Abrasive wheels come in a large range of sizes and configurations, with each being suited to different tasks and functions such as grinding, finishing, cleaning, cutting, buffing etc. The main aspects of an abrasive wheel are:
· Grit size – this means the particle size of abrasive grains. The range is expressed by number, for example very coarse 4 to very fine 1200.
· Coating material bonding – this means the bonding material used in the wheel construction.
· Abrasive type – this means the type of abrasive used in wheel construction.
· Grade of the wheel – this represents the tenacity with which the bonding material holds the abrasive grain in a wheel. Wheels are graded as soft or hard according to their degree of tenacity. The grade scale is expressed in letters from A which is extremely soft to Z which is extremely hard.
· Wheel structure – this means the level of porosity in the wheel. The higher the number, the greater the level of porosity.
The Health and Safety Executive (HSE) lists 33 different types of abrasive wheels. In general, the most commonly used types of abrasive wheels are:
· Type 1 Straight Grinding Wheels – straight wheels are a common type of revolution found on pedestal or bench grinders. It is often also widely used for centreless and cylindrical surface grinding operations.
· Type 2 Cylinder or Wheel Ring – this type of wheel doesn’t have middle mounting support, but it sits on an extended and wide surface. They’re mainly utilised in horizontal or vertical spindle grinders for producing flat surfaces.
· Type 4 Tapered Grinding Wheels – a sharp emery wheel may be a straight wheel that tapers externally towards the wheel’s midpoint. A straight wheel with a sharp wheel is usually used for gear teeth, grinding threads, etc. In tapered cup wheels the sides taper outwards, providing extra strength and therefore accepting higher lateral loads. Both types are primarily used in tool and cutter grinding.
· Type 6 Straight Cup – this straight cup wheel is employed as an option for cup wheels in cutters and gear grinders. It has an additional radial grinding surface, which can be beneficial in some applications.
· Type 9 Segmented Wheels – grinding wheel segments are generally used to grind flat stock or flat surfaces within a workpiece for anything from heavy stock removal to precision grinding.
· Type 12 Dish Cup – this type of wheel is suitable for jug grinding and cutter grinding. It only cuts in crevices and slots because it features a skinny cup-style grinding.
· Type 13 Saucer Grinding Wheels – saucer grinding wheels are used for grinding twist drills and milling cutters. It is often particularly in demand in non-machining areas because the saw filers are employed by saucer wheels to take care of saw blades.
Abrasive wheels are used in two main types of machines, pedestal and portable. A pedestal grinder has a mounted wheel that sits within a pedestal. The pedestal is either bolted to the floor or sits on rubber feet. These types of grinders are often used to sharpen cutting tools and to work extremely hard materials. Portable grinders are handheld devices, such as angle grinders. They are widely used in metalworking and construction, as well as by the emergency services. The types of machines that are mostly associated with abrasive wheels are:
· Angle grinders – also known as disc grinders or side grinders, used to cut or polish hard materials
· Belt grinders – mounted tabletop grinders with two different types of grinding wheels on each side, which can sharpen tools and are used for roughing or finishing
· Cylindrical grinders – used to shape the exterior of rods, tubes or bearing races
· Jig grinders – heavy machines used for complex grinding and cutting work
· Table saws – sometimes called bench saws, these are used for cutting wood
· Chop saws – handheld tools used to make straight cuts in wood
· Petrol cut-off saws – handheld tools used to cut concrete, steel, stone, asphalt and other materials
Every wheel must adhere to the British Standard (BS EN 12413 and BS ISO 525) system for marking. Manufacturers mark all wheels with the type, size, specification and the maximum operating speed of the wheel. The fundamental markings that a wheel should have are:
· Trade Mark
· Test Record
· Restriction for Use
· Expiry Date
· Speed Stripe
· Dimensions in mm
· Specification Mark
· Code Number
· Maximum Operating Speed
· ISO Type No. (shape)
· Mounting Instruction
All organic-bonded wheels for handheld applications will bear a use-by date of three years from the date of manufacture. A code number should be marked on the wheel to indicate the source and manufacturing details of the wheel.
Wheels should be of the correct diameter and speed rating for the machine, and of the correct material and hardness for the tasks to be performed. Selecting the appropriate wheel for the job is equally important for efficient production and for safety.
