How To Choose The Right Flap Disc For Your Project?

How to Choose the Right Flap Disc

When it comes to flap discs, there are a wide variety of discs on the market today. Let's start by understanding the various components of a flap disc so you know how to choose the right disc and flap disc manufacturers for the right task.

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Flap Disc Shape

Is stock removal your main goal, or do you want a smooth surface? Choosing the correct disc shape is the most important variable, and the shape will help you achieve your results efficiently. Flaps are almost always used on right angle grinders where they are at an angle or parallel to your work. Flaps come in two shapes: conical or flat.

Tapered flaps: When you need to remove large amounts of material in a short time, tapered flaps are your best friend. They can be used for edge processing as well as contouring applications. The flaps in a tapered flap disc are angled. As a result, these discs provide a larger surface area for cutting on horizontal surfaces.

Flat Flap Discs: While tapered discs are great for fast cutting, flat flap discs are best suited for mixed and excellent finishing. They are primarily used for flat surfaces. Flap discs have flaps that adhere to the support plate and provide stability during operation.

Flap material

Backing plate material is also an important variable to consider when selecting flaps for your application. Fiberglass, plastic and metal are the most popular backing plate materials in abrasives wholesale.

✱ Fiberglass: Strong, durable, lightweight and safe, fiberglass is the most popular material choice. Fiberglass forms a strong bond with the adhesive and will not contaminate the work surface. This board also consumes during use and absorbs vibrations well. Keep in mind that fiberglass backing is made from layers of fiberglass that are web-bonded and pressed together. With more layers and higher mesh density, the backing will be stronger and more durable - an important consideration when you check the detailed specifications of your flap discs.

✱ Plastic: Another popular backing material is plastic, with nylon being the most commonly used plastic. These backings can be trimmed, allowing longer use of the flaps, especially during mixing and finishing. Today, plastics are becoming an increasingly attractive choice due to their compliance and cost.

✱ Metal: Metal backings are the safest choice, and they are perfect when you need extra strength and solid support. Aluminum is a commonly used metal. Because metal panels are expensive, they should also be used where it makes the most sense. For example, when using baffles in concrete or stone applications, use baffles with metal for strong support and better performance. The metal is not consumed during use, but when the flap disc exceeds its useful life, the metal plate can be easily recycled.

Abrasive Flap Density

What does abrasive flap density mean? Think of density as the total amount of abrasive area provided by the flaps on the flap disc. This area depends on the number of flaps on the disc, their angle relative to the center of the disc, and the spacing between them. Remember that each variable affects the amount of disk area available for work.

✱ Standard Density: Standard density flaps are the best choice for fast cutting and heavy-duty applications.

✱ High Density: High density flaps are best for handling curved or uneven work, and finishing processes. Don't take the description of flap density at face value. Consider the number, angle and spacing of the flaps to distinguish between the two discs, both of which can be designated as "standard density flaps" or "high density flaps".

Abrasive Grain Materials

Flaps can be used for a variety of applications, whether metal or woodworking, concrete grinding or finishing, stone smoothing or finishing, painting or rust removal, etc. To get the most out of flaps, it is important to choose the right abrasive for your specific job requirements. Let's take a look at the most commonly used types of abrasives.

✱ Ceramic Aluminum Oxide: This material is ideal for stainless steel or alloy metal applications. With ceramic alumina, the grit material breaks down at a microscopic level during operation. This produces a continuous supply of sharp cutting surfaces. As a result, it allows for faster cutting while allowing the use of whole grains. Since the entire grain is used up during the cutting process, these discs offer higher durability.

✱ Zirconia Alumina: This is a mixture of zirconia and alumina grains that is ideal for carbon and mild steel applications. Zirconia alumina costs less than ceramic alumina, and it offers excellent cost reduction rates.

✱ Alumina: This is the original grit material used when flap discs were first introduced in the s. It was also the lowest cost option. Today, it is recommended for smaller jobs that produce a lower value product.

If you have been using grinding wheels, you are probably familiar with grit size. Grit size is the ultimate variable that you must choose based on the end goal and what you want to achieve. For cutting or general grinding, use an abrasive with a lower grit. On the other hand, if you want a smooth surface finish, use a higher grit.

