Lecture 10

The problem of vibration protection arose in connection with the rapid development of mechanization and automation. production processes, an increase in speeds on stationary and transport installations, the widespread introduction of pneumatic and electrified tools, as well as robotics equipment.

Vibration- mechanical vibrations with a frequency of more than 1 Hz, arising in elastic bodies or bodies under the influence of an alternating physical field. These vibrations can be transmitted through the material environment to the human body.

Basic vibration parameters. The main parameters characterizing vibration are the vibration frequency f[Hz] offset amplitude A[m, cm], oscillatory speed V[m / s], vibration acceleration a[m / s 2], oscillation time period T[With].

The simplest type of vibration is harmonic vibration. It is characterized by the amplitude and frequency from which speed and acceleration are derived. Vibration acceleration, or vibration overload, is the maximum change in the speed of vibrations per unit time, usually expressed in cm / s 2. In the practice of aviation and space medicine, units of acceleration that are multiples of the acceleration due to gravity q are often used. Frequency vibration - the number of vibrations per unit of time, measured in hertz. An important parameter of vibration is its intensity, or amplitude... If vibration is a simple sinusoidal vibration about a fixed point, then its amplitude is defined as the maximum deviation from this position (measured in millimeters).

Classification.

1. By the method of transmission per person distinguish between:

- general vibration transmitted through the support surfaces to the body of the seated person or standing man; they are exposed to workers of train and locomotive crews, operators of track and self-propelled vehicles, tractor drivers and other workers, as well as passengers.

- local vibration transmitted through the hands of a person. These vibrations are generated by numerous hand tools widely used in a wide variety of jobs. Vibration transmitted to the legs of a seated person and to the forearms in contact with the vibrating surfaces of work tables refers to local vibration.

2. By source of occurrence vibrations are distinguished:

- local from manual mechanized tools (with motors), manual controls for machines and equipment;

- local vibration transmitted to humans from manual non-mechanized tools (without motors), for example, straightening hammers of different models and workpieces;

General vibration category 1 - transport vibration affecting a person at the workplaces of self-propelled and trailed machines, Vehicle when driving on terrain and roads (including during their construction). TO sources of transport vibration include: agricultural and industrial tractors, self-propelled agricultural machines (including harvesters); trucks (including tractors, scrapers, graders, rollers, etc.); snow plows, self-propelled mining rail transport;

General vibration category 2 - transport and technological vibration affecting a person at the workplaces of machines moving on specially prepared surfaces of industrial premises, industrial sites, mines. TO sources of transport and technological vibrations include: excavators (including rotary ones), industrial and construction cranes, machines for loading (filling) open-hearth furnaces in metallurgical production; mining combines, mine loaders, self-propelled drilling carriages; track machines, concrete pavers, floor industrial vehicles;

General vibration category 3 - technological vibration affecting a person at workplaces of stationary machines or transmitted to workplaces that do not have sources of vibration. TO sources of technological vibrations include: metal and woodworking machines, forging and pressing equipment, casting machines, electric cars, stationary electrical installations, pumping units and fans, equipment for drilling wells, drilling rigs, machines for animal husbandry, cleaning and sorting of grain (including dryers), equipment for the building materials industry (except for concrete pavers), installations for the chemical and petrochemical industries, etc.

(By the place of action technological vibration is classified into the following types:

a) at permanent workplaces of industrial premises of enterprises;

b) at workplaces in warehouses, in canteens, utility rooms, duty rooms and other industrial premises, where there are no machines that generate vibration;

c) at workplaces in the premises of the plant management, design bureaus, laboratories, training centers, computing centers, health centers, office premises, work rooms and other premises for knowledge workers.)

- general from external sources: urban rail transport (shallow and open metro lines, tram, railway transport) and motor transport; industrial enterprises and mobile industrial installations (during the operation of hydraulic and mechanical presses, planing, cut-out and other metal-working mechanisms, reciprocating compressors, concrete mixers, crushers, construction machines, etc.);

- general vibration in residential and public buildings from internal sources: engineering and technical equipment of buildings and household appliances (elevators, ventilation systems, pumping stations, vacuum cleaners, refrigerators, washing machines, etc.), as well as built-in trade enterprises (refrigeration equipment), utilities, boiler rooms, etc. .d.

3. By direction of action vibration is subdivided according to the direction of the axes of the orthogonal coordinate system:

Local vibration is subdivided into one acting along the axes of the orthogonal coordinate system X l, Y l, Z l, where the X l axis is parallel to the axis of the vibration source (handle, cradle, steering wheel, control lever held in the hands of the workpiece, etc.) ), the Y axis l is perpendicular to the palm, and the Z axis l lies in the plane formed by the X l axis and the direction of supply or application of force (or the axis of the forearm when no force is applied);

The general vibration is subdivided into one acting along the axes of the orthogonal coordinate system X o, Y o, Z o where X o(back to chest) and Y o(from the right shoulder to the left) - horizontal axes directed parallel to the supporting surfaces; Z o- a vertical axis perpendicular to the supporting surfaces of the body in the places of its contact with the seat, floor, etc.

4. By the nature of the spectrum vibrations emit:

- narrowband vibrations in which the controlled parameters in one 1/3 octave frequency band are more than 15 dB higher than the values ​​in the adjacent 1/3 octave bands;

- broadband vibrations - with a continuous spectrum more than one octave wide.

5. By frequency composition vibrations emit:

- low-frequency vibrations (with a predominance of maximum levels in octave frequency bands of 1-4 Hz for general vibrations, 8-16 Hz - for local vibrations);

- mid-frequency vibrations (8-16 Hz - for general vibrations, 31.5-63 Hz - for local vibrations);

- high frequency vibrations (31.5-63 Hz - for general vibrations, 125-1000 Hz - for local vibrations).

6. By time characteristics vibrations emit:

- permanent vibrations for which the value of the standardized parameters changes by no more than 2 times (by 6 dB) during the observation period;

- fickle vibrations for which the value of the standardized parameters changes by at least 2 times (by 6 dB) during the observation time of at least 10 minutes when measured with a time constant of 1 s, including:

a) hesitant in time of vibration, for which the value of the normalized parameters is continuously changing in time;

b) intermittent vibration, when a person's contact with vibration is interrupted, and the duration of the intervals during which the contact takes place is more than 1 s;

v) impulse vibrations consisting of one or more vibrational influences (for example, shocks), each lasting less than 1 s.

Sources. The main sources vibrations are:

* unbalanced rotating masses (rotating rotors of thermal and electrical machines, machine tools, etc.);

* reciprocating units and mechanisms (pistons, crank units, sliders of heat engines, solenoids of electromagnetic devices, etc.);

* shock mechanisms (gears, clutches (cam, finger), sleeve bearings due to the presence of technological gaps in them, etc.).

Rationing. To prevent vibration sickness, the vibration of the manual mechanism should not exceed the values ​​established in GOST 17 770-72 "Hand-held machines. Permissible vibration levels". Requirements for limiting vibration parameters to permissible values ​​should be contained in all standards and technical conditions for vibration-hazardous equipment and means of transport (GOST 12.1.012-78). Vibration spectrum called the dependence of the levels in decibels of the vibrational speed (or vibrational acceleration) in octave frequency bands from the middle frequencies of these bands.

