Composites Design and Manufacture (Plymouth University teaching support materials)
Contact moulding: spray techniques and hand lamination.
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Gel Coat

Gel coat is a cosmetic and/or functional surface applied to a composite component [1].  It is normally brushed or sprayed onto the mould tool before the laminate is made.

There is currently considerable interest in in-mould gel-coating (IMGC), recently reviewed by Rogers et al [2], to reduce the level of volatile organic compounds (VOC) in the working environment.  ACMC has undertaken research into novel (patented) processes for closed mould composites manufacturing technologies using either a separator layer [3] or a removable silicone shim [4] with funding from the UK DTI ZEE and EU FP7.  Di Tomasso et al [5] reported that the FP7 project outcomes were "[T]he two closed mould technologies significantly reduce the measured styrene levels to lie in the range 0.23–0.37 ppm. The new processes offer a reduction in average styrene emission levels of >98% (worst new/best old) with obvious benefits for worker health and the reduction of environmental burdens".

KraussMaffei [6] have developed the SurfaceRTM process for cost-effective manufacturing of paintable fiber-reinforced visible components for vehicle manufacturing for series applications

See the section on surface finish on the mould tools page.  Customer satisfaction is the key driver for high-quality surface finish.  Two Trouble-Shooting Guides for Gel-Coats exist:

and the CCP University has three videos:

Further information:

Spray techniques

Hand-lamination is described in reference 1.

Hand lamination [1], also known as hand lay-up (HLU), involves wetting the mould tool with resin and progressively adding layers of reinforcement or more resin.  The resin may be delivered from a bucket using a brush (hence the common name: bucket-and-brush lamination), or by a mixing machine and resin spray head.  An impregnation roller (often incorrectly referrred to as a consolidation roller) may be used to help the wetting of the fibres and to cause bubbles to leave the laminate.  There is no solid evidence that the roller increases the fibre volume fraction of the cured laminate?  The laminate is normally cured at ambient temperature and pressure.  Higher fibre volume fractions can be achieved by vacuum bagging the laminate.

Centrifugal casting

Centrifugal casting is a special case of spray manufacture where the spray is directed into the base of a rotating cylindrical mould to manufacture large diameter pipes.  The process can also be used with fabric reinforcement such that the centrifugal force causes resin to permeate the reinforcement fabric or with chopped fibres added to the spray: this creates a smooth finish on the outside of the pipe while excess resin can be added to create a resin-rich corrosion- and abrasion-resistant interior surface.  The process was used at Johnston Pipes in Telford to produce large diameter (~2 m) pipes for water and sewage transport.

Reference:

  1. D Cripps, T J Searle and J Summerscales, Open Mould Techniques for Thermoset Composites, In R Talreja and J-A Månson (editors): Comprehensive Composite Materials Encyclopædia, volume 2: Polymer Matrix Composites, Elsevier Science, Oxford, July 2000, Chapter 21, pp 737-761. ISBN 0-08-043725-7.  MooDLE
    This text also covers vacuum bagging and infusion techniques.
  2. W Rogers, C Hoppins, Z Gombos and J Summerscales, In-mould gel-coating of polymer composites - a review, Journal of Cleaner Production, 1 May 2014, 70, 282-281.
  3. AR Harper, J Summerscales and N Brooks, Production of composite mouldings, GB Patent Application 2432336, 2007.
  4. AR Harper, Production of composite mouldings, Patent WO2013/132211A1, 12 September 2013.
  5. C Di Tomasso, ZJ Gombos and J Summerscales, Styrene emissions during gel-coating of composites, Journal of Cleaner Production, 15 November 2014, 83, 317–328.
  6. First-class surfaces for fiber composite parts at the start, KraussMaffei, accessed 27 February 2015.

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Updated by John Summerscales on 11-Sep-2019 14:37. Terms and conditions. Errors and omissions. Corrections.