A Brief Analysis of Key Issues and Countermeasures in the Maintenance of Portal Cranes (Part 1)

Portal cranes operate under complex conditions of long-term exposure to the elements, heavy loads, dust, salt spray, and weathering. This leads to aging of the metal structure, wear and tear of mechanical parts, and malfunctions in the electrical system. Scientific and standardized maintenance is crucial for ensuring stable equipment operation, preventing accidents, extending equipment lifespan, and reducing operating costs.

I. Metal Structure Maintenance: Preventing Rust and Deformation, Strengthening the Load-Bearing Foundation

The metal structure is the core load-bearing component of a portal crane, encompassing key components such as the boom, gantry, tower, balance beam, and tie rods. Its structural integrity directly determines the safety of equipment operation and is also the most easily overlooked and most hidden area for problem accumulation during maintenance.

In routine maintenance, rust, deformation, weld defects, and loose bolts are four frequently encountered problems. First, in open-air operating environments, rainwater, dust, and coastal salt spray continuously corrode the metal surface of the equipment. The original paint coating ages and peels off; failure to repaint in time leads to corrosion of the base material and thinning of the wall thickness. Long-term accumulation significantly reduces the structural load-bearing strength, especially in hidden areas such as tie rods, balance beam joints, and the equipment base, where localized rust problems are easily detected but difficult to detect in time. Second, long-term heavy-load operation and illegal overloading can cause plastic deformation such as boom bending, gantry deformation, and structural displacement. Most operators only focus on whether the equipment can operate normally, ignoring the hidden dangers of minor deformations, ultimately leading to the risk of structural fracture.

Meanwhile, weld defects pose a significant risk. The vibrations generated by the equipment's long-term rotation and amplitude changes can lead to micro-cracks and weld detachment in the main beam, outriggers, and hinged joints. Initially, these cracks may not produce noticeable noises or deformation, making them difficult to detect with routine visual inspection. Continued crack expansion can directly cause structural collapse. Furthermore, high-intensity equipment vibrations can cause structural connection bolts to loosen or become missing. Some maintenance personnel prioritize maintenance over tightening, failing to periodically re-check the torque of high-strength bolts. This results in excessive gaps in structural connections, uneven stress, and exacerbated equipment vibration and component wear.

To address these issues, a routine structural maintenance mechanism needs to be established. Before and after daily operations, focus should be placed on inspecting concealed areas for paint peeling, water accumulation, rust, and cracks. After rain, fog, or typhoons, promptly clean water and stains from the equipment surface. For rusted areas, grind away the rust and reapply anti-corrosion paint. In coastal salt spray conditions, apply a special rust inhibitor weekly for enhanced protection. Regularly employ professional testing equipment to conduct non-destructive testing on critical welds, accurately identifying even the smallest cracks. Any discovered weld defects or cracks require immediate shutdown and repair. Strictly adhere to equipment technical standards, regularly tightening and torque-checking all structural connection bolts, promptly replacing aged, rusted, or stripped bolts to ensure robust structural connections and balanced stress distribution.

II. Mechanical Transmission System Maintenance: Standardized Lubrication and Inspection to Reduce Wear and Failures The four major mechanical transmission mechanisms of a portal crane—lifting, luffing, slewing, and traveling—are the core of the equipment's power operation. Improper lubrication, excessive component wear, abnormal noises, and leaks are the core pain points in maintenance work and also the systems with the highest failure rates.

Improper lubrication maintenance is the most common problem. On-site maintenance often involves incorrect grease selection, unreasonable dosage, and inconsistent lubrication cycles: Using incompatible grease for high-speed motor bearings and reducer gears can lead to insufficient lubrication and dry gear friction; failing to use high-pressure grease for heavy-duty articulated boom hinges and slewing bearing pins can easily cause hinge jamming and corrosion; there are also two extreme problems: over-lubrication and under-lubrication. Insufficient lubrication fails to form an effective oil film, while excessive lubrication leads to poor heat dissipation and grease buildup and aging. Furthermore, many companies adopt a passive maintenance model of "repairing only when it breaks and replenishing only when it's low on oil," failing to strictly implement regular lubrication procedures. Long-term operation with insufficient oil will accelerate the wear of bearings, gears, and pins, significantly shortening the service life of components. Besides lubrication issues, wear and leakage in transmission components are frequent problems. Hoisting wire ropes, subjected to long-term tensile, bending, and frictional loads, are prone to problems such as broken wires, broken strands, wear, corrosion, and deformation. Some maintenance personnel neglect minor broken wires and surface wear, failing to replace them in time, which can easily lead to wire rope breakage and accidents involving falling loads. Components such as reducers, hydraulic cylinders, and oil pipes are prone to aging seals and oil leaks after long-term operation. Leaks not only waste oil but also cause insufficient equipment power and dry-running damage to components. Furthermore, accumulated oil attracts dust, exacerbating corrosion. In addition, long-term friction and wear on the treads and rims of traveling wheels and guide wheels, if not repaired or replaced in time, can cause equipment deviation and jamming, affecting operational accuracy and safety.

