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Abrasive Wheels
ContentsAbrasiveWheels Contains public sector informa�on, licensed under the Open Government License v.3.0
2 IntroductionAbrasive wheels are dened as:any power driven wheel, cone, cylinder or discwith some form ofbonded abrasivematerial overits surface, that is used for cutting or grinding.The LawThe use of abrasive wheels is covered by :The Provision and Use of Work Equipment Regulations 1998(SIA 1998 No 2306) (PUWER)These regulations require that work equipment should be suitable for the workprocess, maintained in good repair and inspected at suitable intervals.All persons who use work equipment should receive adequate training, beprovided with adequate health and safety information, and be given writteninstructions where appropriate.Proper training isn’t an option, it’s a legal obligation.The primary objective of PUWER is to ensure that work equipment, includingabrasive wheels, do not give rise to risks to thehealth and safety ofthe workforce,regardless of the equipment’s age condition or origin.PUWER applies to all workplaces in situations subject to:the Health and Safety at Work Act 1974 (HASWA)The HazardsAbrasive wheels generally rotate at very high speeds. Contact with therevolving wheel can cause serious injury.In use, abrasive particles are thrown o during the grinding process and these cancause injury, particularly to the eyes. If the work piece is not secure then this mayalso be ejected at high speed.Wheels may also disintegrate or burst, causing fragments of the wheels to beejected at very high speed and in any direction. These fragments could causeserious injury to the operator or to anyone else in the vicinity.Most accidents involving abrasive wheels are due to incorrect use or poormaintenance. In particular the selection of the wrong wheel or over speeding.Loose clothing, long hair or other items may become entangled in therotating wheel and pull the operator into the wheel, causing injury.There are also problems that may arise from breathing in dust, from noise andfrom vibration.
3The Approved Code of Practice and Guidance to the Regulations contains thefollowing advice, specic to the use of abrasive wheels:▪ To minimise the risk of bursting, abrasive wheels should always be runwithin the specied maximum rotation speed.▪ If they are large enough, this will be marked on the wheel (a requirementof regulation 23▪ Smaller wheels should have a notice xed in the workroom, giving theindividual or class maximum permissible rotation speed.▪ The power driven spindle should be governed so that its rotation speeddoes not exceed this.▪ Guarding must be provided to contain fragments of the wheel that mighty o if it disintegrates, to prevent them from injuring anyone in theworkplace. The guarding has an additional role in helping to meet therequirements of regulation 11: it should be designed, constructed andmaintained to full both functions.▪ Providing information and training of workers in the correct handling andmounting of abrasive wheels (including pre-mounting and storingprocedures) is also necessary, to prevent the risk of bursting.Abrasive wheel characteristicsAbrasive wheels generally consist of abrasive particles bonded together usingvarious substances or methods.Inorganic bonds are red in the furnace and will give the wheel a very hard butbrittle structure. The wheels hold theirshape well and are mainly used forprecision grinding applications.Organic bonds come from substancessuch as rubber, shellac or resins.These wheels are not red but cured at alower temperature, producing a toughshock resistant wheel, commonly used forapplications such as cutting o, or cleaningup castings or welds.
