The rotor or armature of an electric motor is balanced when the center of gravity is aligned with the axis of rotation.
After repairing the rotor or armature of an electric motor, they must be subjected to static and sometimes dynamic balancing when assembled with fans and other rotating parts.
Both the rotor and armature of an electric motor consist of large quantity parts, therefore the distribution of masses in them cannot be strictly uniform. Most often, the reason for uneven distribution of masses is different thickness or mass individual parts, the presence of shells in them, unequal projection of the frontal parts of the winding, etc.
Each of the parts that make up the assembled rotor or armature may be unbalanced due to the displacement of its axes of inertia from the axis of rotation. In an assembled rotor or armature, the unbalanced masses of individual parts, depending on their location, can be summed up or mutually compensated. Rotors and armatures in which the main central axis of inertia does not coincide with the axis of rotation are called unbalanced.
Imbalance, as a rule, consists of the sum of two imbalances - static and dynamic.
The rotation of a statically and dynamically unbalanced rotor and armature is common cause the occurrence of vibration during operation of the electric motor, which can destroy the bearings and foundation of the mechanism. The destructive effect of unbalanced rotors and armatures is eliminated by balancing them, which consists of determining the size and location of the unbalanced mass.
Balancing is carried out by our masters using special equipment to identify imbalance of the rotor (armature) masses.
Unbalance is determined by static or dynamic balancing. The choice of balancing methods depends on the required balancing accuracy in each specific situation. With dynamic balancing, better results of imbalance compensation are obtained (less residual imbalance) than with static balancing. When choosing a balancing method, many nuances must be taken into account. For example, static balancing is used for rotors rotating at a speed not exceeding 1000 rpm. A statically balanced rotor (armature) may have dynamic imbalance, therefore rotors rotating at a frequency above 1000 rpm are recommended to be subjected to dynamic balancing, which simultaneously eliminates both types of imbalance - both static and dynamic.
Our specialists undergo special training in working with balancing machines and instruments, have solid experience in balancing and are well versed in all mechanisms of electric motors. By contacting Elpromtekhcenter, you can be sure that all the machines in your production will work smoothly and without failures, because we comply with all the rules and guarantee the high quality of the work performed.
If you have questions about rewinding electric motors, you want to get advice, calculate the cost or sign up for repairs, contact the Elpromtekhcenter specialists in the electrical equipment repair department.
After repair rotors electric machines assembled with fans and other rotating parts are subjected to static or dynamic balancing on special balancing machines. These machines are used to identify imbalance in the rotor mass, which is the main cause of vibration during machine operation. Vibration caused by centrifugal forces, which reach significant values at high rotation speeds of an unbalanced rotor, can cause destruction of the foundation and emergency failure of the machine.
For static balancing of rotors and armatures, a machine is used (Fig. 12, a), which is a support structure made of profile steel and trapezoidal prisms installed on it. The length of the prisms must be such that the rotor can make at least two revolutions on them.
The width of the working surface of the prisms of machines for balancing rotors weighing up to 1 ton is taken equal to 3-5 mm. The working surface of the prisms must be well polished and capable of supporting the weight of the rotor being balanced without deformation.
Static balancing of the rotor on the machine is carried out in the following sequence. The rotor is placed with the shaft journals on the working surfaces of the prisms. In this case, the rotor, rolling on the prisms, will take a position in which its heaviest part will be at the bottom.
To determine the point of the circle at which the balancing weight should be installed, the rotor is rolled 5-6 times and after each stop, the lower “heavy” point is chalked. After this, there will be five chalk lines on a small part of the rotor circumference.
Having marked the middle of the distance between the extreme chalk marks, determine the installation point of the balancing weight: it is located in a place diametrically opposite to the middle “heavy” point. At this point, a balancing weight is installed, the mass of which is selected experimentally until the rotor stops rolling, being left in any arbitrary position. A properly balanced rotor, after rolling in one direction and the other, should be in a state of indifferent equilibrium in all positions.
If it is necessary to more completely detect and eliminate the remaining imbalance, the rotor circumference is divided into six equal parts. Then, laying the rotor on the prisms so that each of the marks is alternately on the horizontal diameter, small weights are alternately hung at each of the six points until the rotor comes out of rest. The masses of cargo for each of the six points will be different. The smallest mass will be at the “heavy” point, the largest at the diametrically opposite point of the rotor.
