came up with aren’t all that
imaginative.
Phenolics
Phenolic is a name for a plastic
which contains phenol (C6H5OH)
(again plastic inventors weren’t the
most original). Phenolics are
thermoset plastics. The first fully
synthetic plastic ever produced was
a phenolic called Bakelite. Phenolics
are typically brittle and relatively
expensive; however they have great
electric and heat insulating qualities
which is why they are commonly
used in circuit boards.
ABS
ABS is tough impact resistant
plastic found quite commonly in the
automotive industry. It is typically
used for the interior trim pieces in
your car. You may have had your
first experience with ABS as a child
playing with LEGO® bricks. It is
more costly to produce than other
materials and it can produce an
intensely hot flame once ignited. It
should also be noted that ABS has
different grades that are based upon
the impact qualities and the
intended forming methods.
Polyethylene (PE/PET)
Polyethylene (and polyethylene
terephthalate) is one of the most
common plastics you will encounter.
In fact, you could be wearing it or
drinking from it right now. PET in
fabric form is something you may
have heard of — polyester. PET is also
common in solid form and is used in
soda bottles, detergent containers,
milk jugs, plastic bags, etc. It is one of
the cheapest plastics and offers good
abrasion resistance and impact
strength. It is a thermoform plastic,
so it is easy to bend into most any
shape your heart desires.
UHMW
Ultra-High Molecular Weight
Polyethylene is a subset of the
previously mentioned polyethylene. I
broke it out in a separate section
because of its frequent use in
robotic applications. UHMW has
excellent wear resistance and a low
coefficient of friction (COF) which
lends itself to being used frequently
as a bushing material. It also has
excellent impact resistance which
makes for a great frame material.
Working with UHMW is easy, as you
can use standard wood and/or
metal working tools to cut, drill, and
tap it. UHMW can be held together
with wood screws or tapped for use
with machine screws. UHMW is
found in artificial joints, as a wear
plate at the bottom of hockey rinks,
and in cutting boards.
Acetal/Delrin
Delrin is a great material for
areas where you are expecting to
have parts moving past each other.
Delrin has impact qualities close to
ABS, but has a lower COF. Delrin is
found in a wide variety of
applications, such as gears and
bushings, and is also used for several
parts in paintball and airsoft guns.
Acetal has fair impact qualities, but
from experience is probably best left
for friction components and not
used for frame material.
Acrylic/Plexiglass
Acrylic is a great plastic if you
are more interested in appearance
and cost than taking an impact.
Acrylics are commonly used as a
cheap and more shatter resistant
replacement to glass. Acrylic will still
shatter under load — especially an
impact load — and is not very
scratch resistant. It is much cheaper
than the more impact resistant
polycarbonate. Due to its strength
and its ability to be produced in
large sheets, acrylic is used for the
large viewing windows in
aquariums. You probably also drove
by acrylic the last time you were in
your car, as it is used frequently to
make large store signs.
Polycarbonate
Polycarbonate is a plastic that
offers exceptional impact resistance
and light transmission, i.e., it’s clear.
Polycarbonate is found in laminated
form to produce the bullet-proof
(bullet-resistant) windows at the
bank. Polycarbonate is the plastic of
choice, and the only one I
recommend for use in combat arena
windows. Polycarbonate is very
expensive and is not very scratch
resistant. For combat arena usage, it
is recommended to apply a thinner,
sacrificial layer to the interior of the
arena that can be replaced once it is
scratched to the point where viewing
becomes an issue. Polycarbonate it
not a brittle plastic, so it is possible to
form without adding heat.
PVC
Polyvinyl Chloride (PVC) is a
good plastic commonly found in the
construction industry. It is cheap to
produce and is easy to bond. PVC is
a controversial plastic because as
certain additives off-gas they may
produce toxins, especially if burned.
It is most notably found as PVC pipe
for plumbing and irrigation. It makes
a good robotic material because it is
readily available at any major
hardware store and is easy to form
into a wide variety of shapes. PVC is
also commonly found in window
and door frames, wire insulation,
shower curtains, and in components
used for IVs.
Wrap-Up
Plastics come in a wide variety
of shapes, colors, opacity, and material
qualities. Hopefully, you’ve found
this article useful in selecting which
material you’ll be using next in your
robotics applications. When it comes
to plastics, there is no replacement
for experience, so get out there and
try some. Feel free to get back with
me with your results. SV
SERVO 07.2011 29
