Views: 2 Author: Site Editor Publish Time: 2021-07-14 Origin: Site
Paper machine: a complete set of equipment linked to the division of the pulp into the paper web, including the headbox, wire section, press section, drying section, calender, paper reel and transmission section and other mainframes such as steam, water, vacuum, Auxiliary systems such as lubrication and heat recovery. The wire part that forms the wet paper web is the core of the paper machine, so the paper machine can be divided into fourdrinier paper machine, clamp paper machine and cylinder paper machine according to the structure of the wire part.
The slurry of appropriate concentration is sent to the equipment on the network evenly and stably through the spreader, rectifier, weir pool, weir plate (lip plate) nozzles and other components, also known as the front box. The functions of each part of the headbox are:
1. The pulp flow is divided into the pulp flow with the same width as the papermaking copper mesh, and the flow rate is consistent across the entire width. There are 3 types of commonly used pulp distributors: cross-flow, double-pipe and orifice.
2. The rectifier device further stabilizes the slurry flow rate on the network. Commonly used devices are baffles, throttling diffusers, orifice plates and orifice rolls (homogenizing rolls), and step diffuser grades.
3. The weir pond is the box body part of the headbox, divided into two types: open type and closed type. The closed type is divided into two types: air pressure type and nozzle type.
4. The weir can spray the slurry onto the copper net at a certain angle to form a uniform thickness of paper. Common weirs are vertical, shotcrete (duckbill) and combined.
Due to the emergence of the sandwich paper machine, there are also a collection headbox and a tube-bundle pressure headbox.
2. Network Department:
After the slurry is sprayed from the headbox onto the copper mesh, wet paper sheets are formed on the mesh and dewatered. Due to the different structure of the wire part, the paper machine is divided into four major types, such as fourdrinier wire, clamp wire and cylinder wire. According to the formation and dehydration process of the wet paper sheet, the plane of the copper mesh of the wire mesh (wire strip) can be divided into 3 main parts:
1. The breast roller and case roller are used to remove 65-85% of the water in the paper material.
2. The vacuum suction box part is used to remove 10-25% of the water and compact the page.
3. The vacuum roll part mechanically squeezes the wet paper to further remove moisture and increase the wet strength of the paper.
In addition, the screen has a fixed frame to block the paper material on the net, a water needle to cut the edge of the wet paper, a guide roller to keep the copper net from running deviation, a tension roller to control the tightness of the copper net, and a support copper The net roll of the net. Modern Fourdrinier wire parts often replace table rolls with dewatering plates to increase dewatering capacity and improve the formation of paper sheets.
The net part of the sandwich paper machine is composed of two endless copper nets. The slurry sprayed from the tube-bundle headbox directly enters the gap between the two meshes running at constant speed, and the slurry is first dehydrated by gravity, and then squeezed and dehydrated by the two meshes. There are several net rolls or dewatering plates for the two nets to gather the two nets and scrape away the filtered water. This kind of net has a good dehydration effect, a small area, the two sides of the paper sheet are the same, and the fiber is evenly combined.
The screen part of the rotary screen paper machine is equipped with a regulating box in front of the screen slot to ensure the uniformity of slurry transportation, and a partition rectifier device is installed in the front half of the screen slot to stabilize the data flow rate. There are two types of net slots:
1. The flow direction of the slurry is the same as the rotating direction of the net cage, which is called the downstream type;
2. The flow direction of the slurry is opposite to the rotating direction of the net cage, which is called counter-flow type.
The function of the flat roller is to form a pre-pressure on the wet paper to form a pre-dewatering. There is a certain offset between the vertical center line of the roll and the net cage, so that the blanket (or rubber) on the roll and the net cage generate enough pressure. The cylinder screen paper machine has simple structure, low price, and small area, but the speed is low and the uniformity of the paper is poor.
3. Press section:
Pressing is to mechanically squeeze out the moisture of the wet paper from the wire to increase the dryness of the paper, at the same time to improve the surface properties of the paper, eliminate web marks and increase smoothness, tightness and strength. Press is divided into two-roll press and multi-roll press (composite press) according to the arrangement of press rolls. It includes ordinary press, vacuum press, groove press, gloss press, high-strength press and wind jacket press. Multi-roll presses are mainly used in high-speed paper machines. According to the dehydration discharge method, there are directional dehydration squeezing and vertical dehydration squeezing. Reverse dehydration means that the water extruded by the pressure roller is discharged in the opposite direction of the felt rotation, and vertical dehydration means that the water extruded by the pressure roller is discharged in the vertical direction of the felt. The drainage distance of vertical dehydration is short, and the possibility of squeezing wet paper is small.
