Stock feed system for a multi-layer headbox and method in the operation of a multi-layer headbox

Abstract: A stock feed system for a multi-layer headbox and a method in the operation of a multi-layer headbox in which into each inlet header of the multi-layer headbox, a stock concept is passed which has been produced out of the same fresh stock by adding the necessary chemicals and fillers to separated portions of the fresh stock. Into the stock feed system of the multi-layer headbox, at least one dilution-water line is passed.

Description: This application is related to U.S. patent application Serial No. 08/323,839 filed October 17, 1994, the specification of which is hereby incorporated by reference herein. BACKGROUND OF THE INVENTION The present invention relates to a stock feed system for a multi-layer headbox and a method in the operation of a multi-layer headbox. In the prior art (see EP-A-0 651 092), systems for the operation of multi-layer headboxes are known in which there are separate fresh stocks for the surface layers of a pulp flow discharged from the headbox and for the middle layers thereof. Thus, in the prior art systems, there have been at least double fresh-stock systems for the formation of the different pulp layers. In the prior art equipment, the stocks introduced along at least two separate fresh-stock lines have been processed in vortex cleaning and in deaeration tanks, and feeds of fillers or starch complying with the required paper grade have been passed into the at least two fresh-stock lines. With the prior art technology, a paper machine into whose headbox stock is fed at different consistencies requires a complete short circulation which comprises more than one stock systems. This is also the case when the stock in the different layers is in the other respects the same, but the consistencies are different. Increased consistency of layers may be necessary, for example, in order that an improved purity of the layers can be achieved. When the middle layer is thicker than the surface layers, water of the middle layer is drained through the surface layers to a relatively limited extent. In such a case, particles of the middle layer are not carried along with the water into the surface layer, and the purity of the layers remains good. A very thick middle layer is highly flocculated, in which case it has a high bulk. Then, the structure of the paper results in a bulky paper of good bending stiffness, in which the formation of the middle layer is poor but the formation of the surface layers is good, which secures good printing properties. OBJECTS AND SUMMARY OF THE INVENTION It is an object of the present invention to provide a new and improved stock feed system for a multi-layer headbox and a method in the operation of a multi-layer headbox in which each layer of a multi-layer pulp web discharged from the headbox can be diluted separately and/or simultaneously, in which case, e.g., the stocks passed into the inlet headers of a multi-layer headbox can be given the desired consistencies. In order to achieve the object stated above, and others, in the present invention, the stock for one or several layers in the feed pipe systems for the inlet headers of the headbox are diluted. The diluting can take place before screens in the feed path through the feed pipe system if each layer has a screen of its own, or after the stock has been divided to be fed into the different layers. In the present invention, in a paper machine that comprises a multi-layer headbox and therein at least two separate inlet headers or equivalent, for the inlet headers, separate stocks are prepared out of the sane fresh stock, and they are passed into the inlet headers from the same stock tank. According to the invention, the fresh stock passed out of the stock tank is divided into two or more component flows. Into these component flows to be fed into the multi-layer headbox, chemicals and/or additives purposeful for the quality or the economy of production of different paper grades are passed. Further, according to the invention, the system also includes dilution-water lines passing to the stock system of the headbox. Preferably, the dilution lines are arranged to pass from a dilution-water header through valves and to join the stock line connected with the inlet header for each stock layer. Thus, according to the invention, in the stock feed system, each layer can be diluted separately and/or simultaneously, in which case, e.g., the stocks passed into the inlet headers of a multi-layer headbox can be given the desired consistencies. When certain additives are added to the stock flow, it may be the case that the stock has a low dry solids content before mixing of the additive. Thus, before the additive is passed into the stock, the stock may be diluted to the desired dry solids content to add the additive concerned into the fresh stock in an optimal manner. In the stock system in accordance with the present invention for a multi-layer headbox, into each inlet header of the multi-layer headbox, a stock concept is passed which has been produced out of the same fresh stock by