What are the safety protection devices of the crane

In order to ensure the crane safety and reliability of lifting operation, the crane is equipped with perfect safety devices to protect parts or remind operators to pay attention in case of accidents, so as to play the role of safety protection.

Each overflow valve in the hydraulic system: it can inhibit the abnormal high pressure in the circuit to prevent damage to the hydraulic oil pump and motor and overload.
Boom luffing crane safety device: when an accident occurs and the high-pressure hose or oil pipe in the boom luffing cylinder circuit is burst or cut off, the balance valve in the hydraulic circuit will work to lock the working oil from the lower chamber of the cylinder so that the boom will not fall, so as to ensure the crane safety of operation.
Boom telescopic crane safety device: when an accident occurs and the high-pressure hose or oil pipe in the boom telescopic oil cylinder circuit is burst or cut off, the balance valve in the hydraulic circuit will work to lock the working oil from the lower cavity of the oil cylinder, so that the crane will retract itself, so as to ensure the crane safety of operation.
Height limit device: after the hook is lifted to the specified height, touch the limit weight, turn on the travel switch, and the "over winding" indicator light will be on. At the same time, cut off the operation of hook lifting, boom extension, boom falling to ensure crane safety.
Outrigger locking device: when an accident occurs and the high-pressure hose or oil pipe leading to the outrigger vertical oil cylinder is broken or cut, the two-way hydraulic lock in the hydraulic system can block the outrigger and block the pressure oil in the two cavities of the oil cylinder, so that the outrigger will not shrink or throw out, so as to ensure the crane safety of lifting operation.
Lifting indicator: the lifting indicator is set on the closing side of the basic boom (i.e. the right side of the control room), which can be clearly observed by the operator sitting in the control room, and can accurately indicate the elevation angle of the boom and the allowable rated lifting capacity of the crane under corresponding working conditions.
Lifting characteristic table: it is set on the front lower wall panel in the control room. The table lists the rated lifting capacity and lifting height under various arm lengths and operating ranges for reference during operation. During lifting operation, the value specified in the table shall not be exceeded.

Safety protection device and function of crane

1. Overload limiter

It is a crane safety protection device for crane to prevent overload, also known as lifting weight limiter. Its safety function is to stop the lifting action when the lifting load of the crane exceeds the rated value, so as to avoid overload accidents. Overload limiter is widely used in bridge type cranes and elevators. Some jib type cranes (e.g. tower cranes, portal cranes) use overload limiters in conjunction with moment limiters. Overload limiters are of mechanical and electronic types.

(1) Mechanical type: the impact bar is driven by the action of lever, spring and cam. When overloaded, the impact bar acts with the switch controlling the lifting action to cut off the power source of the lifting mechanism and control the lifting mechanism to stop operation.
(2) Electronic type: it is composed of sensor, operational amplifier, control actuator and load indicator, integrating crane safety functions such as display, control and alarm. When the crane lifts the load, the sensor on the bearing member deforms, converts the load weight into an electrical signal, and indicates the value of the load after calculation and amplification. When the load exceeds the rated load, cut off the power source of the lifting mechanism, so that the lifting action of the lifting mechanism cannot be realized.

2. Torque limiter

Moment limiter is a comprehensive safety protection device for jib crane.

We know that the jib crane is characterized by the lifting moment of gravity. The lifting moment value is determined by the product of the lifting weight and amplitude, and the amplitude value is determined by the product of the boom length of the crane boom and the cosine of the inclination angle. In this way, whether the crane is overloaded is actually limited by the lifting weight, boom length and boom inclination angle. At the same time, it should also consider that many parameters such as operating conditions also have restrictive effects, which is more complex to control.

At present, the widely used microcomputer controlled torque limiter can integrate many situations and solve this problem better. The moment limiter is composed of load detector, arm length detector, angle detector, working condition selector and microcomputer. When the crane enters the working state, the detection signals of various parameters in the actual working state are input into the computer. After calculation, amplification and processing, they are compared with the pre stored rated lifting moment value, and the corresponding actual values are displayed on the display at the same time. When the actual value reaches 90% of the rated value, it will send an early warning signal. When the actual value exceeds the rated load, it will send an alarm signal. At the same time, the crane stops moving in the dangerous direction (lifting, boom extension, boom lowering and slewing).

Crane moment limiter

3. Buffer

It is a crane safety device arranged at the end of the metal structure of the track running crane. It has the safety function of absorbing the collision kinetic energy of the running mechanism and reducing the impact. The main indicators of buffer safety inspection are whether the installation is firm and reliable, whether the components are intact and the ability to absorb kinetic energy.

