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 |
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 |
| 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
- Conditions of temperature and humidity affect measurements.
- The surface of the test piece shall be flat and smooth without any undulation or warpage.
- 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.
- 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.
- 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.