Types of safety devices in production. Technical condition of the car brake equipment. Procedure in the event of an accident or incident during the operation of equipment under pressure

The main technical means of labor protection serving for the collective protection of workers are protective devices.

Protective devices are devices used to prevent or reduce exposure of workers to hazardous and harmful production factors. In particular, safety devices prevent a person from entering the danger area.

A dangerous zone is a space in which it is constant. but a situation exists or periodically arises that is dangerous to the life and health of the worker. X) the passable zone can be limited (localized around a dangerous piece of equipment) and unlimited, changing in space and time (for example, the space under the transported cargo, etc.).

In addition to protecting a person, protective devices protect equipment from accidents, create the necessary coordination between human and machine actions, prevent the consequences of erroneous actions of personnel, serve to automate the operation of equipment, etc.

Protective devices are very diverse in principle of operation and design. To some extent, they can be conditionally subdivided into: protective, blocking, safety, special, brake, automatic control and signaling, remote control.

Fencing devices represent a physical barrier between a person and a hazardous or harmful production factor. These are all kinds of casings, shields, screens, visors, strips, barriers. Due to their simplicity of design, low cost and reliability, they are widely used in technology.

By the method of installation, fences can be stationary or mobile, fixed and movable (folding, sliding, removable).

The fence should have a simple and compact design, meet the requirements of aesthetics, not itself a source of danger and not limit the technological capabilities of the equipment. It is advisable to make fences in the form of solid casings, shields, screens. It is allowed to use metal meshes and grids, provided that the shape is constant and the required rigidity is ensured. The fence should not lose its protective properties under the influence of factors arising during the operation of the equipment, such as, for example, vibration, high temperature, etc.

If the equipment must not be operated without guard. then it is necessary to provide an interlock that stops the operation of the equipment when the fence is removed, open or in another inoperative state.

/ Blocking is a set of methods and means that ensure the fastening of the working bodies (parts) of devices, machines or elements of electrical circuits in a certain state, which remains even after the blocking effect is removed.

Locking devices are used to prevent accidents and traumatic situations.

There are many types of interlocking devices. Some of them, sometimes called prohibitive-permissive, prevent the improper switching on and off of devices, mechanisms, regulating, starting and locking devices, do not allow the machine to start when the fence is removed, and also prevent other improper actions of the service personnel.

Other interlocking devices (emergency) prevent the development of an emergency situation by automatically shutting off certain sections of the technological system or by including special reset devices, etc.

According to the principle of operation, locking devices are divided into mechanical, electronic, electromagnetic, electrical, pneumatic, hydraulic, optical and combined. For example, a mechanical interlock that prevents the unit from turning on when the guard is removed can be carried out using special stoppers, latches or locks. However, mechanical interlocks are complex and therefore rarely used.

Electrical interlocking is widely used, carried out using electrical connections of control circuits, control and signaling of the blocked equipment. Such interlocks are mainly used to prevent incorrect activation of individual mechanisms or parts of equipment. Electrical interlocking of removable or folding guards is relatively easy to solve by installing limit switches. If the guards are removed or improperly installed, it disconnects the drive motor control circuits. *

Interlocks based on the photoelectric effect are now widely used. The advantage of photoelectric protection is the absence of any barriers that interfere with or obscure the working area. The action of such protection is based on the fact that a beam of light, passing through the danger zone, hits the photocell. When the beam is blocked by any object, the illumination of the photocell stops, the electrical circuit is broken and the machine (machine) stops.

Safety refers to devices that ensure the safe operation of equipment by limiting speeds, pressures, temperatures, electrical stress, mechanical stress and other factors that can destroy the equipment and lead to accidents. Safety devices must automatically operate with a minimum inertial delay when the monitored parameter goes beyond the permissible limits.

Depending on the nature of the hazardous factor, safety devices can be divided into several groups.

Mechanical overload protectors include shear pins and pins, friction clutches, centrifugal governors. Load-bearing shear pins connect the pulley or gear to the drive shaft. If the load exceeds the permissible, then the hairpin collapses (shears off) and the pulley or gear begins to rotate idle. Replace the studs to start the machine.

Friction clutches allow adjustment of the permissible torque value and automatically start working as soon as the load returns to normal. Steam and gas turbines, expanders, diesel engines are equipped with centrifugal regulators, which limit the supply of the working substance to the machine when the rotational speed is increased.

Safety relief valves and bursting discs are related to overpressure protection of steam and gas, the principle of operation of which is described above. The main requirement for safety valves is the reliability of automatic opening of the valve at a certain predetermined pressure (response pressure) and the passage of the working medium in such quantities that a further increase in pressure in the system is excluded. In addition, the safety valve must automatically close reliably at a pressure that does not disrupt the process in the system, and also maintain tightness when closed.

To protect vessels and devices from a very rapid or even instantaneous increase in pressure, safety membranes are used, which, depending on the nature of their destruction when triggered, are divided into bursting, shear, breaking, popping, tear-off and special. The most widespread are rupture discs - flat and pre-bulged (domed). The principle of operation of a bursting disc is based on its destruction under the action of a load exceeding the ultimate strength of the membrane material. Domed membranes are available as bursting and leaching. Bursting membranes are installed with a concave surface towards the pressure side of the leaching - vice versa.

