GB2045194A

GB2045194A - A jet-conveyor or blast box for floatingly conveying strip or sheet material

Info

Publication number: GB2045194A
Application number: GB8005262A
Authority: GB
Original assignee: Vits Maschinenbau GmbH
Current assignee: Vits Maschinenbau GmbH
Priority date: 1979-03-24
Filing date: 1980-02-15
Publication date: 1980-10-29
Also published as: DE2911685C2; GB2045194B; DE2911685B1

Abstract

A blast box for floatingly conveying strip or sheet material has a slit-type jet 3 and an adjoining guide surface 6 to direct the conveying medium emanating from the jet. A plurality of jet holes 7, 8 are provided at or near the edge of the guide surface remote from the slit. The guide surface 6 has a substantially plane region and an adjoining region 9 inclined to the plane region, the jet holes being arranged in the angled region of the guide surface along or adjacent to the junction between the surfaces 6, 9. The slit-type jet 3 may be continuous as shown, or composed of a row of discreet laterally adjacent slit orifices. <IMAGE>

Description

SPECIFICATION A jet-conveyor or blast box for floatingly conveying strip or sheet material This invention relates to a jet-conveyor or blast box for floatingly conveying strip or sheet material, as of paper for example, and comprising a slit-type jet having either a single continuous slit orifice or a row of discreet laterally adjacent slit orifices and a guide surface adjoining said slit-type jet to guide and direct the medium which is ejected through the slit, and wherein a plurality of hole-type jets for the ejection of further conveying medium is arranged at or near the opposite edge of the guide surface remote from the slit.

In a known jet-conveyor box of the above kind (GE-PS 1 774126) the guide surface has a slightly convex curvature in the conveying direction. The hole-type jets are arranged in several rows in such a way that the conveying medium ejected therethrough impinges substantially vertically on the material. The pressure pattern, or behaviour of this type of blast box, that is to say, the force applied by the ejected medium to the material measured in relation to the distance between the material and the box follows a generally hyperbolic curve, but in the regions which are near the box, pressure increases only very slowly with increasing approach of the material to the box to a peak which is not particularly high whilst likewise decreasing rather slowly to zero away from the box.It is desirable that the pressure curve should rise very steeply in the intermediate vicinity of the box and there reach a very high peak whilst having a very shallow orflatform and quickly dropping to zero in the direction away from the box.

Moreover, it is desirable that such a jet-conveyor or blast box should be able to be constructed of very much smaller size than conventional jet-conveyor boxes.

According to the present invention this aim is achieved by virtue of the fact that the guide surface comprises a substantially plane, or level region and an adjoining region which is inclined at an angle of between 30 and 60 relative to said plane region, and that the jet holes are arranged along the junction between said regions or in the angled region near said junction. If the slit-type jet consists of a plurality of discreet slit orifices, a single row of jet holes may be adequate. However, if the slit-jet has a single continuous slit opening it is better to provide a second row of jet holes in the plane region of the guide surface near said junction and, preferably, in staggered, or offset relation to the jet holes which are arranged along said junction.

With the aid of the blast box of the invention it is possible to obtain the desired pressure curve. This means also that the conveying medium is more efficiently used than before. Consequently the mate rial can be floatingly conveyed with less energy and this in turn means that the blast box may be of a smaller size than hitherto customary.

In order to achieve optimum conditions a number of provisions may be applied singly or, preferably, in combination; for preference, further hole-type jets are provided in the plane region of the guide surface, in the vicinity of said junction and, more particularly, in staggered formation relative to the other jet holes.

Blast boxes according to the present invention are particularly well adapted for application to both sides of the conveyed strip or sheet material. In that case an arrangement is preferred wherein the plane guide surface regions of those boxes which are arranged on one side of the material extend in a plane which is spaced by a distance of less than double the width of the jet slit (3) from the corresponding plane in which extend the plane guide surface regions of the blast boxes which are arranged on the opposite side of the material and positionally offset in the direction of conveying by a distance equal to half of the spacing between boxes.

Such close spacing of the boxes is indeed possible due to the improved prevention of contact combined with the steady and flutter-free guidance provided by the blast boxes of this invention. The spacing distance may be zero, or even negative, i.e. the upper blast boxes may dip slightly into the spaces between the lower blast boxes. In that event, e.g. for drying an offset-printed strip material, the latter is so firmly guided that the formerly normally observed longitudinal waves or corrugations due to variations in thickness of superficial colour application and moisture are flattened out. This eliminates a particularly serious disadvantage of roller-offset printing as compared with intaglio or photogravure printing.

The invention is hereinafter more particularly described, by way of example, with reference to an embodiment thereof shown in the accompanying drawings wherein: Figure 1 is a cross sectional view of a blast box of the invention provided with a slit-type jet having a single continuous slit orifice, Figure 2 is a plan view of one end portion of the blast box of Figure 1, Figure 3 is a cross sectional view of a blast box provided with a slit-type jet having a plurality of discreet laterally adjacent slit orifices, Figure 4 is a plan view of one end portion of the blast box of Figure 3, Figure 5 is a diagram showing the pressure curve for the blast boxes of Figures 1 and 3 as compared with conventional blast boxes, and Figure 6 shows an array of upper and lower blast boxes for floatingly conveying a strip or sheet material.

