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Polishing Stainless Steel to a Mirror Finish

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Q. Hello Everyone! My name is Lawrence. I am the Quality Manager at a Precision Machine Shop where we make parts for the Military, NASA, Aviation Industry and Medical Industry.

We are having a problem Polishing a 301 Stainless Steel part to a mirror finish. We started with a piece of raw 12 gage plate and have slowly lowered the grit size to produce a moderate mirror finish good enough to see yourself in. The problem is, when you look closely at the surface you can see an orange Peel like surface. How can we get rid of this and bring the luster out better? Any suggestions on the total polishing process will be greatly appreciated. Thanks!

Lawrence Ariel
Quality Manager - Scottsboro, Alabama


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A. Sounds like a heat problem due to lack or little lubricant or rush. The correct sequence depends on what you or your customer define by mirror, the volume of parts, their weight and surface geometry among other variables. I can speak about low volume, relatively large and heavy parts with complex and selective surfaces to be polished to A-1 (mirror class defined by the Society of Plastics Engineers close to optically perfect with a total roughness and waviness value around 2 or less microinches). You need oil or mold maker stones down to 600. sandpaper down to 1500 or better. Then felt bobs and diamond paste down to 3 microns. A very clean environment (including hands, cloths and hair of the operator). And, above all, patience...a lot of patience. For large volume of small parts you'll have to ask a mass finisher. Good luck.

Guillermo Marrufo
Monterrey, NL, Mexico

Stainless Steel for Design Engineers


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Q. Thank you for the feedback. These parts are for the outside surface of an aircraft window. They are low volume now but may become higher in the future. They are bent to the shape of the aircraft within .06 (in) and they have countersunk holes about every inch or so. They are roughly four foot square but have an odd shape. They have a window opening in them making them around three inches wide from the outside of the part to the inside cut out.
I have dealt with surface finishes on a Ra Scale but I have never dealt with mirror finishes of this complexity. The specification that was given to me said that you have to be able to see a badge clearly with no distortion from one foot away and you have to shine a light from four feet away and have no cloudy spots visible.
I can see right now that our environment is going to be a problem because we sand blast in the same area. Where can we purchase the Oil and Mold makers' stones? I don't mean to sound ignorant but what are bobs? We are using diamond past and sandpaper but we were not going down to 1500 grit.
Again Thank You for taking the time to help us it is appreciated very much.

Lawrence Ariel
Quality Manager - Scottsboro, Alabama


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What is size of your component? Problem maybe because of over heating.

Santosh Kashikar
engineering - Mumbai, India


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A. Add to Guillermo's list, part size and if possible what surface finish you have prior to reworking

AF Kenton
Nova Finishing Sytems Inc. - Hatboro, Pennsylvania

Stainless Steels


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A. Large hardware stores or those specialized on abrasives will have the stones or just type "polishing mold maker stones" on a search engine. Several well known brands (Boride, DME and Gesswein) come to mind. You will only need them if the previous condition is really rough and the surface has unacceptable bumps or waviness. Otherwise you can use flat sandpaper and scotchbrite wheels mounted on rubber cups and high speed rotary motors (you need at least 10,000 feet per min). The felt bobs are pretty much like polishing wheels (they are also known as felt buffs) but are made of non-woven wool (vegetable or synthetic fibers are more prone to over-heat or scratch the surface). Keep in mind that SS has a very low thermal conductivity so it builds up heat quite fast. Use a light oil to thin your polishing compounds and pastes if they are too heavy. Good luck.

Guillermo Marrufo
Monterrey, NL, Mexico
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A. Reread your info. This statement "We started with a piece of raw 12 gage plate and have slowly lowered the grit size to produce a moderate mirror finish good enough to see yourself in.", indicates to me you are blasting these parts before trying to polish. DON'T DO THAT! You also sound like a smaller shop that doesn't have access to a large mass finishing machine, so your best process is probably to work these parts with a non-woven wheel or belt system.

AF Kenton
Nova Finishing Sytems Inc. - Hatboro, Pennsylvania


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A. The orange peel you're seeing is due to large grain size. If possible use material which has been cold worked and not annealed. The orange peel should go away.

jeffrey holmes Jeffrey Holmes, CEF
- Spartanburg, South Carolina

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Q. Thank You for all the responses! I'm sorry that I was misleading on the grit size. I was referring to the sandpaper and diamond past we were using. And "NO" we are not sand blasting these parts (We do know better than that). We have polished smaller parts in the past for the medical industry just nothing of this size and magnitude. AF Were could I get information on a large mass finishing machine. Right now we are using hand power tools.

