Introduction to Safety Protection Devices for Electric Hoist Cranes

A葫芦-type crane refers to a crane that uses an electric hoist as its lifting mechanism. Due to its simple structure, convenient operation, and low cost, it is widely used in industries such as machinery, chemical engineering, light industry, and railways. However, because of the unique nature of this type of crane, ground operators often take on multiple roles simultaneously—handling operation, rigging, and even command tasks—leading to numerous potential safety hazards during use.

To prevent lifting injuries caused by this type of crane, GB6067 ― 1985 Relevant national standards, such as the "Safety Code for Lifting Machinery," already mandate that hoist cranes be equipped with essential safety devices, including limiters, end stops, buffers, and safety braking systems. These safety features have significantly enhanced the operational reliability and safety of hoist cranes. However, due to various factors—such as inherent design flaws or manufacturing defects—current safety measures for hoist cranes remain imperfect. Based on routine inspection experience, issues still persist in areas like phase-loss protection, anti-shaft-breakage safeguards, mechanisms to prevent electric hoists from falling, and the proper installation of buffers.

1. Phase and Phase-Sequence Protection Device. Since hoist-type cranes are equipped with three-phase asynchronous conical-brake motors as their power units, the direction of rotation of the three-phase induction motor depends on the phase sequence of the supplied power. If the phase sequence of the power supply changes, the motor will rotate in the opposite direction compared to its original motion. In such cases, when the "Lower" button is pressed, the lifting attachment actually moves upward—worse still, the limit switch at the upper end fails to activate, significantly increasing the risk of accidents. Every year, these types of cranes experience incidents caused by incorrect phase sequences, leading to issues like drum rupture, deformation of the hook assembly due to compression, and even wire rope breakage. Currently, in China, these devices are widely manufactured and extensively used. CD 、 MD The model electric hoist does not have phase-loss and phase-misconnection protection measures in place. ( There is no requirement to install it even when using an electric hoist. ) To prevent phase failure from causing lifting-related injury accidents, a phase-loss and phase-misalignment protector has been integrated into the electrical control system of the hoist-type crane.

When the power supply experiences phase failure or phase misalignment, the phase-failure protection device activates, causing the main power contactor to open. The crane can only resume operation once the power supply returns to normal. This not only prevents the drum from being crushed due to phase misalignment but also safeguards the motor from damage caused by running on a single phase. Therefore, the role of the phase-failure protection device is absolutely essential.

II. Anti-Disconnection and Anti-Runaway Protection Devices. During operation, electric hoists experience gradual wear on the wheel flanges and treads, leading to an increasing gap between the wheels and the track. If this operational clearance is not adjusted promptly, the hoist could potentially derail and fall, resulting in serious lifting-related injuries. Additionally, due to the unique design of the wheel axle assembly, cracks in the axle may remain undetected. Without proper monitoring and control, these cracks could eventually lead to axle failure and subsequent falling accidents. To prevent such incidents and ensure the safe operation of electric hoists, it is recommended to install additional anti-disconnection and anti-runaway protection devices at appropriate locations on the hoist. These devices will effectively suspend themselves from the track in the event of derailment or axle breakage, thereby significantly reducing the risk of lifting-related injuries.

3. Buffers. According to GB6o67 ― 1985 According to the "Safety Regulations for Lifting Machinery," buffers must be installed at the end points of electric hoist operation. However, since there are no specific guidelines on the exact installation location of these devices, electric hoists currently in use across China typically have their buffers mounted in the middle section of the I-beam. When the hoist's running wheels collide with the buffer, the device effectively absorbs the impact energy. Yet, due to the unique structural design of the electric hoist, when the flange of the suspension wheel strikes the buffer under inertial forces, the buffer experiences exceptionally high levels of wear and tear. Over time, this leads to a gradual loss of the buffer's original functionality, increasing safety risks during hoist operation and significantly reducing the stability of the hoist’s movement. To prevent such failures, an alternative installation approach is recommended: positioning the buffer directly on the lower surface of the I-beam. In this setup, the collision between the buffer and the hoist’s suspension lug serves as the primary buffering mechanism, enhancing both safety and reliability while dramatically extending the buffer’s service life.