Balancing of rotating parts in the repair of machines. How dynamic balancing can increase engine life Static and dynamic balancing of rotating parts

Static balancing (used in fine-grained and single-piece production) of assembly units and parts consists in determining the magnitude of the imbalance and its elimination by rearranging individual structural elements, removing in the right places by drilling, grinding, boring a part of the metal, or, conversely, by adding its corresponding mass by welding, etc.

Dynamic balancing is used to balance rotating assembly units that have a large length compared to the diameter (eg spindle). With such balancing, a system of forces is artificially created in which the resultants, as well as the moments, are equal to zero or constant in magnitude and direction.

Oscillating systems of the balancing machine: 1) with fixed supports (Fig. A). 2) with a fixed axis of oscillation of the axis of the balanced rotor (Fig. B). 3) with a fixed plane of oscillation of the rotor axis (Fig. D). 4) without rigid connections between the rotor axis and the environment (Fig. E).

The unbalance of the mechanisms of mobile machines increases their vibration, which worsens the controllability, adversely affects the strength and adversely affects the health of the attendants.

Parts are usually balanced in machine shops during their manufacture. However, after assembling assembly units, which include balanced parts, it becomes necessary to re-check them, since the displacement of one of the parts, even within the gaps provided for by the drawing, can often cause significant unbalance of the entire assembly unit. In this regard, in the technological processes of assembling many products, balancing is a mandatory operation.

Balancing the final assembled assembly units on special installations or balancing machines is a control and fitting operation, which is often not included in the assembly flow, but is performed in a separate area. Nevertheless, balancing work is an essential part of the assembly process.

The balancing accuracy, permissible imbalances are established by technical requirements, based on the design features and purpose of assembly units and parts, their rotation speed, permissible vibrations of the machine, the necessary reliability and durability, possible physiological sensations of the operator working on the machine under operating conditions, etc.

For example, the static imbalance of the turbine rotor disks is assigned from the condition that the unbalanced force does not exceed 5% of the disk weight. The accuracy of the dynamic balancing of the assembled rotor is often set such that the perturbing force on each bearing does not exceed 1-2% of the mass of the rotor. In some cases, the balancing accuracy is characterized by the so-called permissible residual eccentricity.

Rice. . Static balancing schemes

During the assembly process, static and dynamic balancing of assembly units - rotors is usually performed. Static balancing is carried out on horizontal parallels , on disk rollers, on a spherical heel , on the scales and on special machines.

Static balancing of assembly units and parts consists in determining the magnitude of the imbalance and eliminating it by rearranging individual structural elements, removing parts of the metal in the right places by drilling, grinding, boring, or, conversely, adding its corresponding mass by welding, riveting, etc., as well as combining these ways.

With static balancing, you can ensure the accuracy of:

on parallels or heel - up to 0,001 Gk gf*cm;

In mass production, automated balancing machines are becoming widespread, in which the processes of connecting a balanced part (assembly unit) with a drive, determining unbalance, transferring these results to memory devices, orientation of the part and cutting tool, and the operation of eliminating imbalance are performed automatically. In some of these automata, the processes of determining imbalance and eliminating it are combined (single-position automata); in on-off automata these processes are separated.

In order to carry out dynamic balancing at high speeds and reduce the time for the operation, experiments are currently underway on the use of short-term (less than 1 ms) laser pulses to eliminate excess metal without stopping the balanced part (assembly unit).

As already noted, the imbalance of various rotating assembly units causes vibration of the machine during operation. In high-speed machines (for example, in cars, tractors), this phenomenon is especially noticeable. Increasing the accuracy of balancing parts and assembly units reduces vibration.

Wheel balancing is necessary so that during the movement of the car, the driver does not experience discomfort from such a phenomenon as wheel beating. This happens when there is an imbalance relative to the axis or plane of rotation.

Why do you need wheel balancing?

In the process of manufacturing discs, tubes and tires, it is impossible to make a perfectly balanced product. The main part of the imbalance is brought by the tire. Because it is farthest from the center of rotation. Hence the need for balancing. After all, improper wheel balancing not only makes driving uncomfortable, it also contributes to the rapid wear of suspension elements. First of all, the wheel bearing suffers, which will certainly have to be changed if you drove on unbalanced wheels.