With the static balancing method, the balancing weight is installed only at one end of the rotor and thus eliminates static unbalance. However, this balancing method is applicable only for short rotors and armatures of small and low-speed machines. To balance the masses of the rotors and armatures of large electrical machines with higher rotation speeds (more than 1000 rpm), dynamic balancing is used, in which a balancing weight is installed at both ends of the rotor. This is explained by the fact that when the rotor rotates at a high frequency, each end of it has an independent beating caused by unbalanced masses.
For dynamic balancing, the most convenient machine is the resonance type (Fig. 12, b), consisting of two welded racks 1, support plates 9 and balancing heads. The heads consist of bearings 8, segments 6 and can be fixedly secured with bolts 7 or swing freely on the segments. The balanced rotor 2 is driven into rotation by an electric motor 5. The release clutch 4 serves to disconnect the rotating rotor from the drive at the time of balancing.
Dynamic balancing of rotors consists of two operations: measuring the initial vibration value, which gives an idea of the extent of the imbalance of the rotor masses; finding the placement point and determining the mass of the balancing load for one of the ends of the rotor.
During the first operation, the machine heads are secured with bolts 7. The rotor is driven into rotation by an electric motor, after which the drive is turned off, disengaging the clutch, and one of the machine heads is released. The released head swings under the influence of the radially directed centrifugal force of the unbalance, which allows dial indicator 3 measure the vibration amplitude of the head. The same measurement is made for the second head.
The second operation is performed using the “load bypass” method. Having divided both sides of the rotor into six equal parts, a test load is alternately fixed at each point, which should be less than the expected unbalance. The vibrations of the head are then measured using the method described above for each position of the load. The most convenient place to place the load will be the point at which the vibration amplitude was minimal.
The mass of the balancing load Q (kg) is determined by the formula:
where P is the mass of the trial circle, K0 is the initial amplitude of vibrations before walking around with a trial load, K min is the minimum amplitude of vibrations when walking around with a trial load.
Having finished balancing one side of the rotor, balance the second side in the same way. Balancing is considered satisfactory if the centrifugal force of the remaining imbalance does not exceed 3% of the rotor mass. This condition can be considered fulfilled if the amplitude of the remaining oscillations of the head of the balancing machine is within the limits determined by the expression:
Where Вр is the mass of the balanced rotor, i.e.
After balancing is completed, the weight temporarily installed on the rotor is secured. Pieces of strip or square steel are used as balancing weights. The weight is attached to the rotor by welding or screws. The fastening of the load must be reliable, since a load that is not securely fastened enough can come off the rotor during operation of the machine and cause an accident or an accident. Having secured the load permanently, the rotor is subjected to test balancing, then transferred to the assembly department for assembly of the machine.
Repaired electrical machines are subjected to post-repair tests according to an established program: they must meet the requirements imposed on it by standards or specifications.
The following types of tests are carried out at repair plants: control tests - to determine the quality of electrical equipment; acceptance - upon delivery of repaired electrical equipment by a repair company and acceptance by the customer; typical, after making changes to the design of electrical equipment or technology for its repair to assess the feasibility changes made. In repair practice, control and acceptance tests are most often used.
Each electrical machine after repair, regardless of its volume, is subjected to acceptance tests. When testing, choosing measuring instruments, assembling the measurement circuit, preparing the electrical machine under test, establishing test methods and standards, and also using appropriate standards and resources to evaluate test results.
If, when repairing a machine, its power or rotation speed is not changed, after overhaul the machine is subjected to control tests, and when the power or rotation speed changes, to standard tests.
As is known, an electric motor (hereinafter referred to as an electric motor) consists of two elements - static (stator) and moving (rotor). The latter during operation can rotate at very high speed, which amounts to thousands and tens of thousands of revolutions per minute.
Rotor imbalance not only leads to increased vibration, but can also damage the rotor itself or the entire electric motor. Also, due to this problem, the risk of breakdown of the entire installation where this ED is used increases.
To avoid these negative consequences, produced balancing of electric motor armatures- also known as “rotor balancing” or “electric motor balancing”.
How to balance electric motor rotors
A balanced rotor is a rotor whose axis of rotation coincides with the axis of inertia. True, absolute balance can only be achieved in an ideal world, but in reality there is always at least a slight “distortion”. And the task of balancing is to minimize it.
There are static and dynamic balancing of rotors.
Static rotor balancing is designed to eliminate significant mass imbalance relative to the axis of rotation. It can be done at home because it does not require the use of special equipment. Prismatic or disc clamps are sufficient. This operation can also be performed using specially designed lever scales.
