Source: https://www.scribd.com/doc/77545590/Safe-Use-of-Abrasive-Wheels
Timestamp: 2016-12-05 19:00:19
Document Index: 41793219

Matched Legal Cases: ['art 1', 'art 2', 'art 9', 'art 7', 'art 2', 'art 7', 'art 1', 'art 9', 'art 2', 'art65']

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Regulations covering these hazards as well as other regulations which the user of an abrasive wheel must comply with are listed under Further reading.
6 There is no substitute for thorough practical training in all aspects of the mounting and use of abrasive wheels. blotters. and that employees. mounting and managing the operation of abrasive wheels. PUWER 98 requires. If the number of breakages is to be kept low. Any training programme should cover at least the following: (a) hazards and risks arising from the use of abrasive wheels and the precautions to be observed. among other things. nuts etc. 5 It does not deal with other risks to safety and health which may arise from the use of abrasive wheels. (e) the functions of all the components used with abrasive wheels such as flanges. 1
. and (b) noise and vibration. the guidance should be read in conjunction with the PUWER Approved Code of Practice (ACOP). for example: (a) dust. the initial care exercised in the design.2 2 The risk of breakage is inherent in every abrasive wheel. (c) how to store handle and transport abrasive wheels. 3 In relation to abrasive wheels. including those using. Accident statistics indicate that nearly half of all accidents involving abrasive wheels are due to an unsafe system of work or operator error. manufacture and testing by abrasive wheel and machine makers must be coupled with the adoption of safety measures by the users. size and maximum operating speed. ie bonded abrasives. (d) how to inspect and test abrasive wheels for damage. (b) methods of marking abrasive wheels with their type. 4 This guidance deals primarily with wheels which are formed by abrasive particles being bonded together. For the duties of those people using abrasive wheels to be fully understood. that all machinery is suitable for its intended use and is properly maintained. are fully informed and properly trained in their safe use.INTRODUCTION
1 The purpose of this guidance is to give advice on precautions for the prevention of accidents in the use of abrasive wheels. in particular injury resulting from either wheel breakage or contact with a running wheel. bushes.
for example fettling and cutting off. (b) Grain/grit size means the particle size of abrasive grains. showing the trainee’s name and date of training. for example eye protection (see also paragraph 158). Further information can be obtained from the British Abrasives Federation. Such wheels are tough. 10 Organic bonds are not fired but are cured at low temperature. and are most suited to nonprecision applications. (h) the correct adjustment of the work rest on pedestal or bench grinding machines. rubber (R) and shellac (E). Wheels are graded as ‘soft’ or ‘hard’ according to their degree of tenacity. These wheels are used for precision grinding applications as they hold their shape.
. The higher the number. It is recommended that a record of training in the safe mounting of abrasive wheels is kept. not competence. 7 Training courses are offered by many organisations which usually provide a certificate of attendance. Full details are given in Clause 5.5 (a) Abrasive means the type of abrasive used in wheel construction. The range is expressed by number (very coarse 4 to very fine 1200). There are two main types of bonding agent: inorganic and organic. 2 (d) Structure means the level of porosity in the wheel. 11 The following words in bold are the variable elements in abrasive wheel manufacture. ie the wheel is generally fired in a furnace to give the bond a hard.5 of BS ISO 525: 1999. 9 Inorganic bonds are mainly vitrified. (c) Grade represents the tenacity with which the bonding material holds the abrasive grain in a wheel. the bond agents are resinoid (B).(f) how to assemble abrasive wheels correctly to make sure they are properly balanced and fit to use. (i) the use of suitable personal protective equipment. shock-resistant and self-dressing. the greater the level of porosity.
8 An abrasive wheel is usually defined as a wheel consisting of abrasive particles bonded together with various substances. strong but brittle structure. (g) the proper method of dressing an abrasive wheel (removing dulled abrasive or other material from the cutting surface and/or removing material to correct any uneven wear of the wheel). but require dressing. The grade scale is expressed in letters from A (extremely soft) to Z (extremely hard).
(c) RE3: Not suitable for wet grinding. Traceable number 16 A code number should be marked on the wheel to indicate the source and manufacturing details of the wheel. Shelf life 15 All organic bonded wheels for hand-held applications will bear a use-by date of three years from the date of manufacture. These are: (a) RE1: Not permitted for handheld and manually guided grinding. 3
NOT PERMITTED FOR HAND HELD CUTTING O F F M A C H I N E S V 04/2002
Test record Restriction of use Expiry date
610 x 80 x 254 wa 603 K6V M768453
MOS 50m/s 1600rpm ISO TYPE 1
Dimensions in mm Specification mark
Maximum operating speed ISO Type No (shape)
Figure 1 British Standard system for specifying abrasive wheels from BS EN 12413: 1999
and BS ISO 525: 19995
. or on the blotter or identification label which is sometimes attached to it. (e) RE6: Not permitted for face grinding. Restrictions of use 14 Annex A of BS EN 124133 and BS ISO 5255 specify how wheels should be marked to indicate specific restrictions for use. the maximum permissible speed in rpm of wheels 80 mm in diameter or less should be stated in a notice posted in a position where it can easily be read. (d) RE4: Only permitted for totally enclosed working area.
Marking 12 This should conform to Annex A of BS EN 124133 (see Figure 1). For speeds of 50 m/s and above. (b) RE2: Not permitted for hand-held cutting-off machines (see Figure 1). Maximum permissible speed 13 The maximum permissible speed in revolutions per minute (rpm) and metres per second (m/s) specified by manufacturers should be marked on every abrasive wheel larger than 80 mm in diameter. Since it is not practicable to mark smaller wheels. colour-coded stripes will appear on the wheel.(e) Bond type means the bonding material used in the wheel construction.
Bad storage. and it is essential that every breakage of a wheel should be followed by careful investigation. (c) In spite of these precautions breakage may occur in service due to a defect caused by subsequent misuse or handling. incorrect selection of a wheel. The bore area may also be impregnated by epoxy resin to increase the strength of the wheel. excessive speed. grinding machine defects. These include: (a) Fibre reinforcement: This is normally a resin-coated.SAFETY
17 Abrasive wheel manufacturers take all reasonable precautions. woven. They serve merely as an additional safety device and may not replace the guard. (d) Tapewinding: Adhesive tape. they help to hold the fragments together. (c) Safety inserts: These are threaded nuts incorporating locking teeth and form part of a plate which strengthens the base of a cup wheel used for portable grinding. Two or more of these factors may operate together.
. and malpractices in the grinding operations are all factors that can result in breakage. to supply sound wheels. These two types of reinforcement are used for wheels operating at 63 m/s to 125 m/s. glass-fibre or metallic wire may be used to strengthen thin-walled cup and cylinder wheels. It allows the wheel to withstand high stresses and helps to contain fragments if the wheel breaks in use. In the event of breakage. and various methods are used in their construction to reduce the risk of breakage. (b) Steel rings: These are moulded into the wheel close to the bore and are designed to retain wheel fragments if breakage occurs when the wheel is near to throwaway size. They can also be used to prevent excessive wear on the wheel. excessive out-of-balance conditions. (e) Fine grit centre or similar: A fine grit centre is placed around the bore to increase the strength of a vitrified grinding wheel. improper mounting. glassfibre mat used in organic wheels (resinoid and rubber bonded) for heavy-duty grinding and cutting operations. including speed tests. The centre is moulded together with the wheel. to establish the cause of the breakage and take suitable action to prevent a recurrence.
Storage 20 Suitable racks. (e) plate-mounted wheels. Heavy wheels should be supported on a clean hard floor for the ring test while light wheels should be suspended from their hole on a finger or small pin.Examination. The ring test is not practicable with the following types of wheels because of their shape or size. shellac. Handling 19 All abrasive wheels are relatively fragile.
. (f) inserted nut disc and cylinder wheels. so extra care and vigilance is required during the visual examination: (a) small wheels (100 mm diameter and smaller). the careless use of a tool may cause damage to the wheel. (b) use trucks or suitable conveyors which will provide proper support for transporting wheels which cannot be carried by hand (Figures 2 and 3). The following rules should be observed to avoid chipping. for example due to cracking. a soft. This is known as the ‘ring’ test. Comparison with other wheels of the same lot and specification will allow rejection of any wheel with a suspiciously different ring before use. the manufacturer should be notified. bins or compartmented drawers should be provided to accommodate the various types of wheels used. rubber) will stand rough handling. The soundness of wheels can be further checked by tapping them with a light. They should not be rolled along the floor unless a suitable mat or other protection is available. resilient floor surface is essential. If the wheel sounds dead. cracking and breakage: (a) handle wheels carefully to prevent dropping or bumping. (d) segments. (b) plugs and cones. handling and storage of abrasive wheels
Examination 18 Wheels should be carefully unpacked. Wheels must be dry and free from sawdust for the ring test otherwise the sound will be deadened. Do not roll abrasive wheels. it should not be used. In case of doubt. Where this is unavoidable because of the large size of the wheel. It should not be assumed that organic bonded wheels (resin. Do not pile heavy castings or tools on top of abrasive wheels. In unpacking. cleaned with a brush and examined for possible damage in transit. (c) mounted wheels. It should also be noted that organic bonded wheels do not emit the same clear metallic ring as inorganic bonded wheels. Stack and support wheels carefully on trucks so that they will not topple over and be damaged. The following suggestions
Figures 2 and 3 When handling large wheels use a truck or other suitable conveyance. non-metallic implement.
ie the abrasive wheel face becomes clogged with particles of the material being ground. a contributory cause of wheel breakage. straight wheels. It is therefore essential that the fullest details of the type of grinding operation should be given to the manufacturer to enable the correct wheel to be supplied. taper cup wheels are best stored as shown in the illustration of a typical storage rack (Figures 4a and 4b). Most plain and tapered wheels are best supported on their edges or on a central support. organic bonded wheels such as those used for cuttingoff should be laid flat on a horizontal surface of steel or similar rigid material away from excessive heat and moisture. A wheel may also be either too hard or too fine. the support should take the form of a cradle to prevent rolling. resulting in ‘glazing’. Each type of wheel has its uses and is best suited to certain classes of work. It is recommended that wheels should be marked with the date they are received from the supplier. The operator is then tempted to use excessive pressure for the work on the wheel. soft wheels are preferred on hard material and hard wheels on soft material. However. 23 Selecting the correct wheel for the job is essential for safety. thin.covering the design of facilities may be helpful. To prevent warping. Blotters or other packing should not be placed between stacked thin wheels. 24 As a rough guide. ‘loading’ may result. if the wheels are supplied with blotters attached. straight cup wheels may be stacked on the flat side with corrugated cardboard or other cushioning material between them. A grinding wheel may be
Plain wheels Taper cup wheels
Special face wheels
Inclined shelf for small wheels Flat shelf for cuttingoff wheels and shaped wheels Two point cradle supports
Cutting-off wheels Dish wheels Thin rim and soft grade cylinders Corrugated paper Steel supporting plate Steel supporting plate
Thick rim and hard grade cylinders
Large plain wheels
Medium size plain wheels
Figure 4b A storage rack suitable for all types of wheels
dangerous if used for an application for which it is not intended. or if wheels have been in stock for more than three years. with a sufficient number of partitions to prevent wheels from falling over. The best policy in selecting grinding machinery is to consult machines and abrasive wheels manufacturers and not to experiment without competent advice. Cylinder wheels and large. suitable separators should be used to preserve flatness. the manufacturer should be consulted about their suitability for use. 21 Where the wheels are placed on their edges. With wheels of unsuitable structure for the job. To prevent chipping of edges. 22 To minimise deterioration. When ordering a
Front edge of wheels should not protrude in front of supports
. Older wheels should be issued before newer wheels and if there is any doubt. wheels must be stored in a room
Back enclosed for protection
Figure 4a Typical wheel storage
which is dry and not subject to extreme temperatures. or they may be stored in racks similar to those used for large.
