JPS6146597B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a paper machine headbox and, more particularly, to a papermaking machine headbox in which a trailing piece within the slicing chamber of the headbox has a free flow to the slicing opening to maintain a slight turbulence in the raw material at the slicing opening. Related to the improvement of the head box slicing room.

A freely movable trailing piece within a head box slice chamber was first disclosed in U.S. Pat. No. 3,939,037. No. 28,269 and others disclose trailing pieces that extend from chamber side to chamber side. These trailing pieces can create and maintain microturbulence in the stock flowing towards and past the slicing opening. The patented concept described above can also be used to advantage and operate in a machine for making multilayer paper, in which raw materials of different characteristics are delivered to opposite chambers of a trailing section that extends to the side of the chamber.

A fundamental limitation of headbox design is that the means to create turbulence in the fiber suspension to disperse the fibers is limited to relatively large scale equipment. With such a device, microturbulence can be created by increasing the strength of the generated turbulence.
Therefore, turbulent energy naturally moves from larger dimensions to smaller dimensions, and the greater the intensity and the greater the rate of energy transfer, the smaller the turbulent dimension will remain. However, deleterious effects also arose from this high intensity, large dimension turbulence, ie large wave motions generated in the Fourdrinier table section and free surface disturbances. Therefore, the general principle of headbox performance is that the dispersion process and turbulence level in the headbox outflow are closely interrelated: the greater the turbulence, the better the dispersion.

Then, in choosing a headbox design under these limiting conditions, one could choose between two extremes: a design with high turbulence and well-dispersed runoff, or a design with low turbulence and poorly dispersed runoff. . Since either very high or very low levels of turbulence (resulting in poor dispersion) can cause defects in sheet formation on Fourdrinier machines, headbox design techniques provide a suitable compromise between these two extremes. It's about making a plan. That is, the primary objective of headbox design to date has been to generate turbulence levels high enough for dispersion, but low enough to avoid free surface defects during formation. The best compromise will be different for different types of papermaking machine formulations, consistency, fourdrinier table design, machine design, machine speed, etc. Furthermore, these compromises always result in the best possible dispersion on Fourdrinier wire and
There appears to be great potential for improvement of current headbox designs, since they always sacrifice the best possible flow pattern.

The unique and novel combination of the foregoing patented elements provides a feedstock slurry with a high degree of fiber dispersion with a low level of turbulence in the discharge jet onto the papermaking machine forming surface. Under these conditions, a microdispersion of fibers occurs that does not degrade to the extent that it causes the turbulent dispersion that occurs with conventional headbox designs. Since coagulation is overwhelmingly the result of the decay of microturbulence and the persistence of large turbulence, it has been found that it is the absence of large values of turbulence that prevents recoagulation of the entire fiber. Sustained dispersion in the flow over the Fourdrinier wire therefore leads directly to formation improvement.

In order to achieve the above, i.e. to generate microturbulence without large dimension vortices,
The fiber suspension is passed through a system of parallel transverse water channels of uniform small size but high open area percentage. Both a uniform and small channel size and an opening area with a large exit rate are required. Therefore, the maximum dimension of turbulence generated in the flow of a channel can be reduced by keeping the depth of each channel small.
have the same magnitude as the individual channel depths, resulting in smaller turbulence dimensions. It is necessary to have a large exit rate opening area to prevent the development of large turbulence in the discharge zone. That is, the large non-open areas between the waterway outlets cause large turbulence to follow these areas.

Conceptually, therefore, the flow channel must vary from large inlet to small outlet dimensions. This change should occur at a sufficient distance to allow time for the coarse flow disturbances of large dimensions created along with the inlet structure to reduce to the desired micro-turbulence.
The concept of simultaneous convergence, in which the interchannel area approaches the smaller dimensions it needs to have at the outlet end, is an important design concept of this invention.

Under certain operating conditions, the trailing piece used to obtain microturbulence is not necessarily stable. The instantaneous lateral pressure tends to bend the trailing piece laterally, causing changes in the lateral uniformity of the paper. Resistance to deformation along the longitudinal length of the trailing section causes slight deviations in the uniform velocity of the material flowing down the trailing end surface of the trailing section. Static and dynamic instability occur under certain operating conditions, and resonant vibrations can be spread by dynamic hydraulic forces. The coupling between inertia and hydraulic pressure is broken by the appropriate distribution of mass and elasticity of the trailing structure,
It was also discovered that proper mass distribution and stiffness distribution are important.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to design an improved trailing section, which avoids the disadvantages that occur in certain operating conditions, and in particular provides resistance to lateral deflections, and also improves the structure of the trailing section available hitherto. It is an object of the present invention to provide a trailing piece that provides minimal resistance to deflection in the direction of fluid flow so that the pressures on opposite sides of the trailing ends are balanced.

