19

S A F E T Y I N T H E U S E O F A B R A S I V E W H E E L S

This guidebook is prepared by theOccupational Safety and Health BranchLabour Department

This edition April 2008

Th i s gu idebook i s i s sued f ree of charge and can be obta ined f rom theoff ices o f the Occupat iona l Sa fe ty and Hea l th B ranch o f the La bourDepar tment . I t can a l so be down loaded f rom webs i te o f the La bourDepar tment a t http://www.labour.gov.hk/eng/public/content2_8d.htm. Forenquiries about addresses and telephone numbers of the offices, please visit thewebsite of the Department at http://www.labour.gov.hk/eng/tele/osh.htm or call2559 2297.

This guidebook may be freely reproduced except for advertising, endorsement orcommercial purposes. Please acknowledge the source as “Safety in the Use of AbrasiveWheels” published by the Labour Department.

1

S A F E T Y I N T H E U S E O F A B R A S I V E W H E E L S

SAFETY IN THE

USE OF ABRASIVE WHEELS

2

S A F E T Y I N T H E U S E O F A B R A S I V E W H E E L S

CONTENTS

Page

INTRODUCTION ............................................................................ 3

SELECTION OF WHEELS ................................................................. 3

OPERATING SPEED........................................................................ 4

MARKING SYSTEM FOR ABRASIVE WHEELS ................................. 5

MOUNTING ................................................................................... 5

MOUNTING OF DEPRESSED-CENTRE WHEELS .............................. 6

GUARDS ........................................................................................ 7

WORK-RESTS.................................................................................. 7

PROTECTION OF EYES .................................................................. 7

TRUING AND DRESSING ............................................................... 8

SAFETY AND THE OPERATOR ........................................................ 8

ENQUIRIES AND COMPLAINTS ..................................................... 9

SKETCHES AND TABLES / FORMS ............................................... 10

3

S A F E T Y I N T H E U S E O F A B R A S I V E W H E E L S

Introduction

Abrasive wheels are extensively used in industries for various purposes. The use of abrasivewheels in an unsafe way often causes accidents leading to personal injuries and/ordamage to properties. The main dangers are —

(1) bursting of wheels as the result of:

(i) defective wheel

(ii) overspeeding

(iii) faulty mounting

(iv) misuse

(2) contact with the wheel; and

(3) injury to the eyes from flying particles.

The purpose of this guidebook is to advise readers on the precautions for the preventionof accidents in the use of abrasive wheels. It does not include technical aspects of grindingor operational techniques.

Selection of Wheels

* Consult the manufacturer for the proper type of wheels to suit a particular job.Generally, soft wheels are more suitable for hard materials and hard wheels for softmaterials.

* Do not use defective wheels. Check for soundness of wheels by a ‘ring test’. (Suspendthe wheel vertically and tap the areas as shown in Fig. 1 with a light non-metallic tool,such as a wooden screwdriver handle. It should ring. Do not use the wheel if it soundscracked.)

* Wheels should be kept dry and not exposed to extreme temperatures. If not in use,they should be stored properly in suitable racks as in Fig. 2.

4

S A F E T Y I N T H E U S E O F A B R A S I V E W H E E L S

Operating Speed

* Check that the spindle speed of a machine does not exceed the maximum permissiblespeed of the wheel as specified by the manufacturer. The spindle speed and themaximum permissible speed of the wheel should be marked in revolutions per minute(rpm). But in case the wheel is marked to give the peripheral speed in feet per minute(ft/min) or in metres per second (m/sec), the following formula can be used forconversion into rpm:

∆ Speed in rpm =peripheral speed in ft/min x 12

3.1416 x dia. in inches

or =peripheral speed in m/sec x 1000 x 60

3.1416 x dia. in mm

The conversion of speed measurement for a number of specified speeds and wheeldiameters can be found in the Conversion Table shown in Fig. 3.

