Patent Application
20080060678
The invention relates to improved dust removal apparatus for controlling airborne dust in the vicinity of moving services and particularly moving webs, with particular application to machinery for handling paper.
Machinery that provides for the continuous transport of dry webs of paper over multiple rollers and other components where the web's direction changes can be the cause of substantial dust generation. Dust that accumulates on the machinery can interfere with correct operation, lead to product quality problems in some circumstances, hinder maintenance, and may also present a fire hazard. Dust that is transferred into the air can also represent a fire hazard, and additionally can be breathed by workers.
Much effort has been directed to the development of dust hoods for sucking dust laden air from parts of such machines. However, such devices are themselves imperfect in operation and can require substantial power consumption.
In some applications it is important to remove entrained dust from air in the vicinity of a moving web and to remove dust from the web itself. This is commonly done by dust hoods and the like that use a combination of directed jets of air provided by a compressor and suction applied near the moving web.
Such installations are usually provided at critical points in the path of a moving web, for example near doctor blades that crepe (separate) a web of paper from the surface of a so-called Yankee drum. However, there are often locations in paper making and handling machinery where significant dust is generated by, for example, being entrained in a “boundary layer” of air moving with the web close to its surface or by being thrown off the web near rollers and the like, where it is undesirable or difficult to provide elaborate, costly, high-power consuming and bulky dust removal equipment.
There is thus a need for a method of controlling dust at such locations without these disadvantages or in which they are reduced. The present invention provides apparatus and methods which address this problem.
It is believed that the concepts are not limited in their application to paper processing machinery only.
The invention provides in a first aspect dust collecting apparatus for use in collecting airborne dust adjacent to a moving surface, the apparatus comprising:
an elongate duct extending in a direction transverse to a direction of movement of a moving surface and spaced apart from the surface, the duct having along its length at least one opening permitting entry of air into the duct; and
air extracting means in fluid communication with an interior space of the duct and adapted to draw air therefrom,
wherein said apparatus is positionable adjacent to the moving surface so that the apparatus and the moving surface define an air inlet into which is received at least a proportion of a layer of dust laden air adjacent to and moving with the moving surface at least some of said air being drawn into the duct.
The invention emphasizes collection of airborne dust rather than the active dislodging of dust from a moving web surface, and this can lead to less power consumption, through for example avoidance of the use of compressed air, and the advantageous use of the momentum of air that is moved by the traveling web itself and (as discussed below) parts of the machinery.
In the preferred embodiment, the or a said opening is shaped and positioned so that air enters the duct in a direction approximately tangential to an inner surface of the duct and so that air in the duct moves both rotationally about the length of the duct and longitudinally along the duct. That is a votex motion is induced in the air entering the duct. This aids in keeping the dust entrained so that it is less likely to settle in, and so to foul, the duct.
A scroll-like arrangement may be used for the duct in this case. Specifically, the or a said opening of the duct when seen in section transverse to the length of the duct may comprise a flow passage defined on one side by a first wall extending inwardly of the duct to a free edge of the first wall and on an opposite side by a second wall extending outwardly of the duct, one side of the first wall partially defining the inner surface of the duct.
The said duct may be formed from a tubular member having a wall in which a longitudinal cut is made and a part of the wall is deformed inwardly to form the said first wall. This is useful as the construction of the duct can be comparatively low cost.
Preferably, the or a said flow passage is elongate in the lengthwise direction of the duct and of varying width along its length.
Instead of one slot-like opening, the duct may have a plurality of said openings. Members of the said plurality of openings may be of varying sizes, again so as to provide for control of the flow rate distribution.
Preferably, the first wall is so shaped and sized and the air flow rate in the duct is able to be so chosen that in use in a specified position of the duct relative to the moving surface that air passing the free edge of the first wall in the said flow passage and air passing the said free edge inside the duct travel in substantially the same direction as seen in section transverse to the length of the duct. That is, air flowing past the edge, or “lip” of the first wall should preferably not have to turn sharply when passing beyond the lip. This can be achieved through testing or computation fluid dynamics simulation, and is found to work well.
