If you have determined that the rotor in your hammer drill has failed, but you do not have the funds for a new one, or you want to resurrect the part yourself, then these instructions are for you.

The design of the Makita rotary hammer is so simple that repairing Makita 2450, 2470 does not cause any particular difficulties. The main thing is to follow our advice.

By the way, almost every user with basic locksmith skills can repair a rotary hammer with his own hands.

Where to begin?

Since the structure of the rotary hammer is simple, the repair of the makita rotary hammer must begin with its disassembly. It is best to disassemble the hammer drill according to the already proven procedure.

Algorithm for disassembling a hammer drill:

1. Remove the back cover on the handle.
2. Remove the electric carbon brushes.
3. Disconnect the mechanical block housing and the stator housing.
4. Disconnect the rotor from the mechanical unit.
5. Remove the stator from the stator housing.

Remember, the stator housing is green, the mechanical unit housing with the rotor is black.

Having disconnected the rotor from the mechanical unit, we proceed to determine the nature of the malfunction. Rotor Makita HR2450 pos.54; article 515668-4.

How to find a short circuit in the rotor

Since you are producing do-it-yourself repair hammer drills, you need
Electrical diagram of the Makita 2450, 2470 rotary hammer.

Makita 2470, 2450 rotary hammers use AC commutator motors.

Definition of Integrity commutator motor begins with a general visual inspection. The faulty rotor pos. 54 shows traces of burnt windings, scratches on the commutator, and traces of burning on the commutator lamellas. A short circuit can only be detected in a rotor whose circuit does not have an open circuit.

To determine a short circuit (SC), it is best to use a special device IK-32.

Checking the armature for short circuit using a homemade indicator

After making sure, using the specified device or a homemade device, that the rotor has a short circuit between the turns, proceed to disassemble it.

Before disassembling, be sure to fix the winding direction. This is done very simply. Looking at the end of the rotor from the commutator side, you will see the winding direction. There are two winding directions: clockwise and counterclockwise. Record and write down, you will definitely need this data when winding yourself. The rotor of the Makita rotary hammer has a clockwise winding direction, right.

The procedure for disassembling, repairing, and assembling a hammer drill rotor

Here is the rotor repair sequence with short circuit windings:

1. Trimming the front part of the windings.
2. Removing the collector and frontal parts and measuring the diameter of the wire being removed.
3. Removal and cleaning of groove insulation, counting the number of turns along the sections.
4. Selection of a new collector.
5. Installation of a new collector.
6. Production of blanks from insulating material.
7. Installing sleeves into grooves.
8. Winding the anchor.
9. Wiring of conclusions.
10. Heat shrink process.
11. Shell reservation.
12. Shell impregnation.
13. Collector impregnation
14. Milling the slots of the commutator lamellas
15. Balancing
16. Cleaning and grinding the rotor.

Now let's look at everything in order.

Stage I

At the first stage, the collector must be removed from the armature. The commutator is removed after boring or sawing the end parts of the winding.

If you are repairing a rotary hammer yourself, you can cut the frontal parts of the winding using a hacksaw. Clamping the rotor in a vice through aluminum spacers, saw the frontal parts of the winding in a circle, as shown in the photo.

Stage II

To release the collector, the latter must be clamped gas wrench by the lamellas and turn it together with the cut front part of the winding, turning the key in different directions.

At the same time, clamp the rotor in a vice through soft metal spacers.

Similarly, remove the second frontal part using a gas wrench.

Always check the force of fixing the rotor in the vise by constantly tightening the clamp.

Stage III

When you remove the collector and the sides of the winding, proceed to removing wire residues and traces of insulation from the grooves. It is best to use a hammer and an aluminum or copper chisel for this. The insulation must be completely removed, and the surface of the grooves must be sanded.

But before you remove traces of the winding from the groove, try to count the number of turns laid in several grooves. Using a micrometer, measure the diameter of the wire being used. Be sure to check what percentage of the rotor slots are filled with wire. If the filling is small, you can use a larger diameter wire for new winding.

