Coefficient of Friction
When you’re walking on a slippery surface, it’s easy to understand friction… slippery surfaces have LESS friction. Higher friction surfaces have MORE , and are less slippery.
Coefficient of Friction is defined as “the force causing a body to slide along a plane (in the direction of sliding) to the normal force pressing the two surfaces together.”
Coefficient of friction must be measured experimentally; it cannot be measured using formulas. Static friction and Dynamic or Kinetic friction are the two types of coefficient of friction that are used to determine how safe a floor can be.
Static Coefficient Friction is between non-moving surfaces; it can prevent an object or person from sliding down a gradient surface.
Kinetic friction is between moving surfaces; it measures the friction between two surfaces moving against each other such as a book being pushed across a table, or a sled being dragged across the ground.
Measuring friction can be tricky – many machines have been created to measure the coefficient of friction. Highly regarded agencies use results from these tests to create recommendations and standards that other agencies follow. Many government regulations are based upon ASTM standards. ASTM is an international standards organization that develops and publishes technical standards for a various range of items.
Four types of ASTM tests are done for flooring, ASTM 1679, ASTM E303, ASTM D2047, ASTM F1677 and ASTM C1028.
Which one is the right test for your application?
ASTM 1679 is a type of test that is approved for both wet and dry testing. This test can be used on nearly all surfaces. The ASTM 1679 test is done using the English XL Variable Incidence Tribometer. It relies on a carbon dioxide cartridge, not gravity, therefore providing more accurate results and also allowing for inclined surfaces to be tested. The English XL Tribometer mimics the human stepping motion and allows for synchronized application of vertical and horizontal forces. The tribometer has no motors, springs or anything else that may fail when testing occurs, making it the preferred testing method for ASTM 1679.
The ASTM E303 test is completed with the British Pendulum. The British Pendulum is used in both laboratory tests and tests completed in the field. It measures the energy loss when a rubber slider is moved over the square foot testing surface. ASTM E303 is used for road and paving standards.
The ASTM D2047 test is completed in the lab using the James Machine. The James Machine is a rather large and bulky machine that uses a 3” x 3” testing surface. It is only used for testing dry surfaces, it is not appropriate for wet surfaces because the sensor pads that are attached tend to hydroplane, which will lead to skewed results. The James Machine needs continuous maintenance and adjustment in order to measure correctly due to the fact that an 80-pound weight is part of the test. Currently, there is only one computerized version in production and four versions of the machine have been created since 1975.
ASTM1677 is completed using the Brungraber Mark, also known as a portable inclinable articulated strut slip tester (PISAT). The Brungraber Mark is commonly used to measure slip resistance on ramps, in both the laboratory and the field. This test can be used on both wet and dry walking surfaces. The Brungraber Mark uses an angle that is set to a certain degree, and a 10-pound weight is released. The weight is released each time the angle is moved until a slip occurs.
The ASTMC1028 test is run with the Horizontal Pull Slipmeter. The HPS measures both static and kinetic coefficient of friction. Dry surfaces are mostly tested by this method, wet measurements are possible but erratic. The HPS is comprised of a large pad and 50 pounds of weight that is hand pulled across tiles to measure slip resistance. Because the HPS is so heavy, it makes it rather difficult to test in the field.
Each ASTM standard is complied with by numerous tests being done by various sources. By examining each standard and the test that is performed for each, you can choose which non-skid flooring option best suits your application’s needs. Most engineers feel that ASTM 1679 and ASTM D2047 are the most reliable for measuring coefficient of friction.