Desirably, the or each said opening is so sized and proportioned that in use in a specified position of the duct relative to the moving surface and with a specified air flow rate in the duct a specified distribution of air flow rate per unit duct length is obtained along the length of the duct, preferably a constant air flow rate per unit duct length. This can be achieved in designing the apparatus for a given application by testing, or by computer simulation.
The air extracting means may be connected to the duct at either end or both ends of the duct. Alternatively, the connection may be made at an intermediate point along the length of the duct although this is generally less convenient. Air may be drawn from the duct by the extraction means tangentially or axially.
The dust collecting apparatus may comprise a downstream formation having an edge that is elongate in the direction along the length of the duct the edge being positionable adjacent to the moving surface and in use of the apparatus being passed by a point on the moving surface after the point passes a said opening of the duct. (That is, the term “downstream” is here being used to refer to the direction of movement of the moving surface.)
The apparatus may further comprise an upstream formation elongate in the direction along the length of the duct, the upstream formation and the moving surface defining a space therebetween and in use of the apparatus air being drawn from the said space into the duct, the upstream formation being encountered by a point on the moving surface before the point passes a said opening of the duct. The use of an upstream formation can give more flexibility in actual installations.
In one embodiment, the upstream formation has a leading edge defined by upper and lower surfaces that diverge backwardly therefrom. The said lower surface may extend from the said leading edge to a point on the duct adjacent to a said opening.
It has been found particularly desirable that the dust collecting apparatus further comprise movable support means whereby the apparatus is movable relative to the moving surface. This can greatly assist when access for maintenance (including threading of paper webs, for example, where the application is to paper-handling machinery) is required or to allow correct operation of the apparatus for different modes of operation of the machine to which it is fitted.
The movable support means preferably comprises mechanical actuators supporting opposite ends of the apparatus.
The movable support means is preferably operable to move the apparatus towards and away from the moving surface, and optionally to rotate the apparatus about an axis that extends parallel to the length of the duct.
The invention provides in a further aspect a dust collecting installation in equipment in which a continuous web is transported along its length, the installation comprising dust collecting apparatus according to any of the forms disclosed herein and a surface of the web being the said moving surface, wherein the apparatus is so sized proportioned and positioned and the air extraction means is operated at such an air flow rate that a specified proportion of dust entrained in air moving with the moving surface is drawn into the duct. This proportion may be high, for example more than about 80%, preferably about 90% and more preferably approximately 100%. A user may measure the thickness and dust mass distribution of the moving “boundary layer” of air close to a moving web and provide an installation tailored to extract most of the dust in that layer. This may include providing that the rate of air flow into the duct per unit duct length is approximately constant across the width of the web.
A dust collecting installation can be provided wherein in the said equipment the web passes over a cylindrical roller and the dust collecting apparatus is on the opposite side of the web from the roller, the installation including a guide formation having a cylindrical surface concentric with and facing inwardly towards an axis of rotation of the roller and extending from a leading edge around said axis to said apparatus so that air moving with the surface and dust entrained therein are guided around said roller and drawn into the duct. The guide formation may conveniently be formed from sheet material.
A dust collecting installation can be provided wherein in the said equipment the web passes over a cylindrical roller and the dust collecting apparatus is on the same side of the web as the roller, the installation being characterized in that the or a said duct opening is so positioned that a jet of air generated where the web first contacts the roller augments air flow into the or a said opening of the duct. This use of such windage generated by the machinery is an extension of the invention's use of the momentum of the “boundary layer”.
The upstream formation, where provided, may define a leading edge elongate in the direction along the duct length and the apparatus may be so positioned that the minimum distance between the leading edge and the moving surface is greater than the minimum distance between the downstream formation edge and the moving surface. In effect such an installation may be visualized as “swallowing” the dust-laden boundary layer. The said minimum distance between the leading edge and the moving surface may be a specified proportion of the height of a boundary layer of air moving with the moving surface.
In a further aspect, the invention provides a method for limiting dust concentration in machinery in which a web is transported along its length comprising the steps of providing and operating a dust collecting installation according to any one of the embodiments disclosed herein at at least one position along the length of the web. The invention allows for the possibility at reasonable cost of providing dust-control installations at multiple positions along the web path.