Travel stops are used to prevent the movement of parts of any mechanism or the whole machine beyond the established limits or dimensions. These include limit switches (travel stops) and stops.
They are, for example, used on cranes to restrict the lifting height of the hook block and to restrict the movement of the crane itself, on metal-cutting machines to restrict the movement of the support, etc.

Circuit breakers from exceeding the electric current are used to prevent short circuits, destruction of electrical insulation, etc. The action of fuses (plug or tubular) is based on the fuse blown out when the electric current rises above the permissible value. There are also automatic fuses with thermal relays. Automatic circuit breakers with electromagnetic releases with an unacceptable current produce an instantaneous disconnection of the line (cut-off).

Circuit breakers with combined releases have both thermal and electromagnetic cut-off.

TO special safety devices include protection systems against electric shock, safety devices in elevators and other lifts, double-handed switching on presses, block locks, catchers for tools and materials, limiters of the mass of the lifted load, limiters of rotation and roll of cranes, and many others.

The safety interlock, based on the principle that both hands of the operator are engaged during switching on and during the working stroke of the equipment, is widely used, in particular on pressing equipment. The disadvantage of this type of blocking is the possibility of starting the equipment in case of failure or deliberate unblocking (jamming) of one of the start buttons (handles).

Automatic control and alarm devices include devices designed to control, transmit and reproduce information in order to attract the attention of the operating personnel and make the necessary decisions when a hazardous or harmful production factor appears or is possible.) These devices are subdivided into information, warning, emergency and response; by the nature of the signal - into sound, light, color, sign and combined; by the nature of the signal transmission - to constant and pulsating. By the way they are triggered, they are automatic and semi-automatic.

These signaling devices monitor pressure, altitude, distance, temperature, humidity, air pollutants, noise, vibration, travel speed, wind speed, crane reach, speed, harmful emissions, etc.

"Light and sound alarms are widespread. Light alarms in electrical installations warn of the presence or absence of voltage, the normal mode of automatic lines, maneuvers of vehicles, etc. Sound signals are given with the help of sirens, bells, whistles, beeps. The sound of the signal should be strong to differ from the usual noise typical for a given production environment. Sound signals are supplied to lifting and transport installations; units serviced by a group of workers; hazardous areas, etc. Sound signals can be used to warn of reaching the maximum permissible concentration of harmful substances in the air of the working area, the maximum permissible liquid level in tanks, extreme temperatures and pressures in various installations.

Signaling devices also include various indicator devices: manometers, thermometers, voltmeters, ammeters, etc.

A person perceives and remembers visual images and various colors well. This is the basis of the widespread use of color in factories as a coded carrier of hazard information. Signal colors and safety signs are regulated by GOST 12.4.026-79 (Fig. 28, a-g).

Remote control devices are designed to control a technological process or production equipment outside the hazardous area. These devices can be stationary and mobile.

Figure 27 - Scheme of the pendulum signaling device of the SKM-3 crane.

Devices that ensure the safe operation of machines and equipment by limiting speed, pressure, temperature, electrical voltage, mechanical stress and other factors that contribute to the occurrence of dangerous situations are called safety devices. They should be triggered automatically with a minimum inertial lag when the controlled parameter goes beyond the permissible limits.

Shear pins and pins, spring-cam, frictional and gear-friction clutches, centrifugal, pneumatic and electronic regulators serve as protectors against mechanical overloads.

A pulley, sprocket or gear located on the drive shaft is connected to the drive (driven) shaft with shear pins or pins designed for a certain load. If the latter exceeds the permissible value, then the hairpin is destroyed and the drive shaft begins to rotate idle. After eliminating the cause of the appearance of such loads, the cut hairpin is replaced with a new one.

The diameter of the pin, mm, of the safety clutch, which is usually made of steel 45 or 65 G,

where Mр - design moment, N * m; R is the distance between the axial lines of the transmitting shafts and the pin, m; τav - ultimate shear strength, MPa (for steel 45 and 65 G, depending on the type of heat treatment with a static load τav = 145 ... 185 MPa; with a pulsating load τav = 105 ... 125 MPa; with a symmetric alternating load τav = 80 ... 95 MPa); for calculations it is recommended to take smaller values.

Usually, the design moment Mp is taken 10 ... 20% higher than the maximum permissible moment Mпр, i.e.

Мр = (1.1 ... 1.2) Мпр.

Friction-type clutches automatically engage in case of excess torque, to which they are pre-set. Deactivation condition, e.g. for a toothed-friction overload clutch:

where Mр is the calculated torque, N m; Mpred - maximum allowable torque, N * m; a - the angle of inclination of the lateral surface of the cam (α = 25 ... 35 °); β — angle of friction of the side surface of the cam (β = 3 ... 5 °); D is the diameter of the circle of the points of application of the circumferential force to the cams, m; d - shaft diameter, m; f1 — coefficient of friction in the keyed connection of the movable sleeve (f1 = 0.1 ... 0.15).

Safety clutches for chain and belt drives of agricultural machines with toothed friction washers are standardized.

Diesels, steam and gas turbines, expanders are supplied with speed controllers, mainly of centrifugal type. A regulator is used to prevent an increase in the crankshaft speed, which is dangerous for the machine and service personnel, by limiting the supply of fuel or steam.

Limit switches are necessary to prevent equipment breakdowns that occur when moving parts go beyond the set limits, to restrict the movement of the support on metal-cutting machines, for the path of movement of the load in the vertical and horizontal planes during the operation of lifting mechanisms, etc.

