During technological processing rotating parts(pulleys, gears, shafts, drums, etc.) it is difficult to obtain their complete balance due to the heterogeneity of the metal (voids, shells during casting, some inaccuracies during machining and assembly). The imbalance of a rotating part is expressed in the fact that the center of gravity does not coincide with the axis of rotation. In addition, this axis of rotation is not the main central axis of inertia of the rotating part. The very process of balancing a rotating part is called balancing. There are two types of balancing - static and dynamic.
To statically balance a rotating part, it is necessary to transfer its center of gravity to the geometric axis of rotation. This type of balancing is called static balancing.
Rice. 110. Types of static balancing:
a - the position of the three main central axes; b - an example of balancing; c - installation for static balancing: 1, 3 - guides, 2 - balanced part, d - guide profiles
On fig. 110, and the positions of the three main central axes XX, YY and ZZ are given. If the center of gravity S of a rotating body is moved to the point O of intersection of the main central axes, then this body will be in equilibrium.
Let the center of gravity S of the disk A be removed from the axis of rotation YY at a distance l 1, then when the disk A rotates, the central force of inertia P and will appear. This force P and during the rotation of disk A will create additional pressure on the shaft and on the bearing. In this case, the pressure from the force of inertia far exceeds the given forces, especially at high numbers of shaft revolutions.
The imbalance of centrifugal forces leads to elastic periodic vibrations of the shaft. At high speeds, these shaft vibrations are transmitted through the bearings and frame to the foundation, which may be subject to premature failure.
To balance the force of inertia P and, it is necessary to transfer the center of gravity to the axis of rotation. This can be done by applying force P and " from the opposite side at point S":
Let's explain this with examples.
A mass m 1 is fixed on a round rotating disk (Fig. 110, b), which is at a distance r 1 from the axis of rotation. It is required to balance the mass m 1 with another mass m 2 fixed on the opposite side at a distance r 2 . Full balancing of the disk will occur when the inertial forces P u1 and P u2 developed by the masses m 1 and m 2 will be equal to each other.
The simplest device for static balancing are parallel stands. Their design is clear from Fig. 110, c. The profiles of the guides along which the balanced part rolls are shown in fig. 110, g. To reduce the coefficient of friction, the working part of the guides must be hardened and carefully ground. The width b is made as small as possible so as not to create dents on the surface of the trunnions.
The balancing stand must be equipped with a set of guides with different widths of the supporting part.
Round guides that do not have a flat support surface are used for parts weighing 40-50 kg. The advantage of round guides lies in the ease of processing and the possibility, by turning them at a small angle, to exclude damaged areas from the contact zone.
To balance heavy parts and assemblies, square or rectangular guides are used.
Static balancing is usually performed on special mandrels. Various devices are used to correct and balance the mass (Fig. 111).
Rice. 111. A device for eliminating unbalance by hanging metal weights from a part
Unbalance is eliminated by hanging metal weights from the part. The ruler 1 with a movable load 2 is attached to the balanced part 4 with the help of a clamp 3, and the counterweight 5 is fixed separately. Static balancing can balance a part only relative to its axis of rotation, but cannot eliminate the actions of forces that tend to rotate the longitudinal axis. This applies to parts and assemblies that are longer than the diameter (rotors of large turbines, turbogenerators, electric motors, high-speed machine tool spindles, crankshafts of automobile and aircraft engines etc.).
To fulfill dynamic balancing long shaft, special balancing machines are used, on which the centrifugal force, the magnitude of the eccentricity, the weight of the load for the balancing pair of moments are determined. This work is performed by specialists-balancers.
APPROVE:
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[Job title]
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[Name of company]
________________/[FULL NAME.]/
"____" ____________ 20__
JOB DESCRIPTION
Balancer of parts and assemblies of the 4th category
1. General Provisions
1.1. Real job description determines and regulates the powers, functional and official duties, rights and responsibilities of the balancer of parts and assemblies of the 4th category [Name of the organization in the genitive case] (hereinafter referred to as the Company).
1.2. The balancer of parts and assemblies of the 4th category is appointed to the position and dismissed from the position in the established current labor law by order of the head of the Company.
1.3. The balancer of parts and assemblies of the 4th category belongs to the category of workers and reports directly to [name of the position of the immediate supervisor in the dative case] of the Company.
1.4. The balancer of parts and assemblies of the 4th category is responsible for:
- timely and high-quality performance of tasks for their intended purpose;
- compliance with performance and labor discipline;
- observance of labor safety measures, maintenance of order, compliance with fire safety rules at the work site (workplace) entrusted to him.
