Frequently Asked Questions
rotomolding compare with injection molding and blow
What types of
products most effectively use the advantages of rotomolding?
materials are ideal for rotomolding?
are these ideal for rotomolding as opposed to other materials?
does the rotomolding process work?
has rotomolding grown so popular so quickly?
much does tooling cost to develop and how long will it last?
many pieces are produced per cavity in a 24-hour period?
is mold maintenance and who pays for it?
Q: How does rotomolding compare with injection
molding and blow molding?
A: In comparison to injection and blow molding,
rotational molding can easily produce both large, small
precision and non-precision parts in a cost effective manner
from a tiny medical bulb to a 16 foot kayak and up. Tooling
for rotomolding is less expensive than injection molding
because the process does not require any pressure to be held
and rotomolding tooling is far less expensive than blow
molding because there's no internal core to manufacture. Since
there is no internal core, minor changes can be easily made to
an existing mold, enabling product enhancements and line
extensions to be considerably less expensive to develop and
faster to bring to market.
addition, Rotomolded parts are formed with heat and rotation,
but not with pressure. Therefore, molds don't need to
withstand the high pressure of injection
for product conversions from one material to another are
reduced because rotomolding permits the replacement of
heavier, often more costly materials with lighter, less
expensive materials and does not require extreme or expensive
tooling changes to switch materials. This advantage makes
rotomolding as cost effective for one-of-a-kind prototypes as
it does for large production runs.
Rotomolding also offers significant design advantages
in comparison to injection molding and blow molding. With
proper design and engineering, parts that are assembled from
several injection or blow molded pieces can be molded as a
single part, eliminating expensive fabrication costs and
streamlining the manufacturing process.
Rotomolding also has a number of inherent design
strengths, such as consistent wall thickness and strong
corners that are virtually stress free. If additional strength
is required, reinforcing ribs can be designed and molded into
the hands of skilled engineers, rotomolding delivers the
product the designer envisions without the limitations of
other processes. With counsel from Interpak engineers,
designers can select the ideal material for their application,
including materials that meet FDA or USDA requirements.
Weather resistant, anti-static, dielectric and other
properties may be specified with the use of a host of
Inserts, threads, handles, undercuts, flat surfaces
that eliminate draft angles or fine surface detail are all
designed in from the beginning. Designers also have the option
of multi-wall molding that can be either hollow or foam
filled. Sales and marketing teams always appreciates the range
of colors, permanent, molded-in logos and graphics
Q: What types of products most effectively use the
advantages of rotomolding?
A: Complex products with odd and unique configurations
and products used in demanding applications where there is no
room for error are especially well suited to rotomolding. Fuel
tanks and fuel filler necks can be molded in one, uniform
piece eliminating the potential for dangerous leaks and
Oversized items such as spiral-shaped playground
equipment, bulk, specialty and chemical material handling
containers, kneeboards, toys and recreational and sporting
equipment are also well suited. In addition, any products that
need to withstand marine and outdoor environments are well
suited to rotomolding. Dock floats, marine fuel tanks and
other products with a seemless design are virtually impervious
to attack from the salts and corrosives of the ocean and
harbor while agricultural containers easily stand up to the
harsh conditions of the blistering sun and extreme
Q: What materials are ideal for
A: Cross-linked polyethylene (PE); linear low density
polyethylene (LLDPE); high density polyethylene (HDPE);
Polyvinyl chloride (PVC);
Q: Why are these ideal for
rotomolding as opposed to other materials?
A: Cross-linked polyethylene (PE) excels in cold
temperatures and won't break on impact in extremes of up to 20
degrees below zero F. LLDPE may be used in a diverse array of
applications at relatively low cost. HDPE is used in
agricultural chemical and other outdoor applications for its
ability to withstand a wide range of elements. PVC is ideal
for applications that demand flexibility such as medical
tubing, bags and cases.
Q: How does the rotomolding
A: The rotational molding process starts with a quality
cast or fabricated mold. The mold is placed in a rotomolding
machine that has a loading, heating, staging and cooling
Several molds are placed on the machine at the same
time. Pre-measured plastic resin is loaded into each mold,
then the molds are moved into the oven where they are slowly
rotated on both the vertical and horizontal axis. The melting
resin sticks to the hot mold and coats every surface evenly.
The mold continues to rotate during the cooling cycle so the
parts retain a uniform wall thickness, if that is
the parts are cooled, they are released from the mold. The
rotational speed, heating and cooling times are all controlled
throughout the process and may be adjusted based on the design
of the product.
Q: Why has rotomolding
grown so popular so quickly?
A: Rotomolding offers a relatively low initial tooling
investment and permits very short lead times. It also offers a
relatively low cost in small-to-moderate production runs.
Taken together, these characteristics are quite an advantage
to companies that need to bring new products to market quickly
at low cost and with little up front investment to minimize
Q: How much does tooling
cost to develop and how long will it last?
A: Tooling prices vary based on the complexity and size
of the design. Interpak uses 3-D computer modeling and CAD in
developing the tooling to speed the process and reduce costs.
The lifespan of tooling depends on the intensity of its
production runs. If maintained properly, tooling lasts for
Q: How many pieces are
produced per cavity in a 24-hour period?
A: Amounts vary based on the type of project and the
machine loading but typically range from 15 to 30 pieces per
24-hour period. Our engineers are able to schedule the precise
number to be molded in a given time period and offers JIT
delivery to ensure only the needed amount of product is molded
Q: What is mold maintenance
and who pays for it?
A: The intense heating and cooling process of
rotomolding puts considerable stress on the molds. That's why
it makes sense to develop a high quality mold from the very
beginning. The better the mold, the more able it is to
withstand many long production runs. Over time, every mold
does require maintenance, which consists of reworking framing.
Most rotomolders charge for mold maintenance but Interpak
includes it as an accommodation.