Octave frequency bands are standardized by international agreement. The normalized frequency range is set:

For local vibration in the form of octave bands with geometric mean frequencies: 8; sixteen; 31.5; 63; 125; 250; 500; 1000 Hz;

For general vibration in the form of octave or 1/3 octave bands with geometric mean frequencies of 0.8; one; 1.25; 1.6; 2.0; 2.5; 3.15; 4.0; 5.0; 6.3; 8.0; 10.0; 12.5; 16.0; 20.0; 25.0; 31.5; 40.0; 50.0; 63.0; 80.0 Hz.

The measurements determine the levels in certain frequency bands. Frequency measurement limits are set based on hygienic standards or task conditions.

With harmonic vibrations, the speed and acceleration can be calculated by the formula and in the final form, their maximum values ​​are respectively equal to

Considering that the absolute values ​​of the parameters characterizing vibration vary over a wide range, in practice they use the logarithmic levels of vibration velocity and vibration acceleration:

where V- vibration velocity in the octave band, m / s;

V 0- the threshold value of vibration velocity, equal to 5 · 10 -8 m / s, corresponding to the threshold value of sound pressure at a frequency of 1000 Hz, equal to 2 · 10 -5 Pa;

a- root-mean-square value of vibration acceleration deviation, m / s 2;

a 0- the threshold value of vibration acceleration, equal to 1 · 10 -6 m / s 2.

The influence of vibrations on the human body. Vibration when exposed to humans is a factor of high biological activity.

Vibration with prolonged exposure to the human body not only creates discomfort and reduces labor productivity, but also, under certain parameters, can lead to vibration disease. Vibration disease is a general disease of the whole organism, in which the activity of various organs and functional systems is disrupted. When exposed to local vibrations, the blood vessels and nerve endings of the hands are mainly affected. Prolonged exposure to intense general vibration adversely affects mainly the central and autonomic nervous systems.

Vibration can be transmitted to a person directly by touching vibrating objects and through intermediate media of sufficient density (liquid, solids). It can act on a person directly through the support surfaces and through some secondary contact objects. The indirect effects of vibration are manifested in the vibration of instruments and their arrows, which makes it difficult to read the readings.

As you move away from the place where the vibration is applied, its intensity usually weakens. However, when exposed to vibration of certain frequencies, its intensity can increase in certain parts of the body due to resonance phenomena due to the presence of a certain natural vibration frequency of different parts of the body. For example, the vibrations of the head of a person standing on a vibration platform significantly increase at frequencies from 4 to 8 hz and in the frequency range 20-30 hz.

The nature of the changes arising under the influence of vibration transmitted to the hands depends on its spectral composition. The predominance of high-frequency components in the spectrum causes, as a specific irritant, the development of vascular disorders, as well as local disorders of skin sensitivity with minor changes in the muscular system. The presence of predominantly low frequencies in the spectrum due to microtraumatization of the peripheral nervous system causes trophic disorders and, in addition to osteoarticular pathology, leads, as a rule, to changes in muscles in the absence or weak severity of vascular disorders.

A person can perceive vibration in any part of the body with the help of special vibroreceptors. The skin of the palmar surface of the terminal phalanges of the fingers has the highest vibration sensitivity, determined using a special device (pallestesiometer). The highest sensitivity is observed to vibration with frequencies of 100-250 Hz , and in daytime sensitivity is more pronounced than in the morning and evening. When exposed to vibration of a predominantly high-frequency nature, a decrease in vibration sensitivity is observed, especially at the frequency of a vibration stimulus.

Under the influence of vibration, pain sensitivity can also change significantly, which is measured using an algesimeter.

Exposure to vibration can lead to a decrease in other types of skin sensitivity - discriminatory, tactile, thermal.

It should be noted that a change in the vibration and tactile sensitivity of the fingers can be observed not only under the influence of vibration of hand tools, but also under the influence of vibration of the workplace.

One of the characteristic signs of vibration disease that occurs under the influence of high-frequency vibration transmitted to the hands is a change in the tone of the skin capillaries. In this case, spasm or atony of capillaries is possible, as well as both of these conditions simultaneously in different parts of the capillaries.

The tendency of the capillaries to spasm is judged by the sharp pallor of the skin of the fingers under the influence of 2 to 3 minutes of contact with cold water or a piece of ice. This can be evidenced by the persistence of more than 10 seconds of pallor of the skin of the hand in the area subjected to pressure for 5 seconds (a symptom of a "white spot"). Redness or cyanosis of the hands of lowered hands indicates a tendency of capillaries to atony. Sometimes it is possible to register a decrease in capillary pressure in the fingers. A decrease in peripheral resistance is observed, hypotension is often established, less often - hypertension. Sometimes in the initial stage of vibration disease, hypotension is noted, followed by hypertension in severe cases. In connection with vascular disorders, skin hypothermia is often observed.

Secretory disorders are usually expressed in increased sweating, less often in dry skin of the palms.

Violation of trophism, which occurs mainly when exposed to low-frequency vibration, first of all manifests itself in the abrasion of the skin pattern, thickening and deformation of the nails, and sometimes, on the contrary, in their thinning and flattening. The fingers become inactive, deformed, the nail phalanges can thicken, giving the fingers the appearance of "drumsticks".

In some cases, due to damage to peripheral motor fibers, atrophy of the small muscles of the hands and shoulder girdle develops, and muscle strength decreases. When working with instruments that generate vibrations with a predominance of low-frequency components in the spectrum, changes in the osteoarticular apparatus often occur. In the development of these lesions, the value of the recoil of the instrument is of great importance - the return blow and the muscular static tension that opposes it.

When exposed to vibration, the elasticity of the articular cartilage decreases due to their prolonged functional overstrain; as a result, the joints are less protected from mechanical stress. The phenomena of deforming osteoarthritis develop in the wrist joint and small joints of the wrist. In this case, the movements of the fingers are difficult, the contours of the joints are smoothed. It is also possible to damage the elbow, shoulder and sternoclavicular joints, as well as the spine (more often in the thoracic region) in the form of osteoporosis and deforming spondylosis.

Structural disorders in bones are preceded by changes in mineral and enzymatic metabolism.

The joints on the right side are most often affected due to the greater load usually on the right hand, but bilateral lesions are possible, especially of the elbow joint. Sometimes there are complications in the form of a compression fracture with aseptic necrosis of the lunate bone.

Some of the changes are in the nature of "professional stigma" without affecting the function of the hand.

The severity of osteoarticular lesions largely depends on the length of service with vibroinstruments and the intensity of the impacting vibration.

Conditions conducive to the development of vibration pathology are cooling and noise. Prolonged contact with cold metal parts of various instruments, especially cooled parts of pneumatic tools due to the adiabatic expansion of compressed air, the cooling effect of a jet of exhaust air on the hands contributes to the development of vasospasm.

A high severity of vibration pathology is observed with the simultaneous exposure to vibration of noise, which also has an adverse effect on the central nervous system and a number of other body systems.

According to the clinical course, they distinguish between the initial form, moderate and severe forms of vibration disease that occurs when vibration is applied to the hands. The initial form is characterized mainly by subjective phenomena (pain, paresthesia), accompanied by mild vascular disorders (hypothermia, moderate acrocyanosis, weakly positive cold test, a "white spot" symptom) and changes in skin sensitivity (hypoalgesia, increased vibration sensitivity, followed by a decrease) ... Small trophic changes in the muscles of the shoulder girdle are possible.

