FI81145B - INLOPPSLAODA. - Google Patents

Description

1 81145

PERAL AAH KKO - INLOPPSL ADA

The invention relates to a headbox as defined in the preamble of claim 1, which has pulling elements for maintaining a fine degree of turbulence in the mass s in the tin opening.

An application of a freely movable self-positioning towing element for a headbox nozzle chamber is first disclosed in U.S. Patent 3,939,037 to Hill. U.S. Patent RE 28,269 (Hill et al.) Discloses towing elements from side to side of the basin. These traction elements are capable of producing or maintaining a fine degree of turbulence in the pulp flowing towards and through the nozzle. The applications of the above patents can also be used to their advantage and to operate in a machine in which multilayer paper is made and in which pulps with different properties are fed into chambers on opposite sides of the drawing elements, where the elements pass from one side of the basin to the other.

The basic limitation in the headbox has been that the devices 20 for generating turbulence in the fiber suspension for dispersing the fibers have been only relatively large devices. With such devices, it is possible to generate low-grade turbulence by increasing the intensity of the turbulence produced. Thus, the energy of turbulence naturally transfers from high to low degrees, and the higher the intensity, the higher the rate of energy transfer and thus the lower the degrees of turbulence maintained. However, this very strong high degree of turbulence also has a detrimental effect, namely the development of large waves and free surface disturbance on the table of the planar wire machine. Thus, the general rule of headbox performance has been that the degree of dispersion and the level of turbulence at headbox removal are closely correlated; the higher the turbulence, the better the dispersion.

5 When selecting a headbox design in this limiting situation, either a design that produces a highly turbulent, well-dispersed removal or one that produces a low-turbulent, weakly dispersed removal can be selected in the extreme case. Since both very high level turbulence and very low level turbulence (and thus low dispersion) produce errors in sheet formation in a flat wire machine, the headbox design is suitably formed by compromising the two extreme cases. That is, the primary purpose of the headbox mal-15 has hitherto been to produce a level of turbulence high enough for dispersion but low enough to avoid free surface defects during formation. It is clear that the best compromise is different for different types of papermaking raw materials, compositions, flat wire table model, machine model, machine speed, etc. Furthermore, since these trade-offs always have to make sacrifices for the best possible dispersion and / or the best possible flow pattern on the flat wire machine wire, it seems that there is a great need to improve today's headbox design.

The unique and novel combination of elements of the above patents delivers a pulp suspension to the forming surface of the papermaking machine, with a high degree of fiber dispersion and a low level of turbulence in the discharge nozzle. Under these conditions, a fine dispersion of fibers is produced, which does not deteriorate to the extent that occurs in a turbulent dispersion made with conventional headbox designs. It has been found that the absence of high-grade turbulence is a factor of 3,81145 which prevents a particularly high re-flocculation of the fibers, since the flocculation is primarily the result of the decomposition of low-grade turbulence and the continuity of high-grade turbulence. Maintaining the dispersion in the flow on the wire of the 5 flat wire machine directly results in improved formation.

The method by which the above is carried out produces a fine degree of turbulence without high-degree vortices, conveying the fiber suspension through a system of parallel cross-machine channels with a uniformly small size but a large percentage of open area. Both of these conditions, a uniform small channel size and a high percentage open area of removal, are necessary. Thus, the high degree of turbulence developed in the channel flow has the same magnitude as the depth of the individual channels, keeping the individual channel depth small, so that the degree of turbulence formed is small. It is necessary for the discharge to have a high percentage open area to prevent the development of high-grade turbulence in the discharge area. That is, large fixed areas between the outlets of the channel would cause a high degree of turbulence in the wake of these areas.

The flow channel must then change from a large inlet size to a small outlet size. This change should occur at a substantial distance so that the large-scale coarse flow disturbances developed in the inlet structure have time to decrease to the desired low-degree turbulence. The area between the channels approaches the small dimension it must have at the outlet end. This application of simultaneous convergence is an important embodiment of the present invention.