Flap Disc Uses

Flap discs were initially popular for use with metals, especially in welding abrasives applications. Today, various flap discs can be used for different surfaces.

✱ Flaps for aluminum: Compared to other metals, aluminum has a lower melting temperature and melts easily. This causes the aluminum material to cover the flap disc during the grinding process, covering the grit and exposing only a small amount of aluminum. When cutting, use a T29 tapered disc at a 15 degree angle to provide maximum surface contact. If you need to surface clean or provide a smooth finish, use a T27 flat disc parallel to your work area. For best results, use light and even pressure to optimize the grinding process and reduce the load.

✱ Flaps for wood: Flaps are excellent tools for treating wood. Flaps designed for wood are similar in nature to flaps designed for metal. You can use aluminum oxide grit for wood applications. For wood, you should also use the flap disc on an angle grinder, just as you would with an abrasive wheel. To avoid deep scratches, start with a heavy grit and work your way up to a lighter grit (100+) for the final polish. For wood sanding, use grit sizes 120, 150, 180 and 220 for a furniture grade finish.

✱ Baffles for paint removal: Do you have rusty metal objects that you know you can still extend the life of? Do you have old, chipped paint on your car that needs to be removed to give it a fresh look? Flap discs, especially non-woven discs, are the ideal tool for removing paint and rust. Non-woven flap disc or flap with aluminum oxide can be used for paint or rust removal applications. Like regular flap discs, these discs can be ground and finished in one operation while providing a smooth and controlled grind.

✱ Flaps for concrete: You need silicon carbide or diamond flaps to make strong cuts in concrete. Silicon carbide and diamond are among the hardest materials in the world. Using these discs will allow you to work on concrete surfaces without high pressure. These Flap Discs have a rigid backing and can also be used on other surfaces such as engineered stone, granite, marble and ceramics.

Getting Started with Your Flap Discs

Before starting to use any store tool, you should always make sure that you

1. Know your tool

2. Read the user manual

3. Wear appropriate safety equipment

4. Ensure a safe working area

5. Know what you are using the tool for

With a flip-flop, you need to consider the size and scope of the project. Do you have to aggressively remove inventory, or are you successfully accomplishing your goals? Or do you want to grind somewhere in between? Whatever your answer, there is a flap disc for your situation.

Don't limit flap discs to plain metal. Flaps can also be used on a variety of surfaces, including aluminum, wood, concrete, engineered stone, granite, and more. For each of these applications, whether you are grinding or finishing, be sure to select the correct flap disc. Remember, tapered flap discs are great for cutting and flat flap discs are best for finishing.

The flap disc backing material is important because it provides support during operation. Use metal backing for concrete or manufactured stone, and fiberglass or plastic backing for most metal or wood work. Also consider your abrasive grit material and choose your grit size to get the desired results. For general grinding, use a lower grit size abrasive. For a smooth finish, use a higher grit size.

Using a flap instead of a conventional tool can greatly improve the quality of your work. You can also benefit from lower noise and vibration. Flap Discs can take you into a world of new applications while helping you achieve higher levels of efficiency and effectiveness.

Buy your Flap Discs

You have many choices when it comes to purchasing Flap Discs. However, a reputable company that cares about you and your projects will help you get better results. You should also feel comfortable asking for samples when you try new tools.

Changzhou RMN Abrasives Co., Ltd. has a wide variety of tools, accessories and supplies to meet your current needs and future needs. If you have any questions, our team can guide you to the right tool for your specific job. Contact us today to get started!

When choosing among coated-abrasive flap discs to remove metal and finish parts, grit size is just the beginning.

When it comes to abrasive tools, one is causing a bit of a flap. The flap disc category has been the fastest growing one in metal fabrication over the last decade, according to David Long, director, marketing and strategy for Norton Abrasives North America, Worcester, Mass. “From a product performance standpoint, flap discs offer fast stock removal and provide grinding, blending and finishing with one product,” he said.

For example, a right-angle grinder (a hand-held machine with handles 90° apart) might use a type-27, depressed-center grinding wheel to clean a weld and then change to a bonded-abrasive fiber disc for finishing. A flap disc, however, can be employed on a right-angle grinder for both operations. 