Catchers are used on hoisting and transporting machines, in elevators to keep the lifted load stationary, even in the presence of self-braking brake systems, which, with wear or improper care, may lose their performance. There are ratchet, frictional, roller, wedge and eccentric catchers.

Safety valves and diaphragms are used to avoid overpressure of steam or gas. Safety valves are of the type cargo (lever), spring and special; hull structures - open and closed; placement method - single and double; lifting height - low-lifting and full-lifting.

Lever valves (Fig. 7.3, a) have a relatively small throughput and when the pressure is exceeded in excess of the permissible value, they release the working gas or steam into the environment.

Rice. 7.3. Schemes of safety lever (o), spring (b) valves and diaphragms (c and d):

1 - tension screw; 2 - spring; 3 - valve plate

Therefore, in vessels operating under the pressure of toxic or explosive substances, spring-loaded valves of a closed type are usually installed (Fig. 7.3, b), dumping the substance into a special pipeline connected to the emergency tank. The lever valve is adjusted to the maximum permissible value according to the pressure gauge by changing the weight of the load m or the distance b from the valve axis to the load. The spring valve is regulated by means of a tension screw 1, which changes the pressing force of the valve disc 3 by a spring 2. The main disadvantage of safety valves is their inertia, that is, providing a protective effect only with a gradual increase in pressure in the vessel on which they are installed.

To determine the flow area of the safety valves, the theory of gas outflow from the hole is used. Consider the following dependency:

where Q is the throughput of the valve, kg / h; μ is the outflow coefficient (for round holes μ = 0.85); SK - valve sectional area, cm2; p is the pressure under the valve, Pa; g = 9.81 cm / s2 - acceleration of gravity; M is the molecular weight of gases or vapors passing through the valve; k = cpcv - ratio of heat capacities at constant pressure and constant volume (for water vapor k = 1.3; for air k = 1.4); L — gas constant, kJ / (kg * K), for water vapor R = 461.5 kJ / (kg * K); for air R = 287 kJ / (kg * K); T is the absolute temperature of the medium in the protected vessel, K.

Substituting into the last formula the values of μ, g, R and the average value of k at a known value of Q, it is possible to determine the sectional area of the safety valve, cm2,

SK = Q / (216p√ M / T).

The number and total cross-section of the safety valves are found from the expression

ndкhк = kкQк / pк,

where n is the number of valves (on boilers with a steam capacity of 100 kg / h, it is allowed to install one safety valve, with a boiler steam capacity of more than 100 kg / h, it is equipped with at least two safety valves); dк - inner diameter of the valve disc, cm (dк = 2.5 ... 12.5 cm); hк - valve lift height, cm; kk - coefficient (for valves with low lift height at hk≤ 0.05dk kk = 0.0075; for full-lift valves at 0.05dk< hк≤ 0,25dк kк = = 0,015); Qк — производительность котла по пару при максимальной нагрузке, кг/ч; рк — абсолютное давление пара в котле, Па.

To protect vessels and devices from a very rapid and even instantaneous increase in pressure, safety membranes are used (Fig. 7.3, c and d), which, depending on the nature of their destruction when triggered, are divided into bursting, shear, breaking, flapping, tear-off and special. The most common rupture discs, which break under the influence of pressure, the value of which exceeds the tensile strength of the membrane material.

Diaphragm safety devices are made of various materials: cast iron, glass, graphite, aluminum, steel, bronze, etc. The type and material of the membrane is chosen taking into account the operating conditions of the vessels and apparatus on which they are installed: pressure, temperature, phase state and aggressiveness of the medium, rate of pressure rise, overpressure release time, etc.

To ensure the operation of the membrane, it is necessary to determine the thickness of the membrane plates depending on the value of the bursting pressure. Throughput, kg / s, of membrane safety devices at an increase in pressure in the protected vessel:

Qm = 0.06Srabppr √ M / Tg,

where Srab - working (flow) section, cm2; ppr - absolute pressure in front of the safety device, Pa; Tg is the absolute temperature of gases or vapors, K.

The required thickness of the working part of the breaking membrane, mm,

Rice. 7.4. Low pressure water seal operation diagram:
a - during normal operation: b - with a reverse impact; 1 — shut-off valve; 2 - gas outlet pipe; 3 - funnel; 4 - safety tube; 5 - body; 6 - control valve

b = ppdplkop (4 [σcp]),

where pр is the pressure at which the plate should collapse, Pa; dm is the working diameter of the plate, cm; kon - scale factor, determined empirically (with d / b - 0.32 k - = 10 ... 15); [σav] - shear strength, MPa.

Thickness of membranes made of brittle materials

b = 1,1-pl √pp / [σfrom]

where rpl is the radius of the plate, cm; [σfrom] is the ultimate bending strength of the plate material, Pa.

The safety devices that prevent the explosion of the acetylene generator include water seals (Fig. 7.4), which do not let the flame into the generator. In case of a back blow of the flame, which occurs, for example, when a gas burner is ignited, the explosive mixture enters the starter and displaces part of the water through the gas outlet pipe 2. Then the end of the pipe 4 will receive a message with the atmosphere, the excess gas will come out, the pressure will return to normal and the device will start working again according to the scheme , shown in Figure 7.4, a. To protect electrical installations from an excessive increase in current strength, which can cause a short circuit, fire and injury to a person, circuit breakers and fuses are used.

