183
7
5 Gelation time of resin—The gelation time controls the processability of a composite because it provides the processing
window in terms of time. The gelation time must be sufficiently long so that the reinforcement can be placed on the
mould, reinforcement can be impregnated with the resin, and
the next layer of reinforcement can be placed. The relationship
between gelation time and wettability time is given here.
T G µ
1
h
(7.1)
T W µ
1
h
(7.2)
T
T
W
G
µ
(7.3)
T
MT
W
G
=
(7.4)
where:
η = Viscosity of the resin
T W  = Wettability time for the reinforcement
T G  = Gelation time of the resin
M = Processability constant
a
b
. Fig. 7.2 a B75 windmill rotor blades by Siemens and b moulded windmill
rotor blade [8, 9]
7.1 · Open Mould Processing Technologies