When a gantrycraneis in operation, especially during rotation, brake failure can pose significant risks and disrupt the normal working process. In this regard, a detailed analysis of the causes and corresponding solutions of brake failure during the rotation of the gantry crane is of great importance.
II. Observation of the Problem during Rotation
During the rotation work of the gantrycrane, when the brake fails, upon disassembling the rotating worm gear reduction box, it can be found that the limit torque limiter slips and fails before reaching its designed resistance torque.
III. Cause Analysis of the Brake Failure
(1) Frequent Start and Stop Operations In actual operation, the rotation start and stop of the gantrycraneare extremely frequent. This frequent operation leads to continuous relative motion and subsequent wear between the friction discs of the torque limiter and the tapered surface of the worm gear sleeve. As a result, the upper and lower friction discs gradually move closer along the tapered surface of the worm gear.
The junction of the upper and lower tapered surfaces of the worm gear sleeve forms an included angle, and its diameter is smaller than the diameter of the small end of the friction disc. Consequently, an annular boss is gradually worn out on the inner tapered surface of the worm gear. At this point, the pressing force generated by the compression spring is jointly borne by the conical surface and the plane of the annular boss.
When the pressing force borne by the plane of the annular boss becomes dominant, due to the short rotation arm and small friction surface of this boss plane, the frictional torque is reduced. Once the frictional torque becomes smaller than the originally designed torque, the aforementioned brake failure problem occurs.
To further illustrate this point, let’s consider the principle of torque generation. The frictional torque is calculated based on the product of the frictional force and the radius of the force arm. In the normal state, the frictional force is mainly generated by the contact between the friction discs and the tapered surface of the worm gear sleeve, and the force arm radius is related to the diameter of the relevant surface. However, when the annular boss is formed and the pressing force is mainly borne by its plane, the effective force arm radius corresponding to the frictional force on this plane is significantly reduced. At the same time, the area of the friction surface on the boss plane is also much smaller than that of the original tapered surface. These two factors combined lead to a significant reduction in the frictional torque, resulting in the brake failure phenomenon.
Moreover, the frequent start and stop operations not only cause wear on the surfaces involved but also affect the stability of the torque limiter’s performance. Each start and stop cycle subjects the components to sudden changes in force and motion, which can gradually change the mechanical properties and clearances of the parts. For example, the repeated impacts during braking can cause micro-deformations in the components, further affecting the accuracy of the torque limiter’s function and exacerbating the problem of brake failure.
(2) Influence of Wear on the Friction System The wear between the friction discs and the worm gear sleeve’s tapered surface is not a one-time occurrence but accumulates over time with the continuous operation of the gantry crane. As the wear progresses, the surface roughness and shape of the contact surfaces change. The original smooth and precisely designed contact surfaces gradually lose their ideal characteristics.
For instance, the wear may cause pits or scratches on the surfaces, which reduce the effective contact area between the friction discs and the worm gear sleeve. According to the principle of friction, the frictional force is directly proportional to the normal force and the coefficient of friction, and is also related to the contact area. When the contact area decreases, the frictional force generated under the same normal force will also decrease. This reduction in frictional force directly leads to a decrease in the frictional torque, which is another factor contributing to the brake failure.
In addition, the wear also affects the distribution of the pressing force. As the surfaces wear, the way the compression spring applies the pressing force may change. The spring may not be able to evenly distribute the force as it did originally, resulting in uneven wear and further affecting the stability of the frictional torque. For example, if the spring’s force is concentrated on a certain area due to wear-induced changes, that area will experience more severe wear and a more significant reduction in frictional torque, making the brake failure problem more pronounced.
IV. Troubleshooting Methods
(1) Disassembly and Modification of the Rotating Worm Gear Reduction Box To address the brake failure problem, the following steps are required. First, disassemble the rotating worm gear reduction box. This process needs to be carried out carefully to avoid causing additional damage to the components. During the disassembly, it is necessary to mark the positions and connections of each part clearly to ensure correct reassembly later.
After disassembling the box, remove the worm gear. At this time, pay attention to handling the worm gear carefully to prevent any scratches or other damages that could affect its subsequent use.
(2) Machining the Annular Boss on the Inner Tapered Surface of the Worm Gear Next, machine the annular boss on the inner tapered surface of the worm gear. The purpose of this operation is to eliminate the adverse effects caused by the annular boss. By using appropriate machining tools and techniques, remove the annular boss to make the junction of the two tapered surfaces of the worm gear sleeve a transition cylindrical surface.
It is crucial to ensure that the diameter of this transition cylindrical surface is slightly larger than the diameter of the small end of the friction disc. This size relationship is designed to restore the normal contact and force distribution between the friction discs and the worm gear sleeve. When the diameter of the transition cylindrical surface is set appropriately, the friction discs can be in better contact with the surface of the worm gear sleeve, and the pressing force can be more evenly distributed. This helps to reestablish a stable frictional torque, thereby solving the brake failure problem.
After machining the worm gear, carefully reassemble all the components of the rotating worm gear reduction box in the correct order and according to the marked positions. During the reassembly process, check each connection and fastening to ensure that everything is in place and tightened properly. Finally, test the rotation and braking functions of the gantry crane to verify that the brake failure problem has been effectively resolved.
In conclusion, the brake failure of the gantry crane during rotation is mainly caused by the frequent start and stop operations and the resulting wear on the friction system. By understanding the root causes of the problem and implementing the corresponding troubleshooting methods, such as disassembling and modifying the rotating worm gear reduction box and machining the annular boss on the inner tapered surface of the worm gear, the brake failure problem can be effectively addressed, ensuring the safe and stable operation of the gantry crane.