Rev. No. 1 6.2.1 Safety devices must be installed on equipment and pipelines, the pressure in which can exceed the operating pressure, both due to the physical and chemical processes occurring in them, and due to external sources of pressure increase, calculated taking into account the conditions specified in clause 2.1 .7.

If the pressure in the equipment or pipelines cannot exceed the operating pressure, then the installation of safety devices is not required.

This circumstance must be justified in the project.

The primary circuit equipment and the safety casing must be designed for the loads arising from the depressurization of the reactor pressure vessel and the outflow of the coolant into the safety casing.

All sections of equipment and pipelines with a single-phase medium (water, liquid metal) cut off on both sides, which can be heated in any way, must be equipped with safety devices.

6.2.2. The number of safety devices, their throughput, the setting for opening (closing) must be determined by the design (construction) organization so that the pressure in the protected equipment and pipeline when this valve is triggered does not exceed the operating pressure by 15% (taking into account the dynamics of transient processes in the equipment and pipelines and dynamics and response time of the safety valve) and did not cause unacceptable dynamic effects on the safety valve.

It is allowed to take into account when calculating the dynamics of pressure growth in the protected equipment and pipelines, the anticipatory operation of the emergency protection of a nuclear power plant.

For systems with a possible short-term local pressure increase (for example, under the chemical action of a liquid-metal coolant and water), a local pressure increase is allowed, at which safety devices must operate (taking into account the hydraulic resistance in the section from the pressure rise to the safety devices). This possibility should be provided for in the design and justified by strength calculations.

6.2.3. In equipment and pipelines with a working pressure of up to 0.3 MPa, a pressure increase of no more than 0.05 MPa is allowed.

The possibility of increasing the pressure by the specified value must be confirmed by calculating the strength of the corresponding equipment and pipelines.

6.2.4. If a safety device protects several related pieces of equipment, then it should be selected and adjusted based on the lower working pressure for each of these pieces of equipment.

6.2.5 The design of the safety devices should ensure its closure after actuation when the pressure reaches at least 0.9 of the working pressure, according to which the setpoint for actuation of this valve was selected.

This requirement does not apply to safety diaphragms and water seals.

6.2.6. The setting for the landing of impulse safety devices with a mechanized (electromagnetic or other) drive should be established by the design (design) organization based on the specific operating conditions of the equipment and pipelines.

6.2.7. The number of safety valves and (or) safety diaphragms with forced rupture, installed to protect equipment and pipelines of groups A and B, must be greater than the quantity determined in clause 6.2.2, at least by one unit.

This requirement does not apply to direct burst diaphragms and water seals.

Rev. No. 1 6.2.8. The calculation of the throughput of safety devices must be carried out in accordance with the requirements of the regulatory documents of Gosatomnadzor of Russia.

The capacity of the safety devices must be checked during the corresponding tests of the prototype of the given design, carried out by the manufacturer of the safety fittings.

6.2.9. When choosing the number and capacity of safety devices, the total capacity of all possible pressure sources should be taken into account, taking into account the analysis of design basis accidents that can lead to an increase in pressure.

6.2.10. On the pressure pipelines between the piston pump, which does not have a safety valve, and the shut-off element, a safety valve must be installed, which excludes the possibility of an increase in the pressure in the pipelines above the working one.

6.2.11. The installation of shut-off valves between the safety device (membrane or other protective device according to clause 2.1.7) and the equipment or pipeline protected by it, as well as on the outlet and drain pipelines of safety valves, is not allowed.

It is allowed to install shut-off valves in front of the pulse valves of pulse safety devices (IPU) and after these valves, if the IPU is equipped with at least two pulse valves, and the mechanical blocking of the specified shut-off valves allows only one of these valves to be out of operation.

6.2.12. Lever-operated pulse valves are not permitted.

6.2.13. The nominal diameter of the safety fittings and the impulse valve must be at least 15 mm.

6.2.14. In the safety fittings, the possibility of changing the setting of the spring and other adjustment elements must be excluded. For safety spring valves and impulse valves IPU, the springs must be protected from direct influence of the medium and overheating.

6.2.15. It is allowed to install switching devices in front of the safety valves in the presence of a doubled number of pulse safety devices or safety valves and at the same time ensuring the protection of equipment and pipelines from overpressure in any position of the switching devices.

6.2.16. The design of the safety valves should provide for the possibility of checking its proper operation by opening it manually or from the control panel. In the case of impulse safety devices, this requirement applies to the impulse valve.

Manual opening force should not exceed 196 N (20 kgf).

If it is impossible to check the operation of the safety valves on the operating equipment, switching devices installed in front of the valves should be used that allow checking each of them with disconnection from the equipment.

Switching devices must be such that, in any of their positions, as many fittings are connected to equipment or pipelines as required to ensure that the requirements of 6.2.2 are met.

The requirements specified in this paragraph do not apply to membranes and water seals.

6.2.17. Safety valves (for IPU - impulse channels) protecting equipment and pipelines of groups A and B must have mechanized (electromagnetic and other) drives that ensure timely opening and closing of these valves in accordance with the requirements of clauses 6.2.2 or 6.2.3 and 6.2. 5. These valves must be designed and adjusted so that, in the event of an actuator failure, they act as direct-acting valves and perform the above items. If there are several valves on the protected object, the mechanized drives of these valves must have independent control and power supply channels. Mechanized actuators can be used to check the correct operation and forced pressure reduction in the protected object. For equipment of group C, the need to install valves with such a drive should be determined by the design organization.

