GB2193146A - Apparatus for blowing a treatment medium onto a moving web of material - Google Patents

Abstract

The apparatus has a nozzle finger (1) arranged above and below the web (9) and extending transversely thereto and equipped with blast nozzles (6) directed towards the web. The treatment medium is supplied to the nozzle finger from one side (E). Along a wall (2) remote from the blast nozzles (6), each nozzle finger has a partition (5) which contains uniformly distributed equalizing openings at least in a beginning region and an end region and forms an overflow channel (10). Differences in the velocities at which the medium is blown out of different parts of the blast nozzles (6) are automatically equalized by the overflow channel. The apparatus may be used for heat treating the material by means of a current of hot air. <IMAGE>

Description

SPECIFICATION Apparatus for blowing a treatment medium on to a web of material This invention relates to apparatus for blowing a treatment medium on to a web of material moving in the longitudinal direction, by means of ventilation boxes on nozzle channels arranged above and below and transversely to, the web, and equipped with air outlet nozzles.

In such blower apparatus, a gaseous treatment medium supplied from a blower is normally delivered to the nozzle channels from the side and then blown on to the surface of the web through the nozzles which take the form of slots extending transversely across the width of the web.

DE-AS 1 911 020, for example, discloses an apparatus for the heat treatment of a web of material by means of a current of air. The air current is passed through ventilation boxes or nozzle channels which have air outlet nozzles in the form of slots or holes in their undersurface and/or upper surface. The air current is delivered to the nozzle channels from one of the end faces of the latter and can be adjusted by means of control flaps.

The cross-section of the nozzle channels may remain constant from the air inlet side to the free end of the nozzle channels or, for certain purposes, it may decrease. In such ventilation boxes or nozzle channels which are uniform in cross-section, an adjustment flap is provided in each box to subdivide the interior of the channel into an upper and a lower part. The upper part has nozzles directed upwardly and the lower part has nozzles directed downwardly. The adjustment flap can be pivoted about an axis situated approximately in the middle of the nozzle channel and extending parallel to the length of the web. In this way, the treatment medium may be blown out either upwards or downwards from one and the same ventilation box or nozzle channel, according to the position of the adjustment flap.When the flap is in an intermediate position approximately parallel to the plane of the web, it forms a sort of partition for the nozzle channel and conducts one half of the air current to the upwardly directed nozzles and the other half to the downwardly directed nozzles.

With such a nozzle channel, the stream of air may be blown on to a web above the nozzle channel from below, or on to a web below the nozzle channel from above, or both at the same time.

Nozzle channels of this kind, e.g. nozzle fingers, which are supplied with gaseous treatment medium from one side do not, however, provide for a uniform outflow of treatment medium from the openings of the blast nozzles over the whole length of the slot. This undesirable characteristic persists even if the nozzle channels are sloped off, i.e. if the cross-section of the nozzle channel progressively diminishes, starting from the inlet end for the medium. Moreover, depending on the conditions of inflow into the nozzle channel or the nozzle fingers, further disturbances in the distribution of the outflow velocity from the nozzles may occur due to the horizontal inflow of the stream of gas or due to an injector effect or due to the formation of eddy currents.

Attempts have been made to overcome this defect and to obtain more uniform distribution of the outflow velocities from the nozzles by installing baffle plates such as perforated pistes, deflectors or baffle barriers in the nozzle channels. These devices however, have always had to be adjusted individually to the particular construction and dimensions of the nozzles.

An example may be found in DE-PS 3 007 752, in which the nozzle fingers are subdivided into two air chambers one above the other for the purpose of improving the flow conditions. In this arrangement, a covering in the form of a corrugated plate is provided over a slot nozzle and this covering is partly covered along its edge by partitions both on its upper surface and on its under surface.

Due to the provision of the two air chambers arranged one above the other and a repeated deflection of the stream of gas before it is discharged from the nozzles, the flow conditions are stabilized between the upper and the lower chambers so that the outflow of medium from the nozzle appears to be substantially uniform. The disadvantage of this arrangement lies in the relatively complicated structure inside the nozzle finger. In addition, the arrangements must always be adapted to the conditions and requirements of each individual case, as mentioned above, and even then the outflow conditions are equalized only to a limited extent.

Compared with this known state of the art, it is an object of the present invention to provide a blower apparatus with nozzle channels supplied from one end, in which the velocity distribution of the outflowing gas stream is substantially uniform along a slot nozzle without the aid of special devices and regardless of the dimensions and construction of the nozzle.