adding the necessary chemicals and fillers to the fresh stock. The stock feed system in accordance with the present invention for a multi-layer headbox thus comprises at least one dilution-water line. In the method in accordance with the invention, the stock for each inlet header is prepared out of a single fresh stock by adding the necessary chemicals and fillers to the fresh stock. Dilution water is passed into at least one stock line that passes into an inlet header of the multi-layer headbox. Thus, in one embodiment, the method is used in the operation of a multi-layer headbox having at least two inlet headers into which a respective stock concept is passed, the stock flowing from the inlet headers through a system of distributor pipes into a turbulence generator and further into a slice cone. A single flow of fresh stock is provided and then divided into a plurality of stock flows. Chemicals and/or fillers are independently added to each of the stock flows. Each of the stock flows is then passed after the chemicals and/or fillers have been added thereto into a respective one of the inlet headers, and a diluting-water flow is passed into at least one of the stock flows. Preferably, the diluting-water flow is passed into individual ones of the stock flows which form outer layers of a web discharged from the headbox. The invention will be described in the following with reference to some preferred embodiments of the invention illustrated in the figures in the accompanying drawings. However, the invention is not confined to the illustrated embodiments alone. BRIEF DESCRIPTION OF THE DRAWINGS The following drawings are illustrative of embodiments of the invention and are not meant to limit the scope of the invention as encompassed by the claims. Figure 1 shows an embodiment of the invention in which the stock flow passed out of the fresh-stock tank is divided into three component flows which are passed further, after feeds of chemicals and fillers, into the different inlet headers in the multi-layer headbox, and in which system a dilution-water line is connected with each line passing into an inlet header. Figure 2 shows a second embodiment related to the stock feed system in accordance with the invention for a multi-layer headbox. Figure 3 shows the arrangement of introduction of dilution water with the inlet header and the regulation valves. Figure 4A is a side view of a multi-layer headbox in accordance with the invention. Figure 4B is a top view of the multi-layer headbox as shown in Fig. 4A. Figure 5A shows a first preferred embodiment of the supply of dilution water into the stock. Figure 5B shows a second preferred embodiment of the supply of dilution water. Figure 5C shows a third preferred embodiment of the supply of dilution water. Figure 5D shows a fourth preferred embodiment of the supply of dilution water. DETAILED DESCRIPTION OF THE INVENTION Referring to the accompanying drawings wherein like reference numerals refer to the same or similar elements, Fig. 1 is a schematic illustration of a first preferred embodiment of the invention, which is favorably suitable for the production of SC-paper. As shown in the figure, a multi-layer headbox denoted generally by reference numeral 10 comprises three inlet headers, i.e., the inlet headers 11,12 and 13. From the inlet header 11, a stock M 1 is passed through a distribution manifold having distribution pipes 14a 1.1 , 14a 1.2 ,... to a turbulence generator 15 into turbulence tubes 15a 1.1 ,15a 1.2 ,... therein and further from the turbulence tubes to a slice cone 16. From the inlet header 12, a stock M 2 is passed through respective distribution pipes 14a 2.1 ,14a 2.2 ,... of the distributor manifold 14 to the turbulence generator 15 into respective turbulence tubes 15a 2.1 ,15a 2.2 ,... further into the slice cone 16. Similarly, from the inlet header 13, a stock M 3 is passed through distribution pipes 14a 3.1 ,14a 3.2 ,... of the distributor manifold 14 to the turbulence generator 15 into respective turbulence tubes 15a 3.1 , 15a 3.2 ,... and further into the slice cone 16. Thus, by means of the multi-layer headbox shown in Fig. 1, a paper web is formed out of three stocks or stock concepts M 1 ,M 2 and M 3 . In the present invention, the system comprises a single stock system, the stocks M 1 ,M 2 and M 3 being formed out of the same fresh stock M which is passed out of a single fresh-stock tank 17. As shown in Fig. 1, the fresh stock M is passed out of the fresh-stock tank 17 along a flow line 18a and branched at a branching point P1 into two branch lines 18a 2 and 18a 3 . In the embodiment of Fig. 1, in the branch line 18a 2 , a chemical solution 3a is added to the stock M, and in the branch line 18a 3 , a chemical solution 3b is added. The chemical solutions may be a filler or starch. In the lines 18a 2 , 18a 3 , the stocks are made to flow further by means of pumps 19a 1 and 19a 2 so that, along the line 18a 3 , the stock is passed into a machine screen 20a 1 . A retention agent 5b is fed into the stock before the machine screen 20a 1 , and a retention agent 5bb is fed into the stock after the machine screen