The unwinding mechanism of the rewinding machine is the "starting point" of the entire equipment, and its core task is to stably carry the original roll (the material roll to be rewound), and accurately release the material according to the downstream winding rhythm, while cooperating with the tension system to avoid material relaxation, stretching or deviation. Its design directly affects the quality of subsequent rewinding (such as winding flatness, tension stability), so it needs to be designed according to material characteristics (hardness, thickness, toughness, etc.) and original roll specifications (diameter, width, weight). Here is a detailed analysis:
1、 Core functions
Carrying original rolls: Using mechanical structures to stably support original rolls of different weights and sizes (from small yarn rolls weighing a few kilograms to large cable rolls weighing several tons), preventing shaking or falling during unwinding.
Controllable release of materials: Based on the winding speed and tension requirements, the unwinding speed of the original roll is controlled by braking or active driving to avoid "over speed unwinding" (causing material accumulation) or "unwinding lag" (causing material to be pulled apart).
Coordination with tension adjustment: Linked with the tension system, it provides a stable initial tension for the material by adjusting the unwinding resistance (or driving force), which is the "front-end execution point" of the tension control system.
Correcting original roll deviation: Some devices integrate correction functions to ensure that the edges of the original roll are aligned, avoiding material deviation during the unwinding stage (especially crucial for wide materials such as film and paper).

2、 Key components and their functions
The unwinding mechanism consists of multiple precision components working together, with the core components including:
1. Unwinding support structure (original roll bearing unit)
Unwinding rack/unwinding arm: The basic frame that carries the original coil, and the load-bearing capacity is designed according to the weight of the original coil (aluminum alloy for light weight and steel for heavy weight). Some unwinding racks can be moved by sliding rails, making it convenient to load and unload the original roll; The unwinding rack of large equipment, such as ton level cable rewinding machines, will also be equipped with hydraulic lifting devices for easy manual or forklift loading.
Unwinding reel (core carrier): The shaft that directly passes through the inner hole of the original reel is the key to connecting the original reel and unwinding power. Its design needs to meet two major requirements: "easy loading and unloading" and "firm clamping". Common types include:
Inflatable shaft: The most widely used, with multiple elastic airbags distributed on the surface of the shaft. After compressed air is introduced, the airbags expand and tightly fit the original inner hole of the coil to achieve clamping; After deflation, the airbag contracts and the original roll can be quickly removed. The advantages are uniform clamping force, adaptability to different inner diameters (adjusted by airbag expansion), and suitability for most materials such as film, paper, cables, etc.
Conical shaft: composed of two conical shafts, the distance between the two shafts can be manually or electrically adjusted, and the friction force of the conical surface can be used to clamp the inner hole of the original roll. The advantages are simple structure, low cost, suitable for hard paper core rolls with fixed inner diameter (such as textile yarn rolls), but the clamping force uniformity is slightly worse than that of inflatable shafts.
Steel shaft+flange: For heavy-duty and large-diameter coils (such as metal wire coils), a solid steel shaft is used to position them with flanges on both sides, and the coils are fixed with bolts. This method has strong load-bearing capacity but low loading and unloading efficiency.
2. Unwinding power and braking device (speed control core)
The "speed control" of the unwinding mechanism is the core, which can be divided into two types based on material characteristics: passive unwinding (driven by material tension to rotate the original coil, controlling resistance through braking) and active unwinding (driven by a motor to rotate the original coil, actively releasing the material), corresponding to different power/braking components:
Passive unwinding braking device (suitable for materials with medium to low speed and good toughness, such as paper and film):
Magnetic powder brake: The most commonly used method is to control the friction between magnetic particles by changing the excitation current, thereby adjusting the braking torque (resistance) of the unwinding shaft. The advantages are continuously adjustable braking torque (response speed ≤ 0.1 seconds), high tension control accuracy (error ± 1%~2%), suitable for materials sensitive to tension (such as thin films and fine threads).
Electromagnetic brake: It generates braking force by attracting friction plates with electromagnetic force. It has a simple structure and low cost, but the accuracy of braking force adjustment is low (step adjustment), which is suitable for scenarios with low tension requirements (such as coarse hemp rope and thick plastic tape).
Mechanical friction brake: By compressing the friction plate with a spring or cylinder to generate resistance, the braking force can be manually adjusted. It has low accuracy and slow response, and is only used for simple rewinding machines (such as small textile rewinding machines).
Active unwinding drive device (suitable for high-speed, heavy-duty, or stretchable materials such as cables and metal foils):
Servo motor+reducer: The unwinding reel is directly driven by the servo motor to rotate, and the tension system signal is received through the PLC to adjust the speed in real time (matching the winding speed). The advantages are fast response (speed adjustment accuracy up to 0.1rpm), stable driving force, suitable for high-speed rewinding (line speed>300m/min) or heavy-duty raw rolls (weight>1 ton), and can avoid material stretching deformation caused by "passive pulling" (such as elastic materials, thin metal foils).
Variable frequency motor: The cost is lower than servo motors, and the unwinding drive is achieved through variable frequency speed regulation, with slightly lower accuracy (speed error ± 2rpm), suitable for scenarios with moderate speed stability requirements (such as rewinding of medium thickness plastic pipes).