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The commonly used grinding m/c s in construction are the portable grinding m/cs. The speed of the wheels ranges from 7000 rpm to 14000rpm or sometimes more than that. Even a minor mishandling would lead to a serious mishap. Hence grinding operation ought to be done by a trained operator following the safety norms.

Grinding is a hazardous operation. The grinding wheel rotates at a speed of more than 7000 rpm that cause a very serious injury Grinding machines shape material by bringing it into contact with a rotating abrasive wheel or disk. Grinding includes surface, internal, external cylindrical and centerless operations, as well as polishing, buffing, honing, and wire brushing. Portable machines that use small, high-speed grinding wheels have been dealt under Hand and Power Tools.

6.7.1 Grinding Machine Hazards

Hazards associated with grinding machines include the following: • Failure to use eye protection in addition to the eye shield

mounted on the grinder. • Incorrectly holding the work.

• Incorrectly adjusting or not using the work rest.

• Using the wrong type, a poorly maintained or in- balanced wheeler disk.

• Ringing on the side of a wheel not designed for side grinding. • Taking too heavy a cut.

• Applying work too quickly to a cold wheel or disk. • Grinding too high above the wheel's centre.

• Failure to use wheel washers (blotters).

• Installing flanges of the wrong size, with unequal diameters, or with unrelleved censers.

• Incorrect wheel dressing.

• Contacting unguarded moving parts.

• Using controls that are out of the operator's normal reach. • Using an abrasive blade instead of a grinder disk.

• Failure to run a wet wheel dry, without coolant, for a period of time before turning off the machine.

• Using an untested, broken, or cracked grinding wheel.

• Reaching across or near the rotating grinding wheel to load, unload, or adjust the machine during set-up.

6.7.3 Abrasive Disks and Wheels

An abrasive disk is made of bonded abrasive, with inserted nuts or washers, projecting studs, or tapped plate holes on one side of the disk. This side is mounted on the faceplate of a grinding machine. Only the exposed flat side of an abrasive disk is designed for grinding.

An abrasive wheel is made of bonded abrasive and is designed to be mounted, either directly or with adapters, on the spindle or arbor of a grinding machine. Only the periphery or circumferences of many abrasive wheels are designed for grinding.

6.7.3 Inspecting abrasive wheels:

Ring test :

When unpacking abrasive disks and wheels, inspect them for damage from shipment and perform the "ring' test. This test can be used for both light and heavy disks or wheels that are dry and free of foreign material. To conduct the ring test, suspend a light wheel from its hole on a small pin or the finger, and place a heavy one vertically on a hard floor. Then gently tap the wheel

and disks of various grades and sizes have different pitches. (ring test to be done on receipt by the user.)

Visual Inspection on breakage, expiry dates designed rpm & wear & tear of the wheel etc.

Daily inspection of grinding machines should include the points shown in Figure.

Thoroughly investigate grinding wheel and disk failures, preferably with the manufacturer's representative. This type of investigation, along with immediate corrective action, greatly reduces the possibility of recurrent failures.

6.7.4 Handling abrasive disks and wheels:

! Abrasive disks and wheels require careful handling. ! Do not drop or bump.

! Do not roll large disks and wheels on the floor.

! Transport disks and wheels too large or heavy to be carried by hand

! By truck or other means that provide the correct support.

6.7.5 Storing abrasive disks and wheels: fifo method

Store abrasive disks and wheels in a dry area not subject to extreme temperature changes, especially below-freezing temperatures. Wet wheel might break or crack if stored below 32 F (0 C). Breakage of a wheel or disk can occur if it is taken from a cold room and work is applied to it before it has warmed up.

Store abrasive disks and wheels in racks in a central storage area under the control of a specially trained person.

The length of time abrasive disks and wheels may be stored and still be safe to use should be in accordance with manufacturers'

speed use. The grinding wheel must be rated at the same RPM as the machine or more than the machine rpm. If it is not, the wheel may explode and throw particles into the work area causing serious at times fatal injuries.

Mounting wheels :

Mount all abrasive wheels between flanges. Exceptions to this rule include mounted wheels, threaded wheels (plugs and cones), plate-mounted wheels, and cylinder, cup, or segmental wheels mounted in chucks.

Flanges should have a diameter not less than one-third of the wheel's diameter. Flanges for the same wheel should be of the same diameter and thickness, accurately turned to correct dimensions, and in balance. The requirement for balance does not apply to flanges made out of balance to counteract an unbalanced wheel.

Key, screw, shrink, or press the inner or driving flange onto the spindle. The bearing surface of the flange should run true with the spindle. The outer flange's bore should easily slide onto the spindle. (hand tightening , blotter paper)

Schedule flange inspections frequently. Remove from the spindle a flange found to be sprung, not bearing evenly on the wheel, or defective in any other way. Replace it with a flange that is in good condition.

An incorrectly mounted abrasive wheel is the cause of much wheel breakage. Since rotational forces and grinding heat cause high stresses around the wheel's central hole, follow safety regulations concerning size and design of the wheel.