ISO 21940-2:2017

Overview

ISO 21940-2:2017 is an international standard titled "Mechanical vibration - Rotor balancing - Part 2: Vocabulary", published by ISO. This standard systematically defines terminology related to rotor balancing, a fundamental aspect of mechanical vibration analysis. It complements ISO 2041, the general vocabulary standard on mechanical vibration and shock, by focusing specifically on terms essential for the accurate description, measurement, and management of rotor unbalance and balancing techniques.

The document provides a clear, standardized vocabulary to support engineers, researchers, and technicians in the fields of rotor dynamics, mechanical vibration, and machine maintenance. It enhances communication and consistency across industries where rotor balancing is critical for operational stability, safety, and longevity of rotating machinery.

Key Topics

ISO 21940-2:2017 categorizes vocabulary into several key areas essential for understanding and applying rotor balancing:

• Mechanics of Rotor Systems

  • Principal axis of inertia, speed-related terms (rotational speed, frequency, angular velocity)
  • Resonance speeds including rigid-body and flexural resonance speeds
  • Definitions of service speed, balancing speed, and axis of rotation

• Rotor Systems Terminology

  • Rigid vs. flexible rotor behavior and associated factors like shaft-elastic behavior
  • Components such as journals, journal axes, shaft axis, and types of rotors (inboard, outboard)
  • Important geometric and dynamic terms including mass eccentricity and slow-speed runout

• Unbalance Definitions

  • Types and conditions of unbalance: static, moment, couple, dynamic, initial, and residual unbalance
  • Unbalance vectors, amounts, and angles that specify magnitude and location
  • Concepts such as resultant unbalance and modal unbalance critical for advanced rotor balancing

• Balancing Procedures

  • Definitions of balancing itself and its variations: single-plane, two-plane, multiplane, and modal balancing
  • Correction processes to reduce unbalance and optimize rotor performance

• Balancing Machines and Accessories

  • Vocabulary for equipment used during balancing procedures, illustrated further in Annex A for practical understanding

Applications

The terminology defined in ISO 21940-2:2017 is vital in a wide range of practical applications, including:

• Industrial Machinery Maintenance

  • Ensuring rotating machinery operates smoothly by identifying and remedying unbalances to prevent excessive vibration and wear.

• Design and Testing of Rotors

  • Engineers use standardized vocabulary to describe rotor dynamics accurately and communicate design requirements clearly.

• Condition Monitoring and Diagnostics

  • Interpreting vibration data and correlating unbalance conditions to maintenance actions using consistent terminology.

• Balancing Machine Calibration and Operation

  • Standardized terms improve operator training, calibration, and operation of balancing equipment, ensuring effective balancing results.

• Safety and Compliance

  • Uniform language helps meet international regulations and quality standards concerning machine reliability and worker safety.

By using clear, consistent terms from ISO 21940-2, organizations can improve the efficiency of vibration analysis, maintenance scheduling, and failure prevention strategies.

Related Standards

ISO 21940-2:2017 complements and interfaces with several other international standards:

• ISO 2041: Mechanical vibration - Vocabulary

  • Provides broader terminology on mechanical vibration and shock, forming the foundational vocabulary that ISO 21940-2 extends specifically for rotor balancing.

• ISO 21940 Series

  • The larger series that covers rotor balancing comprehensively with multiple parts addressing methods, equipment, and evaluation criteria.

• ISO/IEC Directives

  • Governing document preparation and maintenance procedures to ensure clarity, coherence, and quality of ISO standards.

Additionally, the terminology databases maintained by ISO and IEC, such as the IEC Electropedia and the ISO Online browsing platform, offer further terminological resources aligned with ISO 21940-2.

Keywords: rotor balancing, mechanical vibration, rotor unbalance, balancing vocabulary, ISO 21940-2, rotor dynamics, vibration analysis, unbalance correction, balancing procedures, mechanical maintenance, balancing machines, resonance speed, flexible rotor, rotor terminology, industrial machinery maintenance, vibration standards.