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AMAZON multi-meters discounts AMAZON oscilloscope discounts Prompting Guides, Storage, and Retrieval Prompting displays on a computer screen guide the operator every step of the way through the program ( FIG. 40). Rotor data are stored electronically and can be recalled at a later date for balancing the same type of rotor. Thus ABC, R1, and R2 rotor dimensions need to be entered into the computer only once. Multiple Machine Control and Programs Different computers may be used depending on the application. They may be mounted in the balancing machine's instrumentation console, or in a central electronic data processing room. A computer may control one balancing machine, or a series of machines. Basic computer programs are available for single and two plane balancing, field balancing, and flexible rotor balancing. Software libraries for optional subroutines are continually growing. Of course, the user may modify the available programs to his particular requirements, write his own programs, or have them written for him. Thus, the potential applications of the computerized hard-bearing balancing machines are unlimited. FIG. 40. Printout of unbalance data. Field Balancing Overview Once a balanced rotor has been mounted in its housing and installed in the field, it won’t necessarily stay in balance forever. Corrosion, temperature changes, build-up of process material and other factors may cause it to go out of balance again and, thus, start to vibrate. However, unbalance is not the only reason for vibration. Bearing wear, belt problems, mis alignment, and a host of other detrimental conditions will also cause it. In fact, experience has shown that vibration is an important indication of a machine's mechanical condition. During normal operation, properly functioning fans, blowers, motors, pumps, compressors, etc., emit a specific vibration signal, or "signature." If the signature changes, something is wrong. Excessive vibration has a destructive effect on piping, tanks, walls, foundations, and other structures near the vibrating equipment. Operating personnel may be influenced too. High noise levels from vibration may exceed legal limitations and cause permanent hearing damage. Workers may also experience loss of balance, blurred vision, fatigue, and other discomfort when exposed to excessive vibration. Methods of vibration detection, analysis, diagnostics, and prognosis have been described by the authors previously in detail 5. A quick review of the hardware required to perform field balancing should therefore suffice. Field Balancing Equipment Many types of vibration indicators and measuring devices are available for field balancing. Although these devices are sometimes called "portable balancing machines," they never provide direct readout of amount and location of unbalance. Basically, field balancing equipment consists of a combination of a suit able transducer and meter which provides an indication proportional to the vibration magnitude. The vibration magnitude indicated may be displacement, velocity, or acceleration, depending on the type of transducer and readout system used. The transducer can be held by an operator, or attached to the machine housing by a magnet or clamp, or permanently mounted. A probe thus held against the vibrating machine is presumed to cause the transducer output to be proportional to the vibration of the machine. At frequencies below approximately 15 cps, it’s almost impossible to hold the transducer sufficiently still by hand to give stable readings. Frequently, the results obtained depend upon the technique of the operator; this can be shown by obtaining measurements of vibration magnitude on a machine with the transducer held with varying degrees of firmness. Transducers of this type have internal seismic mountings and should not be used where the frequency of the vibration being measured is less than three times the natural frequency of the transducer. A transducer responds to all vibration to which it’s subjected, within the useful frequency range of the transducer and associated instruments. The vibration detected on a machine may come through the floor from adjacent machines, may be caused by reciprocating forces or torques inherent in normal operation of the machine, or may be due to unbalances in different shafts or rotors in the machine. A simple vibration indicator cannot discriminate between the various vibrations unless the magnitude at one frequency is considerably greater than the magnitude at other frequencies. The approximate location of unbalance may be determined by measuring the phase of the vibration; for instance, with a stroboscopic lamp that flashes each time the output of an electrical transducer changes polarity in a given direction. Phase also may be determined by use of a phase meter or by use of a wattmeter. Vibration measurements in one end of a machine are usually affected by unbalance vibration from the other end. To deter mine more accurately the size and phase angle of a needed correction mass in a given (accessible) rotor plane, three runs are required. One is the "as