Flap Disc/Wheels vs. Abrasive Discs for Welds on Stainless.

[nfie]

What are the benefits and drawbacks of using flap disc/wheels vs. sanding discs/belts?
---I asked a gent on the production floor about flap discs and he said they were "trash" (this was when a Walter salesman came in). In theory, flap based abrasives seem better because if the right one is selected the wear is even and the abrasive feed does not bald like an ordinary sanding abrasive. The part I am uncertain about is how much control you do or do not have with flap discs on and hand-based grinder. I also see flap-based (A Fladder oscillating deburring system) abrasives as superior for deburring rather than using a 3M belt on a TimeSaver, but again I have only read about it up till this point on online articles and plan to do a simple experiment in the future.

There is a process we have now where we 1. Rough grind a TIG welded stainless steel part 2. rough polish with a belt grinder and 3. Final polish with a polishing wheel. I would like to reduce it down to 2 steps to be 1. Remove weld with a flap wheel and then 2. Final polish and blend with a polishing wheel.

I am looking for and experienced opinion in regards to flap abrasives and sanding abrasives.


See link below for where I got my idea:

http://www.thefabricator.com/article/finishing/a-weld-done-finish

 

[racookpe1978]

It depends on your technique.

The specific angle each flapper disk is held at. The pressure (down into the steel) and the exact point you are touching the steel at. A belt grinder does limit somewhat the depth of the cut (if moving the grinder lengthwise down the pice) because it has a steel backing pad. There are few other advantages though.

A rough grit flapper wheel is best for removing projections down to a flat surface - IF and ONLY IF! - the face of the flapper wheel is kept parallel to the surface of the steel.

Most grinding wheel user (hard disk) users get accustomed to "cutting" with the edge of the tool, using a fairly narrow disk (0.062 or 0.045 inch for cutting, 0.125 or 0.250 for grinding). Which works for a hard disk - but ONLY as long as the edge itself is "almost square". Then, as the hard disk wears, the edge becomes rounded, the user pushes harder, and the wheel keeps rounding off. It "sort of" works. But you have to keep pushing down harder and harder as the wheel gets smaller in diameter and get ever more rounded.

A flapper wheel cuts ON THE FLAT. NOT on the edge. Poor users try to cut (remove steel) with the edge, which rapidly wears off and exposes a rounded no-grit-present slipperly surface. Then they start cursing at management for giving them crappy tools.

If they cut with the FACE of the grit, AND use the proper (usually very coarse 40-36 grit!) rather than a rounded-edge smoothed off 80 grit, then they would remove more steel from flat surfaces faster at less expense per flapper wheel.

I prefer the 13,000 rpm rubber-backed, coarse grit, very thin pads, rather than the more expensive flapper wheels. The individual pads are less than 1.50 each, when a flapper wheel is 4.50 to 6.00 dollars each. A hard-rock stainless wheel is 4.50 to 6.00 each for 1/4 thick wheels.

 

[EdStainless]

The reason that this is done in steps is that each progressive step should remove the damage from the previous one.
Polishing and buffing stainless is bad news unless you already have a very smooth surface. Too much pressure will lead to smearing metal, and this will lead to easy corrosion attack.
And don't use SiC, any embedded abrasive will be a possible site for galvanic corrosion attack.

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P.E. Metallurgy, Plymouth Tube

 

[berkshire]

As Racook says

It depends on your technique. It also depends on what you are welding.

Rough grinding with a flapper wheel tends to result in heavy consumption of flapper wheels without much benefit, the spikes and raised surfaces of a weld tear pieces off the wheels.
The technique you are describing, might work, on an SS hand rail with a smooth Tig weld, anything rougher would be a waste of money.
If you have to duplicate a #4 finish or similar the inflatable wheels and straight-line sanders are your best friend. Talk to your guys on the floor and see what they have the best results with.
B.E.

You are judged not by what you know, but by what you can do.