Rubber Burn Tests

DATE: 6th-May-2019

It is often a challenging task identifying an unknown rubber compound, as they can look and feel very similar to one another. At Jehbco Silicones, we regularly provide 100% silicone alternatives to original equipment manufacturer (OEM) parts, and as such need to know what material the original part was supplied in.

There are multiple methods of determining what type of rubber is used in a product, but methods such as elemental analysis are costly, require specialised equipment, and is not practical in the field. One tried and tested method that we use regularly at Jehbco is a burn test, in which a small sample of the rubber material is combusted. The characteristic burning pattern, smell, smoke colour, and mode of extinguishing are all indicators that can be used to identify what the composition of the burned sample is.

The table below is a basic guide that outlines the main components of the burn test:

Material Burning Pattern Smell Smoke Colour Extinguishing Mode
Natural Rubber Continuous burning Burning rubber Dark black smoke Material melts and leaves sticky residue
Nitrile Rubber Continuous burning with minor cracking Acrylic smell Dark smoke with black soot Leaves a tacky residue
EPDM Continuous burning Chemical smell Dark black smoke Material melts and leaves a tack and charred residue
Silicone Difficult to ignite, infrequent burning Little to no smell White smoke Self-extinguishing, produces a white ash

There have been numerous cases where customers have thought they were purchasing one type of material, but in actuality they have been supplying an inferior grade of material or a different material altogether. We recently had a case where one of our customers wanted to replace what they thought was a nitrile O-Ring, but when we conducted a burn test on the material it melted and had a distinct burning rubber smell, which was indicative of a natural rubber material. Luckily for the customer, they were not using the O-Ring for a sensitive application, but this uncertainty in material could have had catastrophic consequences in a more critical or sensitive application.

Even within the niche area of silicone materials, some manufactures opt to add fillers to reduce costs, at the expense of inferior mechanical and chemical properties. We have conducted burn tests on many silicone parts made overseas, and an alarming amount of these parts did not behave as expected during the burn test (no white ash produced, black smoke) which suggests that fillers have been added.

At Jehbco, we only produce 100% pure silicone products for your guaranteed peace of mind. If you have any doubt about the quality of your existing rubber products, or want to manufacture a custom solution that you can be confident with, feel free to consult our applications page and contact us with any questions.