EP2411579A1

EP2411579A1 - Flow pipe for a turbulence generator of the head box of a fiber web machine and a method for manufacturing a flow pipe for a turbulence generator of the head box of a fiber web machine and a turbulence generator of the head box of a fiber web machine

Info

Publication number: EP2411579A1
Application number: EP10755483A
Authority: EP
Inventors: Jarmo Kirvesmäki; Janne Lappi
Original assignee: Metso Paper Oy
Current assignee: Valmet Technologies Oy
Priority date: 2009-03-27
Filing date: 2010-03-10
Publication date: 2012-02-01
Also published as: FI20095330L; FI122600B; WO2010109059A1; EP2411579A4; FI20095330A0; CN102365407A

Abstract

The invention relates to a flow pipe for a turbulence generator (14) of the head box (10) of a fiber web machine. The flow pipe (17) includes two successive flow sections (18, 19) wherein the cross-sectional flow areas are unequal in size for forming a step (20). The flow pipe (17) including the step (20) is a component manufactured from one continuous pipe billet (21). The invention also relates to a method for manufacturing a flow pipe for a turbulence generator (14) of the head box (10) of a fiber web machine as well as a turbulence generator (14) of the head box (10) of a fiber web machine.

Description

FLOW PIPE FOR A TURBULENCE GENERATOR OF THE HEAD BOX OF A FIBER WEB MACHINE AND A METHOD FOR MANUFACTURING A FLOW PIPE FOR A TURBULENCE GENERATOR OF THE HEAD BOX OF A FIBER WEB MACHINE AND A TURBULENCE GENERATOR OF THE HEAD BOX OF A FIBER WEB MACHINE

The invention relates to a flow pipe for a turbulence generator of the head box of a fiber web machine the flow pipe including two successive flow sections wherein the cross-sectional flow areas are unequal in size for forming a step. The invention also relates to a method for manufacturing a flow pipe for a turbulence generator of the head box of a fiber web machine as well as a turbulence generator of the head box of a fiber web machine .

Finnish patent No. 110700 discloses a flow pipe construction. Flow pipes are used in the head box of a fiber web machine for forming a bank of tubes. The flow pipe includes two successive flow sections wherein the cross-sectional flow areas are unequal in size for forming a step. Due to the step, the stock flow detaches from the flow pipe walls, which efficiently breaks up floes and causes turbulence in the flow. In said patent, each flow pipe is composed of two separate flow sections which are connected together by welding, for example. The first flow section is made of a circular pipe while the second flow section is a hydromolded component. The flow sections are connected together via a spacer sleeve. In practice, the above mentioned spacer sleeve is welded to the end of the first flow section, around it, after which the face of the spacer sleeve is lathed to create a smooth connection on the flow surface side. After this, the hydromolded second flow section is placed on the sleeve and connected to the sleeve by welding.

A known flow pipe includes many demanding manufacturing stages.

Firstly, it involves two separate welding steps. Secondly, the connection must be absolutely clearance-free, which requires lathing. Furthermore, the flow sections must be positioned and adjusted precisely before connecting to ensure that the final flow pipe is absolutely straight. In other words, a known flow pipe is laborious to manufacture and flow pipes of non-uniform quality are easily made, which has an unfavorable effect on the headbox operation and thus on the quality of the final product. Multiple work stages also cause high manufacturing costs, and impurities accumulate in the flow pipes during use. In addition, an unnecessarily strong pipe relative to the pressure level must be used in the manufacture mainly due to lathing. This, too, increases the mass of the turbulence generator and adds to the material costs .

An object of the invention is to provide a novel flow pipe for a turbulence generator of the head box of a fiber web machine the flow pipe being simpler than before to manufacture and for which a construction of an absolutely uniform quality can be achieved. Another object of the invention is to provide a novel method for manufacturing a flow pipe for a turbulence generator of the headbox of a fiber web machine, the method being faster than earlier and easier than before. Still another object of the invention is to provide a novel turbulence generator for the headbox of a fiber web machine wherein the flow speed and the level of turbulence of the stock flow are more uniform than before. The characteristic features of the flow pipe and the turbulence generator according to this invention are that the flow pipe including the step is a component manufactured from one continuous pipe billet. Correspondingly, the characteristic features of the method according to the invention are that the flow pipe including the step is formed of one continuous pipe billet. The flow pipe according to the invention is easy to manufacture by hydromolding, for example. After hydromolding, trimming of the flow pipe ends is sufficient. The step between the flow sections is formed in a moment in hydromolding and hence it is ready at once. The shape of the flow pipe and particularly that of the step are precisely determined by the hydromolding mold. Thus a flow pipe with a uniform quality is achieved. In addition, the final flow pipe is absolutely straight and completely lacks all seams.

