Flap Discs For Metal, Welding Prep And Grind Your Weld

You’ve got your metal – mild steel, stainless steel or Aluminum.

And you need to get it cleaned up ready for you to weld.

Someone told you that flap discs for metal are the thing to buy. But you’re not sure why. Or even what to shop for.

Discover why, buying yourself some flap discs for your metal welding prep is key.

And why they make finishing off your welded metal so much easier.

You pick your flap disc for the metal you plan to use it on. Buy the right flap disc for your mild steel, stainless steel or Aluminum.

Choose your flap disc by shape, grit size and by surface type. Depending on the project and level of grinding you need to do.

Points To Think About Before You Choose The Flap Disc For Your Metal

What is your aim?

And why do you need to think about that?

Because the outcome you want will point you to the right flap disc to use on your metal.

1. Is This A Project That Needs To Look Great?

Are you welding on some light gauge steel to fill in that hole caused by rust?

And when you’re done you want it to look shiny and new like you never touched it.

2. Or The Finished Look Doesn’t Matter That Much?

Because, it’s a lawn mower part that’s broken off. Or some other metal part that’s out of sight.

You just need to smooth up the edges. Clean down to the metal so that you can weld it up good as new. You don’t really care how it looks. You just need a good strong weld and get the part back in doing its job.

3. Do You Have A Restricted Budget And A Small Project?

You just need to clean up the metal before you weld. And, or do some post weld tidy up before you paint or spray galvanize.

4. Or Is Time More Important To You?

You want whatever flap disc you choose to just work and quickly get the job done.

5. Does The Project Have Lots Of Tight Angles And Corners You Need To Get Into?

Or is the metal curved and you want to follow the curves?

The last thing you want is to dig into your metal with a flap disc that’s going to mark up your metal.

6. Is There A Large Surface Of Mill Scale And Dirt To Grind Off?

Then, you’ll need a flap disc that’s going to cover a lot of distance and fast.

What Flap Disc To Buy For Different Metals?

A Flap Disc To Use On Mild Steel Or Low Carbon Steel

Pick a flap disc with a surface designed for mild steel. One that’s suited to the surface you need to grind.

Do you have lots of rust and mill scale to deal with?

Look for a flap disc made for removing heavy mill scale and rust. It’ll make your life easier if that’s what you are dealing with.

Are you working on flat metal? Then pick a flap disc with a flat profile. Curved metal? choose the conical type of flap disc.

You’ll find more information on the shapes, known as types further down in this article.

Flap Discs On Stainless Steel

Your stainless steel may look nice and bright. But even stainless steel straight from the manufacturer will have a layer of dirt on the surface.

And you’ll need to clean that off before you weld.

Buy a flap disc specially made for your stainless steel.

Keep Your Stainless Steel Flap Discs Only For …

Your stainless steel.

Don’t swap your flap discs between grinding on a mild steel. Or a low carbon steel surface and your stainless steel.

Why?

Because tiny particles. Or even not so tiny bits of mild steel will be sitting on your flap disc’s surface.

And as you grind on your precious stainless steel. Preparing your surface. Or doing your after weld clean up. You’ll be embedding those bits of mild steel into your stainless steel.

A disaster.

Why?

The whole idea of using stainless steel is because it’s stainless and rust resistant.

Mild steel and low carbon steel rusts.

Do you really want small metal bits that can rust stuck in your stainless steel?

Or just as bad have those mild steel particles causing you all sorts of trouble to weld through?

You’re best off dedicating a flap disc to your stainless steel.

And Buy A Flap Disc Suited To Stainless Steel

Why?

Because flap discs made to use on stainless steel work on the surface. And protect its rust and corrosion resistance. 

Plus you’ll want your flap disc to run cool on your stainless steel surface.  You wont want heat marks on your stainless steel. Or dig into the surface of your stainless steel.

Flap Discs For Your Aluminum

Aluminum Is well known as a soft metal.

You’ll find it’s much softer than mild, low carbon or stainless steel.

Aluminum also has a different melting point to those metals.

While grinding to prepare. And clean off surface contaminants from your Aluminum.

You’ll want a flap disc that keeps cool while you’re working with it.

And you know what?

Aluminum can easily clog up the surface of a normal flap disc.

The wrong type of flap disc will have you scraping your precious Aluminum up onto the flap disc. Instead of where you want it in your project.

You’ll find it’s best to use a flap disc that’s rated for working on Aluminum.

When you pick the right flap disc for your Aluminum you’ll keep your metal where you want it.

Yet remove the dirt on your Aluminum surface.

And just like stainless steel. It’s best to dedicate the flap disc you use on Aluminum to Aluminum.

The last thing you want is mild steel or stainless steel dug into your Aluminum surface.

And not only that causing your arc to stutter as you MIG or TIG weld. You then risk porosity from contaminants in your weld.

Why Use A Flap Disc On Your Metal?

If you’re used to using grinding wheels and their discs you may wonder why use a flap disc at all.

