garnet abrasive 2

[pogcali]

Greetings
We will use garnet for sandblasting stainless steel. How much iron oxide is allowable percentage of garnet? The high percentage of the oxide can be harmful to stainless steel surfaces or no? Question for me is whether the chemical composition of garnet used as an abrasive in sandblasting stainless important? How much is this composition?

 

[EdStainless]

I have never paid attention to the Fe content, we always pickle after blasting to remove residual surface contamination.

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Plymouth Tube

 

[israelkk]

For aerospace and military use the sandblasting media should be free from Fe particles. Pickle can be harmful for heat treated high strength stainless steel due to hydrogen embrittlement risk. It is safer to receive a clean surface free of Fe particles using sandblasting free of Fe. Even when machining stainless steels (turning and Milling) it is required to replace the cooling fluids if previously used to machine ferrous steels.

 

[EdStainless]

For many critical applications you are only allowed to use abrasive once through.
Even the small particles of SS that it will pick up are detrimental to the surface.

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Plymouth Tube

 

[redpicker]

From the comments, and my reading of the OP, I think there may be some confusion going on.

Garnet is used as an abrasive. Per Wikipedia, Garnet refers to a class of minerals known as nesosilicates that has a crystal structure represented by X2Y3(SiO4)3, where X is a divalent metal ion and Y is a trivalent one. The differences in the various types of garnet depents on whether the divalent ions are Mg, Ca, Fe, etc... and the Trivalent ones are Cr, Al, Fe, etc... (iron exists in both divalent and trivalent states). Perhaps I am just getting confused between the term "iron oxide" and "oxidation state of iron".

My take on the question in the OP is whether or not clean, uncontaminated garnet can be used for sandblasting stainless steel. That is, does it matter if the garnet is Almandine [Fe3Al2(SiO4)3] or Pyrope [Mg3Al2(SiO4)3], ignoring for the moment that all naturally occuring garnets will have some of the either divalent or trivalent oxidation states replaced by iron just due to the natural abundance of iron. Since the Almadine contains iron in the Fe+2 oxidation state, it contains iron oxide. Is there a level at which this would be accepatble or must only Pyrope be used?

I don't have a clue, but I don't believe the OP is asking how much iron oxide contaminaiton is permissible before he has to change out his media, but, rather, can garnet be used to clean SS? And, if it can, is there a limit on the (natural occuring) iron content of the garnet that can be used?

rp

 

[SJones]

If the originator is using ISO 11126 specifications to purchase garnet, then they only address almandite garnet with no technical requirements pertaining to iron oxide, or free iron content. The concern will be constituents that will contribute to the corrosion process of the stainless steel which should be detected by the range of quality control tests required and the results remaining within the acceptance criteria.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[israelkk]

For example, according to MIL-PRF-46010G LUBRICANT, SOLID FILM, HEAT CURED, CORROSION INHIBITING
NATO CODE – S-1738 the sandblast recommended material for cleaning of stainless steels is "Aluminum Oxide" why use Garnet instead?

Here is a quote from the spec:

A.3.6 Application on stainless steels. Preclean the surfaces to be coated with aliphatic naphtha or any environmentally safe cleaner that sufficiently cleans surfaces to pass ASTM F22, but does not harm the surface (i.e. hydrogen embrittlement, etc.). Sandblast the surfaces with 120 grit aluminum oxide. Passivate the surfaces in accordance with ASTM A967, nitric 1, nitric 2 or nitric 3 as applicable.