4 Abrasive wheel characteristicsDescription of the elements forming an abrasive wheel:▪ Abrasive - refers to the type of abrasive used in the construction of thewheel.▪ Bond type - refers to the material used in the construction of the wheel▪ Grade - refers to the strength with which the bonding material holds theabrasive. Grade scale is “A” (very soft) to “Z” (very hard)▪ Grain - refers to the size of the abrasive grains or grit. These range fromvery coarse (4) to very ne (1200)▪ Structure - refers to the openness or porosity in the wheel. Highernumbers refer to greater porosity.Standard wheel marking systemWheel markings should conform to Annex A of BS EN 12413hb Shelf LifeAll organic bonded wheels will bear a use by date of three years from the date ofmanufacture.Traceable numberA code number should be marked on the wheel to indicate the source andmanufacturing details of the wheel
5Abrasive wheel characteristicsA grinding wheel is an abrasive cutting tool.In the wheel the abrasive performs the samefunction as the teeth in a saw.Unlike the saw which has teeth only on its edge,the wheel has abrasive grains distributed through-out. Thousands of these sharp and hard grainsmove againstthe work-pieceto cutaway tiny chipsof material. These chips are usually given o assparks.Abrasives - Grits and GrainsGrinding wheels have two major components; the abrasive grains that do theactual cutting and the bond that holds the grains together and supports them.It is the percentages of grain and bond and the spacing in the wheel thatdetermines the wheel’s structure.The ideal abrasive has the ability to stay sharp with minimal point dulling. Whendulling occurs, the abrasive fractures, creating new cutting points.Each abrasive type is unique and has distinct properties for hardness, strength,fracture toughness and resistance to impact.Types of AbrasivesAluminium OxideThis is the most common abrasive used in grindingwheels, particularly for grinding or cutting steel andother metals.There are many dierent types of aluminium oxideabrasives, each useful for specic types of grinding jobs.Silicone CarbideSilicon Carbide is an abrasive used for grinding sometypes of soft iron, brass, bronze andaluminium.It is also commonly used on stone,ceramics, rubber and other non-ferrous materials
6 Ceramic Aluminium OxideThis is the newest major development inabrasives with a very high purity grain. It hasthe ability to fracture at a controlled rate,constantly creating thousands of new cuttingpoints.It is exceptionally hard and strong and isprimarily used for precision grinding indemanding applications on products andmaterials that are the most dicult to grind.It is normally blended in diering percentageswith other abrasives, to optimise itsperformance.Types of AbrasivesGrit size refers to the size of the individual abrasive grains in the wheel. Highnumbers indicate very small sizes of grit and a ne wheel used for precisionpolishing or grinding. Low numbers indicate a very coarse or large grit, useful forquickly removing large amounts of material.Grit SizeThe bond is the material that holds the abrasive grains together so that they cancut eectively. The bond must also wear away as the abrasive grains wear and areexpelled, so that new sharp grains are exposed.There are three principal types of bonds used in conventional grinding wheels.The type of bond selected depends on such factors as the wheel operating speed,the type of operation, the precision required and the material to be ground.Vitried BondsProbably the most common type, they consist of a mixture of carefully selectedclays. At high temperature, the clays and abrasive grain fuse into molten glass. Asthe glass cools it forms a span that attaches each grain to its neighbour andsupports the grains while they grind.Wheels made with vitried bonds are very rigid and strong and are capable ofremoving stock material at high rates and to work to precise requirements. Theyare unaected by water, acid, oils and variations in temperature.They are, however, very brittle, like glass, and may be subject to breakage if badlyhandled or dropped.They are broken down by the pressure of grinding.Bonding Material
7Bond MaterialOrganic Bond MaterialOrganic bonds are liable to soften under the heat of grinding.They are most commonly made from synthetic resin, which is a good choice forapplications that require rapid stock removal or where better nishes are needed.They are designed to operate at higher speeds and are often used in fabricationshops, foundries and for saw sharpening.Other wheels may be used with an organic bond made from rubber. The rubberbond oers a smooth grinding action. These are useful where a high-quality ofnish is required, such as machining bearings. They are also frequently used ascut-o wheels where burr or burn must be minimised.Strength of the bondThe strengthof thebond is designated inthe grade of thegrinding wheel. It issaidto have a hard grade if the spans between each abrasive grain are very strong andit retains the grains well against the forces tending to loosen them. A soft grademeans that only a small force is needed to release the grains.Hard grain wheels are used for longer wheel life, or for jobs on more powerfulmachines and where there are small or narrow areas of contact.Soft grade wheels are used for rapid stock removal, jobs with large areas ofcontact and for hard materials.
