As-welded surface finish???

By jon20013 (*****)

Date 03-06-2007 15:12

I need some help / guidance.

We have a customer specification which calls out a 125Ra surface finish for some cladding we intend to do. (SAW Strip clad).

Our QA Vice President says 125Ra is a machined surface and as-welded surfaces cannot be compared to such a standard. I agree, and also know for a fact we will NOT achieve a 125Ra finish in the as-welded condition... however, I'm looking for some guidance to a known standard for surface comparison of as-welded surfaces.

Our customer is also very receptive to suggestions as long as they get a "smooth" surface which can be qualitatively and quantitatively measured.

The criterion has to be "measurable" so as to avoid subjectivity. I'm wide open to suggestions... Help?

By js55

Date 03-06-2007 15:25

Jon,
ASME B46.1 is the most comprehensive surface finish standard I know of. This thing will make your head spin. Very detailed, very sophisticated.

By jon20013 (*****)

Date 03-06-2007 15:41

Thanks Jeff, I'll look it up!

By new tito (***)

Date 03-06-2007 17:04 Edited 03-06-2007 17:14

I'm not sure how this post didn't go through the first time. I had to go back and copy and paste it......so here it is again.

Jon, you may have a hard time actually measuring the surface finish of an as welded surface. There are instruments that will give you a value in numerical terms, but I think they will not produce accurate results if the surface is not flat (machined surface compared to a welded surface). The instruments are called.......dang it, i cant find it, but anyway, it works on the same principal as the needle pickup on a record player. If the weld has large crests and valleys, which is almost a given, this will be factored into the roughness average which will give you very high numbers.

A very common, more primative solution is by use of a comparison standard. The have roughness standards that can be "compared" to the actual surface, and the instrument in cases as these are your actual fingernail. I know that sounds wierd, but there are many machine shops that still use the human fingernail for roughness measurements.

I'm not sure if you are familiar with surface roughness and examples of what each would be. A 125rms finish is comaparable to the finish on a B16.5 flange...not the gasket sealing surface (the sealing surfave would be close to 250), but more of the OD, where you can see the machining "lines" where the speed of cutting was fairly quick. A 500 rms finish would be close to a flame cut edge. I would also go as far as to say a SAW weld that is smooth and ripple free, would and could be close to a 125.

If you need anymore help, let me know. I've worked in a few machine shops and am familiar with surface measurements.

edit - BTW, it is also very common to have subjectivity with surface measurements between two companies and inspectors. Surface measurements are not 100% accurate, and even the $5000 machines have variences between them. Oh yeah, those instruments that measure the surface and give you a number......ARE NOT CHEAP!!!!!

edit again - nevermind, I didn't realize thsi topic was posted in two areas. sorry.