SCREWS AND BARRELS | MACHINERY


cooling channels raised efficiency. Adding highly wear-resistant exchangeable sleeves to the barrels helped to save resources. The process was also optimised by adding extra degassing barrels – to make the extruder more flexible in use. As well as requiring design expertise, the project also needed a high degree of manufacturing precision, said the company. “In previous projects, customers have reported savings of 8-15% during heating and operation of the system,” it added. In addition, the company says it offers a ‘wear and


fair’ offer to customers. It says measuring wear on extruder parts is necessary once or twice per year. After measuring screw and barrel wear, the company provides both video images and graphical results. “The smallest indications of wear are detected at


an early stage, allowing customers to decide calmly what needs to be done and when,” it said. On this basis, it says the actual condition of


screws and barrels can be determined – including an accurate estimate of the correct time to carry out a service or renew parts. It adds that it will refund part of the cost of this if it is later commis- sioned to supply spare parts.


Alignment advice In a recent blog post, Davis-Standard recom- mended 10 habits that extrusion companies should adopt “in order to achieve peak equipment performance” – and these included: a review of maintenance checklists; and aligning extruders. The extruder is a good place to start when


reviewing maintenance checklists, it said – and has produced a PDF guide to the quarterly tasks that should be carried out. “We suggest checking 10 extruder components


as part of a healthy maintenance plan,” it said in the blog. For the feedscrew and barrel, advice included:


cleaning and inspecting the pressure gauge transducer; measuring and recording feedscrew flight and barrel diameters (on an annual basis); conducting Liquid Penetrate Non-Destructive Test (NDT) for cracks on the feedscrew and barrel (also yearly); and cleaning and inspecting both feed- screw and barrel. In addition – for barrel heaters – it recommend-


ed: measuring and recording heater amperage and resistance; cleaning and inspecting barrel heater fins; checking all thermocouple and heater terminal connections; and measuring and record- ing blower fan motor temperatures. Davis-Standard added that a poorly aligned


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extruder can lead to excess wear and tear on both screw and barrel. “The longer the extruder barrel, the more significant alignment becomes,” said the company. “We’ve seen misalignment cause costly and unnecessary damage – including premature wear, bent and broken screws and unstable barrels. First, the barrel must be aligned to the driving mechanism – which is the drive quill of the gear- box. Trying to determine alignment by levelling is inaccurate, as it is not indicative of the drive quill – and only measures the vertical plane. “The correct procedure involves using an optical or laser alignment scope inside the drive quill to align the barrel to a fixed centre line by rotating the drive quill,” it said. “The barrel and feed throat are then aligned to that centre line by adjusting the barrel supports, or the mounting faces of the feed throat.”


Using a barrel support system is important, but


several factors must be considered. The barrel must be able to expand freely – and without distortion – through the support as it is heated. It should never be locked down by a support that completely surrounds it – which prevents the barrel from having the room to slide when expanding. Also, the support joints must be made from non-corrosive materials, such as brass, to prevent ‘freezing’ of the support. Finally, the entire barrel support must be rigid enough to maintain its position – and not tip over as the barrel expands: a 4.5in barrel will grow more than 0.3in when heated to typical temperatures.


CLICK ON THE LINKS FOR MORE INFORMATION: � www.erema-group.com � https://extremecoatings.net � www.entek.com � www.extruder-experts.com � www.davis-standard.com


March/April 2023 | PIPE & PROFILE EXTRUSION 23


Above: Screw design can be vital to extrusion efficiency


IMAGE: MESSE DÜSSELDORF, CONSTANZE TILLMANN


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