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Friday, January 9, 2009

Composite Fabrication : Hand Lay Up / Wet Lay Up

Hand Lay-up
In this process resins are impregnated by hand into fibres which are in the form of woven, knitted, stitched or bonded fabrics. Hand lay up process usually accomplished by rollers or brushes.
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 then, 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

Typical Applications of Hand Lay-Up Process:
Standard wind-turbine blades, production boats, architectural mouldings.

Advantages of Hand Lay-Up Process:
Widely used for many years.
Simple principles to teach.
Low cost tooling, if room-temperature cure resins are used.
Wide choice of suppliers and material types.
Higher fibre contents, and longer fibres than with spray lay-up

Disadvantages of Hand Lay-Up Process:
-Quality (mixing, fibre contents, laminate quality) - very dependent on skills ( Low resin/high fibre content cannot usually be achieved)
-Health & safety considerations;
lower molecular weights resins - have potential to be more harmful than higher molecular weight products and also have an increased tendency to penetrate clothing etc.
-Limiting airborne styrene concentrations; becoming increasingly hard without expensive extraction systems.
-Resins need to be low in viscosity to be workable by hand - generally
compromises mechanical/thermal properties (high diluent/styrene levels).

Hand Lay-Up Process