Select and use the correct abrasive for right-angle grinders to minimize costs, increase performance, and ensure safety.
Debbie Gaspich, Saint-Gobain Abrasives, edited by Richard Harris
Matching the grinder, the abrasive product, and the job starts with the use of grinding products made for right-angle grinders. These products must "fit" the machine in terms of size and speed.
Personnel using right-angle grinders need to wear face and eye protection, safety gloves, and, if necessary, the appropriate respiratory protection. Hearing protection is important when noise exceeds mandated thresholds for loudness and duration.
To protect operators and bystanders, every worker, hobbyist, or artist who picks up a right-angle grinder should comply with ANSI Safety Requirement B7.1.
Right-angle grinders have become more useful as manufacturers design more specialized abrasive products for them. To take advantage of the variety of products, end users need information on the products available, what to use for which application, and how to use these products safely and efficiently.
Selecting the right disc or wheel for a grinding job and doing the job safely are more productive in the long run than simply picking whatever abrasive product is handy or moving ahead without taking appropriate safety precautions.
Selecting a cutoff wheel
Made for cutting structural steel, pipe, sheetmetal, and other profiles with a right-angle grinder, reinforced cutoff wheels include those with a premium blend of abrasives for maximum productivity and midrange wheels featuring a durable zirconia-alumina blend. The latter wheels out-perform standard aluminum-oxide wheels that offer high-to-medium cut rates in general-purpose applications.
Cutoff wheels for right-angle grinders come with depressed centers (Type 27) and in flat configurations (Type 01). To en-sure safety, mount flat cutoff wheels on right-angle grinders only with the proper cutoff guard and equal-size flanges. Grinder suppliers should stock the proper guards and flanges.
For material removal, including weld grinding, blending, deburring, and finishing, use coated-abrasive fiber discs. A variety of premium-quality discs are for finishing various metals. For example, a seeded-gel (SG) ceramic formulation offers an outstanding initial cut rate. A self-lubricating formulation improves finishes on stainless steel and steel alloys. A versatile premium product provides finishing on carbon steel, mild steel, and cast iron.
Other fiber discs include a self-sharpening zirconia-alumina product for aggressive cutting, a ceramic-alumina disc for heavy stock removal and another zirconia-alumina formulation for use on stainless steel. In general-purpose applications, try out aluminum-oxide discs, which meet most finish criteria.
Test a few AVOS (Allows View of Surface) fiber discs that have holes to allow viewing of surfaces while grinding. With this product, the operator holds the grinder at a 5° to 15° angle. These angles provide a large cutting surface of the disc, permit aggressive cuts for heavy stock removal, and yield a smooth surface with little gouging. Besides precise grinding, these discs also offer cool cutting and an airflow that pulls away loose, disc-clogging abrasive and swarf, thus extending disc life over conventional products.
Heavy stock removal
For heavy stock removal, including weld grinding and pipe beveling and repair, pick depressed-center grinding wheels. Welders may find the depressed-center wheel with a combination of ceramic-alumina and zirconia-alumina abrasives of interest because they can deliver a 50% better cut rate and 9 the life expectancy of an aluminum-oxide wheel. In tests, these top-of-the-line wheels show excellent results on all grinding jobs from gray iron to exotic alloys and stainless steels.
In the mid-price, mid-performance range are wheels with a high percentage of zirconia-alumina abrasive blended with aluminum oxide. These wheels offer twice the service life of aluminum-oxide-only products and provide a good performance-to-price ratio for a lower total cost. Of course, economical aluminum-oxide depressedcenter wheels in various formulations suit a variety of applications.
In the mid-performance range, depressed-center AVOS wheels have aluminum-oxide grains formed into special patterns. These see-through wheels have a convex design (Type 29) and supply all of the benefits of the AVOS fiber discs.
