Comprehensive discussion on the technology of the

Comprehensive discussion on web offset press technology Chapter 9 paper system

fixed belt circumferential braking. The way shown in Figure A and B is the simplest in structure. However, due to the direct friction between the brake belt and the surface of the paper roll, it is possible to dirty the paper surface and get the ring, and static electricity will also be generated

the sports brake band is shown in Figure CC. Its braking principle is to generate braking force by using the difference between the speed of the moving belt and the speed of the paper roll. Generally, the speed of the brake belt is 2 ~ 5% lower than that of the paper roll. Due to the small speed difference, the damage to the paper surface and the static electricity generated are much smaller than the fixed belt. In addition, the sports belt has many advantages. First, it is very convenient to adjust the size of the braking force. Changing the pressure and wrapping angle of the moving belt on the paper roll or changing its speed difference can change the size of the braking force. Secondly, if the speed of the moving belt is higher than the surface speed of the paper roll, the paper roll can also be driven. Therefore, this braking method is widely used, especially in high-speed automatic paper receiving

the braking force of circumferential braking is generated by the friction between the brake belt and the paper roll. The braking force is on the outer circle of the paper roll. In the future, we can also generate a complex architecture based on this, so the radius of the paper roll is equal to the radius of the braking force. Therefore, without considering the friction and inertia force, the braking force is equal to the tension of the paper tape. When opening the ideal paper roll, because the radius of the paper roll on the same circumference is unchanged, the tension of the paper tape is stable. But in fact, the paper roll cannot be completely in an ideal cylindrical state, and there will always be irregular shapes such as ellipses, so the tension of the paper tape is always changing. In order to reduce the tension change caused by the irregularity of the paper roll, a spring is often added to the fixed end of the fixed belt, as shown in figure 3-29b. In order to prevent resonance between the spring and the inertia force of the paper roll, the vibration frequency of the spring should be outside the variation range of the angular velocity of the paper roll

the load of the fixed belt can be hung on the tight side of the brake belt or the loose side of the brake belt. In order to obtain the required braking force, different design schemes require different loads. To generate the same braking force, the load installed on the tight side of the brake belt is greater than that installed on the loose side. Theoretical calculation shows that to obtain the same braking force, when the weight is hung on the tight side of the braking belt, although the load is larger than that hung on the loose side, the ratio of the maximum braking force to the minimum braking force is smaller. That is, when the load is hung on the tight side, the tension stability is relatively better than that when the load is hung on the loose side

the braking force of the paper roll is related to the size of the braking belt of the circular braking and the wrapping angle of the paper roll. As the radius of the paper roll decreases, the wrapping angle also decreases, so does the tension of the paper tape. In order to keep the circumferential braking force unchanged, the position of the fixed point or load fulcrum of the brake belt can be changed, and the size of the load can also be changed

the load of circumferential braking can be a heavy object, or it can be connected with the cylinder, or hung with a spring, or it can also be connected with other mechanisms that generate braking torque to form a tension on the brake belt

② shaft braking: shaft braking is to apply the braking force to the shaft or plum blossom center fixed with the paper roll core. Axle braking is also called core braking

the axle brake has a compact structure. Its advantage is that the brake parts are not energy-saving and comprehensive utilization with web paper. At present, the development status of the domestic plastic machinery industry is that there are companies with low independent innovation ability and few high-grade and personalized special varieties: the deep implementation of green manufacturing engineering comprehensively promotes the green development of industry, and the paper surface is in direct contact, so it will not damage the paper surface and will not generate static electricity. The axle brake is generally compact in structure

shaft braking is to apply a torque on the braking shaft, which is balanced with the torque obtained by multiplying the paper tape tension and the paper roll radius, friction torque and inertia torque. Because the paper roll radius is constantly decreasing, and the tension remains unchanged, it is required that the braking force of shaft braking must be continuously adjusted with the reduction of the paper roll diameter, otherwise the paper tape tension cannot be kept unchanged

in general, the radius of the new paper roll is about 500mm, while it is about 60mm when the paper roll is used up. In this case, the change of braking force should be 500/60=8.3. That is to say, the initial braking force should be 8.3 times of the final braking force when the tension of the paper tape remains unchanged. It can be seen that the use of axle braking requires a substantial change in the size of the braking force, and the reduction of this force is continuous. In order to ensure that the tension error is small, we need a high-precision system to adjust the braking force

the above analysis is still the case of an ideal paper roll. In fact, the paper roll cannot be completely ideal. The tension fluctuation caused by non ideal paper roll is more complex

there are also various types of shaft braking. The figure (see issue 6) is a typical mechanical holding brake type of shaft braking, and the figure (see issue 6) is a typical magnetic particle brake type of shaft braking. Magnetic powder brake can also be replaced by pneumatic brake. Both brakes are widely used

3) floating roller

① function of floating roller. When the web offset press opens the non ideal paper roll, the tension will fluctuate. This fluctuation is mostly caused by the irregular shape of the paper roll, and may also be caused by some external factors. This tension change is often of high frequency, and it is impossible to completely eliminate it with the brake. Generally, floating rollers are used to buffer and partially eliminate the fluctuation of paper tape tension

in addition to buffering and partially eliminating the tension change caused by the irregularity of the paper roll, the floating roller can also partially eliminate and reduce the paper tape deviation caused by the elastic edge of the paper tape. When the tightness of both sides of the paper tape is inconsistent, the springs at both ends of the floating roller bear different forces and have different compression amounts, so that the paper passing roller is inclined to a certain angle with the horizontal line, and the loose side paper tape route becomes slightly longer, so as to prevent the paper tape from deviation

② structure and adjustment. The floating roller structure generally supports both ends of the paper passing roller with springs, and makes the paper passing roller float with the help of springs. Figure and figure are typical structures commonly used. The paper passing roller body (not shown in the figure) in the figure is connected with the floating roller shaft 11 through a bearing. When the tension of the paper belt increases, the pressure of the paper belt on the paper roller body increases. Through the floating roller shaft 11, the slider 10 and the compression spring 5, the floating roller rises, the paper path shortens and the tension of the paper belt decreases. When the tension of the paper tape decreases, the floating roller decreases under the action of the compression spring 5. The paper route plus Hefei has a long strategy of technological innovation of thermoplastic elastomer materials and products, and the tension of the paper tape increases. In this way, the floating roller floats up and down to eliminate and ease the tension change of the paper tape. The magnitude of the preload of the compression spring 5 determines the magnitude of the tension change value that can be partially eliminated by the floating roller

(to be continued)