Hertfordshire-based manufacturer and refurbisher of screws and barrels for the plastics and rubber industry Magog has improved service life of a screw used for extruding glass-filled highly abrasive polymer blend for a customer in the UK producing double glazing indirectly for consumers.
The extrusion manufacturer faced a problem of excessive wearing of screws, which resulted in significant costs not just in terms of the replacement component price but with excessive down time, lost production and general exposure to failure.
Magog was asked to assist with finding a viable long term solution to the problem. Initially two routes were considered. The first was improving the wear resilience of the existing screw with an alternative surface coating. The second was changing the screw profile to reduce the effect of abrasive wear in the initial melt phase.
For an improved coating specification Magog worked with a specialist surface coating company which was able to recommend a number of coatings, including tungsten carbide and chromium based alloys. Initial tests were unsuccessful, the flight profile being such that certain areas of the root of the screw were not effectively coated. Subsequent development work carried out by Magog with this coating technology has been more successful, and it is currently working on a tri-party development project involving Magog, end user, and specialist surface coating company.
The second path looked at the mechanics of the screw in conjunction with the grooved feed section design. Magog developed a screw design specific for the customer's process based on its previous successful experience of screw design for processing a similar abrasive material, and considering the specific material rheology and flight form. The screw was manufactured to the Magog standard hardfacing specification of Nitrided (a heat treating process that diffuses nitrogen into the surface of a metal to create a case-hardened surface), with weld applied hard facing alloy on the flight tips. Magog says this specification of screw was less expensive to manufacture compared with the coated screw, while for the customer it meant a lower purchase cost compared with the original suppliers' component with similar specification.
The screw manufacturer also says its newly-designed screw provided a significant improvement in the service life of the component without any compromise to process quality or production rates. This screw design has been adopted as standard by the customer, which is making considerable savings