What is Coefficient of Friction? And How To Measure It
Safety-Grip
Coefficient of friction is a term we use a lot in our business. But what is it? This post explains coefficient of friction and methods to measure it.
How do you measure anti-slip levels?
As an anti-slip material manufacturer, it is vital that we give our customers the necessary information to allow them to easily judge which materials are suitable for their grip requirement. Coefficient of Friction (CoF) is a way of objectively expressing the grip levels, there is no one set method for measuring Coefficient of Friction (CoF), there are various methods, I will describe the most commonly seen test procedures and what my personal (being subjective) views are of them.
Let’s discuss some basics
Surface grip levels are affected by contaminants such as water. We always recommend that results are taken dry and wet, although a wet test sounds too onerous, think about it, wet surfaces pose one of the greater risks. To alleviate that risk we must understand the risk level posed and what we are facing.
Do all CoF tests work the same way?
No, the main difference is that the tests rely on testing either the static or dynamic Coefficient of Friction. Static CoF relies on how much momentum is required to achieve movement between the two surfaces. Dynamic CoF tells us how much effort is required to bring two surfaces to a stop.
Pendulum
This is a device ( also known as a TRL slider ) that brings a pendulum striker (with different choices of surface) down onto the substrate. It is covered by standards such as EN 13036-4:2011 (UK, EU etc), ASTM E303-93 (USA) and HB 19:1999 (Australia). It is a dynamic test. If combined with analysis interpretation by bodies such as UKSRG we can then determine what is viewed as a good level of CoF;
UKSRG recommendation | Result
High slip potential | 0~24
Moderate slip potential | 25~35
Low slip potential | 36+
Variable angle ramp tests
This is an extremely unusual test originating in Germany. It consists of the substrate being applied onto the base on a ramp, an operator steps onto the ramp, the operator walks whilst the ramp is angled, the ramp stops when the operator slips. The operator is harnessed and is either barefoot or wears boots. The test is repeated until they determine an average. The main tests are DIN51130 and DIN51097. The data is reported as a number following the letter ‘R’.
ASTM C1028-07
A static test that originated in America and was prevalent. This test is no longer considered valid and has been withdrawn, yet, I am mentioning it as it is still commonly referred to in technical data, specifications etc.
In conclusion…
Firstly ASTM C1028-07 is a curse and should never have been used; if anyone does refer you to it please point out that it was withdrawn due to very questionable results obtained when using it. Static testing does not match the movement of a person who may be slipping. I like Pendulum, as it so tightly controlled you can obtain similar results if the test are undertaken in London, New York or Sydney (moisture and temperature levels might create some movements). It is so scientific and prescriptive that one can have confidence in its output. My personal favourites are the variable ramp tests. They are the most expensive tests to perform (the actual substrate needs to be applied onto each ramp and there is a lot of work involved) but they are the most realistic, a person slips when walking on a surface that may be wet or dry, it may be flat or angled. The test is unusual but is a real-life test! I realise that there are others that I have not mentioned such as SlipAlert, Tortus, BOT-3000, English XL etc but I have decided to stay with the most common methods and the ones that are most likely experienced.
How does this relate to Heskins materials?
We CoF test ALL our non-slip materials! We never test in-house; we always pay for expensive, external tests to be performed at reputable laboratories so our customers (and their insurance companies) can be assured of the accuracy and veracity. We can provide all the data and original test reports as required. We conduct ongoing tests on an irregular basis to ensure that we have recent data.
We are a long-standing company with a well-earned reputation to uphold. This subject is quite detailed and does need more explaining for affected parties.
If you require more information please contact us, we are always happy to help.
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