The invention is described below in detail by making reference to the enclosed drawings that illustrate one of the embodiments of the invention, in which

Figure 1 shows a head box of a fiber web machine including flow pipes according to the invention,

Figure 2a shows a pipe billet for a flow pipe according to the invention,

Figure 2b shows a final flow pipe according to the invention, Figure 2c shows a part of a flow pipe according to the inven- tion in a profile view as well as a cross-section in three different points.

Figure 1 shows the principle of a head box 10. The fiber suspension is led from the manifold 11 via the tube bank 12 to the equalizing chamber 13. The equalizing chamber 13 is followed by the turbulence generator 14, which consists of several flow pipes 17. From the turbulence generator 14 the fiber suspension flows forward to the slice channel 15 and further to the forming fabric (not shown) . This slice channel is additionally provided with vanes 16. Any pressure variations coming from the manifold equalize in the tube bank and the flows of the tube bank join in the attenuator to form a homogeneous flow. In the turbulence generator the consistency profile of the fiber suspension evens out and any floes formed in the fiber suspen- sion break up. Floes are disintegrated by generating shearing forces and turbulence in the flow. The turbulence is sufficient to keep the fibers separated and to break up the floes, however, without disturbing the web formation on the wire. The turbulence generator is followed by the slice channel in which the flow speed of the fiber suspension accelerates to the speed of the fiber web machine. The slice channel is so dimensioned that the turbulence generated in the turbulence generator has time to attenuate to a level suitable for web forming before the slice opening.

The flow pipe is thus meant for the turbulence generator of the head box of a fiber web machine. Figure 2b shows a final flow pipe 17 including two successive flow sections 18 and 19. The mutual cross-sectional flow areas of the flow sections are unequal in size whereby a desired step 20 can be formed. Ac- cording to the invention, the flow pipe 17 including the step 20 is a component manufactured from one continuous pipe billet 21. Advantageously, the flow pipe 17 is formed by hydromolding. Such a component is absolutely straight and completely lacks all seams. The component is also dimensionally and geometri- cally accurate. The pipe billet 21 is shown in Figure 2a, where the flow direction of the fiber suspension is indicated by an arrow. Moreover, a flow pipe according to the invention can be manufactured from a pipe billet with thinner walls than earlier. Generally, the wall strength of the flow pipe 17 is below 2 mm, which also facilitates hydromolding.

Stainless steel is used for the manufacture of the flow pipe due to demanding operating conditions. Advantageously duplex steel, which is easier to mold than stainless steel, is used, and in addition, greater molding and stretching is achieved in the pipe billet. Stainless duplex steel is corrosion resistant, extremely strong and has very low nickel content. Due to the high strength and tensileness of the material it can be used in lower thicknesses. In addition, duplex steel is normally also less expensive than stainless steel.

In addition to the novel manufacturing method, the flow pipe according to the invention is molded and dimensioned in a new way. Firstly, the length of the flow section 19 located second in the flow direction is 20 - 50 %, more advantageously 25 - 35 %, of the total length of the flow pipe 17. In other words, turbulence is generated faster than before and within a shorter distance than earlier. The shearing force effect produced by the step 20 is sudden, which breaks up floes efficiently.

As such conventionally, the flow section 19 that comes second in the flow direction includes two parts 22 and 23. The cross-section of the first part 22 is circular while the cross-section of the second part 23 is a polygon. These cross-sections are specifically illustrated in Figure 2c. According to the invention, the lengths of the parts 22 and 23 are substantially equal. In this way, the turbulence in the second flow section after the step has time to generate first completely, after which the geometry of the cross-sectional flow area in the second part 23 changes smoothly from a circle to a polygon. Hydromolding is based on the molding capability of the pipe billet material and locally on stretching as well. Thus the pipe billet can be stretched for forming the second flow section and thereby the step. According to the invention, the diameter of the first part 22 of the second flow section 19 is 1.1 - 2.0, more advantageously 1.2 - 1.5, times the diameter of the first flow section 18. However, such a difference in diameter is completely sufficient for generating efficient turbulence. In practice, it is sufficient that the flow detaches from the inner surface of the flow pipe.

