grinding wheel safety grinding wheel safety.pdf

7/28/2019 Grinding Wheel Safety Grinding Wheel Safety.pdf

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Grinding Wheel Safety

INTRODUCTION

This section endeavours to answer some of thevital aspects on the safe use and care of grindingwheels.

The advantage of high speed machine toolsshould be obvious to any machinist. As pioneersin the field of bonded abrasive products in India,we are meeting the demand for high production,by producing wheels of greater bond strength,under controlled conditions in each stage ofmanufacture, in addition to maintaining close

limits of balance and truth, thus assuring a safeapplication.

Thus, you will observe that grinding wheels aresafe and necessary cutting tools, but it must beremembered that they are not unbreakable.

The general understanding of the strength ofvarious types of wheels in relation to theiroperating speed and their behaviour combinedwith the knowledge of their handling and storagecoupled with simple rules of safety will result inexcellent safety record in their use in industries.This section is dedicated to these ends.

INSTRUCTIONS FOR THE SAFE

USE OF GRINDING WHEELS ...

MOUNTING THE WHEEL

1. Select correct wheel for your operation.

Ring wheel and inspect for cracks. Neveruse cracked wheel.

2. Never exceed maximum safe speed

established for wheel. Be sure machine

speed is not excessive.3. Never alter hole in wheel or force wheel on

spindle.

4. Use clean, recessed, matching flanges atleast 1/3 wheel diameter.

5. Use one clean, smooth blotter on each sideof wheel under each flange.

6. Tighten nut only enough to hold wheel firmly.

7. Adjust wheel guard and put on safetyglasses before starting wheel.

USING THE WHEEL

1. Adjust dust hood and coolant nozzle (for wet

grinding). Keep work rest adjusted within 1/8 of wheel face (periphery).

2. Stand aside and allow wheel to run idle a

full minute before starting to grind.

3. Dress wheel if out of true.

4. Make grinding contact without bumpingor impact.

5. Grind only on face of straight wheel. Use discwheels for side-grinding. Light side-grindingpermissible on cup or saucer wheel.

6. Never force grinding so that motor slowsnoticeably or work gets hot.

7. Protect wheel when not in use. Store safelyif removed from grinding machine.

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Grinding Wheel Safety


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If you ran a steel tape around the outside of a24 diameter wheel you would find that the wheelmeasured a little over 6 feet around. For every

revolution of a 24 wheel, any given point onthe outside surface of the wheel travels about 6feet. If the 24" wheel is mounted on a machinewhich runs at 1000 RPM, the surface speed is alittle more than 6000 surface feet per minute.

In general, wheel speed is given in surface feetper minute. Machine speeds, however, areusually indicated in RPM, and most speedindicators and tachometers read in RPM. It isfrequently necessary to translate surface speed

into RPM for various sizes of wheels.

Where a wheel is used at the same speed (RPM)until worn out, it is not necessary to make anytranslation. Simply make sure that the speed isnot higher than shown on the wheel blotter orthe wheel tag. In some places it is customary tomaintain a fairly uniform surface speed in orderto keep the grinding action the same. Thismeans that the RPM must be increased as thewheel wears down.

SFPM = diameter of wheel in inches x RPM x 0.262

VITRIFIED AND SILICATE

SPEED LIMIT6500 S.F.P.M. (or 33 metres/sec.)

RESINOID AND RUBBERSPEED LIMIT9500 S.F.P.M. (or 48 metres/sec.)

YES definitely. In actual use, the periphery ofa grinding wheel usually travels at a speed fasterthan a mile a minute. If a wheel should be brokenwhile travelling at that speed, serious personalinjury or damage to machinery or equipmentmight result.

As a rule, vitrified and silicate wheels can besafely used at 6500 surface feet per minute, andresinoid and rubber wheels at 9500* surface feetper minute. Coarse, soft wheels are not strongenough for these speeds. Cup wheels andcylinders should also be run at slower speeds.

Operating speeds recommended by themanufacturer must not be exceeded. Neveroperate a wheel at the Tested at ... speed.

* Excepting cut-off wheels.NO if the wheel is properly mounted and notabused, it is not dangerous. Today, grinding isnot considered a dangerous occupation.

Revolutions Per Minute: is the number ofcomplete axis turns per minute.

Surface Feet Per Minute: is the distance anyone abrasive grain on the cutting face travels inone minute.

