Instruments and safety devices
Crane safety devices and devices must comply with these Rules, state standards and other regulatory documents.
Cranes must be equipped with working movement limiters for automatic stop:
a) the lifting mechanism of the load gripping body (except for electric hoists equipped with a limit torque clutch) in its extreme upper and lower positions. The limiter of the lower position of the load gripping body may not be installed if, according to the operating conditions of the crane, it is not required to lower the load below the level indicated in the passport;
b) departure change mechanism;
c) the mechanism for moving rail cranes (with the exception of railway cranes) and their cargo trolleys, if the speed of the crane (trolley) when approaching the extreme position may exceed 30 m / min. Movement mechanisms of tower, gantry cranes and overhead loader cranes must be equipped with limiters, regardless of the speed of movement;
d) travel mechanisms for overhead, gantry, cantilever, portal cranes or their cargo trolleys operating on the same crane runway.
These devices should also be installed if it is necessary to limit the stroke of any mechanism, for example, the turning mechanism, extending the telescopic section of the boom or sections during the installation of the crane, mechanisms of the load gripping body, lifting the cabin.
2.12.3. Limit switches installed on the crane must be switched on so that the possibility of movement of the mechanism in the opposite direction is provided. Further movement in the same direction is allowed:
for the movement mechanism of the overhead crane - when approaching the landing site or dead end stop at the lowest speed provided by the electric drive;
for the mechanism for lowering the boom of the jib crane into the transport position (without load).
2.12.4. The limiter of the lifting mechanism of the load or boom must ensure that the load gripping body stops when lifting without load and the gap between the load gripping body and the stop for electric hoists is at least 50 mm, for other cranes - at least 200 mm. At a load lifting speed of more than 40 m/min, an additional limiter must be installed on the crane, which operates before the main limiter, switching the scheme to a reduced lifting speed.
2.12.5. For clamshell cranes with a separate drive for lifting and closing winches, the limiter (limiters) must (should) turn off both engines simultaneously when the grab reaches the uppermost position.
2.12.6. The limiters of the movement mechanisms must ensure that the engines of the mechanisms are turned off at the following distance to the stop:
for tower, gantry, gantry cranes and bridge loaders - not less than the full braking distance;
for other cranes - at least half of the braking distance.
When installing mutual travel stops for travel mechanisms of overhead and jib cranes operating on the same crane track, the specified distance can be reduced to 500 mm. The braking path of the mechanism must be indicated by the manufacturer in the crane passport.
2.12.7. Boom-type cranes (except for cantilever cranes) must be equipped with a load capacity (load moment) limiter that automatically disables the mechanisms for lifting the load and changing the reach in the event of lifting a load whose mass exceeds the carrying capacity for a given reach by more than:
15% - for tower cranes (with a load moment of up to 20 tons inclusive) and portal cranes;
10% - for other cranes.
For cranes with two or more load characteristics, the limiter must have a device for switching it to the selected characteristic.
2.12.8. Overhead cranes must be equipped with load limiters (for each cargo winch), if their overload is possible according to the production technology. Cranes with a load capacity variable along the length of the bridge must also be equipped with such limiters.
The load limiter of bridge type cranes should not allow overload by more than 25%.
2.12.9. After the load limiter has been triggered, it should be possible to lower the load or engage other mechanisms to reduce the load moment.
2.12.10. Jib cranes must be equipped with working movement limiters to automatically disable the mechanisms for lifting, turning and extending the boom at a safe distance from the crane to the power line wires.
2.12.11 Bridge-type cranes with a lifting capacity of more than 10 tons and a classification (mode) group of at least A6 according to ISO 4301/1, tower cranes with a lifting capacity of more than 5 tons, portal, railway and jib cranes must be equipped with recorders of their operation parameters. Tower cranes with a lifting capacity of up to 5 tons inclusive must be equipped with devices for recording operating hours in engine hours.
To prevent their collision with obstacles in cramped working conditions, jib cranes must be equipped with coordinate protection.
Cranes, except for those controlled from a pendant console, must be equipped with an audible signaling device, the sound of which must be clearly audible in the crane operation area. When controlling the crane from several posts, the signal must be turned on from any of them.
Gantry cranes and overhead loader cranes must be designed for the maximum possible skew force that occurs during their movement, or equipped with an automatic skew limiter.
For cranes with electric drive, except for cranes with electric hoists having a second load-resistant brake, protection against the fall of the load and boom should be provided in the event of a break in any of the three phases of the power supply network.