In hydromolding, solid material is molded utilizing the effect of a mold and a pressurized medium. The method provides smooth shapes whereby two curved bends 24 are formed on the wall of the flow pipe 17 in the connection point between the flow sections 18 and 19. According to the invention, the radius of curvature r of both bends 24 is 0.2 - 2 mm, more advantageously 0.75 - 1.25 mm, on the inner surface of the flow pipe. Then the step is formed sufficiently sharply without a connection point with steep edges. In practice, particularly the internal corner of the second bend keeps clean due to the curvature. The dimensioning of the flow pipe can vary in different applications. In most cases, it is sufficient to manufacture only a few models that suit most flow speeds. If required, a sleeve 25 ensuring the uniformity of the flow distribution is adapted inside the first flow section 18. In other words, sleeves of different sizes can be used to fine-tune the characteristics of the flow pipe. Advantageously the sleeve is made of plastic. In one dimensioning example, the flow pipe is 600 mm long, in which case the first flow section is 400 mm long and the second flow section is 200 mm long. The inner diameter of the first flow section is 20 mm and the inner diameter of the first part of the second flow section is 24 mm.

According to the invention, the flow pipe 17 including the step 20 is thus formed from one continuous pipe billet 21 by hydromolding. In hydromolding, a two-part negative mold is used the shape of which corresponds to the shape of the final flow pipe. The pipe billet is placed in the mold which is then closed reliably. If necessary, the pipe billet can be slightly flattened to fit in the mold. Both ends of the pipe billet extend slightly out of the mold. The pipe billet is hence slightly longer than the final flow pipe. Spindles that seal against both the pipe billet and the mold are pressed at each end of the pipe billet. When water is used as the medium, a pressure of 2000 bar, for example, is used applying it inside the pipe billet via the spindles. In a few seconds the pipe billet is pressed against the mold by the pressure. One mold can be used to manufacture flow pipes with different diameters if reducing sleeves are used in the mold. In addition, the greater the diameter of the pipe billet the better it is molded due to a larger pressure surface area. Finally the ends of the flow pipe are planed after which the flow pipe is ready.

A turbulence generator for a head box according to the inven- tion, in which the flow pipe with steps is a hydromolded component manufactured from one continuous pipe billet, operates uniformly and the achieved turbulence is sufficient. For example, if a nine meter wide three-row turbulence generator has a hundred flow pipes in one row at a distance of three width meters, the number of flow pipes is over a thousand in the head box concerned. In this case, the flow pipe according to the invention achieves remarkable savings in both work and material costs. At the same time, the mass of the turbulence generator is smaller than conventionally. The flow pipes are also uniform in quality and the turbulence level is even across the entire width of the slice opening.

Claims

1. Flow pipe for a turbulence generator (14) of the head box (10) of a fiber web machine, the flow pipe (17) including two successive flow sections (18, 19) wherein the cross-sectional flow areas are unequal in size for forming a step (20) , characterized in that the flow pipe (17) including the step (20) is a component manufactured from one continuous pipe billet (21) .

2. Flow pipe according to claim 1, characterized in that the flow pipe (17) including the step (20) is a hydromolded component .

3. Flow pipe according to claim 1 or 2 , characterized in that the wall thickness of the flow pipe (17) is less than 2 mm.

4. Flow pipe according to any of claims 1 - 3 , character- ized in that the flow pipe (17) is of stainless steel, advantageously of duplex steel.

5. Flow pipe according to any of claims 1 - 4, characterized in that the flow section (19) that comes second in the flow direction includes two parts (22, 23) , of which the cross-section of the first part (22) is circular while the cross-section of the second part (23) has a polygon shape.

6. Flow pipe according to claim 5, characterized in that the diameter of the first part (22) is 1.1 - 2.0, more advantageously 1.2 - 1.5, times the diameter of the first flow section (18) .

7. Flow pipe according to any of claims 1 - 6, character- ized in that in the connection point of the flow sections (18,

19) there are two curved bends (24) having a radius of curva- ture r of 0.2 - 2 mm, more advantageously 0.75 - 1.25 mm, on the wall of the flow pipe (17) .

8. Method for manufacturing a flow pipe for a turbulence generator (14) of the head box (10) of a fiber web machine wherein two successive flow sections (18, 19) are formed in the flow pipe, the cross-sectional flow areas of which are adapted unequal in size for forming a step (20) , and hydromolding is used in forming, characterized in that the flow pipe (17) including the step (20) is formed from one continuous pipe billet (21) .

9. Turbulence generator (14) of the head box (10) of a fiber web machine including several flow pipes (17) each of which includes two successive flow sections (18, 19) the cross-sectional flow areas of which are unequal in size for forming a step (20), characterized in that the flow pipe (17) including the step (20) is a component manufactured from one continuous pipe billet (21) .

10. Turbulence generator according to claim 9, characterized in that the flow pipe (17) is a flow pipe (17) according to any of claims 2 - 7.