EP0666366B1 - Spiral fabric with low air permeability and process for making the same - Google Patents

Abstract

A linked strip comprises many interlocking synthetic spirals (10) where each winding has a flat shank (12) and a sharp bend (11). The bends of one spiral interlock like a zip with the bends (11', 11") of neighbouring spirals to form channels for securing wires (14) so to connect the spirals. Here, flat wires (15) in the spirals for reduction of linked strip air permeability are tilted w.r.t. the strip plane. A process for strip prodn. entails inter-positioning the spiral windings (11) to overlap, insertion of the securing wires (14) in the channels so formed transverse to the strip path, and insertion of the flat wires (15) into the spirals. Here, it is just after this sequence that the linked strip is thermally locked. The flat wire (15) in the spiral (10) interior is wider than the smallest distance between the two adjacent spirals, runs above one and under the other spiral securing wire (14), is clamped between the spiral inner surface and the outer surfaces of the two adjacent spirals and tapers to a point along its lengthwise edge where the edge angle is less than the wire tilt. The spirals can be formed in the cross-sectional shape of a parallelogram with different diagonals where the securing wires (14) are laid in the angles of the longer diagonal and the flat wires (15) in those of the shorter. The flat wires shrink in their longitudinal direction and expand transversely when thermal fixing occurs and so are inserted with an extra length so that after thermal fixing their length coincides with the breadth of the spiral linked ribbon.

Description

The invention relates to a spiral link belt with a plurality of interconnected spirals, the turns of adjacent spirals being zippered together, so that the overlapping winding areas form a channel. Plug wires run in the channels so that the spirals cannot be separated. To reduce the air permeability of the spiral link belt, flat wires are inserted as filler material in the free space of the spirals. The invention further relates to a method for producing such a spiral link belt.

Such spiral link belts are used in particular in the dryer section of high-speed paper machines. To achieve a low air permeability, it is necessary to fill the free interior of the spirals with filler material. If the air permeability is too high, the spiral link belt generates a very strong turbulent air flow, which can result in unsteady running and even breakage of the paper web. Spiral link belts currently in use still have a permeability of at least 2280 m ³ / m ² / hr / 100 Pa (CFM 140). This is too high for many applications.

Spiral link belts, in which the free space within the spirals is filled with filling material to reduce the air permeability, are known from EP-A-0 050 374 and EP-A-0 101 575 and GB-A-2216914. The filling material can consist of a ribbon yarn or a flat ribbon, among other things.

From US 4,381,612 a spiral link belt with flat wires is known as the filling material. Instead of a single flat wire, two filler threads can also be inserted into the free space of each spiral. An embodiment is also described in which cored wires made of low melting material, e.g. Nylon or polypropylene. When heat setting, these cored wires melt and close the open meshes of the spiral link belt.

Spiral link belts are produced in such a way that the spirals are first inserted into one another and then push-in wires are inserted into the channels which form the overlapping turns of adjacent spirals. If a spiral link belt with the lowest possible air permeability is to be produced, cored wires are then inserted into the free interior of the spirals. When using flat wires as cored wires, precautions must be taken to ensure that the flat wires do not twist. If several round wires are inserted as filling material in the interior of each spiral, it must be ensured that the round wires do not overlap. Twisting the flat wires or superimposing the round wires disturbs the monoplanarity of the finished spiral link belt, which can lead to markings in the paper web. This difficulty is usually countered by pre-fixing the spiral link belt before inserting the cored wires and flattening the originally slightly oval cross-sectional shape of the spirals by heat and pressure to such an extent that the flat wires and the multiple round wires can no longer twist or overlap. After inserting the cored wire, the spiral link belt is then finally heat set. The pre-fixation is therefore an additional step that causes considerable costs.

In the known spiral link belts, the cored wires are also relatively loosely inside the spirals. Although the edges of a spiral link tape are glued, the lateral openings of the spirals are closed so that the cored wires cannot slip out laterally. However, the edges of a spiral link belt are often damaged when running in the paper machine and the cored wires are pulled out.

The invention is therefore based on the object of providing a spiral link belt which has low air permeability with little production outlay.

According to the invention, this object is achieved in that the flat wires, which are located as filling material in the interior of the spirals, are tilted relative to the plane of the spiral link belt.