Bridge-type cranes must be equipped with a device for automatic stress relief from the crane when entering the gallery. For cranes operating indoors, trolleys with a voltage of not more than 42 V may not be turned off.
Overhead cranes, the entrance to which is provided through the gallery of the bridge, such a blockage must be equipped with an entrance door
to the gallery.
2.12.17. The door for entering the control cabin, moving with the crane, from the side of the landing site must be equipped with an electric interlock that prohibits the movement of the crane when the door is open.
If the cabin has a vestibule, then the vestibule door is provided with such a lock.
For magnetic cranes, the electrical circuit must be designed so that when the voltage is removed from the crane by the contacts of the devices and safety devices, the voltage from the cargo electromagnet is not removed.
For tower cranes with a fixed tower and for other cranes, when the cab is located on the rotary part of the crane, to prevent the possibility of people being pinched when moving from the rotary part to the fixed part, a device must be provided that automatically turns off the motor of the turning mechanism when the hatch or door is open.
2.12.20. Cranes whose lifting capacity varies with the overhang must be provided with a load capacity indicator corresponding to the overhang. The scale (board) of the load indicator must be clearly visible from the workplace of the crane operator (driver). The load indicator may be part of the electronic load limiter.
When graduating the scale of the crane load capacity indicator, it is necessary to measure the reach on a horizontal platform with a load on the hook corresponding to a certain reach, and make a mark on the scale after removing the load.
In the cabin of the jib crane, indicators of the angle of inclination of the crane (inclinometers, signaling devices) must be installed. In the case when the crane outriggers are controlled outside the cab, an additional indicator of the crane inclination angle must be installed on the fixed frame of the crane.
Tower cranes with a height of more than 15 m to the top of the tower head, gantry cranes with a span of more than 16 m, portal cranes, overhead loader cranes must be equipped with a device (anemometer) that automatically turns on the sound signal when the wind speed specified in the passport for working condition is reached crane.
The installation locations of the device should be selected in accordance with regulatory documents.
2.12.23. Cranes moving along a crane track in the open air must be equipped with anti-theft devices in accordance with regulatory documents.
Overhead cranes operating in the open air may not be equipped with anti-theft devices if, when the crane is exposed to the maximum allowable wind speed, taken in accordance with GOST 1451 for the non-operating state of the crane, the value of the braking margin of travel mechanisms is at least 1.2 according to regulatory documents.
When using rail grips as an anti-theft device, their design must allow the crane to be fixed along the entire path of its movement.
Anti-theft devices with a machine drive must be equipped with a device for manually actuating them.
Cranes moving along the crane track, and their trolleys, to mitigate a possible impact on the stops or on each other, must be equipped with elastic buffer devices.
Cranes (except for electric hoists) and cargo trolleys moving along the crane track must be equipped with supporting parts in case of breakage of wheels and axles of running gear.
For monorail vehicles with trailer cab, the support parts must be installed on the cab undercarriage. When the cab and lifting mechanism are suspended from a common frame, the supporting parts are installed on each undercarriage.
The supporting parts must be installed at a distance of no more than 20 mm from the rails (riding beams) along which the crane (trolley) moves, and must be designed for the greatest possible load on these parts.
2.12.28. Luffing jib cranes with flexible jib suspension must be equipped with stops or other devices to prevent the jib from tipping over.
For tower cranes, such devices must be installed if, with a minimum reach, the angle between the horizontal and the boom exceeds 70 °.
General conditions for the protection of electrical equipment on cranes from emergencies
According to their purpose, the specifics of work and design features, cranes belong to the category of equipment with increased danger, which is explained by the very process of operation of these mechanisms on sites and in rooms where people and valuable equipment are located at the same time.
General requirements for the safety of cranes and crane electrical equipment are formulated in accordance with the "Rules for the Design and Safe Operation of Hoisting Cranes" and the "Rules for the Construction of Electrical Installations".
All electrical equipment located in the crane control cabins is provided with grounded metal casings or must be completely closed from the possibility of touching live parts. The control cabin must also contain a device that provides direct or remote shutdown of all supply cable routes run through the crane, with the exception of input devices.
Access to the crane platforms, where electrical equipment, trolleys not protected by casings are located, can only be carried out through doors and hatches that have a lock that turns off the power to all power sources of the crane.