in a flow line 21a 1 therefrom. In this manner, a good mixing of the retention agent and the stock is achieved. Along the line 21a 1 , the stock M 2 that was formed is passed into the middle inlet header 12 of the multi-layer headbox. From the line 18a 2 after the pump 19a 1 , from a branch point C, a line 18a 2.1 passes to a machine screen 20a 2 , and from the machine screen 20a 2 , the line 21a 2 passes to the multi-layer headbox. At the front side of the machine screen 20a 2 , a retention agent 5a is fed into the line 18a 2.1 , and after the machine screen 20a 2 , a retention agent 5aa is fed into a line 21a 2 therefrom. Along the line 21a 2 , the stock flow M 3 is passed into the inlet header 13 of the multi-layer headbox. Also from the branch point C, a line 18a 2.2 passes to a machine screen 20a 3 and further into the multi-layer headbox. Into the line 18a 2.2 , before the machine screen 20a 3 , a retention agent 5c is fed, and after the machine screen 20a 3 , a retention agent 5cc is fed into a flow line 21a 3 therefrom. Along the line 21a 3 , the stock flow M 1 is passed into the inlet header 11 of the multi-layer headbox. Thus, in view ofthe above-described construction, the stock will comprise three layers composed of different stock concepts. In Fig. 1, reference arrows 100a 1 ,100a 2 ,100a 3 represent the feed ducts for dilution water and is a preferred embodiment of the invention wherein the dilution water is passed to the front side of the screens 20a 1 ,20a 2 ,20a 3 , seen in the flow direction of the stock flow, after feed points E 1 ,E 2 ,E 3 of the retention agents 5a,5b,5c, respectively. The invention is, however, not restricted to these favorable location of the point of introduction of the dilution-water alone. According to the invention, the desired consistency of the stock flow can be obtained by adding the desired amount of dilution water to each layer. For example, the purity of the layers can be promoted so that the uppermost web layers and the bottommost web layers in relation to the middle layer of the web are kept more dilute, in which case, less water is drained from the middle layer through the surface layers and, thus, the surface layers remain therefore pure. In such a case, out of the middle layer, particles are not removed along with drainage to the same extent as in an embodiment in which a large amount of water is also drained from the middle layer. In the present application, dilution water is understood as a substance in general that is made to flow and by whose means the consistency of the stock can be diluted. For example, clean water may be used a dilution flow or, for example, a water that has a low content of fibers. Fig. 2 shows an embodiment of the invention in which one unified stock flow M is passed out of the stock tank 17 along a line 22a 1 to a branch point D 1 . After the branch point D 1 , a chemical 3a' is added to the fresh stock M into a line 220a 1 branching therefrom. By means of the pump 19a 1 ', the stock is made to flow further into a machine screen 23a 1 , and before the machine screen 23a 1 , a retention agent 5a' is added, and after the machine screen 23a 1 , a retention agent 5aa' is added to flow line 24a 1 . The stock M 3 ' flow is passed along the line 24a 1 into the inlet header 13 of the multi-layer headbox. From the branch point D 1 , the stock M which does not flow into flow line 220a 1 is made to flow along a line 22a' 1 to a branch point D2, from which the stock M is branched into the lines 220a 2 and 220a 3 . Into the line 220a 2 , a chemical 3b', such as filler or starch, is added into the stock M before a pump 19a 2 ' associated with the flow line. By means of the pump 19a 2 ', the stock concept is passed further into a machine screen 23a 2 . Before the machine screen 23a 2 , a retention agent 5b', such as some suitable chemical, is added to the stock, and after the machine screen 23a 2 , the retention agent 5bb' is added to the stock. The stock concept M 2 ' produced in this manner is passed further along a line 24a 2 into the multi-layer headbox, and more particularly into its middle inlet header 12. Similarly, from the branch point D 2 the stock M is passed along the line 220a 3 into the machine screen 23a 3 after the feed of chemical 3c' thereto, by means of the circulation produced by a pump 19a 3 '. Before the machine screen 23a 3 , a retention agent 5c' is added, and after the machine screen 23a 3 , a retention agent 5cc' is added, and the concept M 1 ' thereby produced is passed further along a line 24a3 into the inlet header 11 of the multi-layer headbox 10. Thus, in the concept in accordance with the invention, just a single circulation of stock is used, in which there is just one starting fresh stock M. The fresh stock M is processed further by to it adding chemicals and fillers, whereby out of one fresh stock M all the necessary different stock concepts M 1 ',M 2 ' and M 3 ' are obtained for the different inlet headers 11,12 and 13 of the multi-layer headbox. In Fig. 2, an embodiment is shown in which the dilution-water lines 100a 1 , 100a 2 , 100a 3 are passed to the inlet side of