GB2141989A

GB2141989A - Pneumatic coneying of webs

Info

Publication number: GB2141989A
Application number: GB08413415A
Authority: GB
Inventors: Hilmar Vits
Original assignee: Vits Maschinenbau GmbH
Current assignee: Vits Maschinenbau GmbH
Priority date: 1983-05-25
Filing date: 1984-05-25
Publication date: 1985-01-09
Also published as: FR2547803B1; DE3318861C1; FR2547803A1; JPS6046328A; GB8413415D0; GB2141989B

Abstract

The invention relates to a device for moving webs, in particular for the heat treatment of aluminium strip. In this device, the web is supported and conveyed by air cushion nozzles 5-12 which are assembled in pairs above and below the plane of the web and are mutually offset in the conveying direction. In each nozzle, the blowing air jets point towards one another asymmetrically and the nozzles in the pairs are mirror images of each other in such a way that the blowing air retained between them as an air cushion can flow out only over the outer nozzle edges of one pair. Due to this arrangement and design of the suspending nozzles, an essentially trapezoidal line of the web results, which has a stabilising effect due to its small radii or curvature at the corners of the trapezium. Due to the blowing air flowing out over the outer edges the relatively large area of the web of material between two pairs of nozzles is swept by the blowing air and is therefore adequately treated. <IMAGE>

Description

SPECIFICATION Suspended webs The invention relates to a device for moving suspended webs, particularly (but not exclusively) with a heating device for the heat treatment of aluminium strips, consisting of a housing, with an inlet opening and outlet opening for the web, and of suspending nozzles, which are arranged above and below the plane of the web with an offset in and transversely to the conveying direction and which each have two slots or rows of holes with blowing directions pointing towards one another in order to form an air cushion, the angle of inclination of the blowing directions of the two slots or rows of holes relative to the common centre plane and/or the cross-sec- tion of the two slots or rows of holes being different and mutually matched in such a way that the blowing air flows out of the air cushion substantially over one nozzle edge.

In a known device of this type (German Offenlegungsschrift 2,615,258) which, however, is not fitted with a heating device for the heat treatment of aluminium strip, the upper and lower suspending nozzles are individually offset from one another. With this arrangement of the suspending nozzles, most webs can be moved absolutely without contact, without lateral deflection of the web and without flutter. The sine-shaped line of the web, responsible for this, is preserved during the operation and is not subject to manufacturing tolerances of the outlet slots or to changes in the outlet slots during operation, since the outflow direction is predetermined with sufficient reliability from the start by the setting of the angles of inclination of the slots or rows of holes and/or the sizing of the cross-sections.

In spite of these advantages of the known device over other known devices (German Auslegeschrift 1,292,082) in which there is no defined outflow direction, movement of the web of material without contact and without flutter becomes critical, if no waves of sufficient amplitude can form during the movement of the web of material, for example due to an unduly low air density which, for example, in a heat treatment furnace for aluminium is only about one quarter of the normal air density or due to excessive pulling tension on the web.

SUMMARY OF INVENTION It is the object of the invention to provide a device for moving suspended webs, which device ensures stable movement of the web of material even under unfavourable conditions.

In a device of the type set out above, this object is achieved when the suspending nozzles are mutually offset in pairs on both sides of the common centre plane and, within each pair, the nozzle edges, over which the blowing air flows out, are arranged as mirror images relative to a plane which is located between the two suspending nozzles and perpendicular to the common centre plane.

Preferably, the nozzle edges, over which the blowing air flows out, are located on the outside in each pair of suspending nozzles.

It is particularly advantageous when the angles of inclination of the blowing directions of the adjacent central slots or rows of holes are shallower than those of the outer slots or rows of holes.

The advantages of such a device are that, with suspending nozzles of relatively small cross-section, webs of material can be reliably guided without contact at low air density and/or a strong pull on the web. Although for the above mentioned reasons a sine-shaped line of the web is not obtained, essentially trapezoidal waves with small radii of curvature at the corners of the trapezium are formed. In spite of the larger distance, caused by the arrangement of the suspending nozzles in pairs, between the individual pairs, the treatment of the web of material with the blowing air is satisfactory, whenever the outflow edges of each pair are located on the outside, because the blowing air is then blown into the space having the greatest distance between the suspending nozzles and sweeps over the web in this entire region.However, the region, which is not swept by the blowing air, between two suspending nozzles of an individual pair is shorter than in the case of an alternating arrangement of one suspending nozzle in each case, so that, viewed as a whole, the application of "air" as the treatment agent to the web is not inferior to that in the known device.

It has proved to be advantageous when the suspending nozzle at the housing inletopening, which is the first in the conveying direclion, and the last suspending nozzle at the housing outlet opening are located below the plane of the web of material. This feature has the effect that no large, unsupported section of the web of material results.

Satisfactory suspension properties and satisfactory application of hot air as the treatment agent to the web are obtained, when the shallow angle of inclination of the blowing direction is 10 to 40 , in particular 20 to 30 , and the steep angle of inclination is 45 to 80 , in particular 55 to 65 and the crosssection of one slot is 1 + times to twice the cross-section of the other slot.

Since the lower suspending nozzles carry the web of material, they should be of larger dimensions than the upper suspending nozzles. For the cross-section of the lower nozzles, 1 + to twice the cross-section of the upper nozzles has proved to be advantageous.

