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1、Information on raw materials and paper-makingPaper making123waterwaterwaterWhite waterWhite waTo effluent treatment systemFibre recovery from white waterStock blending stock preparation systemCentrifugal screenMechanical and/or chemical pulp, and/or recovered paper, and/or additives and waterWater c
2、ircuit to stock preparationHeadbox Wire section22Wire section1T H E P R O D U C T I O N O F P A P E RPaper machineThe combined use of a number of special machines is required for the production of paper. The exact construction and combination of the different machines depends on the type of product
3、generated by the process (paper or board), as well as the type of fibre used. There is no such thing as a standard paper mill. However, the stages in the paper-making process can be divided into four main areas: stock preparation; papermaking; coating and laminating; and finishing.S T O C K P R E P
4、A R A T I O N Recovered paper is delivered to the paper mill in dry form, as is chemical pulp as a general rule. Wood pulp, which is usually produced in the same plant, is pumped to the stock preparation section in the form of a fibre/ water slurry. Recovered paper is firstly pre- treated and then w
5、ater is added to it in suffi- cient quantities to ensure that by the time itreaches the stock preparation section it has been fully dissolved. Chemical pulp fibre is converted into pumpable form in the pulper by the addition of water. The bundles of fibres in this fibre/water slurry are then bro- ke
6、n down into single fibres. The mixture then enters the multiple-stage purification process. After being dissolved, the chemical pulp fibre is mechanically treated in a refiner in order to add strength and improve its sheet-forming properties. The mixing of different fibres takes place in the stock p
7、reparation section. Here, filling agents and helping agents are added to the mix- ture to improve the quality of the paper and raise pro- ductivity levels. The most important filling agents areclay (aluminium silicate or kaolin) and chalk. These natural minerals are simply ground and cleaned before
8、they are added to the mixture.P A P E R - M A K I N G The machines used for the manufacture of paper are technically highly sophisticated. The biggest of these machines are up to ten metres wide and up to 120 metres in length. Despite variations in their construc- tion, all of these paper-mak- ing m
9、achines consist of the same basic elements: head- box; wire section; press sec- tion; dryer section; and reel. The actual design of these elements depends on the type of paper being made. The speeds of the individual machines also vary signifi-The paper sheets are melded together.Headbox with Wire S
10、ection45aterPress waterDryer sectionReel upMachine calenderPope roller5Dryer sectionMachine calender345Press sectionPress section34Drying Cylinderscantly: however, up to 1,400 metres of paper per minute can be produced.HEADBOX AND WIRE SECTIONS The function of the headbox is to evenly spread the hig
11、hly diluted fibre mixture over the entire breadth of the paper-making machine. With a Fourdrinier type of machine, the mixture runs through a slit onto a flat, constantly revolving wire mesh or sieve (the wire section). The fibres deposit themselves next to and on top of one another on the wire. At
12、the same time, the water runs through the wire or is sucked off from below. It is in this way that a sheet of paper is formed. However, at the end of the filtering process, the paper sheet (web) still contains 80% water.P R E S S A N D D R Y E R S E C T I O N S The relatively fragile paper web is fu
13、rther drained using mechanical pressure in the press section. The web is guided by means of a highly absorbent, continuous felt cloth between rollers of steel, granite or hard rub- ber. The paper web then proceeds to the dryer section. The dryer section of the paper machine consists of up to 100 ste
14、am-heated drying cylinders. The strengthened paper web is at first guided over the cylinders with help from felt sheets but later threads itself over the cylinders. Additional machine fittings can be used in the dryer section to add spe- cial properties to the paper. An example of such a fitting is
15、the size press (consisting of two smooth rollers), with which a durable solution of either starch or a synthetic-based material is applied to the pre-dried paper web. In this way for instance, the surface strength (tearing strength) of the paper canbe increased. Some paper machines have an extra smo
16、othing process called a Calender, which is added to the dryer section. The Cal- ender consists of several rollers arranged ver- tically one upon the other. By running the almost dry paper web between the rollers under high pressure, the paper is compacted and smoothed.R E E L Finally, the finished paper web is wound up on to a steel shaft (reel). The paper now con- tains only five to eight percent water (which is normal moisture content). The paper stays on the shaft until finishing
