Lifting machinery refers to the machinery that suspends heavy objects with hooks or other fetching devices and carries out cyclic operations such as lifting and moving in space. There are many kinds of cranes, such as "crane", "tower crane", "crown block" and "traveling crane". Usually refers to one or several types of cranes. Safety device of hoisting machinery

Crane is a special kind of equipment, and its safety is very important, so it is very necessary to install safety devices on the crane. Different types of cranes should be equipped with different types and efficiency of safety devices. Common safety devices are as follows:

3. 1 Overwind limiter

According to the regulations, the hoisting mechanism of the crane must be equipped with an overwinding limiter. When the hook pulley is lifted 300 mm away from the crane frame, the motor power supply can be automatically cut off and the motor stops running. This can ensure the safe execution of the crane and avoid accidents such as wire rope being pulled off and heavy objects falling due to over-hoisting.

3.2 Travel limiter

It is a safety device to prevent cranes from approaching the end of the track and causing collision accidents, or two cranes from colliding on the same track. The travel limiter can ensure that the power supply will be cut off immediately when the distance between the rail ends is 200mm and the cranes are approaching each other at 500mm. ..

3.3 Automatic interlocking device

There are many bare wires passing through the bridge crane. In order to prevent inspectors from getting an electric shock, it is required to install an automatic interlocking device at the door of the cab leading to the driver or the bridge to realize power failure during inspection and power supply after inspection to ensure the safety of inspection.

3.4 buffer

Buffer is a kind of safety device that absorbs energy when the crane collides with an object, and it only works after the brake and end switch of the crane fail. When the crane is connected with the column at the end of the track, ensure that the crane stops smoothly. Rubber buffer, spring buffer and hydraulic buffer are commonly used on cranes.

When the vehicle speed exceeds 120m/min, the general buffer can't meet the requirements, so light anti-collision device, ultrasonic anti-collision device and infrared reflector are needed.

Hoisting machinery

3.5 brake

The brake on the lifting device can stop the lifting device at any time in the process of lifting, translation and rotation, so that the heavy objects can stay at any height, which can prevent accidents and meet the work requirements.

There are many kinds of brakes, such as spring brakes and safety cranks. Because the function of brakes is very important for cranes, many accidents are often caused by brake failure or applause. Therefore, in order to ensure the safety of lifting operation, it is necessary to strengthen the inspection and maintenance of brakes, which is generally required to be inspected once per shift.

3.6 Weight limiter

The weight limiter is the overload protection device of the crane. According to the different structure and working principle, it can be divided into mechanical type and electronic type. In the process of lifting operation, when the lifting capacity exceeds 10% of the rated lifting capacity of the crane, the weight limiter will come into play, which will make the mechanism stop working without power supply, thus playing the role of overload limitation.

3.7 Torque limiter

For cranes with luffing jib, such as tower cranes and mobile cranes, besides the load, the change of the distance from the load center to the crane caused by luffing jib should also be considered, that is, the lifting torque problem. Torque limiter is a kind of safety device which combines the factors of lifting capacity and crane execution range to ensure that the lifting torque is always within the allowable range. Can be divided into mechanical and electronic.

There are two kinds of mechanical moment limiters: lever type and horizontal arm type. In lifting operation, when the lifting weight increases to the limit value, the limiter can drive the control block to touch the control switch, disconnect the power supply and stop working.

The electronic torque limiter can automatically compare the actual lifting torque with the rated lifting torque through the instrument during operation. If it is overloaded, the relay will automatically cut off the power supply of the working mechanism to ensure safety. Electronic torque limiter overcomes the shortcomings of mechanical torque limiter and is widely used in various cranes.

3.8 Dangerous voltage alarm

When the jib crane works around the transmission line, due to improper operation, the jib wire rope is too close to the wire and even touches the wire, which will cause electric induction or electric shock accidents. In order to prevent this kind of accident, a dangerous voltage alarm is developed. Its principle is that the transmission line of the alarm is three alternating currents, the phase difference is 120, and the spatial electric field distribution is alternating electric field. Theoretically, the potential of points equally spaced from each phase line should be zero. However, in the actual line layout, there is no point with zero potential. According to the characteristics of electric field distribution, as long as the ideal value and potential gradient of electric shock potential are detected and compared with the preset reference voltage, the distance between the boom and the wire can be judged and the alarm can be given in time.

The alarm consists of a detector and an alarm. The detector is installed at the end of the boom, and a real metal ball on it is used as a probe to detect the electric field around the wire. The preamplifier in the detector amplifies the weak electric field signal and sends it to the alarm for comparison.

4 Prevention of lifting injury accidents

Lifting injury accidents generally include squeezing, falling from a height, falling of heavy objects, collapse, crushing, overturning, electric shock and collision accidents. Every kind of accident is related to its environment. These accidents are caused by man-made and defective equipment or by people and equipment.

4. 1 crane extrusion accident prevention

The occurrence and prevention of crane extrusion accidents have the following three situations:

In the first case, the crane body is squeezed by fixtures and buildings. This kind of accident mostly occurs between the execution crane or the rotating crane and the surrounding fixed objects. For example, between the end beam of the bridge crane and the columns and walls of the surrounding buildings, and between the tail of the tower crane and the truck crane and other facilities when rotating. Most accidents are due to the narrow space, the victim is located in the dead corner of the driver's vision, or the driver lacks observation. Therefore, there should be an appropriate distance between the crane and the fixture, at least 0.5m, and no one is allowed to pass during operation.

The second situation is the extrusion between the spreader and the lifting load and the surrounding fixtures and buildings. In this regard, we must first arrange the site reasonably and pile up heavy objects. When the goods are stacked, a proper gap should be left, and the huge parts and goods that are easy to overturn and overturn should be packed neatly for easy handling. Secondly, it is necessary to choose slings and rigging suitable for the goods to be hoisted, and tie them reasonably to avoid rotating or falling off in the air. It is forbidden to drag rotating heavy objects directly by hand, and the signal commander should command according to the original hoisting scheme.

The third situation is the extrusion accident between the crane and the elevator itself. For example, the maintenance personnel check the extrusion accident between the turntable of the truck crane and other parts. In the material elevator, there are many problems in the building elevator, mainly due to incomplete protective devices, such as no lifting limiter, no protective railing or no protective door. Protective measures include: properly controlling the position of winch; If there is no closed hanging cage, the passage should be closed and no one is allowed to pass through; Protective railings should be set at the entrance of the passage; When checking the equipment close to the upper limit, pay attention to prevent head collision; When working in the pit, pay attention to the falling of the bridge box and counterweight to avoid accidents.