Main parameters of lifting machinery
The main parameters of the hoisting machinery are indicators that characterize the performance characteristics of the hoisting machinery. They are also the basic technical basis for the design and selection of the hoisting machinery. They are also an important basis for the safety technical requirements of the hoisting machinery. The main parameters of the lifting machinery are: lifting weight, span, track gauge, base distance, amplitude, lifting moment, lifting overturning moment, maximum wheel pressure, lifting height and descent depth, operating speed, crane working level, lifting Characteristic curves, etc. Among them, the crane working level is a working characteristic that considers the utilization degree of lifting capacity and time as well as the number of working cycles. It is divided according to the crane utilization level (total number of working cycles during the entire design life period) and load status.
Safety protection devices for lifting machinery
1. Position restriction and adjustment device
(1) Ascent limit position limiter
When the lifting mechanism rises and the spreader continues to exceed the working height range, the spreader will hit the upper support structure, causing the wire rope to break and the spreader to fall. Using a lift limiter and keeping it effective can prevent such over-hoisting accidents. Therefore, the "Safety Regulations for Hoisting Machinery" stipulates that the lifting mechanism (including the main and auxiliary lifting mechanisms) of any power-driven crane should be equipped with a lifting limit position limiter. Its common types are hammer type and screw (or worm gear) type. The weight-type lifting limit position limiter is suspended above the spreader. After the spreader exceeds the working height and hits the position limiter, an electrical switch is triggered to stop the system. The structure of the screw type limiter is connected by the reel shaft end, which leads to the movement relationship and size range. By hitting the head together with the nut, it triggers the switch contact to disconnect the circuit.
(2) Operating limit position limiter
When the crane trolley or trolley reaches the limit position of its stroke, it should stop running, otherwise the trolley body will collide with the rail end stop and buffer, damaging the crane or the track's support system (such as factory building, etc.), and may cause equipment and Personal Accident. Therefore, all power-driven cranes should be equipped with operating limit position limiters at their operating limit positions. The travel limiter generally consists of a travel switch and a safety ruler that triggers the switch.
(3) Buffer
Crane buffers generally work in the following situations: when the crane is running near the end of the stroke, sometimes it cannot stop immediately after crossing the limit switch due to the high speed; when the limit switch fails and the operation is incorrect, the crane will return to its original position. The running speed rushes to the end of the stroke; in addition, if two or more overhead cranes are installed in the same span of the factory building, there are many opportunities for collision during work. At this time, the kinetic energy of the crane's operation will cause damage to itself or its supporting structure through collision, and even lead to personal accidents. Therefore, the "Safety Regulations for Hoisting Machinery" requires that bridges, gantry cranes, loading and unloading bridges, and gantry cranes or lifts must be equipped with buffers. Commonly used buffers for cranes include solid buffers, spring buffers and hydraulic buffers.
2. Windproof and anti-climb device
Cranes operating on tracks in the open air are generally affected by natural wind, and wind factors are taken into consideration during design. When the wind force is greater than the specified value, the crane should stop working. When a crane in a non-working state is hit by strong winds, it may overcome the braking force of the brakes of the trolley's operating mechanism and slide. This uncontrolled sliding caused a strong impact on the end of the track, causing the crane to overturn. The losses caused to our country every year are huge. Therefore, the "Safety Regulations for Hoisting Machinery" stipulates that cranes operating on open-air tracks, such as gantry cranes, loading and unloading bridges, tower cranes and gantry cranes, should be equipped with windproof and anti-climb devices. Bridge cranes working in the open air should also be equipped with windproof and anti-climb devices.
There are three main types of windproof and anti-climb devices for cranes, namely rail clamps, anchoring devices and iron shoes. According to the different modes of action of windproof devices, they can be divided into two categories: automatic action and non-automatic action. The automatic wind protection device means that the wind protection device can automatically work when the crane stops running or the power is suddenly cut off. Non-automatic windproof devices are mostly manual, with a relatively simple structure, light weight, compactness, and easy maintenance, but they are troublesome to operate and cannot cope with sudden storms; and the manual rail clamp has a small clamping force and is mostly used on small and medium-sized cranes. , for large cranes, in order to enhance the safety and reliability of the wind protection device, several wind protection devices are used at the same time.
