ISO 21940-21-2022 PDF

Full title and description

Mechanical vibration — Rotor balancing — Part 21: Description and evaluation of balancing machines (ISO 21940-21:2022). This International Standard specifies requirements and methods for describing, testing and evaluating the performance of balancing machines used to measure and correct unbalance in rotating components.

Abstract

ISO 21940-21:2022 sets out the requirements for evaluating hard- and soft-bearing balancing machines that support and rotate: (a) rotors with rigid behaviour at balancing speed (as described in ISO 21940‑11) and (b) rotors with shaft-elastic behaviour when balanced using low-speed balancing procedures (as described in ISO 21940‑12). The document specifies evaluation tests, acceptance and periodic test procedures and recommended forms for reporting balancing-machine characteristics.

General information

• Status: Published.
• Publication date: 7 November 2022 (Edition 2, 2022).
• Publisher: International Organization for Standardization (ISO).
• ICS / categories: 21.120.40 (Balancing and balancing machines).
• Edition / version: Edition 2 (2022).
• Number of pages: 62 pages (official ISO edition).

Scope

The standard applies to balancing machines that support and rotate rotors showing rigid or shaft-elastic behaviour at balancing speed and which indicate the magnitude and angular position of required unbalance corrections in one or more planes. It covers both hard-bearing and soft-bearing machines, describes acceptance and periodic test procedures for machine performance and specifies the information formats by which manufacturers should present machine characteristics. Special features such as automatic correction systems are not the primary focus of this part.

Key topics and requirements

• Definition of machine types and applicable rotor behaviour (rigid vs. shaft-elastic).
• Requirements and procedures for evaluating balancing-machine performance (acceptance and periodic tests).
• Specified evaluation tests (historically and typically including minimum achievable residual unbalance (Umar), unbalance reduction ratio (URR), couple unbalance interference and compensator tests) and formats for reporting results.
• Guidance on the form and content of manufacturer specifications to enable objective comparison of balancing machines.
• Applicability notes and limitations (e.g., the standard does not itself set balancing acceptance criteria — those are given in other standards such as ISO 1940‑1).

Typical use and users

This standard is used by balancing-machine manufacturers and designers to define and demonstrate machine performance; by test laboratories and quality/acceptance engineers to perform acceptance and periodic verification tests; by maintenance and reliability engineers to select and validate balancing equipment; and by procurement specialists and OEMs specifying balancing-machine capabilities for production and repair facilities. It is also a reference for researchers and educators working on rotor-dynamics and vibration control.

Related standards

ISO 21940 is a multipart series. Key related documents include ISO 21940‑1 (Introduction to rotor balancing), ISO 21940‑11 (procedures and tolerances for rotors with rigid behaviour), ISO 21940‑12 (procedures and tolerances for rotors with flexible/shaft-elastic behaviour) and other parts that cover error assessment and related methods. ISO 1940‑1 is commonly referenced for balance quality grades and acceptance criteria.

Keywords

balancing machine, rotor balancing, mechanical vibration, unbalance testing, hard-bearing, soft-bearing, Umar test, URR test, rotor dynamics, acceptance testing, periodic verification.

FAQ

Q: What is this standard?

A: ISO 21940-21:2022 is the part of the ISO 21940 series that specifies how to describe, test and evaluate the performance of balancing machines used to detect and correct unbalance in rotating components.

Q: What does it cover?

A: It covers requirements for evaluating hard- and soft-bearing balancing machines supporting rotors with rigid or shaft-elastic behaviour, including acceptance and periodic test procedures, recommended reporting formats and guidance to ensure machines meet intended balancing tasks. It does not define balance acceptance criteria themselves.

Q: Who typically uses it?

A: Balancing-machine manufacturers, test and calibration laboratories, maintenance and reliability engineers, OEMs, procurement teams, and researchers and educators involved in rotor dynamics and vibration control.

Q: Is it current or superseded?

A: ISO 21940-21:2022 (Edition 2, published November 2022) is the current published edition and it supersedes ISO 21940-21:2012 (withdrawn). Users should verify national adoptions or amendments for their country.

Q: Is it part of a series?

A: Yes — it is part of the ISO 21940 series on rotor balancing (parts include introductory, procedures and tolerances for rigid and flexible rotors, machine evaluation and related methods). It is intended to be used together with other parts of ISO 21940 and with standards such as ISO 1940‑1 for balance quality grades.

Q: What are the key keywords?

A: Balancing machine, rotor balancing, unbalance, Umar, URR, hard-bearing, soft-bearing, rotor dynamics, acceptance testing, periodic verification.