As a Tower Crane Manufacturer, share with you. Most tower cranes use compact
lifting mechanisms, which are easy to maintain and have few failures. The
mechanism adopts rotor switching resistance to adjust the speed, and is equipped with 2 or 3 electromagnetic clutches. The inner and outer friction plates are compressed by electromagnetic suction to transmit power. Connection; convex
claws on the outer circle of the outer plate are connected with the shift fork,
and the shift fork is connected with the output gear of the transmission,
thereby driving the hoisting drum to rotate.
Top Kit Tower Crane
When the current is input to the electromagnetic clutch coil through the brush, an electromagnetic suction force is generated, and the inner and outer plates are pressed to output power. When the brush is worn or the voltage is too low to keep the solenoid coil engaged, a gap is created between the inner and outer sheets. At this time, the motor is still working normally and the lifting brake is in the open state. The driving force of the motor cannot be output through the gear, which causes the drum to slide under the action of the heavy object, that is, a slip hook appears.
Most domestic tower cranes use a JL14-22Q type 1.5 undercurrent relay to protect the electromagnetic coil. When undercurrent, the control loop will be cut off automatically to prevent the roll from falling. However, this relay's pull-in current range is 30% -65% of the rated operating current, and the release current range is 10% -20%. The adjustment range is wide, the accuracy is low, and the power cannot be turned off reliably. In addition, the circuit design is not reasonable.
When switching SA5 and 1 are closed, the current direction: DC24V → LFA (Under Current Relay) → L42 → H38 → H39 → L43 → KA2 (21/22) → L60 → YC1 → L62, forming a loop. At the same time, another circuit also flows through the LFA undercurrent relay. Current direction: DC24V → LFA (Under Current Relay) → L42 → H38 → H39 → L43 → KA2 (21/22) → KA1 (A1 / A2) → L62, forming a circuit. The comparison between the two circuits shows that the LFA undercurrent relay always has a DC current passing through it. When the electromagnetic coil YC1 is powered off, the LFA cannot be released, so it cannot protect the control circuit from power failure, which will cause slipping.
In order to prevent the occurrence of slip hooks, the circuit must be modified as necessary. An undercurrent relay is connected in series in each electromagnetic coil circuit. At the same time, the protective contact of the relay is connected in parallel to the electrical control circuit.
When switch SA5 and 1 are closed, the current direction is: DC24V → L42 → H38 → H39 → L43 → KA2 (21/22) → LFA (Under Current Relay, → L60 → YC1 → L62), forming a circuit. When the electromagnetic coil YC1 is powered off At this time, the LFA undercurrent relay, the relay protection contact action, so it is protected, the function of the YC2, YC3 electromagnetic clutch coil is the same as that of YC1.
After the circuit is modified, the lifting brake is reliably braked to prevent slipping when the electromagnetic clutch coil is powered off due to low voltage or brush wear.
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