Under certain operating conditions, the traction members used to produce a fine degree of turbulence may not be stable. Short-35 pressures across the machine tend to bend the towing element u 81145 in the cross-machine direction and cause transverse variations in the paper across the machine. The deformation resistance of the towing elements along the length of the machine can cause small deviations in the uniform velocity 5 of the mass flowing from the surfaces at the towing edge of the towing element. Static or dynamic instability can occur under certain operating conditions and resonant frequencies can be achieved depending on hydrodynamic forces. It has been found that the inertial and hydrodynamic couplings 10 can be broken by appropriate mass distribution and elasticity of the drag structure, with proper mass distribution and stiffness distribution being important.

It is therefore an object of the invention to provide an improved traction element design which eliminates the disadvantages of certain market conditions in hitherto commercially available structures, and in particular a traction element which provides resistance to bending in the transverse direction and provides minimal resistance to deformation in liquid flow. so that the pressures are balanced on opposite sides of the towing edge of the towing elements.

Definitions: machine direction: flow direction isotropic: same properties in all directions 25 anisotropic: not isotropic, i.e. different characteristics when tested along axes in different directions.

These tasks are solved by implementing a headbox drawing element according to the characterizing part of claim 1, such that said element is formed of a material having anisotropic properties to provide greater structural rigidity in the transverse direction of the machine.

Using anisotropic material may include factors that are not always available, such as strength, stiffness, corrosion resistance, wear resistance, weight, fatigue life, thermal expansion or contraction, thermal insulation, thermal conductivity, acoustic insulation, shear, vibration, vibration optimal design in manufacturing.

Other objects, advantages and features will become apparent from the description of the principles of the invention in conjunction with the description of the preferred embodiment in the specification, claims and drawings, in which

Figures 1A, 1B and 1C are side elevational sectional views, slightly schematic of a paper machine headbox using the principles of the present invention, and

Fig. 2 is a perspective view, partly in section, of the towing element 1 of the headbox of Fig. 1.

Representation of Preferred Embodiments.

As shown in Figure 1, the headbox 10 is provided with a papermaking pulp 11 which flows through the headbox towards the nozzle chamber. In the headbox, various devices are placed upstream of the nozzle chamber to control the flow and turbulence of the pulp. The pulp flows forward through openings 30 in the nozzle chamber inlet wall 14. The towing elements 18 and 19, Fig. 1A, run downstream in the nozzle chamber and are bent at their upper ends and are free along their length and at their lower ends 6 81145 to position themselves due to the forces exerted by the mass flowing towards the nozzle opening 16. When the pulp is sent out of the nozzle opening 16, it is delivered to a moving forming surface. The towing elements 5 are articulated at their opposite ends and the articulation is immediately followed by a bent or angled part which allows a short part of the towing elements to pass at right angles to the wall 14 and the towing elements 10 to turn immediately and run towards the nozzle chamber.

In Fig. 1B, the two outer towing elements 18 'run substantially along the length of the nozzle chamber and the intermediate towing element 19' is formed over a larger length, passing through the nozzle opening and slightly to its other side.

In the arrangement of Figure 1C, the downstream ends of the drag elements 18 "and 19" are curved, substantially matching the curvature of the nozzle chamber, as shown in Figure 1C. The upper drag element 18 "terminates 20 shortly before the nozzle orifice 16, while the lower drag element 19" extends a short distance to the other side of the nozzle orifice.

Figure 2 shows the shape of the drag element 18 '"in detail. The drag element 18'" has outer layers 18a and 18b and a central integrally layered intermediate layer 18c therebetween. The upper end of the towing elements is articulated to the wall 14 ', such as by an enlarged or spherical brush 24 at the upper end articulated in a notch 25 in the wall 14'. The lines of direction 30 are shown with the machine direction on the 90 ° axis and the direction across the machine is shown 0 On the ° axis and the intermediate direction are shown by double arrow lines, the angle between the double arrow line and the machine direction line being shown as c <.

7 81145

Various shapes of the headbox may be used, as will be apparent to those skilled in the art, including those schematically disclosed in the aforementioned patents RE 28,269 and 3,939,037.

