How Can Different Properties of Rubber Be Tested?

Before choosing a rubber, its properties are well tested. A manufacturer is very well aware of the specifications he is looking for in his raw material. Before circulating the raw material in the production cycle, a quality check is performed to assure the sanity of procured material. A sample is a tester for its different properties, depending upon the application. Say, an eraser has to be hard and non-flexible. On the other hand, the hockey puck must be hard and non-flexible as well, the grip of the handle of scooter has to be soft and flexible. So, the composition of rubber varies and it is the duty of the vendor and manufacturer to satisfy the requirements for managing the quality at very first step.

Let’s check out some tests that tell about the major properties of rubber.

Tensile Tester – Tensile strength assessment is very important to test for almost all industries. But in the rubber industry, it is performed with a twist. As per the requirements, it is first processed in different climatic conditions. The impact of those climatic conditions on the tensile properties of the sample will be evaluated. As per the testing standards, the dumb-bell shaped sample is cut using a press cutting die. As per the intended subjected conditions, it will be either kept in a hot air oven or deep freezer.

And in some cases, it is tested without any environmental treatment. An outward force is applied to the sample to check at what point it breaks without any slippage. In certain cases, proof tests can also be performed.

DIN Abrasion Tester – Due to friction caused by other material, rubber compositions tend to abrade. Broken rubber O rings in bath fittings is a common example of this. Due to excessive use and external stress, the rings gradually lose some parts which lead to breakage. On a Din Abrasion tester, the sample is clamped which is cylindrical in shape. This sample is rubbed against an abrading paper fixed on a cylindrical drum. The sample will move from left to right on the cylinder while remaining in circular motion. On the other hand, the cylindrical drum with abrading paper rotates on its axis. The cylinder rotates 48 times while the sample was covering its journey from left to right. This total makes a sample to cover 40 meters in one test round. The difference in weight of the sample before and after the test is the percentage of abrasion.

Muffle furnace – It is very important to determine the percentage of ash content on the rubber sample. Processed rubber has a predefined quantity of ash in it. Any change in quantity will lead to uncertain behaviour of product in real working conditions. Before incorporating the sample in the production cycle, it is burnt down completely. The carbon content changes into fume and the left over is the ash content and is calculated to determine the percentage with respect to the weight of the sample. Now, what sounds so simple is actually an intricate task. First of all, it is difficult to attain a temperature at which rubber sample burns down completely. Any human error in calculating the weight of left over ash will lead to wrong observations. Muffle furnace is specially designed to perform this job. It attains a temperature of 900°C, 1200°C and 1400°C. It comes with a crucible bowl to burn the sample and ash is weighed along with the bowl.

Hardness tester – As the name shows, it tells about the hardness of the elastomer. How hard it is can be determined by the depth of the indention of an impacting gauge of standard size and shape? By comparing the force applied and the initial stage and the final force, the hardness can be obtained. Rubber hardness degree is calculated on Shore A. This is why, at Presto, we call hardness tester as Shore A Device. It is a simple device which is inserted in the sample and observations are displayed on the screen in human readable format.  Compressibility and recovery tester – A rubber has a tendency to get compressed when force is applied and regain its position when force is released. Sometimes, rubber shows some deflection due to force. In this test, the sample is subjected to a certain load for some time, say some hours or few days. After the test is completed, deflection is measured. In certain applications, it is important to understand the behaviour when the load is applied. A very common application is gasket of the pressure cooker, where rubber experiences force and heat simultaneously. If the gasket deforms, it will lead to leakage of steam.

For more information about rubber testing instruments like Din Abrasion tester, Muffle furnace, Shore A device, contact us