8 Below are listed standardised wheel shapes with their shape numbers.The red arrow denotes the grinding surface.Wheel Shapes
9Hazards and RisksMost hazards and risks that arise from the use of abrasive wheels stem from theabrasiveness of the wheel itself and the fact that it is usually rotating at very highspeed.Failure of the wheelIf the wheel should start to break up, fragments of the wheel may be ejected athigh speed and in all directions. This oers considerable risk of injury to theoperator and to anyone in the vicinity.Ejection of the work piece.If the work piece is not properly secured it may be picked up by the wheel andthrown at high velocity, posing severe threat of injury to operator or anyone else.Contact with the wheelIf esh comes into contact with the wheel the likelihood of injury is serious.Fingers may become wedged between the wheel and work rest and looseclothing can become trapped in the rotating wheel, pulling the operator into it.Noise and VibrationDamage to hearing may result from prolonged exposure to loud noise.Prolonged and repeated use may result in vibration damage, such as VibrationWhite Finger.Respiratory ProblemsBreathing in the dust created by grinding operations could result in respiratorycomplications.InjuriesPenetrating injuries from high velocity particles, particularly to the eyes, severefriction burns, abrasions and crush injuries commonly result from accidentsinvolving abrasive wheels.PrecautionsMachineryMachinery should be in good condition,well maintained and t for purpose.Fixed machinery should be properly mounted and bolted down securely.Warning signs should be displayed stating the maximum speed of its spindle.Starting and stopping procedures should be well displayed and accessible.GuardingGuards should be xed so that only the minimum area of the wheel that isnecessary for the work to be done, is exposed.Fixed guards should be tted for protection against ejection.StorageStorage should be in a cool dry area.Appropriate racks or bins should be provided and precautions taken to preventthe wheels rolling or falling over
10 Wheel SelectionThe selected wheel must be suitable for the jobs for which it would be used.In general, soft wheels are used on hard materials and hard wheels are used onsoft materials.The following factors should be considered when selecting the wheel:▪ The type of machine on which it will be tted.▪ The speed of the machine spindle, not to exceed the maximum speed ofthe wheel.▪ The material to be worked on.▪ The nish required.▪ The contact area between the wheel and work piece.InspectionBefore use the wheel should be carefully inspected and examined for damage.A “ring” test should be performed as part of the examination.Wheel mountingThis should only be done by a competent person who has been properly trainedand then appointed by the employer.The employer should keep a register of appointed persons.Wheels should only be mounted on the type of machine for which they weredesigned. It is essential that the spindle speed does not exceed the maximumspeed marked on the wheel.For wheels less than 55 mm in diameter, this safe maximum speed should bedisplayed next to the machine.OperationOperators should be properly trained.They should not wear loose clothing or jewellery which could become entangled.Guards should be in place as appropriate.Eye protection and other items of personal protective equipment should be usedif necessary.The machine should only be used by one person at a time.Work rests should be positioned as close as possible to the face of the wheel andshould be repositioned as necessary, as the wheel wears.The work piece must be held securely. Clamps or similar devices can be used.Precautions
11Personal Protective EquipmentPersonal protective equipment will onlyprotect the operator and is notconsidered a substitute for properlyselected mechanical protection likeguarding or shielding.PPE is a last resort.Accident prevention takes priorityEmployers have duties concerning the provision and use of personal protectiveequipment (PPE) at work, to meet the requirements of The Personal ProtectiveEquipment at Work Regulations 1992 (as amended)PPE is equipment designed to protect the user against health or safety risks atwork. It might include items such as safety helmets or hard hats, gloves, eyeprotection and safety footwear.Hearing protection and respiratory protective equipment are not covered bythese regulations as there are other more specic regulations that apply to them.They should, however, be compatible with other PPE provided.The regulations require that PPE is▪ Properly assessed before use, to make sure it is t for purpose.▪ Maintained and stored properly.▪ Provided with instructions on how to use it safely.▪ Used correctly by employees.Selecting Personal Protective Equipment▪ Use only products which are CE marked in accordance with the PersonalProtective Equipment Regulations 2002.▪ Choose equipment that suits the wearer, in terms of size t and weight.▪ Involve users in the choice as they are then more likely to use it properly.Assessing PPE for Suitability▪ Does the PPE protect the wearer from the risks involved?▪ Does it take account of the environmental conditions where the task istaking place?▪ Does using PPE add new risks?▪ Can it be adjusted to t the wearer correctly?▪ If more than one item of PPE is worn, are the items compatible?