the stock screens 23a 1 , 23a 2 , 23a 3 , respectively, and to the outlet side of the pumps 19a 1 ',19a 2 ',19a 3 '. The dilution water is passed to the lines 220a 1 ,220a 2 ,220a 3 preferably to the rear side of the feed points E 1 ,E 2 and E 3 of the retention agents 5a',5b',5c', seen in the flow direction. The figure shows an embodiment in which three pump devices 19a 1 ',19a 2 ',19a 3 ' are employed. Within the scope of the invention, an embodiment is, of course, possible in which one pump device only is used, for example, in the line 22a 1 . Thus, it is also possible to make the stock flow out of the tank 17 by means of one pump into the stock lines 220a 1 ,220a 2 and 220a 3 . Fig. 3 illustrates the passing of the dilution water out of an inlet header J 1 into the lines 100a 1 ,100a 2 and 100a 3 . Each of the lines 100a 1 ,100a2 and 100a3 comprise a regulation valve V 1 ,V 2 and V 3 , respectively, by whose means the dilution-water flow can be regulated into stock lines 18a 2.1 ,18a 3 and 18a 2.2 . In the embodiment of Fig. 3, the dilution water is introduced after the points E 1 ,E 2 ,E 3 of addition of retention agents 5a',5b',5c' to the stock line. The dilution water is introduced before machine screens 23a 1 ,23a 2 and 23a 3 , so that the dilution water is mixed efficiently with the stock M, which has been passed out of the common stock tank 17 of the system. Thus, in the stock circulation system in accordance with the invention exemplified by this embodiment, the fresh stock M is passed from one common tank 17 and branched into one or several branch lines, in which the necessary fillers/additives are added and, moreover, the necessary diluting of the fresh stock is also carried out. Fig. 4A is a side view of a multi-layer headbox used in the system in accordance with the invention, it being understood that the system can be used in any number of headbox having similar or different constructions. In the illustrated embodiment, a fresh stock M is passed out of the same stock tank 17 through the points for addition of additives and further into the inlet header 11,12 and 13 of each of the individual layers in the multi-layer headbox 10. As shown in Fig. 4A, the construction is in the other respects similar to those shown in the embodiments of Figs. 1 and 2, except that, after the tube bank or distribution manifold 14 related to each of the inlet headers 11,12,13, the headbox comprises intermediate chambers T 1 , T 2 and T 3 . Thus, the fresh stock is introduced from the stock tank 17 and branched into the branch lines and passed, after possible additions of additives and dilution water, into the respective inlet headers 11,12,13. From the inlet headers, the stock concepts M 1 ,M 2 ,M 3 are passed into the tube bank 14, into the intermediate chambers T 1 ,T 2 and T 3 , respectively, and further, through the turbulence tubes in the turbulence generator 15, into the slice cone 16. The slice cone 16 comprises aprons f 1 ,f 2 . The aprons f 1 ,f 2 are arranged at least between each of the stock concepts M 1 ,M 2 and M 3 to provide separation for the same in the slice cone 16. Fig. 4B is a top view of the system shown in Fig. 4A. In this figure, the dilution-water line 100a 1 for dilution water connected with the inlet header 11 is shown. Fig. 5A shows an embodiment of the invention in which the dilution water is passed at an acute angle α 1 along the line 100a 1 into the stock flow, into the stock line 220a 1 . Fig. 5B shows an embodiment of the invention in which the dilution-water line 100a 1 is passed centrally into the stock line 220a 1 through a tube portion extending into the stock flow. The dilution flow is discharged from the dilution-water line 100a 1 in the direction of the stock flow into the stock line 220a 1 . Fig. 5C shows an embodiment of the invention in which the dilution water is passed along the line 100a 1 into the stock line 220a 1 and at an acute angle α 2 against the stock flow. Fig. 5D shows an embodiment of the invention in which the dilution water is passed along the line 100a 1 centrally into the stock line 220a 1 which has a L-shaped portion, i.e., two portions perpendicular to one another. The dilution water is passed into one of the portions of stock line 220a 1 in the direction of flow of the stock flow. The examples provided above are not meant to be exclusive. Many other variations of the present invention would be obvious to those skilled in the art, and are contemplated to be within the scope of the appended claims. For example, the dilution water may be passed into each of the flow lines 18a 2.1 , 18a 2.2 , 18a 3 in Fig. 1 or 220a 1 , 220a 2 , 220a 3 in Fig. 2 in any of the ways shown in Figs. 5A, 5B, 5C and 5D. A stock feed system for a multi-layer headbox and a method in the operation of a multi-layer headbox in which into each inlet header of the multi-layer headbox, a stock concept is passed which has been produced out of the same fresh stock by adding the necessary chemicals and fillers to separated portions of the fresh stock. Into the stock feed system of the multi-layer headbox, at least one dilution-water line is passed.

