For the defects in the support points of manual hoists (manual arm cranes), such as rotation jamming, structural looseness, and abnormal lifting, the following systematic solutions can be taken, including fault diagnosis, repair methods, and preventive measures:

1、 Solution to Defects in Rotating Systems

Phenomenon: The horizontal rotation resistance of the cantilever increases, it becomes stuck or accompanied by metal friction sound, and in severe cases, it cannot rotate.

Reason: Insufficient lubrication, component wear, foreign object blockage, or loose bearing fixing bolts.

Repair steps:

Power outage and cleaning: Cut off the power supply of the equipment, clean the metal debris, dust, and other foreign objects at the rotating track, rollers, and turntable bearings.

Lubrication maintenance:

Inject specialized lubricating grease (such as lithium based grease) into the bearing and gear meshing areas.

If there is abnormal noise from the gearbox, it is necessary to supplement or replace the medium load industrial gear oil (such as ISO VG 220).

Tightening and replacement:

Check the fixing bolts of the turntable bearing and tighten them with a torque wrench according to the standard torque (such as 50-60N · m for M12 bolts).

If the bearings or gears are severely worn, new components need to be replaced.

Preventive measures:

Add lubricating grease to the rotating system every week and check the tightening of bolts every month.

Avoid long-term use in damp or corrosive environments, and clean promptly after use.

2、 Solution to structural looseness and oil leakage defects

Phenomenon: Loose bolts at equipment connections, oil leakage at the base of the boom or rotating shaft, and abnormal temperature rise of components.

Reason: Failure to regularly inspect fasteners, aging seals, or hydraulic oil leakage.

Repair steps:

Comprehensive tightening: Check the bolts at the connection points of the crane arm and the rotating shaft support, and tighten them with a torque wrench according to the design torque (such as 80-100N · m for M16 bolts).

Seal replacement:

Replace aging gaskets and O-rings (materials can be selected from nitrile rubber or fluororubber).

If hydraulic assist structure is included, it is necessary to supplement hydraulic oil that meets the specifications (such as ISO VG 46).

Oil cleaning: Use a cloth to wipe off oil stains, check the wear of components, and avoid impurities from exacerbating damage.

Preventive measures:

Check fasteners once a month and replace seals quarterly.

The hydraulic system needs to filter the hydraulic oil regularly to keep the oil clean.

3、 Solution to lifting system defects

Phenomenon: Weak lifting ability, difficulty in pulling the hook or chain when hovering heavy objects.

Reason: Chain wear, inadequate sealing of balance valve, or insufficient chain tension.

Repair steps:

Chain inspection and replacement:

Measure the wear of the chain diameter. If it exceeds 10% of the original diameter, it needs to be replaced (such as when the wear of the Φ 8 chain is below Φ 7.2).

Check the chain links for broken wires or deformation, and replace damaged chain links in a timely manner.

Balance valve maintenance: Disassemble the balance valve and replace aging or damaged seals (such as O-rings and gaskets).

Chain tension adjustment:

Loosen the chain tensioner and adjust it until the chain meshes well with the sprocket (without any jumping teeth or jamming).

Ensure that the chain sag is within the range of 1% -2% of the span (such as 10-20mm sag for a 1-meter span).

Preventive measures:

Clean the chain debris after daily use and check the wear of the chain weekly.

Avoid overloading and ensure that the rated load does not exceed 80% of the equipment's nominal value.

4、 Solution for safety device failure

Phenomenon: The limit switch is not triggered and the overload protection device is not sounding an alarm.

Reason: Contact oxidation, sensor calibration deviation, or circuit failure.

Repair steps:

Limit switch test: manually press the triggering component to check if it can cut off the action normally. If it fails, clean the contacts (wipe with alcohol swab) or replace the switch assembly.

Overload protection calibration:

Use standard weights (such as 500kg ± 1% weights required for equipment with a rated load of 500kg) to test the overload protection function.

If there is no alarm, adjust the sensitivity of the sensor or replace the pressure sensor (such as a sensor with a range of 0-1000kg).

Line inspection: Use a multimeter to check whether the wiring of the limit switch and overload protection device is loose or short circuited.

Preventive measures:

Manually test safety devices once a month and contact professionals every six months to calibrate sensors.

It is strictly prohibited to modify or dismantle safety devices without authorization.

5、 General preventive measures

Operation specification training:

Provide safety training for operators, emphasizing principles such as "no overloading", "no standing under the rotating arm", and "no diagonal or horizontal pulling".

Simulate fault scenario drills to improve emergency response capabilities.

Regular maintenance and upkeep:

Daily maintenance: Clean the hook and chain dust after use, check for chain cracks and hook deformation.

Weekly maintenance: Add lubricating oil and check the firmness of the counterweight.

Monthly maintenance: tighten all bolts and test the brake function of the hoist.

Annual maintenance: Entrust a professional organization to inspect the wear of the chain and the curvature of the column (such as the vertical deviation of the column should not exceed H/1000, where H is the height of the column).

Selection and installation requirements:

Choose fixed models (with a load capacity of 300-1000kg) or mobile models (with a load capacity of 100-500kg) according to the workstation requirements.

The fixed version needs to be fixed on the ground with expansion bolts, while the mobile version needs to confirm that the base weight is sufficient (such as the total weight of the weight block should not be less than 50% of the rated load of the equipment).

6、 Case reference

Rotating arm crane in a certain workshop experiences a jamming: After cleaning foreign objects from the turntable bearings and adding lubricating grease, the rotational resistance is reduced by 70% and the failure rate is reduced by 90%.

Oil leakage of a rotary arm crane in a warehouse: After replacing the sealing gasket, the oil leakage problem was completely solved, and the hydraulic oil replacement cycle was extended from 3 months to 1 year.

The main equipment produced by Hebei Makita: stage electric hoist, electric chian hoist, wire rope electric hoist，Hand chain hoist, lever hoist, pneumatic hoist and other lifting equipment