Summarizing it can be stated, that the invention guarantees better suspending results for webs which are difficult to guide in suspension for different reasons (low density of blowing air; great tension; great stiffness, etc).

BRIEF DESCRIPTION OF INVENTION The invention is explained in more detail below by reference to the drawing which represents an illustrative embodiment in which, in detail Figure I shows a device for heat-treating suspended moving aluminium strip, in a diagrammatic representation in side view, and Figure 2 shows an enlarged representation of a suspending nozzle of the device according to Fig. 1.

DETAILED DESCRIPTION OF INVENTION The device consists of a housing 1 with a slot-shaped inlet opening 2 and a slot-shaped outlet opening 3 for the web 4 which is to be transported in suspension through the device.

Suspending nozzles 5 to 1 2 which are designed as air-cushion nozzles and are supplied with blowing air from a heating device 1 3 are arranged in pairs above and below the transport plane. The suspending nozzles 9 and 12, which are the first and last in the conveying direction, are located below the conveying plane.

Each suspending nozzle has the cross-section of an air-cushion nozzle, as shown in Fig.

2. Such a nozzle has two blowing air slots 14, 1 5 of different cross-section and different angles of inclination a, ss of the blowing direction relative to the conveying plane.

Thus, the slot 14 has a greater cross-section, and its blowing direction has a shallow angle of inclination a of 30' whilst the slot 1 5 has only about half that cross-section and its blowing direction has a steep angle of inclination ss of about 60 . The angles of inclination a, and the cross-sections of the two slots 14, 1 5 are mutually matched in such a way that the blowing air collecting between the blow jets as an air cushion flows out over the edge adjoining the slot 1 5.

Suspending nozzles constructed in this way in principle are arranged in the device according to Fig. 1 in pairs, transversely to the conveying direction with respect to their longitudinal axis, above and below the plane of the conveying track in such a way that the outflow edges are on the outside of each pair.

Such an arrangement has the result that the web 4 of material assumes a wavy line which, in an idealised way, could be termed a trapezoidal line. With this line, flat web sections appear above and below the pairs of suspending nozzles, whilst two deflection zones 16, 1 7 which have a relatively small radius of curvature and have a stabilising action on the movement of the web, result in the transition zones.

Since the lower suspending nozzles 9 to 1 2 must bear the weight of the web 4 of material and in addition also the pressure exerted by the blowing air from the suspending nozzles 5 to 8, these are of larger dimensions than the upper suspending nozzles 5 to 8.

The special advantages of the device according to the invention are that, with a relatively small cross-section of the suspending nozzles, the web of material is conveyed without contact in a stable position through the housing 1. The gap between the individual pairs of the suspending nozzles is wide in comparison with a device having an alternating arrangement on only one nozzle in each case above and below the conveying plane, but this has no adverse effect on the treatment with the hot air because, in this region, the web is swept by the blowing air flowing out over the outer edges. The web is not swept by blowing air only in relatively small sections between two suspending nozzles of a pair of suspending nozzles so that, viewed as a whole, good treatment of the web of material is possible. The use of relatively small suspending nozzles leads to good utilisation of the energy content of the blowing air.

Finally it should be mentioned, that the form of the wavy line of the web depends also from the physical properties of the web. What wave form however is achieved, in every case the movement in suspension is improved with respect to the use of the known arrangements.

Claims

1. Device for moving suspended webs, particularly (but not exclusively) with a heating device for the heat treatment of aluminium strips, consisting of a housing, with an inlet opening and outlet opening for the web, and of suspending nozzles, which are arranged above and the plane of the web with an offset in and transversely to the conveying direction and which each have two slots or rows of holes with blowing directions pointing towards one another in order to form an air cushion, the angle of inclination of the blowing directions of the two slots or rows of holes relative to the common centre plane and/or the cross-section of the two slots or rows of holes being different and mutually matched in such a way that the blowing air flows out of the air cushion substantially over one nozzle edge, characterised in that the suspending nozzles are mutually offset in pairs on both sides of the common centre plane and the nozzle edges, over which the blowing air flows out, are arranged as mirror images relative to a plane which is located between the two suspending nozzles and perpendicular to the common centre plane.

2. Device according to claim 1, characterised in that the nozzle edges, over which the blowing air flows out, are located on the outside in each pair of suspending nozzles.

3. Device according to claim 1 or 2, characterised in that, within each pair of suspending nozzles, the angles of inclination of the blowing direction of the adjacent central slots or rows of holes are shallower than those of the outer slots or rows holes.

4. Device according to one of claims 1-3, characterised in that the first suspending nozzle, which is the first in the conveying direction, at the housing inlet opening and the last suspending nozzle at the housing outlet opening are located below the plane of the web of material.

5. Device according to one of claims 1-4, characterised in that the shallow angle of inclination is 10 to 40 , in particular 20 to 30 and the steep angle of inclination is 45 to 80 in particular 55 to 65 .

6. Device according to one of claims 1-5, characterised in that the cross-section of one slot or of one row of holes of each suspending nozzle is 1 + to twice the cross-section of the other slot or of the other row of holes.

7. Device according to one of claims 1-6, characterised in that the lower suspending nozzles have 1 + to twice the cross-section of the upper suspending nozzles.

8. Device for moving suspended substantially as hereinbefore described with reference to and as shown in the accompanying drawings.