We receive the SS sheet of material with a brushed looking finish on them. I would say it is about a 64 Ra finish. We are then sanding it with 180, 240, 600 & 4/0 grit sandpaper. From there we are polishing with diamond past grade #6, #3 & # 1. Using oil has helped a lot (Thanks Guillermo for that tip!) however we are still getting a pitted surface. Is it possible that we are not going deep enough at the first stages to cut this out of the stock or could it be something in our process? Thank You in advance!

Lawrence Ariel
Quality Manager - Scottsboro, Alabama


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A. O.K. I noticed you are using 4/0 paper, we don't use that number here. Could it be proportionally around 2000 according to the depth of lines left? How close are you after that paper to a reflecting surface? Are you getting scattered pits or are they throughout the surface. In what stage do they appear or when do they become visible? Sometimes, the polishing compounds tend to produce pits due to excessive pressure exerted trying to clean previous sandpaper lines, but if you look carefully you can trace them back and find out if they were already there or you caused them. Something else, can you get diamond paste 15 and some hair brushes? Give'em a chance at moderate speed.

Guillermo Marrufo
Monterrey, NL, Mexico
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A. Mirror polish finish as you described is not a problem in sheet form (4'x 10') up to 11 GA or 3.0 mm thick. Ra of 1 microinch even in 11 GA material has not been a problem. However, the raw material substrate must be from the best steel mills in the world to avoid problems with pits and pinholes.

Michael Liu Taylor
   specialty stainless steel distributor
Dallas, Texas



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Mass finishing equipment can work and produce mirror finishes on parts less than 12" square very effectively and efficiently; however, over that size it becomes a little more difficult. I'm not sure you can find enough specific info about this on any website.

AF Kenton
Nova Finishing Sytems Inc. - Hatboro, Pennsylvania


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AF the size of the part in the 3rd post. They are roughly four foot square but have an odd shape. They have a window opening in them making them around three inches wide from the outside of the part to the inside cut out.

45366

Thanks for the help!

Lawrence Ariel
Quality Manager - Scottsboro, Alabama


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Sorry about my confusion on size. Based upon that info, I would not recommend mass finishing. Much too expensive and questionable results.

AF Kenton
Nova Finishing Sytems Inc. - Hatboro, Pennsylvania


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Q. Lawrence:
I'm having the same problem (more or less). The orange peel is cause by a combination of things. Mechanical grinding of the surface causes a "Bielby Layer" to form. If this layer forms before you have removed all the scratches one will try to remove the scratches with a grit or sandpaper that is not coarse enough the remove this layer. The resulting heat and friction just "smears" the Bielby layer causing the orange peel.

I am also looking for a way to avoid or quickly remove this layer. Electropolishing is not an option as my parts are 7 feet tall by 12 feet long by 4 feet deep.

Is there an electrostatic solution to this problem?

Eric Brown
- Oakland, California


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A. Dear Lawrence,

Late response though I hope it reaches you.

I feel that 12 gauge is not such an issue. 301 is also not an issue.
Please note the following;

1. Is it Hot Rolled or Cold Rolled
2. What is the finish of the plate before you start any activity. It is a must to determine where you start!
3. Mirror finish on SS should be achieved at around 3000 Grit (If you want it absolutely impeccable) I know of people stopping at 2000 and being happy. But any thing below that would be really not a great idea.
4. Did you ever explore using Engineered abrasives. If not you must. Any problems with that, ask me.
5. What is the machine you use and the type of abrasive you use? Explain to me please.
6. Are you using any lubrication or cooling media, if yes I would also like to understand that too.

Lawrence, I think Mirrorization of Stainless Steel is not at all Difficult, just that it is Different.

If you have any query, it will be my pleasure to assist you.

Ciao!

