Assembly is final technological process, on the quality of which energy and performance indicators machines - efficiency, vibration and noise levels, reliability and durability. Assembly must be carried out using parts and assembly units belonging to this machine, since impersonal assembly is more complex organizationally and there may be cases when the characteristics of the machine do not meet the requirements of the standards. The quality of assembly is influenced by the correct organization of the workplace and the use of working tools. The assembled machine is run-in and tested.
§ 10.1. Balancing rotors and armatures
Before assembly, the rotors (armatures) and other rotating parts are balanced if they have been repaired or if increased vibration was detected during pre-repair tests. According to GOST 12327-79, compensation for imbalance must be carried out in two correction planes when the ratio of the axial dimension L of the part to the diameter D is greater than 0.2; at L/D<0,2 - в одной плоскости. Детали, устанавливаемые на отбалансированный ротор, балансируются отдельно. Если деталь устанавливают на ротор (якорь) с помощью шпонки, то она балансируется со шпонкой, а ротор - без шпонки.
With one correction plane, the rotor (armature) can be balanced both statically and dynamically, and with two planes - only dynamically.
Static balancing. The rotor is balanced on prisms (10.1). The deviation of the prism plane from the horizontal plane should not exceed 0.1 mm per 1 m of prism length. The surface roughness of the prisms should be no worse than The rotor (anchor) is installed on the prisms and, with a slight push, is brought out of balance, giving it the opportunity to roll along the prisms. After several swings, the unbalanced rotor (armature) will stop. A test load is installed at the top point of the rotor and the experiment is repeated. This is done several times and the load is selected. The rotor is considered balanced if it stops without swinging in a state of indifferent equilibrium. The test weight is weighed and a standard weight equal in weight to the test weight is installed in its place. If the parts being balanced do not have a shaft, then a technological shaft is made on which balancing is performed. Dynamic balancing. The rotor is balanced on the machine as it rotates. Modern balancing machines allow you to determine the installation location and weight of the load. Their use in repairs is highly desirable, but with a large range of machines being repaired, private readjustment reduces the efficiency of the machines and their use is not always justified. The use of a universal balancing machine allows you to solve this problem (10.2). The balanced rotor 4 is mounted on four round supports 2 and 6. The supports are located on a frame 7, consisting of two round beams. Engine 5 drives the rotor through belt 3. The left side of the frame is attached to the base by a flat spring 1 and remains motionless when the rotor rotates, while the right side rests on springs 9 and when the rotor rotates it begins to oscillate under the influence of the unbalanced masses of the right side of the rotor. The magnitude of the oscillations is shown by dial indicator 8. After determining the magnitude of the oscillations, stop the rotor and hang a test weight (plasticine) on the right side of the rotor. If during the next rotation the magnitude of the oscillations increases, this means that the test weight is installed incorrectly. By moving the load around the circle, they find the place where its location causes the least vibration. Then they begin to change the mass of the test load, achieving a minimum of vibrations. Having balanced the right side, remove the test weight and install a constant weight. The rotor is then turned and the other side is balanced. 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. 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: 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. Since you are repairing rotary hammers yourself, you need Makita 2470, 2450 rotary hammers use AC commutator motors. Determining the integrity of a brushed 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. Here is the sequence for repairing a rotor with a short circuit in the windings: Now let's look at everything in order. 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 the aluminum spacers, saw the frontal parts of the winding in a circle, as shown in the photo. To release the collector, the latter must be held by the lamellas with a gas wrench and turned along with the cut front part of the winding, turning the wrench 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. 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. Select a new manifold of the required diameter and design. Installation of a new collector is best done on a wooden block, placing 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. Winding a rotor is a labor-intensive and complex process and requires perseverance and patience. There are two winding options: According to the first option, you need to take the rotor in your left hand, and the prepared wire of the required diameter and the required length with a small margin in your right hand and wind it, constantly monitoring the number of turns. Rotate the winding away from you clockwise. 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 is a video of a simple device for winding rotors of a commutator motor. But you need to start winding with data preparation. The list of data should include: 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 the required number of turns with a step of 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. The rotor is armored to secure the windings, lamellas and ensure the safety of the rotor and its parts when operating at high speeds. Armoring is the technological process of securing the rotor coils using a mounting thread. Impregnation of the rotor should be carried out with connection to an alternating current network. 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. No matter how carefully and carefully you apply the impregnation, its particles end up on the collector lamellas and flow into the grooves. At the next stage, all 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. 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 properly 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. For dynamic balancing