Where a variety of wheels are kept in store. blotter or identification label and always quoting it in full on the order to the manufacturer or stockist. the material to be ground or cut. the rate of stock removal. extremely important. the most important factors are: wheel dimensions. and the area of contact of the wheel and workpiece. in excess of those listed. it is very important that the correct wheel is issued for the machine on which it is intended to be used. Table 1 (see page 38) gives the general maximum operating speeds in m/s for various classes of wheels and grinding processes. and marked with the appropriate maximum operating speed and the code indicating specific restrictions for use.
28 The maximum operating speed is marked on every wheel in two ways: (a) the peripheral surface speed which is given in m/s. As the wheel wears down in use. subject to: (a) the machine being designed for the speed and fitted with a guard specially designed for this purpose. re-ordering the correct wheel can be ensured by recording the information shown on the wheel. 25 Grinding wheel manufacturers establish the maximum operating speeds of different types of wheels after taking into account the requirements of the application and the stresses set up under operating conditions. It cannot be too strongly emphasised that doubling the speed increases fourfold the stress in the wheel and hence the risk of the wheel bursting. Higher speeds. but as the square of the speed. therefore. 26 Once the correct selection has been made. To counteract this. and (b) the wheel being approved by the wheel manufacturer as suitable for the speed and the particular mode of operation. the type of grinding machine. the accuracy and finish required. the speed of the machine or spindle on which the wheel is to be mounted.new wheel. Always ensure that the spindle speed is reduced to its original value before fitting new wheels. the effective peripheral surface speed will reduce if the rotational speed remains constant and may result in a reduced grinding efficiency. providing the maximum peripheral surface speed of the wheel is not exceeded. (b) the rotational speed which is given in rpm. the spindle speed can be increased.
27 Remember that centrifugal force (the ultimate cause of wheel bursts) increases not directly with speed. The speed at which the abrasive wheel revolves is. shapes and recesses (Figure 5). for specially designed and totally enclosed machines may be used.
types (from Table 12 of BS EN 12413: 19993)
denotes grinding face
.Figure 5 Abrasive wheels .
. heat generated by machine bearings in poor condition can be transmitted to the spindle causing thermal expansion which may result in cracking of the abrasive wheel. These appear to be obvious precautions. Loose bearings or any other factor causing an out-of-balance condition will produce vibration and may cause the wheel to knock against the work excessively with the eventual risk of wheel breakage. Overspeeding is one of the main causes of wheel breakage. 32 Pedestal grinders should be heavily built and mounted on good foundations. there will be enough thread for full engagement of the nut on the spindle.
35 In no circumstances should the maximum permissible operating speed specified by the wheel manufacturers be exceeded. In addition.
34 Machine bearings should be maintained in good condition. Bench grinders should be securely anchored to a stout bench. On no account should an abrasive wheel be screwed on to the tapered spindle of a buffing machine. This dangerous method of mounting is likely to result in the breaking of the wheel owing to the wedging action of the tapered spindle. They should be mounted on the type of machine for which they are intended. free from play and adequately lubricated. As a result. To illustrate the point.29 Never operate new abrasive wheels at speeds (in rpm) in excess of that marked on the wheel.
31 Abrasive wheels should not be mounted on makeshift apparatus. 30 Table 2 (see page 40) gives the conversion of rpm to a peripheral speed in m/s for a wide range of wheel diameters. Likewise. vibration is excessive and breakages occur. a fragment from a burst wheel operating at 35 m/s is travelling at 80 mph (126 km/hr) and for 125 m/s at 280 mph (450 km/hr). The thread should extend inside the flange but not into the hole in the wheel. accidents are caused by heavy wheels being fitted to spindles designed to take only the lightest of wheels. the thread should be such that the direction of tightening the nut is opposite to the direction of rotation of the wheel to ensure that the nut will not come loose as the wheel rotates. When the wheel is secured by means of a single central spindle nut.
33 The spindle should be long enough and threaded to a sufficient length to ensure that when the wheel and flanges are mounted. but accidents still occur because wheels are mounted on home-made or improvised apparatus quite unsuitable for the work.
the machine is automatically switched off or made to run at its lowest speed. the notice must show the maximum and minimum speeds. 39 Experience has shown that governor failure is a common cause of wheel breakage. a governor is built into the machine. On other machines it is possible to vary the speed infinitely over a specified range. Where the spindle can be operated at more than one specific speed. or a hinged visor at the top of the guard (Figure 28. Failures have also occurred due to the presence of foreign bodies such as stray washers. To eliminate the loss of efficiency. On these machines. Governors should be designed to prevent incorrect assembly which has been the cause of a number of accidents.36 The maximum speed of the spindle should be marked on every grinding machine so that it is easy to compare the speed marked on the wheel with the speed of the machine spindle. scale or moisture in the air supply. In cutting-off work. so that attention to the governor is most important.
. otherwise a dangerous peripheral speed may be reached leading to the bursting of the wheel. the spindle speed can be increased and an efficient peripheral speed maintained. 38 A constant peripheral speed is maintained automatically on some machines by means of a sensing device which detects small changes in the diameter of the wheel as it wears down. the speed is reduced. and to prevent the wheel from over-speeding. however. a speed lower than that recommended may lead to unnecessary breakages. and increases the speed accordingly. some machines are fitted with stepped pulleys so that as the wheel wears. Defects in governors can be caused by inadequate lubrication or excessive wear due to grit. Air motors in pneumatic grinders can usually attain a very high speed under free-running conditions. an interlocking device should be provided to prevent the spindle speed from being stepped up before the wheel diameter has been sufficiently reduced. The speed of these high-speed machines is controlled by restricting the rate at which air is introduced to or exhausted from the machine to the atmosphere. The correct speed is selected by adjusting the whole of the guard. and here it is usual to control the spindle speed by means of the wheel guard which is connected to a split cone pulley. each speed must be shown. page 26). nuts etc inadvertently left in the governor chamber after maintenance. These devices should be designed so that in the event of an electrical fault. as close as possible to the periphery of the wheel. 37 The peripheral speed of a wheel on a fixed-speed spindle will decrease as the wheel wears and some loss of efficiency will ensue. a method which is also used to a limited extent on larger portable pneumatic machines. An exception to this is the class of small grinding machines on which mounted wheels and points are used. Clean air is therefore essential and an effective filter combined with a pressure regulator and lubricator should be connected in the supply line. Some machine manufacturers incorporate this device on new machines. Governors should never be disconnected when a grinder is in use. Regular maintenance of governors to manufacturers’ instructions is essential and they should be repaired or adjusted only by a competent person. When the guard is moved forward or the visor opened to accommodate a large wheel. and if the speed is infinitely variable within a specified range.
when the spindle speed should be checked with a tachometer. It is also good practice to provide a substantial guard around the machine table as a protection against the workpiece being ejected. securely clamped to the machine. Adjustments to work rests should be made only when the grinding wheel is stationary and the machine isolation switch is in the ‘off’ position.
. causing jamming. a pressure regulator set to the correct pressure should be connected in the air supply line to the machine. break-up of the wheel and possible injury to the operator. The rests should be kept adjusted as close as possible to the periphery of the wheel to prevent the workpiece getting between the wheel and the rest. 41 Some machines have a work rest at the side of the wheel which encourages the dangerous practice of side grinding. The rests should be of substantial construction. The ability of these devices to hold work depends on the material. The operator may apply greater pressure on the workpiece against the wheel and increase the stresses in the wheel. together with the use of stops and suitable fixtures. as this might be the first symptom of a governor defect.
42 Inadequate power at the grinding wheel may be caused by a belt slipping or a driving motor of insufficient power. On portable machines the control should be located so that there is no risk of accidental starting when the grinder is placed on a flat surface. Permanent magnets have great advantages as they do not depend on an electricity supply. 40 Where work-rests are provided on pedestal and bench machines they should be made of steel with renewable top plates. Work rests should be examined periodically and maintained in good condition. and be readily adjustable to follow wheel wear. surface conditions and the area of contact of the work.
Magnetic tables and chucks
44 Magnetic tables and chucks are commonly used on grinding machines. Pneumatic grinding machines should be marked with the maximum working air pressure at the machine inlet. should all be considered. when the workpiece becomes jammed between the wheel and work-rest which cannot be correctly adjusted in relation to the side of the wheel. As a precaution against this pressure being exceeded. These factors. preferably of hardened steel. This is especially important with pneumatic machines which do not incorporate a mechanical governor but depend on the control of the air inlet or exhaust to control the speed. The use of work rests in this manner can cause the wheel to burst or break after being weakened by grooves worn in the side or.
43 Means for starting and stopping grinding machines should be clearly visible and marked. placed in a safe position and within easy reach of the operator.Operators should be instructed to report any instability in speed immediately. as previously mentioned. Flat spots will tend to develop and cause ‘bumping’ and breakage of the wheel. This will cause the wheel to slow down when grinding starts.