Optimizing mechanical transmission maintenance requires adhering to the principles of "precise lubrication, regular inspection, and timely replacement." Select appropriate lubricating media based on the different operating conditions of components: use extreme pressure industrial gear oil for high-speed gears and bearings; apply high-pressure lithium-based grease to heavy-duty articulated parts; and apply special anti-rust grease for wire ropes, strictly controlling the amount added. Fill bearings only 1/2 to 2/3 full to avoid lubrication failure or poor heat dissipation. Establish a tiered inspection system: check the appearance of wire ropes daily for broken wires and rust; check for abnormal noises and oil leaks in the transmission mechanism weekly; and check the wear of the travel wheels and guide wheels monthly. Regularly replace reducer and hydraulic system filters and aged seals, clean oil and dirt deposits, prevent leaks, and promptly replace any worn or aged wire ropes, bearings, gears, or other components. Operation with defects is strictly prohibited.

III. Electrical Control System Maintenance: Identifying Hidden Dangers and Ensuring Stable Operation

The electrical control system is the "brain" of the portal crane, comprising control cabinets, motors, sensors, wiring, limit devices, grounding systems, etc. Electrical faults are characterized by their high degree of concealment, suddenness, and danger, making them a key focus and challenge in maintenance work.

Common problems in routine maintenance fall into three categories. First, environmental corrosion causes faults. During open-air operations, dust, moisture, and salt spray can easily enter electrical cabinets and junction boxes, leading to dust accumulation, moisture absorption, and oxidation of wiring, causing problems such as poor contact, short circuits, and leakage. The incidence of electrical faults increases significantly, especially during the humid rainy season. Many maintenance personnel neglect dust and moisture prevention cleaning of electrical cabinets, only repairing them after a fault occurs. Second, safety protection devices malfunction. Core safety components such as lifting capacity limiters, height limiters, luffing limiters, anti-collision devices, and emergency braking devices are prone to sensor malfunction, signal deviation, and response lag after long-term use. If regular functional testing and calibration are not performed, overload and over-limit operations will fail to trigger automatic warnings and shutdowns, leading to crane safety accidents.

Thirdly, non-standard wiring and grounding, coupled with prolonged rotation and amplitude vibration of equipment, can cause aging of wiring, damage to insulation layers, loosening of terminals, and wiring malfunctions, posing risks of electric shock and equipment malfunction. Simultaneously, some equipment grounding devices may be corroded, loose, or have excessive grounding resistance, rendering lightning and leakage protection ineffective. During thunderstorms, this can easily lead to electrical breakdowns, equipment damage, and electric shock accidents. Furthermore, prolonged operation can cause signal drift and parameter instability in the PLC control system; failure to regularly calibrate and adjust will directly affect the accuracy of equipment operation.

For electrical system maintenance, meticulous and routine protective measures must be implemented. Daily cleaning of dust and stains inside and outside the electrical cabinet is necessary. The integrity of wiring insulation and the tightness of terminals must be checked. Dust and moisture-proof covers should be installed in humid and salt spray conditions. The dryness of the electrical system should be checked promptly after rain to prevent short circuits and leakage hazards. Monthly full-function testing and accuracy calibration of all safety protection devices are required to ensure sensitive limit switches, reliable braking, and accurate overload warnings, preventing the malfunction of protection devices. Regularly inspect the grounding resistance and lightning protection device performance of the equipment, and replace corroded or malfunctioning grounding components to ensure compliant and effective grounding. Establish a regular commissioning system for the electrical system, promptly calibrate sensor signals, and correct control system parameters to ensure precise equipment operation and stable performance.