Equipment selection and production practice of the

2022-09-19
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Equipment selection and production practice of paper machine (II)

2.2 optiformer clip forming Department

Figure 2 is the latest vertical gap former of Valmet company. The dehydration area is short (about 2.6m). In order to make the water removal on both sides of the paper web equal, the forming roll and vacuum couch roll are arranged on the outside and inside; In order to improve the forming of the paper sheet, the loading dehydration plate is added inside, which generates pressure pulse with the dehydration plate shoe on the outside; When the vehicle speed exceeds 1500m/min, it is necessary to add a vacuum suction tank to prevent the paper from falling off the surface. In this arrangement, the external dewatering accounts for 45% - 55% of the dewatering of the forming part, while the dewatering of the forming roll accounts for 70% of the external dewatering, and the dryness of the paper web outlet is 15% - 18%. The former can adjust the water removal on both sides of the paper web and control the uniformity of the paper web, the distribution of fillers, the retention of short fibers and fillers, etc. by making the contact ratio between the upper platen and the sample surface (about 1.04) through multiple vacuum devices and pulp speed. It is the best paper machine in China

2.3 shoe press

press is the bottleneck that limits the increase of the speed of the paper machine. Usually, increase the number of press passes and line pressure to improve the dryness of the paper, increase the strength of wet paper, reduce broken ends, and improve the operation performance of the press. The test shows that the size of the web dryness is directly proportional to the pressing impulse, which is the product of the average pressing area pressure and the paper passing through the pressing area time, and can also be obtained by dividing the line pressure of the pressing area by the vehicle speed. For the dryness of the pressed paper, the time of staying in the press area is more important than the peak pressure. The wide area press is designed according to this principle. Another way to solve the end breakage of the press web is to use vacuum paper guiding, so that the strength of the wet web is separated from the external force of paper guiding (see Figure 3), and the effects of centrifugal force, friction, gravity and stripping force on the stone roller are eliminated. Valmet's Optipress press is designed based on the above two principles, as shown in Figure 4. This kind of pressing has only two pressing zones. The tensile test (stress-strain test) on the first pressing zone is generally to clamp the maximum, minimum and average values of the test data on two ends of the material sample respectively. Each test gives the maximum, minimum and average values of the test data in two fixtures with a fixed distance of 1. The upper roll is symzl roll, and the lower roll is symzs, which is a self loading roll. When pressurized, the roll shell is pressed to the upper roll surface, and the forming design line pressure is 2 and the hail impact of golf ball size is 00kn/m. The second pressing area is wide area pressing. The upper roll is shoe roll and the lower roll is symzl roll. When pressurizing, the shoe plate is pressed down to form a design line pressure of 1000kn/m. The lower roller of the second pressing area is a conveyor belt, which does not dehydrate. It mainly eliminates the problem of the second pressing and rewetting of the paper web, and can reduce a paper guiding vacuum roller and transmission point. The dryness of the paper into the dryer can reach 50%

Figure 3 the relationship between the speed change of the paper machine and the external force of paper guiding and the strength of wet paper

Figure 4 Optipress straight through press

optipress straight through press test run, when the speed is increased to 1400m/min, the first press vibrates and cannot operate normally, and then the oil circuit of the pressurized part and the controllable part of the lower roll symzs is separated, and the rigid coupling is changed to a flexible coupling, And the use of automatic wool fabric swinging device (cocking system) can be solved. In the second press, the wool cloth and the conveyor belt in front of the original pressing area are pressed close to the conveyor belt with the help of the upper pressing roller. Due to the different operating performance of the wool cloth and the conveyor belt, the upper pressing roller is cancelled to separate them. Due to this change, the author believes that this will cause insufficient wrapping angle of the lower roller of the woolen cloth wrapping, so that the operation of the secondary press roller is not ideal. Valmet company has provided a modified drawing to increase the secondary pressure center by 250mm, and shut down and transform it at an appropriate time. (unfinished)

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