Abrasive Wheels Training Certificate Ring Test & Speed Ratings — Questions and Answers
Question 1: What is the purpose of the 'ring test' for abrasive wheels?
- To detect cracks in the wheel by listening for a clear ringing sound when tapped — a dull or dead sound indicates a crack (Correct answer)
- To check whether the wheel is in balance on the spindle
- To verify the wheel bore diameter is correct
- To measure the wheel's RPM rating accuracy
Correct answer: To detect cracks in the wheel by listening for a clear ringing sound when tapped — a dull or dead sound indicates a crack
The ring test (also called the 'tap test') involves suspending the wheel freely and tapping it lightly with a non-metallic implement (wooden mallet or screwdriver handle). An undamaged vitrified or silicate-bonded wheel produces a clear metallic ring. A cracked wheel produces a dull, dead sound indicating internal damage that would not be visible.
Question 2: Which types of abrasive wheel can be reliably ring-tested?
- Vitrified and silicate bonded wheels — resinoid, rubber, and shellac bonded wheels cannot be reliably ring-tested as they absorb sound (Correct answer)
- All abrasive wheels regardless of bond type
- Only wheels above 200mm diameter
- Only new wheels that have never been used
Correct answer: Vitrified and silicate bonded wheels — resinoid, rubber, and shellac bonded wheels cannot be reliably ring-tested as they absorb sound
The ring test relies on the acoustic resonance of a rigid, brittle bond (vitrified or silicate). Resinoid, rubber, and shellac bonds are softer and absorb sound, so they produce a dull sound even when undamaged. These wheels rely on visual inspection only. The ring test should not be used to assess resinoid bond wheels.
Question 3: How should a wheel be supported when performing the ring test?
- Suspended on a finger through the bore or held vertically on a peg, so the wheel is free to vibrate naturally (Correct answer)
- Placed flat on a bench and tapped on the upper face
- Clamped in a vice at the bore
- Held firmly in both hands against the chest
Correct answer: Suspended on a finger through the bore or held vertically on a peg, so the wheel is free to vibrate naturally
The wheel must be suspended freely — on a finger through the bore or on a peg — so it can vibrate freely when tapped. Any physical support contact (bench, vice, hands) damps the vibration and prevents the clear ring from being heard, even if the wheel is undamaged. The free suspension allows the wheel to resonate fully.
Question 4: Where on the circumference of the wheel should the ring test be applied?
- At four points approximately 45 degrees from the vertical (not at the top) to assess the full circumference of the wheel (Correct answer)
- Only at the top (12 o'clock position)
- Only at the sides (3 and 9 o'clock positions)
- At the bore only — the outer rim does not affect ring test accuracy
Correct answer: At four points approximately 45 degrees from the vertical (not at the top) to assess the full circumference of the wheel
The wheel should be tapped at multiple points around its circumference — typically at 45-degree increments from the vertical. Testing at only one point may miss a localised crack. Tapping at the top (12 o'clock) and bottom is less sensitive due to the support point interaction with vibration.
Question 5: What constitutes a failed ring test and what action must be taken?
- Any dull, dead, or inconsistent sound instead of a clear ring — the wheel must be destroyed and disposed of; it must not be used or returned to stock (Correct answer)
- A slightly quieter ring is acceptable for wheels that have been stored for over a year
- The wheel can be used at reduced speed if it produces a dull sound
- A failed ring test can be confirmed by a second test; if the second test passes, the wheel is acceptable
Correct answer: Any dull, dead, or inconsistent sound instead of a clear ring — the wheel must be destroyed and disposed of; it must not be used or returned to stock
Any wheel that fails the ring test — producing a dull, dead, or inconsistent sound — must be rejected and destroyed to prevent it from being accidentally used. The wheel must not be returned to the storage rack, used at reduced speed, or re-tested. Once failed, the wheel has no further use.
Question 6: What additional check must be carried out for large vitrified wheels after mounting, beyond the ring test?
- A static balance check to ensure the wheel runs without vibration, which can cause cracking and bearing wear (Correct answer)
- A dynamic balance check using specialist equipment for all wheels above 150mm
- An ultrasonic scan to confirm no internal voids
- A hardness test at four points around the circumference
Correct answer: A static balance check to ensure the wheel runs without vibration, which can cause cracking and bearing wear
Large vitrified wheels may have a non-uniform mass distribution that causes vibration during rotation. Static balancing — adjusting balance weights on the flanges until the wheel is equally balanced at all positions — ensures the wheel runs smoothly. Excessive vibration from an unbalanced wheel can cause cracking and bearing failure.
Abrasive Wheels Training Certificate Ring Test & Speed Ratings
What is the purpose of the 'ring test' for abrasive wheels?