Reinforced resinbonded flat cutting-off wheels on fixed and portable petrol-engined
. Paragraphs 46-90 explain the purpose of the various components used with abrasive wheels and the precautions which should be taken in the mounting of each type of wheel. many accidents could be prevented if the people mounting the wheels were instructed (see paragraph 6) in the hazards arising from incorrect mounting and in the correct method of assembly. In the case of straight adaptor and hubbed flanges there is an undercut in place of a recess (see paragraph 50). With certain exceptions. 47 The exceptions are: (a) mounted wheels and points. It is therefore important that stresses due to mounting and driving are as far from the hole as practicable. every abrasive wheel should be mounted between flanges which are at least one third of the diameter of the wheel. This is done by recessing the side of the flange next to the wheel.MOUNTING OF ABRASIVE WHEELS
45 The danger of an abrasive wheel bursting is considerably increased if it is not properly mounted.
Straight recessed flanges
Straight adaptor flanges
Hubbed flanges
Straight flange for type 27 wheels
46 The major stresses produced in an abrasive wheel under operating conditions tend to become greatest near the hole. (d) plate-mounted wheels.
NB: The information contained in this section may be subject to revision following publication of proposed CEN standards on grinding machines. (c) abrasive discs (inserted nut discs and cylinders). 48 Reinforced resin bonded depressed-centre grinding and depressedcentre and flat cutting-off wheels up to 230 mm diameter may be mounted between smaller flanges on portable machines. (b) wheels with threaded inserts. (e) cylinder and cup wheels and segments mounted in chucks. (f) wheels of 20 mm diameter or less.
adaptor and hubbed flanges are illustrated in Figure 6. These are not recessed. In view of its low tensile strength and the risks of cracks developing in service. they should be re-trued. and the bearing surface should run true with the spindle.
Material for flanges
49 Flanges should be made from good-quality mild steel such as that specified in BS 970: Part 1: 19966 or another material with sufficient strength and rigidity to resist undue deflection when the flanges are tightened on the wheel. care being taken to maintain the original diameter and depth of recess without unduly impairing the stiffness of the flanges. Flanges for wheels with large holes.7 13
. grey cast iron cannot be regarded as safe for the flanges of abrasive wheels. but the corners of the wheel seatings should be undercut so that there will be no bearing on the side of the wheels within 6 mm of the hole. When re-truing the flanges would result in an unacceptable loss of stiffness they should be replaced by new flanges.cutting-off machines may be mounted between flanges of at least one quarter of the wheel diameter or more. page 20). If the bearing surfaces become damaged. the advice of the machine manufacturer should be sought.
52 The inner (driving) flange should be keyed. Before any attempt is made to re-true cambered flanges. screwed. the inner (driving) flange may be secured by friction only.
54 Dimensions of flanges for different types of abrasive wheels are given in British Standards.
53 As a general rule both the flanges used to secure a wheel to the spindle should be the same diameter and have the same recess diameter to create equal bearing surfaces on the wheel.
50 Flanges should be recessed on the side next to the wheel. shrunk or otherwise secured to the spindle to prevent rotation. for example certain internal and cup wheels (see Figure 18. For small abrasive wheels (for example straight wheels on small bench grinders) flanges of non-ferrous alloys have been used successfully. for example BS EN 13218. An exception is the single flat flanges used with threaded-hole wheels.
51 The surfaces of the flanges which bear on the wheel should be machined true and there should be no exposed rough edges or surfaces. but the shape of some wheels may not allow this rule to be followed. and the recess re-cut. For bench-mounted machines driven by a motor of less than 560 W and fitted with pressed steel flanges.
They should be slightly less than the width of the wheel and blotters. care should be taken to ensure that the bearing area of the flange is in contact with the wheel and not the bush. except for the wheels mentioned in paragraph 56. If the depth of the recess will allow this to happen. the bushes should not be used and a wheel with a hole to suit the machine spindle should be used.5 mm or less in thickness.2 mm thick and not more than 1. This is most likely to occur when two narrow bushes are used one at each end of the hole as an alternative to one bush extending the full width of the wheel. 56 Blotters should not used with the following types of wheels: (a) mounted wheels and points. but they also prevent slipping at lower clamping forces and reduce wear on flanges. If the wheel has been used previously. A blotter can serve as a label. a label cannot act as a blotter. 58 Before using wheel bushes. (b) abrasive discs (inserted nut discs and cylinders). and should be slightly larger than the flanges. if there is one. the depth of the recess in the securing flanges should be measured to see if it is possible for the bush to slide out of the wheel and become loose in the recess of the flange. otherwise high spots will occur leading to severe local stresses when the wheel is clamped tight.0 mm) as supplied by the wheel or machine manufacturer. however.
57 Bushes are inserts made of plastics or metal and used to reduce the hole size in an abrasive wheel so that it can be mounted correctly on a small diameter spindle. (g) wheels with threaded inserts. Blotters should be an easy fit on the spindle or on the wheel locating spigot. any pieces of old blotter or loose grains of abrasive should be carefully removed. (f) taper-sided wheels. Care should be taken to see that each blotter is free from wrinkles. should be used between the wheels and their flanges. Bushes are hand-pressed into the hole of the wheel and are not recommended for use with wheels fitted to portable grinding machines. As the power required to drive a grinding wheel is transmitted to it through the flanges.Blotters
55 Blotters of compressible material (usually cardboard not less than 0.
. (d) cylinder wheels mounted in chucks. (c) plate-mounted wheels. The main purpose of blotters is to distribute the clamping force of the flanges evenly on the wheel. (e) rubber-bonded cutting-off wheels 0.
Spindle contraction along its axis on cooling may distort the flanges so that they exert pressure on the corners of the hole in the wheel and produce a fracture. the nut should be tightened only enough to ensure that the flanges drive the wheel and prevent slip. 63 Threads of screws and tapped holes should kept clean. a check should be made to ensure that the maximum permissible speed marked on the wheel. having ensured that the flange is properly located and seated firmly on the blotter. Screws on multiple screw-type flanges should first be tightened by hand.
Multiple wheel mounting for fixed machines
65 Such assemblies may be complex and advice should be sought from the manufacturer as to the mounting requirements. resulting in a loosely clamped wheel. then fully tightened using the recommended tool. NB: Where different wheel diameters are used on multiple assemblies the maximum operating speed of the largest diameter wheel should not be exceeded. This is particularly important with wheels 150 mm or more in thickness.
66 Before the wheel is mounted. or by hammering. 62 Excessive clamping pressure applied by using an extension to a spanner for example. for example use of blotters. may damage the wheel. 60 Where the wheel is clamped by means of a single central nut. they may touch bottom in tapped holes. 61 Where a tightening torque is recommended by the machine manufacturer a torque wrench should be used.
Figure 7 Sequence for tightening screws
64 If the flange screws are too long. If it grips the spindle or flange location diameter.Securing the wheel
59 The abrasive wheel should fit freely but not loosely on the spindle. heat generated during the grinding operation could cause the spindle to expand and possibly crack the wheel. Care should be taken to avoid excessive tightening which may cause springing of the flanges and result in wheel breakage. Tightening should proceed from the first screw to the one diametrically opposite and then in criss-cross sequence until sufficient pressure is applied uniformly to prevent the abrasive wheel slipping between the flanges (Figure 7). otherwise equal torque applied on a uniform clamping force. Otherwise tightening should be done only by hand pressure on a spanner. If clean screws are should be replaced or the holes in which they be in good condition and all screws will not provide not easily tightened they fit should be re-tapped. when flange screws are tightened under hot operating conditions and the machine is then allowed to cool after use. blotter or identification label is not exceeded by the speed of the spindle marked
The wheel is gripped between two flanges of equal diameter. 71 Wheels for internal grinding are mounted as shown in Figure 10. The flanges are not recessed and washers (blotters) are not fitted
72 One of the types of flanges used for wheels with large holes is the adapter flange shown in Figure 11. New or re-fitted wheels should be run free at full operational speed for a short period before they are used.on the machine. Excessive tightening of this nut is unnecessary and.
Figure 8 A straight-sided wheel with a small hole. Electronic tachometers do not require any contact with the rotating parts and can therefore be used with the guard in place. the guard should be properly adjusted and secured. The flanges are tightened by means of a central nut. 67 It may be necessary to remove the guard in order to measure the spindle speed by means of a tachometer or other instrument.
Blotter Wheel bush if used should be clear of flange
Back flange keyed to shaft
69 Figure 8 shows a wheel correctly mounted. one flange omitted and the nut tightened directly against the wheel. 70 Figure 9 shows a wheel incorrectly mounted. With portable machines the operator should ensure the machine is operated with the guards properly positioned. a close side-fitting key should be used. Such conditions increase the liability of a wheel to fracture because they result in undue concentration of stress near the hole. Each flange has an equal recess and the blotters are slightly larger than the diameter of the flanges. might cause breakage. The guard must then be replaced before operation starts. proper gripping is not obtained even with normal pressure and localised stresses are set up near the hole. The other type of flange is the hub flange (Figure 12).
. and several readings should be taken to obtain an average speed in rpm. The result may be that when the nut is tightened. If the machine is fitted with a work rest.
68 Before the wheel is run. it should be adjusted as close as possible to the wheel and the wheel should then be rotated by hand to ensure that it is clear all the way round. Other unsatisfactory and dangerous conditions which are sometimes found include: flanges unmatched in outside diameter and diameter of recess. The flanges are tightened by a series of clamping screws and the wheel holder or collet is machined to fit the tapered end of the spindle. use of an ordinary washer as a substitute for a properly recessed flange. If the machine manufacturer has provided a keyway. the inner (driving) flange being keyed on the spindle and the outer one tightened by a nut on the threaded spindle end. and during the trial run everyone shoud stand clear. The speed of spindles should be checked at suitable intervals by means of a tachometer. correctly mounted
Plain wheels with large holes
Figure 9 An incorrectly mounted wheel. Here the flanges are not recessed and blotters are not used. by setting up an undue crushing stress in the wheel.
The corners of the wheel seatings should be undercut as shown external grinding
Hub flanges frequently have grooves machined into them to accommodate adjustable balance weights and it is usual to keep wheels of different grits and grades mounted on the collet to facilitate wheel changing and reduce changeover time. these collets should be supported in suitable cradles. However. These flanges are intended to grip large fragments of a broken wheel when a major fracture occurs. flanges.
. 17 The recommended flange size is at least half the wheel diameter. straight. they cannot contain fragments which break off that part of the wheel not covered by the tapered flange. These wheels should never be used with ordinary. such as grinding inside a hole. Blotters are not required.
