Wet/Hand Lay-up


Resins are impregnated by hand into fibres which are in the form of woven, knitted, stitched or bonded fabrics. This is usually accomplished by rollers or brushes, with an increasing use of nip-roller type impregnators for forcing resin into the fabrics by means of rotating rollers and a bath of resin. Laminates are left to cure under standard atmospheric conditions

Materials Options: 

Resins: Any, e.g. epoxy, polyester, vinylester, phenolic. 
Fibres: Any, although heavy aramid fabrics can be hard to wet-out by hand. 
Cores: Any.

Main Advantages

i) Widely used for many years. 
ii) Simple principles to teach. 
iii) Low cost tooling, if room-temperature cure resins are used. 
iv) Wide choice of suppliers and material types. 
v) Higher fibre contents, and longer fibres than with spray lay-up.

Main Disadvantages: 

i) Resin mixing, laminate resin contents, and laminate quality are very dependent on the skills of laminators. Low resin content laminates cannot usually be achieved without the incorporation of excessive quantities of voids. 
ii) Health and safety considerations of resins. The lower molecular weights of hand lay-up resins generally means that they have the potential to be more harmful than higher molecular weight products. The lower viscosity of the resins also means that they have an increased tendency to penetrate clothing etc. 
iii) Limiting airborne styrene concentrations to legislated levels from polyesters and vinylesters is becoming increasingly hard without expensive extraction systems. 
iv) Resins need to be low in viscosity to be workable by hand. This generally compromises their mechanical/thermal properties due to the need for high diluent/styrene levels.

Typical Applications: 

Standard wind-turbine blades, production boats, architectural mouldings.

Published courtesy of David Cripps, Gurit