Organic-bonded wheels, the thickness of which is not more than one forty-eighth of their diameter for those up to, and including, 20 inches (50.8 cm) in diameter, and not more than one-sixtieth of their diameter for those larger than 20 inches (50.8 cm) in diameter, used for a multitude of operations variously known as cutting, cutting off, grooving, slotting, coping, and jointing, and the like. The wheels may be "solid" consisting of organic-bonded abrasive material throughout, "steel centered" consisting of a steel disc with a rim of organic-bonded material molded around the periphery, or of the "inserted tooth" type consisting of a steel disc with organic-bonded abrasive teeth or inserts mechanically secured around the periphery.
All power-driven rotatable discs faced with abrasive materials, artificial or natural, and used for grinding or polishing on the side of the assembled disc.
A system consisting of branch pipes connected to hoods or enclosures, one or more header pipes, an exhaust fan, means for separating solid contaminants from the air flowing in the system, and a discharge stack to outside.
All power-driven rotatable grinding or abrasive wheels, except disc wheels as defined in this standard, consisting of abrasive particles held together by artificial or natural bonds and used for peripheral grinding.
A grinding machine carrying two power-driven, rotatable, coaxial, horizontal spindles upon the inside ends of which are mounted abrasive disc wheels used for grinding two surfaces simultaneously.
All power-driven rotatable wheels composed all or in part of textile fabrics, wood, felt, leather, paper, and may be coated with abrasives on the periphery of the wheel for purposes of polishing, buffing, and light grinding.
Any power-driven rotatable grinding, polishing, or buffing wheel mounted in such a manner that the wheel with its supporting framework can be manipulated over stationary objects.
The kinetic pressure in the direction of flow necessary to cause a fluid at rest to flow at a given velocity. It is usually expressed in inches of water gauge.
Wherever dry grinding, dry polishing or buffing is performed, and employee exposure, without regard to the use of respirators, exceeds the permissible exposure limits prescribed in 1926.55 or other pertinent sections of this part, a local exhaust ventilation system shall be provided and used to maintain employee exposures within the prescribed limits.
Hoods connected to exhaust systems shall be used, and such hoods shall be designed, located, and placed so that the dust or dirt particles shall fall or be projected into the hoods in the direction of the air flow. No wheels, discs, straps, or belts shall be operated in such manner and in such direction as to cause the dust and dirt particles to be thrown into the operator's breathing zone.
Scratch-brush wheels and all buffing and polishing wheels mounted on floor stands, pedestals, benches, or special-purpose machines shall have not less than the minimum exhaust volume shown in Table D-57.2.
Grinding wheels or discs for horizontal single-spindle disc grinders shall be hooded to collect the dust or dirt generated by the grinding operation and the hoods shall be connected to branch pipes having exhaust volumes as shown in Table D-57.3.
Where the work is outside the hood, air volumes must be increased as shown in American Standard Fundamentals Governing the Design and Operation of Local Exhaust Systems, Z9.2-1960 (section 4, exhaust hoods).
Grinding wheels or discs for horizontal double-spindle disc grinders shall have a hood enclosing the grinding chamber and the hood shall be connected to one or more branch pipes having exhaust volumes as shown in Table D-57.4.
Grinding wheels or discs for vertical single-spindle disc grinders shall be encircled with hoods to remove the dust generated in the operation. The hoods shall be connected to one or more branch pipes having exhaust volumes as shown in Table D-57.5.
Grinding and polishing belts shall be provided with hoods to remove dust and dirt generated in the operations and the hoods shall be connected to branch pipes having exhaust volumes as shown in Table D-57.6.
Cradles and swing-frame grinders. Where cradles are used for handling the parts to be ground, polished, or buffed, requiring large partial enclosures to house the complete operation, a minimum average air velocity of 150 feet per minute shall be maintained over the entire opening of the enclosure. Swing-frame grinders shall also be exhausted in the same manner as provided for cradles. (See fig. D-57.3)
Grinding wheels on floor stands, pedestals, benches, and special-purpose grinding machines and abrasive cutting-off wheels shall have not less than the minimum exhaust volumes shown in Table D-57.1 with a recommended minimum duct velocity of 4,500 feet per minute in the branch and 3,500 feet per minute in the main. The entry losses from all hoods except the vertical-spindle disc grinder hood, shall equal 0.65 velocity pressure for a straight takeoff and 0.45 velocity pressure for a tapered takeoff. The entry loss for the vertical-spindle disc grinder hood is shown in figure D-57.1 (following paragraph (g) of this section).
