The hardness is obtained by the difference in penetration depth of a specified dimension ball under two conditions of contact with the rubber.
- with a small initial force
- with a much large final force
The differential penetration is taken at a specified time and converted to a hardness scale value.
The IRHD Tester made a vertical plunger. The lower side of the plunger has an indenter. The lower shape of the indenter is ball type of specified dimension. The upper sides of the plunger have a good eclectic conductive tip. The weight of the plunger and fitting attached to it is the minor force. A big brass weight is the major force of the specified weight.
A dial gauge is attached to the instrument for the measurement of the penentration depth of the indenter to the rubber.
An electricity operated buzzer, for gently vibrating the apparatus to overcome the slight friction is mounted under the cover of the instrument.
The tester is finished in NC based painting and bright chrome plating to give it a corrosion resistance finish.
| Minor Force | 30.6+/- 2gm |
| Major force | 550.5+/-1gm |
| Radio us of indenter Dial gauge | 1.25mm |
| RELATED STANDARD: | 0 – 10 X 0.01mm |
| ASTM D 1415 – 81 –Rubber property – International Hardness | 3400 |
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