This article is from our archives. Let us know in the comments section if you found it helpful or interesting!
Our article on diamond blades drew a lot of interest, so we’re going to follow it up today with a discussion on grinding wheels.
Before we start talking about grinding wheels, though, we should first pin down what we mean by “grinding wheels”. After all, there’s grinding wheels, grinding stones, grinding cups, grinding points, and the list goes on. Therefore, to narrow our discussion, we’re going to confine this article to straight wheels – that is, flat grinding wheels that grind with their faces.
How Grinding Wheels Work: Grinding wheels are similar to the diamond blades that we talked about earlier. They both have some kind of hard, abrasive grit that’s usually held in some kind of bond. The grit scrapes chips out of the material that you’re grinding or cutting, while the bond wears away to shed worn grit and expose fresh, sharp grit buried deeper in the wheel or blade.
Which Grinding Wheel You Should Use: You need to consider three things when choosing a grinding wheel: abrasive, bond, and grit size.
Abrasive: You should match the abrasive in your grinding wheel to the material that you’re grinding. Here’s some of the most common abrasives:
- Aluminum Oxide: Designed for grinding carbon, stainless, and high-speed steel, malleable and wrought iron, aluminum, and bronze.
- Silicon Carbide: Designed for grinding cast, gray, and chilled iron, non-ferrous metals like soft bronze, brass, and aluminum, and non-metallic materials like concrete, brick, marble, stone, rubber, and glass.
- Zirconia Alumina: Designed for high stock removal of steel and steel alloys. Resists higher temperatures and pressures.
- Ceramic Aluminum Oxide: Designed for precision grinding of tough materials like stainless steel, titanium, and high-nickel alloys.
- Superabrasives: Extremely hard and expensive materials like diamond or cubic boron nitride. Designed for grinding very hard materials that may defeat other abrasives.
Bond: Most grinding wheels have their abrasive grit bonded either directly to a metal or rubber disc or within vitrified or organic resin bonds. However, what matters isn’t the bond itself, but its hardness.
Grinding wheel bonds are similar to diamond blade bonds: harder bonds last longer, while softer bonds grind faster and with less pressure. You can tell the hardness of your wheel’s bond by a single-letter code on the wheel, with A as the softest and Z the hardest.
Grit Size: This is a big factor in a grinding wheel’s speed and finish. Grit size works pretty much the same for grinding wheels as it does for sandpaper: larger, lower grit grinds faster and and leaves a coarser finish, while smaller, higher grit grinds slower and leaves a smoother finish.
Dangers of Grinding Wheels: Remember, grinding wheels are designed to grab onto things and scrape chips out them while spinning insanely fast, and they don’t care what they grab onto or where they throw those chips. Therefore, you should always take precautions when grinding, including:
- Wearing personal protective equipment like safety glasses and gloves.
- Making sure your grinding machine’s guards are installed and in place.
- Taking off or tying back loose clothes.
In addition, certain grinding wheels pose their own risks, including shattering and emitting hazardous silicon carbide fibers.
Shattering: Vitrified and resin grinding wheels fly apart if they’re nicked, damaged, or run at too high a speed. These accidents produce shrapnel that can injure or kill the grinder operator.
To prevent shattering, you should check these kinds of grinding wheels for cracks and large nicks before and after using them. The Oklahoma State Regents for Higher Education recommend the “ring test” – that is, lightly tapping the edge of a vitrified or resin wheel with a non-metallic object before starting it up. If you hear a dull thud instead of a metallic ping during this test, throw out the wheel and get a replacement.
You can also help prevent grinding wheel damage by:
- Carrying the grinding wheel to your grinder instead of rolling it, no matter how big it is.
- Running it within its recommended RPM.
- Grinding with only its face instead of its edge.
OSHA also recommends standing off to one side when you start up your grinder and then letting it run for a full minute, just in case your grinding wheel does shatter.
Silicon Carbide Fibers: Grinding wheels with silicon carbide abrasive pose a special hazard: emitting silicon carbide fibers during grinding that can lodge in your lungs. Long-term exposure to these fibers has been linked to increased mortality from asthma, emphysema, chronic bronchitis, pneumoconiosis, and lung cancer. We therefore recommend that you wear a respirator whenever you use or are around silicon carbide grinding wheels.
Of course, you can avoid shattering wheels and inhaling silicon carbide fibers by using a metal grinding wheel instead of a vitrified or resin one, like the Safety Blade Grinder/Cutter. The Safety Blade Grinder/Cutter is made of solid steel, so it won’t shatter or break apart under normal use. In addition, its thick coat of diamonds grinds a wide variety of materials, including iron, steel, non-ferrous metals, high-nickel alloys, welds and welding slag, concrete, asphalt, brick, block, stone, you name it.
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