Grinding wheel integrity: A crack in a grinding wheel is most likely caused by which factor?

Difficulty: Easy

Correct Answer: excessively high wheel speed

Explanation:


Introduction / Context:
Grinding wheels are brittle, bonded abrasive structures designed to operate below a safe limiting speed. Exceeding the maximum safe operating speed (stamped on the wheel) increases centrifugal stresses and can lead to cracking or catastrophic burst. Proper speed selection and ring testing are therefore critical for operator safety.


Given Data / Assumptions:

  • Vitrified or resinoid-bond wheels operated on standard grinders.
  • Safe maximum operating speed is specified by the manufacturer.
  • Wheel is mounted correctly with flanges and blotters; no prior damage assumed.


Concept / Approach:
Centrifugal stress increases with the square of rotational speed. Operating above the rated speed raises tensile stress within the wheel beyond its brittle strength, initiating cracks or causing wheel burst. Although thermal effects and hard work materials can damage the wheel surface, they are less likely to produce internal structural cracks than overspeed conditions or impact damage.


Step-by-Step Solution:

Check nameplate/rating → determine maximum rpm/surface speed.Ensure spindle does not exceed this value at the wheel diameter.Recognize that overspeed → high centrifugal stress → cracking/bursting risk.


Verification / Alternative check:
Safety standards (e.g., ANSI/OSHA) emphasize ring-testing wheels and verifying rpm before mounting. Root-cause analyses of wheel bursts frequently cite overspeed or mechanical damage as primary causes.


Why Other Options Are Wrong:

  • High contact temperature or hard work raises wear/burning risk but not the principal cause of structural cracking.
  • Low speed does not threaten structural integrity.
  • Soft bond choice influences wear rate, not the overspeed-related cracking mechanism.


Common Pitfalls:
Ignoring reduction of safe rpm as wheel diameter wears; using air-turbine spindles without a speed check; mounting damaged wheels without ring-testing.


Final Answer:
excessively high wheel speed

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