GB/T 9239 consists of the following parts, under the general title Mechanical vibration - Rotor balancing:
——Part 1: Introduction );
——Part 2: Vocabulary );
——Part 11: Procedures and tolerances for rotors with rigid behaviour );
——Part 12: Procedures and tolerances for rotors with flexible behaviour );
——Part 13: Criteria and safeguards for the in-situ balancing of medium and large rotors );
——Part 14: Procedures for assessing balance errors );
——Part 21: Description and evaluation of balancing machines );
——Part 23: Enclosures and other protective measures for the measuring station of balancing machines );
——Part 31: Susceptibility and sensitivity of machines to unbalance );
——Part 32: Shaft and fitment key convention ).
This part is Part 14 of GB/T 9239.
This part is developed in accordance with the rules given in GB/T 1.1-2009.
This part replaces GB/T 9239.2-2006 Mechanical vibration - Balance quality requirements for rotors in a constant (rigid) state - Part 2: Balance errors. In addition to editorial changes, the following main technical changes have been made with respect to GB/T 9239.2-2006:
——The scope is extended to include rotors with flexible behaviour (see Clause 1; Clause 1 of Edition 2006);
——Annex B (Informative) is deleted (see Annex B of Edition 2006);
This part, by means of translation, is identical to ISO 21940-14:2012 Mechanical vibration - Rotor balancing - Part 14: Procedures for assessing balance errors.
The Chinese documents consistent and corresponding with the normative international documents in this part are as follows:
——GB/T 6444-2008 Mechanical vibration - Balancing - Vocabulary (ISO 1925:1998, IDT)
——GB/T 9239.1-2006 Mechanical vibration - Balance quality requirements for rotors in a constant (rigid) state - Part 1: Specification and verification of balance tolerances (ISO 1940-1:2003, IDT)
——GB/T 6557-2009 Mechanical vibration - Methods and criteria for the mechanical balancing of flexible rotors (ISO 11342:1998, IDT)
This part was proposed by and is under the jurisdiction of the National Technical Committee on Mechanical Vibration, Shock and Condition Monitoring of Standardization Administration of China (SAC/TC 53).
The previous edition of this standard is as follows:
——GB/T 9239.2-2006.
Introduction
The balance quality of a rotor is assessed in accordance with the requirements of ISO 1940-1 or ISO 11342 by measurements taken on the rotor. These measurements might contain errors which can originate from a number of sources. Where those errors are significant, they should be taken into account when defining the required balance quality of the rotor.
ISO 1940-1 and ISO 11342 do not consider in detail balance errors or, more importantly, the assessment of balance errors. Therefore this part gives examples of typical errors that can occur and provides recommended procedures for their evaluation.
Mechanical vibration rotor balancing - Part 14: Evaluation procedures for balancing errors
1 Scope
This part of GB/T 9239 specifies the requirements for the following:
a) identifying errors in the unbalance measuring process of a rotor;
b) assessing the identified errors;
c) taking the errors into account.
This part specifies balance acceptance criteria, in terms of residual unbalance, for both directly after balancing and for a subsequent check of the balance quality by the user.
For the main typical errors, this part lists methods for their reduction in Annex A.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 1925 Mechanical vibration - Balancing - Vocabulary )
ISO 1940-1 Mechanical vibration - Balance quality requirements for rotors in a constant (rigid) state - Part 1: Specification and verification of balance tolerances )
ISO 11342 Mechanical vibration - Methods and criteria for the mechanical balancing of flexible rotors )
ISO 21940-21 Mechanical vibration - Rotor balancing - Part 21: Description and evaluation of balancing machines
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1925 apply.
4 Balance error sources
4.1 General requirement
Balancing machine balance errors can be classified into:
a) systematic errors, in which the magnitude and angle can be evaluated either by calculation or measurement;
b) randomly variable errors, in which the magnitude and angle vary in an unpredictable manner over a number of measurements carried out under the same conditions;
c) scalar errors, in which the maximum magnitude can be evaluated or estimated, but its angle is indeterminate.
