Filament winding


Filament winding is a fabrication technique involving wrapping pre-tensioned, resin saturated continuous reinforcements around a mandrel (male mould). The mandrel is usually circular in cross-section; however other cross sections are achievable with the correct programming. Specific mechanical properties are achieved through reinforcement and resin selection, careful fibre orientation and thickness.  Suitability to operating environment is primarily determined by the resin matrix and internal lining (however reinforcement selection should also be carefully considered). Programs can adjust settings such as wind angle throughout the laminate build to optimise the properties.

Filament winding with a fixed mandrel restricts the overall length of the finished part by the length of the mandrel.  Manufacturing is best described as a batch process. Continuous filament winding utilises a steel band wrapped to form the mandrel. The band collapses on itself at the end of its travel, and relocating back to the beginning to form the mandrel again. This process is for larger diameter parts, but the length of the part is then less restricted by machinery constraints.

allnex products commonly used:

  • Resin (UPE, vinyl ester or epoxy)
  • Catalyst
  • Single end rovings surface veil
  • Mould release

Steps

  1. A release film can be wound around the mandrel to prevent stick-ups.
  2. If required for added corrosion resistance or surface smoothness, a surface veil1 is wound around the mandrel.
  3. The doffs/cheeses of continuous strand roving are set on creels2 (Bobbins in the case of carbon).
  4. The selected number of ends of continuous strand roving is fed from creels then gathered and tensioned3.
  5. The strands are pulled through a bath of catalysed resin, then through a squeegee or nip-rollers to remove excess resin.
  6. The saturated strands pass through a guide-eye that is mounted on a traversing mechanism which travels along the length of the rotating mandrel.4
  7. When the required number of layers are deposited the feed of strands is discontinued and the part can be cured on the rotating mandrel.5  Curing may occur at room temperature or at elevated temperatures (if a heating mechanism is installed).

Notes:

1For pipes or tanks surface veil selection is critical to the corrosive resistance of the finished part.  C-glass or synthetic surface veils are standard.
2Some reinforcement suppliers are capable of supplying pre-spliced doffs/cheeses which enable high volumes of reinforcement to be run directly from the pallets.
3The tension will influence the glass:resin ratio and finished thickness of each layer.
The ratio of traverse speed vs mandrel rpm determines the angle of the strands, while the shape of the guide-eye and number of strands influences the band width.  In some cases the resin bath can also traverse alongside the mandrel.
5Rotating the mandrel during cure will prevent the resin from sinking to the underside of the part.

Hints & Comments

  1. Filament winding is a medium paced manufacturing technique. Equipment set up cost can be high, but production itself is economical. Careful consideration should be given to mandrel specifications.
  2. Filament winding can be an adaptable process for producing a variety of products.
  3. Where parts with a polypropylene, PVC or liner of other material are required, the prefabricated liner can take the place of the mandrel.
  4. Polyester, vinyl ester and epoxy resins can all be used giving scope to a variety of environmental suitability.
  5. Sand can be included in between layers to bulk up the laminate.
  6. Reinforcement selection and placement, resin type, compatability of resin and reinforcement, all have an impact on mechanicals such as burst strength, hoop and compression strength. Stiffness is determined by fibre angle, wall thickness and stiffening ribs can also be built in in-situ.
  7. Parts can be tapered. A finished inner surface is produced and the outside surface is flowcoated. This process produces parts with high fibre content in a controlled orientation and thus good mechanical properties. Parts have very uniform thickness and resin to glass ratio.
  8. Products currently being produced using this technique range from pipes, masts and spars, golf clubs, power and transmission poles, pressure vessels to missile casings, aircraft fuselages and lamp posts.