6.2.18. Safety devices must be installed on nozzles or pipelines directly connected to the equipment. Installation of safety devices on branch pipes connected to pipelines is allowed. When several units of safety valves are installed on one collector (pipeline), the cross-sectional area of the collector (pipeline) must be at least 1.25 of the calculated total cross-sectional area of the connecting branch pipes of the safety valves must be taken from the protected equipment. It is allowed to take a pulse from the pipeline on which the safety valve is installed, taking into account the hydraulic resistance of the pipeline.

6.2.19. On equipment and pipelines with a liquid metal coolant, as well as group C, it is allowed to use safety membrane devices that break when the pressure in the protected equipment rises by 25% of the working pressure of the medium (if this is confirmed by calculation). It is allowed to install safety diaphragm devices in front of the safety valve, provided that a device is installed between them that allows you to monitor the serviceability of the rupture disk, and also excludes the possibility of parts of the ruptured rupture disk entering the safety valve. In this case, the test shall confirm the functionality of the burst safety valve combination.

The cross-sectional area of the device with the destroyed membrane must not be less than the cross-sectional area of the inlet pipe of the safety fittings. The membrane marking must be visible after installation.

6.2.20. The passport for the safety valves must indicate the value of the flow coefficient and the area of the smallest flow area of the seat with the valve fully open.

The requirements for specifying these data in the passport do not apply to pulse-safety valves.

6.2.21. Equipment operating under a pressure less than the pressure of the source supplying it must have an automatic reducing device (pressure regulator after itself) on the supply pipeline with a pressure gauge and safety valves located on the lower pressure side.

For a group of equipment operating from one supply source at the same pressure, it is allowed to install one automatic reducing device with a pressure gauge and safety valves located on the same line up to the first branch. In cases where maintaining a constant pressure behind the reducing device is impossible or not required for technological reasons, unregulated reducing devices (washers, throttles, etc.) can be installed on the pipelines from the supply source.

On the pipelines connecting the regenerative heaters of the turbine units for the heating steam condensate, the role of reducing devices can be performed by valves that regulate the level of condensate in the bodies of the apparatus.

6.2.22. If the pipeline in the section from the automatic reducing device to the equipment is designed for the maximum pressure of the supply source and the equipment has a safety device, the installation of a safety device after the reducing device on the pipeline is not required.

6.2.23. If the design pressure of the equipment is equal to or greater than the pressure of the supply source and the possibility of pressure increase due to external and internal energy sources is excluded in the equipment, then the installation of safety devices is not required.

6.2.24. Automatic control devices and safety valves are not required:

1) on pump recirculation pipelines;

2) on pipelines after level regulators;

3) on purging, drainage and air removal pipelines when the medium is discharged into equipment equipped with safety devices in accordance with clause 6.2.9.

The need to install throttling washers on these pipelines is determined by the design documentation.

6.2.25. Safety devices for equipment and pipelines must be installed in places accessible for maintenance and repair.

6.2.26. Discharge pipes in the absence of self-draining must be equipped with a drainage device. The installation of shut-off valves on drainage pipes is not allowed.

The internal diameter of the discharge line must be at least the diameter of the outlet of the safety valve and is calculated so that at maximum flow, the back pressure at the outlet does not exceed the maximum back pressure set for this valve. The working medium escaping from the safety devices must be discharged to a place safe for personnel.

6.2.27. Checking the functional ability (serviceability) of the safety valves, including control circuits, with the release of the working medium should be carried out before the first start-up of the equipment to operating parameters and subsequent scheduled start-ups, but at least once every 12 months. If, as a result of the inspection, defects or failures in the actuation of the valve or control circuit are revealed, repairs should be carried out and re-checked.

6.2.28. The adjustment of the safety valves should be checked after installation, after the repair of the valves or the control circuit affecting the adjustment, but at least once every 12 months, by raising the pressure on the equipment, using the devices included in the delivery of this valve, or by testing on a stationary stand ... After adjusting the safety valves to operate, the adjusting unit must be sealed. Adjustment data must be recorded in the safety device operation and repair log.

6.2.29. Checking the serviceability of the operation and setting of systems that protect equipment and pipelines from overpressure or temperature (clause 2.1.7) should be carried out within the timeframes set in clauses 6.2.2 and 6.2.28.

6.2.30. Checking the serviceability of the hydraulic locks, replacing the safety membranes and checking the devices for their forced rupture should be carried out according to the schedule approved by the chief engineer of the nuclear power plant.

Shear pins and pins, spring-cam, frictional and gear-friction clutches, centrifugal, pneumatic and electronic regulators serve as protectors against mechanical overloads.

The diameter of the pin, mm, of the safety clutch, which is usually made of steel 45 or 65 G,

where M p - design moment, N * m; R - distance between the center lines of the transfer shafts and the pin, m; τ av - shear strength, MPa (for steel 45 and 65 G, depending on the type of heat treatment under static load τ av = 145 ... 185 MPa; with pulsating load τ av = 105 ... 125 MPa; with symmetric alternating load τ cf = 80 ... 95 MPa); for calculations it is recommended to take smaller values.

Typically design moment M p take 10 ... 20% higher than the maximum permissible torque M пp, i.e.

M p = (1.1 ... 1.2) M pr.