* The speed of the wheel in rpm may, however, be increased as the diameter of thewheel is reduced through wear as follows:

∆ increased speed in rpm =original speed in rpm x original diameter

reduced diameter

* If the spindle is air driven, make sure that there is a governor or other device fitted soas to control the speed of the spindle. Such device should be effectively maintainedat all time. A suitable pressure reducing regulator should be fitted between thegovernor and the air supply outlet if the working pressure of the outlet is greater thanthat of the grinding machine. Where a filter is incorporated in the air supply system, itshould be properly maintained to prevent clogging by dust or grits. To prevent accidentscaused by snaking hoses when severed under high pressure of air, it is alsorecommended that an automatic hose brake valve be fitted to the hose before joiningthe grinder.

∆ Note: The maximum permissible speed of a wheel may also change upon aging ofthe bonding material of the wheel after prolonged use. Consult the manufacturer orsupplier in case of doubt.

5

S A F E T Y I N T H E U S E O F A B R A S I V E W H E E L S

Marking System for Abrasive Wheels

Abrasive wheels are marked to identify their characteristics. Persons responsible for wheelmounting should be able to recognise the specifications marked on the wheel (See Fig. 4).

Mounting

* All mountings shall only be done by competent persons appointed in writing by theproprietors. Competent persons should be well trained and have the practicalexperience in the mounting job. (See form in Fig. 5 for appointment of a competentperson.)

* A wheel should not be mounted on a machine for which it is not intended and certainlynot on any make-shift apparatus or where there is vibration of the machine.

* Check for soundness of the wheel before it is mounted.

* Do not mount a wheel on a machine the speed of which exceeds the maximumpermissible speed of the wheel.

* Washers, either paper or other compressible material, should be used with all bondedabrasive wheels, except tapered wheels, threaded-hole wheels, discs, cylinder wheels,and the hub section of depressed-centre wheels. Washers should be slightly largerthan the flanges and there should be no wrinkles in them.

* The bush, if any, should not project beyond the sides of the wheel.

* The wheel should fit freely but not loosely on the spindle.

* Flanges should not be less than one-third of the diameter of the wheels and theirbearing surfaces should be true and free from burrs.

* With the exception of the single flange used for threaded-hole wheels, all flangesshould be properly recessed or undercut.

* Flanges on both sides of the wheel should have the same outside diameter anddiameter of recess.

* Clamping nuts and screws should be tightened uniformly in pattern formation(diametrical sequence) and only sufficiently to hold the wheel firmly.

6

S A F E T Y I N T H E U S E O F A B R A S I V E W H E E L S

* Screws for inserted nut for mounting of discs, cylinders or cones should be long enoughto engage a sufficient length of thread, but not so long as to contact the abrasivematerial.

* When re-mounting factory-mounted wheels and points, the overhang (distancebetween end of support and base of wheel as illustrated in Fig. 6) for a particulardiameter of mandrel, speed and size of a wheel should not be exceeded. Also thereshould be sufficient length of the mandrel in the collet or chuck. Consult themanufacturer for details of overhang permissible for a particular wheel.

* Protection flanges are used on tapered wheels which are not provided with safetyguards. Both these flanges and the tapered wheels should be equally tapered to atleast 6% and with the following dimensions:

diameter of wheel diameter of protection flanges

below 300 mm (12 inches) at least half the diameter of wheel

300 mm - 750 mm at least the diameter of wheel minus 150 mm(12 inches - 30 inches) (6 inches)

above 750 mm (30 inches) at least the diameter of wheel minus 200 mm (8 inches)

* Study carefully Fig. 7 to Fig. 11 which show the correct mounting of certain types ofwheels commonly used.

Mounting of Depressed-centre Wheels

Depressed-centre wheels should only be mounted with a flange as shown in Fig. 12.Three points should be noted:

1. When the adaptor has been tightened, there should be a slight clearance betweenthe flange and the wheel at (A). This ensures that clamping pressure is exerted only atthe centre of the hub section.

2. The outer part of the face of the flange adjacent to the wheel should be tapered asshown in Fig. 12. This allows the full width of the flange to support the wheel during thegrinding operation.

3. A paper washer should not be used on the hub section of a depressed-centre wheel.

7

S A F E T Y I N T H E U S E O F A B R A S I V E W H E E L S

Guards

* Unless the nature of the work absolutely precludes its use, a guard shall be providedand kept in position at every abrasive wheel for the following purposes:

(1) to hold the wheel parts in the event of breakage.

