How tube fabricators get the most out of flap disks

Editor’s Note: This article appeared in the September 2024 issue of Canadian Fabricating & Welding.

In the realm of surface conditioning tools, fabricators have many options available to them. In recent years and for a variety of reasons, the flap disk has moved front and center as a choice with many benefits. loram train

Flap disks are designed for right-angle grinders and provide both material removal and finishing. They also can simplify processes that require multiple tools and steps. However, not all fabricators know about the advantages of using these tools.

“Sometimes fabricators stick with what they know or follow how things have always been done,” said Steve Bell, Quebec territory sales manager for PFERD Canada, Mississauga, Ontario. “Having a certain experience and familiarity with a tool can be beneficial, but it’s important to test out other options to see what works best. Trying out a flap disk often demonstrates immediate advantages for the operator and application.”

These advantages include productivity gains, economic benefits, and improved ergonomics.

Advances in welding technology have made it possible to deposit thinner welding beads, making flap disks a suitable choice for most surface preparation applications.

“Prior to the introduction of coated abrasive flap disks, metal surface preparation has usually required the use of bonded abrasive grinding wheels for the initial material removal, followed by finishing with coated abrasive resin fiber disks to achieve the desired quality of finish,” said Jeff Hanna, national sales manager for Flexovit, Brampton, Ontario. “Flap disks are an alternative grinding and finishing product to traditional bonded abrasive grinding wheels and coated sanding disks, offering the characteristics of both the bonded and coated products in one.”

This accounts for significant time and cost savings. Not only does a flap disk eliminate the need to switch out tools, it also lasts longer than resin fiber disks because of its design. In some cases, one flap disk will do the work of several resin fiber disks, ensuring a cost advantage.

Flap disks also offer ergonomic benefits. These tools provide increased operator comfort and safety because they produce less vibration, less noise, and less dust.

However, flap disks aren’t suited for all applications.

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“Having to grind a large portion of metal, like projects in the marine or aircraft industry, a resin fiber disk that can be as large as 9 in. might be a better option,” said Frank Prenda, vice president of sales and marketing for Gemtex Abrasives, Toronto. “That 9-in. disk will cover a larger material removal area. Because of the familiarity with grinding wheels and resin fiber disks, operators often stick with the standard, but flap disks are becoming increasingly popular because of the unique benefits and wide-ranging applications that they can be used in.”

Many factors need to be considered when choosing a flap disk. Different characteristics will directly affect the efficacy and performance of this tool.

“It's in users’ best interest to do research and explore different options available,” said Bell. “Having a flap disk manufacturer come in and explain the benefits of using a new product can be helpful. It’s important to have an open-mindedness for new technology and techniques that can help elevate these tools to a higher level.”

Testing products also can be helpful to understand quality versus price. In some cases, manufacturers can recommend a specific flap disk that can achieve the user’s desired performance for the application.

“Depending on the application and the operators, manufacturers offer different categories of performance,” said Bell. “If you're in a shop doing a small job, you probably don’t need something as high performance, so there are different options to give more price flexibility.”

Shops on the hunt for a suitable flap disk should keep the following characteristics in mind.

Shape. Flap disks are available in two shapes: flat and conical.

“Flat disks, also called Type 27 disks, are preferred for flat surfaces and narrower contact area,” said Hanna.

The Type 27 disk typically grinds best at angles between 0 and 15 degrees, making them better suited for finishing and blending operations. These tools can be used for only slight contours.

“Conical, or Type 29 profile, is ideal for contoured surfaces and broader contact area,” Hanna added.

The Type 29 disk, which often has a built-in angle, allows for more aggressive stock removal.

Abrasive Grit Material. Certain abrasive grits are better suited for use on specific metals, meaning the workpiece material often will dictate the type of abrasive grit needed.

“Ceramic is the next generation of abrasive grits,” said Bell. “When working with stainless steel workpieces, ceramic is definitely the best choice.”

Hanna added that ceramic coated abrasive cloth provides faster material removal rates, cooler grinding action, and longer life. Because of its high-performance characteristics, it can be used for hard-to-grind materials.

Aluminum oxide, which is the original and standard abrasive grit material, is designed for more general-purpose applications as it offers good performance with a lower price. It is best suited for steel and cast iron.

Zirconia grit falls somewhere between aluminum oxide and ceramic grit in its ability to offer high performance and durability. It often is used for cast iron, carbon steel, structural steel, and stainless steel.

Hanna noted that some manufacturers offer flap disks specifically designed for grinding aluminum. These disks feature stearate coated abrasive strip that prevents soft aluminum from loading on the flap disk.

Grit Size. There are five common grit sizes: 36, 40, 60, 80, and 120.

The smaller the grit size number, the larger the abrasive grit, which equates to more aggressive material removal.

For heavy stock removal, 36 to 40 grit is ideal. For weld grinding and some blending, 40 to 60 grit is suggested. Deburring operations generally require 60 grit, while cleaning and finishing operations require 80 to 120 grit.

“One benefit of the flap disk is that you can make a more abrasive grit perform finishing operations depending on how you use it,” said Prenda. “An operator can use a coarse flap disk to remove a lot of material, but through a feathering procedure make this 36-grit flap disk act like a 60- or 80-grit flap disk and perform finishing operations.”

Outside of standard characteristics, flap disks offer enhancements and features that can help boost productivity and expand the range of their efficacy.

“Look at different lengths of flaps,” said Bell. “Conventional flap disks have standard-size flaps, but high-performing-type flap disks have longer flaps, which provide longer life. There also is the radial flap disk that offers three sides of working area. That means you can use the top, side, and bottom of the disk to get into angles of fillet welds.”

Improvements have been made to flap disks’ backing material as well. For example, most companies now offer fiberglass and nylon as backing materials.

“These are often available with either standard 7/8-in. arbors or 5/8-in.-11 spin-on threaded adapters,” said Hanna. “The nylon disks offer more rigidity and may be preferred where a more aggressive grinding action is required.”

While fiberglass tends to be the more standard and popular backing option, nylon and plastic backings are trimmable.

“Fiberglass-backed flap disks naturally wear down and will no longer be able to perform properly,” said Prenda. “A trimmable plastic back allows users to trim the outer diameter of the disk that is worn away, extending disk life. Not all manufacturers offer this, but it is something to consider if you have a large application or you want to extend disk life.”

Another advantage of a plastic trimmable back, according to Prenda, is that it offers a low profile, unlike a heavy-duty zinc hub in the center. The low profile allows it to fit better underneath the guard of a right-angle grinder, ensuring that the protective guard covers it entirely. In some cases, a fiberglass back with a threaded zinc hub may be bulky and protrude below the guard, minimizing the guard’s ability to protect the operator.

The trimmable plastic backing is much lighter for operators, which is especially helpful if they are using the grinder for many hours in a day.

Another area of innovation is the combination flap disk, which incorporates two different types of grit material to achieve the benefits of both.

“For example, a combination flap disk has alternating flaps of zirconia and ceramic,” said Prenda. “The alternating flaps bridge the gap between the performance of a full zirconia and full ceramic flap disk while still keeping it at a lower price point than a full ceramic flap disk. It’s another way to offer an alternative in price and quality.”

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