is" condition, the second with a test mass in one plane, the third with a test mass in the other correction plane. All data are entered into a hand held computer and, with a few calculation steps, transformed into amount and phase angle of the necessary correction masses with two selected planes. To simplify the calculation process even further, software has recently become available which greatly facilitates single plane or multi plane field balancing. Field Balancing Examples As we saw, two methods are available for the systematic balancing of rotors: • Balancing on a balancing machine • Field balancing in the assembled state Both methods have specific fields of application. The balancing machine is the correct answer from the technical and economic point of view for balancing problems in production. Field balancing, on the other hand, provides a practical method for the balancing of completely assembled machines during test running, assembly, and maintenance. It’s the purpose of this section to illustrate the possibilities of field balancing on the basis of three typical balancing problems. The machines chosen for these problems represent examples only and could at any time be exchanged for machines with similar rotor systems. The solutions to the problems indicated, therefore, apply equally to other machines and types of rotor not specifically mentioned here. The following classification will simplify the allocation of different types of machines to the three problem solutions: 1st Problem Solution: Machines with narrow disc-shaped rotors such as blowers, fans, grinding wheels, belt pulleys, flywheels, couplings, chucks, gear wheels, impellers, atomizer discs, etc. 2nd Problem Solution: Machines with long roll-shaped rotors such as centrifuges, paper rolls, electric motors and generators, beater shafts, machine tool spindles, grinding rolls, internal combustion engines, etc. 3rd Problem Solution: Machines having multiple bearing coupled rotors such as standing machines, twisting machines, motor generator sets, turbo generators, cardan shafts, etc. Field balancing of very low speed rotating assemblies (cooling tower fans, etc.) may require special techniques which are not covered here. The reader should discuss special requirements with the machinery manufacturer. First Problem: Unbalance Vibration in Blowers Build-up on blades, corrosion, wear, and thermal loading regularly lead to unbalance in blowers. The presence of such unbalance shows itself externally in the form of mechanical vibration generated by the blower rotor and transmitted via the bearings and the frame into the foundations and finally into the environment. If the danger of this unbalance vibration is not recognized, after a very short operating period costly damage may be caused. This may frequently result in the destruction of the bearings, cracks in the bearing housing and in the air channels, damage to the foundation, and cracks in the building. FIG. 41. Individual stages in the field balancing of a blower using balancing and vibration analyzer "VIBROTEST." FIG. 42. Unbalance vibration of blower is measured at bearing position (1)-"measuring point." The unbalance determined this way is corrected in the center of gravity plane A1-"correction plane." FIG. 43. Vector diagram of field balancing in one plane. Solution: Field Balancing in One Plane For economic reasons rebalancing of a blower should always be carried out in the assembled state. This does away with the need to disassemble the whole plant, to make available a balancing machine and to transport the blower rotor to the balancing machine. Only the electronic balancing instrument needs to be brought to where the blower is installed. The operation of the instrument and the determination of the masses required to correct the unbalance is carried out by trained personnel. Not only does this result in considerable cost savings but the method also provides a significant saving in time compared to rebalancing on a balancing machine. With careful preparation, field balancing of a blower need not take more than 30-60 minutes. It has been shown in practice that in over 95 percent of all blowers field balancing in one plane is sufficient to reduce unbalance vibrations to permissible and safe values. The method is as follows: 1. The balancing instrument is used to measure the unbalance vibration at the bearing positions nearest to the blower rotor ( FIGS. 41 and 42). The instrument suppresses with a high degree of separation any extraneous vibration and shows the amount and the angular position of the rotational frequency vibrations. Both measured values-also designated as "initial unbalance"-are entered on a vector diagram ( FIG. 43). 2. After bringing the rotor to a standstill, a known unbalance (calibrating mass) is applied in the vicinity of the center of gravity plane of the blower. When the blower has again reached its operational speed the unbalance vibration is measured again and the results are also entered in the vector diagram ( FIG. 43). 3. The graphic evaluation of this vector diagram provides amount and angular position of the correction masses required for balancing. 