According to this invention there is provided apparatus for blowing a treatment medium on to a web of material by means of at least one nozzle channel arranged adjacent the web, which nozzle channel is supplied with treatment medium from one end and has at least one air outlet nozzle, wherein a partition is arranged in the or each nozzle channel along a wall thereof not equipped with a nozzle or nozzles, the partition forming an overflow channel together with an external wall of the nozzle channeland having equalizing openings distributed at least in one region situated at the end from which the medium is supplied and in another region at the opposite end, the overflow channel being closed at both ends for direct passage of treatment through the channel.The use of an overflow channel enables the velocity distribution to be reduced from about -6% to about~1.7%, which is a much lower value and amounts to virtual uniformity. The invention is applicable to nozzle channels of virtually any dimensions, e.g. in length and width, and of various geometrical constructions and arrangements, and is suitable both for single nozzle fingers and for nozzle boxes which, viewed in the direction of transport of the web of material, have a plurality of parallel nozzle slots one behind the other.A partition which forms a special overflow channel inside the nozzle channel may extend along any external wall of the nozzle channel, provided only that treatment medium can flow inside the nozzle channel from the inlet end for the medium (optionally through slot coverings) to the nozzle without having to penetrate the partition. The partition with equalizing openings serves only to equalize local pressure differences which may occur in the main channel due to differences in the outflow velocities of medium from the nozzle.

Such equalization also results in more uniform distribution of the outflow velocities from the nozzles. Since differences in outflow velocities of the medium mainly occur only at the beginning and end regions of a nozzle channel, the equalizing openings need not be uniformly distributed over the whole length of the partition but may in some cases only be required at the beginning of the partition at the inlet end, and in an end region of the partition, at the opposite end of the nozzle channel. In that case, there is a portion of closed partition situated between the two regions which have equalizing openings preferable arranged in a uniform distribution. The nature of the distribution of equalizing openings may be different in the two regions.

An embodiment of the invention is described below by way of example, with reference to the drawings, in which: Figure 1 is a longitudinal section through a nozzle finger which is sloped off; Figure 2 is a cross-section through the nozzle finger of Figure 1; Figure 3 is a longitudinal section through a nozzle box with a plurality of nozzle slots; Figure 4 is a cross-section through the nozzle box of Figure 3; Figure 5 is a longitudinal section through a sloped off nozzle finger having a different form of nozzle, taken on the plane A-A of Figure 6; Figure 6 is a cross-section through the nozzle finger of Figure 5; and Figure 7 is a section through the nozzle finger seen from above on the plane B-B of Figure 5.

The invention will first be explained with reference to Figures 1 and 2, which show schematically a nozzle finger 1 with a top surface 2 and two lateral surfaces 3 as boundary walls and a slot nozzle 6 in the lower part 4 of the nozzle finger. The arrangement of a slot covering 4a in the form of a corrugated plate is indicated both at the beginning and end of the slot nozzle 6. The term "slot nozzle" is used hereinafter to include a variation which has a number of individual nozzles arranged one behind the other in a row. The treatment medium is supplied to the nozzle finger 1 from the left-hand end, as indicated by the three arrows E. The treatment medium is kept in motion by a circulation blower (not shown).

The treatment medium supplied to the nozzle finger 1 leaves the slot nozzle 6 in a downward direction to reach the web of material 9 indicated by a dash-dot line. The direction of transport of the material 9 is indicated by an arrow T in Figure 2. The velocity of outflow of the treatment medium from the nozzle 6 is represented by the vertical arrows and by their length. Nozzle finger 1 is sloped off, i.e.

its cross-section progressively diminishes from the inflow end E, as seen in Figure 1.

A partition 5 is arranged in the interior of the nozzle finger along one wall of the finger in this embodiment, and preferably, the top wall 2. This top wall 2 and the partition 5 and parts of the two side walls 3 together form a static overflow channel 10. In the present embodiment, these are equalizing openings in the partition 5, preferably arranged in uniform distribution, as shown. The whole internal crosssection of all the equalizing openings in the partition should be equal to or slightly greater than the total cross-section of all associated nozzle openings. The partition 5 may be, for example, a perforated plate. The equalizing openings in the partition 5 enable the pressure to be equalized between the space in the overflow channel 10 above the partition and the space in the remainder of the nozzle finger below the partition 5. At the inlet end E, the end face of the overflow channel 10 is shut off from the outside by a wall 7 to prevent direct inflow of treatment medium. The overflow channel 10 is also similarly closed at its other end by a wall 8.