Friction-type clutches automatically engage in case of excess torque, to which they are pre-set. Deactivation condition, e.g. for a toothed-friction overload clutch:

where M p - design torque, N m; M limit - maximum allowable torque, N * m; a is the angle of inclination of the side surface of the cam (α = 25 ... 35 °); β is the angle of friction of the side surface of the cam (β = 3 ... 5 °); D - diameter of the circle of points of application of circumferential force to the cams, m; d - shaft diameter, m; f 1 is the coefficient of friction in the keyed connection of the movable sleeve (f 1= 0,1...0,15).

Safety clutches for chain and belt drives of agricultural machines with toothed friction washers are standardized.

Lever valves (fig. 7.3, a) have a relatively small throughput and when the pressure is exceeded in excess of the permissible value, they release the working gas or steam into the environment. Therefore, in pressure vessels

Rice. 7.3. Schemes of safety lever (o), spring (b) valves and diaphragms(v andG):

1 - tension screw; 2 - spring; 3 - valve disc

toxic or explosive substances, usually spring-loaded closed-type valves are installed (Fig. 7.3, b), dumping the substance into a special pipeline connected to the emergency tank. Adjust the lever valve to the maximum permissible value on the pressure gauge by changing the weight of the load T or distance b from the valve axis to the load. Spring loaded valve is adjusted with a tension screw 1 changing the pressing force of the valve disc 3 spring 2. The main disadvantage of safety valves is their inertia, that is, providing a protective effect only with a gradual increase in pressure in the vessel on which they are installed.

To determine the flow area of the safety valves, the theory of gas outflow from the hole is used. Consider the following dependency:

where Q - valve throughput, kg / h; μ - expiration coefficient (for round holes μ = 0.85); S K - valve sectional area, cm 2; R- pressure under the valve, Pa; g = 9.81 cm / s 2 - acceleration of gravity; M - molecular weight of gases or vapors passing through the valve; k = c p c v - ratio of heat capacities at constant pressure and constant volume (for water vapor k = 1.3; for air k= 1.4); L - gas constant, kJ / (kg * K), for water vapor R= = 461.5 kJ / (kg * K); for air R= 287 kJ / (kg * K); T- absolute temperature of the medium in the protected vessel, K.

Substituting the values μ, g, R and the average k with a known value of Q, it is possible to determine the sectional area of the safety valve, cm 2,

S K= Q/(216 p√ M/ T).

The number and total cross-section of the safety valves are found from the expression

nd to h to = k to Q to / p to,

where NS- the number of valves (on boilers with a steam capacity of 100 kg / h, it is allowed to install one safety valve, with a boiler steam capacity of more than 100 kg / h, it is equipped with at least two safety valves); d to - valve disc inner diameter, cm (d k = 2.5 ... 12.5 cm); h to - valve lift height, cm; k to - coefficient (for valves with a low lift at h k ≤ 0.05d k k = 0.0075; for full-lift valves at 0.05d k< h k ≤ 0.25 d k k == 0,015); Q to - boiler steam output at maximum load, kg / h; p to - absolute steam pressure in the boiler, Pa.

Q m = 0.06S slave p pr√ M / T g,

where S slave - working (flow) section, cm 2; p pr - absolute pressure before the safety device, Pa; T g- absolute temperature of gases or vapors, K.

The required thickness of the working part of the breaking membrane, mm,

Rice. 7.4. Low pressure water seal operation diagram:
a - during normal operation: b- on reverse impact; 1 shut-off valve; 2- gas outlet pipe; 3 - funnel; 4- safety tube; 5- building; 6- control valve

b = p p d pl k op (4 [σ cp]),

where p p is the pressure at which the plate should collapse, Pa; d m - working diameter of the plate, cm; k on- scale factor, determined empirically (at d / b - 0,32 k - = 10 ... 15); [σ cf] - shear strength, MPa.

Thickness of membranes made of brittle materials

b = 1,1r pl √p p / [σ from]

where r pl - radius of the plate, cm; [σ from] is the ultimate bending strength of the plate material, Pa.

The safety devices that prevent the explosion of the acetylene generator include water seals (Fig. 7.4), which do not let the flame into the generator. In the event of a reverse blow of the flame, which occurs, for example, when a gas burner is ignited, the explosive mixture enters the starter and displaces part of the water through the gas outlet pipe 2. Then the end of the tube 4 will receive a message with the atmosphere, the excess gas will be released, the pressure is normalized and the device will start working again according to the scheme shown in Figure 7.4, a.

To protect electrical installations from an excessive increase in current strength, which can cause a short circuit, fire and injury to a person, circuit breakers and fuses are used.

Braking devices

Braking devices are designed to hold moving parts, lifted load; reducing the speed of movement and stopping machines, mechanisms, lowering the load; absorption of energy of translationally moving or rotating masses of equipment, machines, mechanisms and cargo.

By design, braking devices can be shoe, tape, disc and conical; according to the switching scheme - open (braking occurs from the force applied to the handle or pedal), closed (the working bodies are constantly pressed by a special load, a compressed spring or a lifted load) types and automatic (included in the work without human intervention); by type of drive - mechanical, electromagnetic, pneumatic, hydraulic and combined; by appointment - working, backup, parking and emergency braking.

When determining the braking torque in order to increase the productivity of machines, it is necessary to strive for the largest allowable decelerations.

On machines driven by internal combustion engines, controlled closed-type brakes with a reliable locking device are most often used, and automatic closed-type brakes are used on lifting mechanisms.

