Cold Steel Rotors

[hgp]

I have been reading posts here for some time with some concern as to where some of the  problems that mill builders are incountering with in particular to steel plate rotors.

To start with steel plate is formed by a process of hot rolling so when it come out of the mill it comes with a nice smooth coating of scale.This grey black finish sucks up moisture with a vengance.You can see what i mean if you get a propane torch and direct it to the surface of the steel plate, you will see the moisture come to the surface.The scale has to come off.To do that you can gritblast it or sand it I prefer grit blasting as it makes good rough surface for the resin to key into. Yes resin sticks better to a rough surface.before sticking on the magnets run a torch over the surface so as to evaporate any moisture that may be on the rotor.This does not require a lot of heat just warm. When you have finished coat it with red oxide primmer one with a rust inhibiter.I grantee you will not get corrision under the resin or the magnets.

Herman

[Phssthpok]

This grey black finish sucks up moisture with a vengance.You can see what i mean if you get a propane torch and direct it to the surface of the steel plate, you will see the moisture come to the surface.

With all due respect, I'm going to lay on the 'B-S Button' with BOTH my thumbs on this one.

Millscale 'sucking up moisture' (which in my 10+ years of building railcars I have yet to encounter) has nothing to do with the moisture you see when directing a propane (MAPP, Acetylene, LPG, butane, etc.) flame onto the steel.

ALL of the aforementioned fuels have one thing in common....they all produce WATER as a byproduct of their combustion. When this hot water vapor comes into contact with the (relatively) cold steel the vapor condenses in a perimiter around the 'hot spot'. As the hot spot grows, so does the perimiter. Anyone can prove this to themselves just by grinding the millscale off a fresh plate, and doing a torch test. Although the water may not be as visible against the bright steel, it'll be there just the same....no more... no less.

That grey mill-scale is, in fact, a naturally PROTECTIVE coating with regard to water....I live in the Pacific Northwest...trust me I know. I have seen fresh plate stored outside for less than a week with a BRIGHT orange edge where the exposed steel (from getting sheared off the coil) is rusting like mad...yet the surface (protected by mill scale) is just a pretty as the day it rolled off the ..well.. rollers.

[stephent]

Geee, Phssthpok--both thumbs and both barrels also.

But you are right.

I always liked the rough scale left on old style wrought iron (the real stuff).

And that type of iron's natural finish (dunk it into a oil barrel to cool it after beating and hammering it on a forge) will last and last when exposed to the elements.

I really liked hammering on old (real old) buggy springs to make knives with. Lots of years ago now. But I have one that came out of the oil quench and nothing has been done to it since, and it's still blueish and just some very minor surface rust---30 + years stored in sheds here and there....outside and unheated--some not so dry.

Just ran across that thing again--little 5 inch skinner blade ---just a couple of weeks ago...going to give it to one of my Electrical Apprentice Students who makes (grinds them out) knives from power hacksaw blades.

Just got to show him the "old" way of doing the same thing.

[hgp]

I am sorry to say this but when it comes to adhesives pretty is no good, just ask Devcon who make a product called steel putty they recomend you grit blast surfaces before applacation.The Question is if you paint something and rust appears under the paint then the moisture had to be there to start with.This is why in the mining industry all structures are gritblasted before application of protective coatings.

Herman  

[Flux]

The moisture you mention comes from the flame.

Whether mill scale is a suitable surface without other preparation is another issue.

Grit blasted surfaces are good. suitably degreased and possibly etched millscale may be just as good. I think a lot of people grind the scale off. I haven't done and structural acrylic sticks to it satisfactorily.

The main worry is about corrosion of neo magnets, I don't think the steel discs are a big issue.

Flux

[jmk]

 A lot of people think primer is a water proofing in itself. It actually attracts water and isn't water proof. It needs to be painted over in the time that is stated by the directions, or resanded. Its just a glue for the paint to bond to.  

[Phssthpok]

By pretty, I in no way meant to imply that it was a suitable surface for bonding to. I simply meant that it was remarkable in it's LACK of rust...either on the surface, or underneath the mill-scale as one would presume to see if, in fact, mill-scale absorbed water as you stated.

You will get no argument from me that grit-blasting the scale away down to bare metal is the penultimate in surface preperation, is much desired.

