In any metal grinding or finishing application, it is important to have the correct product for the job — it minimizes the risk of removing too much material and reduces the time and cost for the process. When working with thinner materials, flap discs are often a good choice. Flap discs offer reliable grinding action, while also allowing for more delicate blending and finishing work.
Flap discs are constructed with the same grain types as found in bonded abrasives, but their layered construction gives them a much softer, more forgiving feel. As a result, they are ideal for grinding and finishing a product — at the same time — which helps save time and money. They do not, however, work as well for finishing rougher surfaces that require more aggressive action, such as a material with torch slag. A grinding disc is better suited here, as the flap disc’s cloth can catch and/or tear too easily.
These discs feature coated abrasives that adhere grains to a backing cloth, typically a cotton, polyester or blended material. This abrasive cloth is then cut into smaller flaps and layered radially to form the flap disc.
How a flap disc performs is largely related to the abrasive material used and the grit size. There are three primary cutting grains used: aluminum oxide, zirconia alumina and ceramic alumina.
The flaps wear away as the grains deplete, which exposes fresh and sharp grains below. When used properly, a flap disc can essentially be used until the cloth is almost completely worn down to the back plate.
In general, flap discs are designed for use on right-angle grinders at angles from 5 to 35 degrees. A Type 27 flap disc is best for finishing and applications that require lower grinding angles ranging from 5 to 15 degrees. A Type 29 flap disc is best for more aggressive, higher-angle grinding, between 15 and 35 degrees.
Choosing the best flap disc for the job and maximizing its effectiveness and longevity can be confusing. Before making your final selection, consider these three main factors: 1) the surface finish requirements and desired aesthetics, 2) the time, productivity and efficiency requirements and 3) the labor and consumable costs involved.
Selecting the best grain and disc size
It is important to choose a grain that is appropriate for the metal being cut and a grit appropriate for the application. Considering the objectives and priorities for the finished weld is key to making the right choice. Generally speaking, to ensure the best possible finish, choose the highest grit possible that gets the job done.
In addition to standard-density flap discs, there are also high-density — or jumbo — flap discs. These flap discs have more cloth on them, which makes them thicker, softer and longer lasting. High-density flap discs are the best choice for grinding on curved or irregular surfaces.
Flap discs are made in different sizes, too, ranging from 2 to 7 inches. A 2-inch disc can essentially replace a blending disc and gives an operator up to 15 times the use. Reducing the number of product changeovers can have an immediate and dramatic effect and significantly lower the overall cost of use.
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Pictures would be awesome on an article like this- finishing is one of the most important and yet poorly understood, (and under-budgeted) aspects of machining. More detailed articles on finishing and proper use of all the varied abrasive formats would be great!
23Thank you for your feedback, Brian. We will certainly look into it for future content.
24Very well explained !! thank you so much for the knowledge about flap disc and techniques.
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