In the form of moderate severity, the pain intensifies, disorders of skin sensitivity are persistent, clearly expressed, observed on all fingers and even the forearm. Vascular changes, along with a general tendency to a spastic state, are manifested in the form of attacks of spasm with blanching of the fingers ("dead fingers") and their subsequent cyanosis due to paresis of the capillaries. The temperature of the skin of the hands drops sharply, hyperhidrosis is observed. Muscle strength decreases, osteoarticular lesions develop. General phenomena are noted in the form of a functional disorder of the central nervous system of an asthenic and astheno-neurotic nature.

Severe forms of vibration disease are of several types. With a syringomyel-like form, skin sensitivity disorders spread to the region of the shoulder girdle, and sometimes the chest. They can be dissociated (the relative preservation of some types of sensitivity when others are disturbed) and be accompanied by muscle atrophy not only of the hands, but also of the shoulder girdle.

The amyotrophic form, in addition to typical sensory disturbances, is characterized by gradually progressive muscular atrophy of the arms, and sometimes legs and shoulder girdle, and the development of paresis. These forms are easily distinguished from similar diseases by the absence of pyramidal symptoms.

Severe cases include severe cerebrovascular crises, coronary circulation disorders due to generalization of vascular disorders.

In the presence of an initial stage of vibration disease in skilled workers, along with treatment, it is recommended to transfer them for 2 months to work not associated with exposure to vibration and cooling. All changes are easily reversible. With moderate severity of vibration disease after treatment, it is also necessary to temporarily remove them from work associated with vibration and cooling. If these measures are ineffective, it is advisable to change the profession with the provision of professional disability for the period of retraining. Severe forms of vibration disease, sharply limiting the ability to work, are always an indication for the transfer of workers to a professional disability.

The clinical picture of the disease caused by exposure to vibration in the workplace largely depends on the predominance of high- or low-frequency components in its spectrum.

Under the influence of vibration of the workplace with a predominance of high frequencies in the spectrum, moderately pronounced changes in peripheral nerves and vessels in the legs are initially observed - impaired sensitivity in the feet and legs, a tendency to spasm of the capillaries of the toes with a decrease in skin temperature, cyanosis, weakening of the pulsation of peripheral vessels, pain in legs without clear localization or in the calf muscles, especially with pressure, rapidly developing fatigue while walking. In addition, there is a slight short-term dizziness, rapid fatigue, recurrent general weakness, noise and a feeling of heaviness in the head.

With a more pronounced form of the disease, symptoms prevail, indicating a dysfunction of the central nervous system: attacks of dizziness, and persistent headache, tremors of the fingers, severe general weakness. There is a feeling of intolerance to vibration and vegetative lability. Sometimes the development of lesions of the central nervous system of an organic nature is observed.

When exposed to vibration of the workplace, typical for vehicles with a predominance of low frequencies in the spectrum, sciatica-radiculitis is most characteristic as a result of irritation and compression of the lumbosacral roots due to trauma to the osteochondral and ligamentous apparatus of the spine, which is often detected radiographically. It is possible to stretch the ligaments on which they are elastically suspended internal organs such as the stomach and female genitals.

As a result of intense vibrations of the stomach, the process of digestion of food is disrupted, irritation of the gastric mucosa is observed and conditions are created for the occurrence of gastritis. The development of gastritis is also associated with dysfunction of the autonomic nervous system under the influence of vibration with high-frequency components of the spectrum. Sometimes there are signs of irritation of the nervous "solar" plexus - solarium with attacks of acute pain in the epigastric region.

There are also possible disorders of the function of the vestibular analyzer, which is a specialized receptor that perceives oscillations of mainly low frequencies and regulates the position of the body in space. In this regard, there is a violation of the stability of balance in the vertical position of the body.

The main methods of struggle with vibrations of machinery and equipment are:

1) reduction of vibrations by acting on the excitation source (by reducing the forcing forces);

In machine design and engineering technological processes preference should be given to such kinematic and technological schemes, in which the dynamic processes caused by impacts, sharp accelerations would be excluded or extremely reduced. The replacement of forging and stamping by pressing leads to a significant reduction in vibration; impact straightening - by rolling; pneumatic riveting and embossing - hydraulic riveting and welding.

The choice of operating modes is of great importance. For example, as the turbine rotational speed increases, the level of vibration velocity on the bearings of its bearing assembly sharply increases.

The reason for low-frequency vibrations of pumps, compressors, motors is the imbalance of the rotating elements. The action of unbalanced dynamic forces is aggravated by poor fastening of parts, their wear during operation. Elimination of the imbalance of the rotating masses is achieved by balancing.

2) detuning from the resonance mode by rational choice of mass or stiffness of the oscillating system;

To attenuate vibrations, the imposition of resonant modes of operation is essential, i.e. detuning the natural frequencies of the unit and its individual units and parts from the frequency of the driving force. Resonant modes during operation technological equipment eliminate two ways: either by changing the characteristics of the system (mass or frequency), or by establishing a new operating mode (detuning from the resonant value of the angular frequency of the driving force). The second method is carried out at the design stage, since in operating conditions, the operating modes are determined by the conditions of the technological process.

3) vibration damping - an increase in the mechanical impedance of vibrating structural elements by increasing dissipative forces during vibrations with frequencies close to resonant;

Installation of a protective device on the protected object - an elastic damping element, consisting of an elastic element and a damping element, connected in parallel. In this case, during the action, the external driving force acts both on the protected object and on the elastic element of the protective device, and the reaction of the latter is completely or partially damped by the damping element of the protective device.

4) dynamic vibration damping - connection of systems to the protected object, the reactions of which reduce the vibration range of the object at the points of connection of the systems;

Most often, dynamic vibration damping is carried out by installing units on foundations. The mass of the foundation is chosen in such a way that the amplitude of vibration of the base of the foundation in any case does not exceed 0.1 - 0.2 mm, and for especially critical structures - 0.005 mm. For small objects, a massive base plate is installed between the base and the unit.

In mechanical engineering, the most widespread are dynamic vibration dampers, which reduce the level of vibration due to the impact on the object of protection of the reactions of the vibration damper. The vibration damper is rigidly attached to the vibrating unit, therefore, at each moment of time, vibrations are excited in it, which are in antiphase with the vibrations of the unit.

5) vibration absorption - reduction of vibration by strengthening the processes of internal friction in the structure, dissipating vibration energy as a result of its irreversible transformation into heat;

This is the process of reducing the vibration level of the protected object by converting the energy of mechanical vibrations of this system into thermal energy.

An increase in heat losses in the system can be done in two ways:

1) use as structural materials with high internal friction;

2) applying a layer of elastic-viscous materials to vibrating surfaces with high internal friction losses.

The value of the parameter - the loss factor characterizing the dissipative forces in the oscillatory system - for the main structural materials (cast irons and steels) is 0.001 - 0.01.

Alloys based on nickel systems have much higher internal friction: copper - nickel, titanium - nickel, cobalt - nickel. of these alloys is 0.02 - 0.1.

From the point of view of vibrations, the most preferable is the use of plastics, wood, rubber as construction materials.

When application polymer materials as constructional it is not possible, vibration-absorbing coatings are used to reduce vibrations. The action of coatings is based on the weakening of vibrations by converting vibrational energy into thermal energy during deformation of the coatings.

Depending on the value of the dynamic modulus of elasticity ( E) coverings are subdivided into rigid ( E= 10 8 - 10 9 Pa) and soft ( E£ 10 7 Pa). The action of the coatings of the first group is manifested at low and medium frequencies, the second - at high frequencies.