The tilting of the flat wires means that the longer cross-sectional axis of the flat wires lies at an angle to the longer cross-sectional axis of the spirals, which lies in the plane of the spiral link belt. The tilt angle can e.g. 15 to 25 ° and preferably about 20 °. The prerequisite for this is, of course, that the flat wire itself lies in one plane and is not twisted.

The tilt angle is preferably so large that one edge of the flat wire lies above the plane of the highest points of the plug wires, while the other edge lies below the plane of the lowest points of the plug wires.

Usually all flat wires are tilted in the same direction. However, the tilt angle can alternately be positive and negative, so that the flat wires, viewed in the axial direction of the spirals, alternately fall and rise from left to right.

By tilting the flat wires, the diagonal within the free space of the spirals is used and there is the possibility of choosing wider flat wires, which reduces the air permeability of the spiral link belt. The flat wires running inside the spirals are preferably wider than the smallest distance between the two adjacent spirals connected to a respective spiral. The term "diagonal" refers to the imaginary square formed by the two and thus a total of four intersection points of a spiral with the preceding and the following spiral. Due to the larger width of the flat wires, they can no longer twist within the spiral.

There is usually only one flat wire inside each spiral. However, there is also the possibility of inserting two flat wires of particularly low thickness on top of one another in a spiral. However, each of these two particularly thin flat wires is then wider than the smallest distance between the two adjacent spirals connected to the respective spiral, as described above.

In order for a spiral link belt to have the lowest possible air permeability, it is not sufficient that it is essentially sealed by filling material, for example a flat wire, in plan view. There must also be no larger, three-dimensionally intertwined paths for air to pass through the spiral link belt. There is space for such a three-dimensionally intertwined path, in particular, between the tips of two adjacent turns of a spiral, since these two turns lie on one side of a plug wire, while the intermediate turn arc of the adjacent spiral lies on the other side of the plug wire, so that there is an opening , which is delimited laterally by the two winding arches and front and rear by the plug wire or the flat wire. Because this space is conventional Spiral link bands with flat wires remain open, the air permeability can not be reduced enough. In the spiral link belt according to the invention, however, the longitudinal edges of the flat wires are almost scissor-like pinched by the adjacent turns and legs of adjacent spirals. The flat wire abuts against the inside of its spiral, that is to say the spiral into which it was inserted, and lies on the outside of the preceding and the following spiral, in each case at places where its spiral is in any case connected with the preceding and subsequent spiral touched. There are therefore no significant through-openings between the winding legs of a spiral, the flat wire lying therein and the winding arcs of the preceding and following spirals. On the other side of the winding arcs considered here, the plug wire and the winding legs are similarly close together, so that there are no significant passage openings here either. Overall, a flat sawtooth or step-shaped surface, which is largely closed, extends through the flat wires, the winding legs and bends and the plug wires, viewed in the axial direction of the spirals. In the spiral link belt according to the invention there are therefore no three-dimensionally intertwined paths of larger cross-section through the spiral link belt, so that it has a very low air permeability.

Another advantage of the spiral link belt is that the flat wires are firmly anchored within the spiral link belt and therefore cannot be torn out of the spiral link belt even if the edges of the spiral link belt are damaged in the paper machine.

The invention further relates to a method for producing the spiral link belt described above, the spiral link belt being heat set only once, namely after the insertion of the flat wires.

It is no longer necessary to pre-fix the spiral link belt before inserting the cored wire. During heat setting, the spiral link belt is heated and simultaneously in the longitudinal direction, i.e. in the plane of the spiral link belt perpendicular to the plug wires, stretched and flattened. The individual spirals are stretched and flattened. The flat wire inside a spiral turns towards the level of the sieve belt, i.e. the tilt angle becomes smaller, and the two longitudinal edges of the flat wire are pinched like scissors by the winding legs of the spiral in which it is located and by the winding arcs of the preceding or following spiral, so that the flat wire is firmly anchored in the screen structure and not from the Spiral can slip out. As a result of the decreasing angle of tilt, the apparent width of the flat wire increases parallel to the plane of the spiral link belt and presses the flat wire against the two adjacent spirals connected to the respective spiral, thereby filling in the gaps that still exist.

Another advantage of the method according to the invention is that the plug wires and the flat wires serving as cored wires can be retracted at the same time.