Definition of terms Longitudinal direction: flow direction Isotropic: Having the same characteristics in all directions.

Anisotropic: not isotropic, i.e. exhibits different properties along axes in different directions. In accordance with the principles of the present invention, the present objective is to achieve greater structural stiffness in the transverse direction than in the longitudinal direction (preferably at the downstream tip). ) and a suitable shape made of an anisotropic material, preferably with transverse stiffness and longitudinal strength and flexibility, either by material properties, direction, dimension or number. This is accomplished by providing a trailing piece made of separate layers of laminate in the form of laminated sheets. Alternatives from woven or needled materials may also be achieved, and the weave direction, material, size or quantity of the filaments adjust the stiffness direction.

Other methods such as strength, stiffness, corrosion resistance, weight, fatigue life, thermal expansion or contraction, thermal insulation, thermal conductivity, acoustic insulation, vibration damping, buckling, low friction and optimal design in terms of manufacturing are not always available. Design elements that are not possible can be included by using anisotropic materials.

Other objects, advantages, and features will become apparent from the principles of the invention as set forth in connection with the description of the preferred embodiments in the specification, claims, and drawings.

Embodiment As shown in FIG.
Contains. Inside the headbox, various devices are arranged upstream of the slicing chamber to regulate the flow and turbulence of the raw material. The raw material flows forward through an opening in the wall 14 at the entrance to the slicing chamber. The trailing pieces 18 and 19 of FIG. 1A are pivoted at their upper ends and free along their lengths, and at their lower ends are located in the slicing opening 1.
It extends to the lower end of the slicing chamber so that it can be positioned independently by the pressure of the raw material flowing into the slicing chamber. When the raw material is discharged from the slicing opening 16, it is delivered onto a running forming surface. The trailing section is pivoted to the upstream end, and this pivoting is immediately followed by a curved or angled section which causes the short section of the trailing section to splay out at a preferred angle relative to the wall 14. , and because of this bending, the trailing piece immediately bends and expands towards the slicing chamber.

In Figure 1B, two outer trailing pieces 1
8' extends substantially along the length of the slicing chamber, and the intermediate trailing piece 19' is of greater length so as to pass through the slicing opening and extend slightly forward.

In the arrangement of FIG. 1C, trailing piece 18''
and 19" are curved to substantially follow the slicing chamber curvature shown in FIG. 1C. The upper trailing segment 18" is shorter than the slicing opening 16; The trailing piece 19'' extends a little to the front of the slicing opening.

In FIG. 2, the shape of the trailing piece 18 is shown in detail. The trailing piece 18 has outer layers 18a and 18b with a central, completely sandwiched intermediate layer 18c therebetween. The upper end of the trailing piece is pivotally supported within wall 14' with an enlarged or spherical ridge 24 at the upper end which is pivotally mounted within a groove 25 in wall 14'. The vertical line is the 90° axis, the horizontal line is the 0° axis, the intermediate direction is a double arrow line, each direction line is indicated, and the angle between the double arrow line and the vertical line is α is shown.

The aforementioned patents RE No. 28269 and No. 3939037
A variety of headbox configurations can be used as will be understood by those skilled in the art, including those schematically illustrated in the above section.

The trailing sections of conventionally available constructions were made of metal or synthetic resins or fabrics and were to some extent isotropic in that the trailing section stiffness (Young's modulus) was the same in the machine and transverse directions. In accordance with the invention, the laterally flat trailing sections, either separate strips or continuous from chamber side to chamber side, are single or multi-layered, flat or curved (in the flow direction).
It may have a uniform thickness or a gradient of thickness. The material is anisotropic so that it has different strength and/or stiffness properties in different directions. The anisotropic trailing piece has a wall-like shape and is more rigid in the lateral direction than in the longitudinal direction. This is more important at the downstream end of the trailing piece.

By increasing the lateral stiffness, deformation due to pressure changes is reduced or eliminated. By having a longitudinally flexible trailing piece, effects or pressure differences upstream of the trailing piece have minimal effect on the position of the downstream end of the trailing piece, so that It acts to keep the velocity of each layer the same, minimizing shear between each layer.

