L68A1 Mast Section Use, type and safety technical requirements of overload limiter of tower crane
(1) the overload operation is very harmful to the tower crane structure, which will not only cause the downward deflection of the main beam of the tower crane, but also cause the instability, crack or weld opening of the upper cover plate and web plate of the main beam, as well as major accidents such as the fracture of the boom or the body of the tower crane.
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(2) the overload operation of tower crane will produce excessive stress, which can break the steel wire rope, damage the transmission parts, burn the motor, and cause the brake failure due to the relatively insufficient brake torque.
(3) because the overload destroys the overall stability of the tower crane, the collapse of the tower crane and other malignant accidents may occur.
II. Use requirements of overload limiter
(1) for bridge tower crane with rated lifting capacity greater than 20t, portal tower crane with rated lifting capacity greater than 10t, loading and unloading bridge, railway tower crane and portal tower crane, overload limiter shall be set according to GB6067-85 safety code for tower cranes.
(2) for tower cranes with rated lifting torque less than 250kN / m, as well as lifting equipment such as elevators and electric hoists, overload limiters shall also be installed if necessary according to user requirements.
III. type of overload limiter of tower crane
1. Overload protection device can be divided into automatic stop type, alarm type and comprehensive type according to its functions.
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Automatic stop type: when the lifting weight of overload limiter exceeds the rated lifting weight, it can stop the tower crane from continuing to operate in the unsafe direction and allow the tower crane to operate in the safe direction. Safety direction refers to the combination of lifting load lowering, boom retraction, reduction amplitude and these actions. The automatic stop type is generally mechanical overload limiter, which is mostly used on tower crane.
Alarm type: the overload limiter can display the lifting capacity and send out the audible and visual signals when the lifting capacity reaches 95% - 100% of the rated lifting capacity.
Comprehensive type: the overload limiter can send out the sound and light signal of alarm when the tower crane reaches 95% - 100% of the rated lifting capacity. When the lifting capacity exceeds the rated lifting capacity, it can stop the tower crane from continuing to operate in the unsafe direction.
2. Overload limiter can be divided into mechanical type, hydraulic type and electronic type. Mechanical overload limiter has lever type and spring type.
In the design of overload protection device, the influence of the smart load is considered. Under the conditions of lifting, braking and vibration, the speed change will produce an additional load, and the lifting dynamic load often reaches 110% - 130% of the rated load. Dynamic load is the inherent dynamic phenomenon of lifting operation and a feature of tower crane operation. Therefore, the overload protection device designs a delay circuit according to this feature, so that it has the ability to judge and deal with this kind of false load, and it can prevent the actual load from exceeding the specified value, so as not to cause misoperation.
IV. safety technical requirements for overload limiter of tower crane
(1) the comprehensive error of mechanical overload limiter shall not be greater than 8%, and that of electronic overload limiter shall not be greater than 5%.
(2) when the load reaches 90% of the rated lifting capacity, it shall be able to send out a prompt alarm signal.
(3) after the overload limiter is set for the tower crane, it shall be adjusted or calibrated according to its performance and accuracy. When the lifting capacity exceeds the rated lifting capacity, it can automatically cut off the lifting power source and send out a prohibition alarm signal.
(4) for bridge type tower crane, railway tower crane and portal tower crane, overload limiter shall be installed; tower crane, elevator and electric hoist can also be installed according to actual needs.
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