4. The calculated correction mass is welded to the blower rotor and a check measurement of the residual vibration is carried out. The balancing process is completed as soon as residual vibration lies within the permissible tolerance. As far as tolerance values are concerned, reference should be made to the standards of FIG. 34. Second Problem: Unbalance Vibration in Centrifuges Centrifuges are high-speed machines. High rotational speeds demand a high balance quality of the rotating parts, mainly the centrifuge drum, the worm, the belt pulley, etc. Balancing of the individual rotors on a balancing machine does not always suffice to achieve the required residual unbalance. Tolerances and fits of the components, errors in the roller bearings, variations in wall thickness of the drum, etc., may mean that the unbalance vibration of the completely assembled centrifuge exceeds the permissible values. The need to correct this may arise when test running a new centrifuge and after repair and overhaul of older installations. Solution: Field Balancing in Two Planes Disassembly, additional machining, excess costs, and user complaints may be avoided by rebalancing on the test stand ( FIG. 44) or at the final point of installation. Because of the geometry of the centrifuge drum, field balancing in two planes is almost always necessary in order to improve the unbalance condition effectively. For this purpose the unbalance vibration is measured at two bearing positions as shown in FIG. 45 and the unbalance determined in this way is corrected in two radial planes A1 and A2. Measurement is carried out with a portable electronic balancing instrument that indicates the amount and angular position of the unbalance vibration for both measuring positions with frequency selectivity. For the evaluation of measured results, graphical methods have been used almost exclusively up to the present. They require experience, accuracy and time (approximately 30 minutes). The appearance of relatively inexpensive programmable pocket calculators ( FIG. 46) in the late 1970s made it possible to replace these methods with more accurate numerical methods. The determination of amount and angular position of the correction masses for both correction planes could be carried out in approximately two-three minutes even by untrained personnel. In detail, the following method could be followed: FIG. 44. A centrifuge is rebalanced on the test stand in two planes. FIG. 45. Sketch of a centrifuge. The two bearing locations (1) and (2) are chosen as measuring points. Unbalance correction is made in the end planes A1 and A2 by applying or removing mass. 1. Using the balancing instrument, the angular position and amount of the unbalance vibration is measured at bearing positions 1 and 2 and the values are entered into the schedule "initial unbalance run" ( FIG. 47). 2. The centrifuge is brought to a standstill and a known calibrating mass is applied in correction plane A1. After again reaching the operational speed the unbalance vibration is measured again and entered "test run 1". 3. The calibrating mass is removed from plane A1 and applied to plane A2. The resulting measured values are again noted down "test run 2." 4. The evaluation of the measurement results listed in FIG. 47 using the pocket calculator gives the correction masses that must be applied at the calculated angular positions. A subsequent check run of the centrifuge will determine the correctness of the balancing measures and will show whether an additional correction process is required. FIG. 46. Programmable pocket calculators with balancing module make it easier and faster to determine the correction masses when field balancing. FIG. 47. Field balancing worksheet. Explanation of Schedule and of Calculator Program The results of the initial unbalance run, of both test runs, and the magnitude of the calibrating masses used are entered in appropriately numbered spaces. After inserting balancing module, the measured values are keyed into the pocket calculator. By calling up the stored data, the pocket calculator immediately indicates the required masses for unbalance correction either in polar form or in the form of 90° components. If the residual unbalance of the rotor exceeds the allowable tolerance, it’s possible to calculate the correction masses for further correction by using the measured values of the check run but without any need for new test runs. The influence coefficients which may on demand be indicated and noted make it possible to rebalance a rotor without test runs even after a long time interval. Third Problem: Unbalance Vibration in Twisting and Stranding Machine Machines for the production of wire rope, cable and flex operate with multi-bearing rotor systems which consist of two or more part rotors coupled together with angular rigidity. A type which frequently occurs in practice is shown schematically in FIG. 48. Rotor systems of this type are difficult to balance in their completely assembled form on balancing machines but are better balanced divided into their individual rotors. After assembling the balanced component rotors, new unbalances can occur