|Publication number||US2506678 A|
|Publication date||May 9, 1950|
|Filing date||Jul 6, 1944|
|Priority date||Jul 6, 1944|
|Publication number||US 2506678 A, US 2506678A, US-A-2506678, US2506678 A, US2506678A|
|Inventors||Jr Harry Whitney Osgood|
|Original Assignee||Warren S D Co|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (4), Referenced by (6), Classifications (6)|
|External Links: USPTO, USPTO Assignment, Espacenet|
May 9, 39% H. w. osaoon, JR
APPARATUS FOR USE IN MAKING PAPER Filed July 6, 194
4 Sheets-Sheet 1 llll II IIIIIIIIIIIIIIIlllllllllllllllil llll IIL J May 9, EQSG H. W. QSGQGD, JR
APPARATUS FOR USE IN MAKING PAPER Filed July 6, 1944 4 Sheets-Sheet 2 May 39% H. w. OSGQ, J gvwgafirjg APPTUS FOR USE IN MAKING PAPER Filed July 6, 1944 4 Sheets-Sheet 3 awe/rm:
May 39% H. W. ussoon, JR
APPARATUS FOR USE IN MAKING PAPER 4 Sheets-Sheet Filed July 6, 1944 Patented May 9, 195
UNITED STATES PATENT OFFICE APPARATUS FOR USE IN MAKING PAPER,
Harry Whitney Osgood, Jr., Westbrook, Maine, assignor to S. D. Warren Company, Boston, Mass, a corporation of Massachusetts Application July 6, 1944, Serial No. 543,647
This invention relates to the dispersion of the fibers in a paper-making stock and the deposition of the resulting dispersion upon a webforming device to form a paper web. The invention provides improved apparatus leading to the production of well-formed paper webs.
In the customary manufacture of paper there is prepared a fibrous furnish comprising an aqueous suspension of paper-making fibers, which may or may not also contain one or more of various auxiliary substances such as mineral filler, coloring matter, resin, alum, starch, silicate, or the like. The furnish as ordinarily prepared is at first of rather thick consistency, say of 5 to 7 solids content, at which consistency it is usually treated or beaten as in a Hollander engine or beater. Subsequently the furnish is commonly subjected to some refining process as in a Jordan engine, and is finally diluted to a consistency of the order of 0.5 to 1.5% solids before it is run out upon a web-forming device to form a paper web. The furnish after the final dilution is often referred to as paper-making stock.
Before the stock is allowed to flow out upon the web-forming device it usually is passed through a slotted plate or screen to remove shives and other coarse material. The screen has considerable effect in breaking up large agglomerates of fibers, but since the slots in said screen are of necessity considerably larger than the dimensions of a single paper-making fiber,
many small agglomerates pass through the screen. After leaving the screen the stock passes through a flow-box, the purpose of which is to even out the flow of the stock until it is uniform across the'entire width of the paper-machine; thence the stock flows into a pond or small reservoir which supplies it under constant head to the slice which delivers it to the web-forming portion of the paper-making machine, such as a Fourdrinier wire.
In its simplest form a slice consists of a bar or .board extending completely across the Width of a Fourdrinier wire and positioned parallel to and adjacent to said wire. In many cases, however, at least two slice-bars are used to form the stock inlet, while in most modern machines the slice takes the form of a stream-lined nozzle. Whatever the form of the slice, its function is to regulate the volume and velocity of the stock flowing therefrom and to effect equable and uniform distribution of said stock across the width of the wire. The function of the pond sure l8, steady flow from the slice. In some installations the pond is eliminated and pressure behind the slice is maintained dynamically, as by means of a pump.
After the stock has flowed out upon the forming wire and the water has drained away, the way the fibers lie with respect to one another in the web determines what is called the formation of the web. The formation can be visually observed in the finished paper by one who examines the sheet while holding it against a strong light. It is apparent that, ideally, an even or uniform formation requires that there shall be no clumps or agglomerates of fibers in the stock at the instant the web is laid down; each individual fiber should be unattached to others up to the moment it comes to rest in the web. Otherwise clumps of fibers will cause thick spots in the web which obviously will result in uneven formation of the web.