Claims: A stock feed system for a multi-layer headbox (10), comprising means (18a; 22a 1 ) for providing a single flow of fresh stock (M), means (18a 2 , 18a 2.1 , 18a 2.2 , 18a 3 ; 220a 1 , 220a 2 , 220a 3 ) for dividing said single flow of fresh stock into a plurality of stock flows (M 1 , M 2 , M 3 ; M' 1 , M' 2 , M' 3 ), means (E 1 , E 2 , E 3 ) for independently adding chemicals and/or fillers (3a, 3b, 5a, 5b, 5c, 5aa, 5bb, 5cc; 3a', 3b', 3c', 5a', 5b', 5c', 5aa', 5bb', 5cc') to each of said plurality of stock flows, and means (21a 1 , 21a 2 , 21a 3 ; 24a 1 , 24a 2 , 24a 3 ) for passing said plurality of stock flows after said chemicals and/or fillers have been added thereto into a respective inlet header (11, 12, 13) of said headbox (10), characterized by diluting means (J 1 , V 1 , V 2 , V 3 , 100a 1 , 100a 2 , 100a 3 ) for passing a diluting-water flow into at least one of said plurality of stock flows (M 1 , M 2 , M 3 ; M' 1 , M' 2 , M' 3 ) prior to entry of said at least one of said plurality of stock flows into the respective inlet header (11, 12, 13) of said headbox (10). The stock feed system of claim 1, further comprising a single fresh stock tank (17), said means (18a; 22a 1 ) for providing a single flow of fresh stock (M) being coupled to said tank and comprising a fresh stock line (18a; 22a 1 ), said means for dividing said single flow of fresh stock comprising a plurality of branch lines (18a 2 , 18a 2.1 , 18a 2.2 , 18a 3 ; 220a 1 , 220a 2 , 220a 3 ) coupled to said fresh stock line. The stock feed system of claim 1, wherein said diluting means (J 1 , V 1 , V 2 , V 3 , 100a 1 , 100a 2 , 100a 3 ) comprise a diluting-water flow line (100a 1 , 100a 2 , 100a 3 ) connected to a flow line (18a 2.1 , 18a 2.2 , 18a 3 ; 220a 1 , 220a 2 , 220a 3 ) containing one of said plurality of stock flows and through which the diluting-water flow is passed. The stock feed system of claim 3, wherein said diluting-water flow line (100a 1 ) has an outlet end extending into a central region of said flow line (220a 1 ) containing one of said plurality of stock flows, the flow out of said dilution-water flow line (100a 1 ) substantially coinciding with a flow direction of the stock flow in said flow line (220a 1 ) containing one of said plurality of stock flows. The stock feed system of claim 1, wherein each of said plurality of stock flows flows through an individual flow line (18a 2.1 , 18a 2.2 , 18a 3 ; 220a 1 , 220a 2 , 220a 3 ) and said diluting means comprise a diluting-water flow line (100a 1 , 100a 2 , 100a 3 ) connected to each of said flow lines of said plurality of stock flows, at least one of said dilution-water flow lines (100a 1 ) being connected to a respective one of said flow lines (220a 1 ) of said plurality of stock flows at an oblique angle (α 1 ) such that the flow out of said at least one dilution-water flow line substantially coincides with a flow direction of the stock flow in said respective flow line. The stock feed system of claim 1, wherein each of said plurality of stock flows flows through an individual flow line (18a 2.1 , 18a 2.2 , 18a 3 ; 220a 1 , 220a 2 , 220a 3 ) and said diluting means comprise a diluting-water flow line (100a 1 , 100a 2 , 100a 3 ) connected to each of said flow lines of said plurality of stock flows, at least one of said dilution-water flow lines (100a 1 ) being connected to a respective one of said flow lines (220a 1 ) of said plurality of stock flows at an acute angle (α 2 ) such that the flow out of said at least one dilution-water flow line is in a direction