The working principle of the buffer is that if the crane (or trolley) of a single crane accidentally rushes to the end of the track travel, the buffer can interact with the track end stop (another crane safety device) at the same horizontal height; If two cranes on the same span track collide, it will act on the buffer set on the opposite surface of the metal structure of the two cranes. Through its own deformation, the buffer quickly converts the collision kinetic energy into elastic potential energy for absorption, so as to reduce the impact of the collision force and avoid damage to the crane. Common are rubber buffer, spring buffer and hydraulic buffer.

(1) Rubber buffer: use the elastic deformation of rubber during collision to realize buffer. Due to less energy absorption, it is generally used in cranes with low moving speed.
(2) Spring buffer: it can quickly convert most of the impact kinetic energy into the compression potential energy of the spring. It is suitable for cranes with medium movement speed and is most widely used. The utility model has the advantages of simple structure and great impact on the crane. However, now through technical means, its performance has been greatly improved.
(3) Hydraulic buffer: it uses the oil squeezed by the cylinder piston to work to consume the kinetic energy when impacted. It is suitable for cranes with higher moving speed. The advantage is that it can absorb greater impact kinetic energy and has no rebound effect; The disadvantage is that the structure is complex, the ambient temperature has a great impact on the oil performance, and the function of the buffer will be affected.

4. Windproof and antiskid safety device

This is a crane safety device to prevent cranes working outdoors from sliding along the track under the action of strong wind. Rail cranes working outdoors shall be installed. Its safety function is that when the crane encounters the maximum wind force in non working state, the crane will not be blown to prevent the crane from overturning at the end of the track. Common windproof devices include rail clamp, anchor device and iron shoes.

(1) Rail clamp: it is widely used in all kinds of outdoor rail cranes. Its working principle is to clamp the two sides of the rail head with clamps, and fix the crane on the rail through the clamping friction of the joint surface, so that the crane can not slide. The design requirement of the rail clamp is that the clamping force of the rail clamp must be greater than the sliding force of the crane to ensure that the crane remains stationary under the action of the local maximum wind force; The closing of the rail clamping pliers shall depend on the weight of the device components or the action of the spring, rather than only the driving action of the power driving device, so as to prevent the rail clamping device from not working when the power supply is interrupted; The rail clamping action driven by power shall lag behind the action of the brake of the operating mechanism to eliminate the violent vibration that may occur when the crane is braked.
(2) Anchoring device: it connects the crane with the track foundation with the help of bolt or plate device, chain or ejector rod, and is used for fixing the crane in case of severe storm in non working state. Since the anchoring device can only be set at a specific position of the track and the crane can only be anchored when it runs to that position, it is not suitable for immediate wind protection in case of emergency.
(3) Iron shoe: it is a wedge-shaped device. When in use, the tip of the wedge-shaped tongue is inserted between the wheel tread and the top surface of the track. The slope of the iron shoe constitutes the resistance to wheel sliding.

5. Limit position limiter

Also known as travel limiter, its crane safety function is to ensure that when the working mechanism is in motion, when it approaches the limit position, it will automatically cut off the forward power source and stop the movement to prevent travel offside.

The limit position limiter is composed of two interacting parts. One is the contact (bump or safety ruler), which is installed on the moving part of the working mechanism; One is the travel limit switch, which is the master electric appliance that controls the movement direction or travel distance of the working mechanism. It is fixed on the rail at the limit position or the metal structure of the crane and connected in series in the control circuit of the working mechanism. When the movement in a certain direction approaches the limit position, the contact touches the travel limit switch to cut off the control circuit of the movement direction and stop the operation in this direction. At the same time, connect the movement circuit in the opposite direction so that the operating mechanism can only run in the safe direction. The limit position limiters of the crane are:

(1) Lifting limit position limiter: the lifting mechanism and luffing mechanism of all types of cranes shall be equipped with at least one set of lifting limit position limiter. Two sets of lifting mechanisms must be installed for cranes lifting liquid metals and other dangerous goods. The switching actions of the two sets of limiters shall be sequential, and different structural types and different circuit breaker devices shall be used as far as possible.
(2) Falling limit position limiter: its safety function shall ensure that when the spreader falls to the lower limit position, it will automatically cut off the falling power source, so as to ensure that the winding of steel wire rope on the drum is not less than the number of crane safety circles specified in the design. The luffing mechanism of tower or portal crane, the lifting mechanism of Port Portal Crane and other mechanisms with lower limit requirements shall be equipped with lowering limit switch. Whether the lifting mechanism of other cranes is equipped with a falling limit position limiter is not a mandatory requirement.
(3) Operation limit position limiter: the crane (or trolley) operation mechanism of rail crane must be equipped with travel limit switch near the rail end, which is generally used together with the safety ruler of limit switch and trigger switch.

