Quy tắc vận hành máy mài

(Theo bộ tiêu chuẩn ANSI EN-B7.1-2010)

Để vận hành quy trình mài một các an toàn, ANSI B7.1-2010 đưa ra các quy định, quy tắc chung. Nguyên văn như sau:

General operating rules

1. User’s responsibility

Competent, trained persons shall be assigned to the mounting, care, and inspection of abrasive wheels and grinding machines. The abrasive wheel operator shall be fully instructed in the use, care and protection of abrasive wheels as defined in this Standard. Any user who alters the wheel other than normal truing or dressing assumes the responsibility of the wheel manufacturer .

2. Airborne particulates control

The user shall install and operate grinding machines so that airborne particulates caused by the grinding operation shall not exceed threshold limit values. Steps shall be taken to control and dispose of the swarf in an approved and safe manner with respect to both health and environment.

3.  Personal protective equipment

3.1 Eye and face protection

Safety goggles or safety spectacles shall be worn by all personnel exposed to grinding operations where dust, swarf, or flying particles are generated. Where the nature of the operation requires additional face protection, a face shield also shall be worn. Such safety devices shall be in accordance with ANSI Z87.1.

3.2 Protective clothing

Protective clothing such as aprons, gloves, safety shoes, and others, shall be worn for protection from sparks, swarf, and flying particles when a grinding operation presents a hazard to the operator or  djacent personnel.

4. Wheel breakage

A cracked or damaged wheel shall not be used. Wheel breakage shall be investigated by the user to determine and correct the cause. In the event of a wheel breakage which causes personal injury, the wheel manufacturer and the machine supplier  hould be notified immediately.

5.  Wheel speed

It shall be determined at time of mounting a new wheel that spindle speed does not exceed the maximum operating speed marked on the wheel or wheel package. When a partly used wheel is remounted, spindle speed in revolutions per minute may exceed the maximum revolutions per minute marked on the wheel provided the maximum peripheral speed (surface feet per minute) established for the wheel when new is not exceeded. Tensioned speed It shall be determined at time of mounting a steel centered diamond cutting-off wheel that spindle speed is within +10%/-20% of the tensioned speed marked on the wheel.

6. Flanges

All grinding wheels or cutting-off wheels shall be mounted with flanges.

7. Safety guard

Grinding wheels shall not be operated on any machine which has had its safety guard removed. At the completion of wheel mounting, the safety guard shall be in place and should be checked for condition and adjustment. All safety guard fasteners shall be in place and properly tightened. For portable machines, safety guards shall be inspected periodically. Safety guards shall be in good functional condition. Damaged, bent, and severely worn guards shall be replaced. A guard which has been subjected to a wheel breakage is likely to be weakened enternally and shall not be reused. On all other grinders, guards may be repairable depending on the amount of damage suffered during the wheel breakage. It is the user’s responsibility to insure that a damaged guard is repaired or replaced to insure the machine is reconditioned to its original state and safe to be operated.

8. Starting the wheel

All abrasive wheels shall be run at operating  speeds with the safety guard in place or in a protected enclosure for at least one minute before applying work. During this time no one shall stand in front of or in line with the wheel.  This provision shall apply each time one of the following conditions occur:

a. a new wheel has been mounted;

b. a used wheel has been remounted.

9.  Vibration

Vibration in a portable grinder mounted with a new grinding wheel may be caused by various conditions. The cause of unusual vibration shall be determined and corrected 

10.  Balance

Out of balance wheels which set up vibrations can result in marred work surfaces, machine damage and also cause stresses which could contribute to wheel failure. Wheels which cannot be corrected for imbalance by the user shall not be used.

11.  Truing and dressing

Truing is the process of forming the abrasive wheel cutting surfaces in order to eliminate runout; to form the geometrical shape and to expose new sharp cutting edges of the abrasive grains

Dressing is the process of removing bond material from around the cutting grains or diamonds in order to expose new, sharp cutting edges and to provide chip clearance for the material removal process.

A bonded abrasive wheel that cannot be trued shall not be used.

12.  Wet grinding

When shutting down a wet grinding operation, the coolant should first be shut off and the wheel allowed to rotate until coolant has been spun out. The strength of organic bonded wheels can be affected by coolants. The concentration and alkalinity of the coolant should be checked regularly and adjusted according to the recommendations of the coolant manufacturer.

13.  Side grinding

Side grinding should only be performed with wheels designed for this purpose. Grinding on the flat sides of wheels designed for peripheral grinding may be dangerous and cause broken wheels. This does not preclude their use for  applications such as shoulder, contour and form grinding where it is recognized a limited amount of side grinding is performed. Extreme caution should be exercised not to use excessive side pressure or substantially reduce wheel width by side dressing.

14.  Lubrication

The machine spindle bearings shall be properly lubricated to prevent overheating or other conditions which might damage the abrasive wheel. Lubrication practices shall comply with the machine or  equipment supplier’s recommended practices.

15.  Machine maintenance

An employer shall maintain grinding equipment in a condition which will not create a hazard for an employee. The employer shall instruct an employee to report defective equipment to an employee supervisor. In the event of a wheel breakage, the grinder shall be inspected and returned to safe operating condition before being returned to service.

16. Work rests

An off-hand grinder shall be equipped with a work rest or other device which shall prevent the work piece from jamming between the abrasive wheel and the wheel guard. The work rest or other device shall not contact the abrasive wheel any time and shall be properly maintained. When work rests are used, the following conditions shall be maintained at all times:

1. The work rest shall be adjusted such that the gap between the work rest and the grinding surface of the abrasive wheel shall not exceed 1/8 inch.

2. The work rest height shall be on the horizontal center line of the machine spindle.

3. The work rest shall not be adjusted while the abrasive wheel is rotating unless the work rest is designed to allow such adjustment.

4. The work rest shall be securely clamped after each adjustment.

When a work rest cannot be used in accordance with items 1 and 2 above, because of job requirements, the work rest can be adjusted, modified, or eliminated to accommodate the operation. In that circumstance, the user assumes all responsibility for this modification and the continued safe operation of the grinding machine. The user shall in this case provide a means for prohibiting the use of the grinder for other than the job for which the work rest was modified.

17.  Large hole inorganic bonded wheel

Large hole inorganic bonded wheels (those with holes in excess of 1/4 of the wheel diameter) should not be used on snagging operations.

18. Wheel discard size

The usable portion of an abrasive wheel shall be considered to be that portion which extends beyond the mounting flanges. A wheel shall not be worn down to a size which would allow the mounting flange assembly to contact the workpiece or workpiece holding fixture.

19.  Wheel type for machine

The type of bonded abrasive wheel used on any machine or tool shall only be that type or types for which that machine or tool has been designed. The machine manufacturers' recommendations shall always be complied with concerning the type of wheel to be used and the machine or tool must have the proper guarding, mounting and maximum speed limiting devices in accordance with this standard.

20. Machine conversions

Bonded abrasive wheels may be used on machines or tools such as sanders which have been converted to a grinder in accordance with the machine or tool manufacturers' specifications and conforming to the provisions of this standard in respect to wheel design, guarding, mounting and speed. 

21. Wheel specification

Bonded abrasive wheels shall only be used to grind materials for which the wheel composition is designed. The wheel manufacturers' recommendations must be followed regarding the kinds of material to be ground with any particular wheel.