Welding is the meticulous process of fusing metals. It encompasses detailed prep and surface cleaning to remove contaminants and rust that can otherwise spoil or weaken the weld, applying heat and current to melt the metals together, and cleaning the finished joint to prevent oxidation for a more presentable look.
While different welding processes and equipment fuse metals of the same or different types, the cleaning stage often catches most newbies off guard. Slag from flux-coated electrodes and wire can be unsightly and hard to remove unless you have a decently powerful grinder and a full set of flap wheels in varying shapes and grit. The combo makes light work of heavy stock removal in thicker pieces, in grinding and deburring tasks, getting deeper chamfered or bevel cuts, and of course, getting the workpiece to a smooth and desirable finish.
Flap Wheel Basics And Uses
Flap discs are versatile tool attachments used with angle grinders. They consist of a backing plate with overlapping abrasive flaps arranged in a circular shape that gives them their name. They come in a range of abrasive materials, different shapes and densities, and in various backing plate materials. To cut confusion, they’re also known as flap or flapper wheels, and used in industries where metal fabrication is the core activity.
Welders and metal fabricators use flap wheels in stock material removal, removing rust, surface cleaning, edge grinding, deburring and finishing welds. Compared to grinding wheels, they offer higher manoeuvrability, improved control and increased precision ensuring cleaner and smoother finishes with less gouging. They also vibrate less so are more comfortable, cause less fatigue in demanding jobs and are quieter to operate. And they last longer. When one abrasive layer wears down, another takes its place, so tasks are completed with minimal downtime or the frequent need to change discs.
Choosing the Right Flap Wheel
With differences in shapes, backing plate materials and abrasive grit materials, choosing the right flap disc for the workpiece can be a daunting task. Here’s what to look for:
Backing Plate Materials
Backing plates provide stability. Go with discs with nylon or plastic plates for reduced vibrations when clearing out uneven surfaces. Choose aluminium plates for heavy stock removal and bevelling, phenolic plates where scratch resistance is important or trimmable composite plates to prevent markings and when working with tight spots due to better access.
Abrasive Grit Material
Abrasive grit materials come in a few types and determine the flap wheel’s efficiency, speed and level of finish on different metals. Choose from:
- Ceramic Alumina – with sharp edges and high grinding rates, ceramic alumina flaps are best for high stock removal. This is ideally used for stainless steel, tool steel, Inconel, titanium, nickel alloys, and other tough metals. The strength of ceramic abrasives means lower temperatures with the grinder spinning at higher RPMs to prevent heat discolouration, and high cut rates to speed up workflow.
- Zirconia Alumina – choose this self-sharpening abrasive for more aggressive stock removal and demanding edge grinding. Like ceramic alumina, it fares well against high temperatures and pressures, ensuring long use. Ideal metals are cast iron, structural and carbon steel.
- Ceramic Alumina/Zirconia Alumina blends – this pairs the benefits of both abrasive alumina types, resulting in wheels ideal for fast grinding. consistent performance and long lifespans. Use this to surface clean structural, carbon and stainless steel and for low loading, with minimal contaminants.
- Alumina Oxide – while not self-sharpening, this general-purpose abrasive is good for most steel types, as well as some aluminium and copper alloys.
Grit Sizes
Grit sizes refer to the finish flap wheels produce, ranging from fine to coarse and stated in numbers. For stock removal and a coarse finish, go with grit sizes between 36 and 40. For chamfering and general or blending grinding, choose a flap disc with a grit size between 30 and 60. To remove burrs and deflash surfaces, abrasives with a 60-grit size get the best results. And in surface cleaning and finishing tasks, the finer 80 to 120-grit sizes get the best results.
Disc Shapes and Density
Flaps are sold in flat, conical, trimmable and angled shapes. These ultimately determine what you can work on. Flat discs are ideal in operations requiring lower pressure, specifically in blending and finishing flat surfaces and outer edges. Conical discs are chosen for aggressive stock removal and working at angles between 15 and 35 degrees. Trimmable discs offer more versatility in that they increase flap overhang, making them a good choice for hard-to-reach areas, such as fillet welds and irregular shapes. Angled types consist of curved flaps on the edge of the backing plate and are good for aggressive grinding or when shaping surfaces at tighter angles.
Lastly, get a flap wheel with the right density. This determines how long it lasts. High-density discs have more abrasive cloth materials, meaning they’re thicker, easier to control and more forgiving, especially when working on irregular surfaces. Common are so-called “Type-27” discs with similar profiles to flat discs, making them ideal for sharp 0 to 15-degree angles; and “Type-29” discs, similar to conical profiles but for grinding angles between 15 and 35 degrees.