73 For portable grinding machines using abrasive wheels of 200 mm diameter or less there are certain grinding operations where the use of a normally guarded abrasive wheel is difficult.Blotters are only required on wheels over 20mm diameter
Figure 10 Methods of mounting small wheels for internal grinding
Figure 12 A method of mounting a precision wheel for Figure 11 A straight-sided wheel with a large hole mounted between adaptor flanges and secured by a central nut. When not in use. These wheels have each side tapered by 6% and are clamped by flanges with matching tapers. The wheel flange seatings should be undercut (Figures 11 and 12) to prevent pressure being exerted on the corners of the wheel. One solution to this difficulty is to use a Type 4 taper-sided wheel (see Figure 13).
The screw holes in the faceplate and the tapped holes in the inserted nuts in the wheel should be accurately matched. the degree of taper of the flanges must correspond with that of the wheel
Discs and cylinder wheels
Inserted nut mounting 76 In this method of mounting abrasive discs and cylinder wheels. They should have square ends so that there will be a full thread to the end of the screw. need to be long enough to engage the threads properly in their inserted nuts. yet not so long that there will be any possibility of the screw ends touching the bottom of the hole. The diameter of the flanges should be at least one-third of the diameter of the wheel and the diameter of the recess should be large enough to accommodate the flange without allowing it to bear on the corner radius in the recess. 77 Bolts. as described in paragraph 62. Where possible. 19 in Figure 5. they should be used with guards.
Figure 14 A cylinder wheel secured to a backplate by means of nuts anchored in the back of the wheel
The screws must not come into contact with the abrasive
Figure 13 Protection flanges used with a tapered wheel. Another. and before mounting.
75 Recessed wheels are used to give a wider grinding face than that obtained by using straight-sided wheels. for example Types 16. and thick enough to provide proper support. To be effective. They should not be used without guards for general fettling operations.No blotters on taper sided wheel
74 Tapered wheels should only be used inside a bore where the workpiece can act as a guard in the event of a wheel fracture. casting or moulding (Figure 14). threaded nuts are anchored in the back of the wheels by cementing. The total depth of recess on each side of the wheel should not exceed half the wheel thickness. both the plate and the wheel clamping face should be cleaned. 18. which should be of high tensile steel. with a diameter not less than that of the wheel. and the screw holes should be large enough to prevent binding. 18R. page 8. The screws should be tightened uniformly in a diametrical sequence. 17. The faceplate should be maintained true and flat to provide even support over the area of contact between plate and wheel. safer possibility is to use a cone or plug wheel. The wheels are secured to a faceplate. They may be recessed on one or both sides and should be mounted in the same way as straight-sided wheels.
the wedges are slackened.
Lipped backplate
Figure 15 A bonded abrasive disc cemented to (a) a plain backplate and (b) a lipped backplate
Adjusting ring to compensate for wheel wear
80 Abrasive wheels consisting of separate segments are generally used for heavy stock removal. The wheel rests against a circular plate and is kept tightly in position by sector wedges which are secured by bolts. the plate is advanced along the screwed boss of the wheel housing by use of a special tool and the wedges are re-tightened. and the manufacturer’s instructions should be strictly followed Epoxy resin adhesives can be used for this purpose. Care should be taken to ensure that the segments. The segments are held by special chucks with provision for the adjustment of segments to compensate for wear. Various cements may be used for this purpose.Cement
Plain backplete Cement
Cementing to a backplate 78 Some wheels have a steel plate permanently cemented to the back. They stand up to heavy grinding and may allow the use of harder grades of abrasive than with solid wheels. Chuck mounting 79 Cylinder wheels may be mounted in protection or safety chucks (Figure 16). When the face of the wheel has worn down. do not protrude from the chuck for a distance exceeding 1. Figure 15a illustrates a plate-mounted wheel of this type. They are used particularly on vertical grinding machines. and this is fastened to the machine plate by screws. Figure 17 shows a typical arrangement of the segments and chuck. The chuck should be kept adjusted to give minimum projection of the wheel beyond the chuck. Other wheels are cemented to a lipped backplate (Figure 15b). when mounted. but with this type of adhesive it may be necessary to discard the backplate or return it to the wheel manufacturer when the abrasive wheel is no longer usable.
Figure 16 A cylinder wheel mounted in a protection chuck
Figure 17 A typical mounting for abrasive segments
.5 times the thickness of the segment. One segment is shown removed to illustrate the method of adjusting the segments to take up wear.
The recessed flange does not provide proper support
. The same principles apply as for the mounting of plain wheels. Portable machines (threaded-hole cup wheels) 83 Threaded-hole cup wheels are screwed on to the end of the machine spindle against a flange. the adaptor flange and back flange should be equal in outside diameter and diameter of recess
84 Cone and plug wheels are manufactured with blind threaded holes. Breakages of this type of wheel may generally be attributed to such faults as a spindle having insufficient thread.
Inner flange must not foul the corner of the wheel
Figure 18 A cup wheel mounting for a fixed machine
Figure 19 An adaptor flange for an unthreaded-hole cup wheel. To provide proper support for the wheel the back flange and adaptor should be equally recessed.`Blotters
Fixed machines 81 Figure 18 shows how a cup wheel should be mounted on a fixed machine. Care should be taken that the clamping flange does not foul the radius in the corner of the wheel. When mounting. but the diameter of the flange and blotter inside the cup must be slightly smaller than the diameter of the wheel recess to prevent any risk of radial pressure on the wheel. be larger than that inside the cup. To provide proper support. When used for work heavier than light tool and cutter grinding. it is important that the hole is free from foreign matter and that the threaded spindle is shorter than the hole so that it will be
Figure 20 A correctly mounted threadedhole cup wheel
Figure 21 An incorrectly mounted threadedhole cup wheel. and blotters should be used. as with plain wheels. or the use of a recessed flange which tends to pull the bush out of the wheel. A blotter must not used. but the diameter of the recess in both flanges must still be equal. with advantage. The flange should be flat and not recessed (Figure 20) as a recessed flange (Figure 21) would tend to strain the threaded bush. Portable machines (unthreaded-hole cup wheels) 82 Wheels of this type used on portable machines are mounted by means of an adaptor flange as in Figure 19. the back flange can.
concentrating the load on a few threads. Figure 22 shows a properly mounted cone wheel while Figure 23 shows examples of common mounting faults. In (a) the spindle is too long and will cause the cone to crack and break up. and a blotter is not required.Clearance at the end of the spindle
Full engagement of threads
Wheel supported by flat flange
Figure 22 A correctly mounted threaded-hole cup wheel
concentrated may the break wheel
on few threads. The flange should not be recessed as this would tend to pull out the bush. Vibration may break the bush
. in (b) the spindle is too short. Vibration A gap here will cause the wheel to break here A Thread too long B Thread too short bond with the bush from its
Bush pull
only is apt
Figure 23 Common faults in the mounting of cone wheels
long enough to give sufficient thread engagement to hold the cone but not to press on the bottom of the hole.
. in (d) a recessed flange has been used which may well result in the bush being pulled out. For cutting non-metallic materials. normally 38 mm long. never on makeshift or improvised machines. with a maximum diameter of 80 mm. unreinforced cutting-off wheels used on fixed machines should be mounted between flanges which are as large as practicable and at least one third of the diameter of the wheel.
Flange diameter Blotters should not be used with depressedcentre wheels
Depressed-centre wheels
85 Depressed-centre wheels are reinforced wheels used mainly on portable machines. straight-sided wheels with a central hole. the use of unequal flanges is liable to cause distortion and breakage of a cutting-off wheel. for example dressing the face of a workpiece.
87 Reinforced cutting-off wheels used on portable machines should be mounted as in Figure 24b. They are not required with smaller wheels.
Figure 24b Mounting for a cutting-off wheel
88 Mounted wheels and points. mobile machine or on any machine where the work is fed into the wheel by hand. Blotters need not be used between the wheel and the flanges for wheels of 400 mm diameter or less. The flanges should be of equal diameter with equal diameter recesses. Type 27 wheels are for grinding. For cutting metal. such as woodworking circular-saw benches. The abrasive point is secured on the end of a spindle. Unreinforced cutting-off wheels are particularly susceptible to shock and should only be mounted on machines designed specially for their use. used at high peripheral speed and may be either reinforced or unreinforced. reinforced cutting-off wheels used on fixed machines should be mounted between flanges which are at least one quarter of the diameter of the wheel. are used extensively in operations such as die finishing where the nature of the work prevents the use of conventional wheels.Undrecut
from its bond with the wheel allowing it to pull out. However. if slippage occurs blotters should be used. They may be mounted between small flanges which grip on the hub. There is a wide variety of standard shapes of mounted wheels and points. in such cases the wheel must be of the reinforced type (see the advice on the use of cutting-off wheels on portable machines in paragraph 87). Type 42 wheels are for cutting-off operations such as the removal of runners and risers on castings and cutting
Figure 24a Mounting for a depressedcentre wheel
reinforcing rods on building and civil engineering projects. as in Figure 24a. in (c) the threaded length of the spindle is inadequate and the cone may work loose.
Flat cutting-off wheels
86 Flat cutting-off wheels are thin.
Blotters should be used with straightsided cutting-off wheels over 400 mm diameter. An unreinforced cutting-off wheel should never be used on a portable grinding machine.