The section of the main trolleys, the main pantographs and current leads that remain energized when all intra-crane wiring is turned off. must be securely guarded against accidental contact. This fence must have a lock with an individual key.
Repair and inspection of current leads can only be carried out when the power to the main trolleys or the common input device located outside the crane is turned off. The chains of several cranes are fed from general workshop trolleys, then a repair site is provided where the trolleys can be turned off without interrupting the power of the remaining cranes.
Cranes are moving installations and are subject to vibrations and shocks during movement, so the possibility of damage to cables and wires on cranes is relatively higher than when they are stationary. In addition, on a number of cranes, the current transfer to moving parts is carried out using flexible hose cables, damage to which cannot be completely ruled out. With this in mind, the first task of protection is to protect electrical equipment on cranes from short-circuit currents.
Short circuit currents in individual circuits within the crane will be the smaller, the smaller the cross-section of the installation wires of these circuits and the smaller the sizes of various current junctions and current connectors. Maximum short-circuit currents in control circuits with a wire cross section of 2.5 mm2 are 1200-2500 A. At the same time, fuses of the PR series for currents of 6-20 A or any types of automatic switches AP 50, AK 63, etc. can be used to protect the circuits. h., A, in the circuits of electric motors approximately, can be determined by the formula
where I kzyuf - short-circuit current in the supply phase, line after 0.04 s; s p - wire section in the considered circuit, mm2.
Since the current k. e. should not destroy the switching device located in this circuit until it is turned off, then it is necessary to observe certain ratios when choosing devices and wire sections that ensure the thermal stability of the device. Assuming that the thermal resistance of most devices used in the crane electric drive is 10I n for 1 s, then the ratio between the maximum allowable wire section, mm2, and the rated current of the device should be as follows:
where I n - rated current of the device, A.
The last relation shows that at possible short-circuit currents. on a feeder with more than 8000 A, it is unacceptable to install devices for 25 A due to thermal stability. Devices for currents of 63 A can only be used with cable sections not exceeding 6 mm2, and devices for current 100 A - with cable sections not exceeding 16 mm2.
With possible currents, short circuit 12,000 A (limit for cranes) devices for currents of 63 A can only be used with cable sections of not more than 4 mm2, i.e., with rated currents up to 30 A. Devices for a current of 100 A can be used with cable sections of not more than 10 mm2, i.e. at rated currents up to 60 A. Thus, for cranes powered by feeders of especially high power, it is necessary either to install devices for currents not lower than 100-160 A, or to limit the wire cross-sections to these devices in order to reduce possible currents k.z.
Protection of the cable network of the crane from short-circuit currents. is carried out using an instantaneous overcurrent relay, and, if necessary, can be carried out by setting machines.
Protection of wires against short circuit currents complicated by a large range of capacities of electric motors of mechanisms within one crane. In accordance with the rules for the installation of electrical installations, protective devices must be designed for a tripping current not exceeding 450% of the continuous current of the protected circuit. The same rules for wires and cables operating with an intermittent load, the allowable heating current is determined by the expression
Where I pv and I n - rated currents of the cable in intermittent and continuous modes of operation.
At PV=40% I pv \u003d 1.4 x I n. Thus, the multiplicity of the protection setting to the allowable current of the wire (cable) should not exceed 450/1.4=320% of the current in the 40% duty cycle mode. Permissible loads on wires and cables within the crane at an ambient temperature of 45 ° C are given in the reference tables.
Crane electric drives have the following main types of protective devices:
Maximum protection for disconnecting the electric drive from the network in case of unacceptable currents in the protected circuit;
Zero protection to turn off the drive when the power supply from the power source is interrupted or interrupted. A variation of zero protection is zero blocking, which excludes self-starting of the electric motor when power is restored to the supply line, if the control is in the working position
End protection to prevent movement of moving structures beyond certain allowable limits.
An important task of the protection system is to prevent unacceptable overloads for all types of electric drives of crane mechanisms associated with a malfunction of control circuits, jamming of mechanisms, an open brake circuit, etc. This is the difference between the requirements for protection against overloads of crane electric drives from overload protection for electric drives of continuous modes .
Due to the uncertainty of the load of crane mechanisms, changing rates of heating of engines, their operation under conditions of frequent starts and stops, it is not even possible to set the task of protecting electric drives from thermal overloads. The only condition for preventing thermal overloads of crane electrical equipment is its correct choice, taking into account any pre-calculated operating modes possible in operation.