The most convenient is a resonance type machine, consisting of two welded stands, support plates and balancing heads. The heads consist of bearings, 6 segments and can be fixed with bolts or freely swing on the segments. The balanced rotor is driven into rotation by an electric motor. The release clutch serves to disconnect the rotating rotor from the drive during balancing. Dynamic rotor balancing consists of two operations:
measuring the initial vibration value, which gives an idea of the size of the imbalance of the rotor masses; finding the placement of the bale and determining the mass of the balancing load for one of the ends of the rotor. During the first operation of the head
the machine is secured with bolts. The rotor is driven into rotation using an electric motor, after which the drive is turned off by 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
by the “cargo 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 advantageous location for placing the load will be the point at which the vibration amplitude was minimal. The mass of the balancing weight Q is obtained from the expression:
Where:
P is the mass of the test load; TO
0
- initial amplitude of oscillations before walking around with a test load; TO
min
- minimum amplitude of vibrations when walking around with a test load.
General AC machine assembly includes:
installation of bearings, insertion of the rotor into the stator, pressing of bearing shields, measurement of air gaps. The rotor is inserted using the same devices that are used during disassembly. This operation requires great attention and experience when assembling large machines, since even a light touch of a massive rotor can lead to significant damage to the windings and cores. The assembly sequence and its labor intensity are primarily determined by the complexity of the electrical machine design. The simplest assembly is asynchronous motors with a squirrel-cage rotor. First, prepare the rotor for assembly by placing ball bearings on the shaft. If the bearing supports have internal covers, they are first placed on the shaft, filling the sealing grooves with lubricant. Bearings are secured to the shaft with a retaining ring or nut, if provided for by the design of the machine.Roller bearings are divided into two parts:
The inner ring together with the rollers is mounted on the shaft, the outer ring is installed in the shield.
After the rotor is inserted into the stator, grease is placed in the bearings, the shields are put on the bearings and pushed into the housing with centering belts, securing with bolts. All bolts are initially screwed into several threads, then, alternately tightening them at diametrically opposite points, the shield is pressed into the body. After assembly, check the ease of rotation of the rotor and run it at idle, checking the bearings for heat and noise. The engine is then sent to a testing station. The assembly of DC machines begins with the preparation of the armature, inductor and bearing shields.
A fan is pressed onto the armature, consisting of a shaft, a core with a winding, a collector and a balancing ring. The inner bearing caps are placed on both ends of the shaft and the ball bearings are pressed on. For roller bearings, only the inner ring is pressed on. A shield is pressed onto the outer ring of the bearing on the side opposite to the commutator. Lubricant is placed in the bearing and closed with an outer cover. Assembling the inductor includes installing the main and additional poles with coils into the housing and making connections between the coils. The poles are first pressed into the coils, installing gaskets, frames, springs, etc. The coil or frame that rests on it must protrude above the surface of the back of the pole to ensure reliable clamping of the coils when tightening the pole mounting bolts. The assembler supports small poles with coils by hand during installation; heavy poles are first secured to the fixture with staples or other means. The device shown in the figure is designed for installing poles in a vertical position of the housing and consists of a round base, a central rod for lifting and transportation and a lever-hinge mechanism that ensures the clamping of the poles after the device is lowered into the housing under the influence of its own weight. The coils of the main and additional poles are connected according to the diagram. Depending on the insulation class, the joints are insulated with several layers of varnished cloth or fiberglass cloth and a protective tape on top. Rubber bushings are placed on flexible leads where they pass through the walls of the frame, protecting the insulation of the leads from damage. The polarity of the poles is checked in the assembled inductor using a compass. The winding is connected to a direct current source, the compass is moved around the circle near the poles. Near each adjacent pole, the arrow should rotate 180°. In the direction of rotation in engines, the main pole is followed by an additional pole of the same name, in generators - an additional pole of a different polarity. The shield on the commutator side is