Satin finishes on stainless steel

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Ed. note: This particular thread is primarily "industry oriented", i.e., it discusses the mechanical and/or chemical ways to apply satin finishes in a factory.

If you are a consumer more concerned with repairing a scratch in a stainless sink, appliance, etc., better starting points might be letter 4148, "Removing scratches from stainless steel appliances" or letter 11404 "Scratches on satin finish stainless steel". We have dozens of threads on such topics if you use the search engine, and you'll probably get the best results if you include the word "scratch" in your search term.

A. There are a number of ways to get a satin finish on stainless steel. Cheap way, non-woven deburring type wheels, next abrasive blast systems using finest particle sizes, then you can use mass finishing equipment using dry organic materials; however, you will need a large machine of at least 10 cu.ft. capacity, maybe bigger depending upon the size of your part. The method you use really depends on the volume of parts needed to be processed and the type of finish you are looking for.

A. True no. 4 satin finish (180 grits) are mass produced using special polishing machines in sheet form.

A. Satin finish is whatever the customer considers satin finish. Commonly, for stainless steel, it is less glossy than a polished surface, with a unidirectional (linear grained) brushed finish having transverse Ra of about 0.5 microns.

See the No. 6 finish per ASTM A480 in 'Special Finishes for Stainless Steel' from http://www.ssina.com, and the 1K & 2K finishes per EN 10088 Part 2 in 'Guide to Stainless Finishes' from http://www.euro-inox.org

A nitric-hydrofluoric acid solution is used for pickling (to remove heat or welding scale). HCl, HF or heated H2SO4 solutions can produce dull (matte, whitish) finishes. These should afterwards be passivated in an appropriate nitric or heated citric acid ⇦this on eBay or Amazon [affil links] solution.

Perhaps best to purchase satin and dull (e.g., No. 2D) finished stainless, and only touch-up marks made in fabricating your product.

Q. Is there anybody who can guide me to do satin finish on Type 304 stainless steel? I have tested using hydrofluoric acid 8% with 25% of nitric acid at 40 °C and time given was 30 minutes -- but results are not so satisfactory.

Regards,

A. Hi Bakhtiar. We've appended your question to a thread where it has already been answered by Ken. Please consult his references and get back to us with any specific questions or updates. Thanks.

Regards,

A. Use this site's search engine for "satin finish". You will get dozens of hits.
You should notice that there is no positive definition -- So you'd better find out exactly what your customer thinks that it is.

A. How big are the parts? Sheet metal? Any shape? Quantity?

A. Have you considered abrasive blasting the bead only? Unless the weld pattern is completely flat, you are going to have problems and or a lot of manual touch up no matter what belts or wheels you use.

A. Hi Brandi. Unfortunately, people have differing visions of what a satin finish is. To some it just means a brushed finish, to others it can mean a translucent "frosted" look.

But most "brushed" finishes (if that's what you want) are actually obtained from scratching with sandpaper (or scotch brite) rather than with a metal brush. If you have a belt sander, try a quick "scritch" with a coarse paper, although it will be very hard to get consistency the length of the rail and around it. The way it's usually done on flat surfaces is with a machine like a "Timesaver" (a brand name) which uses a conveyor belt to convey the work through, and a wide rotating belt of sandpaper (as wide or wider than the work),running in the opposite direction, to to deliver this continuous end-to-end quick "scritch".

A. Hi Brandi, sounds like an interesting project. Ted is right. What is the 'satin finish you seek? A brushed grain finish requires abrasive process in long stroke pattern. A sandblasted finish will provide a random, non pattern stain look. You can use a belt sander or inline sander to obtain line pattern yet the more important issue here is the chromium cap which develops on the surface of SS to protect from rusting and corrosion. Your will want to wax this new finish to protect it and allow the chromium to form a seal.

adv.
We have these products if interested.

A. Hmmmm. You want a satin finish but "it lacks shine". Sounds like a contradiction of wants or needs. Non-woven wheels will produce the satin finish; however, if you apply a lot more pressure you maybe able to get a shine out of them. If not then you may have to do a secondary steel with either a cotton buff or felt with rouge. Then again, you may lose satin finish.

A. Hi Matthew. You could always ask Super T Manufacturing how they do it, but I suppose they would be happy to sell you parts but not reveal their methodology :-)

In my (limited) experience, very fine matte/satin finishes like this on stainless steel are more often obtained by glass bead blasting rather than with sanding/brushing or chemicals. But to get a consistent finish around the turned object, I think you would need to fixture it in a machine which rotates it (and possibly also indexes up and down). Good luck.

Regards,

A. As mentioned there are a number of choices and probably the most common is glass bead blasting. If you need a finer finish than 32RMS or you have a lot of volume, you might want to consider a mass finishing system using a dry organic abrasive mix.

A. Hi!
I think you can reach that surface quality with a simple scotch-brite wheel.
You have to prepare the surface with a grinding or a vibratory process and then using the scotch-brite wheel you can find the satin finish quality.

adv.

It is possible to achieve satin surface on stainless steel by electropolishing in Universal electrolyte in special regimes. Thus you have both - high-strength surface with excellent corrosion protection, and matte, milky surface quality.

A. This might be a solution for you; however, it is only good if you have a flat sheet metal part less than 60" wide. There are wide belt sanding machines on the market that can achieve the results you are looking for. All you have to do is specify the type and grit of the belt.If you are working shaped parts then you have to specify a process

A. Hi Alp. These finishes are usually obtained by glass bead blasting or sand blasting. But you probably ought to start the design with the glass beading machine, and add a conveyor mechanism, rather than starting with a conveyor belt and trying to add a glass bead blasting machine. Good luck.

Regards,

A. A random pattern can be achieved in a couple of ways; however, to give you the best solution, it would be nice to know the size of the part. For big parts Ted has a good solution.

 Thank you for your kind reply. Part sizes change according to the machine type. Max dimension is 1500 mm x 3000 mm. We want to obtain a random surface finish. Actually, it will be good to image acquisition like inox home appliances; however, this is entirely dependant on the operator's attention and mastery.

Therefore, we want to remove operator dependency from the process. These finishes are usually obtained by glass bead blasting or sand blasting. We agree with you, however, nobody could give guarantee under 3mm thickness sheet metal for turbine system blasting machine.