Thus, overload protection is reduced to control of the starting current during step starting and protection against jamming of short-circuited motors or electric drives with current cutoff. With a properly organized start of the electric drive with step acceleration, the starting current should not exceed 220-240% of the current corresponding to the calculated value.
Taking into account the necessary margin for the spread of both the starting current and the setting of the maximum relay, the latter should be designed to operate at a current of about 250% of the calculated one, which can be equal to or less than the motor current in the PV = 40% mode.
According to the above, the maximum current relay in the system of crane electric drives has two functions:
1. protection against short circuit currents. wires (cables) in each pole on direct current and in each phase on alternating current,
2. overload protection, to ensure which it is enough to turn on the relay in one of the poles or one of the phases.
In accordance with the rules, the electric drives of cranes must have, i.e., during a power outage, the electric drive must be turned off, and it can be turned on again only after the control body returns to the zero position. This requirement does not apply to push-button systems from the floor that have self-resetting push-buttons.
The presence of zero blocking excludes the self-starting of the electric drives of cranes, and also excludes re-enabling when various protections are triggered.
Phase failure protection on taps is not applied. An analysis of the possible consequences of phase failure outside the crane and an acceptable phase failure protection system showed that, on the one hand, there is currently no satisfactory technical solution for the use of a reliable, cheap and simple phase voltage monitoring device, and on the other hand, phase failure in inside and outside the tap is unlikely due to the fact that the use of fuses in the main circuit is not currently practiced.
New dynamic braking systems, which are used instead of reverse braking, minimize the risk of falling loads due to phase failure.
Overload protection relay in the crane electric drive
To protect the circuits of crane electrical equipment from overloads, an instantaneous electromagnetic relay of the REO 401 type is used. These relays can be used both in AC and DC circuits. The relay has two designs. On fig. 1 shows a general view of the REO 401 relay.
The relay consists of two main units: an electromagnet 2 and a breaking auxiliary contact 1. The electromagnet coil 3 is located on the tube 4, in which the armature 5 moves freely. The position of the armature in the tube is adjustable in height and determines the value of the relay actuation current. With an increase in the current in the coil above the tripping current, the armature rises and opens the contacts through the pusher of the contact assembly.
In the second version, two to four relay electromagnets are mounted on a common base, which also has a common bracket that transmits the forces of any individual electromagnet armature to an auxiliary contact installed on the base. Thus, in this design, several electromagnets act on one auxiliary contact.
After the current is turned off, the armature returns under its own weight. The relay has one NC auxiliary contact. The auxiliary contact is rated for AC switching up to 10 A at 380 V and or for DC switching 1 A at 220 V and L/R = 0.05
Rice. one . General view of the REO 401 relay
Relay coils for currents over 40 A are made of bare copper. The conclusions of these coils are located on a special insulating panel. Coils for currents up to 40 A - isolated. When choosing a relay to install in. complete devices should be guided by the permissible load of the coil in the duty cycle = 40% and the operating range, taking into account the necessary trip settings.
REO 401 relays can perform their functions provided that the starting current of the electric drive is less than the current of the stalled electric motor when it is turned on at the rated voltage, i.e. protection of short-circuited electric motors and electric drives with current cutoff using the REO 401 relay is not possible. The protection of such electric motors must be carried out using the TPT thermal series.
TRT relays have five dimensions in the current range from 1.75 to 550 A. Relays of all types are enclosed in a plastic casing and differ in the shape of the reacting thermal element, the presence of an additional heater and the size of the leads. The relay of the fifth dimension is mounted on a current transformer. As a reacting thermal element of the relay, a bimetal invarstal is used, streamlined by current and additionally heated by a heater. The relay has one NC contact rated for AC 10 A, 380 V at Cos φ = 0.4 and DC 0.5 A, 220 V at L/R = 0.05.
Technical data of the TRT relay are given in the reference books. The time characteristics of the TRT series relays are shown in fig. 2. The relay does not operate at a current of 110% of the rated current in continuous mode. At a current of 135% of the rated relay, it operates in 5-20 minutes. At a current of 600% of the rated relay, it operates in 3 to 15 s. The regulator available on the relay allows you to adjust the rated current of the setting within ± 15%. The relay contacts return to the on state in 1-3 minutes after the current is turned off.
