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There are two types of abrasion - sliding and impingement.
Sliding is the passing of an adjacent surface across the rubber
surface. Impingement is wearing of the rubber exemplified
by sand particles hitting the surface. Most wear in actual
service occurs as a combination of both sliding and impingement.
When sliding, localized friction
forces can impose high energy levels on the rubber. Abrasion
and wear takes place when the rubber cannot withstand these
forces.
Impingement by particles occurs in applications
such as chutes, rebound plates and sandblast hoses. Elastomers
can yield easily and distribute stresses imposed by particle
impingement. A sandblast test shows that with a 90° impingement
angle, soft resilient rubber is more abrasion resistant than
steel or cast iron. However, not just any elastomer can be
used. Under this same condition, a tough tire tread will wear
out more rapidly than a soft elastomer. The angle of particle
impingement has a significant effect on which material should
be used.
Laboratory abrasion tests are difficult
to correlate with end-use applications. Measurement of properties
can be helpful in selection of materials, but do not compare
to rates in actual service which can be thousands of times
greater with regard to velocities and temperatures.
There are at least 25 laboratory
abrasion test devices, an indication that this type of test
is difficult to correlate with service performance. The most
widely recognized test device in the rubber industry is the
National Bureau of Standards Abrader, a sliding type abrader.
The NBS Abrader uses a constant velocity, under a fixed load
using a specified abrasive grit. See Figure for diagrammatic
sketch.
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DIAGRAMMATIC SKETCH OF NBS ABRADER |
It does not tell how a compound perform
under widely varying conditions, not does it tell anything
about cut resistance, chunking, or flat spotting.
The abrasion resistance of vulcanizates
of Die-Thane urethane rubber, as measured on two laboratory
tests, the National Bureau of Standards test and the Taber
Abrader, are shown in Table 1.
TABLE I
ABRASION RESISTANCE
|
Die-Thane |
Hardness |
NBS Abrasion
index |
Taber Abrasion |
Durometer A |
Durometer D |
ASTM D-394, Method B |
Resistance, Wt. Loss*
ASTM D-1044 |
80 |
- |
110 |
- |
85 |
- |
200 |
- |
90 |
- |
175 |
79 |
95 |
48 |
300 |
118 |
- |
- |
500 |
373 |
*mg/100 rev.; H-18 wheels, 1000 gm,
wts.; 5000 rev.
Note these
two tests give different values. The differences in performances
of vulcanizates of Die-Thane can be explained however. The National
Bureau of Standards tests simulates a very harsh service. In
this case, the hardest vulcanizates hold up best. The Taber
test is much less severe. Softer compounds perform better than
the harder ones because they are more resilient and “give”
under load.
In spite of the difficulties in obtaining
meaningful laboratory abrasion test values. Die-Thane is considered
to have excellent sliding abrasion resistance and has performed
well in many applications where wear is a problem. Die-Thane
has outworn conventional rubber and plastics often by a factor
of as much as 8 to 1. |
Die-Thane Tooling 