Agree, it is much cheaper to do balancing than to change worn parts and tires. Until now, there are people who balance only the front wheels. Allegedly, only the leaders need this, and there is no need to spend extra money on balancing the rear ones. This is a delusion, and such savings will only kill the elements of the rear suspension.

There are several types of balancing:

• on the machine, with the removal of the wheel;
• finishing, produced directly on the car;
• automatic (powder, bead).

There is also a division into dynamic and static.

How is balancing done

static

In the case when the wheel has a static imbalance, its weight along the axis of rotation is uneven, it has a heavy place. This place will hit the road with more force, and the greater the speed of its rotation, the stronger the static imbalance will be.


To avoid this phenomenon, static balancing is done. This service in our country is provided by all tire shops. The wheel is placed on a special machine, in the process of rotation, the automation determines the degree of imbalance, and indicates where it is necessary to install an additional load.

Loads are of two types:

• with a bracket, mounted on the edge of the disk and are used, as a rule, on stamped disks;
• adhesive-based, convenient for balancing cast, forged wheels.

Dynamic

It should be noted right away that not every tire fitting station can offer this service. Since the equipment used in most cases is old, we can say trophy.

So what is dynamic balancing for? The wider the profile of the wheel, the more likely it is to get a dynamic imbalance during movement, relative to the plane of its rotation.

Finishing

This type of balancing is performed after the main static, and if possible dynamic. Special equipment, a balancing stand, is installed under a suspended car, the wheel spins up to a speed of 90 km / h, and the automation takes measurements and indicates in what place and what load should be installed. For this balancing, you need equipment that is often available only to professional tire fitting centers.

Automatic

Automatic is used only on trucks and buses. This happens as follows - special balancing granules, small beads, less often sand are poured into the wheel, because the latter has a high abrasive effect. During driving, under the influence of centrifugal force, the balancing material is attracted to the inner surface of the tire, which leads to self-balancing.

On passenger vehicles, this type of balancing is not used due to the fact that it is not possible to determine exactly how much material needs to be poured into each wheel. Additionally, its weight also increases.

Proper wheel balancing

There are a number of rules, the implementation of which guarantees the highest quality balancing.

1. the disc must be cleaned of dirt. After all, it is often quite a lot both on the outside and on the inside. Automation calculates how many grams of cargo to hang on one or another part of the wheel. Having balanced a dirty wheel, you run the risk of losing balance on the very first bump, when a large piece of dirt falls off the disk and all the work goes down the drain;
2. be sure to remove all old balancing weights;
3. still quite often there is a situation when the tire simply did not fully fit into place. It is not always possible to notice this from the outside, but it can affect the balancing quite strongly;
4. various plastic caps, which are put on immediately after leaving the tire shop, are also capable of introducing an imbalance into a newly balanced wheel.

How often should you do wheel balancing?

Recommended frequency varies. Someone says that it is necessary every 10 thousand kilometers, someone insists on 20 thousand. If you feel that the steering wheel beats while driving, there is excessive vibration of the body, do not be too lazy to visit a tire shop. By doing so, you may save on more expensive repairs.
We hope that after reading this article, you will no longer have questions about why wheel balancing is needed, and whether it should be done.

After assembling a rotating assembly unit, which includes balanced parts (for example: shafts, shell gears, couplings, etc.) and other parts (keys, pins, locking screws, etc.), it becomes necessary to re-balance them, since the displacement of one of the parts, even within the clearances provided by the drawing, causes significant unbalance.

The discrepancy between the center of gravity of the part and the axis of rotation is commonly called static imbalance, and the inequality of zero centrifugal moments of inertia is called dynamic imbalance.

Static imbalance is easily detected when the part is mounted with support journals or on mandrels on horizontal parallels (knives, prisms, rollers) or rollers, and dynamic imbalance is detected only when the part is rotated. In this regard, balancing is static and dynamic.

Static balancing. There are several methods for performing static balancing. The most common in the machine tool industry are balancing on prisms and on disks. Knives, prisms and rollers must be hardened and ground and before balancing adjusted to the horizontal.

