Grinding Wheel Safety, Part 2 (1981)

[Music] Hello, Dave Brown again for Teletrain with the second part of grinding wheel safety. In part one, we followed a person's contact with a grinding wheel from handling and storage right up to wheel mounting. In part two, we'll start where we left off. Now, let's go through the actual mounting of the wheel on the grinder step by step. First, check to be sure that spindle surfaces are clean. Then place a new clean blotter with a diameter slightly larger than that of the spindle against the fixed flange. Now slide the wheel onto the spindle. On larger wheels, the wheel is usually marked mount up or mount down. Make sure the marking is placed in the proper position. This helps to maintain or improve wheel balance when the wheel is tred. The wheel must slide easily onto the spindle. Never force a grinding wheel. The spindle can heat up during the grind and expand. Too tight a fit can cause the wheel to break. Tests have shown that the highest stressed zone in a rotating grinding wheel is the area around the hole. After placing the wheel in position, slide another clean bladder on the spindle, followed by the loose flange. With larger wheels, a multiple screw flange is usually used where bolts are placed into holes and handtightened. It is very important that you tighten these bolts down evenly and uniformly. Otherwise, the flange can distort and cause wheel damage. Tighten the bolts opposite each other around the flange. Use a torque wrench in order to apply the proper amount of torque specified by the machine builder. Mounting a smaller wheel with a central mounting setup is similar to mounting with a multiple screw setup. When tightening the mounting on a thin wheel setup, be extra careful not to overtighten. Thin wheels can break from uneven pressure caused by distorted flanges. After you have mounted the grinding wheel and tightened the assembly, check with a feeler gauge to be sure that both flanges are in good contact with the blotters and to ensure that no springing has occurred. The gauge should not fit between the flange and the blotter. The idea is to tighten enough to prevent the wheel from slipping. After the wheel is mounted and before it is actually used, it may require balancing. Static balancing is accomplished by removing the entire mounting assembly from the machine after it has been tred and placing it in either a balance stand with knife rollers or a balance stand with parallel ways. The balancing weights in the spindle are shifted until the wheel remains motionless in any position. Once this is accomplished, the assembly is now static balanced and may be replaced on the machine. It should then be retrudeed. Okay, you've got the wheel mounted and tred. Stand to one side. Let it run at normal speed for approximately one minute with the guard in place to make sure it isn't going to fly apart. This will test the wheels soundness before you stand in front of it. Grinding wheels must only be used on machines provided with proper safety guards. Check your ANCB 7.1 code for the guard requirements of different operations. An exception to guard use involves internal grinding or grinding with mounted wheels, cones, or plugs with the workpiece itself offering a degree of protection. Safety guards protect you and others in the area by effectively shielding the wheel. The guard contains or deflects pieces if the wheel should accidentally break and it also controls the movement of sparks and flying swarf during grinding. The guard is there for everyone's benefit. So for everyone's sake, use it. Just an additional word right here about portable grinders. Portable grinders should be placed in a rack or holder when not in use. Rough handling or dropping can fracture the wheel, bend the spindle, or dislocate the guard. For air grinders, be sure the speed regulator is checked periodically by using a tachometer on the spindle. The majority of grinding personal injury accidents are caused by abusive or improper use of portable grinders. Remember, accidents don't just happen to the other person. What happens if you do accidentally drop your grinder? There are three things you might do, but only one of them is right. Number one, dismount the wheel. Check it out and check the spindle and guard to make sure they haven't been damaged. That's good, but it's not enough. Option number two is a mistake all the way. You can pick the grinder up, say to yourself, "Well, it didn't hit very hard. I think it's okay." And go ahead and use it. If you choose this option, you are very possibly taking a shortcut to the hospital. Option three is the right thing to do. Return the machine to the tool room. Explain what has happened. The tool room personnel can carefully check it out to see if there's any damage. Let's talk for a bit about wheel speed. Every grinding wheel is assigned a maximum safe operating speed by the manufacturer. The speed is based on the wheel shape and strength. Wheel speeds are expressed in revolutions per minute or in surface feet per minute. Let's take a look at what these two terms mean. Revolutions per minute or RPM is the number of complete turns that a wheel makes in one minute. Surface feet per minute is the distance in feet an abrasive grain on the cutting face of the wheel travels in one minute. The speed of the wheel in surface feet per minute will change as the wheel diameter gets smaller even though the number of revolutions per minute of the wheel stays constant. In general, vitrified bonded grinding wheels are normally operated up to 6,500 surface feet per minute. Vitrified cylinder and cup wheels used in tool room grinding can only be operated up to 6,000 surface feet per minute. Certain special vitrified wheels are made for operation at 8,500 surface feet per minute or higher. Non-reinforced resin bonded wheels operate up to 9500 surface feet per minute and reinforced resin bonded wheels up to 12,500 surface feet per minute or more. What we are giving you here are speeds for the more commonly used wheels, but there are many wheels that have different speeds. Always go by the marking on the wheel or check the ANCB7.1 code to understand why a grinding wheel can be dangerous. Let's look at a grain on the wheel going 12,500 ft per minute. It is traveling more than 140 mph. That's 50% faster than the fastest baseball pitcher can throw the ball. So, you can just imagine what happens if a chunk of the