What is durometer ?

Characteristics

Hardness measurement is an important items for determining the characteristics of rubber, elastomer, and plastic products. With the ease of operation and prompt measurement, durometers are being widely used.

Basic structure

As shown left, durometer measures the hardness of the test piece by pressing the indentor in specified shape onto the surface of the test piece, applying deforming force of a spring, and reading the extent of protrusion of the point of the indentor beyond the face of the pressure foot.

Measured values

As shown above, a durometer incorporates an indicating device for allowing the extent of protrusion of the indentor beyond the face of the pressure foot to be read, giving 0 for the maximum protrusion (0 displacement) and 100 for 0 protrusion, with an equally spaced scale. The load applied to the to the test piece through the intendor is of the flexural force of the spring and thus nonconstant, varing linearly within the range 0 to 100.

Unlike in cases of other property values, no certain unit for durometer measurement values. Therefore it is inadequate to simply describe a hardness value by "50 (degree)"; it should be clearly specified as, for example, "50-durometer hardness, Shore A, in accordance with JIS K 6253-3." Furthermore, each standard prescribes hardness description rules in various ways as the table below shows.

Names, types and description rules of each standard

Standard Name of test Type Description for
50(degree) in a
test time of
1sec. or less
Description for
50(degree) in a test
time of 15 sec.
Test time (Time
between the point of
firm contact and the
point of reading)
JIS K 6253-1997
Hardness test method
for vulcanized or
thermoplastic rubbers
Durometer
hardness test
Type A
durometer
A 50/S A 50/15/S Within 1 sec after
the point of firm contact or
when a certain
period of time elapses
Type D
durometer
D 50/S D 50/15/S
Type E
durometer
E 50/S E 50/15/S

JIS K 7215-1986
Durometer hardness
test method for
plastic hardness

Durometer
hardness test
Type A
durometer
HDA 50 A test time
of 15 sec.
shall be reported.
The maximum value
within 1 sec in
principle, or the value after a
specified period of time elapses
Type D
durometer
HDD 50
ASTM D2240-2005
Standard Test Method for
Rubber Property-
Durometer Hardness
Durometer
hardness test
Type A
durometer
A 50/1 A 50/15 The value within
1 sec. or the
maximum value
in principle, or,
with consent of involved parties,
the value after a specified period of time elapses
Type D
durometer
D 50/1 D 50/15
ISO 48-4
Rubber, vulcanized or
thermoplastic --
Determination of
indentation hardness
Durometer
hardness test
Type A
durometer
A 50/1 or A 50 A 50/15 Within 1 sec. or
when a specified
period of time elapses
Type D
durometer
D 50/1 or D 50 D 50/15
Type E
durometer
E 50/1 or E 50 E 50/15
ISO 868-2003
Plastics and ebonite --
Determination of
indentation hardness
by means of a durometer
Durometer
hardness test
Type A
durometer
A 50/1 A 50/15

15 sec. with the
tolerance of 1, or
within 1 sec.

Type D
durometer
D 50/1 D 50/15
JIS K 6301-1996
Physical Testing of
Vulcanized Rubber
Spring
hardness test
Type A 50Hs JIS A - Immediately after
the contact
Type C 50Hs JIS C -

(JIS K 6301 was abolished in August 1998)

Measurement instructions

  1. Conditions of temperature and humidity affect measurements.
  2. The surface of the test piece shall be flat and smooth without any undulation or warpage.
  3. Measuring repeatedly at the same point causes an attenuation of measurement. When measuring one sample piece at several points, the measuring point shall be at least 6 mm away from the preceding measuring point, and at least 12 mm away from any edges,as provided in national and international standards.
  4. The pressure speed of durometer onto the sample affects measurements; the faster the speed, the higher the indication, and the slower, the lower. Pressing shall be done at a specified speed as much as possible. This shall be noted especially when the sample of which measurement declines immediately after pressing.
  5. Sample for Type A durometer shall be thicker than 6mm.

Inspections

The working condition of Durometers may be checked by using the extension tester for the indentor height check as well as load tester for spring load check.