prepared for assembly by installing a set of brush holders into it and connecting it according to the diagram. The general assembly of DC machines begins with pressing the front (collector) shield into the inductor. This operation is usually performed with the inductor in a vertical position. The shield is inserted from above and pressed into the body with fastening bolts. The armature is inserted and the rear shield is pressed in with a vertical or horizontal inductor. When assembling vertically, the anchor with the shield is lifted by an eye bolt, which is screwed onto the threaded end of the shaft. Page 13 of 14 When the rotors and armatures of electric machines rotate, centrifugal forces arise, tending to push the winding out of the grooves and bend its frontal parts. To counteract centrifugal forces and hold the winding in the grooves, wedging and banding of the rotor and armature windings are used. In repair practice, wire bands are often replaced with glass tapes made of unidirectional (in the longitudinal direction) glass fiber impregnated with thermosetting varnishes. For winding glass tape bandages, the same equipment is used as for bandaging with steel wire, but supplemented with devices. in the form of tension rollers and tape stackers. Repaired rotors and armatures of electrical machines are subjected to static and, if necessary, dynamic balancing when assembled with fans and other rotating parts. Balancing is carried out on special machines to identify imbalance (imbalance) of the masses of the rotor or armature, which is a common cause of vibration during. machine operation. Rice. 155.Methods of static balancing of rotors and armatures: For static balancing, a machine is used, which is a supporting structure made of profile steel with 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 a is determined by the formula: Where: G—load on the prism, kg; E is the elastic modulus of the prism material, kg/cm2; p - design specific load, kg/cm 2 (for hard hardened steel p = 7000 - 8000 kg/cm 2); d—shaft diameter, cm. In practice, the width of the working surface of the prisms of balancing machines for balancing rotors weighing up to 1 ton is taken to be 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. Machines for balancing rotors (armatures) of electrical machines:
a - static, b - dynamic; 1 - stand, 2 - balanced rotor, 3 - dial indicator, 4 - release clutch, 5 - drive motor, b —
segments, 7 - clamping bolts, 8 - bearing, 9 - plate. 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 wheels, will take a position in which its heaviest part will be at the bottom. To determine the point on the circle at which the balancing weight should be installed, the rotor is rolled five times and after each stop, the lower “heavy” point is marked with chalk. 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, the point of installation of the balancing weight is determined: it is located in a place diametrically opposite to the average heavy current. At this point the balancing weight is installed. Its mass is selected experimentally until the rotor stops rolling when stopped 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 of small and low-speed machines. To balance the masses of the rotors of large electrical machines (power over 50 kW) with high 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 high speed, each end of it has an independent runout caused by unbalanced masses. “Repair of electrical equipment of industrial enterprises”, Modern electrical machines mainly use ball or roller bearings. They are easy to operate, withstand sudden temperature fluctuations well, and can be easily replaced when worn out. Sliding bearings are used in large electrical machines. Rolling bearings When repairing an electrical machine with rolling bearings, as a rule, we limit ourselves to washing the bearings and putting a new portion of the appropriate... The final stages of checking the electric motor being repaired are gap measurements and a test run. The gap sizes are measured using a set of steel plates - feeler gauges with a thickness of 0.01 to 3 mm. For asynchronous machines, the gap is measured at both ends at four points between the active steel of the rotor and stator. The gap should be the same around the entire circumference. The dimensions of the gaps are diametrically...
The degree of wear of rolling bearings is determined by measuring their radial and axial (axial) clearances on simple devices manufactured in the electrical workshop workshops of the enterprise. To measure the radial clearance on such a device, bearing 11 is installed on the vertical plate 8 of the device. Having placed a steel hose 10 on the inner ring 2 of the bearing, secure it with a nut screwed onto a rod 9 welded to the vertical plate;... In the practice of repairing electrical machines, there is often a need to calculate the windings or recalculate them to new parameters. Calculations of windings are usually carried out if the electric motor to be repaired does not have passport data or if the motor is received for repair without a winding. The need to recalculate windings also arises when it is necessary to change the speed or voltage, convert single-speed motors to... The current-collection system of electric machines includes collectors, slip rings, brush holders with traverses and a brush-lifting mechanism, short-circuiting rings of phase rotors of old designs. During operation of the machine, individual elements of the current collection system wear out, as a result of which its normal operation is disrupted. The most common defects of the current collection system are: unacceptable wear of the commutator and slip rings, the appearance of irregularities on their working surfaces and...Where to begin?
