Satin finishing on soft steel stamped parts 2

[linamar]

Greetings!
It's not for an industrial setup but for adding a finish touch to small stamped components.
Rather than rubbing on a fine grit emery paper sheet, how else can I get a satin finish?
It's not for volume production, and components are micro mechanical parts.
Thank you.

 

[unclesyd]

You should look at Vapor or Liquid honing. Here is a good place to start if you need the equipment. A lot of coating shops have some type of liquid hone.

http://www.wettechnologies.com/index.html

 

[kenvlach]

Additional mass finishing methods to consider are vibratory shaker and rotating tumbler. Can be used with different size & shapes of ceramic, metal or organic media, and either wet or dry, to get the desired finish. Lots of machine shops use to deburr and surface finish. Good for small, lightweight parts that might blow around during abrasive blasting.

Nova Finishing Systems manufactures small mass finishing equipment.

http://www.novafinishing.com/

 

[gciriani]

I disagree with the two previous replies. Satin finish is characterized by surface appearance, that reflects light in a dull-yet-shiny way. This can only be obtained when the direction of the surface texture is parallel to one main direction.

In my industry (luxury accessories) this is usually obtained with rotating brushes. The micro incisions obtained are between 1.5 and 4 micrometers deep (i.e. 60 to 160 microinches).

Instead, liquid-honing and mass-finishing, suggested in the previous two postings, act in all direction, and the final appearance will not be satin (but mirror polished or dull, depending on the type of media).

You should be able to find rotating brushes for satin finish at jewelry suppliers. Look up the Thomas Register with search word "Satin brushes" (

http://www.thomasnet.com/nsearch.ht...Finishing&heading=8661407&navsec=prodsearch);

you'll find many suppliers. For instance

http://www.divinebrothers.com

seems to have the right satin finish brushes.

Regards, Giovanni Ciriani
Promotion Group +39-348-155-4029

 

[kenvlach]

Re 'satin' finish terminology. The finish so clearly described by gciriani is generally called 'grained satin' or 'brushed satin,' a particular subset of satin finishes, in U.S. industries (luxury accessories may be an exception).

Satin finish is defined as
“A diffusely reflecting surface finish on metals, lustrous but not mirrorlike. One type is a butler finish.*”
-- ASM Handbook, vol. 5, Surface Engineering (1994).
* with fine, parallel lines.

Coatings, both metallic & non, can also have satin finishes.

Some examples:
Satin finish paints & varnishes; e.g.,

http://www.rustoleum.com/product.asp?frm_product_id=19&SBL=1

http://www.specifypaint.com/APL/paintinfo_APL/MpiNumber.asp?ID=57

Chromium and nickel plating solutions are available which for matte, satin (semi-bright) and bright plating. Differences are due to solution additives known as brighteners. For satin nickel:

http://www.atotech.com/start.php3?cl_my_id=843654#

'Satin' and 'fine-grained satin' anodized aluminum have separate IBM finish codes (graining is performed prior to anodizing):

41-201
Anodize (satin finish) water sealed (sulfuric acid electrolyte), 5 micrometers minimum
IBM M-H 6-4220-000, 9808

41-208
Anodized-fine grained satin finish, (suitable for silk screening), 5 micrometers minimum, (decorative).
IBM M-H 6-4220-000, 9808

Chromium/nickel & chromium/nickel/copper plating is available in satin finish (aka. semi-bright). Not grained; note that ASTM B456 considers substrate scratches to be defects.

41-041
Plating, chromium, dull. On steel, copper, and copper alloys: nickel 8-13 micrometers, chromium 0.25-2.5 micrometers...
IBM M-H 6-4104-100, 9808

41-043
Chromium plating, satin. On steel, copper and copper alloys: nickel 8-13 micrometers, chromium 0.25-2.5 micrometers...
IBM M-H 6-4104-300, 9808
ASTM B456, B183, B242, B252, B253, B281, B650, B177
ISO 1456, ISO 1457

41-045
Chromium plating, hard, thickness to be specified.
IBM M-H 6-4104-500, 9808

41-046
Chromium plating, polished On steel, copper, and copper alloys: nickel 8-13 micrometers, chromium 0.25-2.5 micrometers...
IBM M-H 6-4104-600, 9808

https://bomdetail.services.ibm.com/matcodes/matcodes.nsf/pages/mat41.htm

My experience with satin and grained satin finishes is mostly with aluminum and stainless steel. Satin finishing includes light etching of machined aluminum prior to anodizing & light bead blasting of stainless, used for hiding machining scratches & fingerprints. Graining is mostly touch-up of parts fabricated from grained sheet. Air-powered linear sanders, abrasive belts and wire wheels are used.

Polishing of steel is performed prior to plating. Wire brushing can generally be used for cleaning prior to painting. I recommend against satin or other roughening as a final finish on steel (it increases rusting) unless the part is continuously lubricated.

Also, wire brushing is most suited to softer alloys (Al, Cu-based, precious metals, Zn), while coated abrasives are better for steels and other hard alloys. Of course, brushing can follow abrasive use.

Mass finishing methods have enough variables to produce a continuous range of finishes, from matte to mirror.

Suitable finishing methods for linamar's part depend upon its geometry. If a grained surface is desired, often best to start with grained material. Then, only need to touch-up after fabrication.

Cheers,
Ken

 

[gciriani]

First Linmar's problem:
I think that if the purpose is to hide fingerprints and microscratches, then sandblasting with the proper grain size should do.

Back to satin:
thanks Kenvlach for the definition “A diffusely reflecting surface finish on metals, lustrous but not mirrorlike." Are there more examples in the ASM Handbook? I'm very interested in the subject. From what I've learned in my industry, to obtain a satin finish, the surface texture has to be made by many micro-surfaces reflecting in all possible directions (to diffuse most of the incident light). Each of the micro-surfaces has to be almost mirror-like to reflect most of the light back, and give the lustrous aspect.

In my industry this is achieved by first mirror polishing (SS A316L), with a rotating cloth wheel, and then brushing with a rotating brush. In this way the micro scratches obtained still reflect a lot of light, but in many different directions (that's the key to satin). Granted, we perform a mass-finishing in a tumbler (CBF type) between the machining and the mirror polishing (this already imparts a a finishing that to most is already a mirror-polish like).

We never use a metallic wire brush, but rather a brush with bristles made of some other material (perhaps there is an abrasive in it). The rigidity of the bristle has to be just enough to create the micro incisions wanted. Its choice is very dependent on the hardness of the material to satin.

I believe that if the rotating-brush, satin finish were to be substituted by a sand blasting with beads of the appropriate grain-size, a similar satin-finish would be obtained. The secret, again in my opinion, is to have a miriad of micro surfaces, all mirror like, all reflecting a lot of light in many directions.

The satin finishing described by Kenvlach,
"... light etching of machined aluminum prior to anodizing & light bead blasting of stainless,.."
is probably imparted by the light bead blasting. In my opinion the etching and anodizing prepare the surface for the mirror reflection, and while important could be substituted by any other means of making the surface shine.

Although, I intuitively agree with Kenvlach that a satin finish should increase corrosion chances, in practice it may not. I asked a colleague who routinely runs corrosion tests on our products: he tells me that satined surfaces do not exhibit higher corrosion than mirror-polished surfaces (for decorative effects a mirror-polished surface sits side by side a satined surface).

Regards, Giovanni Ciriani
Promotion Group +39-348-155-4029