It is safer to install the brakes directly on the working body (drum, wheel, etc.), but the design of the brake in this case turns out to be cumbersome. To ensure compactness and unload the mechanism from inertial forces, it is customary to install brakes on the drive shaft, which is kinematically rigidly connected to the shaft of the working body.

Shoe brakes are simple and reliable to operate, but relatively bulky. One-shoe brakes are used in mechanisms with a manual drive, two-shoe brakes are used for braking shafts rotating in different directions (the brake shaft does not experience a lateral load).

Band brakes are used in agricultural machines, tracked tractors, lifting mechanisms, etc. The working bodies of such brakes are a steel tape, sometimes sheathed with friction material, and a pulley.

A disc brake is a system of friction discs, some of which rotate, while others are stationary or stop when rotating in one direction. In multi-disc brakes, a large braking torque can be obtained with the same axial force.

The conical brake absorbs the braking moment by a body with an inner conical surface, which is loosely mounted on the shaft and rotates when the load is lifted. A ratchet mechanism is used to lock the body during reverse rotation (descent).

Manual brake control, as well as with the help of hydraulic and pneumatic devices, is used in machines driven by an internal combustion engine, in cranes and agricultural machines, and electromagnet control is used in industrial lifting and transport mechanisms.

In addition to the previously discussed braking devices, reversing and electric braking of electric motors are used. For reversing asynchronous electric motors, a reversing magnetic starter is used, the contactors of which are interlocked to prevent simultaneous switching on and, therefore, short circuit. Dynamic braking of induction motors is usually used to accurately stop an unreversible motor.

Opposition braking is possible in reverse and non-reversible control circuits of short-circuited asynchronous electric motors. However, it is associated with increased losses and heating, therefore, for non-reversible asynchronous electric motors, dynamic braking is most often used, and for reversible ones, opposition braking.

Locking devices

Blocking is a set of methods and means that ensure the fixation of parts of machines or elements of electrical circuits in a certain state, which remains regardless of the presence or termination of exposure.

Guards, guards, brakes and alarms do not always provide the required level of protection for the worker. Therefore, interlocking devices are used that either prevent improper actions of personnel (for example, an operator's attempt to turn on the equipment when the fence is removed), or prevent the development of an emergency situation by turning off certain sections of the technological system or putting into operation special dumping devices.

According to the principle of operation, interlocking devices are divided into mechanical, electrical, photoelectric, electronic, electromagnetic, pneumatic, hydraulic, optical, radiation and combined, and according to their design - into open, closed and explosion-proof. Their choice depends on the characteristics of the environment.

Mechanical devices are connected by means of structural elements of the fence with a braking or starting device or with braking and starting devices together. However, due to the complexity of the design and manufacture, such devices have not found widespread use.

The most common are electrical devices. Basic elements: a converter of the controlled value into an output signal, convenient for transmission and further processing; measuring and commanding device that determines the magnitude and nature of the signal and issues a command to eliminate the dangerous mode; actuating mechanism. An example is the locking device of a sharpening machine with contacts that turn off the electric motor when the protective screen is lifted. When it is lowered, the contacts are closed, including the machine. Tractors with starting engines are equipped with an electric locking device that prevents the engine from starting when the gear is engaged. If the gear lever is not in neutral, the contact breaker will open the primary magneto supply circuit, preventing the starting motor from starting.

Photovoltaic devices are triggered by crossing the light beam directed at the photocell. When the light flux incident on the photocell changes, the current in the electrical circuit changes, which is supplied to the measuring and command device, which, in turn, gives an impulse to turn on the protection actuator. Locking devices are especially effective, locking the pedal or the handle of the press while the worker's hands are in the danger zone. Due to their compactness, the absence of elements interfering with work or limiting the working area, such devices are used in presses, stamps, guillotine shears, etc.; with their help, fences of hazardous zones of great length (up to several tens of meters) are arranged without mechanical assemblies and structures.

Pneumatic and hydraulic devices are used on units where working bodies are under increased pressure: in pumps, compressors, turbines, etc. The main advantage of such devices is their low inertia. In the event of an emergency in machines with a hydraulic or pneumatic drive, the accompanying flow of liquid or gas, acting on a special lever, closes the valves of the supply medium.

There are blocking devices, the principle of which is based on the use of the ionizing properties of radioactive substances. A source of weak radiation in the form of a bracelet is put on the worker's hand. When the hand approaches the hazardous area, the radiation is captured and converted into electrical current. The current is supplied to a thyratron lamp. The latter transmits an impulse to a relay that opens the magnetic starter circuit. The equipment controlled by this starter stops.

SIGNALING AND ITS TYPES

A safety alarm is a means of warning workers about an impending or arising danger. Alarm systems include special automatic devices that turn off a machine or installation in the event that a given signal does not entail the performance of certain operator actions within a specified period of time to bring the equipment back to normal operation or bring environmental factors to standard values. Signaling devices are used to control pressure, height, distance, crane boom, temperature, relative humidity and air speed, the content of harmful substances in it, sound pressure level, rotation frequency, vibration parameters and T-, etc.

According to the alarm device, they are divided into external (side lights, brake lights, direction indicators, reversing lights, etc.) and internal (control lamps for oil pressure in the engine, battery charge, turning on the headlights, opening doors, etc.). speedometer, tachometer, air pressure gauge in the pneumatic brake system, etc.); according to the principle of operation - on sound (sirens, whistles, buzzers, bells, melodies, beeps), visual (light, color, signs, inscriptions), odorization (carried out using special sensors that detect changes in odors) and combined; by the nature of the signal transmission - to continuous and pulsating; by appointment - for informational, warning, emergency and response; by the method of operation - to automatic and semi-automatic.