Coatings made of a layer of viscoelastic material (hard plastic, roofing material, insula) and a layer of foil increase the rigidity of the coating. is 0.15 - 0.4.

Soft coatings - soft plastics, materials such as rubber (foam plastic, technical vinipor), polystyrene, polyvinyl chloride plastics. these coatings - 0.05 - 0.5.

If it is not possible to ensure a high-quality connection of coatings with the treated surface, if the latter has a complex configuration, then mastic coatings are used. The most widespread are mastics of the "Antivibrit" type based on epoxy resins. mastic is 0.3 - 0.45. Mastics are used in mechanical engineering to reduce vibration and noise in ventilation systems, compressors, pumps, pipelines.

Lubricants absorb vibrations well.

6) vibration isolation - installation between the vibration source and the object of protection of an elastic damping device - vibration isolator - with a low transmission coefficient.

This method of protection consists in reducing the transmission of oscillations from the excitation source to the protected object using devices placed between them. An example of vibration isolation is the installation of flexible inserts in the communications of air ducts, the use of elastic gaskets in the attachment points of the air ducts, separation of the floors of load-bearing structures by flexible connection.

Vibration- these are mechanical vibrational movements of the system with elastic connections. Vibration is characterized by a spectrum of frequencies and such kinematic parameters as vibration velocity and vibration acceleration or their logarithmic levels in decibels (dB).

Types of vibrations

Vibration is classified as follows:

1. By the method of transmission to humans:

• local vibration transmitted to the hands of the worker;
• general vibration transmitted through the supporting surfaces of the body while sitting (buttocks) or standing (soles of the feet).

2. By frequency composition:

• low frequency vibration (with a predominance of maximum levels in the octave bands of 1-4 Hz and 8-16 Hz, respectively, for general and local vibration);
• mid-frequency vibration (8-16 Hz for general vibration, 31.5 and 63 Hz for local vibration);
• high frequency vibration (31.5 and 63 Hz for general vibration, 125-1000 Hz for local vibration).

3. In the direction of vibration impact - in accordance with the direction of the axes of the orthogonal coordinate system:

• for general vibration, the direction of the Xо, Yо, Zо axes and their connection with the human body is as follows: Xо axis - horizontal from the back to the chest; Yo axis - horizontal from the right shoulder to the left); Zl - vertical axis perpendicular to the supporting surfaces of the body in the places of its contact with the seat, floor, etc.
• for local vibration, the direction of the axes Xl, Yl, Zl and their connection with the human hand is as follows: the Xl axis - coincides or is parallel to the axis of the vibration source (handle, cradle, steering wheel, control lever held in the hands of the workpiece, etc.); the Yl axis is perpendicular to the palm, and the Zl axis lies in the plane formed by the Xl axis and the direction of supply or application of force, and is directed along the forearm axis.

4. By the nature of the spectrum:

• narrowband vibration - in which the controlled parameters in one one-third octave frequency band are more than 15 dB higher than the values ​​in adjacent one-third octave bands;
• broadband vibration - with a continuous spectrum more than one octave wide.

5. By temporal characteristics:

• constant vibration for which the value of vibration velocity or vibration acceleration changes by no more than 2 times (pa 6 dB) during the observation time;
• fickle vibration (oscillating, variable, impulsive), for which the value of vibration velocity or vibration acceleration changes by at least 2 times (by 6 dB) during the observation time of at least 10 minutes.

Production sources local vibration are machines of percussion, percussion-rotational and rotational action. Local vibration occurs during grinding, emery, grinding, polishing work performed on stationary machines with manual feed of products, as well as when working with hand tools.

General vibration according to the source of occurrence it happens: transport, transport-technological and technological.

Drivers of transport vehicles (tractors, self-propelled agricultural machinery, trucks, earth-moving machines, etc.), as well as operators of transport and technological equipment (excavators, cranes, mining machines, concrete pavers, etc.) are exposed to general and local vibration. A low-frequency jerky vibration of a random nature is transmitted to workplaces, which occurs during the movement of machines on an uneven surface or from the operation of moving parts of mechanisms. On the workplace the driver, including the controls, vibration is transmitted as a result of engine operation.

To sources technological vibrations includes equipment, the action of which is based on the use of vibration and shock (vibration platforms, vibration stands, hammers, stamps, presses, etc.), as well as powerful electrical installations (compressors, pumps, fans, some metal-working machines, etc.).

Effects of increased vibration on the human body

Vibration is one of the factors with significant biological activity. The nature, depth and direction of functional shifts from the side different systems the organism is determined primarily by the level, spectral composition and duration of exposure to vibration.

Health disorders of the worker, caused by local or general vibration, consist of damage to the neurovascular, neuromuscular systems, the musculoskeletal system, changes in metabolism, etc. In all types of vibration disease, changes are often observed on the part of the central nervous system, which are associated with a combined effect vibration and intense noise constantly accompanying vibration processes.

According to statistics, 1/4 of the identified occupational diseases are associated with exposure to vibration and noise. The highest incidence of vibration disease is recorded in heavy, power, transport engineering, coal industry and non-ferrous metallurgy.

Preventive measures to reduce vibration levels

The complex of preventive measures that reduce the vibration levels of the equipment, reduce the time of contact with it and limit the influence of unfavorable concomitant factors in the production sphere includes hygienic regulation, organizational, technical, and therapeutic and prophylactic measures.

The main document governing the parameters industrial vibrations, are Sanitary norms SN 2.2.4 / 2.1.8.566-96 "Industrial vibration, vibration in the premises of residential and public buildings." They contain the classification of vibration, methods of hygienic assessment of vibration, standardized parameters and their permissible values.

Sanitary rules and norms SanPiN 2.2.2.540-96 " Hygiene requirements to hand tools and work organization ”set requirements for hand-held machines (weight), weight perceived by the operator's hands when performing working operations, pressing force required to operate in a nominal mode, pressing force of starting devices. The document also contains the rules for organizing work with hand tools and preventive measures.

There are a number state standards, which regulate the hygienic parameters of vibration of machines and equipment.

Basic methods and means of protection against vibration

The main methods and means of protection against vibration are:

• elimination of direct contact with vibrating equipment by applying remote control, industrial robots, automation;
• reducing the intensity of vibration directly at the source;
• application of vibration damping, dynamic vibration damping, active and passive vibration isolation;
• rational organization of the work and rest regime;
• creation of complex teams with interchangeability of professions;
• use of personal protective equipment;
• organization of active differentiated prophylactic medical examination of workers of vibration-hazardous professions;
• thermal treatments for hands in the form of hydrotherapy or dry air heating;
• mutual massage and self-massage of hands and shoulder girdle;
• industrial gymnastics;
• ultraviolet irradiation;
• vitamin prophylaxis.

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PRODUCTION VIBRATION VIBRATION IN RESIDENTIAL AND PUBLIC BUILDINGS - SANITATION STANDARDS - SN 2-2-42-1-8-566-96 (approved -... Actual in 2018

4. Classification of vibrations affecting humans

4.1. By the method of transmission to a person, they are distinguished:

General vibration transmitted through the support surfaces to the body of a sitting or standing person;

Local vibration transmitted through the hands of a person.

Note. Vibration transmitted to the legs of a seated person and to the forearms in contact with the vibrating surfaces of work tables refers to local vibration.