The rotor is placed on a prismatic or disk clamp. After this, its heaviest side outweighs, and the part scrolls down. Make a mark with chalk at the lowest point. Then the rotor is rolled four more times, and after each final stop, the lowest point is noted.
When there are five marks on the rotor, measure the distance between the outer ones and make a sixth one in the middle. Then, a balancing weight is installed at the diametrically opposite point of this sixth mark (the point of maximum imbalance).
The weight of the load is selected experimentally. At the point opposite to the maximum imbalance, weights of various masses are installed, after which the rotor rotates and stops in any position. If there is still an imbalance, the mass of the weight decreases or increases (depending on which direction the rotor turns after stopping). The task is to select such a mass of weighting material that the rotor does not turn after stopping in any position.
After determining the required mass, you can either leave the weight or simply drill a hole at the resulting sixth point - the point with maximum imbalance. In this case, the mass of the drilled metal must correspond to the mass of the selected load.
So static DIY electric motor balancing quite rough and is designed to eliminate only serious distortions in the mass of the load on the shaft. There are other disadvantages as well. Yes, static DIY motor armature balancing will require numerous measurements and calculations. To improve accuracy and speed, it is recommended to use the dynamic method.
This will require a special machine for balancing electric motor rotors. It spins the shaft placed on it and determines along which of the axes the mass is skewed. Dynamic balancing of electric motor rotors is capable of eliminating even the smallest deviations of the axis of inertia from the axis of rotation.
Dynamic motor shaft balancing produced by computer method. The highly intelligent equipment that is used for this process is able to independently suggest which counterweight should be installed on which side.
However, finding a machine for balancing a very heavy or large rotor is quite difficult. Typically, the dynamic method of eliminating distortion is used for relatively small electric motors, regardless of power. Therefore, choosing methods for balancing and centering electric motors, it is worth paying attention not only to the accuracy of the operation, but also to the physical ability to carry out this process for the existing shaft.
2.16. Balancing rotors and armatures
Repaired rotors and armatures of electrical machines are sent for static and, if necessary, dynamic balancing, complete with fans and other rotating parts. Balancing is carried out on special machines to identify imbalance (imbalance) of the masses of the rotor and armature. The reasons for the uneven distribution of masses may be: different thickness individual parts, the presence of cavities in them, unequal projection of the frontal parts of the winding, etc. Any part of the rotor or armature may be unbalanced as a result of a shift of the axes of inertia relative to the axis of rotation. The unbalanced masses of individual parts, depending on their location, can be summed up or mutually compensated.
Rotors and armatures in which the central axis of inertia does not coincide with the axis of rotation are called unbalanced.
The rotation of an unbalanced rotor or armature causes vibration that can destroy the bearings and foundation of the machine. To avoid this, the rotors are balanced, which involves determining the size and location of the unbalanced mass and eliminating the imbalance.
Unbalance is determined by static or dynamic balancing. The choice of balancing method depends on the balancing accuracy that can be carried out on this equipment. With dynamic balancing we get top scores compensation for imbalance than with static.
Static balancing is performed with a non-rotating rotor on prisms, disks or special scales (Fig. 2.45). To determine imbalance, the rotor is brought out of balance with a slight push. An unbalanced rotor will tend to return to a position where its heavy side is down. After stopping the rotor, mark with chalk the place that is in the upper position. The process is repeated several times. If the rotor stops in the same position, then its center of gravity has shifted.
Rice. 2.45. :
a - on prisms; b - on disks; c - on special scales; 1 - load; 2 - cargo frame; 3 - indicator; 4 - frame; 5 - rotor (armature)
In a certain place (most often, this is the inner diameter of the rim of the pressure washer), test weights are installed, attaching them with putty. After this, repeat the balancing technique. By increasing or decreasing the mass of the loads, the rotor is stopped in an arbitrary position. This means that the rotor is statically balanced.
At the end of balancing, the test weights are replaced with one weight of the same mass.
Unbalance can be compensated for by drilling out a suitable piece of metal from the heavy part of the rotor.
Balancing on special scales is more accurate than with prisms and disks.
Static balancing is used for rotors with a rotation speed of no more than 1000 rpm. A statically balanced rotor can be dynamically unbalanced, therefore rotors with a rotation speed of more than 1000 rpm are subjected to dynamic balancing, which eliminates static imbalance.
Dynamic rotor balancing, which is performed on a balancing machine, consists of two operations: measuring the initial vibration; finding the location point and mass of the balancing load for one of the ends of the rotor.