When balancing on horizontal parallels (Fig. 1), the allowable ovality and taper of the necks of the mandrel should not exceed 0.01-0.015 mm, and their diameters should be the same.

Rice. one. a - on horizontal parallels (1 - center of gravity of the part; 2 - corrective weight); b - on disks (1 - detail; 2 - corrective weight)

To reduce the coefficient of friction, the parallels and neck of the mandrel are recommended to be hardened and carefully ground. The working length of the parallels can be determined by the formula:

where d is the mandrel neck diameter.

The width of the working surface of the parallels (ribbons) is (cm):

where G is the force acting on the parallel, in kg; E is the modulus of elasticity of the material of the mandrel and parallels, in kg/cm2; σ is the allowable compressive stress at the points of contact between the neck and the parallel, in kg/cm 2 (for hardened surfaces σ=2 10 4 ÷ 3 10 4 kg/cm 2).

The value of d in cm is assigned from design considerations, taking into account the convenience of installing the part to be balanced on the mandrel.

The unbalance is determined by trial attachment of corrective weights on the surface of the part to be balanced. The imbalance is eliminated by removing an equivalent amount of material from the diametrically opposite side or by installing and securing appropriate counterweights (corrective weights).

Static balancing of a pulley can be done as follows. On the rim of the pulley, a line is first applied with chalk and rotation is imparted to it. The rotation of the pulley is repeated 3-4 times. If the chalk line stops at different positions, then this will indicate that the pulley is balanced correctly. If the chalk line stops in one position each time, then this means that the part of the pulley located below is heavier than the opposite one. To eliminate this, reduce the mass of the heavy part by drilling holes, or increase the mass of the opposite part of the pulley rim by drilling holes, and then fill them with lead.

Balancing sensitivity of parts weighing up to 10 tons on horizontal parallels (Fig. 1, a):

where F is the sensitivity of the method in G cm; f is the coefficient of rolling friction (f=0.001 ÷ 0.005 cm); G is the weight of the part or assembly unit in kg.

Sensitivity of balancing parts weighing up to 10 tons on disks (Fig. 1, b):

where F is the sensitivity of the method in G cm; f is the coefficient of rolling friction (f=0.001 ÷ 0.005 cm); G is the weight of the part or assembly unit in kg;  – coefficient of rolling friction in disc bearings; r is the radius of the trunnion of the discs, cm; d is the mandrel diameter in cm; D is the diameter of the disks in cm; α is the angle between the axis of the mandrel and the axes of the discs.

The balancing accuracy on discs is greater than on horizontal prisms. Static balancing is most often used for parts such as disks.

Balancing of parts and assembly units can be performed on balancing scales in the resonant mode of an oscillating system, which improves the balancing accuracy.

Balancing parts weighing up to 100 kg on a balancing scale is performed as follows (Fig. 2): the tested structure 1 is balanced by weights 3 and the rotating part 1 of the structure is accelerated to a rotational speed exceeding the oscillation frequency of the system. After acceleration, the electric motor is disconnected from the structure under test, the moving part of which continues to rotate freely, gradually reducing the speed. This eliminates the influence of disturbances from the drive motor on the oscillating system. The amplitude of the displacement of the reference point is measured by instrument 2 at the moment when the spindle speed coincides with the natural frequency of the oscillating system, i.e. at resonance, where the amplitude reaches its maximum value. The value of the residual imbalance with this method of measurement should not exceed 1.5-2 G cm.

Rice. 2.

For a number of products, at present, on the basis of experience, the norms for the permissible displacement of the center of gravity of rotating parts have already been established (Table 1).

Table 1. Permissible amount of displacement of the center of gravity

Parts group	Name	Center Offset gravity, microns	Parts group	Name	Center Offset gravity, microns
BUT	Circles, rotors, shafts and pulleys of precise grinding machines	0,2-1,0	AT	Rigid small rotors electric motors, generators	2-10
B	high speed electric motors, grinding machine drives	0,5-2,5	G	Normal motors, fans, parts of machines and machine tools, high-speed drives, etc.	5-25

Sensitivity of balancing parts weighing up to 100 kg on balancing scales (Fig. 2): F=20 ÷ 30 G cm.

