Abrasive Wheels Training Certificate Speed Calculations and Markings 2 â Questions and Answers
Question 1: What information must be marked on every abrasive wheel according to BS EN 12413?
- Only the manufacturer's name
- Manufacturer, maximum operating speed, wheel dimensions, abrasive type, bond type, and expiry date (for resinoid wheels) (Correct answer)
- Only the wheel colour and weight
- Only the price and barcode
Correct answer: Manufacturer, maximum operating speed, wheel dimensions, abrasive type, bond type, and expiry date (for resinoid wheels)
BS EN 12413 requires the following markings: manufacturer's name/trademark, maximum operating speed (RPM and/or m/s), wheel dimensions (diameter à thickness à bore), abrasive type, grain size, grade, structure, bond type, and for resinoid wheels, the use-by date.
Question 2: What happens to the centrifugal force acting on an abrasive wheel if the RPM is doubled?
- It doubles
- It quadruples (increases by a factor of 4) (Correct answer)
- It triples
- It stays the same
Correct answer: It quadruples (increases by a factor of 4)
Centrifugal force is proportional to the square of the rotational speed (F = mÏÂēr). If the RPM is doubled, the centrifugal force increases by a factor of 2Âē = 4. This is why even a small increase in speed beyond the maximum rating can be extremely dangerous.
Question 3: Before fitting an abrasive wheel to a machine, what speed-related check must the operator perform?
- Check that the wheel's colour matches the machine
- Verify that the machine's spindle speed does not exceed the wheel's maximum rated RPM (Correct answer)
- Check that the wheel spins clockwise
- Verify the wheel weighs less than 5 kg
Correct answer: Verify that the machine's spindle speed does not exceed the wheel's maximum rated RPM
The operator must verify that the machine's spindle speed (RPM) does not exceed the maximum RPM marked on the abrasive wheel. If the machine speed exceeds the wheel's rating, the wheel must not be fitted. This check is one of the most critical safety steps in wheel mounting.
Question 4: What is the speed colour code for an abrasive wheel rated at 80 m/s?
- Blue
- Yellow
- Red (Correct answer)
- Green
Correct answer: Red
The speed colour coding under BS EN 12413 is: 50 m/s = Blue, 63 m/s = Yellow, 80 m/s = Red, 100 m/s = Green. The red band on an 80 m/s wheel provides immediate visual identification of the speed rating.
Question 5: An angle grinder runs at 11,000 RPM. Which of the following disc diameters would be UNSAFE if the disc is rated at 80 m/s maximum peripheral speed?
- 115 mm
- 125 mm
- 180 mm (Correct answer)
- 100 mm
Correct answer: 180 mm
At 11,000 RPM, the peripheral speed for a 180 mm disc would be: (Ï Ã 180 Ã 11,000) / 60,000 = 103.7 m/s, which exceeds the 80 m/s maximum. For 125 mm: 72.0 m/s (safe). For 115 mm: 66.0 m/s (safe). For 100 mm: 57.6 m/s (safe). The 180 mm disc must not be used.
Question 6: Why is it dangerous to remove the speed governor or bypass the speed control on a variable-speed grinder?
- It uses more electricity
- The machine could exceed the maximum RPM rating of the fitted wheel, causing it to burst from excessive centrifugal force (Correct answer)
- It makes the machine louder
- It voids the extended warranty only
Correct answer: The machine could exceed the maximum RPM rating of the fitted wheel, causing it to burst from excessive centrifugal force
Removing or bypassing speed controls can allow the machine to exceed the maximum RPM of the fitted abrasive wheel. Since centrifugal force increases with the square of the speed, even a moderate increase beyond the rated maximum can generate enough force to cause catastrophic wheel failure.
Abrasive Wheels Training Certificate Speed Calculations and Markings 2
What information must be marked on every abrasive wheel according to BS EN 12413?