After-treatment equipment (Figures 1 and 2) makes up the main unit in a viscose staple fiber production line, and its normal operation directly affects stability of the whole production. The LH151 series of after-treatment equipment is the new large-capacity unit developed by Hi-Tech Heavy Industry (HTHI), with a width of 3,200 mm, 3,600 mm and 4,000 mm. The annual capacity can reach between 40,000 and 100,000 tons. The equipment is mainly used to clean impurities such as sulfuric acid, sodium sulfate and zinc sulfate of viscose staple fiber coming from the cutting machine, before it bleaches and finishes the fiber in order to make the fibers have a certain whiteness and good spinnability.
Development of After-Treatment Equipment
The LH151 series of after-treatment equipment includes the CS2 recovery trough (Model NH1501) and refining machine (Model H1511).
The CS2 recovery trough is made from stainless steel, with steam pipes on the bottom. There are two distributors assembled at the fiber inlet, which are driven by a gear motor. The distributors are swinging inside the trough to evenly distribute fibers.
The refining machine is usually divided into two parts, and is a friction drive type with multiple rollers. The first part is used to clean the fibers. There are usually 11-15 zones according to different processing methods, and each zone is equipped with a spraying trough above the sieve. Water overflowed from the spraying trough cleans the fiber. Under the sieve there is a collecting trough, which is used to collect the water. There is one pair of small squeeze rollers after each zone, in order to let as little liquid as possible go to next zone, and as a result improve the washing effect. The second part is used to oil the fiber. There are usually two zones, with the same object as the first part. In the front and rear of the second part, there is a pair of big squeeze rollers. A cylinder pressures the top squeeze roller. The front squeeze rollers are used to remove the water from the fiber layer as much as possible, so as to guarantee even oiling on the fiber layer. The rear squeeze rollers are used to remove redundant oil, to save oil and reduce the load on the drying equipment.
Every top small squeeze roller is driven by a gear motor with frequency control, and every big squeeze roller (both top and bottom rollers) is driven by two gear motors with variable speed control. The first sieve is driven by three gear motors, the second sieve by two gear motors and extra sieve by one gear motor. They all adopt frequency control. Each zone has a hood on the top, which is opened and closed by the cylinder and movable side doors on both sides. There is a set of tension and rectifying device in the first two sieves, respectively, which can ensure the sieve to run normally.
There is a sieve support frame below the sieve, keeping the net surface smooth, and there are baffle plates on both sides of the sieve, which can prevent the fibers from being dispersed. The equipment also has various kinds of alarms, such as sieve deviation alarm, to ensure normal operation of equipment.
Main technical characteristics of after-treatment equipment
The refining machine is a friction drive type with flat sieve and multiple rollers that are frequency controlled. It has the advantages of simple structure, reliable running and easy operation, which is convenient for centralized control. Two sets of correction devices for long sieves are made by the Leimer Company in Germany, and they can accurately adjust the long sieve running deviation. Each small squeeze roller, big squeeze roller and extra sieve are all frequency controlled, which can precisely guarantee the running is synchronous with long sieve.
Through lengthening the bottom squeeze roller, the length of it is longer than that of the top squeeze roller, avoiding the situation where the sieve is broken on the side face of the squeeze rollers while top and bottom squeeze rollers are pressing fibers.
For the large-capacity refining machine, in order to avoid the uneven pressing by top and bottom rollers caused by the weight of the reducer, there is a set of driving devices that is driven by motors separately on both sides of each top small squeeze roller. This device can make the top and bottom rollers bear average force while pressing fibers; the moisture content of fiber after pressing will be even; spraying device can be easily cleaned; quality of fiber improved and stress of sieve can be ameliorated, which is propitious to improve the stability of sieve running and prolong its lifetime.
Structural characteristics of sieve support frame of refining machine
The guide bar of the sieve support frame adopts a chute structure, which not only satisfies expansion release requirements on PTFE material under working temperature, but also avoids rolling out and turning up of guide bars as well as damage of sieve under abnormal operation.
High tightness structure of side hood of refining machine
Side doors, side cover and the last squeeze roller of refining machine adopt high tightness structure, which can prevent dust, etc., from contaminating the fibers, meeting processing requirements of high white fiber and reduce the internal heat losses, thereby improving the workshop environment.
Structural characteristics of CS2 recovery trough
The LH151 CS2 recovery trough adopts the adjustable connecting rod transmission mode driven by an explosion-proof motor. It can adjust the angle of the distributor at will to adapt to the user’s change of production process. The innovative structure of the CS2 recovery trough is more suitable for operation of the fluid. It avoids water in trough from forming into whirlpool and knotting the fiber, which will worsen fiber quality. The extra zone connected with the refining machine is lengthened, increasing the leakage area and improving fiber-cleaning effect.
Application of new material and new technology to after-treatment equipment
The LH151 after-treatment equipment adopts a lot of new material and new technology. High temperature and corrosion resistance stainless steel 904L, 254SMO, SAF2507 and Hastelloy alloy are used for corrosion resistant parts of the CS2 recovery trough and refining machine, which adapts to new production process requirement, improves the equipment reliability and prolong its service life. The manufacturing process of small and big press rollers, main drive roller and sieve support roller have also been improved, adopting red set of interference connection mode, which decreases welding deformation, reduces labor intensity and increases reliability and service life of main parts.
Recently, there has been a demand for large-capacity viscose after-treatment production lines with over 40,000 t/y. Large-capacity production lines not only saves production space, initial investment, utilities, etc., but also greatly reduces the energy consumption during production, saves manpower, improves labor productivity and makes equipment management more simple and reliable. Therefore, large-capacity viscose after-treatment equipment has extensive market prospect and demands.
Other companies that can manufacture viscose after-treatment production lines are Lenzing Company and Maurer Company. Although the two companies have the same process flow, their design idea, main structure, the drive form differs greatly.
HTHI has been developing viscose after-treatment equipment for several decades. Through the efforts of engineers, the company was able to develop viscose after-treatment equipment with various types, capacities and working widths, and obtaining a number of proprietary technologies. Now HTUI’s products and technology has become a leader in the domestic market, and also reached the international market, gaining a 95% market share. Customers are mainly from provinces such as Fujian, Zhejiang, Sichuan, Jiangsu, Jiangxi, Hubei, Henan, Hebei, Shandong, Jilin, and Xinjiang, but the equipment is also exported to India, Thailand, Indonesia, and Pakistan to name but a few.
HTHI’s after-treatment equipment with 40,000 t/y and 80,000 t/y has been successfully deployed in China and beyond. The LH151 high-capacity after-treatment equipment perfects the viscose after-treatment product series. This year, one 100,000 t/y viscose after-treatment production line made by HITI is being installed.
This content is sponsored by Hi-Tech Heavy Industry Co., Ltd.