Why Cast Nylon?
With all the different choices
available, why would
anyone choose cast nylon
over the literally hundreds of other
thermoplastics in today’s market?
There are a number of reasons that
come to mind that relate to performance,
price and availability.
Cast nylons are used in a wide
range of applications, from a simple
equipment support pad, to a sophisticated
drum in a machine that sorts
thousands of coins a minute, to a sheave on a crane that
can lift 1,000 tons, to a component used to eviscerate
chickens! There is perhaps no other process that can produce
parts weighing from one pound to over eight hundred
pounds in tooling that, relatively speaking, costs peanuts.
So what makes this material suitable for so many applications?
A quick look at the material’s basic properties
compared to other common materials shows why. It has
excellent tensile and compressive strength, good wear
properties and is an excellent electrical insulator. It can
also be modified to improve just about any individual
property; plasticizers improve impact strength, lubricants
reduce coefficient of friction, anti-oxidizers improve operating
temperature range, glass fibers improve rigidity,
other additives allow the use of colored nylons in direct
food contact applications.
Let’s compare cast nylon with a couple of the other
more common materials.
Extruded nylons are predominantly made from type
6/6 nylon and have basic physical properties very similar to
those of cast nylon. Performance and size availability however
are another matter. Cast nylon has lower residual
stress levels, more uniform crystallinity and thus better
dimensional stability than extruded. Extruded products are
generally more attractive in the smaller size ranges where
extrusion rates are highest. In sizes over 3” for rod and 1”
for plate, cast nylons become more attractive due to the
slow extrusion rates in producing extruded products.
Acetal – much has been said about the dimensional
stability of acetal based on its low rate of moisture
absorption, which is a fact but only relevant if the part is
either submerged or subjected to considerable moisture
exposure. Acetal comes in two forms, homopolymer and
copolymer, properties shown are for homopolymer which
are the higher than those of copolymer. Acetal and cast
nylon have basically the same coefficient of thermal
expansion however, which means that if temperature
changes then both materials will change by the same
amount. This means then that the only difference would
be in the amount of expansion resulting from moisture
absorption and if sufficient clearance is designed into a
cast nylon part to accommodate this expansion, a cast
nylon part should outperform an acetal part because of
cast nylon’s superior bearing properties.
Both materials are
FDA/USDA listed for direct food
contact. While both materials
machine easily, acetals release
formaldehyde during machining
and adequate ventilation must be
provided to protect the operator
UHMWPE is available in much
wider size ranges than either extruded
nylon or acetal and also costs
much less. It has much lower moisture absorption than
acetal and has better chemical resistance than either acetal
or nylon and also has excellent wet abrasion resistance. Its
downfall is in its physical strength; it has very low tensile and
compressive strength and can not operate at temperatures
beyond 160ºF. Bottom line however is that if UHMWPE will
work for your application, you may as well use it because you
probably won’t find anything cheaper to do the job.
|Basic Physical Property Comparison
|Cast Type 6
Type 6/6 Nylon
||- - -|
|Notched IZOD Impact Strength
|Maximum Continuous Service Temperature
|Coefficient of Thermal Expansion
|Moisture Absorption of Saturation
When evaluating materials for an application, never
make a decision based solely on the materials physical
properties since these are intended to show how the
materials compare when tested under the same lab conditions.
If an application applies a compressive force of 3,500 psi then any of the materials discussed can be
used, as the temperature of the application increases the
material choices diminish. Always look at what the application
is and how the material will perform in the application.
If in doubt, contact the manufacturer for assistance.
Another advantage of cast nylon is that, with the exception
of glass-filled, you can make any formulation in the
same tool, so if you want to switch from a standard nylon
to an internally lubricated nylon to enhance performance,
just change the formulation by adding the desired lubricant.
One of the major features of cast nylon is that you
can make custom cast parts that are very close to the
desired final part and require minimal, if any, cleanup
machining to finish. This can save hundreds of dollars in
material, labor and tool costs.
The nylon casting industry has come a long way in the
past 30 years. There was a time when glass-filled cast nylon
was not possible because we did not know how to keep the
glass in suspension during the reaction process; today it is
a standard product. While the extrusion and molding industries
are often ahead of the casting industry in terms of specialty
products because they do not have to deal with the
idiosyncrasies of the reaction process, they are limited in
terms of size and flexibility and tooling costs are astronomical
compared to those of the casting industry. The casting
industry is catching up with new formulations which, with
existing size capabilities, make it a formidable opponent. As
we discover new applications that require new additives to
improve material performance, we must also develop
means of introducing the additives in a manner that does
not interfere with the reaction process and thus allow us to
maintain the properties of this unique material.
Anyone can buy a molding machine or an extruder and
a truck load of resin and be in business as a manufacturer
of extruded or molded products. It takes imagination,
patience and ingenuity to be a manufacturer of cast nylon.
Written by Michael Worthington, Chief Engineer for Cast
Nylons, Limited, manufacturers of Nycast® rod, sheet, tubular
bars, discs rings, custom castings and Nymetal®, Nyloil®,
Nycast® 12 and Nycast® RX and GX solid lube-filled materials.
For more information, contact Cast Nylons Limited,
4300 Hamann Parkway, Willoughby, OH 44094, 800-543-
3619, Fax: 440-269-2323, E-mail: email@example.com,
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