The spiral link belt can be made from spirals, the cross-sectional shape of which is a parallelogram with diagonals of different lengths, the plug wires inevitably sliding into the angles connected by the longer diagonals and the flat wires lying on the shorter diagonals. The corners of the parallelogram are of course rounded. Even wider flat wires can be inserted in spirals of this cross-sectional shape. When the spiral link belt is heat-set after the flat wires have been retracted, the spirals then take on the usual flattened cross-sectional shape. The edges of each flat wire are at a greater depth between the winding legs the spiral in question and the winding arcs of the preceding or following spiral are clamped like scissors, which enables a further reduction in air permeability.

The spirals can also be triangular, rectangular or square in cross section or have any other cross-sectional shape into which particularly wide flat wires and in particular wider flat wires can be introduced than in the conventional oval spirals.

The spirals can be wound from monofilaments with a circular cross-section. In order to achieve a particularly low air permeability, however, it is generally preferable to wind the spirals from monofilaments with a flattened cross section with an aspect ratio of approximately 1: 1.3 to 1: 3.

The edges of particularly wide flat wires can prevent the winding legs from lying in one plane at these points during heat-setting and thus the spiral link belt becoming monoplan. This difficulty can be remedied by using flat wires with tapered edges. The edges of such flat wires are more flexible because of the smaller material thickness and better fit around the winding legs and arches, from which they are pinched like scissors.

The reduction in the material thickness preferably begins in the central region of the cross section of the flat wires, so that they have a flat diamond-shaped cross section. The flat wires can also have other cross-sectional profiles, for example the cross-sectional profile can only taper on one longitudinal edge, while it is just cut off or rounded on the other longitudinal edge. The cross-sectional profile can also be rounded on both longitudinal edges.

According to a preferred embodiment of the method according to the invention, flat wires are used which contract in their longitudinal direction during heat-setting and expand in their transverse direction. In order for the flat wires to extend over the entire width of the spiral link belt after heat setting, they are preferably inserted into the hollow spaces of the spirals with a speaking excess length. The flat wires therefore protrude slightly from the sides before heat setting. When heat setting, they then shrink in their longitudinal direction so that their final length corresponds to the width of the spiral link belt. The use of such flat wires has the advantage that the flat wires, due to their expansion in the transverse direction, fill the cavities of the spirals even better.

Flat wires with this property to shrink in their longitudinal direction during heat setting and to expand in their transverse direction are commercially available.

In addition to the extremely low air permeability, there are the advantages of the manufacturing process mentioned above, namely the elimination of the pre-fixing, simultaneous insertion of the plug-in and flat wires and the firm anchoring of the flat wires in the spiral link belt.

Fig. 1

schematisch den Querschnitt eines Spiralgliederbandes in Längsrichtung;

Fig. 2

das Spiralgliederband von Fig. 1 nach dem Thermofixieren;

Fig. 3

schematisch die ovale Querschnittsform einer üblichen Spirale für die Herstellung eines gliederbandes;

Fig. 4

die Parallelogramm-Querschnittsform einer Spirale;

Fig. 5

eine Darstellung ähnlich der von Fig. 1, wobei die Spiralen Parallelogramm-Querschnittsform haben;

Fig. 6

zeigt die Unebenheit der Spiralbandoberfläche bei Verwendung eines Flachdrahtes mit stumpf abgeschnittenen Kanten;

Fig. 7

ein Spiralgliederband im Schnitt bei Verwendung von Flachdraht mit zugespitzten Kanten und

Fig. 8

im Querschnitt einen Flachdraht mit sich zu den Längskanten hin verringernder Materialstärke.

Embodiments of the invention are explained below with reference to the drawing. It shows:

Fig. 1

schematically the cross section of a spiral link belt in the longitudinal direction;

Fig. 2

the spiral link belt of Figure 1 after heat setting.

Fig. 3

schematically the oval cross-sectional shape of a conventional spiral for the production of a link belt;

Fig. 4

the parallelogram cross-sectional shape of a spiral;

Fig. 5

an illustration similar to that of Figure 1, wherein the spirals have a parallelogram cross-sectional shape.

Fig. 6

shows the unevenness of the spiral tape surface when using a flat wire with bluntly cut edges;

Fig. 7

a spiral link belt in the cut when using flat wire with tapered edges and

Fig. 8

in cross section a flat wire with a decreasing material thickness towards the longitudinal edges.