In a preferred device, the difference in stiffness between the lateral and longitudinal directions is a minimum of 5%, preferably 500% or more.
Currently, the maximum stiffness limit expressed by Young's modulus in the transverse direction is 7030000 Kg/cm ² (100000000 psi), and the minimum stiffness in the longitudinal direction is 3515 Kg/cm ² due to existing material properties.
(50000psi).

The anisotropic trailing piece is made of a composite material, ie, a laminate, to take advantage of the different physical properties of the different layers. For example, if a three-layer trailing piece is prepared, the outer layer is made of laterally oriented fibers of a material such as graphite, and the inner layer is a longitudinally oriented less stiff material, such as glass fibers. It is made with. This provides greater stiffness in the lateral direction and less stiffness in the longitudinal direction due to the material stiffness and material arrangement within the tissue formation. Anisotropic trailing pieces have substrates made of graphite, Kevlar, boron, glass, carbon, steel, titanium, or aluminum fibers, and also epoxy, polyamide, carbon, polyester, carbolic acid, silicon, alkyd resins, Melamine resin, carbon fluoride, polycarbonate ester, acrylic acid, acetal, polypropylene, ABC copolymer, polysulfone, polyethylene, PB polystyrene, PB, nylon, thermosetting substance, plastic, thermoplastic substance, Made from things like glass, metal or other substrates. Different materials are combined, but not like an alloy, which is homogeneous and isotropic. The advantage of combined laminates is that they can achieve the best properties of the components and can achieve properties that cannot be had alone. Tailoring anisotropic materials not only provides the necessary stiffness, strength, thermal expansion, thermal conductivity, acoustic insulation, fatigue and longevity in defined directions, but also during headbox operation. Related factors that were subsequently investigated include strength, stiffness, thermal expansion, and thermal conductivity. If isotropic materials are used, a compromise must be made regarding the material chosen. This compromise is not necessary for anisotropic tissues, where the favorable properties of different directions can be exploited. Outstanding mechanical properties can be combined with unique flexibility.

Properties that can be improved using anisotropic design include strength,
stiffness, corrosion resistance, abrasion resistance, weight, fatigue, lifespan, thermal expansion or contraction, thermal insulation, acoustic insulation, vibration damping, buckling, low friction and optimal design and manufacturing methods.

Proper mass and stiffness distribution is very important because, by design, inertial and hydrodynamic coupling can be broken by proper mass and stiffness distribution of the structure.
Anisotropic designs can gain stability through improved action of the trailing piece.

Although the present structure shows a trailing piece pivotably attached to the upstream end, and this is the preferred arrangement, other types of attachments that do not require pivoting can be used. However, it is important that the trailing piece is self-positionable so that its position is adjusted by the pressure of the material flowing on its opposite side. Although it is preferred that the main piece is not attached to the side wall, it may be attached to the side wall in some structures where movement due to water pressure is small. Although trailing pieces made of a single material may be used, laminates such as the one illustrated in FIG. 2 can also be used, taking advantage of the different physical properties of the different layers. The trailing end of the main piece can be of various thicknesses, but from 0.254 to 3.048 mm (0.010 to
0.120 inch) was found to be sufficiently satisfactory.

It will therefore be seen that an improved headbox design has been provided which meets the objectives and advantages set forth above and which avoids the problems present in certain operating conditions of the prior art.

[Brief explanation of the drawing]

Figures 1A, 1B and 1C are somewhat schematic cross-sectional side elevational views of a paper machine headbox embodying the principles of the present invention; Figure 2 is a partially sectional perspective view of a trailing section of the headbox; be. 10...Headbox, 11...Paper manufacturing raw material,
14, 14'...Wall, 16...Slice opening,
18, 18', 18'', 18, 19, 19', 1
9″... Trailing piece, 18a, 18b...
Outer layer, 18c... Middle layer, 24... Spherical ridge, 2
5...Groove.

Claims (1)

[Claims] 1. In a headbox that has a slicing chamber and a slicing opening and delivers raw materials to a formation surface,
A trailing piece is disposed within the slicing chamber and induces movement of the material flow, and this piece extends laterally to the head box and has greater structural stiffness in the lateral direction than in the longitudinal direction and has a transitional shape. providing a weak resistance to deformation in the direction of fluid flow in order to resist lateral deflection due to pressure changes and to balance the pressurizing forces on opposite sides, and to securely fix said pieces within the slicing chamber in the upstream part; A converfloat trailing piece, characterized in that the downstream part is non-stick and includes self-positioning means in response to the force generated by the raw material flowing over the surface of the piece.