crane safety protective devices

crane safety protective devices

What are the Protective Devices of the Crane?

Crane safety protective devices refer to the device that prevents the crane from being damaged in an accident. In addition to the commonly used electrical protection devices, sound signals and color lights, there are a variety of other safety devices on the crane.

Overview of crane safety protection device

overload limiter

It is a safety protection device for the crane to prevent overload, also known as a 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 cranes and lifts. Some boom cranes (such as tower cranes, gantry cranes) use overload limiter in combination with torque limiter. Overload limiter has mechanical and electronic types.

Mechanical: The impact rod is driven by lever, spring, CAM, etc., and the impact rod acts with the switch that controls the lifting action to cut off the power source of the lifting mechanism and control the suspension of the lifting mechanism.

Electronic: Composed of sensors, operational amplifiers, control actuators and load indicators, it integrates security functions such as display, control and alarm. When the crane is loaded, the sensor on the load member is deformed, the load weight is converted into an electrical signal, and the value of the load is indicated by the operation and amplification. When the load exceeds the rated load, the power source of the hoist is cut off, so that the lifting action of the lifting mechanism cannot be realized.


Torque limiter

Moment limiter is a comprehensive safety protection device of boom crane.

Boom crane is characterized by the heavy moment of load state. The lifting moment is determined by the product of lifting weight and amplitude, and the amplitude is determined by the product of the cosine of the arm length and Angle of the crane boom. In this way, whether the crane is overloaded is actually limited by the lifting weight, arm length and Angle of the boom, and at the same time, multiple parameters such as working conditions should also be considered, which is more complicated to control.

The moment limiter controlled by microcomputer which is widely used at present can synthesize various situations and solve this problem well. 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 signal of the actual working state parameters is input into the computer, after calculation, amplification, processing, and compared with the rated lifting torque value stored in advance, and the corresponding actual value is 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, and the crane will stop in the dangerous direction (lifting, extending, lowering, turning).



It is a safety device configured at the end of the metal structure of the rail running crane, which has the safety function of absorbing the kinetic energy of the running mechanism and mitigating the impact. The main indicators of the safety check of the buffer 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 large car (or small car) of a single crane accidentally rushes to the end of the track stroke, the buffer can interact with the end stop of the track at a uniform horizontal height; If two cranes on the same span of track collide, the buffer located on the opposite side of the metal structure of the two cranes will act. Through its own deformation, the buffer quickly converts the collision kinetic energy into elastic potential energy absorption, thereby reducing the impact of the collision force and avoiding damage to the crane. Common rubber buffer, spring buffer and hydraulic buffer.

Rubber buffer: The elastic deformation of rubber during collision is used to achieve cushioning. Due to the low energy absorption, it is generally used in cranes with low speed.

Spring buffer: most of the impact kinetic energy can be quickly converted into the compressive potential energy of the spring, suitable for the crane with moderate speed, the most widely used. The advantage is that the structure is simple, and it still has a greater impact on the crane. However, now through technical means of transformation, its performance has been greatly improved.

Hydraulic buffer: Through the cylinder piston to squeeze the oil work to consume the kinetic energy of the impact, suitable for moving faster cranes. The advantage is that it can absorb greater impact kinetic energy and has no rebound effect; The disadvantage is that the structure is complex, and the impact of ambient temperature on the performance of the oil is great, and the function of the buffer will also be affected.

Glory Rail can supply the crane stops and buffers.

We can produce the crane stop according to the customer’s drawings; if you does not have the design scheme, it can be designed for the customer according to customer’s project situation.


Anti-wind and anti-slip safety device

This is a safety device to prevent the crane working in the open air from sliding along the track under the action of strong winds, and the track crane working outdoors should be installed. Its safety function is that when the crane encounters the maximum wind force in the non-working state, the crane is not blown, preventing the crane from overturning at the end of the track. Common windproof devices include rail clamps, anchoring devices and iron shoes.

Rail clamp: It is widely used in all kinds of open-air rail crane, its working principle is to use the clamp to clamp the two sides of the track head, and fix the crane on the track through the clamping friction of the combined surface, so that the crane can not slip. The design requirements of the rail clamp are that the clamping force of the rail clamp must be greater than the sliding force of the crane to ensure that the crane remains motionless under the action of the local maximum wind; The closure of the clamp should rely on the weight of the device component or the action of the spring, and should not only rely on the driving effect of the power drive device, so as to prevent the clamp from working when the power supply is interrupted; The power-driven clamping rail action should lag behind the action of the operating mechanism brake to eliminate the violent vibration that may occur when the crane is braking.

Anchoring device: It connects the crane with the track foundation by means of a latch or plunger device, a chain or a jacking rod, and is used to fix the crane during a large storm in non-working state. Since the anchoring device can only be located in a specific position of the track, the crane must run to the position to anchor, it is not suitable for immediate wind protection in emergency situations.

Iron shoe: It is a wedge device, used to insert the wedge tongue tip between the wheel tread and the top surface of the track, the slope of the iron shoe constitutes a resistance to the wheel sliding.


Limit position limiter

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

The limit position limiter is composed of two interacting parts, one is a contact (bumping block or safety ruler), which is installed on the moving part of the working mechanism; One is the travel limit switch, which is the main command electrical device that controls the movement direction or travel distance of the working mechanism, which is fixed on the track or the metal structure of the crane in the limit position, and is strung in the control line of the working mechanism. When the movement in a certain direction is close to the limit position, the contact contacts the travel limit switch, cuts off the control circuit in the direction of the movement, stops the operation of the direction, and connects the circuit in the opposite direction, so that the operating mechanism can only run in the safe direction. The crane limit position limiter is:

Lifting limit position limiter: the lifting mechanism and amplitude shifter of all types of cranes should be equipped with at least one set of lifting limit position limiter. Lifting of liquid metal and other dangerous goods crane lifting mechanism must be installed two sets, the two sets of limiter switch action should be successively, and should try to use different structural types and control different breaking devices.

