FI107818B - Screen tube for use in dry forming of web material - Google Patents

Description

107818

A screen tube for use in the dry forming of web material

Background of the Invention

The invention relates to a screen tube for use in the dry forming of web material 5 for distributing the fibrous material blown into the screen tube through a tube jacket to a wire arranged to pass through the screen tube when the fibrous material inside the jacket comprises an axial profile groove on the inner surface of the tube, the edge downstream of the tangential component of the fiber material movement and the upstream edge being at different angles to this tangential component, and the bottom of the profile grooves comprising holes or slits through which the fibers exit the screen tube.

A dispensing unit in which a screening tube such as the one described above can be used is known, for example, from Finnish patent 66948. This patent describes the basic structure of a dispensing unit which has long been used in the dry forming of sheet material. The dispensing unit, quite commonly referred to as the former, preferably comprises sieve tubes as described above, preferably arranged in pairs, so as to cause the fiber stream to run in the transverse direction of the wire in opposite directions over the wire. The reason for this is, above all, that making the flow of fiber blown in one direction only uniformly in the transverse direction of the wire, so that the resulting web has a transverse profile: * ·. · Flat, is almost impossible. By arranging the screen tubes in pairs so that they have opposite directions of fiber flow, the cross-sectional profile of the web can be substantially smoothed. In order for the web to be of uniform quality, its variation in thickness * I t across the web must be relatively small. A tolerance of ± 5% of the target thickness is typically accepted.

In spite of the fact that screen tubes are typically used in pairs for the aforementioned reasons, in the distribution unit of Finnish Patent 66948, the cross section profile of the above level is achieved. ** ·. This has proven to be problematic, even though the basic structure of the delivery unit itself is good, providing high fiber unloading efficiency even when the fibers are relatively long.

· ♦:: 35 A screen tube comprising on its inner surface axial directions of the tube, with the downstream edge and the upstream edge of the tangential component of the movement of the fibrous material at different angles to this tangential component are known, for example, from WO87 / 04474. In the screen tube of this publication, the fibrous material is introduced into the tube by means of an axially arranged rotor or a spike 5 having a direction of rotation such that its movable fibers meet an edge of a profile groove at a slight angle to the tangent to the sheath. In this way, it has been shown to provide microturbulence, which facilitates the passage of fibers through the holes or gaps in the screen tube.

The problem with the arrangement described above is above all the capacity by which the fibers can be fed through the screen tube. The higher the speed of the wire and thus the speed of forming the web, the greater the capacity of the dispensing units must also be.

BRIEF DESCRIPTION OF THE INVENTION The object of the invention is thus to provide a screen tube having the best possible and uniform fiber permeability over the entire length of the screen tube. This is achieved by means of a screen tube according to the invention, characterized in that the downstream edge of the profile grooves is at a steeper angle to the tangential component of the movement of the fiber material than the upstream edge. The solution is thus the opposite of the solution known, for example, from WO87 / 04474. The solution · ·: V according to the invention achieves a strong micro-vortex and, as a result, good formation and capacity in dry stripping.

Preferably, the downstream edge of the profile grooves with respect to the shell tangent * · 25 is about 70 ° -110 °, preferably about 90 °, and the upstream edge angle of the profile grooves with the shell tangent is about 100 ° -160 °, preferably about 130 °.

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The edges of the profile grooves may be either substantially straight or also wrapped, whereby their angle with respect to the tangent to the jacket is determined by the segment joining the edge of the profile groove and the hole or slot closest to that profile groove edge. .

• · ··· .1. Pattern List • »• ♦. **. *. The invention will now be described in greater detail by means of preferred embodiments. with reference to the accompanying drawing, in which: »Figure 1 shows a screen tube according to the invention fitted in part 35 of a delivery unit and 3 107818

Figure 2 is a cross-sectional view of a portion of the sheath of the screen tube shown in Figure 1.

DETAILED DESCRIPTION OF THE INVENTION Fig. 1 shows the basic structure of an exemplary dispensing unit 5 containing a screen tube 1 according to the invention. It shows two screen tubes 1 which are arranged to extend transversely over the wire (not shown). In Figure 1, the screen tubes 1 are arranged to pair with each other so that the flow directions A of the fibrous material 3 are opposite. This is achieved by blowing the flow of fibrous material 3 through the feed pipes 7 located at opposite ends thereof. These tubes direct substantially axial air-fluidized fiber material streams into the screen tubes. The screen sheaths 2 of the screen tubes 1 are arranged to be rotated about their axis in the direction of the arrows B in a manner known per se.

Further, in a conventional manner, also known from patent 66948, brush rolls 4 are provided inside the screen tubes, which are intended both to clean the screen surfaces 2 of the screen tubes 1 and to enhance the discharge of the fibers through the screens 2. The structure of these brush rollers is conventional and known, for example, from the aforementioned Finnish patent 66948.

