Hardness is one of the most commonly used properties to specify a rubber. The most commonly used gauges for measuring the hardness of rubber are the durometer and the IRHD meter. The hardness of rubber measured by means of a durometer is expressed in the unit Shore A. A flattened cone is pressed through a spring into the surface of the rubber. When measuring by means of an IRHD meter, using the unit IRHD, a sphere is pressed into the surface of the rubber by loading it with a certain mass. The two measurement methods are hardly related to each other. In this article, you can read more about measuring the hardness of rubber.
Standards for the hardness of rubber
The following standards are used to determine the correct hardness of rubber:
- ISO 48
- ISO 7619-1
- ISO 868
- ASTM D1415
- ASTM 2240
Determining the hardness of rubber with an IRHD meter
In Europe, the ISO 48 standard and the IRHD unit are often used to determine hardness. The IRHD-M (micro) is mainly used, where the test material has a standard thickness of 2 mm. The main advantage of the IRHD-M method is that the hardness of the rubber can also be measured on the end product, in contrast to the Shore A measurement. In this way, hardnesses of different products can be compared with each other. The influence of the shape of the product is minimal.
The IRHD-M measurement is particularly common for measurements on O-rings. There are special tools to position the measuring needle exactly in the middle. Otherwise, deviations can easily occur on a convex surface.
Determining the Shore A hardness of rubber
The most commonly used method is the Shore A measurement. This measurement follows the ISO 7619-1 standard, where the test material has a thickness of 6 mm. A disadvantage of this method is that for smaller and thin products it is not possible to measure the hardness of the rubber. Therefore the hardness in Shore A is measured on specially produced test plates. These test plates are manufactured from the same material as the articles themselves. This is done by means of special laboratory equipment with a standard production method. In this way, the data from different recipes can be easily compared with each other. A comparison between different products is hardly possible. The shape of the product influences the measurement when it is carried out on the final product, despite the fact that the different products are made from the same basic material.
Hardness: an important parameter of rubber
Hardness is one of the few parameters of rubber that is controlled by most customers, from customers in the pharmaceutical industry to customers in the automotive. Due to the limited reproducibility, hardness is mainly a material property and not a product property. However, in the perception of the end users, this is a defining characteristic of a finished product.
At NDS-Seals, we can also test other properties to ensure that the material used is correct and that the product meets the requirements. Take a look at our product range or contact us for more information!