1、 2011 Guideline for Mechanical Balance of Fans and Blowers AHRI Guideline G (SI) Price $10.00 (M) $20.00 (NM) Copyright 2011, by Air-Conditioning, Printed in U.S.A. Heating, and Refrigeration Institute Registered United States Patent and Trademark Office IMPORTANT SAFETY DISCLAIMER AHRI does not set
2、 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 acc
3、ordance 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 te
4、sts conducted under the standards/guidelines will not be non-hazardous or free from risk. Note: This guideline supersedes AHRI Guideline G-2002. For I-P, see AHRI Guideline G (I-P)-2001. TABLE OF CONTENTS SECTION PAGE Section 1. Purpose .1 Section 2. Scope 1 Section 3. Definitions1 Section 4. System
5、 Vibration .3 Section 5. Instrumentation and Measurement .4 Section 6. Balancing Methods 5 Section 7. Unbalance Limit 6 TABLES Table 1. Summary of Balancing Methods .6 Table 2. Unbalance Limits for Impellers 7 APPENDICES Appendix A. References Normative .8 Appendix B. References Informative .8 AHRI
6、GUIDELINE G (SI)-2011 1 MECHANICAL BALANCE OF FANS AND BLOWERS Section 1. Purpose 1.1 Purpose. The purpose of this document is to provide fundamental information and to guide the industry on Balance and vibration technology as applied to impellers used in air moving systems. It includes terminology
7、used and methods of Balancing practiced by the industry. 1.1.1 Intent. This document is intended for the guidance of the industry, including manufacturers, engineers, installers, contractors and users. 1.1.2 Review and Amendment. This document is subject to review and amendment as technology advance
8、s. Section 2. Scope 2.1 Scope. This document is intended to apply specifically to system vibration and mechanical Balancing as related to fans and blowers. The principles presented, however, can be generally applied to many rotating components. This document covers impellers while systems (see AMCA
9、Standard 204 and ANSI Standard S2.19) are covered by Air Movement and Control Association International, Inc. (AMCA) publications. Section 3. Definitions All terms in this document will follow the standard industry definitions in the current edition of ASHRAE Terminology of Heating, Ventilation, Air
10、-Conditioning and Refrigeration 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. (ANSI Stand
11、ard S2.7 does not define the term “Balance”; refer to 3.17, Unbalance.) 3.2 Balancing. A procedure 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 oper
12、ating speed are within specified limits. 3.2.1 Balancing, Two-plane (Dynamic). A procedure by which 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 cause
13、d by the initial Unbalance. 3.2.2 Balancing, Single-plane (Static). A procedure by which the mass 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 machi
14、ne that provides a measure of the Unbalance in a Rotor which can be used for adjusting the mass distribution 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 vibra
15、tory forces or motions due to Unbalance in the Rotor. 3.3.2 Gravitational (Non-rotating) Balancing 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. AHRI GUIDELINE G (SI)
16、-2011 2 3.3.3 Dynamic (Two-plane) Balancing Machine. A Centrifugal Balancing Machine that furnishes information for performing Two-plane Balancing. 3.3.4 Static (Single-plane) Balancing Machine. A Gravitational or Centrifugal Balancing Machine that provides information for accomplishing Single-plane
17、 Balancing. NOTE: Dynamic (Two-plane) Balancing Machines can be used to accomplish Static (Single-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 perpe
18、ndicular to the Shaft Axis of a Rotor in which correction for Unbalance is made. 3.6 Critical Speed. The speed that corresponds to a Resonance Frequency of the Rotor when operating on its own Bearings and support structure. For example, speed in revolutions per unit time equals the Resonance Frequen
19、cy in cycles per unit time. 3.7 Field (Trim) Balancing. The process of reducing the vibration level of a rotating assembly after all the rotating components are assembled to their respective shaft(s) (re. blower wheel or propeller, Bearings and pulleys). Such Balancing is employed to compensate for
20、the vibrational effects of the tolerances of the drive components. 3.8 Journal. The part of a Rotor which is in contact with or supported by a Bearing in which it revolves. 3.9 Journal Axis. The straight line joining the centroids of cross-sectional contours of the Journal. 3.10 Resonance. Resonance
21、 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. 3.11 Resonance Frequency. A frequency at which Resonance occurs in a given body or system. This is often also called natural freq
22、uency. 3.12 Rotor. A body, capable of rotation, generally with Journals which are supported by Bearings. 3.12.1 Rotor, Flexible. A Rotor not satisfying definition 3.12.2 due to elastic deflection. 3.12.2 Rotor, Rigid. A Rotor is considered rigid when it can be corrected in any two (arbitrarily selec
23、ted) planes (refer to 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: T
24、he Rotor has sufficient structural rigidity to allow Balancing corrections to be made below the operating speed. 3.13 Shaft Runout. The wobbling motion produced by a shaft that is not perfectly true and straight. Shaft Runout is often abbreviated TIR (Total Indicated Runout, a measurement of how muc
25、h a shaft wobbles with each revolution). 3.14 Shaft Axis. The straight line joining the Journal centers. 3.15 Should. “Should” is used to indicate provisions which are not mandatory but which are desirable as good practice. 3.16 System Balance. System Balance includes the entire rotating assembly ma
26、ss, operating speed, and the application. 3.17 Unbalance. That condition which exists in a Rotor when vibratory force or motion is imparted to its Bearings as a result of centrifugal forces. AHRI GUIDELINE G (SI)-2011 3 3.17.1 Unbalance Amount. The quantitative measure of Unbalance in a Rotor (refer
27、red to a plane) without referring to its angular position. It is obtained by taking the product of the Unbalance Mass and the distance of its center of gravity from the Shaft Axis. 3.17.2 Unbalance Angle. Given a polar coordinate system fixed in a plane perpendicular to the Shaft Axis and rotating w