4.2. By the source of vibrations, they are distinguished:

Local vibration transmitted to humans from manual power tools (with motors), manual controls of machines and equipment;

Local vibration transmitted to humans from non-mechanized hand tools (without motors), for example, straightening hammers of various models and workpieces;

General vibration of the 1st category - transport vibration affecting a person at the workplaces of self-propelled and trailed machines, vehicles when driving over terrain, agricultural phones and roads (including during their construction). The sources of transport vibration include: agricultural and industrial tractors, self-propelled agricultural machines (including combines); trucks (including tractors, scrapers, graders, rollers, etc.); snow plows, self-propelled mining rail transport;

General vibration of the 2nd category - transport and technological vibration affecting a person at the workplaces of machines moving on specially prepared surfaces of industrial premises, industrial sites, mine workings. Sources of transport and technological vibration include: excavators (including rotary ones), industrial and construction cranes, machines for loading (filling) open-hearth furnaces in metallurgical production; mining combines, mine loaders, self-propelled drilling carriages; track machines, concrete pavers, floor industrial vehicles;

General vibration of category 3 - technological vibration affecting a person at workplaces of stationary machines or transmitted to workplaces that do not have sources of vibration. Sources of technological vibration include: metal and woodworking machines, forging and pressing equipment, casting machines, electrical machines, stationary electrical installations, pumping units and fans, equipment for drilling wells, drilling rigs, machines for animal husbandry, cleaning and sorting of grain (in including dryers), equipment for the building materials industry (except for concrete pavers), installations for the chemical and petrochemical industries, etc.

a) at permanent workplaces of industrial premises of enterprises;

B) at workplaces in warehouses, in canteens, household, duty and other industrial premises, where there are no machines that generate vibration;

C) at workplaces in the premises of plant management, design bureaus, laboratories, training centers, computing centers, health centers, office premises, work rooms and other premises for knowledge workers;

General vibration in residential premises and public buildings from external sources: urban rail transport (shallow and open subway lines, tram, rail transport) and road transport; industrial enterprises and mobile industrial installations (during the operation of hydraulic and mechanical presses, planing, cut-out and other metal-working mechanisms, reciprocating compressors, concrete mixers, crushers, construction machines, etc.);

General vibration in residential premises and public buildings from internal sources: engineering and technical equipment of buildings and household appliances (elevators, ventilation systems, pumping stations, vacuum cleaners, refrigerators, washing machines, etc.), as well as built-in trade enterprises (refrigeration equipment) , utilities, boiler houses, etc.

4.3. According to the direction of action, vibration is subdivided in accordance with the direction of the axes of the orthogonal coordinate system:

Local vibration is subdivided into one acting along the axes of the orthogonal coordinate system Xl, Yl, Zl, where the Xl axis is parallel to the axis of the vibration source (handle, cradle, steering wheel, control lever held in the hands of the workpiece, etc.), the Yl axis perpendicular to the palm, and the Zl axis lies in the plane formed by the Xl axis and the direction of supply or application of force (or by the axis of the forearm when no force is applied);

The general vibration is subdivided into one acting along the axes of the orthogonal coordinate system Xo, Yo, Zo, where Xo (from the back to the chest) and Yo (from the right shoulder to the left) are horizontal axes directed parallel to the supporting surfaces; Zo is the vertical axis perpendicular to the supporting surfaces of the body in the places of its contact with the seat, floor, etc.

The directions of the coordinates of the axes are given in Appendix 1.

4.4. By the nature of the vibration spectrum, there are:

Narrowband vibrations, in which the controlled parameters in one 1/3 octave frequency band are more than 15 dB higher than the values ​​in adjacent 1/3 octave bands;

Broadband vibrations - with a continuous spectrum more than one octave wide.

4.5. According to the frequency composition of vibration, there are:

Low-frequency vibrations (with a predominance of maximum levels in octave frequency bands of 1-4 Hz for general vibrations, 8-16 Hz - for local vibrations);

Medium frequency vibrations (8-16 Hz - for general vibrations, 31.5-63 Hz - for local vibrations);

High-frequency vibrations (31.5-63 Hz - for general vibrations, 125-1000 Hz - for local vibrations).

4.6. According to the temporal characteristics of vibration, there are:

Constant vibrations, for which the value of the normalized parameters changes by no more than 2 times (by 6 dB) during the observation period;

Unstable vibrations, for which the value of the standardized parameters changes by at least 2 times (by 6 dB) during the observation time of at least 10 minutes when measured with a time constant of 1 s, including:

a) vibrations that oscillate in time, for which the value of the standardized parameters continuously changes in time;

b) intermittent vibrations, when a person's contact with vibration is interrupted, and the duration of the intervals during which the contact takes place is more than 1 s;

C) impulse vibrations, consisting of one or more vibration effects (for example, shocks), each with a duration of less than 1 s.

Vibration(lat. Vibratio - vibration, tremor) - mechanical vibrations. Vibration is the vibration of solids.

Vibration is also spoken of in a narrower sense, meaning mechanical vibrations that have a tangible effect on a person. In this case, a frequency range of 1.6-1000 Hz is assumed. The concept of vibration is closely related to the concepts of noise, infrasound, sound.

Sources of occurrence- working electric motors, especially poorly balanced, working wood and metalworking equipment, gas turbine engines vehicles, diesel engines, engines internal combustion and transmission, poor condition of the road surface, hand-held power tools - drills, jackhammers, etc.

The effect of the factor on the human body

When the general vibration acts on the body, the nervous system and analyzers primarily suffer: vestibular, visual, tactile. Changes in the lumbosacral spine are characteristic of car drivers, machinists exposed to low-frequency and jerky vibrations. Workers often complain of pain in the lower back, limbs, in the stomach, lack of appetite, insomnia, irritability, and rapid fatigue. In general, the picture of the effect of general low- and medium-frequency vibrations is expressed by general autonomic disorders with peripheral disorders, mainly in the limbs, a decrease in vascular tone and sensitivity.Local vibration causes vasospasm of the hand and forearm vessels, disrupting the supply of blood to the limbs. At the same time, vibrations act on nerve endings, muscle and bone tissues, cause a decrease in skin sensitivity, salt deposition in the joints of the fingers, deforming and reducing the mobility of the joints. Oscillations of low frequencies cause a sharp decrease in capillary tone, and high frequencies cause vasospasm.

Factor classification

Vibration is classified according to:

– From temporal characteristics is presented in table 1.

Classification method	Vibration type	Vibration characteristic
By time characteristics	Permanent	For which the value of the normalized parameters changes by no more than 2 times (by 6 dB) during the observation time
	Inconsistent, including	For which the value of the normalized parameters changes by at least 2 times (by 6 dB) during the observation time of at least 10 minutes when measured with a time constant of 1 s, including
	Fluctuating in time	For which the value of the normalized parameters changes continuously over time
	Intermittent	When a person's contact with vibration is interrupted, and the duration of the intervals during which the contact takes place is more than 1 s
	Impulse	Consisting of one or more vibrations (e.g. shocks), each lasting less than 1 s

– From the method of transmission is presented in table 2.

– From the source of origin is presented in table 3 (see below).