Courtesy of Superior Abrasives

Superior Abrasives offer a full line of flap discs, such as these ceramic alumina ones.

Courtesy of Coated Abrasive Fabricators Association

A typical coated abrasive has a backing (cotton, polyester, poly-cotton or paper); base coat (hide glue, urea resin or phenolic resin); size coat, which is the top layer of a coated abrasive (also made from hide glue, urea resin or phenolic resin); and top size with a grinding aid, such as a stearate, to reduce friction and heat.

Flap discs are also used for a variety of other applications, such as cleaning flash from molds and castings, removing rust, edge grinding, deburring and weld-seam blending. Flap discs are constructed with cloth coated-abrasive material, cut into squares and glued onto a backing plate.

Coated abrasives provide better grain protrusion than bonded abrasives. That’s because electrostatic coating is the most common method of applying abrasive onto the backing, according to a white paper from the Unified Abrasive Manufacturers’ Association. With that method, the abrasive is placed on a grain conveyor belt, which brings the grits into an electrostatic field at the same time the backing passes through the field, above the abrasive. As the grains pick up an electrostatic charge, they are propelled away from the belt and onto the adhesive-coated backing. The process leaves the grains standing upright, perpendicular to the backing, with the sharper ends of the grains pointing up and away from the backing (see illustration below).

Step It Down

Even when a user only applies fiber discs, the application might require several grit sizes employed in a “step-down” method. That involves, for example, starting with a 24-grit fiber disc, switching to a 36 grit and then a 50 grit and so on until the desired finish is imparted. “What you’re doing is removing the scratch patterns left by the previous disc with a finer and finer disc,” said Shane Miller, executive vice president of Superior Abrasives Inc., Dayton, Ohio. “When it comes to a flap disc, you can skip a couple grains sizes because you can take a 60 grit and get it to finesse like it’s an 80 grit or a 120 grit by adjusting the pressure and allowing the grains and the backing to break down.”

Although a flap disc can reduce the number of products needed for an operation, James Norman, marketing manager for metal fabrication at 3M, Abrasive Systems Div., St. Paul, Minn., emphasized that flap discs, fiber discs and grinding wheels are three distinct product categories. Users primarily buy a flap disc when imparting a fine surface finish is the main goal, whereas a fiber disc provides a fast cut to quickly produce parts, and long life is the main attraction for a wheel, he added.

Lyle Rawlins, general manager of Pacific Abrasive Supply Co. (PASCO), Buena Park, Calif., concurred that flap discs are the product of choice when a fine finish is required. “I was just amazed the first time I ran a flap disc to see the finish,” he said, attributing the result to the cushioning effect provided by the layers of individual abrasive segments. “Even a coarse grit will give you a finish you won’t believe.”

In addition to imparting a fine finish and reducing the number of operations, a flap disc aids the operator of the right-angle grinder. “Ergonomically, a flap disc is a much more comfortable tool to use because you don’t get a lot of the bouncing that you get with a depressed-center wheel,” Long said.

Courtesy of Norton Abrasives

A flat, or type 27, flap disc (top) is for blending and smoothing flat surfaces while a conical, or type 29, shape is best when speed and heavy stock removal are the primary considerations and when working on contours and edges.

He added that, compared to depressed-center wheels, flap discs weigh less, are easier to control and require less downtime for tool changes, especially when equipped with a ⅝-11 threaded, quick-change attachment instead of the standard ⅞" center hole. Less vibration and resulting fatigue, as well as reduced noise, also benefit operators, according to Long.

Contact us to discuss your requirements of Abrasive Flap Disc For Sale. Our experienced sales team can help you identify the options that best suit your needs.

With the benefits flap discs provide, it’s important to know how to select the right one by understanding the variables and how they apply to a metal fabrication application. Those variables include disc size, shape, backing plate material, abrasive flap densities, type of abrasive grit and grit size.

Size and Shape

Flap discs are typically available in 4 ", 4½ ", 5 " and 7 " sizes. To reduce weight of the right-angle grinder and therefore operator fatigue, Rawlins recommends a 4½ " disc even though it has a slower metal-removal rate than larger ones. Smaller discs also generally cost less, he added.