As a side note, if you are not pleased with the quality on your hot-rolled steel plate, you CAN opt to spend the extra $$ (about 30-50% more I think) to purchase COLD-rolled steel. This steel will not have as thick a layer of mill-scale (if any at all) and is generally concidered the ultimate in thickness/flatness consistancy.

[Devo]

I am going to voice in on the magnet corrosion issue as well. I work as a supervisor for a printing company , our cylinders are covered with nickle & there are 2 things I know of that can cause a break down of the nickle coating with us , it might be relivent to the magnet problem & it might not. 1 problem is to high of a ph in the fountain solution the other is any glues that are super strong because when you peel the mylars off the cylinders the glue if strong enough can pull the nickle from the steel.

I have experienced the corrosion on the magnets near the outside & I am starting to wonder if the resin doesn't adhere to the magnets so hard that regular expansion & contraction from stator heat & weather doesn't pull the nickel from the magnets & the resin from the rorors & from there good old condensation takes over. If this is the cause I would think a thin coating of anti sieze or some other compound on the mags before applying the the resin may help especially if they are fully covered.This would allow the resin to expand without pulling on the nickle coating.

Just a thought , could be way off base though...

Devin    

[dastardlydan]

You are so right fire scale is a pain, in you know where,

I had some that would not even sand off.

But the easyest way to take off scale ,and the fastest

it

Muriatic Acid the type for swiming pools.

1/2 cup acid 1 gal warm water, and about a 2min bath.

(you mite want to brush it a little.)

then rinse with water, add baking soda to rinse water,

and your done.

 now acid has its bad side so TAKE CARE handle it properly.

Now the scale is gone the metal will look gary in color

At this point it is so clean that your finger print

will rust.

The pores of the metal are open ,this is a good time

 paint or prime.

DON'T LET IS SET AROUND ,IT WILL RUST!

++++++++++++++++++++++++++++++++++++++++++++++++++++++++

[vawtman]

Ive tried to use muriatic on rusty surfaces.It will remove rust easily but seems to get in the open pores and stay there even after neutralizing.What about good ole navel jelly?

 Stephents idea of heating and dipping in oil not only hardens the steel but seals it.

 An opinion

[RobC]

Personally I vote for sandblasting. Then high grade epoxy or maybe some of the urethane adhesives. RobC  

[Countryboy]

Millscale is a byproduct of metal being exposed to a FLAME.  (Metal placed inside a container, and then ran through the mill fornace will not have millscale, as it was not in direct contact with the flame.)

What is rust?  Oxidation...

What is fire?  Rapid oxidation...

In essence, we can say that millscale is ashes.  Ashes do not oxidize/rust/burn.  (whatever you want to call it.)

Rust doesn't rust either.

[dastardlydan]

Vawtman :

 you are right it has to be

neutralized, that what BACKING SODA

doses.

Then you paint or prim.

If you glue on your magnets wash them and

glue ,the open pores are great for glue,

good bonding.

++++++++++++++++++++++++++++++++++++++++++++++++++++

[vawtman]

Dastardly muriatic solutions work great to etch concrete probably because the concrete is self neutralizing just rinse with water.

 Has far has using it on steel goes no matter how well you neutralize it with carbonates things continue.From my trials.

 Have you done this with good long term results.

 Rust is a good primer.

[stephent]

Buy a cheap side grinder and a good twisted/knotted  (hi-speed rated PLEASE) wire brush for it--knock off the loose scale good (real good) --degrease it--paint or epoxy coat it.....yer done. It won't be all shiny--it will have some discolor to it.

Taking the last little bit of discolored stuff off is a PITA with sandpaper or wire brush---and that last little smidgeon of "stuff"/discoloration is stuck into the pores better then anything you can apply outside of a welder.

That "stuff" is stuck tighter then heck to the metal--IT IS the metal. And it's not gonna "rust" in those spots again.

But if you want a work of art (mag rotor) and something that epoxy will stick like crazy to--have it turned on a lathe and then degrease it--those "turning marks" are just the ticket for helping 'poxy get a hold.

[TAH]

"Buy a cheap side grinder and a good twisted/knotted  (hi-speed rated PLEASE) wire brush for it"

And miss all the fun and enjoyment of pulling embedded wires out of your legs. Never

.