{"id":6168,"date":"2026-09-20T20:57:35","date_gmt":"2026-09-20T17:57:35","guid":{"rendered":"https:\/\/aesinn.com\/muayene-periyodik-kontrol\/mekanik-ekipman-muayeneleri\/iso-21940-rotor-balans-kalitesi-ve-mekanik-titresim-balanslama-bilgilendirme-rehberi\/"},"modified":"2026-09-21T22:08:48","modified_gmt":"2026-09-21T19:08:48","slug":"iso-21940-rotor-balans-kalitesi-ve-mekanik-titresim-balanslama-bilgilendirme-rehberi","status":"publish","type":"page","link":"https:\/\/aesinn.com\/en\/muayene-periyodik-kontrol\/mekanik-ekipman-muayeneleri\/iso-21940-rotor-balans-kalitesi-ve-mekanik-titresim-balanslama-bilgilendirme-rehberi\/","title":{"rendered":"ISO 21940 \u2013 Rotor Balancing Quality and Mechanical Vibration (Balancing) Information Guide"},"content":{"rendered":"<h2 class=\"wp-block-heading\">Why is imbalance a source of vibration and malfunction?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">In a rotating equipment, the situation that arises when the center of mass of the rotor does not coincide with the axis of rotation is called unbalance. As the rotor rotates, this irregularity in mass distribution produces centrifugal forces that increase with the square of the rotational speed; these forces are transferred as periodic stresses to the bearings, housing, and fasteners and manifest themselves as a dominant vibration at the rotational frequency (1X).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Uncontrolled imbalance can lead to consequences such as shortened bearing life, seal and gasket wear, increased noise, bolt loosening, shaft fatigue, and energy transfer to adjacent equipment. Therefore, balancing is a fundamental component of rotating equipment reliability and predictive maintenance. This page provides an overview of the subject.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">ISO 21940 Series and Scope<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The ISO 21940 series is a multi-part family of standards that forms the international framework for rotor balancing. The series covers a wide range of topics, from terminology and balancing quality criteria to balancing error assessment and the identification of balancing machines, and it has replaced the previously widely used ISO 1940 series.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n\n<li>ISO 21940-11: Balance quality requirements, balance tolerances and acceptance criteria for rigid (stationary) rotors \u2013 replaces the previous ISO 1940-1.<\/li>\n\n\n<li>ISO 21940-12: Procedures and tolerances for rotors exhibiting flexible behavior and varying shape and imbalance distribution depending on speed.<\/li>\n\n\n<li>ISO 21940-14: Procedures for the assessment of balancing errors.<\/li>\n\n\n<li>ISO 21940-2: Terms and definitions related to balancing (terminology\/glossary).<\/li>\n\n\n<li>ISO 21940-21: Identification and evaluation of balancing machines.<\/li>\n\n\n<li>ISO 21940-1: Introduction to series and general framework.<\/li>\n\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Balance Quality Grades (G-Classes)<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">ISO 21940-11 defines allowable residual unbalance using balance quality grades called G-class. The G-class number corresponds to a velocity value in mm\/s and is derived from the product of the allowable specific unbalance and the maximum service speed. In other words, each G-class represents a constant orbital velocity of the rotor&#039;s center of mass.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The practical consequence of this is that maintaining the same G-class at higher speeds requires lower allowable imbalance; that is, high-speed rotors must be more precisely balanced. In practice, ratings of the order of G 6.3 are often used for general machinery (pumps, fans, electric motor rotors), and G 2.5 for more sensitive equipment such as turbines and compressors.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n\n<li>G-class = allowable specific imbalance \u00d7 angular velocity; implies a constant trajectory velocity of mm\/s.<\/li>\n\n\n<li>A smaller G-value = tighter tolerance = more precise balancing.<\/li>\n\n\n<li>G 6.3: a commonly cited rating for general-purpose rotary machinery.<\/li>\n\n\n<li>G 2.5: a commonly cited rating for turbines, compressors, and precision equipment.<\/li>\n\n\n<li>The exact G-class selection depends on the equipment type, service speed, and application; the final value will be determined by a qualified engineer \u2013 the values given here are only general examples.<\/li>\n\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Types of Imbalance: Static, Coupling, and Dynamic.<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Imbalance is classified into different types depending on how the mass distribution is positioned relative to the axis of rotation. Accurate identification of the type is necessary to select the correct correction method.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n\n<li>Static (single-plane) imbalance: The rotor&#039;s center of mass is shifted parallel to the axis of rotation. The rotor always rests on the prisms with the heavier side facing down. It is prevalent in thin, disc-shaped rotors (e.g., grinding wheels, narrow fan wheels) and can usually be corrected with a single adjustment weight in a single plane.<\/li>\n\n\n<li>Coupled imbalance: The major axis of inertia intersects the axis of rotation at the center of mass, but is not parallel to it. Equilibrium is maintained in the static state; imbalance manifests only as &#039;wobble&#039; during rotation. It is seen in long cylindrical rotors and is typically corrected in two planes.<\/li>\n\n\n<li>Dynamic imbalance: A combination of static and coupled imbalance, and the most common type in practice. Correction requires mass correction in at least two planes.