By the way, you can clean the insulation by wrapping a piece of wood of the desired profile in sandpaper.

Choose a new manifold required diameter and designs. Installation of a new collector is best done on wooden block, installing the rotor shaft vertically on it.

Having inserted the collector onto the rotor, press the collector into its old place with soft blows of a hammer through a copper adapter.

It was time to install the insulation sleeves. To make insulation sleeves, use electric cardboard, syntoflex, isoflex, and varnished fabric. In short, what is easiest to acquire.

Now comes the most difficult and responsible part.

How to wind a rotor with your own hands.

Winding the rotor is labor-intensive and difficult process and requires perseverance and patience.

There are two winding options:

• Do it yourself by hand without winding devices;
• Using the simplest devices.

Option I

According to the first option, you need to take the rotor in left hand, and the prepared wire is of the required diameter and required length with a small margin to the right and wind, constantly monitoring the number of turns. Rotate the winding away from you clockwise.

The winding procedure is simple. Secure the beginning of the wire to the bearing, thread the lamella into the groove and begin winding in the rotor groove opposite the lamella groove.

Option II

To facilitate the winding process, you can assemble a simple device. It is advisable to assemble the device when winding more than one anchor.

Here's a video simple device for winding rotors of a commutator motor.

But you need to start winding with data preparation.

The list of data should include:

1. Rotor length=153 mm.
2. Collector length=45 mm.
3. Rotor diameter=31.5 mm.
4. Collector diameter = 21.5 mm.
5. Wire diameter.
6. Number of grooves = 12.
7. Coil pitch =5.
8. Number of lamellas on the collector = 24.
9. Winding direction of the rotor coils = right.
10. Percentage of grooves filled with wire = 89.

You can obtain data on the length, diameter, number of grooves and number of lamellas during disassembly of the rotor.

Measure the wire diameter with a micrometer when you remove the winding from the rotor slots.

You need to collect all the data while disassembling the rotor.

Rotor rewinding algorithm

The winding order of any rotor depends on the number of slots in the rotor and the number of collector lamellas. You set the winding direction before disassembling and sketched it.

On the manifold, select the reference lamella. This will be the start of winding. Mark the starting lamella with a dot using nail polish.

When disassembling the rotor, we found that the rotor has 12 slots, and the collector has 24 lamellas.

We also established that the winding direction is clockwise when viewed from the commutator side.

Having installed insulating sleeves made of electric cardboard or its equivalent into the grooves, soldered the end of the winding wire to lamella No. 1, we begin winding.

The wire is placed in groove 1 opposite, and returns through the sixth groove (1-6), and so on until required quantity turns with a pitch z=5. The middle of the winding is soldered to lamella No. 2 clockwise. The same number of turns is wound into the same section, and the end of the wire is soldered to lamella No. 3. One coil is wound.

The beginning of a new coil is made from lamella No. 3, the middle is soldered onto lamellas No. 4, winding into the same grooves (2-7), and the end onto lamellas No. 5. And so on until the last coil ends at lamella No. 1. The cycle is complete.

Having soldered the ends of the windings to the collector lamellas, we proceed to armoring the rotor.

Rotor shell booking process

The rotor is armored to secure the windings, lamellas and ensure the safety of the rotor and its parts when operating at high speeds.

Reservation is called technological process securing the rotor coils using a mounting thread.

Rotor coil impregnation process

Impregnation of the rotor should be carried out while connected to the network alternating current. This is done using LATR. But it is better to do this procedure using a transformer, the winding of which is supplied with alternating voltage through the LATR.

Photo of impregnation with LATR

The problem is that when an alternating voltage is applied, the turns of the wound coils vibrate and heat up. And this promotes better penetration of insulation inside the turns.

The glue is diluted in a warm state according to the instructions. Epoxy glue is applied to the heated rotor winding using a wooden spatula.