This arrangement is based on the principle that in a gas container which is under constant static pressure, flow of gas does not occur until the pressure changes at some point in the container. The flow is then directed to those points which are at a lower pressure.

The insertion of a partition 5 in the nozzle finger 1 produces an arrangement which csn function as a static overflow channel in the sense described above.

When the apparatus is in operation, medium enters the nozzle channel from the inflow end E in the usual manner and flows through the channel. The medium then flows out through the nozzle 6 downwards to the web 9. The partition 5 separates the static overflow channel 10 from the nozzle proper through which a dynamic flow takes place. Points of higher outflow velocity produce a higher static pressure in the nozzle channel than points of lower outflow velocity in accordance with the principle of action and reaction. Thus if, for example, a slight pressure difference Ap 1 < Ap2 is created between some point in the nozzle channel 11 itself and the surrounding medium due to a slightly lower velocity at that point, then the equalizing openings in the partition 5 equalize the pressure differences, as indicated by arrows in the partition 5.The compensation for velocity differences or static pressure differences thus takes place in the overflow channel. The static pressures become equalized and are then converted into dynamic pressure, i.e. into velocity at the nozzle.

The use of the partition 5 for the purpose of forming a static overflow channel 10 can be carried out simply and rapidly. The geometric dimensions of the partition, e.g. distance from the top surface 2 or the crosssection of te equalizing openings compared with the cross-section of the nozzle opening, etc. are not particularly critical but leave scope for variation in construction. Thus, for example, the overflow channel may be of substantially constant cross-sectional area although other constructions are conceivable in which the cross-sectional area diminishes along the length of the overflow channel without the effect being significantly impaired.

Another embodiment is illustrated in Figures 3 and 4 which are intended to illustrate schematically that the invention may be applied not only to a simple nozzle channel but also to nozzle channels of various constructions. The basic structure remains as in Figures 1 and 2.

A nozzle box 16 having a plurality of parallel slots is shown in longitudinal section in Figure 3 and in cross-section in Figure 4. The web is indicated by a dashrdot line 9 and in Figure 4 its direction of transport is indicated by an arrow T. It may be seen from Figure 3 that the cross-section of the nozzle box 16 is constant over its whole length from the inflow end E over the whole width of the web 9 right to the other end wall 8. The top surface and side walls are again indicated by 2 and 3, respectively. The nozzle box 16 is open at the inlet end E for the supply of treatment medium as indicated by the three arrows.

Viewed in the direction of transport T, the box 16 has successive nozzles 6, 6a, and 6b, each formed by sloping walls 4 and these nozzles are again in the form of slots. The nozzle channel proper through which the main flow of medium takes place is indicated by 11. A partition 5 is again provided adjacent the top surface 2. This partition 5 forms an overflow channel 10 together with the top surface 2 and parts of the side walls 3. The overflow channel 10 is closed at its ends by the walls 7 and 8 to prevent direct flow of medium into and out of the overflow channel 10 through the inlet end.

The embodiment illustrated in Figures 3 and 4 is based on the finding that differences in the outflow velocity of medium through the nozzles occur mainly near the beginning and end of the nozzle channel, but less at its centre. It is therefore sufficient in many cases to provide for equalization of flow only in these two outer regions. For this reason, the partition 5 is subdivided in Figures 3 and 4 into three sections, 5a, 5b and 5c. Section 5a at the inlet end E and section 5b at the opposite end of the channel 11 have equalizing openings, but section 5c has no such openings. In Figure 3, the different velocities of outflow from the nozzle 6 are represented by arrows of differing lengths in the three sections as indicated by v1 and v2.The corresponding pressure differences are again marked Api and Ap2. It is assumed that Apl < ;Ap2 and therefore v1 < v2. An equalizing flow therefore takes place in the direction of the arrow from the region Ap2 through the equalizing openings in section 5a and through the overflow channel 10 to the equalizing openings in section 5b. This equalizing of pressure again results in an equalization of velocity distribution along the length of the slots 6.

The dimensions of the two regions 5a and 5b need not be identical and they may also differ in the distribution of their equalizing openings. The sum of the cross-sections of all equalizing openings in the regions 5a and 5b need not in this case be related to the total nozzle cross-section but may again be substantially equal to or greater than the sum of the nozzle cross-sections of the beginning and end regions of the nozzle box which are affected by the equalizing process. Equalization may occur not only along the length of the slots but also between successive nozzles 6, 6a or 6b in the direction T.