It is to be explicitly understood that not all the concepts described herein and believed to be inventive are set out above. Others are set out in the following detailed description.
In order that the inventive concepts may be better understood there will now be described, non-limitingly, certain preferred embodiments as shown in the attached Figures, of which:
Hood 1 is not intended necessarily to remove both airborne dust and dust embedded in web 5, but rather to remove or reduce airborne dust, except where dust embedded in web 5 happens to be dislodged where it is working, for example by being thrown off as mentioned above in relation to
The use of this particular example is not intended to limit the scope of the inventions here disclosed. The inventions are considered to be potentially applicable to many machinery installations where a moving web carries dust on its surface and/or embedded in it and/or entrained in moving air adjacent to its surface. It is believed that the present inventive concepts may be applicable in applications other than paper processing and manufacture.
Unless removed, dust on or around webs such as web 5 may represent a respiratory or fire hazard, or may collect in undesirable quantities on or around the machine section 6. By various mechanisms, dust on or in the web 5 may be transferred into the surrounding air as the web passes over rollers 2, 3 and 4.
Hood 1 is mounted above rollers 2 and 4, and extends between them and lengthwise along them.
The construction of hood 1 between its ends is best seen in the cross-sectional view of
End plates 16, parallel to each other, are secured to opposite ends of outer cover 8 and of lower wall 15. Duct 12 is secured to and extends through each end plate 16. Slot 13, however, only extends between end plates 16, so that outside them duct 12 is simply a closed circular duct. The distance between end plates 16 is slightly greater than the length of rollers 2 and 4 so that rollers 2 and 4 can in use of hood 1 be positioned partially within hood 1.
Air and entrained dust is sucked from under hood 1 through duct 12. To this end, a flexible hose 17 is secured to duct 12 in known manner at one end of duct 12 and connects hood 1 to the inlet of a suitable blower or fan (not shown). A blanking plate 18 is provided at the other end of duct 12, although if required in a particular application, it would of course be possible to provide instead of plate 18 a second hose (not shown) similar to hose 17.
Depending from a rear edge 18 of rear section 10 of cover 8 is a wad catcher plate 19, whose lower edge 20 is in use positioned adjacent to an upper surface of web 5 where it passes over roller 4. Provision of a wad catcher 19 integral with hood 1 is advantageous in that dust accumulation on the front face of wad catcher 19 is limited. Referring to the toilet paper manufacturing application (
Lower wall 15 and front section 9 meet at an acute angle at a leading edge 21 of hood 1. Leading edge 21 is in use of hood 1 positioned adjacent to an upper surface of web 5 where it passes over roller 2.
It will be noted that lower wall 15, front section 9 of upper cover 8 and wall 11, being connected, together define a closed shape so that hood 1 inherently has substantial torsional stiffness, a desirable feature. The duct 12 by itself, with or without cover 8, would of course provide much less torsional stiffness due to the presence of slot 13.
Hood 1 is supported as follows. Saddles 22 are provided to support duct 12 at each end of hood 1 where it protrudes beyond end plates 16. Each one of saddles 22 is able to be raised and lowered as required, using one of two actuators 23. Each actuator 23 is a screw jack type operated by an electric motor. Such actuators are available commercially, and particularly suitable ones are able to provide close control of the position of a load such as hood 1. Actuators 23 are secured to parts of the fixed frame 7.
By means of actuators 23, hood 1 can be raised above rollers 2 and 4 sufficiently far for access when web 5 is to be threaded through machine section 6 and for general maintenance and/or cleaning. Thereafter hood 1 can be lowered accurately to, and held in, a working position of hood 1, as shown in
Although in the interests of clarity not shown in FIGS. 2 to 4, parallel blocking plates may be secured to frame 7 and placed close to each end of rollers 2, 3 and 4 to ensure that airflow into duct 12 through slot 13 is substantially in planes parallel to the direction of motion of web 5 with little airflow entering between runs 24 and 25 of web 5 near the web's edges. That is, hood 1 in its working position, the upper surface of web 5, and the blocking plates define a nearly-closed space 26 in fluid communication with duct 12. The gaps 27 and 28 between edges 21 and 20 and web 5 of course allow some air flow into space 26.