due to fits and tolerances, alignment errors and centrifugal force loading. This is also the case when replacing rotating wear parts such as, For example, the wire guide tube in stranding machines. Any excessively large residual unbalance leads to considerable mechanical vibration and to the excitation of mounting and machine resonances. Both of these factors can lead to damage of the machine and physical and psychological strain on the operating personnel. Frequently the only first aid measure available is a reduction in the production rate by reducing the operational speed. This, however, is only tolerable over a limited time span. The economics of the process require a longer term solution that can only be found in field balancing the complete rotor system. Solution: Field Balancing in Several Planes The unbalance and vibrational behavior of multiple bearing rotor systems may be improved in a systematic manner by multi-plane balancing in the assembled state ( FIG. 48). For unbalance correction, there must be a correction plane for every bearing position on the rotor. For example, the four-bearing rotor shown in FIG. 48 requires four correction planes. The electronic balancing instrument for this task is identical to the instruments used for single and two plane balancing. It’s resting on top of the bunching machine being shown, during field balancing, in FIG. 49. The balancing process only differs in the number of calibrating runs and the way the measured results are evaluated: 1. Using the portable balancing instrument the phase position and amount of the unbalance vibrations is measured at the four bearing positions of the stranding machine. These "initial unbalance values" are entered on four vector diagrams similar to that in FIG. 50. 2. The stranding machine is switched off and a known calibrating mass is applied in the correction plane A1 ( FIG. 48). After running up to the operational speed the unbalance values are again measured at the four bearing positions. These values are also entered in the vector diagram. 3. The procedure described under 2 above is repeated with calibrating masses in the correction planes A2, A3, and A4. 4. The graphical evaluation of the vector diagram gives the amount and angular position of the correction masses which must be applied in the four chosen correction planes. 5. After unbalance correction a check measurement is carried out and the residual vibrations determined by this are compared with the permissible tolerance values. FIG. 48. Sketch of the rotating parts of a stranding machine. Each of the measuring positions (1) to (4) is related to a corresponding correction plane A1 to A4. FIG. 49. Field balancing of a bunching machine. Using the balancing and vibration analyzer "VIBROTEST," the unbalance vibration in the four bearing planes is measured successively in terms of amount and angular position. The Vector Diagram The results from the five measuring runs are entered in four vector diagrams. FIG. 50 shows the vector diagram for plane 1. The vector (a). . . (b) represents the effect of the calibration mass. The other three vectors show the effect which the calibration masses applied in planes A1, A3, and A4 exert in plane 1. The graphic evaluation of the vector diagram is carried out by an approximation method. By means of a systematic trial and error process, combinations of masses are determined which result in a reduction of unbalance in all four planes. For this purpose the effects and influences of the correction masses in all planes must be taken into account and entered into the vector diagram. FIG. 50. Field balancing in four planes. Example of graphic evaluation of measured results. References: 1. Schenck Trebel Corporation, Fundamentals of Balancing, Schenck Trebel Corporation, Deer Park, New York, second edition, 1983, 115 pages. 2. Schenck Trebel Corporation, Aspects of Flexible Rotor Balancing, Schenck Trebel Corporation, Deer Park, New York, third edition, 1980, Pages 1-34. 3. Reference 1, Pages 35-42. 4. Schneider, H., Balancing Technology, Schenck Trebel Corporation, Deer Park, New York. 5. Bloch, H. P. and Geitner, F. K., Machinery Failure Analysis and Troubleshooting, Gulf Publishing Co., Houston, Texas, third edition, 1997, Pages 351-433. Bibliography 1. ISO 1925: Balancing-Vocabulary (1981). 2. ISO 1940: Balance Quality of Rigid Rotors (1973) and DIS 2953 1982 with revised test procedure. 3. ISO 2953: Balancing Machines-Description and Evaluation (1973). 4. Society of Automotive Engineers, Inc. ARP 587A: Balancing Equipment for Jet Engine Components, Compressors and Turbines, Rotating Type, for Measuring Unbalance in One or More Than One Transverse Planes (1972). 5. Society of Automotive Engineers, Inc. ARP 588A: Static Balancing Equipment for Jet Engine Components, Compressor and Turbine, Rotating Type, for Measuring Unbalance in One Transverse Plane (1972). 6. Society of Automotive Engineers, Inc. ARP 1382: Design Criteria for Balancing Machine Tooling (1977). 7. Federn, Klaus: Auswuchttechnik Volume 1, Springer Verlag, Berlin (1977). 8. Luhrs, Margret H.: Computers in the Balancing Industry (December, 1979). 