Skid Tester

TRRL TYPE SKID-FRICTION TESTER TR300

Model 'B'

BS 812 : Part 114 : 1989 prEN 1097/8

List of Standards PDF

This outstanding contribution to road safety is the result of over 10 years' intensive development by the Transport Road Research Laboratory (TRRL) of the Department of Scientific and Industrial Research - a British Government organization concerned with studying problems that arise in designing, building, maintaining and using public highways.

The New Model 'B' version of the instrument has been specially strengthened to meet the demands of countries like Germany, who prefer a more rugged design. Model 'B' also includes an additional scale for use in the laboratory at no extra cost.

The instrument which is direct reading, gives a measure of the friction between a skidding tyre and wet road surface. It provides the Highway Engineer with a practical means of obtaining reliable scientific evidence on which to take the appropriate measures to reduce skidding.

To ensure consistency and maintenance of standard all instruments are submitted to the British Standards Institute for calibration and approval before supply to customers.

Portable Skid Resistance Tester Outfit comprising Tester, 6 rubber sliders, thermometer, perspex setting gauge, sale for use in laboratory, 2 spanners, water bottle, collapsible stool with tool tray, tools and translucent plastic cover, complete with aluminium transport case. Cat No S885

Studies of accident sites have revealed that the polishing of roadstone is a major factor in skidding. An important application of the Skid Tester is in the laboratory determination of the resistance of roadstone to polishing.

Scale for roadstone polishing is built into the machine. 6 special small rubber sliders can be supplied for this test: S886/5

Base Plate for laboratory use of skid tester with specimen mounting block S885/9

As the nature of the rubber used for sliders has a critical bearing on the performance for the Tester, and as no rubber properties can be guaranteed for longer than two years, the date of issue is marked on each slider.

Spare mounted rubber sliders for use with Main Tester: S886/6

Spare mounted rubber sliders for Stone Polishing Tests S886/5

1. Calibration must be carried out in a temperature controlled environment of 20°C .
2. The out of balance moment of the rotating head of the pendulum must be less than 12g.cms. If more, calibration moments and calculations must be adjusted.
3. Mass of pendulum pointer to be less than 85g, excluding felt pads.
4. Pointer to balance on a knife edge about the centre of oscillation.
5. Weigh the complete pendulum arm. 1.5kg ±30g.
6. With the adapter nut in its extreme position and the slider lifting handle down, balance the pendulum horizontally on a knife edge and mark the centre of gravity.
7. With the arm horizontally balanced oil the knife-edge and with the slider lifting handle down, adjust the counterweight until the foot is horizontal.
8. With the arm mounted oil the Pendulum measure the distance of the centre of gravity mark from the centre of oscillation.
9. The arm must fall freely from the catch.
10. Set the pointer to reach tile zero position on the scale by swinging the arm in free air and adjusting the pressure oil the felt pads.

If without pressure from the felt pads the arm fails to reach the zero position on the scale, mechanical problems exist, N.B. bearings, which must be corrected.

11. Check the alignment of the pendulum foot swinging parallel with the base by measuring the difference at the toe of tile foot, of the swing across the front face of the base. ±1mm. This measurement can be corrected by setting cotters oil the pendulum column.
12. Check that the foot is square to the base by measuring the difference between the toe & heel of the foot, related to the front face of the base, in the static vertical position. ±0.5min. Adjustment can be made by setting the clamp oil the adjuster nut.

 

13. Calibration Weights

The following are used in calibration:

CW1 -Applied Weight 2244 g.

CW2 Small Calibration Weight 60 g.

CW3 - Large Calibration Weight 120g.

The calibrating weights should be attached to the lifting arm, after removing the cover plate.

14. With the arm inverted on the calibration rig mounting block and the mean load (CW1 and CW2) applied, raise the slider by turning the screw adjuster anticlockwise until the slider arm just touches the retaining bar. Measure this high point with the micrometer. Turn the screw adjuster clockwise until the slider arm just touches the low stop, measure this low point, set the mean point of these two measurements on the micrometer and turn the screw adjuster anticlockwise until the slider touches the micrometer. This is the mean setting of the slider.

Note:

The adjusting screw on "Type B" units requires a screwdriver applied through the access hole in the adapter nut.

"Type A" units require removal of the adapter nut assembly to access a thumb screw.

15. Remove the small calibrating load (CW2) from the mean load, check that the slider arm is still free of the internal rest and measure this setting. Add the large calibrating weight KW3) to the load and measure the deflection.
16. Set the alignment of the pointer vertically parallel to the arm.
17. Adjust the pointer stop until the cc-titre line of the pointer is parallel with the pendulum arni in a vertical position, with the friction tester assembled and levelled.
18. Adjust the spring tension until the lifting handle is brought to its median position. The complete movement of the slider (parallel to the pendulum arm) when using the lifting handle shall be at least 6.5 mm.
19. The Complete movement of the slider (deflection) shall be at least 11 mm.
20. Force of Swinging Arm (In Newtons)

W=Wx9.806

21. Slider Force (in Newtons)

.037xWx411

22. Change in Slider Force (In Nmm)