Tuesday, 27 August 2013
The goal of balancing is to reduce loads /vibrations on the supporting frames, in order to achieve an acceptable life.
The unbalance introduces internal couples and rotating forces on the bearings. As a consequence, the residual acceptable unbalance can be calculated by stating a maximum acceptable value for the rotating (centrifugal forces) generated by the unbalance in service conditions.
A possible rule is to state that the rotating force is kept below 10 percent of the static load.(USA navy standards)
It is worth pointing out that according to API and to ISO standards, the accepted residual eccentricity (unbalance) varies with the relationship is linear while with the last rule (USA navy standards ) it varies with the inverse of the square of the speed (as the speed increases the accepted residual unbalance decreases rapidly.)
If you would like to speak with a balancing expert then call Cemb Hofmann UK today on 0161 872 3123 to discuss any area of unbalance that you may be experiencing with your rotating parts.
Sunday, 11 August 2013
The following formula is valid:
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 :
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.