Abrasive Wheels Training Certificate Hazards of Abrasive Wheels 2 — Questions and Answers
Question 1: What noise hazard does angle grinder use present, and what control is required?
- Noise levels typically 95–110 dB(A), exceeding the UK upper exposure action value of 85 dB(A); hearing protection and exposure time limits are required (Correct answer)
- Noise is below the lower exposure action value of 80 dB(A) for all angle grinders
- Only large bench grinders exceed 80 dB(A)
- Hearing protection is only required if the grinder is used for more than 4 hours continuously
Correct answer: Noise levels typically 95–110 dB(A), exceeding the UK upper exposure action value of 85 dB(A); hearing protection and exposure time limits are required
Angle grinders typically generate 95–110 dB(A) at the operator's ear. Under the Control of Noise at Work Regulations 2005, the upper exposure action value is 85 dB(A) (8-hour TWA). Above 85 dB(A), hearing protection is mandatory and exposure must be reduced. Above 87 dB(A) peak, hearing protection must keep exposure below the exposure limit value.
Question 2: What is the hazard of 'wheel loading' on an abrasive wheel?
- The pores between grains become clogged with workpiece material, reducing cutting efficiency, increasing heat build-up, and risking wheel cracking (Correct answer)
- Loading only affects the surface finish quality, not safety
- Loading causes the wheel to spin faster, increasing burst risk
- Loading is only a problem with silicon carbide wheels
Correct answer: The pores between grains become clogged with workpiece material, reducing cutting efficiency, increasing heat build-up, and risking wheel cracking
Wheel loading occurs when soft or ductile materials (aluminium, copper) clog the pores between abrasive grains. The clogged wheel cuts poorly, generates excessive heat (which can affect the bond integrity), and may cause vibration. A loaded wheel may need redressing or replacement. The heat from a loaded wheel can also affect the workpiece temper.
Question 3: What is the hazard of 'wheel glazing' during bench grinding?
- Abrasive grains become flattened and polished rather than breaking away, producing a smooth wheel surface that generates excessive heat without cutting (Correct answer)
- Glazing only affects the appearance of the wheel, not its performance
- A glazed wheel cuts more aggressively than a fresh wheel
- Glazing is only possible with resinoid bond wheels
Correct answer: Abrasive grains become flattened and polished rather than breaking away, producing a smooth wheel surface that generates excessive heat without cutting
Glazing occurs with hard-grade wheels on soft workpieces — the soft material wears the grains smooth rather than fracturing them to expose new sharp edges. The glazed wheel heats the workpiece without effectively cutting, causing burn marks and possible thermal stress. Dressing the wheel removes the glazed surface layer.
Question 4: Why is using an angle grinder without a guard particularly dangerous?
- The guard provides direct protection from wheel fragments if the disc bursts, and prevents contact with the rotating disc during operation (Correct answer)
- Guards only reduce noise levels and are not a structural protection
- Guards are only required when grinding above waist height
- An unguarded grinder is less safe but not significantly more dangerous than a guarded one
Correct answer: The guard provides direct protection from wheel fragments if the disc bursts, and prevents contact with the rotating disc during operation
The grinding disc guard performs two critical functions: it deflects wheel fragments away from the operator if the disc bursts (fragment velocities can be lethal), and it physically prevents accidental contact with the rotating disc. Removing the guard eliminates both protections simultaneously and is a serious safety violation under PUWER.
Question 5: What manual handling hazard is associated with heavy abrasive wheels and angle grinders?
- Musculoskeletal injury from sustained awkward postures, repetitive use, and holding the weight of the grinder, especially overhead or at arm's length (Correct answer)
- Manual handling injuries only occur when lifting wheels from storage
- Only a hazard for bench grinder wheels above 300mm diameter
- Manual handling is not a significant hazard as grinders are light tools
Correct answer: Musculoskeletal injury from sustained awkward postures, repetitive use, and holding the weight of the grinder, especially overhead or at arm's length
Angle grinders weigh 2–5 kg and are often used in sustained awkward postures — overhead, at arm's length, or in confined spaces. Sustained gripping against reaction torque, vibration, and weight causes upper limb musculoskeletal disorders. Pre-planning work positioning to minimise awkward postures reduces this risk.
Question 6: What is the hazard of an abrasive wheel that is cracked but not visually obvious?
- A crack weakens the wheel structurally, increasing burst risk during use; a cracked wheel may pass visual inspection but fail the ring test (Correct answer)
- Cracks only affect surface finish and do not cause burst risk
- Cracks are only dangerous in silicon carbide wheels, not aluminium oxide
- A crack that is not visible poses no hazard — only visible damage warrants rejection
Correct answer: A crack weakens the wheel structurally, increasing burst risk during use; a cracked wheel may pass visual inspection but fail the ring test
Internal or hairline cracks may not be visible on inspection but significantly reduce the wheel's structural integrity. A cracked wheel can fail catastrophically at normal operating speed. The ring test (tapping the wheel and listening for a dead sound rather than a clear ring) is designed to detect cracks that visual inspection cannot find.
Abrasive Wheels Training Certificate Hazards of Abrasive Wheels 2
What noise hazard does angle grinder use present, and what control is required?