What Are the Right Abrasives for Your Metal Removal and Finishing Work?
How do you select the right abrasive for the job at hand? More than likely, it’s by trial and error. Learn how to select an appropriate abrasive for your application in this primer.
Abrasives are an often overlooked yet critically important tool for any machine shop. Improper weld preparation, time-consuming deburring operations, surface finishes that fail to meet drawing specifications—these are only a few of the troublesome results of using the wrong abrasive.
Yet with thousands of product options, selecting the best belt, pad, cloth or wheel for this most fundamental metal removal operation can be just as challenging as picking the right end mill or turning tool for that titanium job you did last week. And since polishing and deburring are often the last operation for many workpieces, using the wrong abrasive can be a very expensive mistake.
Use the Right Abrasive Grain for the Job
Despite the wide variety of shapes, grits, bonding agents and abrasive media types available, each can be grouped as either bonded abrasives (wheels, typically), coated abrasives (sandpaper, belts and discs) or nonwoven abrasives (hand pads, flap wheels, etc.). In addition, loose media is used in blasting cabinets and hand-held sprayers. All of these abrasives work in the same manner, using what are essentially sharp, pointy rocks to remove metal from a workpiece.
Workpiece material and geometry are key factors in deciding the type of abrasive to use. As a rule, aluminum requires a different abrasive than iron—and iron needs a different one from Inconel. How do you know if you have the right one for the job? The amount of material removal plays a role. For example, weld preparation and snagging require coarser grades, but finishing operations need finer ones. Each may call for a different bond or type of abrasive, regardless of the workpiece material.
For most parts, these “rocks” fall into one of the following categories: aluminum oxide, silicon carbide and zirconia alumina.
Aluminum Oxide
Used in everything from toothpaste to knee implants, aluminum oxide is a hard, chemically inert material that forms when aluminum interacts with oxygen. Think of it as “aluminum rust.” For abrasive use, aluminum oxide crystals, also known as corundum, are commonly available in white, pink and brown, differing primarily in hardness and purity. Aluminum oxide is one of the most commonly used abrasives, offering a cost-effective, predictable solution across a wide range of applications.
Silicon Carbide
Silicon carbide crystals are hard, thin and very sharp—in fact, the only materials harder than silicon carbide are diamond and cubic boron nitride. Unfortunately, silicon carbide’s hardness and shape make it brittle, so even though it cuts quickly, it also tends to break down a bit faster than other abrasives, especially under extreme forces. So silicon carbide abrasives are best suited for finishing operations such as graining of stainless steel or where light cutting pressures are applied.
Zirconia Alumina
Zirconia alumina is basically aluminum oxide that’s been toughened up with zirconia. This makes it among the most wear-resistant abrasives, ideal for heavy grinding operations, snagging (removing sprues and parting lines on castings) and general grinding of difficult materials. Some manufacturers have taken zirconia even further, blending it with alumina and titania (titanium dioxide) to make abrasives with the best characteristics of each.
Other Abrasives: Hybrid, Garnet, Ceramic, Superabrasives
Aluminum silicate is a mix of aluminum oxide and silicon dioxide, and it is a favorite for sandblasting. So is garnet, a naturally occurring mineral that is also the most commonly used abrasive for waterjet cutting. And ceramics are often added to these and other abrasives, enhancing their cutting properties and extending product life.
In the realm of high-performance machining, superabrasives are intended to work when grinding hardened steels or superalloys—and are used with finishing materials such as glass, ceramics and other composites. They often use diamond or CBN as the abrasive, so they are able to machine a broad spectrum of materials including ferrous and nonferrous materials.
Take Note: Abrasives Will Wear
Abrasives tend to “clog up” with use. In addition, the individual grains will wear down and grow dull. Unless steps are taken to expose fresh material, they soon become ineffective. On grinding machines, this is usually accomplished by dressing the wheel, but for virtually all other abrasives this is not an option.
Abrasive manufacturers have made great efforts to make their products “friable” or semi-friable, which means the abrasive breaks away when dull, bringing fresh material to bear. By adding ceramic to aluminum oxide, for example, a hybrid is created that is both hard and strong yet friable, making it suitable for steels and alloys that would otherwise be difficult to grind.
Workpiece material and geometry are key factors in deciding the type of abrasive to use.
6 Nuanced Tips for Working with Abrasives
Abrasive selection is complex and should not be taken lightly. Here are some key considerations when choosing one.
- Always use the finest grit grade that will get the job done. If the grit is too coarse, it will create rougher-than-desirable surface finishes; if the grit is too fine, it will increase cycle time and cut into job profitability.
- Watch out for “bargain” abrasives. They are rarely a bargain and will only lead to higher labor costs and possibly scrapped parts.