Referring to Figures 1 and 2, these show a blast box 1 supplied through a feed pipe 2 with a suitable conveying medium, e.g. air, notably hot air for drying a strip or sheet material which is to be floatingly conveyed by the air jets. On its side directed towards the material, the blast box is provided with a jet slit 3 through which the medium is ejected in an obliquely angled direction towards the material. One lip 4 of the jet slit extends through a curved or domed region 5 into a substantially plane or very gently curved guide surface 6. At its end remote from the slit 3, the guide surface 6 is provided with two rows of jet holes 7, 8 which are mutually parallel and extend along the length of the blast box 1. The holes 7, 8 are relatively offset, or staggered, by a distance equal to half the spacing between the holes.Adjoining the guide surface 6 is an angled outer edge surface or region 9. The row of jet holes 7 is formed in the plane guide surface 6, whereas the jet holes 8 are arranged precisely at the junction of the surfaces 6 and 9. As a result of this arrangement the medium is ejected from holes 8 at an angle relative to the direction of ejection from holes 7.

For example, a blast box designed for application to typing and printing paper would have the following dimensions: The width of the blast box is 80 mm.

The hole diameter of jet holes 7,8 is 3 mm. The clear width of the slit orifice 3 is also 3 mm. The distance between jet holes 7 and 8 is approximately treble their hole diameter, e.g. 10 mm. The slit 3 is spaced from the two rows of jet holes 7, 8 by a distance of 45 mm. The blasting direction of slit 3 inciudes an angle of approximately 25 with the plane region of the guide surface 6. The angled guide surface region 9 includes an angle of approximately 45" with the plane guide surface region 6.

The blast box shown in Figures 3 and 4 is largely identical with that shown in Figures 1 and 2. Like elements are therefore designated by like references preceded by '1'. The blast box 11 in Figures 3 and 4 differs from that in Figures 1 and 2 essentially in that, instead of the continuous slit orifice in jet 3 the jet 13 comprises a plurality of discreet arcuate slit openings through which the conveying medium is ejected in an outwardly diverging stream. The individual arcuate slits are made by incisions in the inclined wall of the blast box 11 and subsequent pushing out of the arcuate flaps. This blast box 11 comprises only a single row of jet holes 18 along the junction between the surfaces 16 and 19.

In Figure 6 the upper and lower blast boxes are relatively offset or staggered in the conveying direction by a distance equal to half the spacing between the boxes. The delivery angle of the slit orifices 3, 13 faces in the conveying direction.

The dot-and-dash lines in Figure 5 represent the pressure curve of a generically similar conventional blast box according to GE-PS 1 774 126, and the continuous lines represent the pressure curve of a blast box of the present invention whilst the dotted line which falls into the negative range and the dash-double-dot-line illustrate the pressure curves of the blast boxes with, and without perforations at the edge of the guide surface remote from the jet slit.

The curves reflect measurements taken on a plane and rigid surface.

A comparison of the curves shows that the blast box of this invention, which requires no greater but, on the contrary, rather less constructional outlay than the generically similar conventional boxes, affords a surprisingly great improvement in pressure behaviour.

Compared with the other blast boxes its pressure is higher and rises more quickly in the vicinity of the guide surface whilst dropping rapidly to zero, without however falling into the negative range, in the direction away from the guide surface. This provides an effective safeguard against potential contact engagement with the material in the region of the guide surface and also reduces flutter risk at the ends of the guide surface.

Claims

1. A jet conveyor or blast box for floatingly conveying strip or sheet material, comprising a slit-type jet having either a single continuous slit orifice or a row of discreet laterally adjacent slit orifices and a guide surface adjoining said slit-type jet to guide and direct the conveying medium which is ejected through the slit, and wherein a plurality of jet holes for the ejection of further conveying medium is arranged at or near the edge of the guide surface remote from the slit, the guide surface comprising a substantially plane region and an adjoining region which is inclined at an angle of 30 to 60 relative to the plane region the jet holes being arranged along or adjacent to the junction between said regions in the angled region of the guide surface.

2. A blast box according to Claim 1, wherein further jet holes are provided in the plane guide surface region near to said junction and in offset or staggered formation relative to the first-mentioned jet holes.

3. A blast box according to Claim 1 or Claim 2, wherein said adjoining region of the guide surface is inclined at an angle of approximately 45" relative to the plane region of said surface.

4. A blast box according to any one of Claims 1 to 3, wherein the cross section of the jet holes is approximately equal to one third of the cross section of the jet slit.

5. A blast box according to any one of Claims 1 to 4, wherein the width of the jet slit is approximately equal to 1/20th - 1110to of the distance between the jet slit and the jet holes.

6. A blast box according to any one of Claims 1 to 5, wherein the plane guide surface regions of those blast boxes which are arranged on one side of the strip or sheet material extend in a plane which is spaced by a distance of less than double the width of the jet slit from the corresponding plane in which extend the plane guide surface regions of the blast boxes which are arranged on the opposite side of the material and positionally offset in the conveying direction by half their spacing distance.

7. A blast box for floatingly conveying strip or sheet material, substantially as hereinbefore described with reference to Figures 1 and 2 or Figures 3 and 4 of the accompanying drawings.