cause accelerated screw and barrel wear,” he said. Plastics production is typically high volume, so machines tend to be kept running. In this situation, wear is not immediately apparent because machine speed and pressure – or even the material mix – tend to be adjusted first to correct issues of melt quality.
www.pipeandprofile.com “Over time, as the gap between screw and
barrel increases, a melt-film can form – leading to loss of melt quality in output,” he said. For a continuous process like extrusion, this will
be particularly apparent – especially because the melt is likely to move backward across the screw flights instead of going forwards. For a 50mm diameter screw, the minimum gap should be 0.10-0.15mm (maximum); for a larger 152mm diameter screw, the gap should be between 0.30 and 0.35mm. Ideally there should be 0.0254mm per side. This gap is small but crucial for optimum processing, he says. For this reason, he recommends monitoring
screw and barrel wear in-house as part of regular maintenance. Any issues can be picked up and scheduled in by the maintenance team. Measuring instruments, such as portable electronic bore
Summer 2024 | PIPE & PROFILE EXTRUSION 25
Main image: Screws can be refurbished several times before they need to be replaced
IMAGE: MAGOG
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