Classification method	Vibration type	Description
By source of occurrence	Local vibration	Transmitted to humans from manual power tools (with motors), manual controls of machines and equipment
		Transmitted to humans from non-mechanized hand tools (without motors), for example, straightening hammers of various models and workpieces
	General vibration	Category 1 - transport vibration. Affects a person at the workplaces of self-propelled and trailed machines, vehicles. Sources of transport vibration include: tractors, self-propelled vehicles, trucks (including tractors, scrapers, graders, rollers, etc.); snow plows, self-propelled mining rail transport
		Category 2 - transport and technological vibration. Affects a person at workplaces of machines moving on specially prepared surfaces of industrial premises, industrial sites. Sources of transport and technological vibration include: excavators (including rotary ones), industrial and construction cranes, loading machines, self-propelled drilling carriages; track machines, concrete pavers, floor production vehicles
		3 categories - technological vibration. Affects a person at workplaces of stationary machines or is transmitted to workplaces that do not have sources of vibration. Sources of technological vibration include: metal and woodworking machines, forging and pressing equipment, casting machines, electrical machines, stationary electrical installations, pumping units and fans, etc.

– From the direction of action

According to the direction of action, the general vibration is divided into vertical, propagating along the Z axis, perpendicular to the supporting surface; horizontal, extending along the X-axis from the back to the chest; horizontal, extending along the Y-axis from the right shoulder to the left (Figure 1).

Local vibration is subdivided into one acting along the Xl axis parallel to the axis of the place where the vibration source is located, along the Yl axis perpendicular to the palm and along the Zl axis (acts in the plane formed by the Xl axis and the direction of supply or application of force) (Figure 2).

Picture 1

Picture 2

– From the nature of the spectrum is presented in table 4 (see below).

– From the frequency composition is presented in table 5 (see below).

Normalized indicators

constant vibration (general, local) the corrected level (value) of vibration acceleration is measured or calculated.

To assess working conditions by factor intermittent vibration (general, local) the equivalent corrected level (value) of vibration acceleration is measured or calculated.

When exposed to an employee during the working day (shift) as permanent and unstable vibration (general, local) to assess working conditions, the equivalent corrected level (value) of vibration acceleration is measured or calculated taking into account the duration of their action.

When exposed to an employee local vibration in combination with local hand cooling (work in a cooling microclimate of class 3.2), the hazard class of working conditions for this factor is increased by one step.

Normalized frequency range:

- for general vibration in the form of octave bands with geometric mean frequencies: 2; 4; eight; sixteen; 31.5; 63 Hz or in the form of one-third octave bands with geometric mean frequencies: 0.8; one; 1.25; 1.6; 2; 2.5; 4; 5; 6.3; eight; 10; 12.5; sixteen; twenty; 25; 31.5; 40; 50; 63; 80 Hz;

- for local vibration in the form of octave bands with geometric mean frequencies of 8; sixteen; 31.5; 63; 125; 250; 500; 1000 Hz.

Standards

The maximum permissible values ​​of the normalized parameters of industrial local vibration with a vibration exposure duration of 480 minutes (8 hours) are given in Table 6.

Table 6. Maximum permissible values ​​of normalized parameters of production local vibration

vibration category 1 - transport for workplaces are given in table 7.

Table 7.Categories 1 - Transport

Maximum allowable values vibration category 2 - transport and technological for workplaces are given in table 8.

Table 8. Maximum permissible values ​​of vibration category 2 - transport and technological

Vibration limits category 3 - technological type "a" for workplaces are presented in table 9.

Table 9. Maximum permissible values ​​of vibration category 3 - technological type "a"

Vibration limits category 3 - technological type "b" jobs are presented in table 10.

Table 10. Maximum permissible values ​​of vibration category 3 - technological type "b"

Vibration limits category 3 - technological type "b" jobs are presented in table 11.

Table 11. Maximum permissible values ​​of vibration category 3 - technological type "c"

The permissible values ​​of vibration in residential premises, wards of hospitals and sanatoriums are presented in table 12.

Table 12. Permissible values ​​of vibration in residential premises, wards of hospitals, sanatoriums

The permissible values ​​of vibration in administrative premises and in premises of public buildings are presented in Table 13.

Table 13. Allowable vibration values ​​in administrative buildings and public buildings

Classes of working conditions depending on the vibration levels at the workplace are presented in table 14.

Factor name, indicator, unit of measurement	2 (valid)	3.1	3.2	3.3	3.4	4 (dangerous)
Local vibration, equivalent corrected level (value) of vibration velocity, vibration acceleration (dB / times)	<=ПДУ	excess up to 3dB / 1.4 times inclusive		excess up to 9dB / 2.8 times inclusive		> 12dB / 4 times
Vibration total, equivalent corrected level of vibration velocity, vibration acceleration (dB / times)	<=ПДУ	excess up to 6 dB / 2 times inclusive	excess up to 12dB / 4 times inclusive	excess up to 18 dB / 6 times inclusive	excess up to 24 dB / 8 times inclusive	> 24dB / 8 times

Table 14. Classes of working conditions depending on the levels of vibration at the workplace

Measurement technique

To assess vibration exposure per shift, in addition to information about the vibration level, it is also necessary to assess the duration of vibration exposure during the working day. The minimum permissible measurement duration depends on the type of vibration signal, measuring instruments and the work performed by the worker. The total measurement time, which is the sum of individual measurements, must be at least 1 min. It is preferable, instead of one large measurement period, to take several (at least three for each operation) shorter ones. Sometimes it is difficult or impossible to obtain reliable measurements during normal operation because the duration of the vibration may be too short from the point of view of the measurement procedure. In this case, it is allowed to carry out measurements in the process of simulating a working operation, when the periods of vibration are artificially lengthened, but the working conditions are kept as close as possible to those that occur during the normal performance of the working operation.

Measuring instruments

Figure 3 shows the means for measuring vibration levels.

Figure 3 - Means for measuring vibration levels

Measures to eliminate the harmful effects of vibration

There are two main groups of methods for reducing vibration of equipment in industrial buildings and premises - at the source of its occurrence and along the path of propagation. It is necessary to combine these funds correctly.

Reducing vibration at its source... When designing buildings, vibration reduction in the source is ensured by using low-noise equipment and choosing the correct (calculated) mode of its operation; during the construction and operation of buildings - the technical serviceability of the equipment.

Reducing vibration in the path of its propagation(vibration isolation of equipment, vibration isolation of air ducts, vibration isolation pads, rugs, seats) is achieved by a complex of architectural planning and acoustic measures.

1. Architectural and planning measures provide for such a layout of premises in buildings, in which the vibration sources are as far away from the protected objects as possible. Vibration reduction in protected areas can be achieved by appropriate placement of equipment in the building. Equipment that creates significant dynamic loads is recommended to be installed in basement floors or on separate foundations not connected to the building frame. When installing equipment on floors, it is advisable to place it in the places farthest from the protected objects.
2. Acoustic events. These include vibration isolation of engineering equipment. Diagrams of rigid and vibration-insulated fastening of the unit (machine) to the foundation. For vibration isolation of the unit (machine) it is necessary to install it on vibration isolators and isolate the communications suitable for it. A single-link, two-link, and sometimes a three-link vibration isolation scheme is used, when a massive slab (usually reinforced concrete) or a rigid support frame with mass m is placed between the unit and the vibration isolators. The supporting structure on which the vibration-insulated machine rests is called the foundation. This can be a floor slab, reinforced concrete block, beams, etc.

