Flap Discs For Aluminum, Selection and their Use in Welding

By Bill Byers / April 23, 2019
Flap Discs For Aluminum Title Image

Three Reasons to Select a Specialist Flap Discs for Aluminum;

1. Because flap discs are kinder for grinding on your soft Aluminum without removing to much material.

2. Use to clean and prepare your Aluminum for welding without contamination of your Aluminum surface.

3. To keep your Aluminum cool while grinding without clogging up your flap disc.

​First a Bit about Aluminum

If you're not used to working with Aluminum you may not realize some things. Along with being an attractive lightweight metal, it is a soft metal and Aluminum has a lower melting point than steel.

Why is It Matter that Aluminum is Soft?

It matters because it is easy to heat up the surface, burn though when welding and ruin your Aluminum. Which means that the metal's inherent properties need to be borne in mind whenever you handle and work with Aluminum.

And this includes preparing and finishing off your welding using any kind of abrasive materials including flap discs.

Dirt On Aluminum

Dirt On Aluminum

​Why Use a Flap Disc On Aluminum?

One of the biggest problems with welding Aluminum is that it is not clean enough.

And it's easy to think it is clean, because you may not have obvious surface marks. But if your Aluminum has been sitting around for a while it will have Aluminum Oxide formed on the surface from Aluminum's reaction with air.

That layer of Aluminum Oxide will cause your welding arc to stutter and start and is a possible source of porosity in your weld.

The best welds on Aluminum are made when the Aluminum is clean.

Flap discs are used because flap discs are kinder to the soft Aluminum metal and they remove less material.

And because Aluminum tends to come in thinner gauges and you'll want to use something that removes only as much metal as is needed.

Is it Best to Use a Flap Disc Designed for Aluminum?

Yes.

Because ordinary flap discs such as the cheaper flap discs with Aluminum Oxide surfaces are not designed for use on Aluminum.

When you use those flap discs they will run hot on the metal's surface, melting the Aluminum. The flap disc scrapes the soft Aluminum, transferring bits of Aluminum onto the surface of the flap disc, clogging it up.

Incompatible flap discs can scorch the metal, heat up your flap disc till that eventually fails, resulting in the flap disc flying apart. Not the safest thing to happen in your workshop.

Zirconia and Zirconia-Alumina are better but again if not designed for Aluminum you may well find that they scratch your Aluminum surface removing too much material and clog up your flap discs just like the Aluminum Oxide ones.

They also may contain too high a percentage of iron in their construction.

Why is it Important To Use A Flap Disc Designed for Aluminum?

For two main reasons:

1. Because you are dealing with a soft metal it is far too easy to have iron particles imbedded into your Aluminum. They then act as a source of rust creation both within your weld and on the surface of your Aluminum.

2. The second reason is that iron particles are an issue to weld through. Your Aluminum filler metal and the electrical arc of your welder are going to struggle.

Enduro Flex 2 in 1 Turbo

​An Example of a Flap Disc Designed for Aluminum

​Benefits of Using Flap Discs Designed For Aluminum

A flap disc for Aluminum will have a surface designed to stay cooler as the flap disc rotates.

Lowering the risk of scorching your metal.

The flap disc will likely have additives, agents or resins to prevent the soft Aluminum from sticking to the flaps of the flap discs.

Or materials and blends within the flap disc material that is extremely low in or free of iron, sulfur and also chorine. Keeping the contamination of your Aluminum metal to an absolute minimum. So that when you come to weld you have nice clean Aluminum with the best surface to weld with.

Flap Discs Use When Arc Welding Aluminum

1. Before You Weld to Smooth

Edges of your Aluminum uneven, jagged or even burred?

Then a flap disc used to smooth out the edge in preparation before you weld is a good idea. As Aluminum is a soft metal and you'll need to move at a good pace while arc welding to prevent burn through of your metal. The smoother the edge of the joint, the better.

2. Before You Weld to Clean

It's well known that clean Aluminum should be the basis before you start to weld. Even if your Aluminum looks good the betting is that it has a layer of Aluminum Oxide on the metal. Aluminum Oxide is a form of contamination on the Aluminum. It will affect the arc start of your MIG​ or TIG weld. Flap discs can be used to clean off any dirt and Aluminum Oxide before you weld.

3. Before Your Next Aluminum Weld Pass

When you have a joint that is going to take a few weld passes to fill up you may not think you need to do anything before you lay the next weld bead. Run a flap disc over the bead to remove any contaminants brought to the weld surface by your Aluminum welding wire. ​And use to remove any spatter and prepare your surface for the next welding pass.

4. Finishing off With a Flap Disc on Your Aluminum

Flap discs are perfect to use for blending your weld in with the surrounding metal and remove any spatter. The aim is to leave a nice smooth finish after you have welded.

Best Practices For Flap Discs Use on Aluminum

The flap disc you choose may well be able to grind on other metals such as stainless steel, or bronze.