Fig. 1 shows a spiral link belt in section in the longitudinal direction. The spiral link belt is composed of a multiplicity of spirals 10 which lie parallel and one next to the other, each spiral 10 being formed by a multiplicity of turns having an elliptical cross section. Each turn is divided into two turn arcs 11 and two winding legs 12 which are curved or flat to a lesser extent. The spirals 10 mesh with one another so that the turns 11 of a spiral 10 engage in a zipper-like manner with the turns 11 'and 11' 'of the two adjacent spirals 10' and 10 ''. The interlocking winding arches 11, 11 'and 11' 'overlap to such an extent that they enclose channels 13. In this plug wires 14 are inserted, which firmly connect the spirals 11, 11 'and 11' 'so that the spirals can no longer be released from their mutual engagement. The winding legs 12 form the top and the bottom of the spiral link belt.

In the free interior of the spirals 10 there are flat wires 15 as filling material. The flat wires 15 are tilted with respect to the plane of the spiral link belt. As a result, more space is available for the flat wires 15 and can be wider Flat wires 15 are inserted into the spirals 10. The flat wire 15 within a spiral 10 runs approximately in the direction of the diagonal of the rectangle, which in FIG. 1 shows the intersection of the two winding arcs 11 of this spiral 10 with the overlapping winding arches 11 'and 11''of the neighboring spirals 10' and 10 '' is formed.

While Fig. 1 shows the spiral link belt before the heat setting, so that the spirals 11 have approximately their original elliptical or oval shape, Fig. 2 shows the spiral link belt after the heat setting. After heat setting, the individual spirals 10 are flattened to such an extent that the winding legs 12 lie almost in one plane, and thus form a largely smooth surface of the spiral link belt. Although the tilt angle of the flat wires 15 is now smaller, it is still so large that the one in FIG. 1 left, longitudinal edge of the flat wire 15 lies above the plane defined by the highest points of the plug wires 14, while the other, in Fig. 1 right, longitudinal edge of the flat wire 15 is below the plane which is defined by the lowest points of the plug wires 14. The width of the flat wires 15 is selected such that it is larger than the smallest distance between the spirals 10 'and 10' ', which are connected to a spiral 10, even after the heat setting. The flat wires 15 are thereby scissor-like clamped on their longitudinal edges between the turns 11 of a spiral and the interlocking turns 11 'and 11' 'of the preceding or the following spiral 10', 10 ''.

Fig. 3 shows the usual oval cross-sectional shape of spirals, as used for the production of spiral link belts, before the heat setting. According to a second embodiment of the invention, spirals with a parallelogram cross section according to FIG. 4 are used instead of the conventional oval cross section. The parallelogram has angles of approximately 50 ° and 130 ° and the aspect ratio the sides of the parallelogram are around 1.5 to 2.

5 shows in longitudinal section a section comprising a plurality of spirals from such a spiral link belt prior to heat setting. The plug wires 14 lie in the angles of the parallelogram connected by the longer diagonal, so that the position of the spirals 10 is stable during heat setting. 5, the position of the flat wires 15 coincides approximately with the shorter diagonal of the parallelogram. By using spirals with the special shape that is originally similar to a parallelogram, shown in FIG. 4, even wider flat wires 15 can be inserted into the spirals than in the embodiment of FIGS. 1 to 3.

The manufacturing process is otherwise unchanged from the embodiment of Figures 1 to 3, and in particular the plug wires 14 and the flat wires 15 can be inserted into the spirals in one operation.

When using particularly wide flat wires, difficulties can arise with regard to the monoplanarity of the surface of the finished spiral link belt. The previously mentioned flat wires have a rectangular cross section of, for example, 0.5 x 2.8 mm. As mentioned, the edges of the flat wires 15 are clamped like scissors between the winding arcs and legs 11, 12 during the heat setting. In the case of particularly wide and / or thick flat wires 15, there is a risk that the flat wires 15 cannot be pressed completely downward by the winding legs 12, so that the winding legs 12 remain in their original, slightly curved shape and, as a result, the surface of the spiral link band is not monoplan will, s. Fig. 6. In order to achieve 15 monoplane surfaces of the spiral link belt even with particularly wide flat wires, in the embodiment shown in FIG. 7 flat wires 15 become with them Longitudinal edges tapering cross-sectional profile used. In the flat wires 15 shown in Fig. 7, the longitudinal edges are chamfered so that there is a cutting edge 16 parallel to the surface of the spiral link belt, ie the taper angle is approximately equal to the tilt angle of the flat wires. The air permeability is not affected by this, but the monoplanarity of the spiral link belt is preserved.