9. McQueary, Dennis: Understanding Balancing Machines, American Machinist (June, 1973). 10. Meinhold, Ted F.: Measuring and Analyzing Vibration, Plant Engineering (October 4, 1979). 11. Muster, Douglas and Stadelbauer, Douglas G.: Balancing of Rotating Machinery, Shock and Vibration, second edition, McGraw-Hill, New York (1976). SECTION A Balancing Terminology NOTE: The definitions followed by a number are taken from ISO 1925 2nd Edition. Amount of Unbalance (3.3): The quantitative measure of unbalance in a rotor (referred to a plane), without referring to its angular position. It’s obtained by taking the product of the unbalance mass and the distance of its center of gravity from the shaft axis. Angle of Unbalance (3.4): Given a polar coordinate 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 co ordinate system. Angle Indicator (5.18): The device used to indicate the angle of unbalance. Angle Reference Generator (5.19): In balancing, a device used to generate a signal which defines the angular position of the rotor. Angle Reference Marks (5.20): Marks placed on a rotor to denote an angle reference system fixed in the rotor; they may be optical, magnetic, mechanical, or radioactive. Balancing (4.1): 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 service speed are within specified limits. Balancing Machine (5.1): A machine that provides a measure of the unbalance in a rotor which can be used for adjusting the mass distribution of that rotor mounted on it so that once per revolution vibratory motion of the journals or force on the bearings can be reduced if necessary. Balancing Machine Accuracy (5.24): The limits within which a given amount and angle of unbalance can be measured under specified conditions. Balancing Machine Minimum Response (5.23): The measure of the machine's ability to sense and indicate a minimum amount of unbalance in terms of selected components of the unbalance vector. Balancing Machine Sensitivity (5.28): Of a balancing machine under specified conditions, the increment in unbalance indication expressed as indicator movement or digital reading per unit increment in the amount of unbalance. Balancing Run (5.43): On a balancing machine: A run consisting of one measure run and the associated correction process. Balancing Speed (2.18): The rotational speed at which a rotor is balanced. Calibration (5.36): The process of adjusting a machine so that the unbalance indicator(s) read(s) in terms of selected correction units in specified correction planes for a given rotor and other essentially identical rotors; it may include adjustment for angular location if required. Centrifugal (Rotational) Balancing Machine (5.3): 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. Compensating (Null Force) Balancing Machine (5.9): A balancing machine with a built-in calibrated force system which counteracts the unbalanced forces in the rotor. Center of Gravity (1.1): The point in a body through which passes the resultant of the weights of its component particles for all orientations of the body with respect to a uniform gravitational field. Component Measuring Device (5.22): A device for measuring and displaying the amount and angle of unbalance in terms of selected components of the unbalance vector. Correction Plane Interference (Cross-Effect) (5.25): The change of balancing machine indication at one correction plane of a given rotor, which is observed for a certain change of unbalance in the other correction plane. Correction Plane interference Ratios (5.26): The interference ratios (IAB, IBA) of two correction planes A and B of a given rotor are defined by the following relationships: Calibration Mass: A precisely defined mass used (a) in conjunction with a proving rotor to calibrate a balancing machine, and (b) on the first rotor of a kind to calibrate a soft-bearing balancing machine for that particular rotor and subsequent identical rotors. Calibration (Master) Rotor (5.35): A rotor (usually the first of a series) used for the calibration of a balancing machine. Correction Mass: A mass attached to a rotor in a given correction plane for the purpose of reducing the unbalance to the desired level. Correction Mass Set: A number of precisely apportioned correction masses used for correcting a given unbalance in (a) a single plane or (b) more than one plane. For flexible rotor balancing the number of correction masses in a set is usually related to the flexural mode they are intended to correct. Counterweight (5.16): A weight added to a body so as to reduce a calculated unbalance at a desired place. Claimed Minimum Achievable Residual Unbalance (5.41): A value of minimum achievable residual unbalance stated by the manufacturer for his machine, and measured in accordance with the procedure specified in ISO 2953. Couple Unbalance (3.8): That condition of unbalance for which the central principal axis intersects the shaft axis at the center of gravity. Component Correction: Correction of unbalance in a correction plane by mass addition or subtraction at two or more of a predetermined number of angular locations. Correction (Balancing) Plane (4.6): A plane perpendicular to the shaft axis of a rotor in which correction for unbalance is made. Cycle Rate: Cycle rate of a balancing machine for a given rotor having a specified polar moment of inertia and for a given balancing speed is the number of starts and stops that the machine can perform per hour without damage to the machine when balancing the rotor. Differential Test Masses: Two masses representing different amounts of unbalance added to a rotor in the same transverse plane at diametrically opposed positions. NOTE 1. Differential test masses are used, for example, in cases where a single test mass is impractical. 