| HARDNESS
Elastomers
Queensland offer a very wide
hardness range in which items
can be produced. They range
from 20 shore A which is softer
than a gum eraser to over 80
Shore D which is much harder
then a golf ball.
ABRASION
RESISTANCE
In
applications where severe wear
is a problem, Polyurethane
Elastomers offer outstanding
durability when compared with
rubber, plastics or even metals.
It should be emphasised, however
that abrasion resistance is
a complex property. Selection
of the proper formulation of
Polyurethane Elastomer should
be based on actual experience
or simulated service tests.
COMPRESSION
PROPERTIES
Polyurethane
Elastomers have greater load-bearing
capability than do conventional
elastomers of equal hardness.
This capacity is a highly important
advantage in some designs,
eg. stripper springs, whilst
in others it is the very factor
that makes them possible. In
addition to high load bearing
properties both tension and
compression polyurethanes have
a high load bearing capacity
in shear.
MECHANICAL
PROPERTIES
At
lower hardness levels, practically
all elastomeric materials,
including Polyurethane Elastomers,
merely bend under impact. As
conventional elastomers are
compounded up to higher hardness
they tend to lose elasticity
and crack under impact. On
the other hand, Polyurethane
Elastomers when at their highest
hardness levels, have significantly
better impact resistance than
almost all plastics.
Such great toughness, combined with the many other outstanding
properties associated with the high hardness Polyurethane leads to
many applications in engineering.
LOW
TEMPERATURE PROPERTIES
Many
Polyurethane Elastomers remain
flexible at very low temperatures
and possess outstanding resistance
to thermal shock. The low temperature
resistance of Polyurethane
has lead to many applications
in below zero degrees celcius
conditions.
DRY
HEAT RESISTANCE
Whilst
many Polyurethane Elastomers
are only suitable for continuous
operation up to 80 degrees
celcius, intermittent use of
up to 100 degrees celcius is
possible.
OXYGEN
AND OZONE RESISTANCE
Products
made from Polyurethanes are
highly resistant to degradation
by atmospheric oxygen and ozone.
OIL,
GREASE AND CHEMICAL
RESISTANCE
Whilst
many rubbers and plastics have
excellence to one or more specific
solvents, oils or chemicals,
the wide resistance of Polyurethanes
to chemical attack means that
they can be used in a multitude
of environments with the exception
of strong acids and alkalis
and certain strong solvents.
As with all materials being
examined for oil and chemical
resistance, it is best to place
a sample of the material in
actual service. If this is
not practical, tests should
be devised which simulate actual
service conditions as closely
as possible.
MOULD,
MILDEW, FUNGUS RESISTANCE
Suitably
compounded Polyurethane Elastomers,
usually polyether based, do
not support fungus growth and
are generally resistant to
such attack. This makes them
particularly suitable for tropical
environments.
MACHINEABILITY
Polyurethane
Elastomers can be machined
using conventional equipment
but you should consult us for
specific recommendations and
procedures.
BONDING
TO OTHER MATERIALS
During
the initial moulding process
and under controlled conditions,
Polyurethanes can be bonded
to a wide variety of materials. High strength
bonds can be obtained to most
metals, wood
and many plastics. Bond strengths
often exceed the tear strength
of the Polyurethane itself. |
|
TENSILE
PROPERTIES
Polyurethanes
are characterised by high elongation,
high tensile strength and high
modulus. This provides a combination
of toughness and durability
in fabricated parts.
TEAR
STRENGTH
Especially
high split tear, is a strong
indicator of toughness.
In actual use, especially in impingement abrasion applications,
high tear strength is important. Polyurethanes in this regard have
a distinct advantage over conventional rubber.
RESILIENCE
Resilience
in conventional rubbers is
generally a function of hardness.
This often undesirable relationship
does not hold true with Polyurethanes.
Formulations are available
in a very wide range of resilience.
For shock-absorbing uses, low rebound compounds are usually
used ie. rebound value of 10-40%. For high frequency vibrations or
where quick recovery is required, compounds in the 45-65% rebound
value, are used.
In general, toughness is enhanced by high resilience.
FLEX
PROPERTIES
Polyurethane
Elastomers resist cracking
under repeated flexing. As
with any elastomer, the rate
of cut growth under flexing
may be reduced by decreasing
the thickness of the part.
Unlike other elastomers, Polyurethane
Elastomers can be used practically
in very thin sections because
of their strength and toughness.
WATER
RESISTANCE
Depending
on the type, Polyurethane Polyether
Elastomers are very resistant
to the effects of water immersion
and have excellent long-term
stability in water up to 50
degrees celcius. Continuous
use in hot water over 80 degrees
celcius is not recommended.
Water absorption is very low,
in the range of 0.3-1% by weight
and volume swell is negligible.
ELECTRICAL
PROPERTIES
Some
Polyurethanes are very good
insulating properties and are
used in many potting and encapsulating
applications.
RADIATION
RESISTANCE
Polyurethane
Elastomers are considered to
have the best resistance to
gamma radiation of all elastomers.
They retain a high proportion
of their original flexibility
and toughness whilst exposed
to gamma radiation.
FLAME
RESISTANCE
Special
compounds containing flame
retardants can be formulated
to meet several self-extinguishing
or non-burning specifications.
FRICTIONAL
PROPERTIES
Polyurethanes
resemble most plastics and
elastomers in that friction
against non-lubricated surfaces
generally decrease with increasing
hardness. A high co-efficient
of friction is valuable for
such products as solid industrial
tyres, feed rollers, drive
rollers etc.
High hardness compounds have the lowest co-efficient of friction,
and formulations having very low values are available. Such formulations
are widely used for bushings, bearings and wear strips.
NOISE
REDUCTION
Special
formulations are available
for sound deadening and anti-vibration
applications.
|