1.5. A person with an average professional education in this specialty and work experience of at least 1 year.
1.6. In practice, the balancer of parts and assemblies of the 4th category should be guided by:
- local acts and organizational and administrative documents of the Company;
- internal work schedule;
- rules of labor protection and safety, ensuring industrial sanitation and fire protection;
- instructions, orders, decisions and instructions of the immediate supervisor;
- this job description.
1.7. The balancer of parts and assemblies of the 4th category must know:
- arrangement of balancing machines of various models;
- ways of adjusting and checking the accuracy of the serviced equipment;
- device and rules for the use of control and measuring instruments;
- features of balancing parts and assemblies of complex configuration.
1.8. During the period of temporary absence of the balancer of parts and assemblies of the 4th category, his duties are assigned to [deputy position].
2. Job responsibilities
The balancer of parts and assemblies of the 4th category performs the following labor functions:
2.1. Static balancing of armatures and rotors of large electrical machines with a speed of over 1500 to 3000 rpm, as well as rotors and armatures of small and medium-sized electric machines with a speed of over 3000 rpm on balancing machines of various models.
2.2. Static and dynamic balancing of parts and components of machines of complex configuration on special balancing machines of various models with a spark disk.
2.3. Measuring angles in degrees to determine imbalance.
2.4. Adjustment of serviced balancing machines.
In case of official necessity, the balancer of parts and assemblies of the 4th category may be involved in the performance of duties overtime, in the manner prescribed by law.
3. Rights
The balancer of parts and assemblies of the 4th category has the right to:
3.1. Get acquainted with the draft decisions of the management of the enterprise relating to its activities.
3.2. Submit proposals for the management to improve the work related to the responsibilities provided for in this job description.
3.3. Notify the immediate supervisor of all identified in the process of fulfilling their official duties shortcomings in production activities enterprise (its structural subdivisions) and make proposals for their elimination.
3.4. Request personally or on behalf of the immediate supervisor from the heads of enterprise departments and specialists information and documents necessary for the performance of their duties.
3.5. Involve specialists from all (separate) structural divisions of the Company in solving the tasks assigned to him (if this is provided for by the provisions on structural divisions if not, with the permission of the head of the Company).
3.6. Require the management of the enterprise to assist in the performance of their duties and rights.
4. Responsibility and performance evaluation
4.1. The balancer of parts and assemblies of the 4th category bears administrative, disciplinary and material (and in some cases provided for by the legislation of the Russian Federation - and criminal) responsibility for:
4.1.1. Non-fulfillment or improper fulfillment of official instructions of the immediate supervisor.
4.1.2. Failure or improper performance of labor functions and the tasks assigned to him.
4.1.3. Unlawful use of the granted official powers, as well as their use for personal purposes.
4.1.4. Inaccurate information about the status of the work entrusted to him.
4.1.5. Failure to take measures to suppress the identified violations of safety regulations, fire and other rules that pose a threat to the activities of the enterprise and its employees.
4.1.6. Failure to enforce labor discipline.
4.2. The evaluation of the work of the balancer of parts and assemblies of the 4th category is carried out:
4.2.1. The immediate supervisor - regularly, in the course of the daily implementation by the employee of his labor functions.
4.2.2. Certification Commission enterprises - periodically, but at least once every two years based on the documented results of work for the evaluation period.
4.3. The main criterion for evaluating the work of the balancer of parts and assemblies of the 4th category is the quality, completeness and timeliness of its performance of the tasks provided for in this instruction.
5. Working conditions
5.1. The mode of operation of the balancer of parts and assemblies of the 4th category is determined in accordance with the internal labor regulations established by the Company.
5.2. In connection with the production need, the balancer of parts and assemblies of the 4th category is obliged to leave for business trips(including local values).
Acquainted with the instruction __________ / ____________ / "____" _______ 20__
When rotating at a high speed of unbalanced parts and assemblies, additional loads arise that act; both on these parts and assemblies, and on their supports. Parts and assemblies that require balancing include: crankshaft, crankshaft pulley, water pump shaft pulley, fan blades, compressor pulley, crankshaft assembly with flywheel and clutch, propeller shaft assembly, wheel with tire assembly, etc. Balancing (balancing) of such parts and assemblies is one of the conditions for increasing the reliability and durability of vehicles. When repairing cars, the balancing of parts and assemblies can be disturbed, so they must be checked and, if necessary, re-balanced.
The balance of parts and assemblies can be static and dynamic.
