grinding white iron with silicon carbide masonry discs or even diamond discs 3

[Tmoose]

We may need to do some gentle grinding on some ASTM A532 white iron castings. > 500 BHN. Their wear resistance comes from the formation of nasty chrome carbides.

The purpose of the grinding is to remove shallow heat checks (cracks!) caused by previous grinding, without creating more cracks, or worsening the ones there.
These materials are extremely prone to cracking with the slightest touch of a grinding wheel, so I'm guessing we need something that stays sharp and free cutting.

I'm trying to determine if there is a hardware store solution.
I'm also thinking that using something slower than the typical 10,000 rpm 4 inch angle grinder might reduce heating, at the expense of good cutting action.

 

[arunmrao]

Tmoose,

One must be very careful while grinding high chrome iron castings. Any high pressure applied or raise in temperature will lead to cracking.

Use 7inch grinding disc ( from Norton AJ7) . Also wet the castings by placing a damp rag away from the grinding area.

Finally I hope the castings are in hardened and tempered condition.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[EdStainless]

If they haven't been tempered, do it.
Many of the synthetic abrasives will work (Norbide for example).
I would suggest doing it wet, with a water mist sprayed while grinding.
There is the real possibility that you can can't grind these out.

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P.E. Metallurgy, Plymouth Tube

 

[dik]

Can you do a topical repair using a penetrating epoxy and surface cosmetic touch up? rather than trying to repair using grinding?

Dik

 

[metengr]

Sage advice from our castings expert - arunmrao

 

[Tmoose]

Hi dik,

These are fan blades, so the concerns are 100% structural, not cosmetic.

thanks anyhow ,

Dan T

 

[Tmoose]

Hi arunmrao,

A few searches of the Norton US website didn't get anything resembling AJ7.
That was with Google advanced search aimed right at

http://www.nortonabrasives.com

, as well as using the built-in search feature of that web site.

https://www.nortonabrasives.com/en-us/searchproducts?search=AJ 7

Is there another product number or identifier ?

thanks,

Dan T

 

[EdStainless]

Call you Norton or 3M abrasives rep.
They will have all of the details that you need.

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P.E. Metallurgy, Plymouth Tube

 

[arunmrao]

@Tmoose

Can you pl check for "SpitFire" Depressed Centre AJ7 grinding discs. In India manufacturer is Grindwell Norton company now an unit of St.Gobains. Hope it helps.

Recently I lost 4 Horizontal Shaft Impactor ,hammer castings due to operator error. A simple DP test revealed it. Please do perform a DP test.

Happy Grinding!!

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[dik]

DP? Dye Penetrant?

Dik

 

[arunmrao]

@ dik

Agree with you. Sorry, my mistake.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[dik]

These are fan blades, so the concerns are 100% structural, not cosmetic.

I've not heard of cast fan blades... maybe replace them with something ductile?

Dik

 

[metengr]

I have seen a number of large industrial fans supplied with cast steel blades.

 

[arunmrao]

Yes,Induced Draught fan blades commonly are cast in wear resistant irons.If they are in cast steel, usually they are hard faced at the tips.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[dik]

metengr and arunmrao... thanks for the info... I cannot imagine something with as low a tensile strength as cast iron being used for anything in tension.

Dik

 

[Tmoose]

thanks all.

"SpitFire" Depressed Centre AJ7 grinding discs seem "foreign" to the USA.

A major, stinky St Gobain plant is just a few miles from here in Worcester. ( For several decades this company was located even closer, starting back when St G was Norton )

I'll try to get the "SpitFire" and " AJ7" material crossed over.

 

[Tmoose]

Hi dik,

"I cannot imagine something with as low a tensile strength as cast iron being used for anything in tension."

The wear resistant cast irons' UTS probably start around 30ksi/200MPA.

https://www.foundry-planet.com/fileadmin/redakteur/pdf-dateien/13-Adel-Nofal.pdf

In practice A pretty big limitation is the ductility ~ zero.
So the design must consider yield strength ~ tensile strength, so the tensile stress better stay the heck away from the UTS.
Some would say max tensile simply should not exceed 0.25 UTS.

Grinding is high energy process, guaranteed to leave all kinds of trouble behind on the finished surface, regardless of materials.

http://www.gearsolutions.com/articl...asons-for-grinding-cracks-and-their-detection

That is what is giving us all the grief on these pulverized coal handling parts, which must be made of extremely erosion resistant materials to provide a service life measured in years .

 

[EdStainless]

These are very high strength alloys, just as TM said; Yield = UTS, and elong =0
I used to cast pump parts from these alloys. We would shake them out of the molds the next day and then HT with all runners and sprues in place. After temper we would start cutting them apart. We did all touch up grinding with ceramic abrasives and water spray.

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P.E. Metallurgy, Plymouth Tube

 

[dik]

TMoose and Ed... thanks for the information... I guess I live a sheltered life...

Dik

 

[dik]

TMoose:
Note that the one reference is to Deardon and O'Neall for carbon equivalency. This has an upper range of 0.35 for weldability and I assume it's the same value for grinding. The article makes no reference to the limits of the CE value. In general does the CE value for welding relate to the CE value for grinding?

Dik