28、ith the Rotor, the polar angle at which an Unbalance Mass is located with reference to the given coordinate system. 3.17.3 Unbalance Mass. That mass which is considered to be located at a particular radius such that the product of this mass and its centripetal acceleration is equal to the Unbalance
29、force. 3.17.3.1 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. 3.17.4 Unbalance Residual. Unbalance of any kind that remains after Balancing. 3.18 Unbalance Limit . I
30、n the case of Rigid Rotors, that amount of 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. System Vibration 4.1 General. All equipment with rotating components wil
31、l have some vibration. The amount of vibration present is the cumulative effect of factors such as residual Unbalance and alignment of all the rotating components (including shafts, pulleys and Bearings) and the dynamic characteristics of the complete assembly. 4.2 Effects of Resonance. The dynamic
32、characteristics of the assembly often create vibration problems that are erroneously attributed to Unbalance. This situation occurs when the equipment is operating at, or near, Resonance Frequency (the rotational frequency is too close to the Resonance Frequency of one or more of the equipments comp
33、onents). This results in high vibration amplitudes even when the driving forces due to Unbalance are small. Another characteristic of such a system is that large changes in vibration level occur with small changes of input frequency (operating speed). Usually, such a vibration problem cannot be solv
34、ed by reducing the Balancing Tolerance, since there are limits to the reduction of the driving force which can be achieved in practice. The user or designer should consider the fallacy in this approach in that small changes in system Balance due to damage from mishandling, shipping, field service, o
35、r normal build up of dirt may result in the return of high amplitudes of vibration. 4.3 Analyzing Resonance. The equipment designer can determine if a Resonance problem exists by running a series of tests to determine the sensitivity of the complete unit to Unbalance in the rotating components. With
36、 the unit running at its design speed, the Rotor should be balanced to the minimum achievable residual Unbalance. The Rotor is then unbalanced by small amounts of increasing size and the resultant displacement or velocity is recorded for each increment of Unbalance. This process should be continued
37、until the effects of the Unbalance can be detected above the level of other disturbances or until the Unbalance noticeably and adversely affects the running smoothness or function of the unit. With the Rotor unbalanced at an acceptable level at operating speed, the vibration level should then be mea
38、sured at various speeds above and below the operating speed. This can be accomplished by varying the voltage, line frequency or pulley ratio while measuring the vibration level at some reference point on the unit. The vibration level determined in the first test should be plotted versus the amount o
39、f Unbalance and versus speed for the second test. Large changes in vibration level caused by small changes in speed indicate resonant condition in the support structure. The use of a variable speed drive generator to power the motor on direct drive equipment is very useful since the system can be op
40、erated up through synchronous speed and above. This will indicate if a Resonance is just above the operating speed and, with manufacturing tolerance, the possibility of this point dropping into the operating range. Another useful aspect of the ability to have a large speed range capability during te
41、sts is the advantage of excitation above a Resonance at the operating speed. This dramatically shows the effect of the exciting frequency since the vibration level will be reduced substantially with an increase in unit speed. 4.4 Recommendations. By understanding the effect of system characteristics
42、 on vibration levels, the designer can avoid the special Balance requirements, which are costly in terms of initial product and potential future field problems. AHRI GUIDELINE G (SI)-2011 4 Below is a partial listing of some common factors to be considered to minimize vibration problems: 4.4.1 Struc
43、tural support must be adequate. The vibration characteristics must not coincide with the frequencies of excitation caused by the rotating components. 4.4.2 Single phase motors have an inherent torque pulsation at twice line frequency (sometimes referred to as “single phase hum”). This vibration can
44、be isolated by proper mounting techniques. 4.4.3 Assembly methods using screws or other fasteners must follow specified hole size, alignment and tightening torques to prevent unwanted vibration at various operating speeds. 4.4.4 Drive components can be a source of vibration problems. Characteristics
45、 such as Shaft Runout (TIR), Balance of the pulleys and the condition of the belt(s) can be factors. 4.4.5 Proper field installation of the equipment is important. Section 5. Instrumentation and Measurement 5.1 Instrumentation to Measure Vibration. Vibration meters and stroboscopic equipment are use
46、d 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 of electrically filtering the vibration signal so that it can be tuned to the rotati
47、ng 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 the rotating speed or from some frequency due to other causes of vibration. Many hand
48、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 displacement, velocity or acceleration. Velocity as a measure of vibration is coming int
49、o general use and is favored for several reasons. The destructive forces generated in a machine because of Unbalance are much more proportional to velocity than either displacement or acceleration. Such electronic instrumentation will pick up the vibration signal, convert it to a convenient unit, such as kilogram-millimeters and locate the point of Unbalance. 5.2 Instrumentation to Measure Unbalance. There is a variety of instrumentation available to measure amounts of Unbalance in Rotors. This instrumentation varies from simple knife edge or roller ways to complex electronic production