Limit position limiter: Its safety function should ensure that when the spreader drops to the lower limit position, the power source of the fall is automatically cut off to ensure that the winding of the wire rope on the drum is not less than the number of safety circles specified in the design. The lifting mechanism of the tower or gantry crane, the lifting mechanism of the port gantry crane and other mechanisms with lower limit requirements should be equipped with a lowering limit switch. Whether the lifting mechanism of other cranes is equipped with a descending limit position limiter is not a mandatory requirement.

Operation limit position limiter: the trolley (or trolley) operating mechanism of the rail crane must be set near the track end of the travel limit switch, which is generally used by the limit switch and the safety ruler of the trigger switch.


Interlock protection

Also known as the interlock switch or the door switch, its safety function is to link the state of the interlock switch with the movement of a working mechanism of the crane, in the switch on state, the corresponding restricted working mechanism can not start, 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 door switch is opened, the stop command is given. Interlock protection can prevent a mechanism of the crane from operating under specific conditions. The parts that need to be protected by interlocking and the working mechanisms that are restricted are as follows:

Between the door of the driver’s cab of the crane and the operation mechanism of the truck;

Between the hatch door or channel railing door of the main beam of the bridge mounted by the driver’s cab and the running mechanism of the car;

When the driver’s cab is located in the moving part, between the door of the passageway entering the driver’s cab and the running mechanism of the car;

In this way, it can prevent when someone is stepping into and out of the crane from the building, or when someone is doing equipment maintenance on the crane main beam, because the driver does not know and operates the crane, making the mechanism run and hurt.


Zero protection

The three working mechanisms of the bridge crane, such as lifting, truck running and car running, are controlled by the three operating devices respectively, and must be set up zero protection. Its protective effect is that as long as the controller of one mechanism is not in zero position, all mechanisms can not start; The motor of the working mechanism is only possible to start when the controller of the mechanism is placed in the zero position first. The zero position protection is used to prevent the accidental injury caused by the sudden operation of one or several institutions when the crane starts to operate or the power is restored after the loss of power.


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 located in a convenient place for the driver to operate.

Interlock protection, travel limit, zero protection, emergency switch, etc., often play a role in the control circuit of the crane, as long as there is a device in an abnormal state, the crane can not start or stop running in the direction of danger.


Deviation adjustment and display device

For gantry crane and loading bridge with long span, the device can indicate the deviation and adjust the deviation when the two legs of the gantry crane are tilted due to the forward speed is not synchronized.


Amplitude indicator

It is installed on a crane with a amplitude changing mechanism, which can correctly indicate the amplitude of the spreader.


Installed on the mobile crane, you can check the tilt of the leg crane, showing the horizontal state of the crane body.


Device to prevent boom from tipping backward

It is installed on the boom crane of the flexible amplitude changing mechanism. When the amplitude changing travel switch of the amplitude changing mechanism fails, the boom can be prevented from leaning backward.


Limit torque limiting device

When the rotating resistance moment of the boom crane is greater than the torque specified in the design, the friction element in the device slides, cuts off the power input, stops the rotating motion, and thus plays a protective role.


Wind speed alarm

Mounted on a crane working in the open air. When the wind is greater than 6, an alarm signal can be sent, and the instantaneous wind speed can be displayed. Cranes working on the coast can be set to send alarm signals when the wind is greater than level 7.


Leg retraction locking device

It is installed on the mobile crane that needs to hit the leg when working, and its safety function is to lock the leg bidirectional to ensure that the crane does not have “soft leg” retraction phenomenon when hitting the leg for lifting operations; When the crane ends the lifting operation, the leg can be reliably locked when the leg is withdrawn to prevent the crane from extending the leg itself in the driving state.


Rotary positioning device

When the mobile crane is driving on the road, it ensures that the lifting structure on the turntable is kept in a fixed position to prevent swing during driving.


Anti-tip safety hook

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

Check the hanging cage

It is used for the repair of conductive slip wire in high air. Its reliability should not be lower than that of the driver’s cab.


Rail sweep plate, support frame and track end stop

Rail sweep and support frame are used to sweep away obstacles on the track in the direction of the crane; The track end stop is arranged at the end of the laid track and works with the buffer on the moving structure of the crane (or running car) to prevent the crane (or running car) from derailing.


Conductive slide wire protection plate

A protective shield designed to prevent accidental contact of persons with live sliding lines resulting in electric shock accidents. The use of sliding line crane, the parts prone to electric shock should be equipped with the device:

When the cab of the bridge crane is located at the end of the trolley slide line, the ladder leading to the crane and the protection plate between the platform and the slide line should be set up.

Under the end beam at the end of the bridge crane, a protective plate should be set up to prevent accidental contact between the rope of the spreader and the slip line.

When the multi-layer arrangement is made with the straddle crane, the sliding line of the lower crane should be provided with a protective plate along the full length.


Protective cover

Exposed moving parts on the crane, such as open gear, coupling, drive shaft, sprocket, chain, drive belt, pulley, etc., should be installed with protective cover. Crane working in the open air, its electrical equipment should be equipped with rain cover.


Backward alarm device

When the mobile crane runs in the backward direction, it can send a clear alarm sound signal and a light signal between light and light, and the personnel quickly avoid the prompt.