Choosing the Right Rubber Compound

Most rubber component problems come down to material choice. Pick the right compound and the part does its job for years. Pick the wrong one and you get cracking, swelling, leaks, or early failure — often months after it went into service.

The polymer type is just the starting point. What really drives the decision is where the part has to work and what it has to do. Here's what to think through.

Temperature. Start with the operating temperature and the extremes at both ends. Rubbers vary a lot here. Natural rubber and SBR are fine at moderate temperatures. EPDM takes more heat and handles the cold well. Silicone and fluoroelastomers sit at the top end. A compound that's fine at room temperature can harden or break down once things get hot.

Environment. Sun, ozone and weather are what kill outdoor rubber. Natural rubber, SBR and nitrile don't cope — they crack and harden in sunlight. EPDM and silicone are made for the outdoors and last.

Chemicals and fluids. Work out everything the rubber will touch — oils, fuels, acids, solvents, water. This one trips people up. Nitrile is great with oils but poor outdoors. EPDM handles water and many chemicals but swells in oil. Fluoroelastomers deal with the aggressive stuff that wrecks everything else. Get it wrong and the rubber swells, softens or falls apart.

Function. What the part actually does — seal, grip, cushion, insulate, isolate — sets the hardness and often the shape. Softer compounds seal and grip at low closing forces. Firmer ones hold their shape and resist being squeezed out under load.

Mechanical demands. Think about flexing, abrasion, load and repeated compression. Tear strength, abrasion resistance and compression set all come into it. A seal that's held under compression for years needs a compound that won't take a permanent set — or it'll stop sealing.

Service life. A part that has to last decades — common in structural and infrastructure work — needs good ageing resistance, and under load, low compression set. Slow degradation that doesn't matter over a few years becomes the deciding factor over a few decades.

Compliance. Food contact, drinking water, medical and fire-rated jobs need certified compounds with the paperwork to match. This can override everything else, so sort it out early.

Appearance. Black is the most UV-stable and the cheapest. Coloured and white compounds need proper stabilising or they'll chalk and fade outdoors.

It comes down to balance. One factor rarely decides everything. The right compound is the one that handles the temperature, survives the environment, stands up to the chemicals, does its mechanical job, lasts the distance, and meets any standard it has to. There are usually trade-offs — the trick is weighing them up for the job in front of you.

This is where talking to a manufacturer early helps. Tell us what the part has to do and where it has to do it, and we'll point you to the right compound — and flag anything that might cause trouble down the track.

Talk to MOR Industries about your next rubber component.