TABLE D-57.1 - GRINDING AND ABRASIVE CUTTING-OFF WHEELS
Wheel diameter, inches (cm)
Wheel width, inches (cm)
Minimum exhaust volume (feet3/min.)
To 9 (22.86)
11/2 (3.81)
220
Over 9 to 16 (22.86 to 40.64)
2 (5.08)
390
Over 16 to 19 (40.64 to 48.26)
3 (7.62)
500
Over 19 to 24 (48.26 to 60.96)
4 (10.16)
610
Over 24 to 30 (60.96 to 76.2)
5 (12.7)
880
Over 30 to 36 (76.2 to 91.44)
6 (15.24)
1,200
For any wheel wider than wheel diameters shown in Table D-57.1, increase the exhaust volume by the ratio of the new width to the width shown.
Example:
If wheel width = 41/2 inches (11.43 cm), then (4.5/4) x 610 = 686 (rounded to 690).
Exhaust systems for grinding, polishing, and buffing operations should be designed in accordance with American Standard Fundamentals Governing the Design and Operation of Local Exhaust Systems, Z9.2-1960.
Exhaust systems for grinding, polishing, and buffing operations shall be tested in the manner described in American Standard Fundamentals Governing the Design and Operation of Local Exhaust Systems, Z9.2-1960.
It is the dual function of grinding and abrasive cutting-off wheel hoods to protect the operator from the hazards of bursting wheels as well as to provide a means for the removal of dust and dirt generated. All hoods shall be not less in structural strength than specified in the American National Standard Safety Code for the Use, Care, and Protection of Abrasive Wheels, B7.1-1970.
Due to the variety of work and types of grinding machines employed, it is necessary to develop hoods adaptable to the particular machine in question, and such hoods shall be located as close as possible to the operation.
Swing-frame grinders shall be provided with exhaust booths as indicated in figure D-57.3. Figure D-57.3 -- A Method of Applying an Exhaust Enclosure to Swing-Frame Grinders
Portable grinding operations, whenever the nature of the work permits, shall be conducted within a partial enclosure. The opening in the enclosure shall be no larger than is actually required in the operation and an average face air velocity of not less than 200 feet per minute shall be maintained.
Vertical-spindle disc grinders shall be encircled with a hood so constructed that the heavy dust is drawn off a surface of the disc and the lighter dust exhausted through a continuous slot at the top of the hood as shown in figure D-57.1.
Figure D-57.1 -- Vertical Spindle Disc Grinder Exhaust Hood
and Branch Pipe Connections
Dia. D inches (cm)
Exhaust E
Volume Exhausted at 4,500 ft/min ft(3)/min
Note
Min.
Max.
No Pipes
Dia.
20 (50.8)
1
4 1/4 (10.795)
500
When one-half or more of the disc can be hooded, use exhaust ducts as shown at the left.
Over 20 (50.8)
30 (76.2)
2
4 (10.16)
780
Over 30 (76.2)
72 (182.88)
2
6 (15.24)
1,770
Over 53 (134.62)
72 (182.88)
2
8 (20.32)
3,140
20 (50.8)
2
4 (10.16)
780
When no hood can be used over disc, use exhaust ducts as shown at left.
Hoods for polishing and buffing, and scratch-brush wheels shall be constructed to conform as closely to figure D-57.4 as the nature of the work will permit.
Figure D-57.4
Standard Buffing and Polishing Hood
Wheel dimension, inches (centimeters
Exhaust outlet, inches (centimeters) E
Volume of air at 4,500 ft/min
Diameter
Width, Max
Min= d
Max= D
9 (22.86)
2 (5.08)
31/2 (3.81)
300
Over 9 (22.86)
16 (40.64)
3 (5.08)
4
500
Over 16 (40.64)
19 (48.26)
4 (11.43)
5
610
Over 19 (48.26)
24 (60.96)
5 (12.7)
51/2
740
Over 24 (60.96)
30 (76.2)
6 (15.24)
61/2
1,040
Over 30 (76.2)
36 (91.44)
6 (15.24)
7
1,200
Entry loss = 0.15 velocity pressure for tapered takeoff; 0.65
velocity pressure for straight takeoff.
(5)(iii)/0)
(5)(ix)/0)
(5)(v)/0)