Manufacturing Technologies for Turbine Power Blades - Hybrid Anisotropic Materials for Wind Power Turbine Blades - page 110

Unload-load station

Molded part

Mold open

Two-direction of rotation mold

Counterweight

3. Cooling station

2. Heating station

Mold is closed

Water spray

Rotational molding process

FIGURE 4.13
Rotational.molding.process.

. 3.. Cooling.the.mold,.usually.by.fan..This.stage.of.the.cycle.can.be.quite.

lengthy..The.polymer.must.be.cooled.so.that.it.solidiies.and.can.be.
handled.safely.by.the.operator..This.typically.takes.tens.of.minutes..
The. part. will. shrink. on. cooling,. coming. away. from. the. mold,. and.
facilitating.easy.removal.of.the.part..The.cooling.rate.must.be.kept.
within.a.certain.range..Very.rapid.cooling.(e.g.,.water.spray).would.
result.in.cooling.and.shrinking.at.an.uncontrolled.rate,.producing.a.
warped.part.

. 4.. Removal.of.the.part.

4.9.6 Recent Improvements

Until. recently,. the. process. was. largely. empirical,. relying. on. both. trial. and.
error. and. the. experience. of. the. operator. to. judge. when. the. part. should. be.
removed.from.the.oven,.and.when.it.was.cool.enough.to.be.removed.from.
the. mold.. Technology. has. improved. in. recent. years,. allowing. the. air. tem-
perature.in.the.mold.to.be.monitored,.removing.much.of.the.guesswork.from.
the.process.
Much. of. the. current. research. is. into. reducing. the. cycle. time. as. well. as.
improving.part.quality..The.most.promising.area.is.in.mold.pressurization..
It.is.well.known.that.applying.a.small.amount.of.pressure.internally.to.the.
mold.at.the.correct.point.in.the.heating.phase.accelerates.coalescence.of.the.
polymer.particles.during.the.melting,.producing.a.part.with.fewer.bubbles.