Another embodiment showing the versatility of the invention will now be described with reference to Figures 5, 6 and 7. Figure 5 is a longitudintal section on the plane A-A of Figure 6, while Figure 7 is a section on the plane B-B of Figure 5. The web is again indicated by a dash-dot line 9 and its direction of transport by the arrow T. In Figure 7, the web 9 is outlined in top plan by dotted lines. This embodiment is based on a nozzle finger 15 of the kind described in the above-mentioned DE PS 3 047 752. The top surface and side walls of the nozzle finger 15 are again indicated by 2 and 3. Horizontal partitions 12 and 13 are provided on the lower part of the side walls 3 and a covering 4a in the form of a corrugated plate is placed between these two partitions.Below the horizontal partitions 13,' the side walls 3 are continued with sloping outer walls 14 which form a nozzle slot 6 at their ends. The corrugations of the covering 4a extend transversely to the length of the slot 6.

The covering 4a subdivides the nozzle finger into an upper air chamber 1 1a and a lower air chamber 1 1b which faces the nozzle 6: A partition 5 is arranged between the inner, free end of each horizontal partition 13 and the adjacent sloping outer wall 14. This partition 5 extends substantially vertically and parallel to the length of the slot 6. Each partition 5 extends from the inflow end of the nozzle finger to the other end. On each side, the partition 5, the separating walls 13 and the outer wall 14 together form an overflow channel 10 which is triangular in cross-section, these overflow channels being situated to the right and left, respectively, of the nozzle opening 6.

The partition 5 may again be subdivided into sections with and without equalizing openings.

The overflow channels 10 are closed by walls 7 at the inflowend E and by walls 8 at the opposite end to prevent direct inflow and outflow of medium into and from the overflow channel 10. A beginning region 5a and end region 5b of the partition, containing equslizing openings for passage of equalizing flow, are indicated in Figure 7. Between these two regions, the partition again has a closed part without equalizing openings. The pressure differences Api and Ap2 which are assumed to exist and the corresponding. differing outflow velocities v1 and v2 for the medium are again included. It is again assumed that Api < Ap2 and v1 < v2. The equalizing flow which becomes established from the region Ap2 through the overflow channel 10 to the region Ap1 is indicated by arrows in Figure 7. The partitions could, of course, have equalizing openings over their whole length.

In this embodiment, it is immaterial whether the cross-section of the nozzle finger progressively decreases along its length or whether it is uniform. The requirement concerning the sum of equalizing cross-sectionsHd the relationship of this sum to the nozde cross-sec- tion is in the main fulfilled automatically if the partition 5 has equalizing openirigs over only part or all of its surface and if these openings are distributed more or less uniformly in each region.

Claims (9)

1. Apparatus for blowing a treatment medium on to a web of material by means of at least one nozzle channel arranged adjacent the web, which nozzle channel is supplied with treatment medium from one end and has at least one air outlet nozzle, wherein a partition is arranged in the or each nozzle nozzle channel along a wall thereof not equipped with a nozzle or nozzles, the partition forming an overflow channel together with an external wall of the nozzle channel and having equalizing openings distributed at least in one region situated at the end from which the medium is supplied and in another region at the opposite end, the overflow channel being closed at both ends for direct passage of treatment medium through the channel.

2. Apparatus according to claim 1, wherein the partition has eqalizing openings over its whole length.

3. Apparatus according to claim 1 or claim 2, wherein the overflow channel has a substantially constant cross-section and is arranged along that wall of the nozzle channel which is situated opposite the nozzles.

4. Apparatus according to any of claims 1 to 3, wherein the sum of all the cross-sections of the equalizing openings in the partition is equal to or greater than the sum of the nozzle outlet cross-sections which are influenced by the equalizing flow.

5. Apparatus according to any of claims 1 to 4, having nozzle boxes which have a plurality of nozzle slots arranged one behind the other in the direction of transport of the web.

6. Apparatus according to any of claims 1 to 4, having nozzle fingers equipped with nozzles in the form of slots.

7. Apparatus according to claim 6, in which the nozzle fingers are subdivided into an upper and a lower air chamber by a covering of corrugated profile resting on lateral horizontal partitions, the lower air chamber facing a nozzle in the form of a slot and being bounded laterally by external walls which are adjacent the partitions and extend obliquely to the nozzle, wherein a partition extending substantially vertically and parallel to the nozzle is arranged between the inner edges of the partitions and the corresponding lateral external walls.

8. Apparatus according to any of claims 1 to 7 wherein the nozzle channels decrease in cross-section from the inlet end for the treatment medium.

9. Apparatus for blowing a treatment medium on to a web of material, the apparatus being constructed and arranged substantially as herein described and shown in the drawings.