FI64335C - ANORDING FOR THE EXCHANGE OF BANKS - Google Patents

Description

64335

Apparatus for turning and spreading the web Anordning för vändning och utbredning av bana

The invention relates to a device for non-contact support, spreading and possible turning of a web, in particular a coated paper or board web, which device consists of a flat or curved surface in which the web passes between this web and the web supported by blown air. the nozzle members comprise curved guide surfaces and a pressure surface therebetween, on both sides of which nozzle slots transverse longitudinal to the web run direction for directing a gas such as air to said pressure surface, the nozzle slots being bounded on the other side by said curved guide surfaces, and substantially in the same plane as the adjacent pressure surfaces.

These devices are already known in a number of different constructions, 15 but they all have some drawbacks. For example, patent application EP 0.003.414 is a known device in which this function is performed by Coanda-type nozzles placed on a surface curved transversely to the direction of travel of the web. However, such a nozzle has not obtained good results in all conditions, 20 mm. because when the guide edge of the nozzle is below the curved part of the carrier surface, the air jet does not always follow along the other side of the nozzle to the carrier surface, but the moving web may overturn the jets in the forward direction, resulting in reduced support and wavy web propagation. In addition, this known device does not perform the spreading of the web satisfactorily because the used air leaves the grooves between the nozzles and does not spread the web by leaving the edge of the web.

U.S. Patent No. 4,197,972 discloses a device consisting of a single uniformly curved surface having nozzles directed between the surface and the web at both edges and ends. However, this known device is poorly suited for handling light grades of paper because it has to use a relatively high jet speed, which causes pressure waves in the web. This known device also has no web spreading effect.

64335

Various structures based on hole nozzles are also known from the prior art, for example from U.S. Pat. No. 3,290,795 and U.S. Pat. No. 3,567,093. However, these known structures cause flow peaks at the holes and are not particularly suitable for handling delicate coated papers.

It is an object of the present invention to provide an improved web support, spreading or turning device which avoids the disadvantages of known devices. The device consists of a flat or in particular curved surface 10 on which the web passes between this surface and the web, supported by the air to be blown, which air is passed between the slots perpendicular to the direction of travel of the web.

The invention is therefore mainly characterized in that the ratio of the width of the nozzle slots to the radius of curvature of the guide surface is chosen so that the gas flow follows the curved guide surface up to the pressure surface at its current flow rates and the

The structure according to the invention provides a very stable load-bearing capacity with low energy consumption and is well suited for handling webs of different qualities. When air exits under the web from its sides, this creates a force of 25 webs, which has the advantage of preventing the web from wrinkling.

The invention will now be described in detail with reference to an embodiment shown in the accompanying figures, to which the invention is not limited.

Figure 1 shows an axonometric overview of a device according to the invention.

3,64335

Figure 2 shows a cross-section of the device.

Figure 3 shows the nozzle structure in more detail.

The device 10 shown in the figures consists of a curved surface 12 on the body, over which a web W, the edges of which are indicated by the reference WR, passes.

According to Figures 1 and 2, the device 10 consists of an interior 20 delimited by planar walls 24 and end walls 26. Through duct 25, air or other treatment gas is led through a curved perforated wall 23 to said interior 20, from where it is further led to support the web Vi through nozzle slots 16. later with a more detailed t ava11a.

15

According to Fig. 2, on the support surface 12, the direction of the web W is changed at an angle β, which is at the same time the sector to which the curved support surface 12, the radius of curvature of which is preferably constant, extends.

The surface 12 consists of pressure surface slats 14 and intermediate surface slats 15 with directional openings 16. Air is blown through these nozzles below the web W from the interior 20 of the device, where it is led by a fan (not shown) so that the web W is supported at a suitable distance M from the support surface. .

25

Nozzle slots 16 are formed between the slats 14 and 15 so that the edges of the slat acting as a pressure surface 17 pivot inwards through the rounded surface 18 and the edges of the slat acting as an intermediate surface 19 join this surface through a sharp edge 21. The edge 21 extends in the flow direction 30 of the jet to such an extent that it, together with the rounded surface 18, gives the jet a starting direction which forms an angle α with respect to the web W at the gap. Since it is intended to cause the air jets S to follow without detaching the curved surface 18 up to the pressure surface 17 in order to obtain the most efficient and stable support for the web W, the gap width a, radius of curvature R and angle α of the nozzle 35 are dimensioned specifically. In this context, we refer to D.W. McGlaughlin and J. Greber, "Experiments on the Separation of a Fluid Jet from a Curved Surface," The American Society of Mechanical Engineers, 4,64335

Advances in Fluids, 1976, pages 14-29, which shows that in a structure such as the one shown, at the relevant flow rates, the jet is able to follow a curved surface of about 45 ° -70 °. The sharp edge is positioned relative to the rounded surface 18 so that in the cross section the normal line between the edge 5 and the center of the rounded surface forms an angle with the web running direction of at most 70 °. In this case, the lengths L, of the pressure surface 17 and the intermediate surface 19, and are preferably chosen such that the ratio of their total length to the width a of the nozzle openings 16 is between about 20 ... 200.

The intermediate surfaces 19 are located substantially at the same level as their adjacent pressure surfaces 17. Each edge of the intermediate surfaces 19 has a sharp edge 21. Said sharp edge 21 prevents jets discharging from the nozzle slot 16 from turning to the intermediate surfaces 19. The Coanda effect of the curved guide surfaces 18 15 is so strong the mobile Taina is not able to change the direction of the showers.

The blowing air or other similar gas discharged from the nozzle members can only escape from the sides of the web W, because the control, pressure and intermediate pins 20 close all other air outlets. The flow of air under the web to the side creates a spreading effect on the web W, which is important to prevent the wet and moistened web from wrinkling.

The following are claims within the scope of which the various details of the invention may vary.

Claims (3)

5,64335 A device for non-contact support, spreading and possible turning of a web (W), in particular a coated paper or board web, which device consists of a flat or curved support surface (12) according to the passage of the web (W), in connection with which the web (W) passes. supported by blown air between the surface (12) and the web (W), the nozzle members of the device consisting of curved guide surfaces (18) and a pressure surface (17) therebetween. to guide said pressure surface (17), the nozzle slots (16) abutting on one side of said guide surfaces (18) and the nozzle members comprising intermediate surfaces (19) located substantially in the same plane as the adjacent pressure surfaces (17), characterized in that the ratio of the width (a) of the nozzle slots (16) to the radius of curvature (R) of the guide surface (18) is chosen so that the gas flow (S) follows at its present flow rates, curve the guide surface (18) to the pressure surface (17), and that the delimiting edges (21) of the nozzle openings (16) of the intermediate surfaces (19) are sharply angled to prevent the gas flow from turning to the intermediate surfaces (19). 20 Device according to Claim 1, characterized in that the nozzle gap (16) is oriented in such a way that the angle (α) between the outlet direction of the jet and the web is at most 70 °. Device according to Claim 1 or 2, characterized in that the ratio of the total length (L 1 + L 2) of the pressure surface (17) and the intermediate surface (19) to the width (a) of the nozzle gap is between 20 and 200.