For newly installed electric hoists or those reinstalled after disassembly and inspection, several no-load trial runs should be carried out first. However, it is strictly forbidden to power on for a trial run before the installation is completed.
During the installation process, a series of preparatory work needs to be done meticulously. The installation site should be clean, dry, and free from excessive dust and debris, as these can interfere with the smooth operation of the hoist’s moving parts. The mounting brackets or rails must be firmly fixed, with their horizontal and vertical alignments checked using precision leveling instruments. Any misalignment can cause uneven stress on the hoist during operation, leading to premature wear and potential safety hazards. Technicians also need to ensure that all electrical connections are tight and properly insulated, following the wiring diagrams provided by the manufacturer. Before the no-load trial runs, a visual inspection of the entire hoist structure, including the housing, gears, and pulleys, is essential to detect any signs of damage during transportation or assembly.
Before normal use, a static load test should be conducted. Lift a load of 125% of the rated capacity about 100 mm off the ground and hold it for 10 minutes to check if everything is normal.
This static load test is of great significance. It simulates a situation where the hoist is operating near its limit, allowing engineers to observe how the mechanical structure, such as the frame, bearings, and lifting mechanism, responds under heavy stress. Specialized load sensors can be installed to accurately measure the actual load applied, and strain gauges on key components can monitor the internal stress distribution. If any abnormal deformation, excessive vibration, or strange noises occur during the test, it indicates potential flaws in the design, manufacturing, or assembly of the hoist, which need to be addressed immediately.
The dynamic load test involves repeatedly lifting, lowering, and moving a load of the rated weight left and right. After the test, check whether the mechanical transmission parts, electrical parts, and connection parts are normal and reliable.
During the dynamic load test, the hoist’s performance under real working conditions is evaluated. High-speed cameras can be used to record the movement of the hoist and the load, enabling technicians to analyze the smoothness of the lifting and traversing motions. Vibration analyzers can detect any abnormal vibrations that might suggest issues in the balance of the rotating parts or misalignment of the drive system. For the electrical parts, insulation resistance testers are used to ensure that there is no electrical leakage, and the control circuits are checked for proper functioning of switches, relays, and limit switches.
During operation, it is absolutely prohibited to use the electric hoist in an unpermitted environment, exceed the rated load, or exceed the rated number of switch closures per hour (120 times).
The operating environment of the electric hoist is strictly regulated. For example, in explosive atmospheres, special explosion-proof electric hoists must be used. High humidity, extreme temperatures, and corrosive environments can also severely damage the hoist. To monitor the load, load cells can be integrated into the lifting system, which can send real-time load data to a control unit. If the load approaches or exceeds the rated value, an alarm can be triggered to prevent overloading. The number of switch closures can be counted electronically, and when the limit is reached, the control system can lock out further operation to avoid overheating of the electrical contacts.
During installation, commissioning, and maintenance, it is necessary to strictly check whether the limit devices are flexible and reliable. When the hook reaches the upper limit position, the distance between the hook housing and the drum housing must be greater than 50 mm (for 10t, 16t, 20t, it must be greater than 120 mm). When the hook reaches the lower limit position, ensure that there are sufficient safety turns of the wire rope on the drum, and the effective safety turns must be more than 2.
The limit devices are crucial safety features. They are often mechanical switches or proximity sensors. Regular maintenance includes cleaning the contact surfaces of mechanical switches to ensure good electrical conductivity, and calibrating proximity sensors to maintain accurate detection of the hook’s position. Measuring the distances between the hook and drum housings precisely requires the use of calipers or laser distance measurement devices. For the wire rope on the drum, visual inspection and counting of the safety turns should be done regularly, and any signs of rope wear or misalignment on the drum should be corrected promptly.
It is not allowed to press the two push-button switches on the hand-held controller simultaneously to make the electric hoist move in opposite directions.
This safety rule is designed to prevent electrical short circuits and mechanical collisions within the hoist. The control system of the electric hoist is programmed to disable such conflicting commands. To further enforce this, interlock circuits can be installed in the control panel. These circuits physically prevent the simultaneous activation of opposing movement commands, adding an extra layer of safety to the operation.
After work is completed, the main power switch must be turned off to cut off the power supply.
This simple step is a fundamental safety measure. Regularly turning off the power not only saves energy but also reduces the risk of electrical accidents, such as electrical leakage or unexpected startup. A lockout/tagout system can be implemented, where the person responsible for shutting down the hoist attaches a lock and a tag to the power switch, clearly indicating that the equipment is not to be operated. This is especially important in shared workplaces or during maintenance periods.
Electric hoists should be operated by specially trained personnel. Operators should fully master the safety operation procedures, and it is strictly prohibited to pull or lift loads in a slanted manner.
Operator training programs should cover theoretical knowledge, such as understanding the hoist’s mechanical and electrical principles, and practical skills, including proper load handling and emergency response. Simulators can be used in training to create various operating scenarios, allowing trainees to practice correct operation techniques and learn how to handle abnormal situations. Regular refresher courses are also necessary to keep operators updated on the latest safety regulations and equipment improvements.
During use, specialized personnel must regularly inspect the electric hoist. If any faults are found, take immediate measures and record them carefully.
The inspection routine should be comprehensive. It includes checking the appearance of the hoist for signs of corrosion, cracks, or paint peeling; inspecting the wire rope for wear, broken wires, and proper lubrication; and examining the electrical components for loose connections, overheating, or burnt-out parts. A detailed inspection checklist can be used, and all findings, whether normal or abnormal, should be logged in a maintenance record book. This record serves as a reference for future maintenance, helps to track the degradation of the hoist over time, and provides evidence of compliance with safety regulations.
