What is Shore A Hardness?

This is one of the most used scales for measuring the hardness of elastomers. Although it is not the only one, apart from scale A there are scales B, C, D, 0 and 00. Of these, the Shore D scale is also used to measure the hardness of harder elastomers.

The hardness of an elastomer represents its stiffness against moderate stress, such as those that it frequently subjected to in an application.

There are two methods for obtaining the hardness of O-rings and other seals:

Durometer

A durometer is an instrument with a frusto-conical tip that, on penetrating the elastomer, produces a reaction in the calibrated metal spring. When the Shore A durometer indicates readings of greater than 90°, the use of the Shore D durometer, which has a tapered tip and a stiffer spring, is recommended.

To ensure the correct use of this measurement tool, we at JIOrings recommend:

• Using the durometer on a flat, clean, polished surface.

• Measuring perpendicular to the durometer´s indenting foot.

• Repeating the test 3 times in a different place on the part/seal each time.

Due to its simplicity and convenience, the Shore hardness form of measurement is widely used as a production control. The use of IRHD hardness is recommended for the purpose of more exact classification or specification:

Macro IRHD

This durometer is designed to obtain hardness in all types of elastomers and plastics with a minimum thickness of 6 mm. The system consists of a stand with a testing table and a macro head designed to accommodate IRHD N, IRHD L, IRHD H and Shore inserts. The inserts feature 1, 2.5 and 5 mm diameter ball indenter and test loads from 2.65 to 5.70 N.

Micro IRHD

A micro durometer is used to obtain hardness in all types of elastomers and plastics with a maximum thickness of 5 mm. The system consists of a stand with a testing table and a micro head with a 0.395 mm diameter ball indenter and test loads from 8.3 mN to 153.3 mN. The measurement stroke is 0.3 mm and the range is between 30 and 100 micro IRHD.