Environmental Engineering Reference
In-Depth Information
cost.for.the.size.of.product.produced..It.is.also.available.in.smaller.scale.for.
schools.and.prototyping
4.9.4.5
Carousel Machine
This. is. one. of. the. most. common. machines. in. the. industry.. It. can. have. up.
to.six.arms.and.comes.in.a.wide.range.of.sizes..The.machine.comes.in.two.
different.models:.ixed.and.independent..A.ixed.carousel.consists.of.three.
ixed.arms.that.must.move.together..One.arm.will.be.in.the.heating.cham-
ber.while.the.other.is.in.the.cooling.chamber.and.the.other.in.the.loading/
reloading.area..The.ixed.carousel.works.well.when.working.with.the.same.
mold..The.independent.carousel.machines.are.available.with.more.arms.that.
can. move. separately. from. the. others.. This. allows. for. different. size. molds,.
with.different.heating.and.thickness.needs.
43
4.9.5
Production Process
The. rotational. molding. process. is. a. high-temperature,. low-pressure. plas-
tic-forming. process. that. uses. heat. and. biaxial. rotation. (i.e.,. angular. rota-
tion.on.two.axes).to.produce.hollow,.one-piece.parts..Critics.of.the.process.
point.to.its.long.cycle.times—only.one.or.two.cycles.an.hour.can.typically.
occur,.as.opposed.to.other.processes,.such.as.injection.molding,.where.parts.
can.be.made.in.a.few.seconds.. The.process.does.have.distinct.advantages..
Manufacturing.large,.hollow.parts,.such.as.oil.tanks,.is.much.easier.by.rota-
tional. molding. than. any. other. method.. Rotational. molds. are. signiicantly.
cheaper.than.other.types.of.molds..Very.little.material.is.wasted.using.this.
process,.and.excess.material.can.often.be.re-used,.making.it.a.very.economi-
cally.and.environmentally.viable.manufacturing.process.(Figure 4.13).
The.rotational.molding.process.consists.of.four.distinct.phases:
.
1.. Loading.a.measured.quantity.of.polymer.(usually.in.powder.form).
into.the.mold.
.
2.. Heating. the. mold. in. an. oven. while. it. rotates. until. all. the. poly-
mer. has. melted. and. adhered. to. the. mold. wall.. The. hollow. part.
should.be.rotated.through.two.or.more.axes,.rotating.at.different.
speeds,. in. order. to. avoid. the. accumulation. of. polymer. powder..
The.length.of.time.the.mold.spends.in.the.oven.is.critical,.too.long.
and. the. polymer. will. degrade,. reducing. impact. strength.. If. the.
mold.spends.too.little.time.in.the.oven,.the.polymer.melt.may.be.
incomplete.. The. polymer. grains. will. not. have. time. to. fully. melt.
and. coalesce. on. the. mold. wall,. resulting. in. large. bubbles. in. the.
polymer..This.has.an.adverse.effect.on.the.mechanical.properties.
of.the.inished.product.
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