Fig. 8 shows in section flat wires 15 with a cross-sectional profile that tapers at a particularly acute angle 17, so that the cross-sectional profile is almost diamond-shaped.

Examples:

For three different spiral link belts, the dimensions of the spirals, the plug wires and the filler flat wires as well as the air permeability achieved are given below. The material was polyester. table example 1 Example 2 Example 3 Shape of the spirals (mm x mm) 5.3 x 3.2 5.5 x 3.3 5.3 x 3.2 Spiral wires (⌀ mm) 0.6 0.6 0.7 x 0.43 Plug wires (⌀ mm) 0.9 0.9 0.9 smallest distance between neighboring spirals (mm) 1.1 1.3 1.78 Filling material flat wires (mm x mm) 2.2 x 0.5 2.3 x 0.5 2.8 x 0.62 Air permeability (CFM) 130 90 50

The values given are the dimensions before the heat setting. The air permeability was of course measured after heat setting. The free distance between the adjacent spirals is calculated from the longer cross-sectional dimension of the spirals minus 4 x diameter of the spiral wire minus 2 x diameter of the plug wire. In all three cases, this distance is significantly smaller than the longer cross-sectional dimension of the filler flat wires. Of course, the relations shift somewhat due to the heat setting. Even after heat setting, the flat wires are still wider than the just defined distance of the neighboring spirals.

Claims (10)

1. Spiral link belt with a plurality of plastic helices (10) connected to one another which consist of flat winding limbs (12) and of winding arcs (11), wherein the winding arcs (11) of a helix (10) interlock in the manner of a slide fastener with the winding arcs of a neighbouring helix (10', 10'') and the overlapping winding arcs (11, 11', 11") form a channel (13), with pintle wires (14) which run through these channels (13) and thereby connect the helices (10, 10', 10''), and with flat wires (15) in the helices (10) to reduce the permeability to air of the spiral link belt, characterized in that the flat wires (15) are tilted relative to the plane of the spiral link belt.
2. Spiral link belt according to claim 1, characterized in that the flat wire (15) running inside a helix (10) is wider than the smallest distance between the two helices (10', 10'') connected to this helix (10).
3. Spiral link belt according to claim 1 or 2, characterized in that the flat wire (15) running inside a helix (10) runs below one pintle wire (14) and above the other pintle wire (14) by which this helix (10) is connected.
4. Spiral link belt according to one of claims 1 to 3, characterized in that the flat wire (15) running inside a helix (10) is clamped between the inside of this helix (10) and the outside of the preceding and/or of the following helix (10', 10'').
5. Spiral link belt according to one of claims 1 to 4, characterized in that the cross-section of the flat wires (15) tapers at an acute angle to their longitudinal edges.
6. Spiral link belt according to claim 5, characterized in that the angle (17) at which the cross-section of the flat wires (15) tapers is smaller than the angle of tilt of the flat wires (15).
7. Method for the production of a spiral link belt according to one of claims 1 to 6, wherein the helices (10) are fitted into one another in such a way that the windings (11) of successive helices (10) overlap and form a channel (13) running transversely to the longitudinal direction of the spiral link belt, a pintle wire (14) is inserted into the channel (13), a flat wire (15) is inserted into the helix (10) and the spiral link belt is thermoset, characterized in that the spiral link belt is thermoset only after the insertion of the flat wire (15).
8. Method according to claim 7, characterized in that helices (10) are used whose cross-section shape is a parallelogram with diagonals of different lengths, wherein the pintle wires (14) lie in the angles connected by the longer diagonal and the flat wires (15) on the shorter diagonal.
9. Method according to claim 7 or 8, characterized in that flat wires (15) are used which, upon thermosetting, shrink in their longitudinal direction and expand in their transverse direction.
10. Method according to claim 9, characterized in that the flat wires (15) are inserted into the helices (10) with such an excess length that, after the shrinkage caused by the thermosetting, their length roughly corresponds to the width of the spiral link belt.

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