Impregnation of the rotor of a Makita 2470 rotary hammer at home

After thoroughly soaking, allow the rotor to cool. During the cooling process, the impregnation will harden and become a solid monolith. All you have to do is remove the streaks.

The process of cleaning the collector from excess impregnation

No matter how carefully and carefully you apply the impregnation, its particles end up on the collector lamellas and flow into the grooves.

On next stage and all the grooves and lamellas must be thoroughly cleaned and polished.

The grooves can be cleaned with a piece of hacksaw blade, sharpened as for cutting plexiglass. And the lamellas can be cleaned with fine sandpaper by clamping the rotor into the chuck of an electric drill.

First, the surface of the lamellas is cleaned, then the collector grooves are milled.

Let's move on to balancing the anchor.

The armature balancing process

It is mandatory to balance armatures for high-speed tools. The Makita rotary hammer is not one, but it’s a good idea to check the balancing.

A correctly balanced rotor will significantly increase the operating time of the bearings, reduce vibration of the tool, and reduce noise during operation. Balancing will be performed on knives, two guides aligned, to the horizon using a level. The knives are set to a width that allows the assembled rotor to be placed on the shaft. The rotor must lie strictly horizontal.

7-6. ROTOR BALANCING

If the rotating part of the machine is not balanced, then when it rotates, vibration (vibration) of the entire machine appears. Vibration causes damage to bearings, foundations and the machine itself. For elimination

vibrations, rotating parts must be balanced. There are static balancing, performed on prisms, and dynamic balancing during rotation of the part being balanced. If, for example, the rotor shown in Fig. 7-9,a, has a heavier half //, then during rotation the centrifugal force of this half will be greater than the centrifugal force of half /. It will create pressure on the bearings, varying in

Rice. 7-9. Displacement of the rotor center of gravity,

control and cause the machine to shake. Such imbalance is eliminated by static balancing on prisms. The rotor is placed with the journals of the shaft and the prisms, precisely aligned horizontally, and at the same time, naturally, turns with the heavy side down. On the upper side, in special grooves that are provided in pressure washers and winding holders, lead weights of such weight are selected and placed so that the rotor remains on the prisms in an indifferent position. After balancing, the lead weights are usually replaced with steel ones of the same weight, which are securely welded or screwed to the rotor. However For long armatures and rotors, static balancing is not enough. Even if both halves of the rotor are balanced so that the weights of both halves are the same (Fig. 7-9.6), it may turn out that the centers of gravity are shifted along the axis of the machine. In this case, the centrifugal forces of the two halves cannot balance each other, but create a couple of forces that cause alternating pressure on the bearings. To eliminate the action of this pair of forces, special weights must be placed (Fig. 7-9.6) in order to create a pair of forces acting inversely to the unbalance pair of forces. Find the magnitude and position of these

loads can be achieved by balancing the rotating rotor (dynamic balancing).

Before performing dynamic balancing, you should check the rotor working surfaces (shaft journals and ends, commutator, slip rings, rotor steel) for runout and, if necessary, eliminate it. If you use a

Rice. 7-10. Dynamic balancing circuit,

“If any mandrels are used, they must be checked for runout and unbalance.

There should be no loose parts on the rotor, since in this case balancing is impossible. To carry out dynamic balancing, the rotor is placed in the bearings of a special machine. These bearings are mounted on flat springs and, if desired, can either be fixed motionless with a special brake, or perform free vibrations together with the spring (Fig. 7-10, a). The rotor is driven into rotation using an electric motor and clutch. The resulting unbalance force, which is directed radially, will rock the machine bearings. To carry out balancing, one bearing is fixed motionless by the brake, the second is released and oscillates under the influence of unbalance. On any precisely machined surface of the rotor, concentric with the shaft axis, make a mark with a colored pencil showing the point of greatest deflection of the rotor (Fig. 7-10.6).