End users apparently agree, as 4½ " discs are the most popular, representing about half of all sales, Long noted, followed by 7 " discs. In Canada, however, 5 " right-angle grinding machines are popular.

Courtesy of Coated Abrasive Fabricators Association

Electrostatic coating is the most widely used process for applying abrasive onto the backing of coated-abrasive products. The process leaves the abrasive grains standing upright, perpendicular to the backing, with the sharper ends of the grains pointing up and away from the backing.

Standard flap discs are available in two shapes: conical (type 29) and flat (type 27). Long recommends the flat shape for blending and finishing flat surfaces with a 60-grit abrasive or finer. The conical shape features 15° to 25° angled flaps and is for aggressively grinding contours and edges because the angle increases surface contact. Conical is the best choice when speed and stock removal are the primary considerations, he noted.

Superior Abrasives’ Miller added that the conical shape is also more effective for beveling and weld grinding. “If you need to bear down and get rid of material, a type-29 disc will work the best,” he said, noting that the two types cover about 90 percent of the market.

As previously noted, operator comfort plays a role, and conical flap discs reduce stress on the back and arms, according to Rawlins.

Back It Up

Another consideration when selecting a flap disc is the type of backing plate, which the abrasive flaps adhere to. The plate provides stability during use. 

There are three basic backing material types: fiberglass, plastic and metal—typically aluminum. “Fiberglass tends to be the most common,” said Erik Vanstrum, technical service manager for 3M. “Metal is for extreme applications.”

Courtesy of 3M

A giant flap disc (top) is for working on uneven or curved surfaces whereas a standard-density flap disc is for rapid stock removal.

Fiberglass is the most popular backing plate material because of its high strength and light weight, according to Long. Fiberglass backing plates help absorb vibration and can be consumed during operation without smearing the workpiece, he added. “The fiberglass will erode with the flaps as you grind at a 15° to 20° angle,” he said, “but if you flatten the disc and take it to a 5° angle or less, then the fiberglass won’t necessarily erode as easily.”

According to Long, plastic backing plates are becoming more popular because they provide some conformability and, unlike other available material types, are “trimmable.” Being trimmable allows more use of the flaps, especially when blending and finishing. (To view a Norton video about how to trim plastic backing plates, visit hpmvideo.saint-gobain.com/wsi-ab-sga-na/video/trimmable_backing.MPG.) “In many cases, you trim the backing plate of a flap disc so you can expose the leading edge of the disc,” Long said.

Metal backing plates are the third choice and the least popular, according to Long. They are for applications that demand extra-high strength and rigid support. Although not consumed during use, an aluminum plate can be recycled, he added.

Although a metal plate can scratch the workpiece, this product line has its following. “Some people are traditionalist and like that metal hub because they feel it adds rigidity,” Miller said. “We like the fiberglass backing. It gives great support and strength and is cost-effective while not scratching the work surface.” Plastic also doesn’t scratch during use.

Regardless of the backing plate material, Norman noted that the flaps are designed to wear down to the plate.

Density and Grit

The quantity, angle and spacing of the flaps on the backing plate can vary substantially, which is referred to as flap density. The basic densities are standard and high. The standard density is for heavy-duty applications and rapid stock removal, and the high density is for abrading uneven and curved surfaces, as well as for blending with finer grits, Long explained. “A high-density disc gives you a bit more flexibility for doing slight contours and radius work,” he said. “The higher the disc is stacked, the more cushioning or compression you have.”

Norman noted that high-density, or giant, discs also last longer because 3M’s giant flap discs, for example, contain up to 25 percent more abrasive material than standard discs.

Manufacturers offer flap discs with a host of abrasive grits, including silicon carbide, diamond, garnet, emery, chrome oxide and crocus. For metalworking, three grits are effective: aluminum oxide, zirconia alumina, or alumina zirconia, and ceramic alumina.

Courtesy of Norton Abrasives

Three types of abrasive grains are suitable for metalworking: aluminum oxide (left), zirconia alumina (middle) and ceramic alumina.

Al2O3 is generally the low-price alternative, Vanstrum said. However, he added, zirconia is the most common mineral, so it seems to be the lowest cost option, and alumina-zirconia grits self-sharpen to provide longer life than Al2O3 grits, which “dull out.”