2. In practice, the threaded portion and height of the head of the test mass are kept the same. The diameter of the head is varied to achieve the difference in test mass. 3. The smaller one of the two differential test masses is sometimes called tare mass, the larger one tare-delta mass. Differential Unbalance: The difference in unbalance between two differential test masses. Dynamic Unbalance (3.9): That condition in which the central principal axis is not coincident with the shaft axis. NOTE The quantitative measure of dynamic unbalance can be given by two complementary unbalance vectors in two specified planes (perpendicular to the shaft axis) which completely represent the total unbalance of the rotor. Dummy Rotor: A balancing fixture of the same mass and shape as the actual rotor it replaces. NOTE A dummy rotor is used when balancing one or more rotors of an assembly of rotors, simulating the mass of the missing rotor. Field Balancing (4.11): The process of balancing a rotor in its own bearings and supporting structure rather than in a balancing machine. NOTE Under such conditions, the information required to perform balancing is derived from measurements of vibratory forces or motions of the sup porting structure and/or measurements of other responses to rotor unbalance. Index Balancing: A procedure whereby a component is repetitively balanced and then indexed by 180° on an arbor or rotor shaft. NOTE After each indexing, half of the residual unbalance is corrected in the arbor (or rotor shaft), the other half in the indexed component. Indexing: Incremental rotation of a rotor about its journal axis for the purpose of bringing it to a desired position. Mass Centering: The process of determining the mass axis of a rotor and then machining journals, centers or other reference surfaces to bring the axis of rotation defined by these surfaces into close proximity with the mass axis. Measuring Plane (4.7): A plane perpendicular to the shaft axis in which the unbalance vector is determined. Method of Correction (4.5): A procedure whereby the mass distribution of a rotor is adjusted to reduce unbalance, or vibration due to unbalance, to an acceptable value. Corrections are usually made by adding material to, or removing it from, the rotor. Multi-Plane Balancing (4.4): As applied to the balancing of flexible rotors, any balancing procedure that requires unbalance correction in more than two correction planes. Outboard Rotor (2.12):A two-journal rotor which has its center of gravity located other than between the journals. Overhung Rotor: A two-journal rotor with inboard CG but with significant masses and at least one correction plane located other than between the journals. Perfectly Balanced Rotor (2.10): A rotor the mass distribution of which is such that it transmits no vibratory force or motion to its bearings as a result of centrifugal forces. Plane Translation: The process of converting a given amount and angle of unbalance in two measuring (or correction) planes into the equivalent unbalance in two other planes. Polar Correction: Correction of unbalance in a correction plane by mass addition or subtraction at a single angular location. Parasitic Mass (5.31): Of a balancing machine, any mass, other than that of the rotor being balanced, that is moved by the unbalance force(s) developed in the rotor. Permanent Calibration (5.33): The property of a hard-bearing balancing machine that permits the machine to be calibrated once and for all, so that it remains calibrated for any rotor within the capacity and speed range of the machine. Plane Separation (5.27): Of a balancing machine, the operation of reducing the correction plane interference ratio for a particular rotor. Plane Separation (Nodal) Network (5.30):An electrical circuit, interposed between the motion transducers and the unbalance indicators, that per forms the plane-separation function electrically without requiring particular locations for the motion transducers. Practical Correction Unit (5.15): A unit corresponding to a unit value of the amount of unbalance indicated on a balancing machine. For convenience, it’s associated with a specific radius and correction plane; and is commonly expressed as units of an arbitrarily chosen quantity such as drill depths of given diameter, weight, lengths of wire solder, plugs, wedges, etc. Production Rate (5.45): The reciprocal of floor-to-floor time. NOTE: The time is normally expressed in pieces per hour. Proving (Test) Rotor (5.32): A rigid rotor of suitable mass designed for testing balancing machines and