Crane limit position limiter

6. Interlocking protection

Also known as interlocking switch or hatch switch, its safety function is to connect the state of the interlocking switch with the movement of a working mechanism of the crane. In the switch on state, the corresponding working mechanism restricted by it cannot be started. Only in the switch off state, the movement of the interlocked working mechanism can be executed; When the mechanism is moving, if the corresponding hatch switch is opened, the shutdown command will be given. Interlocking protection can prevent a mechanism of the crane from injuring people under specific conditions. The parts requiring interlocking protection and the working mechanism of restriction are as follows:

(1) Between the door of the crane cab from the building and the crane operating mechanism;
(2) Between the hatch door or channel railing door of the bridge girder mounted by the cab and the trolley running mechanism;
(3) When the cab is set at the moving part, it is between the door of the access port to the cab and the trolley running mechanism;

In this way, when someone is stepping into or out of the crane from the building, or when someone is doing equipment maintenance on the main beam of the crane, the driver does not know and operates the crane, so that the operation of the mechanism will hurt people.

7. Zero protection

The hoisting, crane operation and trolley operation of bridge crane are controlled by three operating devices respectively, and zero position protection must be set. Its protection function is that as long as the controller of one mechanism is not in the zero position, all mechanisms cannot be started; The motor of the working mechanism can be started only when the controller of each mechanism is set to the zero position first. The zero position protection is used to prevent the accidental injury caused by the sudden operation of one or more mechanisms when the driver starts the main switch without ideological preparation when the crane starts running or when the power supply is restored after power loss.

8. Emergency switch

All cranes must be equipped with an emergency switch or device that can quickly disconnect the main power supply in case of emergency, and shall be set at a place convenient for the driver to operate.

Interlocking protection, travel limit, zero position protection and emergency switch often play a role in the control circuit of the crane. As long as one device is in an abnormal state, the crane cannot start or stop running in the direction of danger.

9. Deflection adjustment and display device

For long-span gantry crane and loading and unloading bridge, when the outriggers at both ends deflect due to asynchronous forward speed, the device can indicate the deflection and adjust the deflection.

10. Amplitude indicator

Installed on the crane with luffing mechanism, it can correctly indicate the amplitude of the spreader.

11. Level gauge

Installed on the mobile crane, it can check the inclination of the outrigger crane and display the horizontal state of the crane body.

12. Device for preventing boom from tilting back

It is installed on the jib crane of the flexible luffing mechanism. When the luffing travel switch of the luffing mechanism fails, it can prevent the boom from tilting backward.

13. Limit torque limiting device

When the jib rotation resistance moment of the jib crane is greater than the torque specified in the design, the friction elements in the device slide, cut off the power input and stop the rotation movement, so as to play a protective role.

14. Wind level and speed alarm

Installed on cranes working in the open air. When the wind force is greater than level 6, it can send an alarm signal and display the instantaneous wind speed and level. Cranes working in coastal areas can be set to send out alarm signals when the wind force is greater than 7.

15. Outrigger retraction locking device

It is installed on the mobile crane that needs to hit the outrigger during operation. Its safety function is to lock the outrigger in both directions to ensure that the crane will not retract the "soft leg" during the lifting operation; When the crane finishes the lifting operation and the outrigger is retracted, the outrigger can be reliably locked to prevent the outrigger from extending automatically when the crane is running.

16. Rotary positioning device

It is used to ensure that the lifting structure on the rotary table is kept in a fixed position when the mobile crane is driving on the road to prevent swing during driving.

17. Anti tipping safety hook

It is installed on the single main beam crane with the hook on one side of the main beam to prevent the trolley from tipping.

18. Maintenance cage

It is used for the maintenance of conductive sliding wire in high altitude. Its reliability shall not be lower than that of the cab.

19. Rail sweeping plate, support frame and rail end stop

Rail sweeping and support frame are used to remove obstacles on the track in the traveling direction of the crane; The rail end stop is set at the end of the laying rail to cooperate with the buffer on the moving structure of the crane (or running trolley) to prevent the crane (or running trolley) from derailing.

20. Conductive sliding wire protective plate

The protective baffle is used to prevent personnel from accidentally contacting the live sliding wire and causing electric shock accidents. For the crane with sliding wire, the device shall be set for the parts prone to electric shock:

(1) When the bridge crane cab is located at the sliding line end of the crane, a protective plate shall be set between the ladder and platform leading to the crane and the sliding line.
(2) A protective plate shall be set under the end beam at the end along the crane of the bridge crane to prevent accidental contact between the wire rope of the spreader and the sliding wire.
(3) When the same span bridge crane is arranged in multiple layers, the sliding line of the lower crane shall be provided with protective plates along the whole length.

21. Protective cover

The exposed moving parts on the crane, such as open gear, coupling, transmission shaft, sprocket, chain, transmission belt, pulley, etc., shall be equipped with protective shield. For cranes working in the open air, their electrical equipment shall be equipped with rain cover.

22. Reverse alarm device

When the mobile crane runs in the reverse direction, it can send out clear alarm sound signal and light signal between light and off to prompt the personnel behind the machine to avoid quickly.