How to find a short circuit in the rotor
Electrical diagram of the Makita 2450, 2470 rotary hammer.
The procedure for disassembling, repairing, and assembling a hammer drill rotor
Stage I
Stage II
Stage III
How to wind a rotor with your own hands.
Option I
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
Rotor shell booking process
Rotor coil impregnation process
The process of cleaning the collector from excess impregnation
The armature balancing process
43. Sequence of operations when assembling electrical machines after repair.
Bandaging.
The method of fastening the windings (with wedges or bands) depends on the shape of the rotor or armature slots. For half-open and half-closed grooves, only wedges are used, and for open grooves, bandages or wedges are used. The grooved parts of the windings in the cores of armatures and rotors are secured using wedges or bandages made of steel bandage wire or glass tape, as well as simultaneously with wedges and bandages; the frontal parts of the rotor and armature windings are covered with bandages. Reliable fastening of the windings is important, since it is necessary to counteract not only centrifugal forces, but also the dynamic forces to which the windings are exposed during rare changes in the current in them. To bandage the rotors, tinned steel wire with a diameter of 0.8 - 2 mm, which has a high tensile strength, is used.
Before winding the bands, the frontal parts of the winding are hammered through a wooden spacer so that they are evenly positioned around the circumference. When banding the rotor, the space under the bands is first covered with strips of electrical cardboard to create an insulating spacer between the rotor core and the band, protruding 1 - 2 mm on both sides of the band. The entire bandage is wound with one piece of wire, without soldering. On the frontal parts of the winding, in order to avoid swelling, turns of wire are placed from the middle of the rotor to its ends. If the rotor has special grooves, the wires of the bandages and locks should not protrude above the grooves, and if there are no grooves, the thickness and location of the bandages should be the same as they were before renovation.
The brackets installed on the rotor should be placed over the teeth, not over the slots, and the width of each should be less than the width of the top of the tooth. The brackets on the bands are placed evenly around the circumference of the rotors with a distance between them of no more than 160 mm.
The distance between two adjacent bands should be 200-260 mm. The beginning and end of the bandage wire are sealed with two locking brackets 10-15 mm wide, which are installed at a distance of 10-30 mm from one to the other. The edges of the staples are wrapped around the turns of the bandage and... soldered with POS 40 solder.
To increase strength and prevent their destruction by centrifugal forces created by the mass of the winding during rotation of the rotor, fully wound bandages are soldered over the entire surface with POS 30 or POS 40 solder. Soldering of bandages is carried out with an electric arc soldering iron with a copper rod in diameter. 30 - 50 mm, connected to the welding transformer.
In contrast to banding with steel wire, the rotor is heated to 100 °C before wrapping glass tape bands around it. Such heating is necessary because when a bandage is applied to a cold rotor, the residual stress in the bandage during baking decreases more than when bandaging a heated one.
The cross-section of a fiberglass bandage must be at least 2 times larger than the cross-section of the corresponding wire bandage. The last turn of glass tape is attached to the underlying layer during the process of drying the winding during sintering of the thermosetting varnish with which the glass tape is impregnated. When banding the rotor windings with glass tape, locks, brackets and under-band insulation are not used, which is an advantage of this method.Balancing.
