Discussion on quality control of drawing film wind

2022-08-18
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Discussion on the quality control of stretching film reeling

after preheating, stretching, shaping and cooling, the plastic sheet is output by the stretching machine and enters the film traction device. The function of the traction device is to flatten, cool, detect the longitudinal and transverse thickness of the stretched film, then cut off two waste edges (and recycle the waste edges through the crusher), and finally send the film to the winder at a constant speed

the stretched film passes through the tension control roll, flattening roll, tracking roll (also known as pressing roll) of the winder, and finally winds on the winding core of the winder to complete the film forming process. The film on the roll core (commonly known as the master roll) is generally only used as a semi-finished product of the production line. According to the needs of users, it needs to be cut and rewound again

film winder is one of the most important equipment in the film production line. Its performance and quality directly affect the quality and yield of the finished film. The main structure of the winder is shown in the right figure

I. mechanism of film winding

1 Tension detection roller

this roller is the main component to control the reasonable tension of the film during winding. Usually, the tension of the film is detected by the pressure sensor under the bearings at both ends of the tension roller, and the detected signal controls the speed of the winding motor through the electronic circuit to ensure the appropriate winding tension

the research, development and utilization of high-performance natural fibers and their composites have become a hot topic in global research. 2 The flattening roller

flattens the film and eliminates some longitudinal wrinkles produced by the film under the action of tensile stress

3. The tracking roller

is equipped with a tracking roller (also known as the pressing roller) that can change the position in front of the winding core of the winder. Its main function is to press the film against the winding core to implement contact winding or small gap winding, so as to quickly turn the flat film onto the winding core and realize the purpose of flat winding. At the same time, with the help of the tracking roller, a certain amount of pressure is exerted on the master coil to timely eliminate the air between the film layers during winding, so that the master coil is not loose. Generally, the air content in the master coil can be reduced to 12% - 18% after using the tracking roll

4. The winding roller

is driven by the winding motor. The control system of the winding speed is connected with the drive system of the stretching machine, synchronized with the stretching machine, and controlled by the feedback of the tension controller

5. Rotary table and empty winding core

when the film is full of a mandrel, it is not allowed to stop the machine to replace the winding core, so the rotary table turns back 180 °, the mother coil turns away, the empty winding core enters the winding position, then cut off the film, stick the film on the new winding core, and continue winding

second, the influence of film tension on the winding quality

in order to pull the film and roll it onto the winding core, a certain pulling force of stretching and tensioning must be applied to the film, in which the force of tensioning the film is tension. Generally, due to the different material thickness and properties of the film and the different winding methods, the tension can be set between 100 ~ 600N

the winding tension directly affects the quality and yield of product winding. If the tension is too large and the winding is too tight, the film is easy to wrinkle; The tension is insufficient, the amount of air brought into the film is too much, and the density of the mother roll film is small. The film is easy to produce axial slip and serious dislocation on the core roll, so that it cannot be unloaded. During slitting, the winding shaft swings greatly, which affects the quality of the slitting film. Therefore, the winder must have a good tension control system

third, the control system of the winding roll

the control of the winding roll mainly includes two parts: speed control and tension control. When winding the film, with the increase of the diameter of the mother coil, if the speed of the winding roll is still unchanged, with the increase of the speed of the winding line, the winding tension will inevitably increase (because the speed of the film sent from the traction device is constant), which will not only cause the inner looseness and outer tightness of the film coil, and the outer film will wrinkle the inner film, but also increase the difficulty of rewinding and affect the quality of slitting. Therefore, the winding speed of the winding roller must decrease with the increase of the diameter of the mother coil

there are three main control schemes for the winding roll:

1 The tension sensor is installed under the bearing of the tension detection roller. The detected film tension is converted into an electrical signal and sent to the tension regulator. After comparing with the original set tension signal, PID calculation is carried out, and then input into the winding motor controller to control the speed of the winding roller

generally, the linear speed of the winding roll is set to 105% - 110% of the output speed of the tractor. In fact, due to the influence of the elasticity of the film and the tension torque, the linear speed of the winding roll will not exceed the output speed of the tractor. The advantages of this scheme are high control accuracy, good dynamic performance and wide application range

2. Control scheme of indirect tension detection using floating rollers

this scheme is to install a set of floating rollers in front of the tracking roller, and the position of the floating roller is detected by a potentiometer. The way of tension control is to keep the tension constant by maintaining the position of the floating roller as unchanged as possible. Due to the complex mechanical structure, it is rarely used

3. The magnetic particle clutch is used to control the rotating torque of the input winding roll to achieve stable tension. The precision is the data case

the magnetic particle clutch is composed of the driving part and the driven part, which is connected with the winding roll through the universal coupling and other transmission mechanisms, and the middle is filled with fine iron magnetic particles as the torque transmission medium. The exciting coil is connected with a certain current to form a magnetic field. Magnetic particles are magnetized. Magnetized magnetic particles attract each other to form a chain arrangement. When the active part rotates at a constant speed, it destroys the coupling force between the magnetic particle chains and forms a circumferential tangential force. The product of the tangential force and the radius of the magnetic particle coil is the rotating torque that drives the winding of the driven part, realizing the coupling of the output torque from the active part to the driven part in continuous rotation

if the given exciting current remains unchanged, the output torque:

m = R ·∑ τ= Constant

where: R magnetic particle clutch magnetic particle ring radius; τ Tangential resistance formed by magnetic particle chain. And the film tension is: F = m/p = R ·∑ τ/ρ Where: ρ Roll radius

with the ρ The value increases gradually. If the torque M does not change, the tension f will decrease. The change of tension triggers the sensing mechanism to send a feedback signal U2, which is superimposed with the given signal U1 to form a comprehensive signal △ u increases (set △ u = u1u2). After circuit conversion, the output torque M increases, and the tension f remains unchanged. Achieve stable tension

IV. attenuation of winding tension and tension compensation

it is generally believed that maintaining a constant film tension during film winding is the most conducive to the apparent quality of the finished film. But in fact, because there is a certain amount of air (12% - 18%) between the film layers, even under constant tension, the outer film will wrinkle the inner film. The solution to this problem is to automatically attenuate the tension of the film according to a certain law with the increase of the diameter of the mother coil. Usually, the tension attenuation under different diameters should be input into the computer in advance before winding. During the production process, the operator can adjust it at any time according to the film winding situation

when changing the film, Shandong Province not only has Wanhua, Dongyue, Luxi and other new chemical material giant enterprises with an annual output value of more than 10 billion yuan to the new core surface, the coil diameter suddenly changes, the speed of the winding roll and the moment of inertia of each system change greatly, causing sudden changes in tension, so that the film is often broken during changing. Therefore, in the tension control system of the film, a tension compensation device must be set to realize soft start and soft stop and prevent wrinkles of the rolled film

v. conclusion

1 The quality of film reeling is mainly affected by the tension of film reeling, so the control system of reeling roll is the key

2. The reeling quality of the film is also affected by other factors, such as the material, temperature, properties (such as elastoplasticity) and the uniformity of the film thickness. Therefore, the set winding tension must be adapted to these characteristics of the film

3. Tension attenuation and tension compensation during film reeling are also important factors affecting reeling quality

4. In order to ensure the accuracy of tension detection, before use, the tension detection roller of the winding mechanism must be dynamically balanced at a speed 125 times higher than the maximum production speed, and the film should have a large enough wrap angle on its surface during use

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