Metalworking abrasives microfracture to self-sharpen during operation, but Al2O3 grains expose rounder edges as they wear compared to the other two types, according to Vanstrum.

Al2O3 is suitable for low-alloy steels, carbon steels and general-purpose grinding.

Zirconia alumina provides a good cut-rate-to-cost ratio and is effective on high-alloy steels and high-tensile materials. Zirconia alumina is also effective for stainless steel, Miller noted. “It helps to decrease discoloration of the workpiece and provides an excellent cut rate.”

Rawlins pointed out that PASCO sells more zirconia-alumina discs than it does Al2O3 discs. “Our cost is the same, so you might as well get the zirconia because you’re going to get a little longer life,” he said.

The best of the three metalworking abrasives is ceramic alumina because it cuts twice as fast and lasts up to 10 times as long, according to Long. That’s because the grain microfractures to allow a continuous supply of the sharpest cutting edges, providing the best utilization of the entire grain for longest life, especially on stainless and high-alloy steels.

The abrasive grains for metalworking often have a grinding aid applied. This enables them to run cooler and add lubricity to help minimize disc loading. 

A typical grinding aid is cryolite, according to Miller. “Just like any cutting tool, heat is the enemy and dulls a cutting edge,” he said. “The longer you can keep that edge cooler, the more aggressive and sharper it will be. In abrasives, you want the edge to eventually break or fracture once it begins to dull. This creates a new, sharp contact point.”

Vanstrum noted that grinding aids are particularly effective when finishing 300 series stainless steel and nickel-base alloys. “Grinding aids are lubricants and they react with the metal, so they help make better metal chips for more efficient grinding,” he said.

Although grinding aids help minimize disc loading, Miller explained that aluminum has a high tendency to load and there isn’t a lot a user can do other than knock the loading off. “It just loads by the nature of the beast,” he said, adding that Al2O3 is a good abrasive for aluminum because it’s cost-effective.

When loading is an issue, Vanstrum recommends applying a lubricant, such as Accu-Lube from ITW Rocol. Lubrication options include a wax applied to a disc while it is moving or stationary and a liquid in which a small quantity is sprayed at the disc/workpiece interface.

The Nitty Gritty

Grit size is the final component an end user must select to match a flap disc to an application. The standard range is from 24 to 120 grit. “Eighty grit is the most popular size we carry,” said PASCO’s Rawlins.

When performing heavy metal removal, selecting too coarse a grit can cause shelling, cautioned Norman of 3M, which offers abrasive as coarse as 36 grit. “Shelling means the grit is just falling off the edge of the flap before you’ve actually broken it down and got full usage of it,” he said. “Sometimes customers find longer life with a 40 grit than a 36 grit because it has better mineral retention.”

Courtesy of Norton Abrasives

Operators can select how coarse or fine the grit is based on the flap disc application.

At the other end of the spectrum, users seeking an abrasive finer than 120 grit to remove, for instance, a coating without damaging the underlying metal surface, probably require a duplex flap disc. That type of disc contains nonwoven, surface-conditioning material blended with traditional coated material. Miller noted that Superior Abrasives recently introduced duplex flap discs that are as fine as 180 grit. “In one fell swoop, you can remove a weld on stainless and produce a No. 4 finish very easily,” he said.

Long pointed out that a flap disc with nonwoven material can impart a finish finer than 10 rms, but hand-held operations using right-angle grinders generally don’t require that fine a finish. “That’s why, at this point in time, we think nonwoven hasn’t increased in popularity,” he said.

Once users understand the variables for selecting the correct flap disc for an application, they will be able to realize the tool’s effectiveness. “If you have not tried flap discs yet, I recommend you do so as they are a versatile solution to most metal fabrication applications,” Long said. “Be sure to consult your sales representative to help understand their total line to provide you with the best grinding, blending and finishing solution.” CTE

About the Author: Alan Richter is editor of CTE. He joined the publication in . Contact him at (847) 714- or [ protected].

Contributors

Norton Abrasives North America 
(508) 795-
www.nortonindustrial.com/metalfab/muscle.aspx

Pacific Abrasive Supply Co.
(800) 755-
www.pacificabrasive.com

Superior Abrasives Inc. 
(937) 278-
www.superiorabrasives.com

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