Coefficient of Friction, static and kinetic, for paper and board by horizontal plane method

Test Summary

Test standard ISO 15359 enables the calculation of the static coefficient of friction, µ_s, and the kinetic (or dynamic) coefficient of friction, µ_k. This standard tests the friction of paper and board products, such as bank notes, printer, or copier paper which may need to be evaluated for frictional characteristics between layers in order to optimise production machine feed settings and other processing variables.

Test Procedure

ISO 15359 covers two procedures:

• static coefficient of friction at the first slide, and
• static coefficient of friction at the first slide, static coefficient and kinetic coefficient of friction at the third slide.

Each procedure is repeated to obtain six valid results for the average force value.

Test Apparatus

• Sled, with neoprene cellular rubber backing between 1.5 mm and 3.0 mm thickness. Alternatively, the backing may be between the table and the table test piece. The sled mass must be (800 g ± 100 g) in order to exert a normal pressure of 2.2 kPa ± 0.6 kPa.
• ISO 15359 specifies a horizontal test table and a connection between the sled and the loadcell which should ideally be rigid for kinetic friction measurement.
• Test system, with loadcell, capable of applying a vibration-free increasing force and the capability to measure the force against time.
• Elevator mechanism to lower and lift the sled and return it to the initial position within a tolerance of ± 2 mm. Lifting is only required if kinetic coefficient of friction is being determined.

Preparation

The test pieces should not be touched by hand or rubbed together, as the measurement of the coefficient of friction is extremely sensitive to contamination.
Prepare the test pieces, enough for six tests, to the required minimum sizes:

• Attached to the sled: at least 60 mm x 60 mm.
• Attached to the table: at least 60 mm wide and long enough to cover the length of the sled and the actual sliding distance. If the COF at the third slide is required, the length of the test piece must allow for a sliding distance of 70 mm.

Method

To test for the static coefficient of friction:

1. Lower the sled, using the elevator, onto the table at a rate of 3.0 mm/s ± 2.0 mm/s, ideally such that the sample surfaces meet simultaneously over the test contact area.
2. Allow the sled to rest for at least 1 s, but not more than 20 s, ensuring the sled does not move at all during this dwell time.
3. Start the drive mechanism, which must increase the force reading such that the initial ramp time is between 0.5 s and 5 s. in order to be a valid test. If the ramp time falls outside this range, adjust the rate of force increase to bring the time into range. Discard the samples and repeat the test until the ramp time condition is achieved. Record the force, FS1, required to initiate the motion.
4. Discard the test pieces after each test.
5. Repeat the test procedure until at least six valid results have been obtained.

To test for the kinetic coefficient of friction:

1. Repeat the above process steps 1-3.
2. Once sliding commences, control the motion as follows:
3. During first 20 mm of travel, increase the sled’s speed to (20 ± 2) mm/s.
4. During the next 40 mm of travel, maintain constant sled speed of (20 ± 2) mm/s.
5. During the next 15 mm ± 6 mm, the speed may be reduced and the sled must be lifted clear of the table.
6. Return the test pieces to their initial positions, maintaining the orientation and outer surfaces. Repeat the sliding procedure a second time, and a third time.
7. Record the force, FS3, required to initiate the third sliding motion.
8. Record/calculate the average friction force, FK3, over the distance 40 mm to 60 mm for the third sliding motion.

Calculate the coefficient of friction from the formula: µ = F/mg, where the force value is averaged over the six tests.

The test report should indicate the coefficient of variance and clearly indicate the machine orientations applicable to the test pieces.

Mecmesin Test Equipment Required for Testing Based on ISO 15359 for Paper and Board

COF horizontal friction tester, with the following features, compliant with ISO 15359:

• Horizontal table.
• Elevator to lower and lift the sled-mounted test piece to guard against reverse sliding and blooming-induced inaccuracies (manual lowering and lifting prohibited).
• Elastic linkage for static coefficient of friction measurement.
• Rigid linkage for slip-stick control during kinetic coefficient of friction measurement.
• Emperor™ (Force) software.

Please refer to the latest official ISO 15359 standard for more detailed information. This overview is intended to provide a basic understanding of the test procedure and suitable equipment to meet the standard.

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