Tag Archives: Science and Technology

From the Archives: How Do Grinding Wheels Work?

SCIENCE! and Technology Articles on Desert Diamond Industries' Blog

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.

Works Cited

“Abrasive Wheel Grinder Safety.” System Safety, Health and Environment Resource Center. Oklahoma State Regents for Higher Education, n.d. Web. 28 Aug. 2013. < http://www.okhighered.org/ssherc/newsletters/osrhe/abrasive-wheel-grinder-safety.html >.

“Grinding Wheel.” Wikipedia. Wikipedia, 9 Apr. 2013. Web. 28 Aug. 2013. < http://en.wikipedia.org/wiki/Grinding_wheel >.

“Grinding Wheel and Abrasives Basics.” Georgia Grinding Wheel. Georgia Grinding Wheel, 25 Nov. 2008. Web. 28 Aug. 2013. < http://www.georgiagrindingwheel.com/grindingwheels_basics.htm >.

“Hand and Power Tools – Hazard Recognition.”  Occupational Safety and Health Administration. Occupational Safety and Health Administration, May 1996. Web. 28 Aug. 2013. < https://www.osha.gov/doc/outreachtraining/htmlfiles/tools.html >.

“How a Grinding Wheel Works.” Flexovit Abrasive Products. Flexovit Abrasive Products. Web. 28 Aug. 2013. < http://www.flexovitabrasives.com/education/performance/how-a-grinding-wheel-works/ >.

“How Do Diamond Blades Work?” Desert Diamond Industries’ Blog. Desert Diamond Industries, 27 Aug. 2013. Web. 28 Aug. 2013. < https://desertdiamondindustries.wordpress.com/2013/08/27/how-do-diamond-blades-work/ >.

Sullivan, Joe. “Choosing The Right Grinding Wheel.” Modern Machine Shop. Gardner Business Media, 15 Dec. 2000. Web. 28 Aug. 2013. < http://www.mmsonline.com/articles/choosing-the-right-grinding-wheel >.

“Q. What’s the Difference between Abrasive Wheels and Blades and Diamond Grinders and Blades?” Desert Diamond Industries Blog. Desert Diamond Industries, 2012. Web. 28 Aug. 2013. < https://desertdiamondindustries.wordpress.com/2013/11/13/q-whats-the-difference-between-abrasive-wheels-and-blades-and-diamond-grinders-and-blades/ >.

How Do Diamond Blades Work?

SCIENCE! and Technology Articles on Desert Diamond Industries' BlogSo you have a diamond blade, it cuts stuff, and it cuts it well. That’s good enough for most people. Are you one of those rare and troublesome folk, though, who’s wondered how it works? If you are, then this article was written for you.

We’ve tackled this topic before, but we want to focus on it a bit more today. First, let’s talk about how most diamond blades work.

How Most Diamond Blades Work: Most diamond blades have cutting segments that are made up of diamond grit suspended in some kind of metal matrix or “bond”. Some of these diamonds are on the surface, but most are buried within the cutting segment’s bond.

It’s important to remember two things about these surface diamonds. First, they grind instead of cut, an important distinction that we’ll get back to in a moment. Second, they do all the cutting work on your blade. All the bond does is hold these surface diamonds in place, while the diamonds buried within the bond do, well, nothing.

Now, diamonds are one of the hardest substances on Earth (they lost the top spot in 2009 to two other materials), but even they’ll wear down and stop cutting on a diamond blade.

This is where the bond comes into play. Ideally, the bond will wear away just fast enough to shed worn surface diamonds and expose fresh, sharp diamonds buried deeper in the cutting segment. This means that you shouldn’t notice any change in your cutting speed as your blade wears down.

Problems with Most Diamond Blades: Of course, nothing happens “ideally”. Your blade bond won’t exactly match the materials that you cut. It will either be too soft or too hard.

If your bond is too soft, your blade will wear down faster than normal. This means that you’ll have to replace your blade more often, which in turn means that you’ll spend more than you should on replacement diamond blades.

If your bond is too hard, on the other hand, the surface diamonds – the diamonds that do all of your blade’s cutting – will wear down faster than the bond. This can lead to your blade “glazing over”, where the surface diamonds wear down completely before they can be shed. When this happens, your blade will cut slower and then refuse to cut.

Worn and glazed blades are both dangerous, and for similar reasons.

Soft-bonded blades can have their cutting segments “undercut” in abrasive materials, like asphalt, green concrete, and sandstone, especially if they don’t have undercut protection. Glazed blades, on the other hand, hammer the material instead of cutting it, which increases friction and overheats the welds holding the cutting segments. Undercutting and overheating can both break cutting segments off the blade, injuring or even killing the saw operator.