The amount of imbalance:

where ω is the difference in instrument readings 2.

Dynamic balancing parts and assembly units is used to more accurately determine the imbalance that occurs during rotation under the action of centrifugal forces. To carry out dynamic balancing of parts and sets such as bodies of revolution, balancing machines are used.

Parts and sets such as couplings, gears, pulleys are balanced on mandrels. A mandrel with a part or an assembly unit for balancing is installed on a balancing machine and connected to the machine spindle.

The magnitude of the imbalance and its location are determined by the instruments installed on the machine. The imbalance is usually eliminated by drilling a hole in the part or by directing the metal on the side of the part opposite from the place of imbalance.

The balancing accuracy required by technical specifications depends on the design and purpose of parts and assemblies, their rotation speed, permissible vibrations of the machine, and the required durability of supports.

Static balancing can balance a part relative to its axis of rotation, but cannot eliminate the action of forces that tend to rotate the part along its longitudinal axis.

Dynamic balancing eliminates both types of imbalance. High-speed parts with a significant ratio of length to diameter (rotors of turbines, generators, electric motors, fast-rotating spindles of machine tools, crankshafts of automobile and aircraft engines, etc.) are subjected to dynamic balancing.

Dynamic balancing is carried out on special machines by highly skilled workers. In dynamic balancing, the amount and position of the mass that must be applied to or removed from the part are determined so that the part is statically and dynamically balanced.

Centrifugal forces and moments of inertia caused by the rotation of an unbalanced part create oscillatory movements due to the elastic compliance of the supports. Moreover, their fluctuations are proportional to the magnitude of unbalanced centrifugal forces acting on the supports. Balancing of parts and assembly units of machines is based on this principle.

Dynamic balancing, performed on modern automated balancing machines, in the range of 1-2 minutes gives data: the depth and diameter of drilling, the mass of loads, the dimensions of the counterweights and the places where it is necessary to fix and remove the loads, as well as the amplitude of the oscillations of the supports.

Parts and assemblies with a length greater than the diameter (crankshafts, spindles, rotors of bladed machines, etc.) are subjected to dynamic balancing. The dynamic imbalance that occurs during the rotation of the part due to the formation of a pair of centrifugal forces P (Fig. 3, a) can be eliminated by applying a corrective moment from the forces P 1. The choice of correction planes is determined by the design of the part and the convenience of removing excess metal. The most common case of part unbalance encountered in practice is shown in Fig. 3b.

Rice. 3. Schematic diagram of dynamic balancing parts:a - dynamic unbalance of the part; P - centrifugal forces from unbalanced masses m, located on the arm r; Pt - centrifugal forces from corrective weights; b - static and dynamic unbalance of the part; P’ is the centrifugal force from the mass m’, decomposed into forces P and P”, causing static unbalance

Unbalance detection is carried out on balancing machines. In the conditions of individual production, dynamic balancing is performed using simple means, which include, for example, a device for installing supports of a balanced part on elastic beams or on elastic (rubber) linings.

The part is brought into rotation to a speed exceeding the conditions of resonance.

The drive is turned off (for example, by resetting the belt) and the amplitude of the maximum oscillations of one of the supports is measured. By attaching a test load to the part, the vibration of this support is stopped. A similar procedure is performed for the other support. Balancing ends when the oscillations of the supports stop.

with elastic supports, used for parts and assemblies weighing up to 100 tons (rotors of powerful turbines) - in fig. four.

Rice. four. 1 – balancing object; 2 - electromagnetic clutch; 3 - electric motor; 4 - bearings; 5 - supporting elastic racks (springs); 6 - stops, alternately locking the bearings; 7 - a mechanical lever indicator for determining the imbalance plane by marks 8 drawn by the tip of the indicator on the painted oscillating neck of the object; 9 - compensating test weights attached to the object

Balancing is carried out with alternately fixing the supports. The angular position of the imbalance is found using mechanical or electrical indicators. The amount of imbalance in the selected correction planes is determined by attaching test compensating weights. The sensitivity depends on the weight and dimensions of the object.