In the sectional view of
Generally, it is found that a moving web 5 (especially of dry paper toilet-type tissue) causes a body of air to move lengthwise with the web 5, that body of air carrying a burden of dust. As shown in
Lower wall 15 is so shaped that in the working position of hood 1 there is only limited variation in the distance between web 5 and lower 15 in the region 34 behind leading edge 15. This lessens deceleration of air after it passes through gap 27 by comparison with the deceleration that would happen if hood 1 did not include lower wall 15 (as is the case in hood 30). Such deceleration could also lead to undesirable accumulation of dust under hood 1.
The arrangement (as seen in cross-section) of duct 12 with its inlet slot 13 positioned under rear section 10 of cover 8 promotes vortex flow of air within duct 12 superimposed on the longitudinal flow of air within duct 12. Arrow 35 in
Note that hoods based on the principles set out herein may be made to suit other parts of web-transporting machinery. For example,
It is of course not desirable to provide a complete dust removal hood at every conceivable location on a large machinery installation, on cost and accessibility grounds. It has been found that at some locations it is beneficial to provide a simple shaped air flow guide formed from sheet material at locations adjacent to moving webs, and particularly where webs pass over rollers. As an example,
A guide such as guide 202 may be combined with a hood. As an example,
The first wall section 508 is found to be able to provide better performance of the hood 500 than if it is absent. First wall section 508 is preferably shaped and sized (using results from suitable testing, computer simulation or the like) so that air inside the space 505 and passing lip 509 (indicated as to its direction by arrow 516) and air in passage 504 passing lip 509 (indicated as to its direction by arrow 517) travel in approximately the same directions, parallel to first wall section 508 at lip 509. This condition is believed to work well.
It will be appreciated that hood 500 can be very simply constructed. Duct 503 could for example be formed from a tube (for example an extrusion, preferably an aluminum alloy extrusion) by cutting lengthwise and bending the wall 507 inward (form the position shown in chain-dotted line) to form wall section 508. Second wall section 510 is then secured to the unbent part of wall 507 to obtain the shape shown in
Hood 500 has been described by reference to a cross-section, however, it should be understood that its ends may be treated similarly to the other hoods described, for example hood 1. For example an end may have a blanking plate or a exhaust connection, and may be supported by a mechanical actuator (all not shown).
As with all the other hoods described herein, by suitable design, including choice of air extraction rate, substantially all or a specified proportion of the “boundary layer air can be drawn into the space 505, with its entrained dust for removal.
Many variations and extensions of the concepts set out herein will be readily apparent to persons skilled in the art and may be made without departing from the spirit or scope of the present invention.
For example, referring back to hood 1, it is believed that in at least some circumstances a rounded leading edge may be preferable to a sharp leading edge such as leading edge 21.
Another variation appears also to have potential importance. In the various hoods described herein, elongate slots are provided whereby air enters a duct that forms part of a hood assembly. These may be of variable width. For example in hood 1, air enters elongate duct 12 through a slot 13 that extends substantially along its length. Similarly, as other examples, hood 70 has a slot 74 by which air enters duct 73, and hood 50 has a slot 174 by which air enters duct 175. It is desirable in many cases, particularly where there are no end plates in use such as end plates 16 of hood 1 or end-positioned blocking plates (not shown) as mentioned above in relation to hood 1, that the slot width vary along its length. See
The use of multiple slots or openings described by reference to
Still further variations will readily suggest themselves to persons skilled in the art that remain within the spirit and scope of the inventions as described herein.
In this specification, the words, “comprise”, “comprises”, and “comprising”, used in relation to a specified set of integers, elements or steps are to be taken as meaning that the integers, elements or steps are present, but not as precluding the possibility of other integers, elements or steps being present.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004905335 | Sep 2004 | AU | national |
| 2004906680 | Nov 2004 | AU | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/AU05/01413 | 9/19/2005 | WO | 3/19/2007 |