balanced sufficiently to permit the introduction of exact unbalance by means of additional masses with high reproducibility of the magnitude and angular position. Quasi-Rigid Rotor (2.17): A flexible rotor that can be satisfactorily balanced below a speed where significant flexure of the rotor occurs. Rigid Rotor (2.2): A rotor is considered rigid when it can be corrected in any two (arbitrarily selected) planes and, after that correction, its unbalance does not significantly exceed the balance tolerances (relative to the shaft axis) at any speed up to maximum service speed and when running under conditions which approximate closely to those of the final supporting system. Rotor (2.1):A body, capable of rotation, generally with journals which are supported by bearings. Resonance Balancing Machine (5.7):A machine having a balancing speed corresponding to the natural frequency of the suspension-and-rotor system. Setting (5.37): Of a hard-bearing balancing machine, the operation of entering into the machine information concerning the location of the correction planes, the location of the bearings, the radii of correction, and the speed if applicable. Single-Plane (Static) Balancing Machine (5.4): A gravitational or centrifugal balancing machine that provides information for accomplishing single-plane balancing. Soft-Bearing (Above Resonance) Balancing Machine (5.8): A machine having a balancing speed above the natural frequency of the suspension and-rotor system. Swing Diameter (5.11): The maximum workpiece diameter that can be accommodated by a balancing machine. Specific Unbalance "e" (Mass Eccentricity) (3.17): The amount of static unbalance (U) divided by mass of the rotor (M); it’s equivalent to the displacement of the center of gravity of the rotor from the shaft axis. Static Unbalance (3.6): That condition of unbalance for which the central principal axis is displaced only parallel to the shaft axis. Service Speed (2.19): The rotational speed at which a rotor operates in its final installation or environment. Shaft Axis (2.7): The straight line joining the journal centers. Slow Speed Runout. The total indicated runout measured at a low speed (i.e., a speed where no significant rotor flexure occurs due to unbalance) on a rotor surface on which subsequent measurements are to be made at a higher speed where rotor flexure is expected. Two-Plane (Dynamic) Balancing (4.3): A procedure by which the mass distribution of a rigid rotor is adjusted in order to ensure that the residual dynamic unbalance is within specified limits. Test Plane: A plane perpendicular to the shaft axis of a rotor in which test masses may be attached. Trial Mass: A mass selected arbitrarily and attached to a rotor to deter mine rotor response. NOTE A trial mass is usually used in trial and error balancing or field balancing where conditions cannot be precisely controlled and/or precise measuring equipment is not available. Test Mass: A precisely defined mass used in conjunction with a proving rotor to test a balancing machine. NOTES: 1. The use of the term "test weight" is deprecated; the term "test mass" is accepted in international usage. 2. The specification for a precisely defined Test Mass shall include its mass and its center of gravity location; the aggregate effect of the errors in these values shall not have a significant effect on the test results. Traverse (Umar) Test (5.46): A test by which the residual unbalances of a rotor can be found (see ISO 1940 or ISO 2953), or with which a balancing machine may be tested for conformance with the claimed minimum achievable unbalance (Umar, see ISO 2953). Turn-Around Error: Unbalance indicated after indexing two components of a balanced rotor assembly in relation to each other; usually caused by individual component unbalance, run-out of mounting (locating) surfaces, and/or loose fits. (See also index balancing). Unbalance (3.1): That condition which exists in a rotor when vibratory force or motion is imparted to its bearings as a result of centrifugal forces. NOTES: 1. The term "unbalance" is sometimes used as a synonym for "amount of unbalance," or "unbalance vector." 2. Unbalance will in general be distributed throughout the rotor but can be reduced to: a. static unbalance and couple unbalance described by three un balance vectors in three specified planes, or: b. dynamic unbalance described by two unbalance vectors in two specified planes. Unbalance Mass (3.5): 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 force. NOTE: 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. Unbalance Reduction Ratio (URR) (5.34): The ratio of the reduction in the unbalance by a single balancing correction to the initial unbalance. …where U1 is the amount of initial unbalance; U2 is the amount of unbalance remaining after one balancing correction. Vector Measuring Device (5.21): A device for measuring and displaying the amount and angle in terms of an unbalance vector, usually by means of a point of line. Vertical Axis Freedom (5.47): The freedom of a horizontal balancing machine bearing carriage or housing to rotate by a few degrees about the vertical axis through the center