Balancing on frame type machines with adjustable imbalance compensators, it is mainly used for parts and assemblies of small and medium sizes weighing up to 100 kg.

Unbalance balancing is carried out manually and mechanically.

On fig. 5 shows a diagram of a balancing machine with manual movement of compensating weight 3 on the machine spindle.

Rice. 5. 1 - frame; 2 - balanced part, assembly; 3 - imbalance compensator

The load 3 is moved in the radial and circumferential directions and its weight is adjusted manually. This determines the equivalent amount of material to remove from the part. The imbalance is determined only in the plane of correction 1–1. Therefore, to determine the unbalance of the part in another plane 2–2, it is necessary to reinstall it with a rotation of 180 ° to determine the size and location of the compensator in this plane. The machine requires pre-setting according to the reference part; frame oscillations around the horizontal axis are noted by a mechanical amplitude meter; the value of unbalanced moments in the selected correction planes is determined with an accuracy of 10 -15 G cm 2 .

The dynamic unbalance of the rotor is characterized by the presence of both static and moment unbalance, when both the main imbalance vector (D) and the main imbalance moment (M) are non-zero:

When the rotor is dynamically unbalanced, its axis of rotation and one of the main axes of inertia either intersect outside the center of mass or cross in space.

The elimination of the dynamic imbalance of the rotor is carried out by the methods of dynamic balancing, in which the static and torque imbalances of the rotor are simultaneously reduced. In practice, dynamic balancing is the process of checking the mass distribution of a rotating rotor and, in the presence of imbalances, changing this distribution with the help of corrective masses until an acceptable unbalance value is reached.

The choice of this or that method of dynamic balancing, first of all, is determined by the type of rotor - rigid or flexible. If the rotor does not bend during rotation and behaves like an absolutely rigid body, making only movements due only to vibrations of the bearing assembly, then such a rotor is called rigid. In fact, in any real-life rotor, there are always dynamic bending deformations due to the distribution of imbalances along the length of the rotor. But if these deformations are negligible compared to the displacements characteristic of rigid rotors and are within tolerances at all rotor speeds, then such a rotor is considered rigid. It is important to note that with an increase in the rotation speed and a decrease in the value of the permissible unbalance, the rotor, previously considered as a rigid one, begins to exhibit the properties of a flexible rotor and requires a change in the choice of the balancing method.

Balancing of rigid rotors is carried out by methods regulated by GOST ISO 1940-1, and flexible rotors - by GOST 31320. The choice of one or another method is determined by the configuration of the rotor and its speed.

The rotors of most known machines at operating speeds can be considered as rigid and dynamic balancing methods regulated by GOST ISO 1940-1 can be applied to them. These methods provide for the elimination of the main vector of imbalances - the installation of a corrective mass in one correction plane, and the elimination of the main moment of imbalances - the distribution of masses in two correction planes.

As for GOST 31320, as can be seen from Table 1, it provides for several methods of dynamic balancing:

Modern methods of dynamic balancing are based on the proportionality of the amplitude and phase of the vibration to the existing unbalance. In other words, by measuring the vibrational characteristics of a rotating rotor, it is possible to accurately determine the size and location of the corrective masses in the selected correction planes. Let us illustrate this by the example of the BALTECH VP-3470 mobile balancing device from the Baltech company, which allows dynamic balancing in its own supports of most rotary mechanisms: smoke exhausters, cooling towers, turbines, compressors, electric motors, etc. The balancing procedure with the BALTECH VP-3470 device takes just over half an hour and includes only three stages:

1. Determination of initial vibration and vibration phase.
2. Installing a test weight of known mass and obtaining data on the mass of the corrective weight and the angle of its installation.
3. Installing a corrective weight and conducting a control measurement of the vibration level.

Balancer BALTECH VP-3470 allows balancing in 1-4 planes by 16 control points and is equipped with BALTECH Expert software, which saves all trends, protocols and reports.

The BALTECH VP-3470 set is not the only portable Baltech balancer. Together with it, the company offers the PROTON-Balance-II device and a balancing system based on the CSI 2140 vibration analyzer, as well as the BALTECH-Balance balancing program (calculator).