Anti-vibration elements can be presented:

a) in the form of separate supports:

- spring vibration isolators, the main working element of which is one or more steel coil springs;

- elastic gaskets, often having a complex shape;

b) in the form of a layer of elastic material laid between the machine and the foundation;

c) in the form of a floating floor on an elastic base. The floor on an elastic foundation is a reinforced concrete screed, arranged on an elastic foundation over the load-bearing slab of the building. It is usually used in a two-tier scheme with other vibration isolators.

The design of vibration-isolating structures is reduced to the choice of a structural scheme of vibration isolation, the selection of the type and parameters of vibration isolators according to the known nomenclature (less often they are calculated and designed), the choice of a floor structure on an elastic foundation (if required), and the calculation of the effectiveness of the adopted structure (vibration isolation).

All considered vibration isolating structures reduce vibration transmitted to the foundation only at frequencies exceeding the fundamental frequency of natural vertical vibrations f0 (resonant frequency) of a system consisting of a machine (M) installed on a vibration isolating base.

Calculation of vibration damping structures consists in the selection and calculation of vibration dampers and other elements of which they consist, as well as in the calculation of vibration damping.

For vibration isolation of units (machines) with operating frequencies less than 18 ... 20 Hz, spring vibration isolators should be used. Spring vibration isolators, having a lower frequency f0, provide greater vibration isolation at low frequencies than other types of vibration isolators made of elastic materials... However, the latter at medium and high frequencies are more effective, since wave resonance phenomena, which worsen vibration isolation, occur in them at higher frequencies than in springs and, moreover, are less pronounced due to significantly higher internal energy losses.

Due to these phenomena, vibration isolation by springs at medium and high frequencies decreases and is very small. Some increase in it is achieved when installing rubber gaskets between the springs and the foundation. At high frequencies, the additional vibration isolation increases with frequency and becomes the higher, the greater the loss factor, thickness and shape factor of the gasket. Therefore, they should be made of perforated rubber rather than solid rubber. It should be noted that thin rubber gaskets do not eliminate the main disadvantage of spring vibration isolators - low vibration isolation at medium and high frequencies. Floating floors without special vibration isolators can only be used with equipment with operating frequencies over 45 ... 50 Hz. These are, as a rule, small machines, vibration isolation of which can be provided in other ways. The performance of resilient floors at such low frequencies is low. Therefore, they are used only in combination with other types of vibration isolators, which provides high vibration isolation at low frequencies (due to vibration isolators), as well as at medium and high frequencies (due to vibration isolators and a floating floor).

The floating floor screed (see Fig. 4.2) must be carefully insulated from the walls and the supporting floor slab, since the formation of even small rigid bridges between them can significantly impair its vibration-insulating properties. Therefore, when designing a floating floor, measures are taken to prevent the seepage of concrete into the elastic layer during the manufacture of the floor. In the places where the floating floor adjoins the walls, a seam made of non-hardening materials that does not allow water to pass through is required.

When the linear dimensions of the floating floor screed are more than 8 ... 10 m, in order to prevent cracking of concrete, it is recommended to perform separation joints, which should not pass near the installation site of engineering units. Large units should be located in the center of individual slabs, into which the entire floating floor screed is broken by the seams.

The floating floor should be designed to be capable of supporting static loads from the equipment. By installing the machine on a reinforced concrete slab, the vibration level of the machine itself is reduced and its stability on the springs increases. At low frequencies, even with a constant value of f0, a slight increase in vibration isolation is possible due to the separation of different spatial modes of vibration of the machine installed on vibration isolators, which is not taken into account in the one-dimensional design scheme. However, in the audio frequency range as a whole, vibration isolation increases markedly due to an increase in the impedance of the vibration isolation unit.

When using foundation reinforced concrete slabs in certain frequency bands, there may be a decrease in vibration isolation. This happens in cases when, due to the increase in the mass of the vibration isolation unit and the use of large springs, the octave band, into which the first wave resonant frequency of the springs falls, and from which the “failure” of the vibration isolation by the springs begins, is shifted one octave down. Therefore, it is better to install the unit on spring vibration isolators of smaller numbers (with a larger number) than large ones (fewer of them are required), since the latter begin to decline earlier in vibration isolation.

In the sound frequency range, reinforced concrete slabs work better if (for a given mass) they have minimum dimensions in plan, but greater thickness. To increase the acoustic vibration isolation, one should not make large reinforced concrete slabs on which several machines are installed at once - for example, the main and reserve pumps.

A reinforced concrete slab is also installed in cases where the stiffness of pipelines with flexible inserts suitable for the machine is comparable to or exceeds the total stiffness of vibration isolators that would be required to install the machine without this slab. This can be the case, for example, when vibration damping of pumps. Due to the installation of a reinforced concrete slab, the total mass of the vibration-insulated installation increases and the frequency of its natural vibrations decreases, since the influence of the rigidity of the connected pipelines decreases. As a result, in addition to the above, an increase in vibration isolation is achieved at low frequencies. In some cases, the rigidity of pipelines with flexible inserts connected to the machine turns out to be so great that it cannot be vibration-insulated at all without installing a reinforced concrete slab.

When constructing massive vibration-insulated bases, it is necessary to take into account the presence of internal vibration-insulating elements in ventilation and compressor equipment. In these cases, it is recommended that the internal vibration damping elements be shunted using threaded or screw connections.

Vibration isolation of non-supporting links(pipelines, air ducts, etc.) is performed in order to ensure the required freedom of movement of the vibration-insulated machine by reducing the rigidity of the considered connections. This is necessary for the effective operation of vibration isolators and to reduce the sound energy propagating through these connections.

For vibration isolation, flexible connectors are installed on each pipeline (or air duct) connected to the machine. They should be located as close to the vibrating unit as possible. If the rigidity of these inserts is small compared to the rigidity of vibration isolators (for example, in fans), then it does not matter how they are oriented. In cases where the rigidity of flexible inserts is comparable to the rigidity of vibration isolators (pumping units, compressors), the inserts should be positioned so that the effect of their rigidity is minimal in the directions of action of the greatest dynamic forces developed by the unit (machine). For example, flexible connectors for pumping units have greater rigidity in the longitudinal direction and less in the transverse direction. Therefore, they should be placed parallel to the axis of rotation.

In some cases, two flexible inserts are installed on one pipeline at two mutually perpendicular sections located side by side. Then, a relatively low stiffness of this connection in all directions, useful for vibration isolation, is ensured. An increase in the number of flexible connectors on a pipeline by more than one or two does not lead to a decrease in sound vibration propagating through it, which still propagates through the water (air) contained in it.

In the sections of pipelines (air ducts) between the unit and the flexible insert, it is not recommended to carry out attachments to building structures (even vibration-insulated ones). Pipelines (air ducts) should not have rigid contact with the enclosing structures. Often, rigid fastening of pipelines and air ducts to building structures is the reason for unacceptable noise levels in remote rooms located several floors from of this place fastening.

Fastening of pipelines and air ducts to building structures must be carried out using vibration-isolating fasteners with an elastic element. Laying pipelines (air ducts) through walls and partitions should be performed using vibration-free sleeves. For vibration isolation, use non-combustible elastic pads. Joints and gaps between air ducts and sleeves must be sealed with a non-drying vibroacoustic sealant. It is recommended to vibration-isolate pipelines and sections of rigid air ducts with a foam rubber material. It is recommended to fix pipe insulation to the pipe surface using a special adhesive.