of the support. NOTE: This feature is required when dynamic or couple unbalance is to be measured in a rotor supported on sleeve bearings, cylindrical roller bearings, flat twin rollers, or in cradles, stators or tie-bars. +++++++ SECTION B Balancing Machine Nomenclature +++++++ SECTION C Balancing and Vibration Standards Balancing Standards ISO 1925 Balancing Vocabulary. Contains definitions of most balancing and related terms. (Same as ANSI S2.7-1982.) ISO 1940 Balance Quality of Rotating Rigid Bodies. Classifies all rigid rotors and recommends balance tolerances for them. (Same as ANSI S2.19-1975.) ISO 3080 The Mechanical Balancing of Marine Steam Turbine Machinery for Merchant Service. Furnishes guidance in applying ISO 1940 to this type of rotor. ISO 2371 Field Balancing Equipment-Description and Evaluation. Recommends to the equipment manufacturer how to describe his systems, and to the user how to evaluate them. (Same as ANSI S2.38-1982.) ISO 2953 Balancing Machines-Description and Evaluation. Tells a prospective balancing machine user how to describe his requirements to a balancing machine manufacturer, then enumerates the points that a proposal should cover, and finally explains how to test a machine to assure compliance with the specification. ISO 5406 The Mechanical Balancing of Flexible Rotors. Classifies rotors into groups in accordance with their balancing requirements and gives guidance on balancing procedures for flexible rotors. (Same as ANSI S2.42.) ISO 5343 Criteria for Evaluating Flexible Rotor Unbalance. Recommends balance tolerances for flexible rotors. Must be read in conjunction with ISO 1940 and ISO 5406. ISO 3719*1 Balancing Machines-Symbols for Front Panels. Establishes symbols for control panels of balancing machines. DIS 7475*2 Enclosures and Other Safety Measures for Balancing Machines. Identifies hazards associated with spinning rotors in balancing machines, classifies enclosures, and specifies protection requirements. Vibration Standards ISO 2041 Vibration and Shock Vocabulary. Contains definitions of most vibration and shock related terms. ISO 2372 Mechanical Vibration of Machines with Operating Speeds from 10 to 200Rev/s. Basis for specifying evaluation standards. ISO 2373 Mechanical Vibration of Certain Rotating Electrical Machinery with Shaft Heights Between 80 and 400mm. Measurement and evaluation of vibration severity. ISO 2954 Mechanical Vibration of Rotating and Reciprocating Machinery. Requirements for instruments for measuring vibration severity. ISO 3945 Mechanical Vibration of Large Rotating Machines with Speed Range from 10 to 200RPS. Measurement and evaluation of vibration severity in situ. US National Standards ANSI S2.l9-1975:*3 Balance Quality of Rotating Rigid Bodies (Identical to ISO 1940-1973) ANSI S2.l7-1980: Techniques of Machinery Vibration Measurement ANSI S2.7-1982: Balancing Terminology (Identical to ISO 1925 1981) ANSI S2.38-1982: Field Balancing Equipment-Description and Evaluation (Identical to ISO 2371-1982) ANSI S2.42-1982: Procedure for Balancing Flexible Rotors (Identical to ISO 5406-1980) All standards (ISO as well as ANSI) may be ordered from: American National Standards Institute, Inc. 1430 Broadway New York, NY 10018 * 1 ISO = International Standard Organization, Geneva, Switzerland. * 2 Draft International Standard to be released 1983. * 3 ANSI = American National Standards Institute. For Jet Engine Balancing: May be ordered from: Society of Automotive Engineers, Inc. (SAE) 400 Commonwealth Drive Warrendale, PA 15096 Tel. (412) 776-4841 SAE ARP 587A Balancing Equipment for Jet Engine Components, Compressors and Turbines, Rotating Type, for Measuring Unbalance in One or More Than One Transverse Planes. Contains machine and proving rotor parameters and the all important SAE acceptance test for horizontal machines. SAE ARP 588A Static Balancing Equipment for Jet Engine Components, Compressor and Turbine, Rotating Type, for Measuring Unbalance in One Transverse Plane. Contains machine and proving rotor parameters and acceptance test for vertical machines. SAE ARP 1340 Periodic Surveillance Procedures for Horizontal Dynamic Balancing Machines. An abbreviated test that may be run periodically to assure proper machine function. SAE ARP 1342 Periodic Surveillance Procedures for Vertical, Static Balancing Machines. An abbreviated test that may be run periodically to assure proper machine function. SAE ARP 1382 Design Criteria for Balancing Machine Tooling. Describes rotor supports, cradles, arbors, shrouds and other typical accessories for horizontal and vertical balancing machines. Also useful for general balancing work. SAE ARP 1202 Bell Type Slave Bearings for Rotor Support in Dynamic Balancing Machines. Specifies dimensions and tolerances for special balancing bearings. SAE ARP 1134 Adapter Interface-Turbine Engine Blade Moment Weighing Scale. Standardizes adapter tooling interface for blade moment weighing scales. SAE ARP 1136 Balance Classification of Turbine Rotor Blades. Standardizes blade data and markings for classifying moment weight. ++++++++ SECTION D Critical Speeds of Solid and Hollow Shafts ++++++++++++++++++ |