SUMMARY OF MOUNTING PROCEDURES
91 Wheel mounting should be carried out only by an appropriately trained person. a high speed of rotation is necessary for efficient working. A wheel should be mounted only on the machine for which it was intended. Before mounting. 96 Flanges should be of equal diameter and have equal bearing surfaces (but see paragraph 53). Some collets are made to close and grip at each end by means of opposing tapers. Small air or electrically driven portable grinders are available with speeds exceeding 100 000 rpm. This type of collet is also capable of tolerating a greater variation in spindle diameter than other collets which only grip at one end. 92 The speed marked on the machine should not exceed the speed marked on the wheel. 95 W ith the exception of the single flange used with threaded-hole wheels. blotters and flanges should be free from foreign matter. 94 Flanges should not be smaller than their specified minimum diameter. if any. The wheel should fit freely but not loosely on the spindle. all flanges should be properly recessed or undercut. all wheels should be closely inspected to ensure that they have not been damaged in storage or transit. blotter or identification label. size of point. the diameter of the spindle. should not project beyond the sides of the wheel and blotters. The correct operating speed depends on three factors: the shape and dimensions of the point. (The overhang is the part of the spindle which is exposed between the collet and the part of the abrasive material nearest to the collet. 97 Wheels. and their bearing surfaces should be true and free from burrs. Clamping nuts should be tightened only sufficiently to hold the wheel 23
. 4 and 5). and the overhang of the point from the collet (see Tables 3. Protection flanges should have the same degree of taper as the wheel. should be used with all abrasive wheels except those listed in paragraph 56. 93 The bush. Wrinkles in blotters should be avoided. and diameter of spindle.) Further information is also available in Annex C of BS EN 12413: 1999 Safety requirements for bonded abrasive products 3 to ensure that the overhang does not exceed that appropriate to the speed.89 The factors to be considered in the safe use of mounted wheels and points are more complex than for ordinary wheels. Because of the smaller diameter of the abrasive surface. slightly larger than the flanges. Operation above the recommended speed is liable to cause fracture of the spindle or result in the spindle bending through a right angle and the point flying off. and it is possible that the collet may also fracture. For longer spindle lengths and overhangs the wheel manufacturer should be consulted. Blotters. 90 Severe injuries to eyes and face have occurred as a result of overspeed accidents.
the guard is returned by the spring to its original position covering the wheel
Bracket Outer tube Lug Spring-loaded tube Spring
102 The internal grinding machine in Figure 26a is enclosed to control the emission of noise. On fixed internal grinding machines. the overhang appropriate to the speed. The valves controlling the movement of the air
. as far as possible. The sliding door is interlocked to ensure that access to the workpiece is prevented until it has stopped rotating. however. guarded by the workpiece itself. The abrasive wheel is guarded by a pneumatically operated telescopic guard which retracts and extends like the mechanical guard shown in Figure 25. cylinders and cones should be long enough to engage a sufficient length of thread.
Figure 25 A spring-loaded telescopic guard for use on an internal grinding machine. When the work is withdrawn. and secondly to prevent. while operating. Screws for inserted nut mounting of discs. manufacture and testing of wheels. 98 When mounting the wheels and points.firmly. and there should be sufficient length of mandrel in the collet or chuck. 101 Internal grinding wheels are. but not so long that they contact the abrasive. the risk of a burst is inherent in every abrasive wheel and a guard of adequate strength must be provided to prevent injury from flying fragments. arrangements can be made so that a guard may be placed in position automatically when the wheel in motion is withdrawn from the work (Figures 25 and 26a-c). 100 A guard has two main functions: firstly to contain the wheel parts in the event of a burst. When the flanges are clamped by a series of screws they should be tightened uniformly in a criss-cross sequence. As the workpiece advances towards the wheel the bracket strikes the Lugs and retracts the guard to expose the wheel. A guard also has the secondary functions of protecting the wheels against inadvertent damage and preventing an oversize wheel from being fitted. vapour and splash. the operator from coming into contact with the wheel.
GUARDS Purpose of guards
99 In spite of the care exercised by abrasive wheel manufacturers in the design. diameter of the mandrel and size of the wheel should not be exceeded.
Figure 26a An internal grinding machine with an enclosure to control the emission of noise. and to keep the opening as small as possible. consistent with the nature of the work. The abrasive wheel is separately guarded by a telescopic guard (see Figures 26b and 26c)
Figures 26b Pneumatically operated telescopic guard in the retracted position to expose the wheel
Figure 26c The guard in the extended position to cover the wheel
cylinder are operated by a cam attached to the traversing table. shown in the open position. Figure 26b shows the guard retracted to expose the wheel while Figure 26c shows the guard fully extended to cover the wheel. The sliding door. is interlocked to prevent access to the rotating work spindle. 105 The aim is to enclose the wheel to the greatest possible extent. Guards of this kind should only be used after extensive tests involving the bursting of an abrasive wheel have been conducted in safe conditions. be as effective as a heavier all-metal guard. Examples include BS EN 132187 for stationary machines and BS EN 14548 for internal combustion portable cutting-off machines. This combination can.
Figure 27 A cup wheel enclosed by an energy absorbent foam-lined steel guard
104 The relevant European Standard (published in the UK as a BS EN standard) for any particular machine should be consulted for details of guard design and material. splash and vapour. in some circumstances. 103 Another example of guard design can be seen in Figure 27 where an energy absorbent foam lining is contained inside a light sheet-metal housing.
Figure 28 A wheel guard with an adjustable vizor for a pedestal grinder. though robust. To protect against this hazard it is advisable to provide substantial steel plates high enough around the table to contain any flying components. It is usually necessary to construct the outer side member with a hollow boss which will enclose the projecting spindle and nut. and the guard should be adjustable vertically to restrict the exposure of the wheel below the guard to a minimum. have been attached to the frame by bolts of inadequate strength. 107 Cylinder wheels. In addition to the risk of wheel breakage. The guard has side members to limit the exposed area of the wheel and to contain flying fragments. cup wheels and segmental wheels can be guarded by a band-type guard (Figure 29). Surface grinding by vertical spindle machines is generally performed wet and the splash screen surrounding the table should not be confused with safeguards to protect the operators in the event of a wheel burst. the fastening should be strong enough to prevent disintegration of the guard in the event of a burst and the dangerous projection of the various parts into the surrounding working area.Adjustable vizor
Lug of wheel dresser engaged with work rest
To compensate for the increased exposure caused by wheel wear. Accidents have occurred when guards. This illustration shows the correct method of using a revolving cutter wheel dresser with the lugs of the dresser firmly engaged with the work rest
106 The entire assembly should be securely anchored to the machine frame. The inside diameter of the guard should not exceed the diameter of the wheel by more than 25 mm. When a guard is constructed from several component parts. accidents have occurred from flying components in surface grinding. with the result that a burst wheel has projected the entire guard bodily from the machine. such as the
Figure 29 A band-type guard for cylinder and segmental wheels on a fixed machine
. either an adjustable vizor is provided (Figure 28) or the guard is constructed so that it can be adjusted manually as the wheel wears down.
The fastening elements should be designed so that they remain attached or retained by the clamp or grinder
. some additional enclosure. other than ordinary wheel guards. The size and positions of these openings are shown in Figure 30.
Wheel enclosure angles for fixed machines
108 Abrasive wheels should be enclosed to the greatest extent practicable and this will depend on the nature of the work.
Figure 31 Alternative methods of attaching guards to portable grinding machines. The clearance between the inside of the guard and the periphery of an unused wheel should not be greater than 6 mm. the guard remains attached to the machine (see Figure 31).
These holes may be elongated to allow the guard to be positioned to give maximum protection
109 Guards for portable machines should be so designed that in the event of a wheel bursting or breaking.Stationary grinding machines7 should comply with the guarding requirements contained in that standard. The design and construction of the clamp should allow the guard to be positioned directly between the wheel and the operator. where large wheels may be used with a long horizontal traverse between the wheel and the work.Safety . Machines supplied after the publication of BS EN 13218 Machine tools .(a)
Figure 30 Wheel enclosure angles for various fixed machines (the
minimum enclosure 270° minimum enclosure 180°
dotted line indicates an alternative guard profile)
(a) Bench and pedestal grinder
(b) Cylindrical grinder
(c) Stationary cutting-off and peripheral surface grinder
(d) Swing frame and high-pressure
minimum enclosure 210° minimum enclosure 180°
stone industry. For particular grinding operations there are recommended openings in the guard which allow almost all grinding operations to be carried out. is desirable around the machine to restrict the exposure of the wheel below the guard to a minimum.
175° minimum enclosure
Figure 33 A wheel guard for use with a non-reinforced straight-sided wheel on a portable machine
Figure 34 An adjustable band-type guard for straight and taper cup wheels mounted on a portable machine
. The front curtain should be designed to facilitate easy replacement of the wheel. cutting-off wheels and reinforced straightsided wheels other than cutting-off wheels (Figures 32a and 32b) 110 A guard for these wheels should have a minimum enclosure of 175° and the side towards the machine should be covered by the guard.Minimum enclosure 175°
At least 1/4 the diameter of the wheel
Figure 32 Alternative types of guards for reinforced depressed-centre cutting-off wheels and reinforced straight-sided wheels other than cutting-off wheels over 130 mm used on portable machines
Reinforced depressed-centre. Cup wheels (Figure 34) 112 These should be provided with an adjustable guard which covers the periphery and back of the wheel. The guard should be adjustable to compensate for wear of the wheel and to restrict the wheel exposure to a minimum. Non-reinforced straight-sided wheels (Figure 33) 111 At least 175° of the abrasive wheel periphery. When the machine is in use the guard should always be positioned between the operator and the wheel. If the wheel is larger than 130 mm diameter the guard should have a front lip of at least 5 mm or a curtain segment with a minimum height of one quarter of the diameter of the wheel. and both sides. should be covered by the guard.
polishers and disc-type sanders. for wheel shapes). implements CENELECDH400. The preferred voltage for these machines on construction sites is 110 volts. accessible metalwork has to be effectively earthed so as to provide protection for the operator if the metalwork is made ‘live’ because of an internal fault. if a 240-volt supply has to be used then the supply to a portable machine should be protected by an RCD (residual current device). Part 2 Section 3 Grinders. Cables manufactured to British Standard 6500: 1994 Specification for insulated flexible cords and cables.
. The only exception is for the use of vitrified mounted wheels and points (see Figure 5. Specifications for grinders. Cables and connectors 117 Hand-held tools are often required to withstand constant handling and rough usage. For Class I tools. but where the cable is vulnerable to damage. protection is provided by the use of all insulated or double insulated construction. 116 These tools are classified according to the way in which protection against electric shock is provided. page 8.PORTABLE AND HAND-HELD GRINDING MACHINES
113 The largest number of abrasive wheels used are those found on hand-held machines. These machines are often used by people who have a wide range of skills. from the domestic user to the skilled tradesman.11 with an abrasion-resistant sheath would be satisfactory for normal use. 114 The general safety precautions for abrasive wheels apply equally to all wheels used on all classes of portable machine. The unguarded wheel will then be running at a speed in excess of the wheel manufacturer’s recommended maximum with the consequent risk of a wheel burst. additional precautions such as heavy-duty sheathing or protective braiding will be necessary. often fatal. For Class II tools. Electrical safety must be considered as well as the safe use of the wheel. and accessible metalwork should not be earthed. usually fibre glass. Only organic-bonded wheels should be used. Those intended for cutting-off operations should additionally have some form of reinforcement. marked with the symbol . However. All portable electric machines should comply with BS EN 51044 Safety of hand-held electric motor operated tools. It is important that all machine guards are secured in place and are adjusted so that the guard is between the user and the rotating wheels. disc type sanders and polishers when published.2C)10 can still be used. Serious.