It’s worth trying using a flap disc for preparing and finishing your steel. Stainless steel or Aluminum as;

Flap discs are lighter weight and are easier to use in your grinder. Because they move lightly over your metal’s surface.

You’ll find that flap discs operate with lower vibration and noise. A real advantage when you have a lot of metal to prepare. All that noise can get pretty wearing after a while, not to mention the potential damage to your ears.

Flap discs are popular because they tend to last longer than grinder wheel discs. This is because as the surface area of the flaps on your flap discs wear down. New abrasive surfaces are uncovered.

You’ll see that flap discs are perfect to use on your thinner metal gauges. Because they work gently on the metal. The last thing you want on thin dirty metal is to remove too much. And make your metal weaker.

What you want is to remove your surface dirt down to your good clean metal below. No more, no less.

The Four Areas Where You Use Flap Discs On Metal

1. In Metal Preparation

It doesn’t matter if you’re flux core welding, stick welding, MIG or TIG welding.

Before you start to weld, good clean metal can be crucial.

Can Be?

When you’re flux core welding you can get away with some dirt on your metal.

The same when you’re stick welding.

But when you’re MIG welding. And especially when you’re TIG welding, clean metal is a must.

And unfortunately, even on brand new bought metal you think must be clean. You’ll find an oxide layer on the top. And you’ll need to clean that scum off before you weld.

Flap disc off all rust and paint off your metal. Before you start. And when working on galvanized steel, use a flap disc to remove that galvanization

2. Fix Your Metal Weld Joints With A Flap Disc

Are the joints on your metal jagged or burred?

Deburr them with your flap disc. And grind prep those metal joints so you have nice, even joints to weld together,

3. Use Your Flap Disc Between Your Weld Passes

Welding on thick gauges of metal?

And using welder designed for the home?

Will likely involve you welding multiple passes to build up the weld in the joint.

Between each weld pass. All your welding slag or mill scale needs to come off before you lay down your next weld bead on your metal.

Run your flap disc over your joint before your next pass. Grind out your welding slag, mill scale. Or metal contaminants bought to the surface by your filler metal. And set yourself up nicely for your next weld pass.

4. Once You’ve Done Welding Your Metal

Clean up your metal with a flap disc.

Unless you’re well skilled and can lay down some smooth dimes straight off the bat. For the rest, you know who you are. After you’ve welded you’re going to want to smooth down those weld beads.

When your friends see your joint, you want it to look good. And you’ll need it looking great when you’re wanting to paint it up. Or spray galvanize to finish off your project.

Flap Disc Shapes And Types For Metal Grinding

There are two main types of flap discs you use on mild steel, low carbon steel, stainless steel and Aluminum.

They are type 27 and type 29 flap discs.

Type 27 Flap Discs On Metal

You’ll hear them talked about as flat flap discs.

When in fact they have a 5 to 15 degree angle on the face.

You’ll find them ideal for preparing your metal. And or cleaning off your welding slag.

And after MIG welding removing mill scale and getting into those tight angled spaces.

A good for instance for when you’d use a type 27 flap disc is for filet welds. – link to what is MIG welding

Got large flat metal surfaces? Use a type 27 flap disc for blending and finishing off after you’ve welded.

Type 29 Flap Discs On Metal

Are known as conical flap discs and have a depressed center. You’ll find the surfaces of these flap discs angled at 15-35 degrees.

You use type 29 flap discs on metal where there’s heavy surface dirt. And you need a tough grinding action.

Type 29 flap discs remove more metal than flat flap discs.

You buy to use on metals that have a curved or contoured profile. Because the more angled shape of the type 29 flap disc will glide over fitting the contours well.

Pick Type 29’s when you’ve a large area to clean and grind. Because you’ll get your grinding done quickly.   And use where you have edges to deburr or bevel before you weld.

Flap Disc Surface Grit Types, Costs, And What Metal

Aluminum Oxide Flap Discs

Is the original flap disc surface. The Aluminum Oxide grit surface has been around for years.

You’ll find it’s a cheaper flap disc surface with the lowest cost flap discs.

But the downside is you won’t find it lasting very long.

Pick to buy a flap disc with an Aluminum Oxide grit when your metal prep task is small. And when you’re working to a tight budget with low carbon and mild steel to get ready.

Zirconia Flap Discs

You’ll find this flap disc grit surface is a premium flap disc surface. And that’s reflected in its cost.

For sure it’s longer lasting than Aluminum Oxide. And keeps its grinding and cutting edge far better than.

Zirconia-Alumina Flap Discs

Zirconia-Alumina made flap disc combine Zirconia and Aluminum Oxide on the surface. And you’ll find it comes at a premium cost because it’s a great flap disc surface on metal.

You’ll see it’s a great surface choice for mild and low carbon steel when you need great performance.

Plus these flap discs have better heat resistance on metal. And you’d pick to buy this flap disc grit surface for your stainless steel.

Zirconia and Zirconia-Alumina surfaces last well and keep their cutting power for longer.

Look for the surface designs with grit rated for stainless steel. Or Aluminum when you’re grinding on those metals.

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