To get maximum performance from a depressed-center wheel, run a grinder at the highest speed marked on the wheel and at the correct angle. Most grinding wheels and discs perform best when run at the specified angle or within a range of angles. Exceeding the maximum angle can damage the wheel or disc. Always check information supplied with a grinding product or consult the supplier's catalog or technical staff to determine the most productive and safest grinding angle for a specific product.
Blending and finishing
For blending and finishing welds in one step with medium-to-light stock removal, use coated-abrasive flap discs. These products also work well for chamfering edges, debur-ring, and cleaning.
Top-of-the-line flap discs have a ceramic-and-zirconia-alumina abrasive blend in two configurations: flat (Type 27) or conical with an angled face (Type 29). Both offer outstanding performance on stainless and carbon steels, according to tests.
Mid-performance flap discs with zirconia-alumina abrasive have as much as 30% longer service lives than aluminum-oxide products. In addition to these two configurations, manufacturers offer high-density, jumbo (thicker) models that are more robust than standard Type 27 discs and last as much as 40% longer.
Conical flap discs are intended for more aggressive grinding than flat discs, while flat flap discs are the better choice for fine finishing. High-performance zirconia-alumina flap discs, recently introduced in flat configurations, offer a combination of fast stock removal and fine finishing.
For surface preparation and cleanup, including the removal of rust and corrosion, light weld spatter, and mill scale, use strip discs and depressed-center wheels made with an open web of thick synthetic fibers and extra-coarse abrasive held together by a smear-resistant adhesive. These products conform to difficult part profiles and uneven surfaces while minimizing loading on grinders.
Last, but not least — safety first
Every worker, hobbyist, or artist who picks up a right-angle grinder should have reviewed ANSI Safety Requirement B7.1. Abrasive-products suppliers can provide a copy. These suppliers also include written safety procedures with products. Safety guidelines often appear on products and packaging immediately after a prominent "Warning" icon. Read all warnings that accompany grinding wheels and discs and comply with them.
In general, grinding-safety considerations fall into four categories:
- Using appropriate personal safety equipment.
- Matching the abrasive to the equipment and the job.
- Grinding safely.
- Maintaining both the equipment and grinding media (wheels and discs).
Mandatory use of personal-safety equipment makes sense because grinding creates metal particles and sparks, dust, and abrasive particles. If a grinding wheel breaks during use, operators may have to contend with pieces of shrapnel flying around at high speed.
Given these potential hazards, personnel using right-angle grinders need to wear face and eye protection. Use safety gloves and leather aprons along with the appropriate respiratory protection, such as a dust-control system or mask, for the material being ground. Since grinding can be noisy, wear hearing protection when noise exceeds mandated thresholds for loudness and duration.
Matching the equipment, the abrasive product, and the job entails more than simply picking up a catalog and selecting a wheel or disc listed for the appropriate application. First, select only grinding products made for use on right-angle grinders. Then be sure the product "fits" the machine in terms of size and speed, so the right size wheel runs at its recommended speed.
In addition, never alter a guard to accommodate an oversized wheel or disc. Users should also inspect every wheel before use and test run it for a minute while standing out of the plane of rotation. This test ensures the operator will not be injured if a cracked wheel breaks.
Grinding safely means that the operator understands how to correctly mount abrasive devices on a right-angle grinder. It also means that he never mounts or removes a wheel or disc without disconnecting the power to the grinder. When actually grinding, he makes sure that the guard is positioned correctly for his protection. He also checks that any spark stream from the grinder will not hit another person or flammable materials.
Maintaining grinders and grinding media averts injuries and increases productivity. Give electric grinders monthly checkups and check the rotational speed with a photo or contact tachometer after any maintenance or repair. Excess speed can cause grinding wheels to fly apart and injure operators or other workers.
To properly maintain grinding media, especially grinding wheels, store them properly when new and between uses, inspect them before each use, and treat them with care in all cases. Rough treatment can break or crack grinding wheels, making them dangerous on the job.
About the author Debbie Gaspich is the product manager for welding grinding products at Saint-Gobain Abrasives, Worcester, Mass. For more information call: (715) 795-5000, saint-gobain.com