When choosing a relay, you should be guided by the conditions:
1) RMS current of the protected circuit must not exceed the rated current of the heater;
2) with three starts in a row, the relay should not work;
3) the operating time at the starting current should not be higher than the allowable time of the electric motor standing under current in this mode.
When using the time characteristic of the operation of the TRT relay, it should be taken into account that the possible actual deviations of the operation current are about ± 20% of the setting current.
Protective panels
In accordance with the requirements, each crane must be equipped with a device designed to supply power to the electric drives of the mechanisms and turn it off, and switching on, that is, power supply, can be carried out after unlocking the enabling device using an individual brand key.
Rice. 2. Timing characteristics of the TRT series relays.
In turn, the key cannot be removed without performing a trip operation. This interlock ensures that the crane is brought into a usable condition only by a person authorized to operate the crane.
On all types of electric cranes, except for construction tower cranes, an individual brand key is used in. For construction tower cranes, the specified key is used to block the main switch (or machine) in the tower crane power cabinet, to which the flexible power cable is connected.
Rice. Fig. 3. Diagram of control circuits of protective panels: a - when controlling cam controllers; b - when controlling magnetic controllers; 1P-ZP - fuses; KB - "return" button; KL - hatch contact; AB - emergency switch; L - linear contactor: MP1, MP2 - contacts of maximum relays; KVV, KVN - limit switches; PP - check switch; K12 - zero contacts of controllers.
Occupational safety at urban construction and economy when using cranes and hoists.
Educational-methodical, practical and reference manual.
Authors: Roitman V.M., Umnyakova N.P., Chernysheva O.I.
Moscow 2005
1. OCCUPATIONAL HAZARDS WHEN USING CRANES AND LIFTS.
1.1. The concept of industrial hazard.
1.2. Dangerous zones at the construction site.
1.3. Examples of characteristic accidents and accidents associated with the use of cranes and hoists.
1.4. The main causes of accidents and accidents when using cranes and hoists.
2. GENERAL ISSUES OF LABOR SAFETY WHEN USING CRANES AND LIFTS.
2.1. General condition for ensuring labor safety.
2.2. Regulatory bases for ensuring labor safety when using cranes and hoists.
2.3. The main tasks of ensuring labor safety when using cranes and hoists.
3. ENSURING WORK SAFETY WHEN USING CRANES AND LIFTS.
3.1. Selection of cranes and their safe binding.
3.1.1. Crane selection.
3.1.2. Cross-tie of cranes.
3.1.3. Longitudinal binding of tower cranes.
3.2. Determination of the boundaries of hazardous areas of operation of cranes and hoists.
3.3. Ensuring labor safety in hazardous areas of cranes and hoists.
3.3.1. Instruments and safety devices installed on cranes.
3.3.2. Ensuring safety when installing cranes.
3.3.3. Protective grounding of crane tracks.
3.3.4. Ensuring safety in the joint operation of cranes.
3.3.5. Ensuring safety when using lifts.
3.4. Measures to limit the dangerous zone of the crane.
3.4.1. General provisions.
3.4.2. Forced restriction of the crane operation area.
3.4.3. Special measures to limit the danger zone of the crane.
3.5. Ensuring labor safety when installing cranes near power lines.
3.6. Ensuring labor safety when installing cranes near recesses.
3.7. Ensuring safety in the storage of materials, structures, products and equipment.
3.8. Ensuring safety during loading and unloading operations.
4. SOLUTIONS TO ENSURE LABOR SAFETY IN ORGANIZATIONAL AND TECHNOLOGICAL DOCUMENTATION (PPR, POS, etc.) WHEN USING CRANES AND LIFTS.
4.1 General provisions.
4.2. Stroygenplan.
4.3. Technological schemes.
3.3. Ensuring labor safety in hazardous areas of cranes and hoists.
3.3.1. Instruments and safety devices installed on cranes.
Safety instruments and devices are designed to automatically turn off the units and mechanisms of the crane when any parameter characterizing the operating mode of the equipment deviates beyond the permissible values.
The main instruments and safety devices installed on cranes include (Fig. 3.7):
- load limiters (load moment);
- boom limiters;
- Limit switches;
- hook lift limiters;
- limiters for turning the rotating part of the crane;
- anemometer;
- anti-theft devices, outriggers, brakes, fencing, galleries, platforms and stairs.
Crane movement limiters must be installed in such a way that the engine of the movement mechanism is turned off at a distance not less than the braking distance to the dead end stop.
