Balancing Tolerances according to API 610 Standards

The following formula is valid:

Where:

U [gr mm] = Admitted residual unbalance referred to the bearing journals

W [kg] = Static load on the considered bearing(mass)

N [RPM] = Maximum service speed

Modifying previous formula , we obtain:

The equivalent ISO formula is :

 Important notes:

1) Unbalance tolerance according to API standards is more severe than ISO grade G=1. It is 1,5 more precise and it seems sometimes not obtainable.

2) It is important to point out that the required tolerance, according to API standards, is referred to the bearing journals and not to the two balancing planes. (I will be blogging further about this later this month)

3) The unbalance tolerance measured in microns, (Eccentricity = unbalance per unit of mass) is related to the required mechanical precision , especially when adapters are necessary to mount the rotor on the machine spindle.(the used adapter shall have a mounting precision below the required tolerance

4) For balancing qualities equal to or below G 1 ISO, standard recommends to balance the rotor complete with its own bearings .(The eccentricity between the inside and the outside bearing race can be of the same level as the requested eccentricity).

I will be blogging again shortly to explore "Balancing tolerances calculated according to the maximum admitted load on the bearings".

In the meantime, feel free to contact Cemb Hofmann UK on 0161 872 3123 should you have any specific questions about balancing.

We specialise in dynamic and static balancing as well as the provision of an outstanding sub contract dynamic balancing service from Cemb Hofmann UK

 As a manufacturer of some of the most high precision and accurate balancing machines on the market today, Cemb Hofmann UK is extremely well placed to offer advice on any area of unbalance - from industrial to agricultural and avionic.