(2) to protect the wheel from accidental damage.

(3) to prevent the operator from coming into contact with the wheel.

(4) to prevent an oversized wheel from being fitted.

* Guards must be of rigid construction, proper dimensions and securely anchored tothe machine frame. For maximum protection, the guards have to be adjusted to limitthe exposure angles as in Fig. 13.

Work-rests

For bench and floor stand grinders, a work-rest has to be provided and properly adjustedas close as possible, in any case not exceeding 3.2mm (1/8 inch), to the wheel. Lack ofadjustment is the cause of many serious accidents in that the workpiece was jammedbetween the wheel and the work-rest which forced the operator’s fingers against thewheel face.

Protection of Eyes

Persons carrying out dry grinding operations and truing or dressing an abrasive wheelshould wear properly fitted eye protectors or be protected by suitable transparent screenswhich are fitted in front of the exposed part of the wheel so as to intercept flying particles.See Fig. 14. Regulation 5 of the Factories and Industrial Undertakings (Protection of Eyes)Regulations requires that approved eye protectors, shields or fixed shields shall be providedto employees engaged in:

1. Dry grinding of metals or articles of metal applied by hand to a revolving wheel, bandor disc driven by mechanical power.

2. Truing or dressing of an abrasive wheel.

8

S A F E T Y I N T H E U S E O F A B R A S I V E W H E E L S

Truing and Dressing

* The wheel should be dressed when necessary to remove loading or glazing at thewheel surface, both of which reduce the cutting action. Eccentric force will be createdat wheels used for hand grinding rendering them out of balance if they are not trued,and if the force becomes excessive, it may damage the spindle and cause the wheelto burst.

Safety and the Operator

* Ensure that the floor in the vicinity is in good condition, free from obstruction and notslippery.

* If there is more than one speed of the machine, choose the one which does notexceed the maximum permissible speed of the wheel.

* Remember grinding on the sides of straight-sided wheels is dangerous.

* Before operating a bench or floor stand grinding wheel, ensure the proper provisionand adjustment of:

(1) the wheel guards with minimum exposure angle

(2) the clearance between the work-rest and the wheel should be less than3.2 mm (1/8”)

(3) the protective screen (or wear eye protectors)

* Always report any fault or unusual signs of the machine to your foreman or supervisor.

* Do not operate a grinding machine unless you have been properly trained in its safeuse.

* Do not mount an abrasive wheel yourself. It is the job for a competent personappointed by the proprietor.

* Do not apply sudden pressure to the wheel.

* Do not allow the wheel to revolve unattended. Switch it off before you leave.

9

S A F E T Y I N T H E U S E O F A B R A S I V E W H E E L S

Enquiries

If you wish to enquire about this guidebook or require advice on occupational safetyand health, you can contact the Occupational Safety and Health Branch of the LabourDepartment through:

Telephone : 2559 2297 (auto-recording after office hours)

Fax : 2915 1410

E-mail : enquiry@labour.gov.hk

Information on the services offered by the Labour Department and on major labourlegislation can also be found by visiting our homepage at http://www.labour.gov.hk.

Information on the services offered by the Occupational Safety and Health Council canbe obtained through hotline 2739 9000.

Complaints

If you have any complaints about unsafe workplaces and practices, please call theLabour Department’s occupational safety and health complaint hotline at 2542 2172.All complaints will be treated in the strictest confidence.

10

S A F E T Y I N T H E U S E O F A B R A S I V E W H E E L S

TAP HERE

FLOOR

Fig. 1: Tap points for the “ring test”

Sketches and Tables / Forms

Fig. 2: Proper storage of wheels

45o 45 o

45o 45 o

11

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12

S A F E T Y I N T H E U S E O F A B R A S I V E W H E E L S

Maximum operation speed

TESTED AT

6445 R.P.M.

OPER. SPEEDNOT TOEXCEED3600 R.P.M.