To dampen the residual speed of the crane and prevent it from leaving the end sections of the crane track in emergency situations, in case of failure of the limiter of movement or the brakes of the crane movement mechanism, dead ends must be installed at the ends of the rail track (at a distance of at least 0.5 m) 12 (Fig.3.7.).
The stops must be installed in such a way that the crane hits the stops at the same time. When installing dead ends, it is necessary to take into account the distance from the ends of the track, the dimensions of the dead ends, the distance between the paired dead ends for heavy cranes and the distance between the dead ends and the dimensions of the crane located in the extreme parking lot at the dead end.
Boom limiters are used to automatically turn off the mechanism that provides a change in the reach of the boom 5 (Fig.3.7.) when the boom reaches the maximum or minimum working reach.
Hook height limiter 3 , 4 (Fig. 3.7.) serves to automatically turn off the hook lifting mechanism when it approaches the upper extreme position. This limiter consists of a switch 4 and cargo 3 with two guide brackets, in which the branches of the cargo rope are inserted. When the load suspension rests against the load 3 and lifts it, the switch lever released from the load 4 , opens the contacts of the electrical supply of the hook lifting mechanism.
Turn limiter 7 (Fig.3.7.) of the rotating part of the crane serves to prevent the rotation of the rotary part of the crane in one direction more than two times, in order to prevent breakage of current-carrying wires when one end of these wires is fixed on the running frame, and the other - on the rotary part crane.
Anemometer 1 (Fig.3.7.) is designed to automatically determine the wind speed at which work stops and emergency devices are turned on. Anemometer 1 connected to the dashboard in the crane operator's cab. Light and sound alarm system 6 responds to an increase in wind strength to the maximum permissible value and to excess wind speed of the permissible value.
Rice. 3.7. Instruments and devices that ensure the safe operation of a tower crane.
1
– anemometer; 2
- sensor - load limiter force; 3
– load of the hook lifting limiter; 4
– switch of the hook lifting height limiter; 5
– boom angle sensor; 6
- sound signal; 7
- limit switch for the turret rotation limiter; 8
– limiter signaling panel; 9
– relay block of the limiter of loading capacity; 10
– limit switch of the limiter of movement of the crane; 11
- inventory track line; 12
- dead end stop.
Instruments and safety devices
| Parameter name | Meaning |
| Article subject: | Instruments and safety devices |
| Rubric (thematic category) | Sport |
Overhead crane safety devices and devices are designed to prevent overloading of the crane and ᴇᴦο mechanisms, derailment from the crane track as a result of random factors, inattention and inefficiency of the driver; disabling the crane mechanisms in emergency situations, as well as to protect operating personnel from electric shock, falling from a height, etc.
Two types of safety devices are used in overhead cranes: limiters and signaling devices.
Limiters are the main safety devices that automatically turn off the mechanism or group of crane mechanisms in the event of a dangerous load or violation of safe operation conditions. There are limiters for carrying capacity, lifting heights, paths for the movement of the cargo trolley and the bridge, and skew of the bridge (in overhead cranes with a large span). The contacts of the limit switches of the limiters are included in the crane control circuit. Resuming the operation of the disconnected mechanism is only possible to return the working body (cargo, trolley, bridge) to a safe position. For example, after disengaging the load lifting mechanism as a result of attempting to lift a load that is 25% more than the crane's rated capacity, the mechanism should only be engaged to lower the load. In the event that the load lifting height limiter is activated, when the distance between the top of the hook suspension and the bottom of the cargo trolley becomes 200 mm, the load lifting mechanism can also be switched on only for lowering the load.
In order to prevent the bridge or cargo trolley from derailing from the track, end stops are installed at the ᴇᴦο ends, which take up loads when stopped. To mitigate a possible impact, the bridge and the cargo trolley are equipped with buffers with shock absorbers.
Overhead crane signaling devices are audible signaling devices designed to notify maintenance personnel about the start of any operation.
Chapter 4 test questions˸
1. Tell the scope of overhead cranes.
2. What is the main parameter of the overhead crane?
3. List the main parameters of overhead cranes.
4. List the main mechanisms of overhead cranes.
5. How are overhead crane designs different?
6. List the devices and safety devices for overhead cranes.
7. Tell the principle of operation of the overhead crane load limiter.
TOWER CRANES
Safety devices and devices - concept and types. Classification and features of the category "Safety devices and devices" 2015, 2017-2018.
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