AHRI GUIDELINE G SI-2016 Mechanical Balance of Impellers for Fans.pdf

1、 2016 Guideline for Mechanical Balance of Impellers for Fans AHRI Guideline G (SI) Price $10.00 (M) $20.00 (NM) Copyright 2016, by Air-Conditioning, Heating, and Refrigeration Institute Printed in U.S.A. Registered United States Patent and Trademark Office IMPORTANT SAFETY DISCLAIMER AHRI does not s

2、et safety standards and does not certify or guarantee the safety of any products, components or systems designed, tested, rated, installed or operated in accordance with this standard/guideline. It is strongly recommended that products be designed, constructed, assembled, installed and operated in a

3、ccordance with nationally recognized safety standards and code requirements appropriate for products covered by this standard/guideline. AHRI uses its best efforts to develop standards/guidelines employing state-of-the-art and accepted industry practices. AHRI does not certify or guarantee that any

4、tests conducted under the standards/guidelines will not be non-hazardous or free from risk. Note: This guideline supersedes AHRI Guideline G-2011. For I-P, see AHRI Guideline G (I-P)-2016. TABLE OF CONTENTS SECTION PAGE Section 1. Purpose 1 Section 2. Scope . 1 Section 3. Definitions . 1 Section 4.

5、Instrumentation and Measurement 3 Section 5. Balancing Methods 4 Section 6. Unbalance Limit . 5 TABLES Table 1. Summary of Balancing Methods . 5 Table 2. Unbalance Limits 6 APPENDICES Appendix A. References Normative 7 Appendix B. References Informative 7 Appendix C. System Vibration Informative 8 A

6、HRI GUIDELINE G (SI)-2016 1 MECHANICAL BALANCE OF IMPELLERS FOR FANS Section 1. Purpose 1.1 Purpose. The purpose of this document is to provide fundamental information and to guide the industry on Balance as applied to Impellers used in air moving systems. It includes terminology used and methods of

7、 Balancing practiced by the industry. 1.1.1 Intent. This document is intended for the guidance of component suppliers and equipment manufacturers. 1.1.2 Review and Amendment. This document is subject to review and amendment as technology advances. Section 2. Scope 2.1 Scope. This document is intende

8、d to apply specifically to system vibration and mechanical Balancing as related to Impellers for Fans. The principles presented can however be generally applied to many rotating components (Rotors). This document covers Impellers and propellers while fan systems are covered by Air Movement and Contr

9、ol Association International, Inc. (AMCA) Standard 204. For information on system vibration, see Appendix C. Section 3. Definitions All terms in this document will follow the standard industry definitions in the ASHRAE Terminology website (https:/www.ashrae.org/resources-publications/free-resources/

10、ashrae-terminology) unless otherwise defined in this section. 3.1 Balance. The unique and ideal condition of a Rotor when it has neither static nor dynamic Unbalance. Such a Rotor does not impart any vibratory force or motion to its Bearings as a result of centrifugal forces. 3.2 Balancing. A proced

11、ure by which the mass distribution of a Rotor is checked and, if necessary, adjusted in order to ensure that the vibration of the Journals and/or forces on the Bearings at a frequency corresponding to operating speed are within specified limits. 3.2.1 Dynamic (Two-plane) Balancing. A procedure by wh

12、ich the mass distribution of a Rigid Rotor is resolved into two planes and adjustments made by adding or removing mass in those planes in order to reduce the primary force and secondary force couple caused by the initial Unbalance. 3.2.2 Static (Single-plane) Balancing. A procedure by which the mass

13、 distribution of a Rigid Rotor is resolved into one plane and adjustments made by adding or removing mass in that plane only in order to reduce the initial Unbalance force. 3.3 Balancing Machine. A machine that provides a measure of the Unbalance in a Rotor which can be used for adjusting the mass d

14、istribution of that Rotor. 3.3.1 Centrifugal (Rotational) Balancing Machine. A Balancing Machine that provides for the support and rotation of a Rotor and for the measurement of once per revolution vibratory forces or motions due to Unbalance in the Rotor. 3.3.2 Gravitational (Non-rotating) Balancin

15、g Machine. A Balancing Machine that provides for the support of a Rigid Rotor under non-rotating conditions and provides information on the amount and angle of the static Unbalance. 3.3.3 Dynamic (Two-plane) Balancing Machine. A Centrifugal Balancing Machine that furnishes information for performing

16、 Two-plane Balancing. 3.3.4 Static (Single-plane) Balancing Machine. A Gravitational or Centrifugal Balancing Machine that provides information for accomplishing Single-plane Balancing. AHRI GUIDELINE G (SI)-2016 2 Note: Dynamic (Two-plane) Balancing Machines can be used to accomplish Static (Single