Depending on the manufacturing processes used, the same error can be placed in one or more categories.
Examples of error sources which may occur are listed in 4.2, 4.3, and 4.4.
Some of these errors are discussed in greater detail in Annex A.
4.2 Systematic errors
Examples of balancing machine systematic error sources are:
a) inherent unbalance in the drive shaft;
b) inherent unbalance in the mandrel;
c) radial and axial runout of the drive element on the rotor shaft axis;
d) radial and axial runout in the fit between the component to be balanced or in the balancing machine mandrel (see 5.3);
e) lack of concentricity between the journals and support surfaces used for balancing;
f) radial and axial runout of rolling element bearings which are used to support the rotor;
g) radial and axial runout of rotating races (and their tracks) of rolling element bearings fitted after balancing;
h) unbalance due to keys and keyways;
i) residual magnetism in the rotor or mandrel;
j) reassembly errors;
k) balancing equipment and instrumentation errors;
l) differences between service shaft and balancing mandrel diameters;
m) universal joint defects;
n) temporary bend in the rotor during balancing;
o) permanent bend in the rotor after balancing.
4.3 Randomly variable errors
Examples of balancing machine randomly variable error sources are:
a) loose parts;
b) entrapped liquids or solids;
c) distortion caused by thermal effects;
d) windage effects;
e) use of a loose coupling as a drive element;
f) transient bend in the horizontal rotor caused by gravitational effects when the rotor is stationary.
4.4 Scalar errors
Examples of balancing machine scalar error sources are:
a) changes in clearance at interfaces that are to be disassembled after the balancing process;
b) excessive clearance in universal joints;
c) excessive clearance on the mandrel or shaft;
d) design and manufacturing tolerances;
e) runout of the balancing machine support rollers if their diameters and the rotor journal diameter are the same, nearly the same or have an integer ratio.
5 Error assessment
5.1 General
In some cases, rotors are in balance by design, are uniform in material and are machined to such narrow tolerances that they do not need to be balanced after manufacture. Where rotor initial unbalance exceeds the permitted values given in ISO 1940-1 or ISO 11342, the rotor shall be balanced.
5.2 Errors caused by balancing equipment and instrumentation
Balance errors caused by balancing equipment and instrumentation can increase with the magnitude of the unbalance present. By considering unbalance causes during the design stage, some error sources can be completely eliminated (e.g. by combining several parts into one) or reduced (e.g. by specifying decreased tolerances). It is necessary to weigh the cost due to tighter specified tolerances against the benefit of decreased unbalance. Where the causes of unbalance cannot be eliminated or reduced to negligible levels, they should be mathematically evaluated.
5.3 Balance errors caused by component radial and axial runout
When a perfectly balanced rotor component is mounted eccentrically to the rotor shaft axis, the resulting static unbalance, Us, of the component, in g⋅mm, is given by Equation (1):
Us=m×e (1)
where,
m——the mass of the component, in g;
e——the eccentricity of the rotor component relative to the rotor shaft axis, in mm..
Note: The mass can be stated in kg, the eccentricity in µm, but the static unbalance remains in units of g⋅mm.
The static unbalance of the component creates an identical static unbalance of the assembled rotor. An additional moment unbalance results if the component is mounted eccentrically in a plane other than that of the centre of mass. The further the plane distance is from the centre of mass, the larger the moment unbalance.
If a perfectly balanced component is mounted concentrically, but with its principal axis of inertia inclined to the rotor shaft axis, the moment unbalance results are as shown in Figure 1.
For a small inclination angle, ∆γ, between the two axes, the resulting moment unbalance, Pr, in g·mm2, is approximately equal to the difference between the moments of inertia (Ix and Iz) about the component x- and z-axes, multiplied by the angle, ∆γ, in radians; see Equation (2):
Foreword i
Introduction iii
1 Scope
2 Normative references
3 Terms and definitions
4 Balance error sources
5 Error assessment
6 Combined error evaluation
7 Acceptance criteria
Annex A (Informative) Examples of errors, their identification and evaluation