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GRINDING WHEEL SAFETY


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IN most cases they are not accidents at all. Theyare due to carelessness or to lack of knowledge.The most common causes are:

1. Using the wrong wheel for the job.

2. Careless handling

3. Improper mounting

4. Too high speed

5. Too much pressure

FIRST, you must have a general understandingof the strength of various types of wheels.

THEN if it is your job to mount the wheels, youshould learn how to mount them properly, and

FINALLY, you should learn how to grind so thatthere will be no danger of damaging the wheel.

NO They are all breakable, but some kinds ofwheels may be actually ten times stronger thanothers. Some are quite brittle, others tough. Thebond in vitrified wheels is similar to glass andcan be broken easily. Careless handling caneasily damage such wheels. Rubber andresinoid bonded wheels can usually standharder usage and can be used at higher speeds.

The tough, strong wheels would not be suitablefor all kinds of grinding. On some classes ofgrinding, relatively soft wheels are necessary toprevent burning and spoiling sensitive andexpensive steels. If you tried to sharpen a high-speed steel cutter with the same kind of wheelthat is used for grinding castings, the cutter



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would be quickly ruined. On the other hand, ifyou used a cutter grinding wheel on a high-speed portable grinder for grinding castings, thewheel would probably break.

Use only the kind of wheel which has beendesignated for your job by your foreman orsomeone in authority. As a check, the tag orblotter on the wheel shows the highest speedwhich the wheel manufacturer recommends. Ifyou do not know the speed of your machine,make it a point to find out. If the machine speedis faster than the speed stamped on the wheel,tell your foreman about it.Never borrow a wheel from another job. It mightnot be the right kind of wheel for your job.

All wheels are breakable vitrified and silicatewheels are very similar to a piece of glass andcan be broken or cracked by dropping, bumpingor merely tipping over from an upright position.Rubber and resinoid wheels can usually stand

more abuse, but they can be brokennevertheless. To be on the safe side, handle allgrinding wheels as carefully as though they weremade of glass.

Inspect it carefully for cracks or any marks thatlook as though the wheel might have beendamaged. If anything looked suspicious, show it

to your foreman. Even if no cracks are visible, givethe wheel a ring test. Tap the side with a woodenmallet or the handle of screw driver and notice ifit gives a clear ring. If not, ask your foreman to testit. Then, if it appears to be O.K., mount it on themachine. When starting the machine, stand toone side of the wheel for atleast a minute beforestarting to grind. If it is portable machine, hold itunder a bench or inside a heavy casting for aminute or so.



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There are so many kinds of machines andwheels, that these can be no simple rule to coverall. The best general advice is to get properinstruction from your foreman or someone whohas authority to instruct you. Unless you havepreviously mounted wheels on a similarmachine, do not take a chance on mounting anew wheel without proper instruction.

1. Use of flanges of uneven diameter.2. Use of washers instead of flanges.3. Flanges without proper clearance or relief.4. Excessive tightening causing flanges to

bend.5. Failure to clean all dirt and foreign material

from sides of wheels and flanges.6. Forcing a wheel onto an arbor where fit is

tight.7. Use of just any lose washers or bushings to

try to make a wheel fit a machine for which itwas not intended.

8. Failure to use blotters on wheels.

Not if the original surface speed is not exceeded.There might be a very real danger if the RPM isincreased too soon, or if, when mounting a newwheel, the RPM is not reduced to the properspeed for the full-sized wheel. This is veryimportant.

Side pressure on thin straight wheels isdangerous. Most wheels will stand quite a lot ofstraight radial pressure, but there is a limit towhat they can take. Heavy pressure with vitrifiedwheels is apt to cause the wheel to get hot. If itgets too hot too quickly, it is apt to break.

Sudden bumping or pounding is moredangerous than steady, even pressure.



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Hoods and other protection devices makegrinding really safe. If all of the safety rules werealways followed, breakages would never occurand hoods would not be necessary. There isalways the chance, however, that someone willsome day forget one of these things andbreakage might result.

Breakages do not occur often, but because ofthe high speed at which grinding wheels travel,the results are apt to be serious unless proper

guards are in place.It is always expected that the wheel will notbreak, and if it has been properly handled andmounted and is not in any way abused it willnot, but the guard should always be in place

just in case.

A hood cant possibly keep in all the smallparticles of grit and steel which are loosenedduring any off-hand dry grinding job. It doesnttake a big particle to do a lot of damage to aneye. Goggles are the best protection againstthis.


grinding wheel safety grinding wheel safety.pdf

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