17、-plane) Balancing, but Static Machines cannot be used for Dynamic Balancing. 3.4 Bearing. A part which supports a Journal and in which the Journal rotates. 3.5 Correction (Balancing) Plane. A plane perpendicular to the Shaft Axis of a Rotor in which correction for Unbalance is made. 3.6 Critical Spe

18、ed. The speed that corresponds to a Resonance Frequency of the Rotor when operating on its own Bearings and support structure. 3.7 Fan. A device that uses a power-driven rotating Impeller to move air. 3.8 Field (Trim) Balancing. The process of reducing the vibration level of a rotating assembly afte

19、r all the rotating components, such as an Impeller or Propeller, motor armature or rotor assembly, or Bearings and pulleys, are assembled to their respective shaft(s). Such Balancing is employed to compensate for the vibrational effects of the tolerances of the drive components. 3.9 Impeller. The as

20、sembled rotating component of a Fan, designed to increase the energy level of the airstream. 3.10 Journal. The part of a Rotor which is in contact with or supported by a Bearing in which it revolves. 3.11 Propeller. A type of Impeller that produces a useful thrust of air in the direction parallel wi

21、th the Shaft Axis. 3.12 Resonance. Resonance of a system in forced vibration exists when any change, however small, in the frequency of excitation (such as rotor speed) causes a decrease in the vibration amplitude. 3.13 Resonance Frequency. A frequency at which Resonance occurs in a given body or sy

22、stem or in a Rotor at Critical Speeds. This is often called natural frequency. 3.14 Rotor. A body, capable of rotation, generally with Journals which are supported by Bearings. 3.15 Rigid Rotor. A Rotor is considered rigid when it can be corrected in any two (arbitrarily selected) planes (refer to S

23、ection 3.5) and after that correction, its Unbalance does not significantly exceed the Balancing Tolerances (relative to the Shaft Axis) at any speed up to maximum operating speed and when running under conditions which approximate closely those of the final supporting system. Note: A Rigid Rotor ha

24、s sufficient structural rigidity to allow Balancing corrections to be made below the operating speed. 3.16 Shaft Runout. The wobbling motion produced by a shaft that is not perfectly true and straight. Shaft Runout is often abbreviated as TIR (Total Indicated Runout, a measurement of how much a shaf

25、t wobbles with each revolution). 3.17 Shaft Axis. The straight line joining the Journal centers. 3.18 Should. “Should” is used to indicate provisions which are not mandatory but which are desirable as good practice. 3.19 System Balance. System Balance includes the entire rotating assembly mass, oper

26、ating speed, and the application. 3.20 Unbalance. That condition which exists in a Rotor when vibratory force or motion is imparted to its Bearings as a result of centrifugal forces. 3.20.1 Residual Unbalance. Unbalance of any kind that remains after Balancing. 3.20.2 Unbalance Amount. The quantitat

27、ive measure of Unbalance in a Rotor (referred to a plane) without referring to its angular position (refer to the Unbalance Angle). It is obtained by taking the product of the Unbalance Mass and the distance of its center of gravity from the Shaft Axis. 3.20.3 Unbalance Angle. Given a polar coordina

28、te system fixed in a plane perpendicular to the Shaft Axis and rotating with the Rotor, the polar angle at which an Unbalance Mass is located with reference to the given coordinate system. AHRI GUIDELINE G (SI)-2016 3 3.20.4 Unbalance Mass. That mass which is considered to be located at a particular

29、 radius such that the product of this mass and its centripetal acceleration is equal to the Unbalance force. 3.20.4.1 The centripetal acceleration is the product of the distance between the Shaft Axis and the Unbalance Mass and the square of the angular velocity of the Rotor in radians per second. 3

30、.21 Unbalance Limit. In the case of Rigid Rotors, that amount of Residual Unbalance with respect to a radial plane (measuring plane or Correction Plane) which is specified as the maximum below which the state of Unbalance is considered acceptable. Section 4. Instrumentation and Measurement 4.1 Instr

31、umentation to Measure Vibration. Vibration meters and stroboscopic equipment are used on complete systems with the Impeller or Rotor on its own Bearings and supporting structure rather than a Balancing Machine. This is commonly referred to as Field Balancing. Vibration meters used should be capable

32、of electrically filtering the vibration signal so that it can be tuned to the rotating frequency of the Rotor being balanced. The vibratory motion caused by Unbalance occurs at this frequency. The use of a tunable vibration meter will allow the operator to determine if the maximum vibration is at th

33、e rotating speed or from some frequency due to other causes of vibration. Many hand held vibration meters do not have electrical filters and only measure total vibration amplitude. These meters are of questionable value in solving vibration problems. Vibration levels can be measured in terms of disp