opposite to a flow direction of the stock flow in said respective flow line. The stock feed system of claim 1, wherein each of said plurality of stock flows flows through an individual flow line (18a 2.1 , 18a 2.2 , 18a 3 ; 220a 1 , 220a 2 , 220a 3 ) and said diluting means comprise a diluting-water flow line (100a 1 , 100a 2 , 100a 3 ) connected to each of said flow lines of said plurality of stock flows, at least one of said flow lines (220a 1 ) of said plurality of stock flows having a substantially L-shaped portion, one of said dilution-water flow lines (100a 1 ) being connected to said L-shaped portion of said at least one flow line of said plurality of stock flows such that the flow out of said dilution-water flow line substantially coincides with a flow direction of the stock flow in said L-shaped portion. The stock feed system of claim 1, wherein each of said plurality of stock flows flows through an individual flow line (18a 2.1 , 18a 2.2 , 18a 3 ) and said dilution means comprise a diluting-water inlet header (J 1 ), dilution-water flow lines (100a 1 , 100a 2 , 100a 3 ) each having a first end connected to said diluting-water inlet header and a second end connected to one of said flow lines of said plurality of stock flows, and regulation valves (V 1 , V 2 , V 3 ) arranged in association with said dilution-water flow lines, said regulation valves regulating the flow of dilution-water into said flow lines of said plurality of stock flows. The stock feed system of claim 2, further comprising pumps (19a 1 , 19a 2 ; 19a' 1 , 19a' 2 , 19a' 3 ) coupled to a respective one of said branch lines (18a 2 , 18a 3 ; 220a 1 , 220a 2 , 220a 3 ) for pumping said stock flows through said branch lines. The stock feed system of claim 9, further comprising a machine screen (20a 1 , 20a 2 , 20a 3 ; 23a 1 , 23a 2 , 23a 3 ) coupled to each of said branch lines (18a 2.1 , 18a 2.2 , 18a 3 ; 220a 1 , 220a 2 , 220a 3 ) and arranged after said pumps (19a 1 , 19a 2 ; 19a' 1 , 19a' 2 , 19a' 3 ) in a flow direction, said means (E 1 , E 2 , E 3 ) for independently adding chemicals and/or fillers (3a, 3b, 5a, 5b, 5c, 5aa, 5bb, 5cc; 3a', 3b', 3c', 5a', 5b', 5c', 5aa', 5bb', 5cc') to said stock flows (M 1 , M 2 , M 3 ; M' 1 , M' 2 , M' 3 ) being structured and arranged to add chemicals and/or fillers before said pumps, after said pumps and before said machine screens and after said machine screens such that each of said stock flows has a desired composition before being passed into the headbox (10). Method in the operation of a multi-layer headbox (10) having at least two inlet headers (11, 12, 13) into which a respective stock concept is passed, the stock flowing from said inlet headers through a system (14) of distributor pipes into a turbulence generator (15) and further into a slice cone (16), comprising the steps of: dividing a single flow of fresh stock (M) into a plurality of stock flows (M 1 , M 2 , M 3 ; M' 1 , M' 2 , M' 3 ), independently adding chemicals and/or fillers (3a, 3b, 5a, 5b, 5c, 5aa, 5bb, 5cc; 3a', 3b', 3c', 5a', 5b', 5c', 5aa', 5bb', 5cc') to each of said plurality of stock flows, and passing each of said plurality of stock flows after said chemicals and/or fillers have been added thereto into a respective one of said inlet headers (11, 12, 13), characterized by passing a diluting-water flow into at least one of said plurality of stock flows (M 1 , M 2 , M 3 ; M' 1 , M' 2 , M' 3 ) prior to entry of said at least one of said plurality of said stock flows into the respective one of said inlet headers (11, 