To avoid broken segments, you should, as a rule of thumb, choose harder bonds when cutting softer materials and softer bonds when cutting harder materials. This isn’t a perfect rule, though, and could force you to change blades whenever you change the material that you’re cutting.

Advantages of Vacuum-Brazed Blades: Vacuum-brazed blades like the Ductile Iron Safety Blade and Fire Rescue Safety Blade avoid these problems because they have their diamonds vacuum-brazed onto the surfaces of their cutting segments. None of the diamonds are buried inside a bond. Instead, they’re all on the surface, ready to cut.

This means that you don’t have to match up the bond of a vacuum-brazed blade to the hardness of your material. Vacuum-brazed blades cut almost everything, including metals, asphalt, stone, and concrete, and are more versatile than other diamond blades.

Remember, we’ll be at the Tri-State Seminar On-The-River here in beautiful Las Vegas, NV from Sept. 24 to Sept. 26! Visit us in Booth 1222 at the South Point Convention Center. See our press release for details.

Works Cited

“Our Vacuum Brazing Process Gives You a More Versatile Blade That Can Tackle Any Cutting Job.” Desert Diamond Industries Product Catalog. N.p.: n.p., n.d. 27. Print.

“Frequently Asked Questions.” Desert Diamond Industries. Desert Diamond Industries, n.d. Web. 27 Aug. 2013. < http://www.desertdiamondindustries.com/frequently-asked-questions.php >.

“Frequently Asked Questions – Why Is My Diamond Blade’s Bond Important? How Does It Affect What I Can Cut and My Cutting Speed?” Desert Diamond Industries’ Blog. Desert Diamond Industries, 12 Dec. 2012. Web. 27 Aug. 2013. < https://desertdiamondindustries.wordpress.com/2012/12/12/frequently-asked-questions-why-is-my-diamond-blades-bond-important-how-does-it-affect-what-i-can-cut-and-my-cutting-speed/ >.

“Q. My diamond blade isn’t cutting. Is it defective?” Desert Diamond Industries’ Blog. Desert Diamond Industries, 29 Nov. 2012. Web. 27 Aug. 2013. < https://desertdiamondindustries.wordpress.com/2012/11/29/q-my-diamond-blade-isnt-cutting-is-it-defective/ >.

How Do Control Joints in Concrete Work?

SCIENCE! and Technology Articles on Desert Diamond Industries' Blog
You know those long, straight grooves that you sometimes see in concrete slabs, driveways and roads? Those are called control joints. Ever wonder why they’re there? Let us enlighten you.

Why They’re There

Simply put, concrete shrinks as it hardens or cures, according to Scott Tarr and Peter Craig at Concrete Construction. There’s two reasons for this: cooling and drying.

Concrete shrinks because of a chemical reaction between the concrete mix and water that gives off heat as it cures, and anything that radiates heat will eventually cool. Concrete also loses excess water as it cures. Anything that cools or dries tends to shrink, and that applies to concrete as well as anything else.

The problem, according to Tarr and Craig, is that, as concrete cures, it shrinks before it gains enough strength to resist this shrinkage. Because of this, it cracks.

There’s not much that can be done to prevent cracking. According to the Portland Cement Association, contractors can try reinforcing the concrete with steel, but this reinforcement can actually increase random hairline cracks inthe surface. As a result, most contractors opt to control cracking by cutting control joints.

How They Work

Control joints are a brilliantly simple way to control cracking in curing concrete.

According to the U. S. Federal Highway Administration, a sufficiently deep groove weakens a concrete slab along that joint and encourages cracks to develop in and underneath it, instead of elsewhere on the slab. This groove, needless to say, is called a control joint.

The good news, according to Concrete Network, is that you can plan your joints so that they run underneath walls and carpets, where they won’t be seen. You can’t just place them anywhere, though, or cut them anytime you want.

How to Make Them

The Portland Cement Association recommends cutting control joints to produce panels that are as square as possible, with a length-to-width ratio of no more than 3:2. Concrete Network adds that joints should be set no more than two to three times in feet the slab thickness in inches. The example they give is a four-inch slab; this slab should have joints no more than eight to 12 feet apart.

The joint also has to be deep enough, otherwise it won’t encourage cracking. Joints should be at least one-quarter the thickness of the slab. For the four-inch slab above, that means control joints that are at least one inch deep.

Then there’s the timing.

You have narrow window in which to cut your control joints. They must be cut before the slab cures, typically within 12 hours after it’s been laid. However, many factors can affect concrete curing. According to the Portland Cement Association, cracking can begin within six to 12 hours in hot weather, and control joints are useless once cracking begins.