34、lacement, velocity or acceleration. Velocity as a measure of vibration is coming into general use and is favored for several reasons. The destructive forces generated in a machine because of Unbalance depends much more on velocity than on displacement or acceleration. Such electronic instrumentation

35、 will pick up the vibration signal, convert it to a convenient unit, such as kilogram-millimeters and locate the point of Unbalance. 4.2 Instrumentation to Measure Unbalance. There is a variety of instrumentation available to measure Unbalance Amounts in Rotors. This instrumentation varies from simp

36、le knife edge or roller ways to complex electronic production Balancing. The following outlines the variety of equipment and instrumentation available and their normal use and application. 4.2.1 Balancing Machines: Normally used for production or inspection of Impellers and Rotors. Machines availabl

37、e are: 4.2.1.1 Non-rotating Types. i.e. knife edge, roller ways and vertical arbor (single-plane, non-rotating). 4.2.1.2 Rotating Types. i.e. horizontal arbor (single-plane, rotating), horizontal arbor (two-plane, rotating), vertical arbor (single-plane, rotating) and vertical arbor (two-plane, rota

38、ting). 4.2.2 Rotating Balancing Machines equipped with either hard or soft Bearings. 4.2.2.1 Hard (stiff suspension) bearing machines use force transducers to measure the force(s) exerted on the Bearings due to centrifugal force(s) acting on the Unbalance Mass(es). 4.2.2.2 Soft (flexible suspension)

39、 bearing machines use motion transducers to measure the Bearing motion caused by centrifugal forces acting on the Unbalance Mass(es). 4.2.2.3 To evaluate the accuracy of Balancing Machines, refer to ISO Standard 21940-21. 4.2.3 Measuring Units for Unbalance. All Balancing Machines provide informatio

40、n on the magnitude of Unbalance and a location where correction is to be made. Unbalance is usually reported in kgmm. AHRI GUIDELINE G (SI)-2016 4 Section 5. Balancing Methods 5.1 Types of Balancing. A Rotor can be balanced either by Static Balancing or by Dynamic Balancing. The method chosen is dep

41、endent upon many factors such as physical size, shape, mass, and unbalance limit requirements (see ISO Standard 1940). For instance, Dynamic Balancing would usually be employed if a Rotor is relatively wide, compared to its diameter, so that measurements and adjustments can be made in two axially se

42、parated Correction Planes. Static Balancing, however, would be employed on a narrow Rotor, where measurements and adjustments can be made in only one Correction Plane. It is important to note that, Static Balancing can be accomplished by either rotating or non-rotating means while Dynamic Balancing

43、can only be accomplished by rotating means. 5.2 Methods of Balancing. 5.2.1 Non-rotating. The simplest method of Static Balancing consists of a Rotor mounted with its axis horizontal and allowed to pivot about its Shaft Axis. Any deviation of the center of mass relative to the Shaft Axis will cause

44、it to pivot. Mass can then be added to or subtracted from the Rotor until there is no pivoting. The latest technology for non-rotating Static Balancing utilizes a vertical arbor or axis, and uses the force of gravity to provide electronic signals to indicate the amount of correction required and its

45、 location. 5.2.2 Rotating. Dynamic Balancing is normally accomplished with an electronic Balancing Machine which usually has a rotating horizontal arbor, with either hard or soft Bearings (refer to Section 5.2.2), capable of measuring the amount and location of Unbalance in each of two axially separ

46、ated planes. Two-plane rotating Balance is the preferred method for Balancing Impellers when the width to diameter ratio is greater than 0.30. The narrow width of propeller Fans and narrow Impellers make plane separation impractical, and corrections are only made in one plane. When an Impeller is ba

47、lanced dynamically, corrections are made in each of two correctional planes. This compensates for the “couple” effect caused when the Unbalance locations for each plane are out of phase with each other. 5.3 Correcting for Unbalance. Correcting for Unbalance is accomplished by adding or removing an a

48、ppropriate amount of mass from one or more locations on an Impeller. 5.4 Summary of Balancing Methods. Refer to Table 1. AHRI GUIDELINE G (SI)-2016 5 Table 1. Summary of Balancing Methods Type of Balancing Method Instrumentation (Section 4.2) Static Balancing Single-plane Non-rotating Horizontal Kni

49、fe edge, Roller ways Vertical Pendulum (electric or non-electric read-out) Single-plane Rotating (centrifugal) Electronic Balancing Machine (horizontal or vertical arbor) Dynamic Balancing Two-plane Rotating (centrifugal) Electronic Balancing Machine (usually horizontal arbor) Section 6. Unbalance Limit 6.1 When an Impeller or Propeller is balanced separately as a component, Balancing is done as described in Section 5 and the Unbalance Limit is expressed in mass displacement units. 6.2 Unbalance Limits that result in acceptable vibration levels for