132HC Mast Section What are the limit devices of tower crane and what are their functions?
The limit devices of tower crane include lifting limiter, moment limiter, height limiter, travel limiter, amplitude limiter, etc. the following are detailed descriptions of various limit devices of tower crane.
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1. Lifting limiter, also known as overload limiter, is a kind of safety device that can make the crane run without overload. When the lifting load exceeds the rated lifting load, it can automatically cut off the power supply of the lifting mechanism to stop or give an alarm. There are two types of lifting limiter, mechanical and electronic.
2. The moment limiter is only allowed to lift a certain amount of lifting weight for a certain range of luffing crane. If the crane is overweight, it may overturn. The moment limiter is a kind of protection device developed according to this characteristic. In a certain range, if the lifting object exceeds its corresponding weight circuit, it will be cut off, so that the lifting can not be carried out to ensure the stability of the crane. There are three types of moment limiters: mechanical, electronic and composite.
3. The height limiter, also known as the hook height limiter, is generally installed at the head of the boom to lift the lever when the hook reaches the limit position. The hook can only be lowered when the lower limit switch disconnects the circuit and stops for reclosing.
4. The travel limiter is a safety device to prevent the crane from colliding or driving within a certain range. It is generally installed in the inner side of the driving trolley, mainly to install a stroke switch that can move the handle. In addition, a fixed limit position baffle shall be installed at the end of the track at the position limited by the operation. When the tower crane reaches this position, the limit baffle will touch the handle of the travel switch to cut off the power supply for controlling the travel. When the tower crane is closed, it can only run in the opposite direction.
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5. Amplitude limiter is also called luffing limit or amplitude indicator. Generally, an amplitude indicator is hung on the boom of boom crane. It is composed of a fixed circular indicator disk, and a plumb movable pointer is arranged in the center of the disk. When luffing, the pointer indicates the rated lifting capacity under various amplitudes. When the boom moves to the upper and lower limit positions, press the lower limit switch respectively to cut off the main control circuit and stop the luffing motor to reach the limit.
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