GB/T 3785.1-2023 Mechanical vibration - Rotor balancing - Part 31: Susceptibility and sensitivity of machines to unbalance
1 Scope
This document specifies methods for determining machine vibration sensitivity to unbalance and provides evaluation guidelines as a function of the proximity of relevant resonance rotational speeds to the operating speed. This document is only concerned with once-per-revolution vibration caused by unbalance. It also makes recommendations on how to apply the numerical sensitivity values in some particular cases.
It includes a classification system that can be applied to machines which is related to their susceptibility to a change in unbalance. Machines are classified into three types of susceptibility and five ranges of sensitivity. The sensitivity values are intended for use on simple machine systems, preferably with rotors having only one resonance speed over their entire operating speed range. The sensitivity values can also be used for machines that have more resonance speeds in their operating speed range if the resonance speeds are widely separated (e.g. by more than 20 %).
The sensitivity values given are not intended to serve as acceptance specifications for any machine group, but rather to give indications regarding how to avoid gross deficiencies as well as specifying exaggerated or unattainable requirements. They can also serve as a basis for more involved investigations (e.g. when in special cases a more exact determination of the required sensitivity is necessary). If due regard is paid to the values given, satisfactory running conditions can be expected in most cases.
The consideration of the sensitivity values alone does not guarantee that a given magnitude of vibration in operating is not exceeded. Many other sources of vibration can occur which lie outside the scope of this document.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 21940-2 Mechanical vibration - Rotor balancing - Part 2: Vocabulary
Note: GB/T 6444-2008, Mechanical vibration - Balancing - Vocabulary (ISO 1925:2001, IDT)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 21940-2 apply.
Note: Some of the terms used are explained in Annex A.
4 Machine susceptibility classification
4.1 General
Machine susceptibility classification is based on the likelihood of a machine experiencing significant unbalance during operation. Machines with low susceptibility are allowed higher sensitivity values (require less damping), and machines with high susceptibility are restricted to lower sensitivity values (require more damping).
4.2 Type I: Low susceptibility
Machines of this type have a low likelihood of experiencing significant unbalance changes during operation. Typically they have a large rotor mass in comparison to their support housing and operate in a clean environment, have negligible wear and exhibit minimal rotor distortion caused by temperature change.
Examples: Paper machine rolls, printing rolls, and high-speed vacuum pumps.
4.3 Type II: Moderate susceptibility
Machines of this type have a moderate likelihood of experiencing significant unbalance changes during operation. Typically they are machines which operate in environments with large temperature changes or experience moderate wear.
Examples: Pumps in clean media, electric armatures, gas and steam turbines, generators, and turbo compressors.
4.4 Type III: High susceptibility
Machines of this type have a high likelihood of experiencing significant unbalance changes during operation. Typically they are machines which run in deposit producing (e.g. pumps operating in sludge) or corrosive environments.
Examples: Centrifuges, fans, screw conveyors, and hammer mills.
4.5 Machine susceptibility correction factors
The remainder of this part of ISO 21940 focuses on moderate susceptibility classification machines (type II). For evaluation of low susceptibility or high susceptibility machines, a correction factor can be applied to adjust the sensitivity range. Table 1 shows correction factors that are applied to the sensitivity values (see Clause 5) based on machine susceptibility type (see 4.2 to 4.4).