- Be consistent in the application of any abrasive. Develop a process plan that balances throughput and part quality—then stick to it.
- If you are using abrasive pads or paper, use an appropriate block or holder for more consistent results.
- Set aside time for testing any new abrasive to determine how long it should last and how much material it can remove in a given period. Document these values as part of your work instructions. Don’t be afraid to try something new.
- Pushing an abrasive too long leads to unpredictable part quality. But not pushing one long enough can lead to higher expenses when abrasives are disposed of prematurely.
So the next time you need to shine up some parts, don’t just grab whatever 80-grit paper the tool crib has handy. Instead, consult with your supplier to discuss what’s best for your application.
What kind of challenges have you faced with abrasives in your shop? Share your experience here.
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Thanks for explaining how you can dress the wheel of your grinding machine to avoid having the abrasives become ineffective. Taking the necessary steps for your equipment would be important to keep it working so that you can get the best results. When choosing a grinding machine, it could help to figure out the best way to care for it based on how you plan to use it in order to make sure it's as effective as possible.
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25I have bronze castings furniture mounts .I chased them to refine the detail as for a french furniture maker the hardware is very important. but the finish could be smoother, and cetrtain parts need alittle shaping. I have metal files , but they leave scratches. Can you please give me some advice on this .
28Hi Robert, non-woven (Scotch-Brite) wheels, discs, or hand pads will help to improve the finish of the bronze without making any dimensional changes. For the parts that need shaping, a little die grinder using carbide burrs would allow you to clean those parts up nicely. Carbide burrs have tiny cutting teeth and their cutting action is more akin to a grinding wheel than a cutting tool. Thanks for commenting!
38Sir,
I want to ceramic tiles sizing and surface grinding . Which abrasive and bond material use.Its mold presser and it's firing temp pl send me detail.
Best regards
Ratilal Patel
31Fired ceramic tile is typically ground with a fine diamond abrasive, resin bonded grinding wheel. A good place to start would be with a 320 grit diamond wheel with copious amounts of water to keep the dust in check. I don't have any information on grinding green ceramic, nor do I know about mold pressure and firing temperature. You would probably have to discuss that with a potter.
26Thank you for sharing that the type of grain is important when deciding on the grinding wheel. I like that this post emphasized that it is important to decide on what needs to be ground before choosing the grain. I will definitely heed your advice and keep this tip in mind.
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31Sir.
Here in my proceses we have to give mirror finish to stainless steel, today we are using aluminium carbide to work the surface on three grind steps from 120,240,320 Do you reccomend me to alternate diferent abrasives on the diferent steps?
31When you start getting into extremely fine finishes and fine grits, all sorts of factors come into play. What form of abrasives are you using now? Are you grinding with a belt or disc or are you using a grinding wheel? What type of machine are you using? My short answer would be that if you are getting the results you want in just three steps and a reasonable amount of time, I probably wouldn't change anything. If there is some other issue here, then we would need to look at the overall operatiion to see what might be going wrong and come up with ways to fix it.
32abrassive: aluminium oxide
method: grinding wheel
machine: bosch GWS 22-230
31You might want to try some flap discs. A zirconia alumina abrasive will be faster cutting and longer lasting that aluminum oxide but is only available as fine as 120 grit. You can get aluminum oxide to as fine as 600 grit from some manufacturers. I think you will find that the flap disc will allow you much more flexibility in finish and stock removal and give you more control over the operation.
32What abressive i use to polish titanium
24There are so many types of abrasives. Great description !! Thank you for the knowledge.
32I am trying to polish pl-130 (alumina Titania) it is a plasma sprayer coating and I'm trying to achieve a RA reading or 10 or better what is the best abrasive and or compounds to use to achieve this
31You made a good point that consistency is very important to consider when it comes to using abrasives on metal. I'm interested in looking for a good metal distributor soon because I'd like to find a reliable supplier for the materials of my new home's construction. Hopefully, I will be able to find one that's close enough to the site so that there wouldn't be many problems with it.
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28When it comes to fixing things yourself, I'm grateful for your advice to employ a professional. Thank you for sharing this helpful and engaging content with us!
32Thank you for mentioning the grain type while choosing a grinding wheel. I appreciate how this piece emphasizes deciding what to grind before choosing the grain. I will take your advice and remember this.
33Hello I have some steel parts that got painted and the painters messed up and forgot to cover some holes that were not ment get painted and the holes are in a tight space so I will be using a pencil grinder but not sure what product to use for taking paint of. The shake size I can use is 1/8 inch. Please let me know ur recommendations thank you. Also can you recommend some good ideas for grinding stones or anything for deburring stainless steel in corners that will leave a smooth finish
42What is the best sanding disc for inconel
33we need to do smooth finishing for lead (pb) pole, suggest the abrasive to have shining finishing
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