Balancing grades ISO 1940 vs API 610

[nirlt]

please explain the relationship between ISO balance grades and grades specified in API 610 (such as 4W/N,4W/N etc W - mass of rotor, N- RPM).

In API 610 it mentioned as a note that 4W/N is equivalent to ISO 1940 Gr 1.0. Also that the grades mentioned in API are mid values of the range of the equivalent ISO grade.

Please clarify How should one interpret the above?

 

[WCFoiles]

4W/N is in traditional American units (with a conversion factor) - oz.-in. of unbalance.

ISO permisable imbalance for balance grade G would be:

Uper = G M/Omega - M mass of rotor Omega - rad/sec (rad/time)

Uper = M e_per Omega/Omega - e_per = unbalance eccentricitgy

Uper_oz-in in oz-in = W lb 16 oz/lb 1 in/25.4 mm 60 sec/min/(N rpm 2 pi rad/rev) === or

U_oz-in = 6.0153 W/N - W in lbs N in rpm

API = 4W/N or equivalently

G_API = 4/6.0153 = 0.665

So, a balance grade G=1 does not quite meet API.



Regards,

Bill

 

[WCFoiles]

The following equation had a G left out

U_oz-in = 6.0153 W/N - W in lbs N in rpm
SHOULD BE

Uper_oz-in = 6.0153 G W/N - W in lbs N in rpm

With G being the ISO balance grade.


Regards,

Bill

 

[Tmoose]

http://www.irdbalancing.com/downloads/TechPaper1BalQualityReqmts.pdf

page 8 has a chart showing various balance grades for a 1000 lb rotor from ~500 to 7000 rpm.

Just looking at that chart on a Suday afternoon I'd say 4W/N is equivalent to ISO 1940 Gr 0.7ish.