In static equilibrium, the center of gravity is located on the axis of rotation of the part or assembly. In dynamic equilibrium, it is necessary that the center of gravity of the part or assembly is also located on the axis of rotation, and at the same time there are no moments of centrifugal forces acting in the plane passing through the axis of rotation.
Static balancing. As an example, consider balancing a part mounted on a shaft (or on a special mandrel) resting on horizontal guides. 3. Under the influence of an unbalanced mass t this part will spontaneously turn and take a position in which the unbalanced mass will be in its lowest position.
When the part rotates, an unbalanced centrifugal force arises, which, as noted above, creates an additional load on the shaft and on its supports.
To balance the part, you need to attach a balancing weight to it, placing it on the diametrically opposite side with respect to the unbalanced mass. In this case, the moments of gravity of the unbalanced mass and the balancing load relative to the axis of rotation of the part must be equal. This ensures the balance of the part.
Equilibrium can also be achieved by removing part of the metal part from the side of the unbalanced mass (by sawing or drilling).
Usually flat parts and subgroups are subjected to static balancing - for example, flywheels, clutch discs, fans, as well as some components - wheel hubs assembled with brake drums, clutch pressure plate assembly with casing.
Static balancing is carried out with the help of fixtures, by installing parts on horizontal prismatic parallels or on rotating disk rollers installed in pairs. Disc rollers in such devices are mounted on ball bearings, which minimizes rotational resistance. Therefore, roller fixtures give greater balancing accuracy.
When balancing, it is very difficult to eliminate the imbalance completely, therefore specifications allowable imbalance for a particular part is provided.
dynamic balancing. When the shaft rotates, two oppositely directed centrifugal forces arise. These forces are separated from each other , create a moment that causes dynamic disequilibrium of the shaft. As a result, the shaft and its bearings will experience additional load.
The moment of this pair of forces can be balanced by another pair of forces applied to the shaft, acting in the same plane and creating an equal counteracting moment. Thus, dynamic disequilibrium can be eliminated only by a pair of forces balancing it.
For dynamic balancing of the part to it, in the plane. the action of the moment, two masses must be applied m 1\u003d m but at an equal distance from the axis of rotation, as a result of which, during the rotation of the shaft, centrifugal forces P 1 and P 2 will arise, which will create a moment of a pair of forces P 1 L, opposing moment F 1 L and balancing it. Such balancing is called dynamic balancing.
Dynamic balancing of parts and assemblies is carried out on special balancing machines, their work is based on the method of dividing the total imbalance of the balanced assembly to correct it in two given planes. In the case of dynamic unbalance of the node, the supports will oscillate; along with them, the coils will also oscillate in the magnetic fields of permanent magnets and an EMF will appear in their windings.
The magnitude of these emfs will be proportional to the amplitude of the oscillations of the coils. The voltage of the electric current in the circuit of the coils is amplified by the transformer-amplifier and is measured using a device that has a scale graduated in unbalance units. Simultaneously with the rotation of the balanced unit, the generator rotor rotates. The stator of this generator can rotate and, due to the special location of the coils in it, change the readings of the device.
The balancing machine has two parallel electrical circuits, which allows, when turned on with a switch, 14 each scheme separately determine the imbalance in two planes - I-I and II-II.
The planes in which it is necessary to make corrections are set in advance and depend on the design of the balanced unit. In these planes, to eliminate the imbalance of the assembly, metal is removed (by drilling), washers are installed or special metal plates are welded. The place of installation of washers and welding of plates or the place where metal can be removed is indicated in the technical conditions for balancing a particular unit. In this way, it is ensured that the unbalance of the node is within the tolerances established by the specifications. Electric balancing machines make it possible to balance parts and assemblies with great accuracy.
At repair enterprises, some components are subjected to balancing, since as a result of replacing individual parts, it may be violated. In addition, it is necessary to balance the crankshafts of engines after the restoration of their necks by surfacing. The balancing accuracy depends on the design and purpose of units and parts, their rotation speed and permissible vibration during operation /
§ 1. Balancer of parts and assemblies (2nd category)
Characteristics of works. Static balancing of fans, armatures and rotors of small and medium electrical machines general purpose with rotation speed up to 1500 min. Identification and elimination of imbalance by attaching a load. Drilling holes with pneumatic and electric machines or simple drilling machines. Thread cutting by hand taps.
Must know: ways to determine the imbalance in static balancing; cargo securing rules; the principle of operation of the serviced equipment; purpose and rules for the use of simple devices, measuring and cutting tools; purpose of balance items and technical requirements presented to them.