3. Safety hook, anti-reverse device and rotation locking device
(1) Safety hook
For single main girder cranes, since the lifting of heavy objects is carried out on one side of the main girder, the heavy objects produce a tipping moment on the trolley. The anti-tilting moment generated by the vertical anti-rail wheels or horizontal anti-rail wheels keeps the trolley balanced. Will not tip over. However, this method alone cannot guarantee safety in the event of wind disaster, accidental impact, broken wheels, maintenance, etc. Therefore, this type of crane should be equipped with a safety hook.
(2) Anti-reverse device
When a crane that uses a flexible wire rope to pull the boom for luffing encounters sudden unloading, a force will be generated to tilt the boom backward, causing the boom to exceed the minimum amplitude and causing an accident in which the boom tilts backward. The "Safety Regulations for Hoisting Machinery" clearly stipulates that mobile cranes and luffing jib tower cranes should be equipped with anti-back tilt devices (except for hydraulic luffing).
The anti-back tilt device first limits the luffing position through the luffing limit switch, and then blocks the boom through a mechanical device. Safety ropes and safety bars are two other commonly used anti-rollback devices. The safety rope is a fixed-length steel wire rope that limits the inclination of the boom. The working principle of the safety rod is to connect the safety rod to the boom and the turntable. The safety rod is a sleeve telescopic mechanism. A buffer spring is installed in the sleeve, which has buffering, vibration reduction and limiting effects on the boom.
(3) Rotary locking device
The slewing locking device refers to a device that locks the slewing part so that it cannot rotate when the jib crane is in transportation, driving or non-working state.
Common types of rotary locks include mechanical locks and hydraulic locks. The structure of the mechanism lock is relatively simple, usually using the lock pin insertion method, the pressure plate pressing method or the bolt fixing method. Hydraulic lockers usually use double-acting piston cylinders to lock the turntable.
Overload protection device
Overloading operations are one of the main causes of lifting accidents. In the mild case, the crane parts are damaged, the motor is overloaded or the structure is deformed; in the serious case, it causes major accidents such as broken beams, collapsed towers, broken arms, and overturning of the entire machine. The use of sensitive and reliable overload protection devices is an effective measure to improve the safety performance of cranes and prevent overload accidents. Overload protection devices include lifting weight limiters and lifting torque limiters.
Overload protection devices can be divided into two types: automatic stop type and comprehensive type according to their different functions. According to the structural type, there are two types: electrical type and mechanical type.
The automatic stop type means that when the lifting mass exceeds the rated lifting capacity, it can stop the crane from continuing to move in unsafe directions (raising, extending the arm, lowering the arm, etc.). Comprehensive type means that when the lifting mass reaches about 90% of the rated lifting capacity, it can send out a sound or light warning signal. When the lifting mass exceeds the rated lifting capacity, it can stop the crane from continuing to move in unsafe directions and send out audible and visual alarm signals.
The electrical type converts the detected mechanical quantities such as load into corresponding electrical signals, and then amplifies, compares, calculates and processes them; the mechanical type refers to detecting the load through a lever, eccentric, spring or hydraulic system, and the limit switch (control valve) action.
(1) Lifting weight limiter
Lifting weight limiter. It is mainly used in bridge type cranes, and its leading product is the electric type. Electrical products generally consist of load sensors and secondary instruments. The load sensor uses a resistance strain gauge or piezomagnetic sensor, and special installation accessories are prepared according to the installation location. There are three main structural forms of sensors: compression type, tension type and shear beam type.
(2) Torque limiter
The torque limiter is divided into a boom luffing torque limiter and a trolley luffing torque limiter.
Tower cranes with luffing booms can use mechanical torque limiters.
Trolley luffing tower cranes generally use a lifting weight limiter and a lifting moment limiter to jointly implement overload protection.
Anti-collision device
With the development of science and technology, lifting machinery has further tended to be high-speed, large-scale, complex, and used more intensively. In many enterprises, it is common for multiple cranes to operate on the same floor, and there are also places where cranes operate on two or even three floors. In this case, relying solely on the safety ruler and stroke
Traditional methods such as switches or simply relying on the driver's visual inspection to prevent collisions can no longer guarantee safety. Since the 1960s, some industrially developed countries have developed non-contact crane anti-collision devices such as light, ultrasonic, and microwave. This new anti-collision device. It has the characteristics of long detection distance, multiple alarm distances can be set at the same time, high accuracy, full functions, and good environmental adaptability. A product series was quickly formed and widely used by various enterprises. The lifting machinery introduced by Baosteel and other companies in our country are basically equipped with this anti-collision device.
