Surface Roughness

[dR3w]

Hi,

Could someone tell me (or point me at a resource or standard) that can identify the difference between surface roughness measurements Ra and AA (Average Roughness). I have values in both scales, and need to compare them for a model I am building.

 

[Yallapragada1022]

Go to this website:

http://www.innovativeorganics.com/m...01030/SURFACE ROUGHNESS VALUE CONVERSIONS.pdf

Rao Yallapragada

 

[EdStainless]

Do you even know what you have measurements of? do you know the stylus type, size, stroke, cut off? Remember what these measurements really mean.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[dR3w]

Thanks for replying.

First to Yallapragada1022, that link doesn't work for me.

Second to EdStainless, let me further explain my problem. I am using a thermal hydraulics program that requires surface roughness for piping materials, or any metal surfaces over which fluid my flow. We are using French mechanical drawings that specify stainless steel component roughnesses with a default surface roughness of 6.3 micros Ra. I am used to working with american drawings where surface roughness is specified in average roughness. I know that the code asks for absolute roughness which is equivalent to 2 times the AA or 1.8 times the RMS. I am not sure how to convert Ra into absolute roughness, but from what I have read, think that Ra is similar to AA in regards to piping materials.

Does this help?

Eventually the roughness is used in a fit of a Moody diagram to calculate friction loss (pressure loss) in the fluid system.

 

[EdStainless]

If you read the current American standards you will find Ra as the standard value. You need to look in the ANSI and see how the values are calculated. After all, RMS cannot really be converted. It is a different weighting, and these factors must be applied at teh time of measurement. Afterward you can only approximate teh conversions. Up in that range (150-200 micro inches) this is a pretty good description of surface texture.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[Schipperus]

dR3w
the pdf says in the first alinea: Ra or Roughness Area (also known as CLA and AA).

Which means: exactly the same...

IJsbrand

 

[dR3w]

Thank you.