How to Make Early Entry Joints

One way to address early cracking is to cut “early entry” joints as soon as the concrete is hard enough to be walked on, usually within one to four hours of being laid. This is a relatively new development in joint cutting, according to Martin McGovern at Portland Cement Association’s Concrete Technology Today, with Soff-Cut, the first commercially-available early entry saw model, being introduced by concrete contractor Ed Chiuminatta only 35 years ago.

Early entry saws differ from other joint cutting saws in several ways:

  • Lighter: Early entry saws are typically lighter than conventional joint cutting saws.
  • Dry-cutting: Early entry blades blades are designed to cut without water, unlike other joint cutting saws.
  • Up-cutting: Early entry saws have cutting edges that move upward during operation, which helps sweep debris out of the joint.
  • Skid Plate: Some saws, like Soff-cut, have “skid plates” that prevent the joint edges from raveling during cutting.

This advantages allow early entry saws to cut joints sooner in the curing process without ruining the slab’s finish and without the necessity of a water feed or cleaning up slurry after the joints are cut.

According to Tarr and Craig, the joints are also cut when the concrete is softer, resulting in faster cuts. Early entry joints can also theoretically be shallower than conventional cuts because of how concrete shrinks when it’s very young – that is, from the surface down – although it’s still a good idea to make early entry joints as deep as conventional joints.

Several studies cited by the Federal Highway Administration found that early entry cuts are at least as good as conventional cuts. However, according to one contractor in McGovern’s article, “Sometimes the quality of the cut isn’t as good as a wet cut. If the skid plate isn’t flat, or if you get on the slab too soon, or if the blade is worn, you can get raveling.” Tarr and Craig add that the high tolerances between blade and skid plate can mean frequent replacements to minimize raveling during cuts.

Works Cited

“Be Active in Deciding Where Control Joints Will Be Placed.” Concrete Network. N.p., n.d. Web. 06 Aug. 2013. < http://www.concretenetwork.com/concrete/slabs/controljoints.htm >.

“Contraction/Control Joints.” Portland Cement Association. N.p., n.d. Web. 06 Aug. 2013. < http://www.cement.org/tech/basics_joints.asp >.

“Early-Entry Sawing of Portland Cement Concrete Pavements.” U. S. Department of Transportation Federal Highway Administration. N.p., June 2007. Web. 6 Aug. 2013. < http://www.fhwa.dot.gov/pavement/concrete/pubs/07031/07031.pdf >.

McGovern, Martin. “The Latest on Early-Entry Sawing.” Portland Cement Association. Concrete Technology Today, Nov. 2002. Web. 6 Aug. 2013. < http://www.cement.org/tech/pdfs/CT023Saw.pdf >.

Tarr, Scott, and Peter Craig. “Early-Entry Joint Sawcutting Provides Long-Term Benefits.”Concrete Construction. N.p., 5 Aug. 2008. Web. 06 Aug. 2013. < http://www.concreteconstruction.net/concrete-construction/early-entry-joint-sawcutting-provides-long-term-b_2.aspx?printerfriendly=true >.

Thanks for Helping a Firefighter Get His Google Glass!

SCIENCE! and Technology Articles on Desert Diamond Industries' BlogWe’re happy to report that firefighter Patrick Jackson met his $2,000 fundraising goal to claim a Google Glass set on Sunday! Here’s what he posted on his Google+ page after reaching his goal:

NYC here we come! Met my goal and getting #googleglass !
Super excited can’t wait to make some apps for firefighters!

We first wrote about Patrick’s fundraising campaign on Indiegogo back on June 28. He began the campaign in order to pick up a Google Glass set in New York City, which he’ll use to develop an app for firefighters. (You can read more about his app on the Android in the Fire Service blog)

We think his app is a good idea that deserves development, and we’re happy that he raised the money to make it happen. Congratulations, Patrick!

We’ll be in Booth 943 at Firehouse Expo 2013 in Baltimore, MD from July 25 to July 27! Read our press release for details.

Second Chance to Help a Firefighter Get a Set of Google Glasses

SCIENCE! and Technology Articles on Desert Diamond Industries' BlogYou may remember firefighter Patrick Jackson. We wrote before the Independence Day weekend about him trying to get a set of Google Glasses to help him develop an app for firefighters. Well, we have some good news and some bad news about that.

The good news is that his Indiegogo campaign to claim his Google Glasses has been extended to July 15!

The bad news? He’s less than halfway to his $2,000 goal.

We think Patrick’s app, which would feed important information like dispatch details, location information and hazard alerts to firefighters, is a good idea, and we think he deserves a chance to develop it. Contribute to his Indiegogo campaign today and help make this happen!

We’ll be in Booth 943 at Firehouse Expo 2013 in Baltimore, MD from July 25 to July 27! Read our press release for details.