1、2002 GUIDELINE for A I R -CON O TI ON IN G refer to 3.16, 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 andor forces on the Bearings at a frequency corresponding to operati
2、ng 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 caused b
3、y 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. 3.2.3 Balancing Tolerance. Refer t
4、o 3.17. 3.3 Balancing Machine. A machine 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 Centrifgal (Rotational) Balancing Machine. A Balancing Machine that provides for the support and rotation of a Rotor and for the mea
5、surement of once per revolution vibratory 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 of the amount and angle of the st
6、atic Unbalance. 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 Singl
7、e-plane 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 plan
8、e perpendicular 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
9、Frequency in cycles per unit time. 1 Copyright Air-Conditioning and Refrigeration Institute Provided by IHS under license with ARINot for ResaleNo reproduction or networking permitted without license from IHS-,-,-AR1 GUIDELINE G-2002 3.7 Eccentricify, Mass. The amount of static Unbalance divided by
10、the mass of the Rotor. It is equivalent to the displacement of the center of gravity of the Rotor from the Shaft Axis (as defined in 3.14). 3.8 Field (Trim) Balancing. The process of reducing the vibration level of a rotating assembly, after all the rotating components are assembled to their respect
11、ive shaft(s) (re. blower wheel or propeller, Bearings and pulleys). Such Balancing is employed to compensate for the vibrational effects of the tolerances of the drive components. 3.9 or supported by a Bearing in which it revolves. Journal. The part of a Rotor which is in contact with 3.10 Journal A
12、xis. The straight line joining the centroids of cross-sectional contours of the Journal. 3.11 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. 3.12 Resonance
13、Frequency. A frequency at which Resonance occurs in a given body or system. This is often also called natural frequency. 3.13 Rotor. A body, capable of rotation, generally with Journals which are supported by Bearings. 3.13.1 Rotor, Flexible. A Rotr not satisfying definition 3.13.2 due to elastic de
14、flection. 3.13.2 Rotor, Rigid. A Rotor is considered rigid when it can be corrected in any two (arbitrarily selected) 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 operatin
15、g speed and when running under conditions which approximate closely those of the final supporting system. NOTE: The Rotor has sufficient structural rigidity to allow Balancing corrections to be made below the operating speed. 3.14 Shafi Axis. The straight line joining the Journal centers. 3.15 Shoul
16、d. “Should“ is used to indicate provisions which are not mandatory but which are desirable as good practice. 3.16 unbalance. That condition which exists in a Rotor when vibratory force or motion is imparted to its Bearings as a result of centrifugal forces. 3.16.1 Unbalance Amount. The quantitative
17、measure of Unbalance in a Rotor (referred 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. 3.16.2 Unbalance Angle. Given a polar coordinate system fixed in a plane perpend
18、icular 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. 3.16.3 Unbalance Mass. That mass which is considered to be located at a particular radius such that the product of this mass and its centripetal
19、acceleration is equal to the Unbalance force. 3.16.3.1 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. 3.16.4 Unbalance Residual. Unbalance of any kind that remains af
20、ter Balancing. 3.17 Unbalance Tolerance. In 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. A
21、ll equipment with rotating components will 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 assemb
22、ly. 4.2 Effects of Resonance. The dynamic 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 Frequ
23、ency of one or more of the equipments components). 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). Usuall
24、y, such a vibration problem cannot be solved by reducing the Balancing Tolerance, since there are limits to 2 Copyright Air-Conditioning and Refrigeration Institute Provided by IHS under license with ARINot for ResaleNo reproduction or networking permitted without license from IHS-,-,- AR1 GUIDELINE
25、 G-2002 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, or normal build up of dirt may result in the return of high
26、 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 the unit running at its design speed, the Rotor should be
27、 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 until the effects of the Unbalance can be detected above t
28、he 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 measured at various speeds above and below the operating spee