When adjusting the braking slip of the electric hoist, under the rated load, the braking slip S should satisfy S ≤ V/100 (V is the stable lifting distance within one minute under load).
To accurately measure the braking slip, precise sensors are required. Encoders can be installed on the lifting mechanism to record the position of the load accurately. A dynamometer can be used to ensure the load is at the rated value during the test. By gradually adjusting the braking system, which may involve fine-tuning of brake pads, springs, or hydraulic components, the desired braking slip can be achieved while maintaining safe and efficient operation.
The scrapping standard of the wire rope: The inspection and scrapping standards of the wire rope shall be implemented in accordance with CB/T 5972 – 1986 “Practical Code for Inspection and Scrapping of Wire Ropes for Lifting Machinery”.
This standard provides detailed guidelines on when a wire rope should be scrapped. It takes into account factors such as the number of broken wires, the degree of wear, and the extent of corrosion. Regular inspection of the wire rope using tools like wire rope gauges, magnifying glasses, and ultrasonic flaw detectors helps to determine its compliance with the standard. Once the wire rope reaches the scrapping criteria, it must be replaced immediately to avoid catastrophic failure during operation.
During the use of the electric hoist, sufficient lubricating oil must be maintained, and the lubricating oil must be kept clean, free from impurities and dirt.
Proper lubrication is essential for the smooth operation of the hoist. The lubrication system should be designed to ensure that oil reaches all critical moving parts, such as gears, bearings, and pulleys. Oil filters can be installed in the lubrication circuit to remove contaminants. Regular oil sampling and analysis can be carried out to monitor the quality of the lubricant, and when the oil’s viscosity, acidity, or particulate content exceeds acceptable limits, it should be changed promptly.
When lubricating the wire rope, a hard-bristled brush or small wooden pieces should be used. It is strictly prohibited to directly lubricate the working wire rope by hand.
Using the correct tools for wire rope lubrication is crucial. The hard-bristled brush can evenly spread the lubricant on the rope’s surface, while the small wooden pieces can be used to work the lubricant into the gaps between the wire strands. Direct hand contact with the working wire rope is extremely dangerous as it can easily get caught in the moving parts, resulting in serious injury.
When the electric hoist is not working, it is not allowed to leave heavy objects suspended in the air to prevent permanent deformation of parts.
Leaving a load suspended can cause stress relaxation in the hoist’s components over time. Springs, cables, and structural members may gradually deform, affecting the hoist’s accuracy and safety when it is next used. To avoid this, proper storage procedures should be followed, with the load lowered to the ground or onto a designated storage platform.
If a fault is detected during use, the main power supply should be cut off immediately.
Quickly cutting off the power can prevent further damage to the hoist and avoid potential safety risks to the operator and surrounding equipment. After powering down, a thorough inspection should be carried out to identify the root cause of the fault, which may involve testing electrical circuits, checking mechanical linkages, or examining the control system.
Special attention should be paid to the condition of wearing parts during use.
Wearing parts, such as brake pads, gears, and bearings, have a limited lifespan. Regular visual inspections can detect signs of wear, such as thinning of brake pads or pitting on gear teeth. Monitoring the temperature of these parts can also provide clues, as abnormal heating often indicates excessive friction due to wear. By keeping a close eye on wearing parts, timely replacement can be arranged to avoid sudden breakdowns.
For 10 – 20-ton electric hoists, after long-term continuous operation, automatic power-off may occur. This belongs to the overheating protection function of the motor. At this time, the load can be lowered, and after a while, when the motor cools down, work can continue.
This overheating protection mechanism is designed to safeguard the motor from damage. Temperature sensors are installed in the motor to monitor its operating temperature. When the temperature reaches the preset limit, the control system automatically cuts off the power. To reduce the frequency of overheating, proper ventilation around the hoist should be ensured, and the motor’s cooling system, if applicable, should be maintained regularly. Additionally, optimizing the work cycle of the hoist, such as reducing continuous operation time and allowing for sufficient rest intervals, can also extend the motor’s lifespan.
In modern industrial applications, electric hoists are often integrated into complex automated material handling systems. These systems may consist of multiple hoists, conveyors, and robotic arms, all coordinated by a central control unit. To ensure seamless operation, communication protocols between different devices need to be standardized. For example, industrial Ethernet or wireless communication technologies are used to enable real-time data exchange, allowing for precise control of the electric hoist’s movements within the overall system.
Advanced diagnostic tools are also emerging. Predictive maintenance technologies, such as vibration signature analysis, oil debris monitoring, and thermal imaging, can detect potential failures of electric hoists long before they occur. By analyzing the vibration patterns of rotating components, tiny changes that indicate developing faults can be identified. Oil debris analysis can reveal the presence of metal particles from worn parts, while thermal imaging can quickly spot overheating areas in the electrical or mechanical parts.
Moreover, with the increasing focus on environmental protection, efforts are being made to develop more energy-efficient electric hoists. New motor designs, such as permanent magnet synchronous motors, are being adopted. These motors have higher efficiency, reducing energy consumption and also contributing to a quieter operation. The use of biodegradable lubricants is also on the rise, minimizing the environmental impact in case of lubricant leakage.
In terms of safety, the development of smart safety systems is accelerating. These systems can detect the presence of operators or obstacles in the hoist’s working area using technologies like laser scanners or cameras. If an unexpected object or person is detected, the hoist can automatically stop its operation to prevent collisions. Additionally, emergency stop buttons are being redesigned to be more accessible and tamper-proof, further enhancing the safety of electric hoist operations.