Ajay Madan
- New Delhi, India

Lapping and Polishing Handbook


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thumbsup2I want to thank everyone for the help and advice you have given me. We are now able to produce the mirror polished finish that we were trying to obtain. I want to share the information that we found on our quest in hopes that it will help others obtain their goals.
1) One of the biggest things we learned is not to rush through the polishing steps. If you read the previous post you will hear this over and over. Follow their advice they are right!
2) Make sure every line from the previous operation has been taken out before you continue to the next step. If you go 90 degrees to the last operation you will be able to see the lines you have not taken out yet.
3) Don't put too much pressure on your tool. We found that too much downward pressure is counter productive. It does not get the lines out faster! It actually creates larger grain lines forcing you to back up a polishing step or two just to get the grain out (It also wears belt out prematurely).
We invited 3M to come out to our facility and they recommended a product line called the Trizact series. This is by far the best sanding belts we have found to date. We put it on a hand drum sander with an air pneumatic drum (Dynisher).

We are also using Nushine II made by Nuvite for the final polishing.

Here is our sequence:
1) Sand out all defects with a 90 deg hand sander using 180 grit disk pad.
2) Go over entire part with Trizact A45 using hand drum sander.
3) Go over entire part with Trizact A16 using hand drum sander. (90 deg to last cut)
4) Go over entire part with Trizact A6 using hand drum sander. (90 deg to last cut)
5) Go over entire part with Nuvite F9 polishing compound. (Make sure ALL defects are out.)
6) Finally go over entire part with Nuvite Grade A polishing compound.
That's It!

Thanks again for all the help.

Lawrence Ariel
Quality Manager - Scottsboro, Alabama


August 24, 2012

thumbsup2Thank you for this thread, it saved my life! I was ending up with an uneven "granularity" that looked like a cross between brushed stainless and smeared fingerprints. Then I came across this thread and read Laurence's words:

"If you go 90 degrees to the last operation you will be able to see the lines you have not taken out yet."

Laurence, you are my new best friend! That was my whole problem, and now that I'm using the 90 degree technique, I can see where the granularity came from and I can also see that I'm spending all of my free hours sanding! Maybe you're not my best friend after all, ha ha! I took it back down to 80 grit and I'm only at 220 now and the results are fantastic. It's great knowing when I'm done and ready for the next grit! Thanks again!

Dave Roe
- Cupertino, California, USA


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December 5, 2008

Q. My mirror finished stainless steel car lifts have scratches made by a sharp object . How do I clean and remove the scratches

L.S.Pinto
- Mumbai, Maharashtra, India

January 6, 2009

Q. I'm trying to add a swirl effect to 300 Series stainless with a #4 satin brush finish.
I'm using a Chicago Pneumatic CP7200S Mini Random Dual Action Air Sander Kit 15000 RPM, 10.5 CFM. Mini Random Dual action orbital sander kit with regulator. What grit/style/manufacturer paper would you recommend?

Ken Furtsch
- Menomonee Falls, Wisconsin

March 14, 2009

Q. I have a flat sheet of stainless steel. I would like to bring the mirror look out in it.
How do I do this.

Kenneth Reynolds
hobbyist - Alabama

June 9, 2009

Q. Hi everyone,
Please teach me the steps how to polish a stainless steel lost wax casting part with dimension 4" x 2" x 0.25" to mirrorable. Thanks in advance.
Nam

Thanh Nam
- Ho Chi Minh City

June 26, 2009

Hi, L.S., Ken, Kenneth, and Thanm. I hope you are well.

Sorry that your inquiries all remain unanswered, despite heavy traffic, and the fact that Lawrence's inquiry immediately triggered a very active dialog with 17 postings. This is merely an observation: Lawrence described his job, his situation, and his results in detail and asked for help to solve a specific narrow problem he was encountering and working on.

Your questions are broader and more general, and reveal nothing about your job, your situation, what your tried & didn't try, and what problems you encountered when you tried them. I am sure that the thought in many readers' minds upon seeing your postings is: "Anything I take the time to describe, you probably already tried." Please see if you can get the kind of help Lawrence got, by posting in his style. Good luck!

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

August 21, 2009

Q. Hi I am fabricator/polisher for a new company; being new there is no experience I can draw on. My boss is happy to supply me with almost anything I find that helps the job and I would like to invite any key tips that any polisher should know. We work almost exclusively with SS, all hand tools, I've found trizact, pneumatic drums, I think I've found most of the right equipment but I can't find enough brain food.

i achieve a good dull, satin, brush finish I can achieve a confident mirror finish but not close to the finishes you speak of and it takes me far too long, and polishing interior angles drives me crazy best I've found for this is dyna-brade for taking weld fillets out then a thin mop, if it's a brushed finish I finish the inch or so where the wheel can't reach by hand with scotch cloth but it leaves a finer finish than our brush finish.Any pointers in any area will be greatly received.Even if you think surely everyone knows that! Try me; no one will think you are amateur for giving me really basic advice, only me for not knowing it already but I don't mind, I know I have a LOT to learn.

richard jowsey
- leeds, UK


November 9, 2011

A. Hi, I don't know if this issue has been resolved, or if there is still any interest in this question. Still;

Eric Brown's answer describes the issue nicely. The cause of the "orange-peel" is usually the result of the lap material being too soft for the substrate being polished.

