Manufacturing Technologies for Turbine Power Blades - Hybrid Anisotropic Materials for Wind Power Turbine Blades - page 106

4.8.2 Conclusion

The. automatic,. 3. axial. braiding. process. with. the. automation. VARTM. pro-
cess. and. Smart. Molding. Control. were. proposed. for. use. for. wind. blades.
manufacturing.

4.9 RotationalMolding

4.9.1 Introduction

Rotational.molding,.also.known.as.rotomolding,.rotocasting,.or.spin.casting,.
is.a.molding.process.for.creating.many.kinds.of.mostly.hollow.items,.typically.
of.plastic,.that.can.be.used.for.molding.web.spars.for.wind.turbine.blades.
A. three-motor-powered. (tripower). rotational. molding. or. spin. casting.
machine.was.developed.recently..This.is.a.robust.manufacturing.process.for.
web.spars.for.wind.turbine.blades.
A.heated,.hollow.mold.is.illed.with.a.charge.or.shot.weight.of.material..
It. is. then. slowly. rotated. (usually. around. two. perpendicular. axes). causing.
the.softened.material.to.disperse.and.stick.to.the.walls.of.the.mold..In.order.
to. maintain. even. thickness. throughout. the. part. and. to. avoid. sagging. or.
deformation. during. the. cooling. phase,. the. mold. continues. to. rotate. at. all.
times.during.the.heating.phase..The.process.was.applied.to.plastics.in.the.
1940s,.but,.in.the.early.years,.it.was.rarely.used.because.it.was.a.slow.process.
restricted.to.a.small.number.of.plastics..Over.the.past.two.decades,.improve-
ments.in.process.control.and.developments.with.plastic.and.ceramics.pow-
ders. have. resulted. in. a. signiicant. increase. in. usage.. (For. a. description. of.
basic.principles.of.rotational.molding,.see.Wikipedia. 37 )

4.9.2 History

In.1855,.R..Peters.of.Britain.documented.the.irst.use.of.biaxial.rotation.and.
heat..This.rotational.molding.process.was.used.to.create.metal.artillery.shells.
and.other.hollow.vessels..The.main.purpose.of.using.rotational.molding.was.
to. create. consistency. in. wall. thickness. and. density.. In. 1905,. in. the. United.
States,.F..A..Voelke.used.this.method.for.the.hollowing.of.wax.objects..This.
led.to.G.S..Baker's.and.G.W..Perks'.process.of.making.hollow.chocolate.eggs.
in.1910..Rotational.molding.developed.further.and.R..J..Powell.used.this.pro-
cess.for.molding.plaster.of.Paris.in.the.1920s..These.early.methods.using.dif-
ferent.materials.directed.the.advancements.in.the.way.rotational.molding.is.
used.today.with.plastics. 38
Plastics. were. introduced. to. the. rotational. molding. process. in. the. early.
1950s.. One. of. the. irst. applications. was. to. manufacture. doll. heads.. The.
machinery.was.made.of.an.E.Blue.box-oven.machine,.inspired.by.a.General.