THE MAINTENANCE CONNECTION, INC. Grinding Wheels
Safety Requirements for the Use, Care and Protection of Abrasive Wheels. ANSI B7.1-1978 / Approved Feb.18, 1988
TYPE 1 - STRAIGHT WHEELS Flanges not matched Both the fixed and loose flanges between which a wheel is mounted must be of the same diameter (minimum 1/3 diameter of wheel) and properly relieved. See Fig. 5 for an example of correct mounting. If they are not the same diameter, the wheel is under a bending stress which is likely to cause fracture. (See Fig. 6) If they are not properly relieved, the flange pressure is concentrated on the sides of the wheel near the hole, a condition which must be avoided. Distorted Flanges Uneven flange pressures, caused by distortion of the flanges due to excessive tightening, create a dangerous condition. When flanges are sprung or distorted, the effective area of contact is reduced and the pressure is moved nearer the hole. (See Fig 7).
In Fig. 8 the outer flange has been omitted and the nut tightened directly against the wheel. This sets up a cross bending stress which is likely to break the wheel. Substitute flange A washer is a dangerous substitute for a properly relieved flange. (See Fig. 9) The bending stress imposed is likely to cause fracture of the wheel. Outer Flange Reversed The condition illustrated in Fig. 10 results in unequal bearing against the wheel, and has the same effect as using flanges of unequal diameter.
Causes of Wheel Breakage If the breakage of abrasive wheels could be prevented, there would be no need for a guard. Conversely, if all machines could be completely guarded there would be no cause for worry about wheel breakage. Outer Flange Omitted However, both must be considered. Both flanges serve a useful purpose and it Everything must be done to prevent wheel is extremely dangerous to omit either. breakage and proper guards must be used. Fig. 5 Flanges are equal in outside diameter and relieved to produce equal and opposite bearing area.
Fig. 6 Flanges are not matched in diameter or relief.
Fig. 7 "Sprung" flanges caused by excessive tightening.
Loose flange
Inner flange fixed to machine CORRECT spindle
Contact here only
Blotters
A B R A S I V E S
No contact here
INCORRECT
INCORRECT
Fig. 8 Outer flange omitted.
Fig. 9 Unsatisfactory substitute for properly relieved flange.
Fig. 10 Outer flange reversed.
INCORRECT
INCORRECT
INCORRECT
P-69