All polished surfaces appear to have a Beilby layer. Acid etching can remove the layer, but that just exposes the microscratches that are present beneath this layer in almost all polishing processes.

Very hard laps produce scratches, but not orange-peel. Progressing from softer lap materials to harder lap materials (Buehler PoliPad, to TexMet to MicroCloth just as examples) gives a clear indication of the situation. The PoliPad with 1 micron diamond as an abrasive will produce very refined, flat surfaces, with some haze or "sleeks" evident. Following with a very short polishing on the MicroCloth (with lubricant-soap) will remove the haze.

However, extended polishing on the velvet-like MicroCloth will result in orange-peel. I believe the orange-peel is the result of differential hardness domains; areas of agglomerated polishing compound versus soft lap.

Buffing wheels by their nature produce orange-peel as well as localized galling.

Peter Thelin
- Livermore, California, USA

November 15, 2011

A. Hi Mr. Laurence,

I am Daniel Ocampo working as a tool maker in past 14 years.

Your issue caught my attention.
Regarding the orange pill like appearance on the stainless steel it only means you over polish the workpiece. It has also co relation with the speed of your polishing machine and grit of material you use in polishing. I will give some points which may resolve your problem. If you are using silicon carbide the sequence must from rougher to finer. example use grit 600 then follow by grit 800 and then 1000. To achieve the mirror like finish after the silicon carbide you should follow by the diamond paste. Application of diamond paste same as silicon carbide rougher to finer.
Since you have already polish by silicon carbide you use finer diamond paste. Sequence must be grit 15 mic followed by 8-6 micro and for finishing use grit 1 micro.

Hope this suggestion will help you....

Daniel Ocampo
- Saudi Arabia

February 23, 2012appended

Q. I'm an Italian stainless steel worker.
We manufactured a dcurve piece of furniture 180 cm x 120 cm with a polished stainless steel metal sheet.
After welding it we manually polished the welded parts.

The 2 polished finishes have a different mirror finish tone.
Does anyone have a suggestion to manually finish the piece (mirror finish) with a uniform/constant finish?

Maria

Maria Dela
- Salerno, Italy


March 23, 2012

Q. I have a question about how to specify the mirror finish on stainless steel. We are a manufacturer of cameras and use stainless steel mirrors as part of the optical path so we need a true optical mirror finish with almost no scratches. The mirrors are typically 1 inch diameter 304 stainless. Currently, the surface finish specification for our stainless steel mirrors is "FLAT TO 2 WAVELENGTHS W/ 80-50 SCRATCH/DIG, MIRROR FINISH". We have used the same machine shop for years without many problems but recently we have been receiving the mirrors with lots of long small scratches. After measuring the scratches, I believe they are within spec but do not meet our optical quality requirements. Can anyone tell me what surface spec I should be using?

Bob Dobson
- Horseheads, New York, USA


April 25, 2012

A. Thought of Electropolishing?

Stan Martin
BioMed Eng. - Portland, Oregon, USA


August 25, 2012appended

Q. Hi, this is Abhishek Purohit, from Mumbai, India. I want to know how to do mirror finishing on stainless steel sheets. Currently I am using red oxide with nitric acid and water combination. But I am not getting good finish from above combination. Can anyone suggest me any other idea.

Abhishek Purohit
- Mumbai,India
contact


August 25, 2012

A. Hi Abhishek. As you see, we appended your question to a thread which answers it.

Sorry, I don't understand your description of what you are currently doing, but mirror polishing is a multiple step operation -- never a single step operation. While you must use extremely fine abrasive in the final step, it would take you more than a lifetime to polish a rough surface with an extremely fine abrasive, so you must progress through the steps from coarse through fine. Lawrence describes how to do it in 6 steps. Good luck.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

August 25, 2012

Q. Mr.Ajay Madan,

Thanks for your help. Can you suggest if the chemicals I am using are the right one?

Abhishek Purohit
- Mumbai, India

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