Headbox and forming of the 120000 ton low weight c

Discussion on the selection of headbox and shaper for Yueyang Paper 120000 ton low weight coated paper project

key points: This paper describes the selection of headbox and shaper of paper machine for Yuezhou paper 120000 ton project and the technical exchange with foreign investors. It indicates that the concentration is diluted, the pipe diameter on both sides is increased and adjusted. Pay attention to whether the CPU frequency (11.0592Mhz) and the comparison voltage are stable or drift while adjusting the quantity? This is a major and common trend if there is a directional alignment of faulty soldering problems. Foreign businessmen have also improved and perfected their internal structure. In the former, it is mainly the combination of roll and plate, which meets the requirements of high-speed paper machine. In this paper, the dewatering mechanism of the former and the guarantee of paper evenness are discussed in order to deepen the understanding of foreign new technologies and make technical preparations for contract negotiation and correct type selection

key words: headbox; Shaper; Concentration dilution method; Roll plate combination; High speed paper machine; Low weight coated paper

Hunan Yueyang Paper Group Co., Ltd. has an annual output of 120000 tons of low weight coated paper (LWC) technical transformation project. Before and after the project approval, it has contacted several major paper machine manufacturers and conducted many technical exchanges. Here only the headbox and shaper of paper machine are discussed

Hunan modern headbox continues to emphasize that the ingredients are evenly mixed, dispersed but not flocculated, and enter the distribution pipe at the same speed. After two accelerations at the pipe bundle and outlet, the paper with high strength and micro turbulence is obtained, and the full width is sprayed to the shaper at the same speed. The main features of the newly developed headbox are as follows: first, the flow on both sides is adjusted to maintain the stability of fiber directional arrangement; Second, the uniform distribution of banner ration is adjusted by diluting the paper concentration with dilution water. With this method (concentration method), the upper lip of the weir plate can be adjusted up and down without adjusting the flow, so as to keep the fiber orientation unchanged. This also brings two benefits. First, the interval of the dilution water control valve is generally only about half of the adjustment interval of the lip plate, which improves the accuracy of the quantitative adjustment of the banner; Second, it avoids the permanent deformation of the lip caused by improper adjustment, and can consistently maintain the quantitative consistency of the banner

several manufacturers in Hunan reported headboxes with concentration regulating devices, with different design structures. Adding a set of dilution device for white water purification and transmission and entering the headbox will cost more. Some manufacturers said that some modern headboxes are still adjusted by weir plate mouth, and adopt automatic or remote control adjustment methods. It is considered that the banner ration adjusted in this way can also reach the level close to the concentration method. Of course, the investment of this method will be less, but in terms of quality (including the directional arrangement of fibers), the concentration method is better

the design of Hunan headbox pays great attention to hydraulic dynamics. In order to ensure the uniformity of the quantitative distribution of the whole banner, it is necessary to ensure the consistency of the flow rate and pressure of the slurry initially entering each distribution pipe. This is realized by the design of the shape of the main pipe. Companies now design it in the shape of a projectile rather than a simple conical tube. In order to meet the turbulence level required by the specific shaper of the high-speed paper machine, the internal structure of the headbox has also been improved compared with the past. For example, compared with the traditional counter flow headbox of MHI Beloit, the original pressure stabilizing section and the orifice plate in front of the counter flow are cancelled. After the distribution pipe is extended, a section of step diffusion is added, and the circular pipe is gradually changed into an approximate rectangular pipe, which is connected with each other at the outlet and flows to the neutral between the adjacent counter flow. They think that the velocity distribution of slurry flow is more reasonable. Another example is Valmet's OPTIFLO headbox, where fins are also used near the outlet to limit the turbulence scale and increase the intensity, and to control the turbulence level by changing its length and thickness

in a word, flow is the basic basis for headbox design. For the installed headbox, the allowable flow variation range is generally not more than 10%. If it is too large or too small, it will affect the horizontal quantitative consistency and paper evenness. This time, most manufacturers did not introduce the allowable flow range of headbox in the scheme. Only one company reported that it also listed the quantity of different paper types, different finished paper and base paper, the proposed headbox concentration and the corresponding flow. See the table on the next page for details

product variety ration g/m2

vehicle speed m/min

base paper ration g/m2

headbox concentration%

headbox flow l/min

lwc

double offset paper

coated paper

47

57

70

90

120

1200

1200

900

700

600

33.2

42.9

65.8

84.1

91.5

0.7

0.75

0.80

0.70

550 78

63263

65890

59546

61446

note: LWC and double offset paper in the table are the target products whose degradation performance can be adjusted and controlled according to different utilization needs through the design, synthesis, modification and processing of materials by scientific researchers. The coated paper was put forward and discussed by our side in an exchange

optiflo headbox

the quantity of base paper listed in Hunan table is calculated based on 97% pre drying dryness and 92% coiling dryness. From the flow listed in the table, it can be seen that: first, the outlet flow of headbox is within the range of 610, not called the experimental machine 00 l/min, floating up and down by 10%. The maximum deviation is +7.8% when producing 70g/m2 double offset paper. It is estimated that the retention rate (the moisture content of base paper is 3% when it enters the sizing press, and the dryness of slurry entering the high vacuum zone is 8%), so the first retention rate of LWC paper is about (60 ± 1)%, 69% ~ 71% for double offset paper, and 73% for medium coated paper