The rotor and armature consist of a large number of parts and therefore the distribution of masses in them cannot be strictly uniform. The reasons for the uneven distribution of masses are different thicknesses or weights of individual parts, the presence of cavities in them, uneven projection of the frontal parts of the winding, etc. Each of the parts included in the assembled rotor or armature may be unbalanced due to the displacement of its axes of inertia from. axis of rotation. In the assembled rotor and 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.
a - on prisms, b - on disks, c - on special scales; 1 - load, 2 - load frame, 3 - indicator, 4 - frame, 5 - balanced rotor (anchor)
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 causes vibration that can destroy the bearings and foundation of the machine. 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;
Unbalance is determined by static or dynamic balancing. The choice of balancing method depends on the required balancing accuracy, which can be achieved with existing equipment. With dynamic balancing, better results of imbalance compensation are obtained (less residual imbalance) than with static balancing. Such balancing can eliminate both dynamic and static unbalance. If it is necessary to eliminate imbalance (imbalance) at both ends of the rotor or armature, only dynamic balancing should be performed. Static balancing is performed with a non-rotating rotor on prisms (Fig. 155, i), disks (Fig. 155.5) or special scales (Fig. 155, c). Such balancing can only eliminate static imbalance.
To determine imbalance, the rotor is brought out of balance with a slight push; An unbalanced rotor (armature) will tend to return to a position in which its heavy side is down. After the rotor stops, mark with chalk the place that is in the upper position. The technique is repeated several times to check whether the rotor (armature) always stops in this position. Stopping the rotor in the same position indicates a shift in the center of gravity.
Test weights are installed in the space reserved for balancing weights (most often this is the inner diameter of the rim of the pressure washer), attaching them with putty. After this, repeat the balancing technique. By adding or decreasing the mass of weights, the rotor is stopped in any arbitrary position. This means that the rotor is statically balanced, that is, its center of gravity is aligned with the axis of rotation. At the end of balancing, the test weights are replaced with one of the same cross-section and mass, equal to the mass of the test weights and putty and the part of the electrode reduced by weight, which will be used for welding the permanent weight. Unbalance can be compensated for by drilling out a suitable piece of metal from the heavy side of the rotor.
Balancing on special scales is more accurate than with prisms and disks. The balanced rotor 5 is installed with the journals of the shaft on the supports of the frame 4, which can rotate around its axis at a certain angle. By rotating the balanced rotor, we achieve the highest reading of the indicator J, which will be provided that the center of gravity of the rotor is located in the figure (at the greatest distance from the axis of rotation of the frame ). By adding an additional frame weight 2 with divisions to the load 1, the rotor is balanced, which is determined by the indicator arrow. At the moment of balancing, the arrow aligns with the zero division.
If you rotate the rotor 180, its center of gravity will approach the frame swing axis by double the eccentricity of the displacement of the rotor center of gravity relative to its axis. This moment is judged by the lowest indicator reading. The rotor is balanced a second time by moving the load frame 2 along a ruler with a scale graduated in grams per centimeter. The magnitude of imbalance is judged by the readings of the scale.
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 most often subjected to dynamic balancing, in which both types of imbalance - static and dynamic - are simultaneously eliminated.
Dynamic balancing during the repair of electrical machines is carried out on a balancing machine at a reduced (compared to the operating) speed or when the rotor (armature) rotates in its own bearings at the operating speed.
For dynamic balancing, the most convenient machine is the resonance type (Fig. 156), consisting of two welded racks U support plates 9 and balancing heads.
Rice. 156. Resonant type machine for dynamic balancing of rotors and armatures
The heads, consisting of bearings 8 and segments 69, can be fixedly secured with bolts 7 or freely swing 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, 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 2 is driven into rotation using an electric motor 5, after which the drive is turned off, disengaging the clutch, and one of the machine heads is released. Released head under the action of a radially directed unbalance force
swings, which allows you to measure the amplitude of the head oscillation with dial indicator 3. 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 fixed at each point in turn, which should be slightly 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 required location for placing the load will be the point at which the vibration amplitude is minimal. The weight of the load is selected experimentally. -
After balancing one side of the rotor, balance the other side in the same way. Having finished balancing both sides of the rotor, the installed load is finally secured temporarily by welding or with screws, taking into account the weight of the weld or screws.
Pieces of strip steel are most often used as cargo. The fastening of the load must be reliable, since a load that is not securely fastened can come off the rotor during operation of the machine and cause a serious accident or accident.
Having secured a permanent load, the rotor is subjected to test balancing and, if the results are satisfactory, it is transferred to the assembly department for assembly of the machine.
V.B.Atabekov