In addition to the above-mentioned devices for balancing in their own supports, Baltech produces a wide range of horizontal, vertical and automatic balancing machines that allow balancing rotors of various configurations and weights.

Baltech balancing machines are distinguished by high structural strength, fully automated processing of measurement results, high balancing accuracy - up to 0.5 g * mm / kg.

Modern balancing devices and machines "Baltech" imply the presence of professional skills in handling them. Taking this into account, the Training Center of the Baltech Company regularly conducts the Course TOR-102 "Dynamic Balancing" for the professional training of technical specialists to work on Baltech machines and devices.

Large parts such as pulleys, flywheels, rotors, and blowers rotating at high speeds must be well balanced to avoid wobble, vibration, misalignment, and increased stress on bearings. There are three types of imbalance:

Unbalance caused by the shift of the center of gravity of the part relative to the axis of rotation, in which the force of inertia is reduced to one resultant centrifugal force. Such an imbalance is typical for parts with a small axial length compared to the diameter (flywheels, pulleys, gear wheels) and is eliminated by static (single-plane) balancing;

Unbalance, in which the forces of inertia are reduced to a resultant pair of forces that creates a centrifugal moment of inertia about the axis of rotation;

Unbalance, in which the forces of inertia are reduced

To the resultant force and to the pair of forces.

The second and third types of imbalance are typical for parts that have a significant length compared to the diameter (rotors) and are eliminated by dynamic (two-plane) balancing.

It is believed that the permissible displacement of the center of gravity is equal to

The quotient of 2-10 divided by the square of the speed of the part.

static or force balancing is based on the use of a static unbalanced moment, under the action of which the part rotates until the heaviest part is vertically under the axis of rotation of the part and it becomes possible to carry out balancing by installing additional weights on the diametrically opposite side of the part or by lightening the heaviest part of the part. Static balancing is performed by mounting the part on prisms, rotating supports, scales or directly at the installation site of the part. Sometimes the part is pre-fixed on the mandrel. Balancing prisms, manufactured with high precision from hardened steel, are installed on the balancing device in parallel and horizontally with an accuracy of 0.02 mm / m. The balancing process consists of two operations.

First operation is to correct the underlying imbalance. To do this, the circumference of the end face of the part to be balanced is divided into 6-8 parts and, turning the part on prisms by 45 °, each time they find and mark the lower point, i.e. the heaviest part. If at the same time the same point occupies the lower position, then a diameter is drawn through it and, picking up a load at its opposite end, the imbalance is compensated, i.e., an indifferent equilibrium is reached. The load can be putty or small pieces of metal glued to the part. Then the temporary weights are replaced with permanent ones, firmly fixed to the part in the right place, and the correct balancing is controlled. Sometimes, on the contrary, the weighted parts of the part are lightened by drilling small recesses.

Second operation consists in determining the residual imbalance due to the presence of friction forces between the prisms and the mandrel or eliminating the so-called undetected imbalance. At the same time, on each of the marked divisions, the weights are fixed alternately in the horizontal plane at points equally distant from the center, until the part begins to rotate on the prisms. The masses of test weights are entered in the table, and on its basis a curve is built that fixes the extreme points that correspond to the largest difference in weights (Fig. 7.16). The lowest point of the curve corresponds to the heaviest part of the part. The final balancing weight must be installed in a diametrically opposite place. The value of the load is determined by the formula

Q(^max -

Where Q - the size of the cargo; Amax and Aiin - respectively, the maximum and minimum mass of loads located on the same diameter.

An additional weight is attached to the part at the point corresponding to the highest point of the curve, and a final check is made, determining the residual unbalance. The permissible value of static imbalance depends on the design of the machine and its mode of operation. The accuracy of static balancing on prisms makes it possible to detect a residual displacement of the center of gravity of the part from the axis of rotation by 0.03-0.05 mm, and on balancing scales up to 5 microns.

Dynamic bachelor are carried out at machine-building plants, since it is difficult to implement it under the conditions of installation and repair in the workshops of dairy industry enterprises.

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