115 These are the most common machines on which abrasive wheels are mounted. with the predominant user being semi-skilled.9 Machines in service marked BS 2769 (Hand-held electric motor-operated tools. Additionally machines when supplied after 1/1/97 should carry the CE marking. accidents have happened when a guard is removed to allow an oversize wheel to be mounted on a machine. and the conditions of use should be taken into account when selecting flexible cables for the tools.
(b) BS 196:1961 Specification for protected-type non-reversible plugs. 30 (iii)a combined inspection and test every three months (eg a detailed inspection and tests by a person competent to do so). including extension leads. 121 The user of a hand-held tool should carry out a visual check on the tool before using it so that obvious defects can be identified. The register should indicate how often each item should be recalled for inspection. sockets and couplers for different electrical supply systems are not interchangeable. An efficient maintenance system will also reduce days lost due to tools being out of commission.118 In the case of single-phase tools. loose plug connections etc. 13
120 Routine checks. a three-core cable is essential. 122 Routine visual checks are in addition to and are not a substitute for planned maintenance of hand-held tools. inspection and testing for portable electric grinders is: (a) For 110-volt machines the user is to carry out: (i) a weekly safety check.c. two-core cable is suitable for Class II tools. socket outlets and couplers for industrial 12 purposes. such as a plug and socket. circuits up to 250 volts. regular inspection and preventive maintenance are essential if accidents are to be avoided. socket-outlets. The cable should be connected to the supply by a properly constructed connector. The recommended frequency of checks. for example an earth pin or a scraping earth (ie a sliding connection between the earthed metalwork on the plug and the earthed metalwork on the socket). it is essential that plugs.
. cable-couplers and appliance-couplers with earthing contacts for single-phase a. If there are no instructions. the following system of planned maintenance is recommended. for example damage to the cable sheath. Connectors conforming to the following British Standards are recommended for industrial applications: (a) BS EN 60309-2:1998 Plugs. (ii) a formal visual inspection (eg a detailed inspection by a person competent to do so). Any tool in an unserviceable or unsafe condition must be withdrawn from use until defects have been rectified by a person competent to carry out this class of work. but for Class I tools. 119 In order to ensure correct matching between the electrical supply and the portable tool. For Class I tools the connector should incorporate an effective means of maintaining earth continuity. should be identified by a serial number which should be recorded in a register. 123 All tools should be accompanied by specific instructions from the manufacturer. All hand-held apparatus.
Ingress of dust into the governor is often a cause of failure. 124 For all the apparatus there should be a careful inspection for signs of damage or deterioration including. (b) any form of pressure reduction valve that will prevent overpressurization. Any defects should be rectified. Particular attention must be paid to the maintenance of two devices: (a) the maximum speed governor. (iii) combined inspection and tests before first-time use and then every month (eg a detailed inspection and tests by a person competent to do so). and the casing of the portable tool. Extension leads should be treated as for 240-volt tools. (ii) a formal visual inspection every week (eg a detailed inspection by a person competent to do so). BS EN 1454 Portable. This may be due to a number of causes such as petrol/air ratio (mixture setting).16a and Part 9 Die Grinders . New machines should carry the CE marking. are mainly used for cutting operations using reinforced resin-bonded abrasive wheels or diamond and CBN wheels. the cable sheath (particularly near the terminations). together with its controls. under no circumstances should the speed marked on the wheel be exceeded .Safety Requirements 16b New machines should carry Part 7 Grinders . for example. However.(b) For 240-volt machines the user is to carry out: (i) a daily safety check.14
125 Although there should be no electrical risk with these machines it is vital that the compressed air supply is clean and water-free.Safety 8 is the relevant standard. hand-held. plug pins. terminals and cable anchoring devices. One particular safety hazard with this type of machine is overspeeding. usually powered with a petrol engine. The relevant standard for this class of machine is BS 4390: 1969 Specification for portable pneumatic grinding machines 15 to be replaced by BS EN 792 Hand-held non electric power tools . internal combustion cutting-off machines . together with ignition timing. For further guidance and information see Maintaining portable and transportable electrical equipment.
Internal combustion grinding machines
126 These machines. The speed-governing device should be given close attention.
. brush gear and commutators. the CE marking. the ingress of dust being a common cause of failure.
(d) care should be taken to prevent the possibility of dressing tools becoming jammed between the abrasive wheel and work rest or any fixed part of the machine.
129 The use of bushes to reduce the bore size of an abrasive cutting-off wheel is not recommended on portable hand-held machines. (c) haphazard methods of dressing. This will invariably result in damage to the abrasive wheel surface.
. should be forbidden. such as ‘loading’ or ‘glazing’. or the workpiece being trapped in a similar way.
128 The use of blotters on cutting-off wheels less than 400 mm diameter is not required. concrete or plaster. No attempt should be made to mount more than one wheel with a spacer between them or with the wheels in contact with each other. as there is a risk of pieces of aggregate or debris being forced between the wheels causing one or both to burst. A wheel ‘out-of-round’ will cause excessive vibration and periodic knocking of the work against the wheel.Multiple wheel mounting for portable machines
127 Portable machines are often used to chase or cut grooves in masonry. and frequent light dressings are generally preferable to occasional severe dressings. Nor should wheels be stuck together with an adhesive to increase their width. their possibility is minimised by frequent truing to keep the wheel concentric on its spindle. Although such accidents are more frequently caused by poor adjustment of the work rest. page 26). and a trapped piece of material can become a missile if it is flung out of the guard opening. unless designed specifically for that purpose.
130 The operator’s fingers may become trapped between the work-rest and the wheel. The following important precautions should be taken: (a) hand dressers should be properly supported so that leverage may be applied without undue effort. (b) with a dresser of the revolving cutter type. the lugs provided as an anchor should always be used (Figure 28. or even striking the work against the wheel. Dressing the wheel is therefore essential for efficient production. such as the use of a chipping hammer. which impair the cutting action and may induce the operator to compensate by additional pressure of the workpiece on the abrasive wheel.
An oriented wheel is marked with an arrow to facilitate its assembly on the grinding machine in a specific position (see Figure 35). Excessive dressing could however create a dangerously weak section which may cause the wheel to break under side loading or due to centrifugal force. on a balancing arbor and stand. for example the thrust face on a stepped shaft.(e) it is important that the work rest is in good condition before wheel dressing and it is helpful to fit a spare rest with a straight edge especially for this purpose. wheel and machine manufacturers should be consulted on the technical aspects of the subject. The choice of a suitable grinding fluid depends on the requirements of the work and the type of
. If necessary. and in this case the side of the wheel may be lightly dressed with a diamond to create a shallow relief. Generally. it may result in damage to the wheel and spindle. closer limits of balance may be required and this is obtained by various methods such as the use of heavy paint or by an arrangement of sliding weights which are incorporated in the flanges or collet. For precision grinding. With some instruments it is necessary to move the balance weights by trial and error until the meter shows that the out-of-balance force is eliminated. for certain precision grinding operations it may be necessary to allow the side of the wheel to lightly touch a face adjoining the surface being ground. 134 Some large wheels are supplied as ‘oriented wheels’. wheels used for off-hand grinding can become out of balance if they are not frequently trued. Adjustment of the sliding weights is normally done with the wheel assembly removed from the machine. 133 As the wheel wears. the greater the importance of correct wheel balancing. unless there is a restriction marked on the wheel.
132 Abrasive wheels are balanced by the manufacturers within normal limits but after they have been taken into use. 131 There are many types of abrasive wheel dressers. particularly when it is appreciably worn or when sudden pressure is applied.
136 Abrasive wheels may be used wet or dry according to type. but more sophisticated instruments show the angular position of the out-of-balance force. However. An accelerometer probe is placed in contact with a fixed part of the machine near the wheel and a measure of the outof-balance force is then shown on a meter. If the out-of-balance force is allowed to become excessive. the larger the wheel and the higher the speed.
Figure 35 An oriented wheel with the marking indicating the correct mounting position
135 Grinding on the side of a straight-sided wheel used for off-hand grinding is dangerous. and various methods by which these operations may be carried out. it may be necessary to re-balance it.
This is important from the safety aspect because with some wheels prolonged contact with fluids containing alkalis. shellac-bonded wheels.
Grinding of magnesium alloys
138 These alloys usually contain a large proportion of magnesium. when mixed with air. and the provision of protective clothing. Explosions resulting in fatalities have also occurred in dust extraction and settling systems. 139 A spark from a grinding machine may act as a source of ignition.wheel. or other suitable transparent material allowing clear vision as shown in Figure 36. Screens should be of toughened or reinforced glass. which should be safely removed from the scrubber and the workroom. The soaked portion will throw the wheel out of balance when the machine is started. The dust produced by grinding and similar operations will burn freely and. the provision of appliances for the interception. The removal of a foreign body from an eye requires skill and should always be done by a medically trained person. Vitrified wheels are not normally affected by grinding fluids. 137 A wheel should not be allowed to stand partly immersed in grinding fluid. removal and drenching of dust by exhaust appliances and scrubbers. They may embody a light source and this is useful from a production as well as a safety aspect. open lights. fire and other causes of ignition. Magnesite wheels may be damaged by any fluid. At the completion of a wet grinding operation the fluid should be drained off and the wheel run free until it is dry. in contact with alkaline solutions with a soda content exceeding 3% may suffer damage. Severe accidents including fatalities have occurred when dust from the clothing of workpeople has been ignited. The pH of the fluid should not exceed 8 to 9.
. Inexpert attention may do more harm and could even cause permanent damage. Particular care should therefore be taken to follow the fluid manufacturer’s instructions.
Figure 36 Screens of toughened glass are useful at machines used for short periods by different workers
140 Fixed shields are particularly useful on machines used for short periods by different workers. Measures which are intended to cope with these dangers include: precautions against causing sparks. Dust extraction and settling systems should be kept clean and free from deposits of dried sludge. Other wheels may be affected to a greater or lesser extent by some of the fluids normally used in grinding operations. the prohibition of smoking. is capable of forming an explosive mixture. acids or other organic or inorganic solvents may ultimately affect the strength of the wheel. It may also be desirable that eye protection be provided and used for wet grinding work. For example.
