Abrasive Wheels Training Certificate Abrasive Wheel Types and Selection 2 — Questions and Answers
Question 1: Which grade of abrasive wheel should be selected for grinding hardened steel?
- A hard grade wheel (R-Z)
- A medium grade wheel (I-P)
- A soft grade wheel (A-H) (Correct answer)
- Grade does not affect performance on hardened steel
Correct answer: A soft grade wheel (A-H)
A soft grade wheel (A-H) should be used for grinding hard materials. Soft wheels release worn grains more easily, exposing fresh cutting edges. Hard wheels are used for soft materials. This is known as the 'reverse rule'.
Question 2: What is a Type 27 abrasive wheel commonly known as in the workplace?
- A straight wheel
- A depressed centre grinding disc (Correct answer)
- A cup wheel
- A cylinder wheel
Correct answer: A depressed centre grinding disc
Type 27 wheels are depressed centre grinding discs, commonly used on angle grinders. The depressed centre allows the wheel to grind flush against the workpiece without the spindle nut interfering.
Question 3: What is the main difference between an organic bond and a vitrified bond in abrasive wheels?
- Organic bonds are only used on diamond wheels
- Vitrified bonds are more flexible and shock-resistant
- Organic bonds (resinoid/rubber) are more flexible and shock-resistant than vitrified bonds (Correct answer)
- There is no practical difference between the two
Correct answer: Organic bonds (resinoid/rubber) are more flexible and shock-resistant than vitrified bonds
Organic bonds (resinoid and rubber) are more flexible and shock-resistant, making them suitable for portable and hand-held grinding. Vitrified (ceramic) bonds are rigid and brittle but offer excellent heat resistance and are used for precision grinding.
Question 4: When selecting an abrasive wheel for use on an angle grinder, which specification must always match?
- The wheel colour must match the grinder brand
- The bore size must match the grinder spindle diameter (Correct answer)
- The abrasive type must be aluminium oxide
- The grain size must be 60 or above
Correct answer: The bore size must match the grinder spindle diameter
The bore size (centre hole) of the wheel must exactly match the spindle diameter of the grinder. An incorrect bore size will cause the wheel to be off-centre, leading to dangerous vibration and potential wheel failure.
Question 5: What does an 'open' structure number (7-14) in an abrasive wheel marking indicate?
- The wheel has fewer abrasive grains with more spacing between them (Correct answer)
- The wheel is designed for wet grinding only
- The wheel has a very dense concentration of abrasive grains
- The wheel is only suitable for bench grinders
Correct answer: The wheel has fewer abrasive grains with more spacing between them
Structure numbers range from 0 (dense/closed) to 14 (open). Higher numbers indicate wider spacing between grains, which provides better chip clearance and is suited for softer, gummier materials that would otherwise clog the wheel.
Question 6: Which type of abrasive wheel is specifically designed for use in cutting-off operations and is typically very thin?
- Type 1 (flat/straight) cutting disc (Correct answer)
- Type 6 (cup) wheel
- Type 11 (flaring cup) wheel
- Type 5 (recessed one side) wheel
Correct answer: Type 1 (flat/straight) cutting disc
Type 1 flat cutting discs are specifically designed for cut-off operations. They are manufactured very thin (typically 1-3mm) to minimise material waste and reduce heat generation during cutting. They must never be used for side grinding.
Abrasive Wheels Training Certificate Abrasive Wheel Types and Selection 2
Which grade of abrasive wheel should be selected for grinding hardened steel?