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Forum HostPermalink Reply by Larry Buskirk on January 28, 2012 at 7:12am

John,

I use steel on cast iron parts, brass on sheet metal.

Only because I find the steel holds up better doing cast, and are cheaper to buy. They are sometimes a little rough on sheet metal, so I use brass wheels on sheet.

 

Larry

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JourneymanPermalink Reply by Ken Rasmussen on January 28, 2012 at 9:15am

Steel

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My job is to give my kids things to discuss with their therapist

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Master CarpenterPermalink Reply by steven newman on January 28, 2012 at 10:23am

  IF it is on the grinder, then a steel wheel is used.     The brass BRUSH is to both get into the little spots a wheel can't get into, and, it tends to LEAVE any small details (like the "76" on a Liberty Bell) intact.    I also used the brass to scrub the gunk raised by any soaking I do to parts.     A nice soak in Simple Green, with a scrub with the hand-held brush works just fine.    I like to leave the details in place.  

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'and may the road raise up to meet ye'

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Site AdminPermalink Reply by John Morris on February 6, 2012 at 10:09pm

Thanks for the info guys!!!!! I'll get back on my DP soon enough!!

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John Morris
The Patriot Woodworker
Proud Supporter of Wounded Warrior Project and Homes For Our Troops

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JourneymanPermalink Reply by Cliff on February 25, 2012 at 12:22pm

Depends. If I care about not scratching:  Brass. If all I want is rust removal: Steel

If I want to not transport plain steel to SST  ( and cause rust)  then it's SST.

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Site AdminPermalink Reply by John Morris on February 25, 2012 at 2:03pm

Thanks Cliff, can you go into a little more detail on the last line of your reply. I am lost. I am kind of new to metal working so forgive my ignorance.

Cliff said:

Depends. If I care about not scratching:  Brass. If all I want is rust removal: Steel

If I want to not transport plain steel to SST  ( and cause rust)  then it's SST.

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John Morris
The Patriot Woodworker
Proud Supporter of Wounded Warrior Project and Homes For Our Troops

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JourneymanPermalink Reply by Cliff on February 26, 2012 at 8:40am

Yah sure.

SST is corrosion free only because the  base metal (steel)  has been alloyed with no less than 12% chrome. More is better and  adding nickel  also is better still, but 12% chrome is the  minimum for SST. The different grades of SST 304 316 400 etc are different in the amount of chrome and nickel.  Super alloys like Inconel and Monel are super saturated with nickel and chrome inter alia

At 12%,  when  the metal exposed to atmosphere  it will  experience a deposition of a chrome oxide layer on the surface. 

That layer is what is called the passive layer.  Passivisation is just an etching process that removes a little  iron  (but not the chrome) leaving a  denser layer of chrome on the surface to form a denser chrome oxide layer.

When plain steel or iron is abraded against the chrome oxide layer it can scrape it away and  - can - leave some plain steel behind.   That steel that is left behind - can - bond to the  SST and once it starts rusting can communicate the corrosion through itself into the SST where the passive layer can not form because it is  never exposed to air ( O2).

I say - can - because it also might not.  But the fact that it can is cause for concern.  For machine  operations the wise engineer will specify that after machining the SST  items made  will also  undergo an abrasive finishing process  preferably followed by a passivisation process to ensure that any steel that may be stuck to the SST is removed.

All that said: A steel wire brush is a good candidate for damaging a SST surface.

If you have  damaged SST surfaces you can passivate thm yourself with Citric Acid in water.  Adding a little EDTA to chelate the iron is also a good idea.  Industrial pssivation uses a specific molarity of nitric acid at a specific temperature over a specific time but Citric is  way easier and  strength of solution  temp and time are  things you can work with if you please but you can ignore them too.

Conversely, muriatiac acid   ( & others too) will etch off the chrome and cause rust.

 

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Site AdminPermalink Reply by John Morris on February 27, 2012 at 3:45am

Great stuff Cliff, thank you so much, this is one to stick in my arsenal of knowledge as I jump into the realm of restoring old woodworking machinery. It's amazing the knowledge on our site, thanks again Cliff, that was great.

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John Morris
The Patriot Woodworker
Proud Supporter of Wounded Warrior Project and Homes For Our Troops

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