However, at this point it is still impossible to accurately determine

the place where the rotor imbalance is located, since the greatest rotor deflection is obtained after the unbalance force passes through horizontal plane, in which the marker (pencil) is located.

The shear angle (i.e., the angle between the unbalance point and the mark) depends on the ratio of the rotation speed to the natural frequency of oscillation of the rotor on the supports, i.e., to the frequency of oscillations that will occur if a non-rotating rotor mounted on the machine supports is pushed.

When the number of revolutions per second coincides with the natural frequency, resonance occurs. The oscillations acquire the greatest scope and, therefore, the machine becomes the most sensitive. Therefore, they strive to balance at the resonant speed. In this case, the above angular shift becomes close to 90° and, therefore, the place of unbalance can be found by counting from the middle of the mark - 90° forward in rotation (and the place where the load is installed is 90° against rotation). If for some reason it is impossible to work at the resonant speed, then to determine the location of the unbalance, repeat the described experiment in the opposite direction of rotation at the same number of revolutions per minute. The mark is made with a pencil of a different color. Then the midpoint between the two marks determines where the imbalance is located. A balance weight is installed at a diametrically opposite point. The size of this load is determined by selection until the vibration of the bearing disappears. Instead of strengthening the load, balancing can be obtained by drilling out the opposite part of the anchor. After one side of the rotor is balanced, the bearing of this side is fixed motionless, and the bearing of the second side is released and the second side is balanced using similar techniques. After this, the balancing of the first side is checked and, if necessary, adjusted, etc.

Currently, there are a large number of machines for dynamic balancing, on which the location and size of the load are determined quite conveniently and accurately. Operating methods for these machines are given in the manufacturer's instructions.

In the absence of special machines, dynamic balancing can be carried out on durable wood.

withered beams laid on rubber gaskets. On these bars either the shaft journals of the rotor being balanced are placed directly, or the bearing shells in which the shaft journals lie. With the help of wedges, the beams can be fixed motionless. The rotor is rotated by a belt drive that encircles the steel directly, then the wedge is removed, and the bearing is allowed to vibrate on rubber pads. The balancing process is similar to that described above.

In repair conditions, especially for large machines, it is advisable to balance in assembled form [L. 8]; for this purpose, the machine is started idle and the vibration of the bearings is measured. This measurement should be made using vibration meters (for example, types VR-1, VR-3, 2VK, ZVK).

In the absence of vibrometers, vibration can be measured with an indicator mounted on a massive heavy handle. By pressing the probe of such an indicator to the vibrating part, you can determine the magnitude of the vibration swing by the width of the blurred outline of the arrow

It should be borne in mind that the readings of such a vibrometer strongly depend on the rotation speed and that therefore its readings can be used mainly as comparative ones at the same number of machine revolutions, which is sufficient for balancing purposes.

By measuring the vibration of the bearing in various directions, the point of greatest vibration is found. Balancing is carried out at this point.

To find the size and location of the balancing weight, a test weight is placed on the rotor at an arbitrary point and the vibration is measured again. It is obvious that by studying how vibration is affected by a test load, the size and location of which is known, it is possible to determine both the magnitude of the unbalance and its location. If it is possible to measure how the magnitude and phase of vibration changes as a result of installing a test weight (see below), then you can get by with two measurements: before and after installing the test weight. If it is impossible to determine the phase change, then it is necessary to make a larger (3-4) number of vibration measurements. The test weight is placed first at any arbitrary point, and then alternately at points located one unit of the circle to the right and left of the first.

To determine the phase change, you can resort to marks on the shaft, as described above. At the same time, the shaft is painted over with chalk and a sharp scribe; carefully, marks are applied (as short as possible), the middle of which corresponds to the greatest deviation of the shaft in the plane where the mark (scriber) is located. The angular distance (angle a) between the marks in the absence of a test load and in its presence is a measure of the oscillation phase shift caused by the introduction of a test weight.