<\/li>\n\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Single-Plane and Two-Plane Balancing<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The number of axial planes in which correction weights are applied during balancing depends on the rotor geometry and the type of imbalance. Single-plane balancing is suitable for thin\/disk-type rotors where static imbalance predominates; the correction is performed in a single plane.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Two-plane balancing is necessary in rotors with a large length relative to their diameter, where coupled or dynamic imbalance is present; correction is performed in at least two separate planes. Since the imbalance of a rigid rotor can be fully defined by a static imbalance and a balance coupled, a rigid rotor never requires more than two planes. Flexible rotors are dealt with separately under ISO 21940-12.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Field Balancing and Balancing on a Balancing Machine<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Balancing can be performed in two main environments. Shop balancing involves removing the rotor from the equipment and connecting it to a special balancing machine for balancing under controlled conditions and generally with higher precision. The identification and evaluation of balancing machines are covered under ISO 21940-21.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Field\/in-situ balancing is the balancing of the rotor in its own bearings and operating conditions. It is advantageous because it eliminates disassembly costs and allows for evaluation of the rotor under actual assembly conditions; however, due to measurement conditions and access restrictions, the selection of the appropriate method requires technical evaluation. Which approach is suitable should be determined by a qualified engineer based on the equipment and conditions.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Relationship between Balancing and Vibration Assessment (ISO 20816)<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Balance and vibration assessment are two complementary concepts. Imbalance is often a root cause, while vibration is a measurable consequence of this and similar causes. The ISO 20816 series (and its predecessor ISO 10816) defines the framework for measuring and evaluating the general vibration levels of machinery; ISO 21940, on the other hand, directly targets the balance quality of the rotor.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In practice, these two areas are used together: Vibration measurement can indicate a possible imbalance by showing a dominant component in the rotational frequency (1X); balancing provides the correction aimed at eliminating this root cause. However, imbalance is not the only cause of high vibration \u2013 factors such as misalignment, looseness, bearing defects, and resonance can also play a role. Therefore, interpreting vibration findings and making balancing decisions requires a holistic engineering assessment.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n\n<li>Imbalance: root cause (rotor mass distribution) \u2013 ISO 21940 scope.<\/li>\n\n\n<li>Vibration: result\/indicator \u2013 ISO 20816 \/ ISO 10816 scope.<\/li>\n\n\n<li>The two frameworks complement each other; vibration guides the diagnosis, balancing reduces the root cause.<\/li>\n\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Which Equipment Requires Balancing?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Balancing is relevant to virtually any equipment with a rotating mass. In industry, the rotating equipment most frequently requiring balancing includes fans and blowers, centrifugal pumps, compressors, steam and gas turbines, electric motor and generator rotors, shafts, couplings, centrifuges, and rotating parts of drive units.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The appropriate balance quality grade (G-class), type of imbalance, and number of balancing planes vary from piece to piece. These selections should be made by a qualified engineer based on the type of equipment, service speed, operating conditions, and relevant standards.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">AES Accreditation Scope<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">AES (aesinn.com) is a Type A inspection body accredited by T\u00dcRKAK. AES&#039;s accreditation scope is limited to 6.1 Electrical Installations. The ISO 21940 rotor balancing and mechanical vibration assessment topics discussed on this page are outside the scope of AES&#039;s accredited inspections and are presented here for general informational purposes only.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Information Note<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">AES is NOT an accredited inspection\/certification body in this context. The content on this page is for informational purposes only and is based on the technical assessment of an authorized engineer.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The given G-class examples and general descriptions do not replace the application-specific provisions of the relevant standards. The exact balance levels, balancing method, and acceptance criteria are determined by a qualified engineer according to the equipment, standard, and site conditions.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Related Services<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n\n<li><a href=\"https:\/\/aesinn.com\/en\/muayene-periyodik-kontrol\/mekanik-ekipman-muayeneleri\/titresim-analizi-ve-kestirimci-bakim-pompa-fan-kompresor-motor\/\">Vibration Analysis and Predictive Maintenance<\/a><\/li>\n\n\n<li><a href=\"https:\/\/aesinn.com\/en\/muayene-periyodik-kontrol\/mekanik-ekipman-muayeneleri\/guvenilirlik-merkezli-bakim-rcm-ve-guvenilirlik-verisi-iso-14224-ve-sae-ja1011\/\">Reliability-Centered Maintenance (RCM)<\/a><\/li>\n\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Frequently Asked Questions<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">What is the relationship between ISO 21940 and the older ISO 1940?