Work examples
Static balancing:
1. Fans of asynchronous electric motors of a single series.
2. Rotors, armatures and flywheels of AC and DC electric machines up to 100 kW.
§ 2. Balancer of parts and assemblies (3rd category)
Characteristics of works. Static balancing of rotors and armatures of large general-purpose electrical machines with a speed of up to 1500 min. Dynamic balancing of rotors and armatures of small and medium electrical machines with a speed of over 1500 to 3000 min on simple balancing machines. Static and dynamic balancing of parts of a simple configuration on special balancing machines with a spark disk, on prisms and rollers. Removal of unbalance by drilling or on grinders. Adjustment of balancing machines under the guidance of a balancer of higher qualification.
Must know: ways to determine the value of unbalance in static and dynamic balancing; device and principle of operation of balancing machines; device, purpose and rules for the use of control and measuring instruments; methods of installation and fastening of parts; permissible deviations of the parts to be balanced.
Work examples
1. Desktop fans - dynamic balancing.
2. Flywheels, pulleys of all diameters, gear wheels - balancing.
3. Chucks and faceplates for lathes and boring machines - balancing.
4. Rotors and armatures of small and medium electrical machines with power up to 100 kW and speed up to 3000 min - dynamic balancing.
5. Rotors of turbogenerators, centrifugal pumps - static balancing.
6. Rotors, armatures and flywheels of AC and DC electrical machines with a power of over 100 kW - static balancing.
§ 3. Balancer of parts and assemblies (4th category)
Characteristics of works. Static balancing of armatures and rotors of large electrical machines with a rotation speed of over 1500 to 3000 min, as well as rotors and anchors of small and medium electrical machines with a rotation speed of over 3000 min on balancing machines of various models. Static and dynamic balancing of parts and components of machines of complex configuration on special balancing machines of various models with a spark disk. Measuring angles in degrees to determine imbalance. Adjustment of serviced balancing machines.
Must know: arrangement of balancing machines of various models; ways of adjusting and checking the accuracy of the serviced equipment; device and rules for the use of control and measuring instruments; features of balancing parts and assemblies of complex configuration.
Work examples
1. Flexible shafts - balancing.
2. Crankshafts of the car "Moskvich" - balancing of the two ends of the shaft with the removal of excess metal from the cheeks.
3. Springs - balancing.
4. Rotors of engines of precision instruments - balancing in liquid.
5. Rotors and armatures of electric machines of direct and alternating current with a power of over 100 kW - dynamic balancing.
6. Multistage turbine rotors - balancing.
7. Rotors of turbogenerators up to 30000 kW - dynamic balancing.
8. Spindles of large-sized turning and boring machines - balancing.
§ 4. Balancer of parts and assemblies (5th category)
Characteristics of works. Dynamic balancing of rotors and armatures of high-speed electrical machines for special purposes with a speed of over 3000 to 10000 min on complex balancing machines. Dynamic balancing of rotors and armatures of large DC and AC electrical machines in assembled bearings. Static and dynamic balancing of parts and assemblies of complex configuration. Performing calculations to determine the magnitude of the imbalance, marking, determining the mass of goods and their attachment points. Adjustment of balancing machines of various models.
Must know: the design of the serviced equipment; technical requirements for high-speed electric machines for special purposes; balancing features in assembled bearings; ways of setting up balancing machines of various models; calculation method for determining the imbalance value.
Work examples
1. Cardan shafts and crankshafts of cars - balancing.
2. Inductors up to 800 mm in diameter - dynamic balancing.
3. Rotors and armatures of special-purpose electrical machines with low rotational speed - dynamic balancing.
4. Rotors of turbogenerators with a power of 30,000 kW and above - dynamic balancing in assembled bearings on the stand.
5. Anchors of rowing electric machines with a diameter of up to 800 mm - dynamic balancing.
§ 5. Balancer of parts and assemblies (6th category)
Characteristics of works. Dynamic balancing of armatures and rotors of special electrical machines with a speed of over 10,000 min on special balancing machines with a complex kinematic control scheme. Dynamic balancing in assembled bearings of armatures and rotors of unique large AC and DC electrical machines and powerful turbogenerators.
Must know: design, methods and rules for checking the accuracy of various types of balancing machines; rules for determining the most advantageous ways to eliminate the imbalance.
Work examples
Dynamic balancing:
1. Indicators.
2. Anchors of rowing electric machines with a diameter of more than 800 mm.
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