51A 36 L 5V 23

sequence of symbols

Order ofmarking

Example

M

Type ofabrasive*

51

N

Nature ofabrasive

A

O

Grain size

36

P

Grade

L

Q

Structure*

5

R

Nature ofbond

V

S

Type of bondetc*

23

Aluminium abrasives A

Silicon carbides C

coarse medium fine very fine

U PM TM OOM

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NO QS VM OUM

NQ RQ NMM POM

NS SM NOM QMM

OM NRM RMM

OQ NUM SMM

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M U

N V

O NM

P NN

Q NO

R NP

S NQ

T ÉíÅK

V îáíêáÑáÉÇ

S ëáäáÅ~íÉ

R êìÄÄÉê

B resinoid(synthetic resins)

BF resinoid(synthetic resins)reinforced

E ëÜÉää~Å

Mg ã~ÖåÉëá~

* Optional symbols – The symbols 0 and 6 are the manufacturer’s own setting

Soft Medium Hard

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Fig. 4: Marking system

13

S A F E T Y I N T H E U S E O F A B R A S I V E W H E E L S

Fig. 5: Form*(Regulation 7(2))

Factories and Industrial Undertakings (Abrasive Wheels) Regulations

k~ãÉ=çÑ =fåÇìëíêá~ä=råÇÉêí~âáåÖ

^ÇÇêÉëë=çÑ =fåÇìëíêá~ä=råÇÉêí~âáåÖ

^ééçáåíãÉåí=çÑ =`çãéÉíÉåí=mÉêëçåë=íç=ãçìåí=~Äê~ëáîÉ=ïÜÉÉäë

* This is not a prescribed form because the law does not require one. This form is merely offered for the convenienceof proprietors for the purpose of appointing a competent person.

Date ofAppointment

Name of competentpersons appointed

Identity cardnumber

Address ofcompetent person

Signature ofproprietor

Signature ofcompetent person

14

S A F E T Y I N T H E U S E O F A B R A S I V E W H E E L S

chuck mounted wheel

overhang

Fig. 6: Sketch defining “overhang”

inner flange keyed on spindle

washers fitted

flange recessed here

Fig. 7: A straight-wheel with a small bore

15

S A F E T Y I N T H E U S E O F A B R A S I V E W H E E L S

washers fitted

flange undercut hereinner flange keyed on spindle

Fig. 8: A straight-wheel with a large bore

Flat flange, no relief — to provide propersupport for steel bushing and wheel

Fig. 9 : A threaded-hole wheel

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S A F E T Y I N T H E U S E O F A B R A S I V E W H E E L S

Flat flange, no reliefS p i n d l e i s s h o r t e r t h a n h o l e a n dsufficiently threaded

Fig. 10: A cone wheel

wheel tapered to 6%

flange tapered hereequally

Fig. 11: A tapered wheel

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S A F E T Y I N T H E U S E O F A B R A S I V E W H E E L S

Fig. 12 : Flange assembly for a depressed-centre wheel. The outer part of the flangeadjacent to the wheel should be tapered as shown and there should be aslight clearance at A.

ATapered surface

65º MAX.

90º MAX.EXPOSURE

BENCH AND FLOORSTAND GRINDERS

(WHEEL CONTACT IN GENERAL)

65º MAX.

125º MAX.EXPOSURE

BENCH AND FLOOR STAND GRINDERS(GREATER WHEEL CONTACT BELOW,

OR OF SPINDLE IS REQUIRED)

60º MAX.

TOP GRINDER

180º MAX.EXPOSURE

SWING-FRAME GRINDER

65º MAX.

180º MAX. EXPOSURE

CYLINDRICAL GRINDER

15º MIN.

150º MAX.EXPOSURE

15º MIN.

SURFACE GRINDERS ANDCUTTING-OFF MACHINES

Fig. 13: Maximum exposure angles for various grinding applications

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S A F E T Y I N T H E U S E O F A B R A S I V E W H E E L S

protective screen

3.2mm maximum (1/8”)

wheel guard, with minimum exposure angle

work-rest

Fig. 14 : A grinding wheel fitted with wheel guard, work-rest and protective screen.