Following recommended disc storage guidelines, using proper equipment, wearing the right personal protective equipment, and employing safe methods of operation can reduce the likelihood of disc breakage and personal injury when using coated abrasive fiber discs.
Coated abrasive discs have an excellent safety record with few reported disc breakages and personal injuries. Still, every effort should be made to prevent them. As with most accidents, operator error is a major factor. Following established safety rules reduces the probability of such an occurrence.
How Moisture Affects Discs
Temperature and humidity are two very important environmental factors that influence coated abrasive disc performance and safety. Improper or inadequate storage can damage discs and make them unsafe. Backings and adhesives are sensitive to climatic changes and gain or lose moisture according to the relative humidity of their surroundings.
Excessive humidity can cause the fiber backing of a disc to absorb excessive moisture, which can make the disc curl up in a convex shape (like a taco shell),called cupping. Cupped discs should never be used because they can snag on the workpiece and break.
Excessive moisture also can soften the adhesive bond and cause the disc to suddenly shed or lose large amounts of abrasive grains.
Excessive dryness can make the disc curl or arch down in a concave manner, which causes it to become brittle and lose its flexibility. In short, high and low humidity can cause convex and concave cupping, respectively.
To keep your coated abrasive discs flat and safe follow proper storage recommendations:
- Store discs at 40 to 50 percent relative humidity and 60 to 80 degrees F (15 to 29 degrees C).
- Store discs at least 4 inches (10 or more centimeters) above the surface of concrete floors; away from open windows; out of direct sunlight; and away from heat sources such as radiators, steam pipes, and air-conditioner exhaust vents.
- Protect them from exposure to water and other fluids and solvents.
- Always follow the abrasive manufacturer’s storage instructions.
- Never use hooks when handling or transporting coated abrasive disc containers.
- Do not drop or in any way damage the discs’ packaging.
- Do not use the discs if their packaging is damaged; return any damaged product to its manufacturer.
- Rotate stock; use on a first-in, first-out basis.
- Store the discs in their original packaging.
Another major cause of disc breakage and injury can be traced to equipment problems. Using the wrong grinder or sander, failure to use the correct backup pad, jamming or catching the disc on the workpiece, and using excessive operating speeds are all leading causes of breakages that must be avoided.
To eliminate some of these problems:
- Never run a coated abrasive disc on an unfamiliar machine without obtaining and following machine instructions.
- Select the proper grinder or sander for the job. Abrading heavy amounts of material from a workpiece may require a grinder; for light sanding or blending, a sander may be the best tool. If the tool is too large, it can be awkward to work with and may cause personal injury. Using a tool that is too small or underpowered can put undue force on the machine and disc and cause the disc to slip,
snag, or break.
- Match the coated abrasive disc and backup pad to the machine. For example, never use a 9-in. coated abrasive disc or backup pad on a 5-in. sander.
- Review and follow all of the machine manufacturer’s recommendations.
- Review and follow all of the fiber disc manufacturer’s recommendations.
- Before mounting a disc or for any type of machine repair, disconnect the grinder/sander from its power source; this eliminates the possibility of the machine accidentally starting.
- Check the sander/grinder spindle for runout (wobble). If there is any runout in the tool’s spindle, repair or replace it.
- Inspect the backpad on the machine. Check that it is the correct size (remember: maximum disc overhang is ¼ in.), and shape, and is free of irregularities such as fractures (cracks), excessive wear, nicks, and cuts at the edges or in the center hole. Check it for concentricity.
- Never exceed the speed rating (marked in RPM) of a backup pad.
- Never use another disc as a backup pad.
- Never use a disc without a backup pad.
- Don’t alter the size or shape of an abrasive disc.
- Never alter the size or shape of a backup pad.
- Check the disc retainer nut for thread wear. Also check for a snug fit and full three-point contact, except when using quick-change or nonwrench systems.
- Use the proper disc-mounting equipment. Never use adhesives to fasten discs to backup pads.
- Don’t use a coated abrasive disc with nicks, cuts, tears, or any other visible damage.
- Only use a disc that fully contacts the backup pad. Never use a warped disc.
- If a grinder is used, or if the sander is equipped with a guard, the guard must be used. Never remove a guard provided by the machine manufacturer. Guards prevent injures and are highly recommended.
- Many air-driven sanders, such as pistol-grip types, are ungoverned machines. Therefore, as with all pneumatic tools, air regulars must be used at each workstation. The speed of the sander is determined by the air pressure provided to the tool. If the machine is designed to operate at 20,000 RPM at 90 PSIG, and the air pressure is allowed to exceed 90 PSIG, the speed of the machine can go up
exponentially. Never mount a bonded grinding wheel on a pistol-grip air sander.
- If you selected an electrical power tool, make sure you are using the correct voltage. Never attach a sander/grinder designed for 110 volts into a 220-V power source. Take all normal electric tool precautions.
- Electric cords or air hoses should be checked regularly for cracks and worn areas.
- Check with the manufacturer of the materials you are going to grind for special grinding and handling instructions. If you are grinding combustible or other hazardous materials, check these instructions for any special fire containment equipment, extinguishing materials, or other requirements.
Personal Protective Equipment (PPE)
Wearing personal protective equipment is an important safeguard for operators and bystanders of coated abrasive operations. Doing so saves eyes, limbs, hearing, and helps prevent future respiratory problems. This equipment includes face shield with eye protection, gloves, safety shoes, arm guards, apron, and long pants.
When required, use a dust mask or approved respiratory tract protection appropriate for the materials being abraded or ground. Hearing protection is required if you are exposed to noise levels exceeding the established threshold.
Safe Sanding/Grinding Methods
How you use the grinding system can affect safety for you and your co-workers.
Always follow these safety rules:
- Start the tool just off the workpiece and bring it up to full operating speed before you begin to grind or sand.
- Ease the disc into the workpiece at a 5- to 10-degree angle to the workpiece surface.
- Look for and avoid any areas on the workpiece where the disc may become caught or jammed.
- When grinding depressions, moldings, lips, and heavy welds, move the grinder away from the work area and not into it.
- Do not allow a disc used for heavy stock removal to rest flat on the workpiece. Doing so can cause the whole tool assembly to be thrown into a rough, jumpy mode.
- Avoid jamming or snagging the edge of the disc on the sharp edge or jagged surface of a workpiece. Instead, work the disc down gradually into the jagged surface before allowing the edge to bite into it. Excessive punishment of the disc’s edge will break even the strongest coated abrasive disc.
- When grinding or sanding small, movable workpieces, secure these pieces to prevent them from moving when the disc makes contact with them.
- Grind or sand in well-ventilated areas.
- Direct sparks away from your body and away from bystanders.
- Do not grind near flammable materials.
- Do not wear loose-fitting clothing.
- Do not store or rest the grinder/sander on the disc and pad.
- Do not put the grinder/sander down until the disc has stopped rotating.
- If you drop the grinder/sander, replace the backup pad and disc before using it again.
- Avoid body or any other unintended contact with the rotating disc or backup pad.
- If chatter or vibration occurs during use, stop the tool at once. Determine the cause of the problem and correct it before continuing.
- When using a nonround disc and backup pad, avoid tight corners and any area where the nonround disc can catch.
- If you’re using an AVOS (allows view of surface) disc (with scooped holes), do not start the equipment with an object protruding through the scooped holes in the product.
- Do not stick objects in the scooped holes while mounting or in use.
- Follow all safety rules set by your employer, governmental agency, or others in authority.
If you comply with these instructions and use the greatest safety tool of all, common sense, you can prevent disc breakages and injuries.