29、d. 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 of Unbalance and versus speed for the second test. Large ch
30、anges in vibration level caused by small changes in speed indicate resonant condition in the support structure. The use of a variable frequency generator to power the motor on direct drive equipment is very useful since the system can be operated up through synchronous speed and above. This will ind
31、icate if a Resonance is just above the operating speed and, with manufacturing tolerance, the possibility of this point dropping into the operating range is a potential problem. Another useful aspect of the ability to have a large speed range capability during tests is the advantage of excitation ab
32、ove 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 on vibration levels, the designer ca
33、n avoid the special Balance requirements, which are costly in terms of initial product and potential future field problems. Below is a partial listing of some common factors to be considered to minimize vibration problems: a. Structural support must be adequate. The vibration characteristics must no
34、t coincide with the frequencies of excitation caused by the rotating components. b. Single phase motors have an inherent torque pulsation at twice line frequency (sometimes referred to as “single phase hum“). This vibration can be isolated by proper mounting techniques. Assembly methods using screws
35、 or other fasteners must follow specified hole size, alignment and tightening torques, to prevent unwanted vibration at various operating speeds. Drive components can be a source of vibration problems. Characteristics such as shaft runout (TIR), Balance of the pulleys and the condition of the belt(s
36、) can be factors. 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 used on complete systems with the Impeller or Rotor on its own Bearings and supporting struc
37、ture, 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 rotating frequency of the Rotor being balanced. The vibratory motion caused by Unbalance occur
38、s 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 held vibration meters do not have electrical filters and only measure total vibration am
39、plitude. 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 into general use and is favored for several reasons. The destructive forces generated in a
40、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 ounce-inches and locate the point of Unbalance. 5.2 Instrumentation to Measure Unb
41、alance. 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 Balancing. The following outlines the variety of 3 Copyright Air-Conditioning and Refrigeration Instit
42、ute Provided by IHS under license with ARINot for ResaleNo reproduction or networking permitted without license from IHS-,-,-AR1 GUIDELINE G-2002 equipment and instrumentation available and their normal use and application. 5.2.1 production or inspection of impellers and Rotors. Balancing Machines:
43、Normally used for Machines available are: 5.2.1.1 Non-Rotating Types. - Knife edge - Roller ways - Vertical arbor (Single-plane, non-rotating) 5.2.1.2 Rotating Types. - Horizontal arbor (Single-plane, - Horizontal arbor (Two-plane, - Vertical arbor (Single-plane, - Vertical arbor (Two-plane, rotatin
44、g) rotating) rotating) rotating) 5.2.2 with either hard or soft Bearings. Rotating Balancing Machines are equipped 5.2.2.1 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). 5.2.
45、2.2 Soft (flexible suspension) bearing machines are also available. They use motion transducers to measure the Bearing motion caused by centrifugal forces acting on the Unbalance Mass(es). 5.2.2.3 Balancing Machines, refer to IS0 2953. To evaluate the accuracy of 5.2.3 Measuring Units for Unbalance.
46、 All Balancing Machines provide information on the magnitude of Unbalance and a location where correction is to be made. Unbalance is usually reported in oz-in kg-mm. Section 6. Balancing Methods 6.1 Types of Balancing. A Rotor can be balanced either by Static Balancing or by Dynamic Balancing. The
47、method chosen is dependent upon many factors such as, physical size, shape, weight, and Balance Tolerance requirements. 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 s
48、eparated 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 Balancin
49、g can only be accomplished by rotating means. Single-plane Balancing, either rotating or non-rotating, should always be referred to as Static Balancing. Two-plane Balancing should always be referred to as Dynamic Balancing (refer to Section 3). This would eliminate the confusion caused by mistakenly referring to a rotating Static Balance (Single-plane) as “Dynamic Balance.“ 6.2 Methods of Balancing. 6.2.1 Non-Rotating. The simplest method of Static Balancing consists of a Rotor mounted with its axis horizontal and allowed t