5 In the structures hitherto marketed, the towing elements are formed of metal or plastic or fabric and are isotropic in nature in that the stiffness of the towing element (Young's modulus) is the same in the direction of flow and in the direction transverse to the flow. According to the present invention, the towing elements running directly in the direction transverse to the flow, either in separate strips or continuously from one side of the basin to the other, can be single-layered or multi-layered, straight or curved, (in the flow direction) uniformly thick, or tapered, thin or thick. The material is anisotropic so that it has different strength and / or stiffness properties in different directions. In a preferred embodiment, the anisotropic drag elements have greater rigidity in the cross-machine direction than in the machine direction. This is more important in the downstream of the drag elements; off.

By increasing the stiffness in the transverse direction, the deformations caused by pressure fluctuations are reduced or eliminated. 25 When the towing element is flexible in the machine direction, the effects or pressure differences upstream of the towing element have a minimal effect on the position of the downstream end of the towing element so as to maintain equal velocities in the layers protruding from the edge to minimize interlayer shear stress.

In a preferred arrangement, the difference between the transverse direction of the machine and the stiffness of the machine direction is at least 5% and preferably more than 500%. Currently, according to Young's modulus, the stiffness limit is a maximum of 100,000,000 psi in the spring direction of the machine due to the existing material properties.

Anisotropic drag elements can be formed from a mixed material, i. laminate, which can take advantage of the different physical properties of the different layers. For example, if a three-layer expansion element is provided, the outer layers may be formed with fibers in the transverse direction of a material such as graphite, with the inner layer containing a less rigid material oriented in the machine direction, such as glass fiber. This would give greater stiffness in the transverse direction and less stiffness in the machine direction due to the stiffness of the material and the position of the material in the matrix. Anisotropic drag elements can be formed from mixed materials such as graphite, kevlar, boron, glass, carbon, beryllium, steel, titanium or aluminum fibers in a matrix such as epoxy, polyamide, carbon, polyester, phenol, silicone, alkyd, melamine, fluorocarbon, polycarbonate, acrylic, acetal, polypropylene, ABS copolymer, polysulfone, polyethylene, PEEK, polystyrene, In PPS, nylon, disposable, plastic, thermoplastic, glass, metal or other matrices. Different materials can be combined, not as in alloying, where the result is homogeneous and iso-25 tropical. The advantage of a mixed laminate is that it can provide the best qualities of the ingredients and often offers qualities that they do not have on their own. The fabrication of the anisotropic material not only produces stiffness, strength, thermal expansion, thermal conductivity, acoustic insulation, fatigue life, which is required in a certain direction, but it works in an improved way during the use of the headbox. Relative searchable factors are: strength, stiffness, thermal expansion, thermal conductivity, etc.

If an isotropic material were used, a compromise 35 would have to be reached with respect to the material chosen. This compromise is not necessary in an anisotropic structure, 9 81145 where the desired properties in different directions can be exploited. Significant mechanical properties can be combined with unique flexibility. Properties that can be improved using anisotropic mold include strength, stiffness, corrosion resistance, abrasion resistance, weight, fatigue, service life, thermal expansion or contraction, thermal insulation, thermal conductivity, acoustic insulation, vibration damping, bending, optimum friction, low friction and manufacturing.

10 By design, the inertial and hydrodynamic couplings can be broken by the appropriate distribution of the mass and the elasticity of the structure, making the correct distribution of mass and stiffness very important. The anisotropic model can provide stability with better performance of the drag-15-road.

Although the structure is shown with the towing elements articulated at their upstream end, this is one of the preferred shapes and other forms of installation that do not need to be articulated may be used. However, it is important that the towing element be self-positioning so that the station is controlled by the mass pressure flowing on opposite sides of the towing element. The element is preferably free of attachments on the sides of the basin, but may be attached to the pool sides in some structures where there is little movement due to hydraulic forces. Although a drag element formed of a simple material can be used, the laminate can be used, as shown in Fig. 2, in which different physical properties of different layers can be obtained advantageously. Different thicknesses of the drag edge of the elements can be used, but a thickness of 10 to 120 millimeters has been found to be satisfactory.

