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About Rotational Molding
Rotational molding is a process by which plastic goods
are formed and manufactured for numerous applications. The process begins
with a rotational molding machine with attached spindles. The spindles
support the molds in which the plastic material is contained. The molding
machine moves the molds past loading, heating and cooling areas. From
start to finish, there are four different stages that are completed in
anywhere from 15 to 90 minutes. The first stage, referred to as the charging
phase, is the loading and sealing of the material in the metal mold.
From there, the mold is heated to a specified temperature while revolving
on the vertical and horizontal axes of the spindles. Phase three is a
cooling stage that begins to solidify the plastic within the mold. The
mold is then reopened, and the solid plastic part is removed. For applications
that require additional strength, reinforcing ribs can be fabricated
into the part. Additives to make the part flame retardant, corrosion
resistant or static free can also be included in the plastic resin.
Common rotationally molded plastics are cross-linked polyethylene (PE),
high density polyethylene (HDPE), linear low density polyethylene (LLDPE)
and polyvinyl chloride (PVC). PE is ideal for products that will be exposed
to extremely cold temperatures, as it has high impact strength in temperatures
to -20ºF. HDPE is able to withstand a wide variety of environmental factors,
making it highly useful in the agricultural and chemical industries.
LLDPE is a low-cost material that has a wide range of uses. PVC is used
for its flexible properties in applications, such as medical tubing,
bags and cases. Lighter materials are used more often in rotomolding,
making it less expensive than other methods, and making it cost effective
for sizeable production runs and prototypes. Examples of other rotomolded
products include football helmets, plastic
tanks, large trash containers
and juice/pop bottles.
Rotational molding services have several advantages over blow
molding and injection
molding. The tooling in the rotomolding process can be
designed to undercut and core features in a part. This option would be
very costly in the blow molding process. Rotationally molded plastic
parts have thickness in outside corners, which is critical to durability.
This formation of thickness is inherent to the rotomolding process, but
not to the blow molding process. Rotational molding also provides freedom
of design that would be constrained by the process and tooling of blow
molding. Rotational molding does not require pressure to be used, so
the molds do not endure the same pressure as in injection molding, and
this makes the process less expensive.
There are many other advantages to the rotational molding process. While
being heated and rotated, the plastic resin adheres to the hot mold,
coating it very evenly and seamlessly, producing strong outside corners
with virtually no stresses. Rotomolding can produce one-piece constructions.
Complex parts can be formed without any part assembly required. The plastics
used for rotomolds are lightweight and relatively cheap. The low cost
of the materials and tooling makes rotational molding just as cost effective
for producing prototypes as it is for large production runs. A variety
of finishes and colors are available. Rotomolding is a versatile process
that provides durability to products.
Featured
Articles
http://www.plasticstechnology.com/articles/200303cu2.html
http://www.foamandform.com/minutes/frm.php
Types of Rotationally Molded Plastics
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is an ideal material for rotomolded products that will be exposed to
extremely cold temperatures.
- offers high-flow molding and high molecular weight performance
in rotationally molded parts. Properly rotomolded HDPE products will
have interior gloss development, ductile cold temperature impact performance
and an off-gas odor that confirms the chemical cross-linking reaction.
- provides superior fit and finish to rotationally
molded products. Rotomolded LLDPE products also have high impact, tensile
and dielectric strength.
-
is a lightweight plastic that has a low modulus of elasticity. Rotationally
molded PE products are thick in desired places and have good impact
resistance.
- , also referred to as “vinyl,” has excellent
transparency, chemical resistance, long-term stability, good weatherability,
flow characteristics and stable electrical properties. PVC can be either
rigid or flexible.
- are used to fabricate hollow plastic parts.
- is the low pressure process used to create hollow plastic components.
-
are seamless polyethylene (PE) tank structures that retain molded-in
logos, warnings, serial numbers and other full color graphics when exposed
to salt water, sunlight, solvents, cold weather and other severe conditions.
- are one-piece products created on a rotational molding machine.
- is the four-step process used to make hollow plastic components.
- are machines used to make hollow, one-piece plastic parts.
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