Balancing is done on one side of the rotor, and then on the other. After balancing is completed, the load is secured by welding or screws. Then perform test balancing.
Unbalance of any rotating part Failure of a diesel locomotive can occur both during operation due to uneven wear, bending, accumulation of contaminants in any one place, when the balancing weight is lost, and during the repair process due to improper processing of the part (displacement of the axis of rotation) or inaccurate alignment of the shafts. To balance the parts, they are subjected to balancing. There are two types of balancing: static and dynamic.
Rice. 1. Scheme of static balancing of parts:
T1 is the mass of the unbalanced part; T2 is the mass of the balancing load;
L1, L2 - their distances from the axis of rotation.
Static balancing. For an unbalanced part, its mass is located asymmetrically relative to the axis of rotation. Therefore, in the static position of such a part, i.e. when it is at rest, the center of gravity will tend to take a lower position (Fig. 1). To balance the parts, they are added diametrically opposite side load with mass T2 so that its moment T2L2 is equal to the moment of the unbalanced mass T1L1. Under this condition, the part will be in balance in any position, since its center of gravity will lie on the axis of rotation. Equilibrium can also be achieved by removing part of the metal of the part by drilling, sawing or milling from the side of the unbalanced mass T1. In the drawings of parts and in the Repair Rules, a tolerance is given for balancing parts, which is called imbalance (g/cm).
Flat parts that have a small length-to-diameter ratio are subjected to static balancing: the gear wheel of a traction gearbox, the impeller of a refrigerator fan, etc. Static balancing is carried out on horizontally parallel prisms, cylindrical rods or on roller supports. The surfaces of prisms, rods and rollers must be carefully processed. The accuracy of static balancing largely depends on the condition of the surfaces of these parts.
Dynamic balancing. Dynamic balancing is usually carried out on parts whose length is equal to or greater than their diameter. In Fig. Figure 2 shows a statically balanced rotor, in which mass T is balanced by a load of mass M. This rotor, when rotating slowly, will be in equilibrium in any position. However, with its rapid rotation, two equal but oppositely directed centrifugal forces F1 and F2 will arise. In this case, a moment FJU is formed which tends to rotate the rotor axis at a certain angle around its center of gravity, i.e. dynamic imbalance of the rotor is observed with all the ensuing consequences (vibration, uneven wear, etc.). The moment of this pair of forces can only be balanced by another pair of forces acting in the same plane and creating an equal reaction moment.
To do this, in our example, we need to apply two weights of masses Wx = m2 to the rotor in the same plane (vertical) at an equal distance from the axis of rotation. The loads and their distances from the axis of rotation are selected so that the centrifugal forces from these loads create a moment /y counteracting the moment FJi and balancing it. Most often, balancing weights are attached to the end planes of parts or part of the metal is removed from these planes.
Rice. 2. Scheme of dynamic balancing of parts:
T—rotor mass; M is the mass of the balancing load; F1, F2 - unbalanced, reduced to the rotor mass planes; m1,m2 - balanced, reduced to the rotor mass planes; P1 P 2 - balancing centrifugal forces;
When repairing diesel locomotives, dynamic balancing is carried out on such rapidly rotating parts as a turbocharger rotor, an armature of a traction motor or other electrical machine, a blower impeller assembled with a drive gear, a water pump shaft assembled with an impeller, and gear wheel, cardan shafts for driving power mechanisms.
Rice. 3. Scheme of the balancing machine console type:
1 - spring; 2 — indicator; 3 anchor; 4 - frame; 5 — machine support; 6 — bed support;
I, II - planes
Dynamic balancing is in progress on balancing machines. Schematic diagram such a console-type machine is shown in Fig. 3. Balancing, for example, the armature of a traction motor is carried out in this order. The anchor 3 is placed on the supports of the swinging frame 4. The frame rests with one point on the support of the machine 5, and the other on the spring 1. When the armature rotates, the unbalanced mass of any of its sections (except for the masses lying in plane II - II) causes the frame to swing. The amplitude of frame vibration is recorded by indicator 2.
In order to balance the anchor in the I-I plane, test loads of different masses are attached alternately to its end on the side of the collector (to the pressure cone) and the frame oscillations are stopped or reduced to an acceptable value. Then the anchor is turned over so that plane I—I passes through the fixed support of the frame 6, and the same operations are repeated for plane II—II. In this case, the balancing weight is attached to the rear pressure washer of the armature.
After completion of all assembly work, the parts of the selected sets are marked (with letters or numbers) in accordance with the requirements of the drawings