Roughness testing of of a rotating disk?

[cymeryss]

I am not sure if this is even possible, but if so it would definitely be of use to me. I have spent some time looking into ways of measuring (in situ) surface roughness (Ra) of a rotating Cu disk, to determine changes in surface roughness with time, while is it being abraded. Since this experiment runs in a certain environment, having to stop the experiment and measure roughness every so often is a pain and an in situ method would be ideal for this application. I expect Ra anywhere from 10 to 250. The unit would have be portable since space is limited and I could not use any large system, especially when it comes to the probe.
Any suggestions would be appreciated.

 

[Skogsgurra]

How fast does the disk spin?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[cymeryss]

Thanks for the interest. The disk spins at maximum of 500rpm, which based on diameter gives you 12 m/s surface speed, but most of the time it would operate between 5-7 m/s.

 

[IRstuff]

So a 1 nm feature will be blurred if the dwell time is any longer than about 3.6 picoseconds.

That's not even in the realm of plausibility. You're going to have to stop the disk to realistically get meaningful measurements. None contact profilometers take upwards of 0.1 seconds to get their scans:

http://www.veeco.com/pdfs.php/21

TTFN

FAQ731-376

 

[tomwalz]

Not sure how relevant this is but I’ve been playing with a red laser to measure surface roughness. If you have flat, hard surface you get a sharp red dot. As the surface gets rougher the dot gets bigger and fuzzier. This is with both the dot on the target and the reflected dot.

I guess I’d take photos and use the astronomer’s technique of overlaying them to spot changes.


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

 

[btrueblood]

cymerss, your roughness values are in micro-inches correct? And is the roughness specified in the circumferential direction only, or is radial direction included? If radial is to be included, please forget about it.

IRstuff, a 1nm surface feature is about 254 times smaller than a 10 micro-inch feature (the OP's original minimum). That still rules out laser displacement sensors such a Keyences':

http://www.keyence.com/products/vision/laser/laser.php,

since a 12 m/s speed means a min. 47 MHz response, or more like 90 MHz to avoid aliasing, whereas the fastest availablve sensor is about 50 kHz.

OP: Can the disk be slowed to (for instance 1/2 rpm) for the duration of roughness testing?

 

[IRstuff]

Unless the units are angstroms.

TTFN

FAQ731-376

 

[cymeryss]

Yes, the units are micro-inches, and it seems like I am asking for the impossible. I am now thinking that as btrueblood mentioned I would be able to slow the rotation to possibly 0.5 rpm. It is basically a copper disk, and the path that is being abraded is approximately 1cm wide. Currently I am using a mechanical (needle) type roughness tester that runs a along the surface in the radial direction, simply because I don't have access to measure in the circumferential direction. I am interested in the roughness of the circumferential grooving that is time dependent.
I really appreciate the comments and the help. Thank you.

 

[IRstuff]

Styli aren't terribly good for this sort of application, both because of the size of point required and the motion artifacts that have to be accounted for.

A non-contact approach for this type of application should be seriously considered:

http://www.microphotonics.com/PhotoMap3d.html

The above looks to be adaptable for an over-hung installation.

TTFN

FAQ731-376

 

[0707]

Surface Roughness Parameters

Go to

http://www.discountgage.com/MMGAUGES/IMAGES/sj201P.pdf

http://www.mitutoyo.co.uk/MitProd/mtopr.nsf/UNIDS/3D78B3E2A12F82D3882569B9007C4345!Opendocument

Luismarques