Thus, it will be seen that we have provided an improved rear box design that fulfills the above functions and advantages and eliminates the problems encountered under certain conditions of use in the prior art.

Claims (11)

11 81145 A headbox (10) for feeding pulp (11) to a forming surface, the headbox (10) comprising a nozzle chamber and a lip slot (16), a drag element (18,19; 18 ', 191; 18 ", 19"; 5 18' ") placed in the nozzle chamber so that the element ti can move under the influence of the mass flow, the element (18,19; 18 ', 19'; 18", 19 "; 18 '") extending transversely to said headbox (10) and has a greater structural rigidity in the transverse direction of the machine than in the machine direction, so that the element (18,19; 18 ', 19'; 18 ", 19", 18 '") resists the displacement caused by transient pressure variations in the transverse direction of the machine and forms a small resistance to deformation (18,19; 18 ', 19'; 18 ", 19"; 18 '") for balancing the compressive forces on opposite sides, and means (14,14'; 24,25) for said element (18,19; 18 '); 19 '; 18 ", 19", 18' ") from the front part of the nozzle chamber in the flow direction with the rear portion unattached and constructed to self-align so as to react with the el e-20 element (18,19; 181, 19 '; 18 ", 19", 181 ") to the forces exerted on it by the mass (11) flowing over the surfaces, characterized in that said element (18,19; 181,191,18", 19 ", 181") is formed of a material , which has anisotropic properties to provide greater structural rigidity in the transverse direction of the machine. Headbox according to claim 1, characterized in that the maximum transverse stiffness of the element (18,19; 18 ', 19'; 18 ", 19"; 18 '") in the machine direction is substantially 689,500 MPa expressed by the Young's modulus and 30 machine direction mi name stiffness substantially 68.95 MPa expressed by Young's modulus. Headbox according to Claim 1 or 2, characterized in that the element (18, 19; 18 ', 19';, 2 81145 18 ", 19") is constructed of graphite epoxy so that the laminate material has unidirectional layers. Headbox according to one of Claims 1 to 3, characterized in that the element (18 '') is designed in such a way that at least a part of it has a greater structural rigidity in the transverse direction of the machine than in the machine direction. Headbox according to claim 4, characterized in that the element (18 '") consists of layers (18a, 18b, 18c) of one of the layers forming said part having a higher structural rigidity in the cross-machine direction or in the machine direction and the other of the layers has similar stiffness in both directions. Headbox according to Claim 5, characterized in that the element (18 '") has outer layers (18a, 18b) and an intermediate layer (18c) and the intermediate layer has a greater structural rigidity in the transverse direction of the machine than in the machine direction. Headbox according to Claim 5, characterized in that the element (18 '") has outer layers (18a, 18b) and an intermediate layer (18c), the at least second outer layer (18a, 18b) having greater structural rigidity in the transverse direction of the machine than in the machine direction. . Headbox according to any one of claims 4 to 7, characterized in that said part is formed of an anisotropic material selected from the group consisting of graphite, kevlar, boron, glass, carbon, beryllium, steel, titanium - or aluminum fibers in matrices selected from the group consisting of epoxy, polyamide, carbon, polyester, phenol, silicone, alkyd, melamine, fluorocarbon, polycarbonate, acrylic, acetal, polypropylene, ABS copolymer, polyethylene, polysulfone, polystyrene nylon, plastic, durable plastic, thermoset, glass or metal. 13 81145 Headbox according to one of the preceding claims, characterized in that only the rear part of said element (18, 19; 181, 191; 18 ", 19") in the downstream direction has a greater structural rigidity in the transverse direction of the machine 5 than in the machine direction. Headbox according to one of the preceding claims, characterized in that the thickness of the trailing edge of the element (18, 19; 18 ', 19'; 18 ", 19", 18 "1) is in the range from 0.254 to 3.048 mm. Headbox according to one of the preceding claims, characterized in that the nozzle chamber has a plurality of structurally similar drag elements (18, 19; 18 ', 19'; 18 ", 19", 18 '").