146 Guarding. Grinding on the sides of straight-sided wheels used for off-hand grinding is dangerous. 153 Wet grinding.SUMMARY OF OPERATING PRECAUTIONS
141 Given an abrasive wheel of sound manufacture. safe operation depends largely on proper maintenance and on the treatment to which the wheel is subjected when in use. Lack of compensation for wheel wear is the main reason for the work rest to be out of adjustment. Wheels used for off-hand grinding should be trued frequently to eliminate out-of-balance conditions and to enable the work rest to be adjusted close to the wheel surface. and free from obstruction. 149 Truing and dressing. 145 Speed. Operators should be properly trained in the safe use of grinding machines (see paragraph 6). 152 Stopping wheels. 151 Starting new wheels. The maximum operating speed marked on the wheel should under no circumstances be exceeded (see paragraphs 28-30). Wheels should not be brought to rest by applying pressure to the periphery or face. Before a wheel is stopped the coolant should be turned off. 150 Lubrication. some of which are discussed in greater detail elsewhere in this booklet. 148 Side grinding. mounted on a welldesigned machine. The following are among the main operating precautions to consider. Work rests should be kept adjusted as close as possible to the wheel. Splash guards should be used when appropriate to prevent the floor from becoming slippery. 144 Mounting. Prolonged immersion of a stationary wheel in coolant can throw the wheel out of balance when the machine is started. Spindles should not be allowed to become overheated due to lack of lubrication (see also paragraph 34). New wheels should be run free at normal operating speed for about a minute. The wheel guard should always be secured in position and properly adjusted before the wheel is run (see paragraphs 99-112). and the wheel run free until it is dry. Work rests should therefore be inspected and adjusted at frequent intervals. 142 Training of operators. particularly when they are appreciably worn or when sudden pressure is applied (see paragraph 135). 147 Work rests. Operators and others should stand clear during the trial run. The floor immediately surrounding fixed grinding machines should be maintained in good condition. 143 Floors. Mounting of abrasive wheels should only be done by appropriately trained people (see paragraph 6).
Before mounting. Eye protectors should be worn in all dry grinding operations or. cutting-off wheels should be inspected for possible warping or other defects. Cutting-off wheels should be mounted only on machines designed for their use.
159 To comply with the Personal Protective Equipment Regulations 199217 and other regulations. (c) Physical injury due to flying wheel fragments or ejected workpieces. alternatively. Pressure should be applied evenly. People who use abrasive wheels on any type of machine are exposed to a number of risks: (a) Injury to the eyes from flying abrasive and metallic particles. (e) On construction sites there will be a need for head protection as well as for feet and hands in addition to the other precautions mentioned. Care should be taken to avoid twisting or exerting pressure on the side of the wheel. Components in the tray should be carefully inspected before grinding. 156 Cylinder wheels. Care should be taken not to damage the wheel when removing the wires or tape. The overhang should not exceed that appropriate to the speed. The workpiece should be rigidly supported and firmly clamped.or tape-bound cylinder wheels should be worn down to the first tape or group of wires before any are removed.154 Centreless grinding. size of point and diameter of the mandrel. Power should be adequate. (d) Noise and vibration. (b) Inhalation of dust from dry grinding operations (for example petrolengined cutting-off machines). transparent screens should be fitted to fixed machines to intercept sparks and particles. 157 Mounted wheels and points. Only the reinforced type should be used on handheld portable machines. A warped wheel should not be used as it may cause excessive vibration. should be used. 36
. as an oversize piece may damage the wheel or may be projected back. otherwise stresses may build up and the wheel may stall and break.19 appropriate protection must be worn. W ire. 158 Eye protection. recommended by the wheel manufacturer. The correct wheel for the job. for example the Control of Substances Hazardous to Health Regulations 199918 and the Noise at Work Regulations 1989. side pressure. 155 Cutting-off and depressed-centre wheels. Lack of rigidity either in the wheel or in the workpiece can lead to wheel breakage. or heating and possible wheel breakage.
Optical test methods.160 Eye protection should conform to the relevant BS EN standard such as BS EN 166 Personal eye protection.21 and BS EN 168 Personal eye protection. Non-optical test methods.20 BS EN 167 Personal eye protection. Specifications. 22 161 Dust protection (face masks) etc should comply with BS EN 149 Specification for filtering half masks to protect against particles.
. 23 162 Loose clothing Loose clothing such as ties or coat sleeves are easily drawn in between the wheel and the workpiece and should not be worn. Rags and waste should not be used near a revolving wheel as they may also become entangled. 163 Supervision Frequent checks should be made by management to ensure that the safety precautions in paragraphs 142-162 are being observed.
5. 7 20-26 1. 37
32 50 50 32 32 50 50 32 32 50 50 32
inorganic bonds organic bonds organic bonds vitrified bonds inorganic bonds organic bonds organic bonds vitrified bonds inorganic bonds organic bonds organic bonds vitrified bonds
2. 5. 37 6 35. 36. 7 1. 7 1. 7 1. 7 1. 37 6 35. 5 52
45 See Annex C of BS EN 12413: 1999 3
Surface horizontal spindle reciprocating table
horizontal spindle rotary table 1. 7 1 5. 7 35
2. 37 6 35. 5. 36. 37
2. 5.Table 1 General maximum permissible peripheral speeds of abrasive wheels in metres per second The maximum speeds listed in this table are not necessarily the recommended speeds of operation for optimum grinding efficiency Machine classification and grinding operation External cylindrical Tool room (universal) Crankshaft Camshaft Thread Thread Centreless Control wheels Type of wheel See Figure 5 1. 5. 7 Maximum speed m/s Special conditions
45 45 45 45 60 45 35 16
1. 5. 5. 36
Tool cutter Grinding and sharpening Off-hand grinding and fettling bench and floorstand pedestal face grinding Billet and slab mechanical control swing frame manual control Cutting-off
1. 5. right angle grinding cutting-off
6. 5. 36
vitrified bond organic bond
special high-density organic bond organic bond
unreinforced organic bond reinforced organic bond organic bonds only reinforced organic bonds only reinforced organic bonds only organic bonds only
Portable. 42
Portable vertical spindle grinder Portable straight grinder
6. 17. 11. 18R. 7 1 6. 35. 13
1. 7 6. 12. 18. 4 16. 52
organic bonds only
. 11 27 41.
Table 2 Speed conversion table for speed of rotation (rpm) vs peripheral operating speed (m/s) of various wheel diameters Maximum operating speed in m/s 20 25 80 000 143 500 107 500 86 000 66 200 59 700 60 200 48 200 37 600 30 100 24 100 19 100 15 100 12 100 10 500 9 650 8 050 6 400 5 350 4 800 4 200 3 850 3 200 2 870 2 460 2 150 1 910 1 700 1 550 1 300 1 200 1 050 895 840 750 670 615 585 560 510 320 410 640 610 560 450 1 050 960 850 765 680 730 695 640 400 510 1 720 1 450 1 300 1 150 1 075 955 860 820 785 720 575 2 750 2 400 2 150 1 950 1 600 1 450 1 300 1 200 1 100 960 910 870 800 640 6 700 6 050 5 250 4 850 3 450 4 050 3 450 3 050 2 700 2 450 2 050 1 850 1 650 1 550 1 350 1 250 1 150 1 100 1 050 805 48 000 38 200 30 600 24 300 19 100 15 300 13 300 12 250 10 200 8 500 7 650 6 650 6 150 5 100 4 400 3 850 3 400 3 100 2 550 2 350 2 050 1 950 1 700 1 550 1 500 1 400 1 300 1 050 61 200 47 800 38 200 30 000 23 900 19 100 15 200 12 000 9 550 8 350 7 650 76 500 75 200 95 500 53 750 43 000 34 500 27 000 21 500 17 200 13 650 10 750 8 600 7 500 6 900 5 750 4 780 4 300 3 750 73 500 92 600 118 000 120 000 95 500 76 500 60 000 47 200 38 200 30 250 23 900 19 100 16 650 15 300 12 700 10 650 9 550 8 350 7 650 6 400 5 500 4 800 4 250 3 850 3 200 2 900 2 550 2 400 2 150 1 950 1 850 1 750 1 600 1 300 95 500 120 500 191 000 147 000 153 000 120 000 150 500 191 000 60 000 48 000 35 600 29 850 23 900 19 100 24 500 19 100 16 750 19 100 15 300 12 150 9 550 7 650 6 650 6 150 5 100 4 250 3 850 3 350 3 100 2 550 2 200 1 950 13 400 10 650 8 400 6 700 5 850 5 350 4 500 3 750 3 350 2 950 2 700 2 250 1 950 1 700 1 500 1 350 1 150 15 300 12 250 9 750 7 650 6 150 5 350 4 900 4 100 3 400 3 100 2 700 2 450 2 050 1 750 1 550 1 400 1 250 1 050 930 820 765 20 900 23 900 26 800 30 600 14 950 11 950 9 550 7 600 6 000 4 800 4 200 3 850 3 200 2 700 2 400 2 100 1 950 1 600 1 400 1 200 1 100 960 800 725 640 600 535 480 455 435 30 600 33 500 38 200 38 200 41 800 47 800 47 100 51 500 58 800 61 200 67 000 95 500 76 500 76 500 84 000 102 000 112 000 128 000 160 000 201 000 32 63 64 000 48 000 38 200 29 500 23 900 19 100 15 300 11 950 9 550 7 650 6 100 4 800 3 850 3 350 3 100 2 550 2 150 1 950 1 700 1 550 1 300 1 100 960 850 765 640 580 510 480 425 385 365 350 320 255 35 40 45 50 80 125 184 000 150 000 120 000 95 500 75 000 59 700 47 750 37 900 29 850 23 900 20 800 19 100 16 000 13 300 11 950 10 400 9 550 8 000 6 850 6 000 5 350 4 800 4 000 3 650 3 200 3 000 2 700 2 400 2 300 2 200 2 000 1 600 100 -
Wheel diameter in millimeters
30 600 23 550
350/356 400/406
500/508 600/610
1 000/1 016
1 050/1 067
from BS EN 12413: 1999
Group A (shaped wheels)
6.0 or 6.3 mm diameter mandrels Shape number A1 A3 A4 A5 A11 A12 A13 A14 A15 A21 A23 A24 A25 A26 A31 A32 A34 A35 A36 A37 A38 A39 Wheel diameter mm 20 22 30 20 21 18 25 18 6 25 20 6 25 16 35 25 38 25 40 30 25 20 Wheel thickness mm 65 70 30 28 45 30 25 22 25 25 25 20 26 20 10 10 10 6 25 20 13 mm overhang and threaded mandrels 19 800 16 100 29 840 45 000 19 860 48 000 33 950 53 050 72 750 34 500 39 370 76 500 35 620 59 680 27 260 38 200 25 130 38 200 23 520 29 840 34 500 47 250 Overhang 25 mm 16 500 13 080 24 750 33 750 15 100 35 250 32 250 40 500 47 620 26 250 30 370 49 500 27 370 46 500 26 250 38 200 25 130 38 200 23 520 29 840 26 250 35 250
.Table 3 Maximum permissible speed in revolutions per minute of mounted wheels and points in relation to the overhang .
