calculations of flatness based on EN 485-3 1

[cervantes]

Hi

I have some problems with understanding idea of calculating overall deviation - does anyone of you are familiar with this standard?

a) "%" is not strictly clear for me, what are they reffering to when considering percentage values?

b) why widthwise deviation is percentage larger than longwise deviation? shouldn't this be opposite?

thanks

 

[3DDave]

In rolling to thicknes, the lengthwise flatness can be more easily changed by changing the position of rollers after thickness operation. Width curvature would require convex/concave rollers to change the flatness.

 

[pmarc]

cervantes,

a) Take a look at the attached pdf containing some screenshots from EN 485-3:2003. This should help you to better understand what the table with general flatness tolerances is about (at least in the standard it is clear what the letters "L", "W" and "l" represent):

http://files.engineering.com/getfil...-d20cc6912ece&file=EN_483-3_2003_excerpts.pdf

b) Usually length of the sheet or plate (L) is n times greater than its width (W), so even though the total/overall percentage deviation is greater widthwise than lengthwise, the dmax for length will most likely be greater.

 

[cervantes]

Thanks but my point is that result of dividing mms by mms is not "%"
I can't figure out how they transform deviation scale between mms and percentage

 

[3DDave]

Dividing "mm" by "mm" and multiplying by 100 is per cent (Of 100)

 

[pmarc]

cervantes,

Just divide the percentage values from the table by 100 and the problem is gone - 0.3% becomes 0.003; 0.4% becomes 0.004 etc.

 

[cervantes]

Thanx that was too easy so I thought that's not the correct way