Operation practice of the hottest soft calender

2022-10-14
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Operation practice of soft calender

Abstract: This paper summarizes the problems existing in the operation of soft calender and the countermeasures taken, and points out the matters that operators should pay attention to and the measures to upgrade the performance of soft calender

key words: soft roll; Vibration; crackle; Gluing material; About the author: Yang Zhenyu, engineer, equipment director of the third paper workshop of Yueyang Paper Group Co., Ltd

1 overview

the 3800mm soft roller calender put into operation by Hunan Yueyang Paper Group at the end of 1998 was supplied by Voith sulze. Therefore, generally, single column calender is used, The basic parameters of the machine are as follows: 〓〓

● the coverage width of the soft roll is 3950mm

● the designed maximum operating line pressure is 350kn/m

● the maximum temperature of the hot roll surface is 160 ℃

● the designed speed is 1000m/min

● the power distribution heating hot oil system

● the arrangement is four rolls and two pressure zones, that is, 2 × 2 arrangement structure. Since it was put into production, it is mainly used for finishing double offset paper, paper, LWC, high-quality magazine paper, etc

The structural diagram of the soft calender is shown in Figure 1

Figure 1 Schematic diagram of soft calender

1-cylinder 2-hard roll (main drive roll) 3-soft roll (SR) 4-frame

2 problems

the soft calender of our company has the following main problems in the operation practice of more than two years:

● the operation cycle of soft roll in the first pressing area is short, and the grinding roller cost is high

● the soft roller in the first pressing area vibrates greatly, and after running for a period of time, there are streaks ("ridges") on the rubber covering surface, affecting the paper quality

● the rubber coating at both ends of the soft roll against the outer edge of the paper web is cracked, affecting the safe operation of the production line

● the oil pump in the hydraulic system is worn out too early, resulting in the inability to adapt to the production of paper grades that require high-speed pressing to finish

● early failure of mechanical seal of hot oil rotary joint

3 cause analysis and Countermeasures

3.1 streaks appear on the rubber covering surface of the soft roller

the operation cycle of the soft roller is short, the vibration is large, and streaks appear on the rubber covering surface (at the same time, streaks appear on the paper). When producing paper, the linear pressure with streaks is 120 ~ 150kn/m; For high-quality magazine paper, the line pressure is 100kn/m; At LWC, the line pressure is 100 ~ 330kn/m

according to the analysis, the operation cycle of the first softening roller for the production of low quantity paper (49g/m2) is relatively short, and they all get off the machine due to large vibration and streaks on the paper. The operation cycle of high-quality magazine paper and double offset paper (55 ~ 75g/m2) with large production quantity is longer, but rich energy-saving schemes have been developed from various angles. The reason for getting off the machine is the same as that of producing paper

3.1.1 cause analysis

● roller grinding quality is very important. Once, the surface roughness of soft roll grinding did not meet the requirements, and it only operated for 10 days

● from November 1999 to May 2000, the soft pressing roll was changed once every 24 days on average, while from July to November 1999, the soft pressing roll was basically changed in 15 to 17 days. Although there are relevant research reports and analysis of this kind of polyurethane material in China, it has a great relationship with the operating conditions. Figure 2 is the operating reference data relative to the soft roll material of top Tec Ⅳ. During operation, the pressurization conditions should generally avoid entering the dangerous area (that is, the shaded part in Figure 2)

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