154HC Mast SectionTypes and safety technical requirements of overload time limiter of crane
Overload operation will produce excessive stress, which can break the steel wire rope, damage the transmission parts, burn the motor, and lead to brake failure due to the relative lack of brake torque. Overload operation is very harmful to the crane structure, which will not only cause the downward deflection of the main beam of the crane, but also the instability, crack or weld opening of the upper cover plate and web plate of the main beam, as well as the breaking of the crane boom or tower body and other major accidents. Because the overload destroys the overall stability of the crane, the whole crane may overturn and overturn.
154HC Mast Section：
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The overload limiter shall be set for the bridge crane with rated lifting capacity greater than 20t, gantry crane with rated lifting capacity greater than 10t, loading and unloading bridge, railway crane and gantry crane according to GB6067-85 safety code for cranes. For tower crane with rated lifting moment less than 250kN? M, as well as lifting equipment such as elevator and electric hoist, overload limiter shall also be installed if necessary according to user requirements.
(I) type of overload limiter
According to its function, overload protection device can be divided into automatic stop type, alarm type and comprehensive type.
When the lifting capacity exceeds the rated lifting capacity, the automatic stop type overload limiter can stop the crane from continuing to move in the unsafe direction and allow the crane to move in the safe direction at the same time. 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.
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The alarm type 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.
The comprehensive overload limiter can send out the sound and light signal of alarm when the crane reaches 95% - 100% of the rated lifting capacity. When the lifting capacity exceeds the rated lifting capacity, it can stop the crane from moving in the unsafe direction.
According to the structure, 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 hoisting operation and a feature of hoisting machinery operation. Therefore, the overload protection device has designed 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 and from misoperation.
(II) safety technical requirements for overload limiter
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 lifting machinery, 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 overload limiter shall be installed for bridge crane, railway crane and portal crane; tower crane, elevator and electric hoist can also be installed according to actual needs.
154HC Mast Section：
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