It is best not to share a flap disc used on Aluminum for grinding on other metals. Aluminum's inherent softness and low melting point means that it is really easy to pick up contamination. Particles of the other metals can easily scratch and become lodged in the surface of your Aluminum.

And not only that the foreign metal on the edges where you want to weld, makes it difficult to weld and cause porosity in your weld. 

Flap Disc On Aluminum

Flap Disc On Aluminum

Flap Discs Recommended for Aluminum

To help you in your search for the right flap discs to use on your Aluminum project I've put together a list of four I've researched and I think are the best.

You can click on the links to hop over to Amazon to check them out for yourself.

1. ​Enduro-Flex 2-in-1 Turbo

Cost Indication: $$$

Ceramic blend grit, type 27 flap disc, with a coated surface designed for Aluminum.

This flap disc offers more aggressive grinding when compared to the Enduro-Flex 2-in-1 which is more aimed at TIG welding work.

The Enduro-Flex 2-in-1 Turbo has its own proprietary cooling agent to prevent marking and heating up of the Aluminum surface.

Available as a 4 1/2 inch and 5 inch flap disc with a 5/8th inch arbor hole.

For weld removal, grinding, blending, deburring and finishing.

Pack of 10.

Reason to Buy

A quality and high performing flap disc for Aluminum MIG welding work.

A threaded arbor hole makes it easy to put this flap disc on without tools.

Reason Not to Buy

These flap disc are towards the high end and are expensive. Just the one blended surface available.

YouTube Video: Enduro-Flex 2-in-1 Turbo

Want to take a look at the Enduro-Flex 2-in-1 Turbo in action.  Then watch this one minute 11 second video.

​Video Credit: Walter Surface Technologies

2. Mercer Industries 337060

Cost Indication: $$

Zirconia type 29 Flap Disc

Can purchase in sizes 36, 40, 60, 80 and 120 grit.

Available in a 4 inch size with a 5/8 inch arbor hole.

A High Density flap, which means it is a thicker, softer flap disc than standard density ones. Good for soft Aluminum.

This flap disc has a resin treatment on the surface to resist the Aluminum clogging the flaps.

The surface treatment also withstands heat and moisture.

A low iron flap disc with less than 0.1% iron, sulfur and chlorine.

Pack of 10.

Reason to Buy

Is a more budget friendly flap disc for Aluminum with a reasonable quality.

Choose when you need more aggressive grinding on your Aluminum or need to weld across a large surface area and for the contours in your metal.

Reason Not To Buy

It's not the Enduro-Flex 2-in-1 Turbo but then you're not paying those prices.

3. Benchmark Abrasives for Aluminum

Cost Indication: $

Type 27 stearate coated flap disc.

Available in 36 and 60 grit.

Comes in 4 1/2 inch size with a 7/8 inch arbor hole.

These Benchmark Abrasives flap discs are made to grind on Aluminum.

The Stearate coating is designed to liquefy as the flap disc spins and is heated and so prevent clogging up of the flap discs.

Pack of 10.

Reason to Buy

Is your budget choice for grinding on Aluminum.

Works well for the money.

Reason Not to Buy

Just the 36 and 60 grit sizes and you may want finer finishing and blending.

​​Types 27 and Type 29 Flap Discs for Aluminum

There are two main types of flaps discs you can buy for grinding on Aluminum; type 27 and type 29.

Type 27 have a flatter profile. They have a small angle to them of between 5 and 15 degrees. They are gentler on Aluminum and have a less aggressive grinding action than type 29's. They are good for using on flat level metal and for getting into tight corners and angles.

Type 29 are more contoured with a higher angle on the flaps surfaces of around 15 and 35 degrees. These flap discs are more aggressive on Aluminum and are used when you have a large surface area to grind and work across quickly. And for those curved surfaces where the angled flap discs work at their best.

Flap Disc Smoothing Edge

​Grit Size Surfaces for Aluminum

Although flap discs come in 24, 40, 60, 80 and 120 grit (the lower the grit number the rougher the surface) it is likely that unless you are dealing with a lot of marking and contamination of your Aluminum it is the higher grit numbers you'll be using.

60 grit for medium grinding, surface dirt removal, deburring and beveling of edges

80 Grit for light Aluminum grinding, finishing off and blending

120 grit for fine finishing.

You may well need to get several grit sizes and use each flap disc on your grinder as you need.

Last Words

The best flap discs for Aluminum will allow you to remove impurities yet keep your Aluminum cool.

And once you have removed the worst of the dirt on your Aluminum you can go ahead and use a specialist wire brush. Use one designed for Aluminum. Check out my post all about finding the right kind.

​Be confident that the right flap disc for your Aluminum should feel like it floats over the metal's surface. The disc should remove what you want not gouge your precious Aluminum. It should prepare the metal well for your welding.

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