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The ISO 21940 series is the current international standard family for rotor balancing and has replaced the previous ISO 1940 series. For example, ISO 21940-11, which defines the balancing quality requirements for rigid rotors, replaces the old ISO 1940-1. The balancing quality grades (G-classes) and the basic method have been largely retained.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">What does G-class (balance quality rating) mean?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The G-class number is a speed rating in mm\/s and is derived from the product of the allowable specific imbalance and the service speed. A smaller G value means tighter tolerances and more precise balancing. G 6.3 is commonly cited for general machinery, while G 2.5 is for precision equipment such as turbines\/compressors; however, the exact value varies depending on the application and is determined by a qualified engineer.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">What is the difference between static, coupled, and dynamic imbalance?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">In static imbalance, the center of mass is shifted parallel to the axis of rotation and is usually corrected in a single plane. In coupled imbalance, the axis of inertia intersects the axis of rotation but is not parallel; it appears balanced in the static state, only creating wobble during rotation, and is corrected in two planes. Dynamic imbalance is a combination of these two, is the most common type, and requires at least two-plane correction.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Do we need single-plane or two-plane balancing?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">This depends on the rotor geometry and the type of imbalance. Thin\/disk-type rotors, where static imbalance is dominant, are generally balanced in a single plane. In rotors with a length relative to diameter, two planes are required when coupled or dynamic imbalance is present. Selection of the appropriate approach requires evaluation by a qualified engineer.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Are balancing and vibration measurement the same thing?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">No. Imbalance is often a root cause, while vibration is a measurable result. ISO 20816\/10816 addresses the vibration assessment framework, while ISO 21940 deals with the rotor&#039;s balance quality. The two fields complement each other; vibration measurement can indicate potential imbalance, while balancing aims to eliminate the root cause. High vibration can also have causes other than imbalance.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Does AES perform rotor balancing inspection or certification?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">AES is not an accredited inspection\/certification body in this context. AES&#039;s T\u00dcRKAK accreditation scope is limited to 6.1 Electrical Installations. The content on this page is for informational purposes only and is subject to the technical assessment of an authorized engineer.<\/p>","protected":false},"excerpt":{"rendered":"<p>D\u00f6ner ekipmanlarda balanss\u0131zl\u0131k (unbalance) titre\u015fimin ba\u015fl\u0131ca k\u00f6k nedenlerindendir. Bu bilgilendirme sayfas\u0131 ISO 21940 serisini, balans kalite derecelerini (G-s\u0131n\u0131flar\u0131), balanss\u0131zl\u0131k t\u00fcrlerini ve balanslaman\u0131n ISO 20816 titre\u015fim de\u011ferlendirmesiyle ili\u015fkisini objektif bi\u00e7imde a\u00e7\u0131klar.<\/p>","protected":false},"author":1,"featured_media":6172,"parent":4099,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"_kad_blocks_custom_css":"","_kad_blocks_head_custom_js":"","_kad_blocks_body_custom_js":"","_kad_blocks_footer_custom_js":"","_kadence_starter_templates_imported_post":false,"_kad_post_transparent":"","_kad_post_title":"","_kad_post_layout":"","_kad_post_sidebar_id":"","_kad_post_content_style":"","_kad_post_vertical_padding":"","_kad_post_feature":"","_kad_post_feature_position":"","_kad_post_header":false,"_kad_post_footer":false,"_kad_post_classname":"","slim_seo":{"title":"ISO 21940 Rotor Balancing Quality | Information","description":"ISO 21940 rotor balancing series provides engineering-focused information on balance quality grades (G-classes), types of imbalance, and vibration relationships."},"_pplb_hide_from_list":false,"footnotes":""},"class_list":["post-6168","page","type-page","status-publish","has-post-thumbnail","hentry"],"acf":[],"taxonomy_info":[],"featured_image_src_large":["https:\/\/aesinn.com\/wp-content\/uploads\/iso21940-aes-kart-1024x1024.png",1024,1024,true],"author_info":{"display_name":"Emre Metin","author_link":"https:\/\/aesinn.com\/en\/author\/yonetim\/"},"comment_info":"","_hostinger_reach_plugin_has_subscription_block":false,"_hostinger_reach_plugin_is_elementor":false,"_links":{"self":[{"href":"https:\/\/aesinn.com\/en\/wp-json\/wp\/v2\/pages\/6168","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/aesinn.com\/en\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/aesinn.com\/en\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/aesinn.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/aesinn.com\/en\/wp-json\/wp\/v2\/comments?post=6168"}],"version-history":[{"count":2,"href":"https:\/\/aesinn.com\/en\/wp-json\/wp\/v2\/pages\/6168\/revisions"}],"predecessor-version":[{"id":6177,"href":"https:\/\/aesinn.com\/en\/wp-json\/wp\/v2\/pages\/6168\/revisions\/6177"}],"up":[{"embeddable":true,"href":"https:\/\/aesinn.com\/en\/wp-json\/wp\/v2\/pages\/4099"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/aesinn.com\/en\/wp-json\/wp\/v2\/media\/6172"}],"wp:attachment":[{"href":"https:\/\/aesinn.com\/en\/wp-json\/wp\/v2\/media?parent=6168"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}