In the dispensing unit of Fig. 1, an impeller 5 is disposed inside the screen tube 1 at an opposite end to its fiber inlet end 20, the purpose of this impeller being to retard the fiber flow 3 within the filter tube 1. This flow retardation, especially at the end of the screen tube where the impeller is located, allows for a more even discharge of fibers over the entire length of the screen. Above all, a positive effect is achieved at the end of the • 25 screen strainer where the impeller is located. When the screen tubes according to the exemplary embodiment shown in the drawing are arranged in pairs so that the flow direction of the fiber material is opposite **, the impeller inside the second screen tube also allows the flow to be retarded and the fiber material to be deposited on one edge of the web material. In this way, the transverse profile of the web can be smoother across its width.

9 ···. Figure 2 is a cross-sectional view of an envelope of an exemplary embodiment of a screen tube according to the invention. The direction in which the screen is rotated is indicated by arrow B and the direction in which the spindle roller 4 is rotated is indicated by arrow C. As can be seen, the directions of these arrows are opposite to each other. However, a central feature of the screening tube of the invention is the direction in which the groove of the diaper meets the fiber stream circulating within the diaper. According to the invention, the axial grooves 8 of the screen tube jacket 2 are asymmetric in that they have a groove edge 8a downstream of the spin roll direction, i.e., direction C, at a steeper angle to the upstream edge 8b. As shown in Figure 2, the angle of the downstream edge of the profile grooves 8a with respect to the tangent of the sheath is about 90 ° and more generally within the range 70 ° -110 ° and perhaps most preferably about 90 °. ° and 10 most preferably about 130 °.

The aim with the asymmetry of the profile is to achieve a strong microcortical vortex and, as a result, good formation, i.e. uniform distribution of fibers as a function of surface area, and also good capacity in dry stripping. The groove profile causing the strong turbulence and the resulting micro-vortex 15 prevents the so-called. fine mesh formation, whereby even the longest fibers pass through the sheath with good efficiency. The solution is particularly advantageous for synthetic staple fiber and is also ideal for pulp fiber.

The holes or slots 9 through which the fibers exit the inside of the screen tube 1 are located at the bottom of the profile grooves 8. In the embodiment shown in Fig. 2, the holes or slots, which may be, for example, 0 3 to 4.5 mm or 1.5 to 2 mm x 30 mm, are shown to be at the same cross section at the bottom of every other groove. The total surface area of the holes or gaps may vary considerably from • the total surface area of the diaper, to a few tens of percent, such as, for example, about 25%. The thickness of the sheath 2 may be, for example, 3-5 mm.

In Fig. 2, the edges 8a and 8b of the profile grooves are shown to be substantially ·: ··: straight, but also the edges of the profile grooves could also be curved:: T: Then their angle with respect to the tangent to the jacket would be determined or slot 9 based on a segment joining the edge closest to that edge of the profile groove. Thus, the career profile is cracked ·· ». The shape of the screen tube of the present invention can be varied without departing from the scope defined by the appended claims and the basic idea of the invention according to which the edge of the groove receiving the fiber stream is steeper or steeper than the upstream edge, which is * * the downstream side edge.

35 • 't • f · · * · · ·· * • • · ·· 9

Claims (4)

1. Sieve tube to be used in dry forming of web material to distribute fiber material (3) injected into the sieve tube (1) through the sleeve (2) of the tube onto a wire arranged to run under the sieve tube when the fiber material inside the sieve tube (1) e.g. moved by means of a spike roller (4) arranged inside the sight tube, which exhibits both a radial and a tangential component in relation to the sight tube sheath (2), which sheath on its inner surface comprises profile groove (8) in the axial direction of the tube, edge (8a), which in relation to the tangential component for the movement of the fibrous material lies downstream, and whose edge (8b), which in relation to said component is opposite to the current, has different angles with respect to said tangential component and the bottom of the profile bar comprises slit or slits (9), through which the fibers are removed from the sieve tube (1), characterized in that the edge (8a) of the profile groove lying in the downstream direction has a steeper angle relative to the tangential component of the movement of the fiber material than the edge (8b) which is countercurrent. Sieve tube according to Claim 1, characterized in that the winkein for the co-current edge (8a) of the profile bulb relative to the key for the male is about 70 ° -110 °, presumably about 90 °, and the winkkein for the profile current counter-current edge (8b) in the relative to the key for the male. is about 100 ° -160 °, presumably about 130 °. Sieve tube according to claim 1 or 2, characterized in that. . the edges of the profile bulb are substantially straight. • ·: 4. Sighting tubes according to claim 1 or 2, characterized in that the edges of the profile bar are bent, whereby their angle in relation to the key of the men is determined on the basis of the distance connecting the edge of the profile bar *: **: 25 and the edge of the heel or slot (9) at the bottom of the closest latch: T: the edge of the respective profile latch. ·· »• ·« • · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 3 * ·