12, 13). The method of claim 11, wherein the diluting-water flow is passed into those individual stock flows (M 1 , M 3 ; M' 1 , M' 3 ) of said plurality of stock flows which form outer layers of a web discharged from the headbox (10). The method of claim 11, further comprising the steps of arranging a single fresh stock tank (17) from which said single flow of fresh stock (M) is passed, providing branch points (P 1 ; D 1 , D 2 ) in said single flow of fresh stock such that said single flow of fresh stock is divided at said branch points and passed into different lines (18a 2 , 18a 3 ; 220a 1 , 220a 2 , 220a 3 ), and adding a chemical solution (3a, 3b; 3a', 3b', 3c') into each of said lines in accordance with the requirements of the particular stock concept to be fed into the inlet headers (11, 12, 13) of the multi-layer headbox (10). The method of claim 13, further comprising the step of pumping said stock flows through said lines (18a 2 , 18a 3 ; 220a 1 , 220a 2 , 220a 3 ) via pumps (19a 1 , 19a 2 ; 19a' 1 , 19a' 2 , 19a' 3 ). The method of claim 14, further comprising the steps of coupling a machine screen (20a 1 , 20a 2 , 20a 3 ; 23a 1 , 23a 2 , 23a 3 ) to each of said lines (18a 2.1 , 18a 2.2 , 18a 3 ; 220a 1 , 220a 2 , 220a 3 ) after said pumps (19a 1 , 19a 2 ; 19a' 1 , 19a' 2 , 19a' 3 ) in a flow direction, and adding chemicals and/or fillers (3a, 3b, 5a, 5b, 5c, 5aa, 5bb, 5cc; 3a', 3b', 3c', 5a', 5b', 5c', 5aa', 5bb', 5cc') before said pumps, after said pumps and before said machine screens and after said machine screens. The method of claim 11, further comprising the steps of dividing said single flow of fresh stock (M) into only two separate flows, passing said two flows through branch lines (18a 2 , 18a 3 ), dividing said branch line (18a 2 ) of a first one of said two flows to provide stock concept (M 1 , M 3 ) for an uppermost and a lowermost inlet header (11, 13) in the headbox (10), and passing a second one of said two flows into a middle inlet header (12) arranged between the uppermost inlet header and the lowermost inlet header. A stock feed system for a multi-layer headbox (10), including a plurality of stock flows (M 1 , M 2 , M 3 ; M' 1 , M' 2 , M' 3 ) formed from a single flow of fresh stock (M), inlet headers (11, 12, 13) and means (21a 1 , 21a 2 , 21a 3 ; 24a 1 , 24a 2 , 24a 3 ) for passing said plurality of stock flows into a respective one of said inlet headers of said headbox, characterized by diluting means (J 1 , V 1 , V 2 , V 3 , 100a 1 , 100a 2 , 100a 3 ) for passing a diluting-water flow into at least one of said plurality of stock flows (M 1 , M 2 , M 3 ; M' 1 , M' 2 , M' 3 ) prior to entry of said at least one of said plurality of stock flows into the respective one of said inlet headers (11, 12, 13) of said headbox (10). The stock feed system of claim 17, further comprising means (E 1 , E 2 , E 3 ) for independently adding chemicals and/or fillers (3a, 3b, 5a, 5b, 5c, 5aa, 5bb, 5cc; 3a', 3b', 3c', 5a', 5b', 5c', 5aa', 5bb', 5cc') to each of said plurality of stock flows (M 1 , M 2 , M 3 ; M' 1 , M' 2 , M' 3 ), and said plurality of stock flows being passed into said headbox (10) after said chemicals and/or fillers have been added thereto. The stock feed system of claim 18, wherein said diluting-water flow is added after said chemicals and/or fillers have been added.

Inventors: HUOVILA JYRKI, LINSURI ARI, HUOVILA, JYRKI, LINSURI, ARI
Applicants: VALMET CORP, VALMET CORPORATION (REG.NO.763281)
Application year: 1996
Main classification: D21F1
IPC codes: D21F1, D21F9, D21F11