What type of flap disc is best for grinding metal?

Flap discs are generally the best abrasive wheel for fast stock removal and provide grinding, blending and finishing with one product. Designed for both mild and stainless steel, flap wheels made from zirconia (or zirconium) abrasive ribbon (blue / green in colour) are ideal for use on most metals including stainless steel. Other flap discs on the market made from using aluminium oxide abrasive ribbon are not suitable for use on stainless steel.

Why are Flap Discs so Effective?
The design of a flap disc is critical to its effectiveness in removing material efficiently. The abrasive grain must be attached in such a way as it holds to the fabric for as long as possible – facilitating the effective removal of the material being worked on, but when that section of abrasive grain is depleted, it falls away cleanly exposing the fresh new abrasive material on the underlying flap to start working on the surface at hand.

Flap discs are designed to allow the backing on the outer edge of the wheel to wear away as the abrasive grain on that area of the product becomes used. This causes new grain to be exposed and is what gives the wheel the characteristic of providing a more consistent finish and uniform cut rate than other types of conventional abrasives.

Flap discs also feature cooler cutting with less gouging and burning than bonded abrasives such as grinding discs. Another key design aspect of a well-engineered flap disc is the backing plate needs to stop approximately 5mm short of the outer edge – allowing the flaps to extend past. This provides two important advantages. Firstly it allows for a thinner / finer edge to the tool allowing the user to access tight spaces if required. Secondly, it offers the user an element of flexibility to allow for finer blending allowing for smoother finishes to the job.

Types of Flap Discs
The flaps on a flap disc can be applied to the work at an angle or flat. The shape of the flap disc, whether conical / depressed centre (Type 29) or flat (Type 27), provides different performance features. The conical Type 29 disc has a slight bevel angle down and away from the centre of the disc and is best for speed and aggressive stock removal – at a comfortable angle for the user, whilst the flat Type 27 is ideal for blending and finishing.

Best Flap Disc Abrasive Grain
Probably the most important criteria are the type of abrasive on the flap and the appropriate grit size. For metalworking, there are three primary abrasive types:

1. Aluminium oxide —This grain is not long lasting and is recommended for smaller projects where a consistent, low-cost product is needed. This grain is best for alloy steel and low-alloy steel – these discs cannot be used on stainless steel because they contain Iron (Fe).

2. Zirconia — Zirconia provides a very good cut rate-to-cost ratio. This grain is best for high-alloy, stainless steel, and heat-treated steel; high-tensile, non-ferrous metals. This is the most popular grain for metalworkers and DIY users.

3. Ceramic —Although expensive, this grain provides the fastest cut as well as the best utilization of the entire grain for the longest life, especially on stainless or high-alloy materials

Others include Silicon Carbide, also called carborundum, this grain is best for marble, stone, glass, and non-ferrous metals. Scotch-brite—Scotch brite is not used for grinding or sanding. This material is perfect for surface conditioning and polishing on all metal.

Best Flap Disc Grit
As displayed on the below chart, there are around 5 grits ranging between 24 grit and 120 grit. Your selection of grit will depend on the work you need to complete. 24 Grit: Rough stock removal 40 Grit: Aggressive grinding and weld removal (very popular) 60 Grit: When medium grinding and finishing are required in one step 80 Grit: Light grinding with more emphasis on finishing 120 Grit: Extra fine surface finishing

Where You Can Buy The Best Flap Discs?
If you are searching for the best abrasive wheel for grinding and finishing all types of steel, then zirconia (zirconium) flap discs are a popular and proven wheel, to complete the job quickly within a reasonable cost basis.

Smith & ARROW Abrasives offers a full range of 40, 60, 80, 120 grit zirconia and scotch-brite flap discs. We stock these abrasive sandpaper discs in 2” 50mm, 4” 100mm, 4.5” 115mm, 5” 125mm, 7” 180mm to suit roloc tools and angle grinders.

Listen to your grinder - When the grinder is working properly it should provide a consistent pitch. If you hear the grinder dip and start making a lower noise this indicates the machine is being overworked and you are applying too much pressure. If the pitch goes higher, the abrasive disc may be bouncing along the metal ridges and you will need to apply more pressure.

Link to Hengxuan Abrasive

For more information, please visit 125 mm flap discs.

Consistency is key - Try to apply the same pressure moving forward and backwards. You may naturally apply more pressure moving forward than backward. This can make things even worse as you will overwork and overheat the disc moving forward (you will notice the edging turning orange as the grains glaze over), and the disc will bounce off the metal on the way back. This will be a very inefficient process as not much metal will be removed with each motion.

For more depressed center grinding wheelinformation, please contact us. We will provide professional answers.