Flap discs are essential abrasives for metal fabrication and are often the go-to choice for a wide variety of applications.
In any grinding application, selecting the right product is critically important to the success of the process, this definitive guide examines all-things flap discs to help you choose the right product for whatever challenge comes your way.
What is a flap disc?
A flap disc is an abrasive product found in the coated abrasive family.
The discs are made up of many layered, overlapping sections of abrasive material or ‘flaps’ (hence the name).
These flaps are formed of a polycotton or polyester backing material to which abrasive grains are adhered, these are then layered and bonded to a backing plate).
The backing plate provides stability to the flap disc and imparts its own unique properties to the product.
Backing plates for flap discs are typically made of following materials:
This type of backing material gives the flap disc some degree of flexibility, which helps reduce the level of vibration generated, making it a good choice for uneven surfaces.
In addition, some plastic backing plates are readily trimmable and (in the case of Norton EasyTrim) can be colour coded for ease of identification.
You can read more about EasyTrim here.
Strong, rigid and lightweight, fibreglass is the most commonly used material for a backup plate for a flap disc.
Its rigidity and vibration absorbing properties help the operator maintain greater control over their process.
Leading products from the Norton abrasives portfolio such as Vulcan, Quantum, NorZon flap discs all use a fibreglass backing plate.
The flaps gradually wear away as the grain diminishes during use, exposing a new layer of abrasive grains.
Its effectiveness will of course decrease over time and use but a flap disc can actually be used until the cloth is practically down to the resin.
What are the different flap disc shapes?
Conical shaped flap discs
Conical flap discs are the best choice for removing stock in a short space of time.
The conical shape is perfect for working on the edge of the flaps, the small area of contact assists with increasing the grind pressure which in turn improves the material removal rate.
Conical discs are shaped at the perfect angle so the chance of hitting your workpiece and damaging it with the angel grinder M14 hub is also reduced.
Flat shaped flap discs
Conversely, when comes to operations that require a lower grinding pressure and more control, you should opt for a flat shaped flap disc.
This is the ideal shape for blending and finishing on flat surfaces and outer edges.
Care must be taken as the M14 grinder hub often protrudes further than the disc, increasing the possibility of hitting your component with it.
Flap Disc Abrasive Grits
Ceramic grains have a unique microcrystalline structure that is highly friable at high pressure and therefore is said to be self-sharpening.
Newly exposed sharp edges are continually exposed to the surface of the workpiece – making ceramic grained abrasives stay sharper and more effective over a long period of time.
As it does the job quicker, the heat build up in the ceramic grain is lower, therefore these abrasives tend to cut at a cooler temperature, which reduces glazing and improves their overall efficiency. Norton Quantum Flap Discs feature this abrasive grain.
Like ceramic, Zirconia Alumina has a self-sharpening characteristic, which gives it a long product life and is great for aggressive heavy grinding of metals such as carbon steel and stainless steel.
Zirconia has a larger crystalline structure and is a very tough grain with a good product life. T
hese features make it an excellent choice for high performance jobs. Norton EasyTrim Trimmable Flap Discs feature the Zirconia Alumina grain.
Generally recommended for grinding steel but it can also be used on some high tensile aluminium and bronze alloys.
Aluminium Oxide is manufactured in varying qualities and is a blocky, friable grain.
The friability of the abrasive depends on the purity and carbon content. Norton’s Vulcan R265D Flap Disc features and Aluminium Oxide Grain.
When to use a coarse gritted flap disc:
For rapid stock removal and where the final surface finish does need to be highly refined or where the customer has no regard for the finish and just wants to get the job done fast.
The coarser the grit, generally the quicker material removal rate (depending on the material) but the scratches left behind may be too deep to blend out at a later stage.
This is particularly apparent when comparing finishing processes on carbon steel and stainless steel. The temptation is to always opt for the coarser grains but this can hinder and prolong your finishing options at a later stage.
Coarse grits are also the best choice for soft such as soft steel and aluminium.
When to select a fine gritted flap disc:
Fine grits should be used when a blended and more refined finish is essential to the project. They are typically used at the latter stages of the grinding process to clean up deeper scratches imparted by the coarse grain in stock removal.
Stainless steel for instance usually requires additional surface finishing processes because of the properties that each imparts on the material.
A highly refined finish is primarily used for decorative purposes example or the number 4 finish that is chosen for its anti-fingerprint, anti-bacterial properties in commercial hand rails etc.
After initial stock removal from a coarser grained flap disc or grinding wheel, the scratch would look unsightly on a stainless steel surface.
To blend this out and deliver more refined surfaces, we would use increasingly finer grits. More about this process can be found in our article about weld removal and finishing.
Finer grits are also more effective over smaller areas of contact and better suited to harder and more brittle materials.
What are flap discs used for?
Flap discs are incredibly versatile abrasive products, available in a vast array of different abrasive grains and grit sizes designed to cater for all customer requirements.
They are the ideal choice for multiple stages and processes within metal fabrication, from stock removal to smoothing out surface imperfections and deburring.
More information on flap disc applications can be found in our latest right angle grinder solutions brochure.
Flap discs vs. grinding wheels
So why would you choose a flap disc over a grinding wheel?
Grinding wheels are a key part of our product portfolio and, like the flap disc, are highly versatile and suitable for a whole raft of metal fabrication applications.
Grinding wheels are a great choice for rapid stock removal when the surface finish isn’t such a key concern and there are not multiple steps involved proceeding the grinding.
One such example is removing a weld seam from carbon steel, as the surface as is usually just painted, there is no great requirement for a highly blended or refined finish afterwards.
In this instance, a grinding wheel such as the Norton Quantum3 presents the best value proposition. You can read more about material differences in grinding processes here.
However as great as grinding wheels are, flap discs generally have the following key advantages over them:
1. Less re-work
A flap disc will provide much more controlled stock removal. They are often lighter and cooler cutting (less glazing), which reduces the requirement for re-work.
2. Smoother finish, no gouging
In the same vein, grinding wheels are extremely aggressive and can have a tendency to gouge the surface and leave a very rough finish, particularly when in the hands of a less experienced user.
Whereas with a flap disc, the abrasive flaps are made from cloth or polyester, providing conformability to the disc, which reduces the possibility of damaging the workpiece whilst removing material effectively.
3. Fewer vibrations
As the flap disc is less rigid and has far more flexibility than its grinding wheel counterpart, fewer vibrations are generated when grinding. Not only does this make for a drastically more comfortable experience for the operator but it is also significantly less noisy.
For more information about flap discs please do get in touch via the online web form.