More accurately, the phase shift is determined using the stroboscopic method. In this case, a mark is applied to the end of the shaft, illuminated by flashes of a gas-light lamp. This lamp is controlled by a special contact available h vibrometer, which closes once per shaft revolution at a moment close to the greatest swing of the vibration.

The mark on the rotating shaft appears stationary (since the lamp illuminates it every time it reaches exactly the same position after one revolution), and a mark can also be applied against it and the stationary part of the machine.

After introducing a test load, the mark on the shaft moves relative to the mark on the stationary part. By making a second mark on the stationary part, corresponding to the new position of the mark on the shaft, and measuring the angular distance (angle a) between them, we determine the angle of the oscillation phase shift.

The ability to determine the phase using a stroboscopic method is provided in special balancing vibroscopes of the Kolesnik 2VK, ZVK system, produced by the Leningrad Instrument Plant, and in vibroscopes of the BIP type of the Kyiv Electromechanical Plant

The graphical method for determining the location of the load is visible from Fig. 7-11, a. Here the segment is a “vector” oa on a certain scale is equal to the amplitude of bearing oscillations before the introduction of a test load. Trial load R tr placed in a plane shifted from the mark obtained on the shaft by some angle, for example by 90°, - line About V. Having now measured swing range of the bearing (while same number of revolutions per minute), marking the new mark And Having determined the angular shift between the marks - a, we now plot it on the same scale at an angle “to the vector oa vector ob,

Obviously, if the vector oa depicts vibration from imbalance, vector ob vibration from the combined action of the test load and imbalance, then the difference age. torus ab determines the magnitude and phase of vibration caused by the test load.

Figure 7-11 Determining the size and location of balancing weights

In order to eliminate vibration from imbalance, you need to rotate the vector ab by the angle § and increase it so that it is equal to the vector oa and directed against him. Obviously, for this, the test load P gr must be shifted from the point IN exactly WITH(by angle S) and increased in relation to the segments ^-. Balancing weight

i must therefore be equal to:

The second side of the machine is balanced in a similar way, but the load specified for this side Q"z distributed over two loads Q 2 and Q H . This is done in order not to upset the balancing of the first side.

Cargo<2г помещается в точку, определенную описанным выше способом для второй стороны, а груз СЬ Д переносится на первую сторону и закрепляется в точке диаметрально противоположной Q 2 (рис.-7-11,6). Величины грузов Q 2 I'm Qia are determined from the expressions:

where are the dimensions t, p, a, b, RiR^R 3 are visible from Fig. 7-111, b. Despite this distribution of the weight Q"2, it is usually necessary to carry out (corrective) balancing of the first side again after the weights have been installed Q 2 and SJ D.

The easiest way to check the quality of balancing is by installing the machine on a smoothly planed horizontal slab. When balanced satisfactorily, the machine operating at rated speed should not have any rocking or movement on the plate. The check is performed at idle speed in engine mode.

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 part, a load of mass T2 is added from the diametrically opposite side 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 fast-rotating parts as a turbocharger rotor, the armature of a traction motor or other electric machine, a blower impeller assembled with a drive gear, a water pump shaft assembled with an impeller and a gear wheel, and drive shafts of power mechanisms.

Rice. 3. Diagram of a console-type balancing machine:

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. The schematic diagram of 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

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 a 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, 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.

After repair, the rotors of electrical machines, complete 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 point of installation 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 action of the radially directed centrifugal force of the unbalance, which allows the dial indicator 3 to measure the amplitude of the head oscillation. 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 the technology for its repair to assess the feasibility of the 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, selecting measuring instruments, assembling a measurement circuit, preparing the electrical machine under test, establishing test methods and standards, as well as evaluating test results, appropriate standards and resources are used.

If during the repair of a machine its power or rotation speed is not changed, after a major overhaul the machine is subjected to control tests, and if the power or rotation speed is changed, to standard tests.