wheel breaks off and hits you at that speed. Check your machine speed. Be sure the spindle speed of the machine doesn't exceed the maximum operating speed of the grinding wheel. Air driven grinders should be checked every 20 hours or once a week, whichever comes first, and after maintenance or repair when issued from the tool crib. and at each wheel change. Electric grinders should be checked monthly and after maintenance or repair. As the wheel wears down through use, the number of revolutions per minute can be increased, provided the number of surface feet per minute does not exceed the maximum allowed for the wheel. If you are given the wheel speed and surface feet per minute, refer to the wheel speed conversion table in your ANIE B7.1 code for various surface speed limits. You can find the required revolutions per minute for any wheel diameter. One manufacturer has arrived at a unique solution to the problem of slower surface feet per minute as a wheel wears down. With this unit, as the wheel wears, the operator adjusts the hand wheel, bringing the wheel assembly forward to within 1/8 inch of the guarding gauge point. This increases the spindle RPM and maintains a constant surface feet per minute. This unit also goes one step further. This mechanism operates automatically. It closes around the wheel so rapidly that little or no part of the wheel escapes the housing. Each job is different and the most efficient grinding speed is not necessarily the maximum operating speed. You will frequently get better grinding results at lower than maximum operating speed. Always wear approved safety glasses when doing any type of grinding. Everyone in the area around the grinding operation must have eye protection. Insist this procedure is followed. Make no exceptions. Now, with constant use, the abrasive grains on the surface of a grinding wheel may become dull or loaded by the material being ground. When this occurs, the wheel needs to be dressed to expose new sharp abrasive grains that will maintain efficient grinding action. A dressing tool is used for this purpose. Handheld dressing tools must be properly supported on a work rest adjusted to allow the dresser to move evenly across the wheel face. If the workpiece is not properly positioned and supported for grinding, it can jam against the wheel, causing breakage and possible injury. Before starting operation, make a final check to be sure the machine is set up correctly and the workpiece is secure and correctly positioned. Off-hand grinders should have a work rest which supports the workpiece and prevents it from jamming between the abrasive wheel and the work rest. Never bump or jam the workpiece against the wheel. The work rest should be positioned within 1/8 inch but not touching the grinding wheel at the same height as the machine spindle. Always adjust the rest while the wheel is stopped and the switch is off. Observe grinding rules concerning feed rate and pressure. Excessive heat up or loading of the wheel face tells you there's a problem. The grinding operation must then be reviewed. Also, be aware of any unusual sound which can be a tip off to a wheel crack. Always turn off a grinding machine when it's not in use. If you are grinding with a coolant, turn off the coolant before stopping the wheel. This will prevent heavy spots from forming in the wheel, which can throw it out of balance. A grinding wheel should never break except from accidental abuse. Too often, an injury occurs after a previous breakage was ignored. Any wheel breakage should be checked out and unsafe conditions corrected. Contact the wheel manufacturer if there's any question. If someone is injured by a wheel breakage, immediately notify the machine builder and wheel manufacturer. Grinding wheels are manufactured in a wide variety of shapes and sizes for different machines and grinding applications. Always use a wheel that is designed for your machine and grinding operations. Straight wheels and recessed wheels are made for peripheral grinding on the edge of the wheel. Always grind on the proper surface of the wheel. Organic bonded depressed center wheels and vitrified bonded dish or saucer wheels have flared shapes to allow grinding on both the periphery and side. Mounted wheels, cones, and plugs are designed for grinding over a broad surface of the abrasive. Never grind on the side of a wheel made for peripheral grinding only. Excessive side pressure can cause the wheel to break. For safe operation and best results, always use a grinding wheel designed for your grinding job. In this program, we've talked about the steps that the grinding wheel operator can take to ensure safety. We've seen the importance of establishing and maintaining safe work habits in storage and handling, preparation for grinding, wheel mounting, and grinding operations. We've shown you the ANI code B7.1 and recommended that you have it nearby and use it in the final analysis. The rest is up to you. EA2 to General Hospital. We've got a 1018 emergency traffic. Code red. Code red. We've got a white male approximately 30 years old. Industrial accident with severe head injuries. Termination of respiratory functions and extensive bleeding. We're applying local pressure and administering O2 and IV. EA2. What is your ETA? EA2. Our ETA is 4 minutes. Standby for vital signs. Woo! Woo! [Music] Don. Don, wake up. You're going to be late for work. Oh man, after that dream, I'm going to play it by the rules. Hey Stan, drop the darn wheel. Might be damaged. I'll check it out, Don. Thanks, Stan. I'm still going to make sure this wheel is okay. Fits nice and easy over the spindle. The spindle can heat up and expand. RPMs are okay for this wheel on this machine. I've got the right flange for the wheel and the flange is in good shape. Okay, now tighten it up, but not too much. Work rest is set correctly. Shield is in place. Okay, stand to one side and let the wheel run for a minute. Put on my gloves. Safety glasses in place. Now, don't slam the work into the wheel. Let's hope he will continue to remember his dream and always practice grinding wheel safety. Our point has been to stress safety responsibility in your job. If you have any questions, see your supervisor or get in touch with your wheel manufacturer or supplier. For your sake, for your family's sake, for heaven's sake, make safety your job. or Don's dream may become your reality. I'm Dave Brown for Teletrain. [Music]