Group B (shaped wheels)
B42 B43 B52
3 or 3.3 mm diameter mandrels 13 mm overhang and threaded mandrels 59 680 59 680 81 000 81 000 47 750 71 250 59 680 61 500 Overhang 25 mm
23 250 23 250 51 000 42 370 28 500 28 500 38 020 24 370 26 400 48 000 41 250 22 500 51 000 64 500 64 500
46 500 46 500 54 370 54 370 47 750 47 620 59 680 42 000 -
.15 m m d i a m e t e r mandrels Shape Wheel Wheel number diameter thickness mm mm B41 B42 B43 B44 B51 B52 B53 B61 B62 B71 B81 B91 B92 B96 B97 16 13 6 5.Table 4 Maximum permissible speed in revolutions per minute of mounted wheels and points in relation to the overhang . 6 11 10 8 20 13 16 20 13 6 3 3 16 20 8 10 20 20 16 8 10 3 5 16 6 6 10 13 mm overhang and threaded mandrels 33 750 33 750 61 370 68 400 45 370 45 370 60 000 38 250 41 020 59 680 47 750 34 500 81 370 105 000 105 000 Overhang 25 mm
3 mm diameter mandrels 13 mm overhang and threaded mandrels 59 680 66 000 81 000 73 460 61 500 81 000 Overhang 25 mm
23 250 41 250 42 370 23 250 28 500 64 500 28 500 37 720 61 820 64 500 22 500 28 500 33 000 38 020
46 500 46 500 54 370 54 370 -
42 000 54 300 -
. 5 13 10 5 3 13 10 10 6 18 5 10 18 13 3 13 13 10 13 13 mm overhang and threaded mandrels 33 750 59 680 68 400 33 750 45 370 105 000 45 370 61 650 104 250 105 000 34 500 45 370 54 000 60 000 Overhang 25 mm
6 or 6.15 mm d i a m e t e r mandrels Shape Wheel Wheel number diameter thickness mm mm B101 B103 B104 B111 B112 B115 B121 B122 B123 B124 B131 B132 B133 B135 16 16 8 11 10 2.B81
B91 B92 B96 B97
B101 B104
B121 B122 B123 B124
B131 B132 B133 B135
3 or 3.
Group W (plain wheels)
3 or 3.Table 5 Maximum permissible speed in revolutions per minute of mounted wheels and points in relation to the overhang .15 m m d i a m e t e r mandrels Shape Wheel Wheel number diameter thickness mm mm W144 W145 W146 W149 W152 W153 W160 W162 W163 W164 W174 W175 W176 W177 W178 W182 W183 W184 W185 W187 W188 W194 W196 W197 W200 W201 W202 W203 3 3 3 4 5 5 6 6 6 6 13 10 10 10 10 13 13 13 13 13 13 16 16 16 20 20 20 20 6 10 13 6 6 10 6 10 13 20 3 10 13 20 25 3 6 10 13 25 40 13 25 50 3 6 10 10 13 mm overhang and threaded mandrels 105 000 105 000 105 000 105 000 105 000 80 850 81 370 68 400 60 000 45 900 69 000 54 000 45 370 33 750 26 250 73 460 51 750 41 020 34 500 20 620 29 400 17 620 47 750 38 250 30 000 25 500 Overhang 25 mm
6 o r 6.3 m m d i a m e t e r mandrels 13 mm overhang and threaded mandrels 81 00 66 000 55 200 73 460 73 460 71 250 61 500 30 370 55 400 32 250 21 000 47 750 47 750 47 750 Overhang 25 mm
64 500 64 500 64 500 64 500 64 500 52 500 51 000 42 370 38 020 30 000 41 250 33 000 28 500 23 250 18 750 43 650 31 870 26 400 22 500 13 870 19 120 11 620 33 520 24 370 19 500 15 900
54 380 46 500 40 500 62 400 54 750 47 620 42 000 24 000 39 750 27 000 16 500 47 750 44 100 36 370
3 or 3.3 mm diameter mandrels 13mm overhang and threaded mandrels 42 34 24 18 38 38 38 38 25 19 15 29 29 29 20 14 25 25 22 15 19 750 500 000 750 200 200 200 200 500 120 900 840 840 840 400 250 130 130 500 600 100 Overhang 25 mm
12 000 24 900 18 600 -
30 25 18 15 38 38 38 32 19 14 12 29 29 22 18 10 25 25 17 12 15
750 870 520 370 200 200 200 770 120 620 370 840 840 500 750 650 130 130 620 000 950
.15 mm diameter mandrels Shape Wheel Wheel 13mm overhang number diameter thickness and threaded mm mm mandrels W204 W205 W207 W208 W215 W216 W217 W218 W220 W221 W222 W225 W226 W228 W230 W232 W235 W236 W237 W238 W242 20 20 20 20 25 25 25 25 25 25 25 30 30 30 30 30 40 40 40 40 50 20 25 40 50 3 6 10 13 25 40 50 6 10 20 30 50 6 13 25 40 25 18 900 38 200 30 520 Overhang 25 mm
. 10/2000)
10 BS 2769: Part 2: Section 2.2C 1 1 BS 6500: 1994 Specification for insulated flexible cords and cables 12 BS EN 60309-2: 1998 Plugs.Safety requirements .Stationary grinding machines (not yet published at time of going to print. polishers and disc-type sunders. 10/2000) BS EN 1454: 1997 Portable.c.REFERENCES AND FURTHER READING
1 The Supply of Machinery (Safety) Regulations 1992 SI 1992 No 3073 The Stationery Office ISBN 0 11 025719 7 Safe use of work equipment. Provision and Use of Work Equipment Regulations 1998. internal combustion cuttingoff machines . alloy and stainless steels BS EN 13218: Machine tools .Safety requirements Part 7: Grinders (not yet published at time of going to print. cable-couplers and appliance-couplers with earthing contacts for single phase a. Approved Code of Practice and guidance L22 HSE Books 1998 lSBN 0 7176 1626 6 BS EN 12413: 1999 Safety requirements for bonded abrasive products Health and Safety at Work etc Act 1974 BS IS0 525: 1999 Bonded abrasive products .General requirements BS 970: Part 1: 1996 General inspection and testing procedures and specific requirements for carbon. hand-held. Specifications for grinders.Part 9: Die grinders (not yet published at time of going to print. Part 2-3: Particular requirements for grinders. Dimensional interchangeability requirements for pin and contact-tube accessories 13 BS 196: 1961 Specification for protected-type non-reversible plugs. disc-type sanders and polishers (not yet published at time of going to print. carbon manganese. 10/2000) 46 16b BS EN 792-9 Hand-held non-electric power tools .Safety .3: 1984 Hand-held electric motor-operated tools. socket-outlets. socket-outlets and couplers for industrial purposes.Safety BS EN 50144-2-3: Safety of hand-held electric motor operated tools. Implements CENELEC HD 400. circuits up to 250 volts 14 Maintaining portable and transportable electrical equipment HSG107 HSE Books lSBN 0 7176 0715 1 15 BS 4390: 1969 Specification for portable pneumatic grinding machines 16a BS EN 792-7 Hand-held non-electric power tools .
their future availability cannot be guaranteed. Specifications 21 BS EN 167: 1995 Personal eye-protection.
. They are also available from bookshops. PO Box 276. Optical test methods 22 BS EN 168: 1995 Personal eye-protection. The Stationery Office (formerly HMSO) publications are available from The Publications Centre. Approved Codes of Practice L5 HSE Books 1999 ISBN 0 7176 1670 3 19 Reducing noise at work. Tel: 0870 600 5522. Personal Protective Equipment at Work Regulations 1992 Guidance on Regulations L25 HSE Books 1992 ISBN 0 7176 0415 2 18 General COSHH ACOP (Control of substances hazardous to health. 389 Chiswick High Road. Control of Substances Hazardous to Health Regulations 7999. Approved Code of Practice and guidance L21 HSE Books 2000 ISBN 0 7176 2488 9 A step-by-step guide to COSHH assessment HSG97 HSE Books 1993 ISBN 0 7176 1446 8 Occupational exposure limits EH40/2000 HSE Books 2000 ISBN 0 7176 1730 0 (revised annually) HSE Books publications are available from the address on the inside back cover and from good booksellers. Guidance on the Noise at Work Regulations. Carcinogens ACOP (Control of carcinogenic substances) and Biological agents ACOP (Control of biological agents). London W 4 4AL Tel: 020 8996 9001 Fax: 020 8966 7001. Management of Health and Safety at work Regulations 1999. British standards are available from BSI Customer Services. 1989 L108 HSE Books 1998 ISBN 0 7176 1511 1 20 BS EN 166: 1996 Personal eye-protection. While every effort has been made to ensure the accuracy of the references listed in this publication. London SW8 5DT. Fax: 0870 600 5533.17 Personal protective equipment at work. Non-optical test methods 23 BS EN 149: 1992 Specification for filtering half masks to protect against particles
The Supply of Machinery (Safety) (Amendment) Regulations 1994 SI 1994 No 2063 The Stationery Office ISBN 0 11 045063 9 Management of health and safety at work.
Printed and published by the Health and Safety Executive Cl20 10/00
MAIL ORDER HSE priced and free publications are available from: HSE Books PO Box 1999 Sudbury Suffolk CO 10 2WA Tel: 01787 881165 Fax: 01787 313995 Website: www.uk RETAIL HSE priced publications are available from good booksellers HEALTH AND SAFETY ENQUIRIES HSE InfoLine Tel: 08701 545500 or write to: HSE Information Centre Broad Lane Sheffield S3 7HQ Website: www.hse.hsebooks.co.
717 6 .173 9 .£7.50
I SBN O .4
9 7 80 71 7 61 7 3 95 HSGI7
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