1. Limit position limiter of electric hoist
(1) The electric hoist shall be provided with limit position limiters for ascending and descending, and can ensure that the power supply is automatically cut off when the hook is lifted and descended to the limit position, and the action in the opposite direction shall be possible at this time.
(2) The electric hoist for lifting and transporting molten metal should be equipped with different forms of double limit protection devices at the rising limit position, and can control different electrical circuits.
(3) The lifting height limiter should act reliably. When the fire limiter is used, the following requirements should be met:
① The surface of the shell of the fire stopper should be smooth, and there should be no obvious burrs or cracks on the edge.
② The surfaces of all ferrous metal components, accessories, fasteners, etc. in the fire stopper should be protected against rust.
③ The electrical clearance, creepage distance and temperature rise of the fire limiter shall comply with the relevant regulations.
2. Lifting weight limiter of electric hoist
(1) Electric hoists with a rated lifting capacity of 1t and above should be equipped with a lifting capacity limiter. When the actual lifting capacity exceeds 95% of the rated lifting capacity, the lifting capacity limiter is prone to send out an alarm signal (except the automatic stop type); when the actual lifting capacity is between 100% and 110% of the rated lifting capacity, the lifting capacity limiter starts At this time, the lifting power supply should be automatically cut off, but the mechanism should be allowed to make a downward movement.
(2) From the overload lifting of the electric hoist to the lifting weight limiter, the lifting action stops. At this time, the height of the load should not exceed the distance traveled by the nominal lifting speed for 1s. For two-speed electric hoists, slow speed is not assessed.
3. Brake of electric hoist
(1) The lifting electric wire rope hoist should be equipped with a normally closed working brake, and the braking safety factor of the brake should meet the following requirements:
a) The working level is M5 and below, and should not be lower than 1.5;
b) The working level is M6 and above, and should not be lower than 1.75.
(2) When the electric hoist is used as the hoisting mechanism to lift molten metal, the setting of the brake shall meet the following requirements:
a) When the rated lifting capacity is greater than 5t, in addition to a working brake, the electric hoist should also be provided with a safety brake on the low-speed stage of the electric hoist;
b) When the rated lifting capacity is less than or equal to 5t, in addition to a working brake, the electric hoist should be equipped with a safety brake on the low speed stage of the electric hoist, otherwise the electric hoist should be designed according to 1.5 times the rated lifting capacity.
(3) When setting the safety brake, its function should meet the following requirements: when the transmission part fails or the working brake fails and the load falls, it should be able to support the rated load reliably.
(4) It is strictly forbidden for non-professionals to adjust the brake, and it is not allowed to adjust the brake of the hoisting and luffing mechanism under load. The adjusted brake should make the test load stop reliably, and the suspended test load should be started in the air. At this time, the test load should not act in the opposite direction. For cranes lifted by hoists, the braking distance should not be greater than 1/100 of the stable lifting distance within 1 minute.