Vibration protection systems on pneumohydraulic supports... These systems are designed to protect structures, foundations and maintenance personnel from harmonic vibrations of machines. These are passive vibration protection systems based on anti-vibration devices with linear elastic elements, the mass of which is not more than 2% of the mass of the machine. Passive-active systems are based on pneumohydraulic bearings. These supports, in addition to the hydraulic device, have elastic elements. The liquid flow rate through the hydraulic device is determined by the capacity of the positive displacement pump and, as a result, does not depend on the back pressure in the support cavity. During dynamic compression, a hydraulic resistance force is generated in the hydraulic device. The resilient element provides the bearing resistance under static compression and recovery when the compressive force is reduced. As an elastic element, you can use springs or gas chambers, in which the gas balances the external load with its pressure. The overall stiffness of the support depends on the stiffness of the gas and the stiffness of the hydraulic expansion joint. Vibration protection systems can reduce vibration of the foundation by 3 ... 5 times.

Organizational measures (protection by "time")... For this purpose, specially developed work regimes are used, which provide for special breaks. It is recommended to use work modes with limited working time with vibration of no more than 2/3 of the work shift, as well as the introduction of technological processes that provide for micro-pauses during vibration-hazardous operations, 2-3 breaks of 20-30 minutes per shift. They are arranged 1-2 hours after the start of the shift and 2 hours after the lunch break (the duration of which should be at least 40 minutes) and are used for outdoor activities, conducting a special complex of industrial gymnastics, physiotherapy procedures.

Work modes for specific vibration-hazardous professions should be included in the technological documentation. Working regimes are a preventive measure aimed at rational organization of work with vibrating equipment, and in cases of exceeding sanitary standards, and at reducing the time of adverse effects of vibration on workers in vibration-hazardous professions.

Facilities collective protection ... These include:

- anti-vibration pads and rugs;

- vibration-insulated seats;

The vibration-insulated operator's seat is one of the main personal protection equipment against vibration. Modern chair designs are made according to two schemes. Passive, non-adjustable vibration isolation, uses coil springs in combination with dry dampers mounted under the seat. In this case, it is possible to reduce the harmful effect of vibration by 1.5 - 2 times at frequencies above 63 Hz. At low frequencies, the effectiveness of passive means is significantly reduced due to the proximity of resonances. It is almost impossible to overcome this limitation, since at reduced rigidity, operator stability is lost and motion sickness is possible. In addition, large operator displacements are dangerous as a source of control errors. This problem is partially solved by using guiding mechanisms, for example, a parallelogram in combination with elastic elements. However, in this case, there is a sharp decrease in efficiency at high vibration frequencies.

Another direction in the design of chairs is developing under the influence high tech... The suspension of these seats is carried out on low-stiffness gas springs to eliminate low-frequency resonances. To stabilize the operator's position, servo motors are used, which react to the operator's weight using special sensors. Typically, these designs have guiding elements, which affects the efficiency in the high frequency region.

Automatic systems for lowering the stiffness within the vibration amplitude (stiffness correctors) have been developed and successfully tested. The use of correctors doubles the effectiveness of vibration isolation.

- protective equipment for the upper extremities (vibration-resistant gloves, mittens, inserts);

- protective equipment for the lower extremities (vibration-resistant boots, insoles, liners).

What are the main sources of industrial vibration?

Unlike noise, a person feels vibration when in contact with vibrating solid objects: tools, equipment, building or technical structures, which have unbalanced and unbalanced parts that rotate or reciprocate.

The source of vibration are self-propelled mechanisms, transport during their work or movement. So the drivers of self-propelled vehicles are affected by vibration, the source of which is the chassis and the engine. The undercarriage, wheels interact with unevenness of the road, soil, field and transmit through the frame and the mounting system to the cab or the working platform of the unit.

The source of vibration can be the motors of stationary machines and equipment, as well as those with working bodies that produce vibrations, vibration: electric drives, compressors, pumping units, metalworking machines, potato sorting machines, conveyors, presses, woodworking machines, drilling rigs, fans, construction equipment (concrete mixers, cranes, concrete pavers, etc.), feed preparation machines (crushers, root tubers, etc.)

Vibration can also be experienced through vibrations of the structure of bridges and crossings, overhead roads, as well as from a tool that does not have a mechanical drive (straightening hammer, saw, etc.).

At workplaces, mechanized tools can be used: a vibrating electric drill, a jackhammer, electric saws, electric mixers, electric knives, etc., from their work a person also experiences vibration.

What are the types of vibration?

Vibration is classified according to various criteria.

1. By the method of transmission to the human body:

- general - vibration is transmitted to the human body through the supporting surfaces when he is in a standing or sitting position;

- local - vibration is transmitted only through the hands of workers in contact with a hand-held power tool, a machine or equipment control body, parts that it processes, etc.

A tool from which the worker can be affected by local vibration: jackhammers, mining drills, grinders, chipping hammers, wrenches, concrete breakers, rammers, riveting hammers, etc.

It is also possible the simultaneous action of two types of vibration - general and local. For example, when road-building and agricultural machines are operating, local vibration from the controls is transmitted to the hands, and general vibration is transmitted to the whole body from the machine through the seat (Fig. 1).

Fig. 1 Scheme of vibration transmission to the seats and working bodies of the tractor.

1. From the source of origin, general vibration is subdivided into categories:

Category 1 - transport, which affects a person at the workplaces of self-propelled, trailed machines, vehicles when driving over the terrain, roads and agricultural phones (fields, meadows). These are combines, trucks, cars, tractors, scrapers,

graders, rollers, snowblowers, self-propelled mining rail transport.

Category 2 - transport and technological, which acts on a person in the workplace of machines with limited mobility or moving on specially prepared surfaces of industrial premises or sites, mine workings. These are construction and industrial cranes, loading machines for open-hearth furnaces, mining combines, self-propelled drilling carriages, road machines, concrete pavers, transport of industrial premises, i.e. machines with a working body that performs technological operations.

On-site general process vibration Category 3 subdivided into:

Category 3 in - at the workplaces of the plant management, design bureaus, classrooms, computing centers, first-aid posts, laboratories, office premises - for knowledge workers and personnel who are not involved in physical labor, i.e. in non-production premises

1. By source of origin local vibration subdivided into one that:

Transmitted from hand-held machines or hand-held power tools, machine controls or equipment;

It is transmitted from hand tools without a drive (hammer, saw, etc.) and from parts.

4. By exposure time, general and local vibration subdivided into:

- constant , for which the value of vibration velocity or vibration acceleration changes less than 2 times per work shift (less than 6 dB);

- fickle , for which the above parameters change more than 2 times per work shift (6 dB or more);

Intermittent vibration is classified into:

- hesitant , the vibration level is continuously changing over time;

- intermittent when contact with vibration during operation is interrupted (the interval between contacts is more than 1 second);

- impulse - vibration consists of several impacts (for example, shocks), each of which is less than 1 s in duration, with a frequency of less than 5.6 Hz.

Rice. 2 Classification of industrial vibration.

1. Direction of action general vibration characterize taking into account

the action of the coordinate system - X, Y, Z. Vibration acting along the horizontal axis from the back to the chest is the X axis.On the vertical axis along the spine is the Z axis.Vibration acting along the horizontal axis from the right shoulder to the left is the Y axis (Fig. 3-a, b)

For local vibration, the X-axis coincides with the axis of the place where the vibration source is swept, the Z-axis is directed along the forearm, and the Y-axis is directed from the hand to the vibrating surface (Fig. 3-c)