How to use flexible shafts properly in polycrystalline furnace lifting devices

Thread Content

With the development of solar cell applications, the output of polycrystalline furnaces has increased significantly. This article explains the proper use of flexible shafts in furnace lifting devices. It features a typical three-column furnace structure; in the past, electric control technology was used to operate the closing of the furnace. The lifting mechanisms for the three columns rely on motors and sensors to ensure synchronized lifting and lowering, enabling smooth operation without any jamming. Currently, some manufacturers use flexible shafts to connect and drive the lifting devices of the three columns, which effectively solves the synchronization issue and significantly reduces costs. Below are the two common methods for driving via flexible shaft connections. 1. In the series type, the motor-driven lifting device 1 drives the lifting device 2 via a flexible shaft 1, and drives the lifting device 3 via a flexible shaft 2. It is clear that flexible shaft 1 has to support two lifting devices, while flexible shaft 2 only has to support one lifting device. Advantages ； With the same rotation direction for the flexible shaft, it is easy for designers to determine which rotation direction to use. Two completely identical flexible shaft assemblies can be used. Disadvantages: A. The two flexible shafts are subjected to different forces; therefore, the diameter of flexible shaft 1 must be determined based on the torque of the two lifting devices, which results in a relatively large diameter. B. The soft shaft experiences rotational lag when subjected to force, meaning there is a slight delay between lifting device 1 and lifting device 3. II. The parallel-type motor-driven lifting device 2 is connected via flexible shaft 1 and flexible shaft 2. Advantages of drive lift device 3 and lift device 1 ； A. The soft shaft experiences rotational lag under load; theoretically, lifting device 3 is the same as lifting device 1. B. The two flexible shafts are subjected to the same force, so flexible shafts of the same diameter can be used. Disadvantages: A. It is a bit difficult to determine the rotation direction of Soft Shaft 1 and Soft Shaft 2; the schematic diagram above explains this, and the viewer can use a pen to simulate and determine the rotation direction of the soft shafts. B. Since the diameter of the flexible shafts is the same, obvious markings must be made for visual identification, and care must also be taken to the rotation direction during assembly. Next, we will explain some knowledge about flexible shafts. First, a flexible shaft is usually composed of a steel wire in the center, with several layers of steel wires wound around it alternately. Each layer contains 4 to 12 steel wires, and the winding directions of the wires in adjacent layers are opposite. Finished flexible shafts are distinguished by left-hand and right-hand rotation, which is necessary to accommodate different motor rotation directions and to ensure the shaft’s lifespan. The most basic component of a flexible shaft is steel wire, and most of the parameters of such a shaft depend on the steel wire. As shown in the figure, the flexible shaft is composed of several layers of steel wires, with 4–12 wires per layer; carbon steel is used for the majority of these wires. 2. Parameters of the flexible shaft: 1. Breaking torque: The torque required to break the flexible shaft. Note that the torque required to tighten the outermost steel wire of the flexible shaft is the highest, while it is lower otherwise. This parameter can be measured, but it is destructive. Generally, the applied torque should be 25% or less of the torsional breaking torque in the same rotation direction. 2. Rotation direction: The rotation direction of the outermost steel wires is right-handed when it is the same as that of ordinary screws. 3. Minimum bending radius: For cables of the same diameter, the greater the torque, the larger the bending radius. 4. Rotational speed: The smaller the diameter, the higher the rotational speed. III. Selection principles 1. Determine the diameter based on torque. At the same power transmission level, it is recommended to use a high rotational speed and low torque. Small diameter for flexible shafts. 2. Determine the rotation direction of the flexible shaft based on the direction of use; if force is applied in both directions, select the diameter corresponding to the minimum torque. Modify the flexible shaft structure and the wire diameter to ensure that the torque in both directions of the flexible shaft is similar. 3. The quality of flexible shafts available on the market varies greatly; the breaking torque can be easily measured using a torque wrench, and this value represents a static parameter. Differences in materials, processing methods, and heat treatment all affect the lifespan of flexible shafts. 4. Calculate the bending radius of the flexible shaft during operation; it should not be less than the allowable radius. Try to avoid excessive bending during design. The more bending there is, the greater the power loss and the shorter the lifespan of the flexible shaft. 5. Protective tubes for use in conjunction with other components: metal hoses, as well as PU, POM, and PA plastic hoses. When using plastic hoses, pay attention to the grease; synthetic greases are recommended as they have good compatibility with plastic. If the flexible shaft sways frequently during use, it is recommended to use a hose with a steel wire braided layer in the middle. Ordinary single-filament or double-filament hoses will deform when pulled by hand, while hoses with a steel wire braiding layer will not deform. 6. Allowable tightening torque for the flexible shafts commonly used in polycrystalline furnace systems, for reference: A. Torque-resistant type, diameter 10mm: 9.8 N.m B. Torque-resistant type, diameter 12mm: 13.5 N.m C. Transmission type, diameter 15mm: 16 N.m D. Transmission type, diameter 20mm: 24 N.m