Abrasive Wheels Training Certificate Abrasive Wheel Types & Grades 1 — Questions and Answers
Question 1: Which BS EN standard specifies the safety requirements for abrasive wheels used with angle grinders?
- BS EN 13743 and BS EN ISO 603 (Correct answer)
- BS EN 50144
- BS 8888
- BS EN 60745
Correct answer: BS EN 13743 and BS EN ISO 603
BS EN 13743 and BS EN ISO 603 cover the dimensions, tolerances, and safety marking for resinoid and vitrified grinding wheels for portable grinding machines. These standards define maximum operating speed, dimensions, and marking requirements.
Question 2: What does the 'grade' of an abrasive wheel refer to?
- The hardness of the bond holding the abrasive grains together (Correct answer)
- The grit size of the abrasive particles
- The maximum operating speed in RPM
- The diameter of the wheel in millimetres
Correct answer: The hardness of the bond holding the abrasive grains together
The grade (or hardness) of an abrasive wheel describes how strongly the bond holds the abrasive grains. A hard-grade wheel retains its grains longer; a soft-grade wheel releases worn grains quickly, exposing fresh sharp ones. Selecting the correct grade for the workpiece material is critical to safe performance.
Question 3: What is the purpose of the 'structure' designation of an abrasive wheel?
- To indicate the spacing (porosity) between abrasive grains — open structure for soft materials, dense structure for hard materials (Correct answer)
- To describe the wheel's thickness
- To specify the operating temperature range
- To indicate the bonding material used
Correct answer: To indicate the spacing (porosity) between abrasive grains — open structure for soft materials, dense structure for hard materials
Structure refers to the volumetric distribution of abrasive grains, bond, and voids (pores). An open structure (widely spaced grains) provides chip clearance for soft, sticky materials. A dense structure suits hard materials requiring fine surface finish. Incorrect structure can cause glazing or wheel loading.
Question 4: Which bonding material is most commonly used in abrasive wheels for general grinding?
- Vitrified bond (ceramic) (Correct answer)
- Resinoid bond (synthetic resin)
- Rubber bond
- Shellac bond
Correct answer: Vitrified bond (ceramic)
Vitrified bond wheels are the most common for general precision grinding. The vitrified (ceramic) bond is rigid, porous, and temperature-resistant. Resinoid (resin) bonds are used where strength and some flexibility are needed, such as cut-off wheels and angle grinder discs.
Question 5: What is the purpose of the abrasive grain type designation on a wheel specification?
- To identify the abrasive material (e.g., aluminium oxide for steel, silicon carbide for non-ferrous) for matching to the workpiece (Correct answer)
- To indicate the depth of cut achievable
- To specify the maximum workpiece hardness
- To describe the wheel's colour coding for RPM rating
Correct answer: To identify the abrasive material (e.g., aluminium oxide for steel, silicon carbide for non-ferrous) for matching to the workpiece
Aluminium oxide (Al2O3) abrasive is suited to ferrous metals (steel, iron). Silicon carbide (SiC) is used for non-ferrous metals (aluminium, brass), stone, and ceramics. Using the wrong abrasive for the material results in inefficient cutting, overheating, or wheel damage.
Question 6: What does 'grit size' (also called grain size) specify on an abrasive wheel?
- The coarseness or fineness of the abrasive particles — lower numbers indicate coarser abrasive, higher numbers indicate finer abrasive (Correct answer)
- The number of abrasive particles per square centimetre
- The particle size in microns only
- The maximum depth of cut per revolution
Correct answer: The coarseness or fineness of the abrasive particles — lower numbers indicate coarser abrasive, higher numbers indicate finer abrasive
Grit size is expressed as a number inversely proportional to particle size. Coarse grits (e.g., 24, 36) remove material quickly but leave a rough finish. Fine grits (e.g., 120, 220) remove less material but produce a finer surface. The correct grit size depends on the material removal rate and finish required.
Abrasive Wheels Training Certificate Abrasive Wheel Types & Grades 1
Which BS EN standard specifies the safety requirements for abrasive wheels used with angle grinders?