The most common are light and sound alarms. Light signaling is used as one of the main means of ensuring safety on motor vehicles. It serves to warn drivers and pedestrians about maneuvers made by this or that vehicle, tractor or other mobile machines. In electrical installations, a light alarm notifies about the presence or absence of voltage, the normal mode of automatic lines.

Sound signals are supplied to lifting and transport installations; units serviced by a group of workers; complex agricultural machines with a large number of operating parameters, simultaneously controlled by the operator, etc. For example, a sound signal is automatically turned on on combine harvesters when the drum of a thresher or auger is clogged. When the unit is being serviced by several workers, a signal is generated when the unit is turned on to warn them that they are taking appropriate safety measures. Sound alarms are used to alert workers about reaching the maximum permissible liquid level in any tank, the maximum temperatures and pressures in various installations, as well as about exceeding the maximum permissible concentrations or levels of harmful production factors.

In manual production, a worker directly performs technological operations on a machine, often in contact with moving and rotating parts and assemblies. To prevent accidents, the equipment must be equipped with various protective, protective and safety devices.

These devices are used to prevent accidental entry of a person into the dangerous area of the equipment: various fences of moving parts, fences of the cutting zone, safety interlocks, forced protection against accidental start-up of the machine, etc. Regardless of the type of fence, its purpose and design, it must be simple and durable, reliably cover the hazardous area and can be easily removed for repairs.

Protective and safety devices are made in the form of rigid covers, casings, shields or nets on a rigid frame, organically connected to the main parts of the machine into a single structure. In modern machine tools, presses and other equipment, all moving and rotating parts are located inside the beds, housings and boxes, and there is no need to install any additional fences. For intermediate links of machines (belt transmission of couplings, shafts, etc.), stationary or movable solid, mesh or lattice fences are used.

A movable fence, for example, is installed on the protruding ends of a shaft or screw in the event that the length of their overhang changes during operation within significant limits. A movable fence is made in the form of a telescopic casing or a spiral spring. Often, fences are made interlocked with the mechanisms for starting and stopping the equipment: in this case, the machine can only work if the fence is in the working position. When the fence is open, a special device stops the movement of certain parts of the machine. The interlocking device is most often a system of contacts that close or open the power supply circuit with electric current of certain working bodies.

For equipment, during the operation of which it is possible to fly off metal fragments, shavings, scraps, sparks, splashes of coolant, special safety devices are provided to ensure the safety of workers. Such devices are most often made removable or folding in the form of transparent shields or screens for easy monitoring of the process.

The greatest danger when working on metal-cutting machines is represented by flying off chips, therefore, much attention is currently paid to its safe removal. Many methods of protection against swarf are known from the practice of machine-building plants. These include: the use of safety glasses; individual shields and screens installed on the machine; equipment of cutting tools with chip breakers, chip winders and chip removers, etc.

Goggles, individual head nets are such means of protection that do not depend on the shape of the chips, the direction of their flight and the design of the machine. Their main disadvantage is that they constrain the worker (his work area, observation area, etc.), are inconvenient, take time to install and, most importantly, are not structurally connected with the machine, which leads to rare use of them. The most acceptable means of protection against chips should be considered such devices that ensure their safe removal from the processing site. Structurally, such devices can be of three types.

1. Design of machine tools with inclined or 180 ° rotated supports, which ensure the removal of chips to the rear walls, while the chips are removed in the opposite direction from the working side.

2. The use of devices that use the kinetic energy of the chips for its removal. A box-shaped attachment, mounted on the cutter, catches the chips and, using its kinetic energy, directs the chips to a safe area. Such devices are additionally equipped with suction devices that allow shaving and dust to be removed outside the machine and exclude the possibility of dusting the air in the workshop.

3. Equipping the equipment with shields and screens of various shapes and sizes. Such barriers are an obstacle to the flow of chips to the workplace. Reflecting from the screen, the chips fall into a safe area. As a rule, such a fence should be constructively connected with the machine and satisfy a number of requirements, in particular, isolate the worker from the danger zone as much as possible, be automatically set according to the size of the processed parts, not worsen the working conditions (conditions for monitoring the process, do not reduce labor productivity, quality and cleanliness of processing, etc.), differ in simplicity and safety during maintenance, commissioning and adjustment, have sufficient strength, be combined with a waste disposal system, be interlocked with the mechanisms for starting and braking the machine, etc.

Shields and screens as a means of protection are used in mechanical engineering not only on machine tools, but also on presses, furnaces and other equipment. Screens or reflectors to reduce heat radiation through open windows near reheating ovens also obstruct the flow of radiant energy to the workplace. Similar methods of protection are used to protect the worker from sparks and dross in forging and foundries; from ionizing radiation when working with radioactive substances; from the harmful effects of ultraviolet rays, electromagnetic fields. The design of these protective equipment depends not only on the nature of the hazard or hazard, but also on the design of the equipment. If, for example, a water curtain with a thickness of 1-2 mm, acting as a screen near a heating furnace, completely absorbs radiant heat, then for a powerful radioactive emitter, a concrete partition with a thickness of 1 m or more is required.