4. Drying Department:
The function of the drying section is to further dehydrate the wet paper sheet after pressing, so that the paper sheet shrinks, the fibers are tightly bonded and the strength is increased. The drying method is mainly contact drying. The drying part has four types: single drying cylinder and double drying cylinder, two-row type and multi-row type.
1. Single drying cylinder, with only one drying cylinder, the diameter of the cylinder is 1~6 meters, the drying efficiency is high, and it is suitable for drying thin paper sheets.
2. Double drying cylinders: There are two drying cylinders on the paper machine, with a diameter of 1.2~1.8 meters, and the wet paper sheet is closely attached to the surface of the drying cylinder with a supporting roller and a pressing roller respectively. Adjusting the pressure of the supporting roller and pressing roller can make the paper sheet get different smoothness and tightness.
3. Double-row type: The dryers are arranged in two layers up and down.
4. Multi-row type: The drying cylinders are arranged in three or four layers.
The drying section is the energy-intensive part of the paper machine. The cost of evaporating 1 kg of water in the drying section is dozens of times higher than that of removing 1 kg of water in the squeezing section. In order to save energy, in addition to improving the thermal efficiency of the drying section, it is necessary to minimize the moisture entering the paper sheet of the drying section.
After calendering the paper sheet from the drying section, the smoothness, gloss and tightness of the paper sheet can be improved, the thickness of the whole paper sheet can be consistent, and the air permeability can be reduced. The calender consists of 3 to 10 metal rollers made of nickel-chromium steel or cold cast iron. The driving roller is driven by a motor below, and the other rollers are driven by friction. There is a ventilation device on each intermediate roller, which can prevent the roll and improve the smoothness of the paper when steam is introduced. The pressure of the calender mainly depends on its own weight, and some calenders have a pressure device. In order to compensate for the deflection and deformation of the roller after pressurization, the bottom roller and top roller of the calender are made into waist drum-shaped middle and high rollers. After the 1960s, there appeared controllable middle and high rollers that rely on hydraulic mechanisms to compensate for the deflection and deformation. cylinder.
6. Paper reeling machine:
A machine that rolls paper webs into paper rolls. The paper roll should be tight and uniform, and there should be no ripples in the middle of the paper roll. The reel is divided into two types: shaft type and cylinder type. Shaft reels are generally not used. Cylindrical roll paper feeding machines are widely used. They use the friction of the rolls to drive the paper rolls to rotate, which can adapt to various speeds. The paper rolls are tight and uniform, the paper web bears small tension, and it is not easy to break during operation.
Seven, the transmission of the paper machine:
The paper machine drive should meet the following basic conditions:
1. The speed of the whole machine should have a certain adjustment range (2~5 times) to adapt to the change of product or ratio.
2. The running speed must be stable, <±0.3%, to ensure stable quantitative and reduce broken ends.
3. The speed of each roller should be relatively adjustable and stable.
4. There is a crawling speed of 15-25m/min during maintenance and cleaning.
The transmission of the paper machine can be divided into two types: main shaft transmission and partial transmission. The main shaft drive is driven by a DC motor or a variable-speed AC motor, and all parts are driven by a tapered wheel or a speed-regulating V-belt wheel or a differential wheel. The divisional drive adopts multiple DC motors to directly drive each part, and the timing is adjusted by thyristor.
8. Finishing and processing machinery
In order to meet different needs, the following machines are also installed behind the paper reel in the papermaking workshop.
1. Calender: It is similar in structure to the calender, but there are more rollers, and the pressure between the rollers is greater. Calenders are divided into two types: general writing paper and printing paper and industrial technical paper. Except for the two paper rolls in contact, the rest are arranged alternately with paper rolls and metal rolls. The bottom roller and top roller have a larger diameter. Generally, the bottom roller is used as the driving roller, which is connected with the motor and reducer, and is attached with a pressure and lifting mechanism. The inside of the metal roller in the middle can be steamed or cooled with water, and is equipped with a scraper.
2. Rewinder: The paper produced by the paper machine has irregular edges after calendering. In order to meet printing or other needs, it must be rolled into a roll of paper that meets the specifications. In terms of structure, the rewinding machine is divided into two types: top threading and bottom threading. The rewinder is equipped with two upper and lower longitudinal knife rollers, and each knife roller has several "cutting knives". The disc-shaped upper knife is pressed against the bowl-shaped lower knife by a spring. The rewinding speed can reach 1000~200m/min, which is a fast-running machine in papermaking machinery.
3. Paper cutter: a machine that cuts roll paper into flat paper. The speed of the paper cutter is 30-60 m/min.
4. Coating machine: A machine that coats a special surface layer on paper to improve printing and moisture resistance. According to the structure, it can be divided into air knife coater, hybrid coater and knife coater.
The above is the detailed introduction of the paper machine.