Significant advantages of filament winding

Filament winding is a fabrication technique in the manufacture of composite material, usually in the form of cylindrical structures. With this process, the mould or mandrel rotates as a carriage moves horizontally at certain temperature, laying down fibres in the desired pattern for the finished product. The process has been recognised as highly effective in manufacturing lightweight composites because of its speed and precise method of placing layers of composite material.

The mandrel can be cylindrical, round or any shape without re-entrant curvature. Amongst the applications of filament winding are cylindrical and spherical pressure vessels, pipe lines, oxygen and other gas cylinders, rocket motor casings, helicopter blades, large underground storage tanks (for gasoline, oil, salts, acids, alkalies, water etc.).

Over the years, filament winding has advanced with machines offering freedom of design, with precision achieved through the use of software that enable data processing resulting in more accurate motion and fibre placement. 

Environment-friendly filament winding technology

A wet-filament winding technology was developed through a joint R&D project undertaken by The University of Birmingham’s School of Metallurgy and Materials and a consortium of companies in the United Kingdom. The technology has paved the way for environment-friendly ‘clean’ filament winding technology for the production of high-performance composites.

The design components of this wet-filament winding technology include a custom-built modular fibre bundle spreading station and a mixed resin fibre impregnation unit, which together provide effective fibre wetting.  Waste and solvent usage has also been significantly reduced compared with traditional wet bath filament winding production, whilst up to 80% less cleaning solvent consumption has been achieved, along with reduction of mixed resin waste.  A variety of thermosets, including faster curing resins, have been successfully tested in this clean filament winding technology, which can be retrofitted and adapted for other manufacturing processes, such as pre-pregging and pultrusion. The technology was presented during the JEC Europe 2013 exhibition in Paris by the UK consortium on the Pultrex.

The cleaner wet-filament winding process

For manufacturers, there are several major productivity advantages over a conventional wet resin bath in using this new filament winding technology with its metered static mixer and resin impregnation head.   The custom built metering system automatically draws the resin and hardener in the required stoichiometric ratio as needed from the individual bulk reservoirs.  This eliminates the need to do any pre-weighing and manual mixing of the resin and hardener, with the subsequent benefits of no longer needing to use any disposable consumables, such as containers, stirrers and paper and, more importantly, avoiding the problem of air entrapment, a real issue with manual mixing.   The other key productivity and cost saving gain of this new automated clean technology system is that the process can be truly ‘continuous’ and not limited by the mixed resin volumetric capacity of a wet bath, which must be replenished manually; the resin and hardener reservoirs can be replenished  during production with no interruption to the line.

This significantly cleaner wet-filament winding process, which has achieved up to an 80% reduction in cleaning solvent consumption along with an equivalent reduction of mixed resin waste, is due to two key factors.   Firstly, with no resin bath, the need to thoroughly clean the equipment at the end of each production run is eliminated; depending on the dimensions of the resin bath, the cleaning operation consumes several litres of solvent plus the associated consumables, which all have to be disposed of along with the waste mixed resin; the need to take exotherming precautions with waste mixed resin is also eliminated.   Secondly, the unit has been designed such that final roller of the resin applicator is positioned above the mandrel.  Therefore, unlike a conventional wet-filament winding process, with this configuration the problem of resin dripping from the impregnated tows on to the floor is eliminated.