From the very nature of a paper-making furnish its ingredients tend to agglomerate or flocculate whenever the motion of the stock becomes comparatively mild. Almost inevitably some clumps or agglomerates already exist or actually form in the flow-box or pond preceding the slice on a paper-machine. Many of said agglomerates are undoubtedly broken up as the stock flows through the slice. No slice hitherto known, however, has been capable of dispersing anywhere near all of the agglomerates which pass through it; consequently a large proportion of the clumps which enter a slice also appear as such in the finished paper. Naturally the desirability has long been appreciated of having the stockissue upon a paper-making wire entirely free from clumps or fiber agglomerates. Nevertheless success in achieving this desirable condition has in most cases been notably lacking, in spite of many attempts to bring it to pass. It has been frequently recommended that use be made of :a stirrer, such as a rotating horizontal cylinder, placed in the pond adjacent and :parallel to the slice. Such mechanical stirrers have to a considerable extent been effective in dispersing soft clumps and fiber agglomerates. At the same time, however, such stirrers have, in general, had the unfortunate effect of causing small hard knots of fibers in the stock, and this undesirable effect has been greater in those furnishes containing a preponderance of long fibers, the very kind of furnish in which the need for good dispersion is greatest. As, a result the is to provide a constant hydrostatic head to endispersing effect of such stirrers is so largely offset by their undesirable knot-making effect that said stirrers are not very generally used.
In contrast to the prior are, the present invention achieves the desired substantially complete dispersion of paper-making stock delivered .to the web-forming screen without use of any mechanical stirring, but wholly by application of principles of hydraulic flow. Likewise the invention provides a stock-inlet of new design in which the desired hydro-dynamic dispersion may take place completely and effectively.
Another aspect of formation quite apart from the evenness or uniformity previously referred to is the question of alignment or non-alignment of the fibers in the direction of wire travel or machine-direction. When paper stock rushes from a nozzle r slice and flows out over a Fourdrinier wire the fibers tend to align themselves parallel to the direction in which they flow. This gives the web what is frequently referred to as a grain. In some cases it is desirable to have most of the fibers lying parallel to the machinedirection. On the other hand, in other cases it is preferred to have as little as possible of orientation of fibers in any single direction, so that the fibers will lie haphazardly in the web and make saidweb equally strong in all directions. 'As a matter of fact, this usually preferred condition is almost never even closely approached in practice, though'in most cases an attempt is made to bring about the desired disorientation of the fibers by vibrating or shakingthe forming-wire while the stock is flowing thereon. One modification of the present invention makes possible considerable control of the degree of fiber orientation in the finished web by making it possible to deliver the stock upon the forming wire with the majority of the fibers not aligned in the direction of the stock flow.
According to the invention paper-making stock of a consistency suitable for running out into a web upon a Fourdrinier paper-making machine is, immediately prior to its emission upon a paper-forming wire or screen, subjected to the action of hydraulic forces which move said stock through cycles of alternate decreasing and increasing velocity and also cause a more or less violent turbulent or swirling motion in said stock at at least one place in its path. The intensity of said motion is made sufficient to break up all clumps or agglomerates in the stock so that the individual fibers are dispersed; likewise the rate of change in the velocity of flow in the stock after it has been dispersed is kept sumcient to prevent reagglomerating or re-clumping of the fibers up to and including the instant said stock debouches upon a web-forming device.
The desired ends are accomplished by feeding paper-making stock at suitable Velocity through a closed tortuous passageway of varying cross section and discharging upon a web-forming wire or screen. The top and bottom surfaces of said passageway do not possess identical shapes; instead the two surfaces converge and diverge with respect to each other to form a passageway of varying thickness so that stock flowing therethrough continuously changes velocity. In at least one place, and preferably in more than one place, the passageway is enlarged to form a swirl chamber in which the stock is caused to eddy with sufficient velocity that all agglomerates are dispersed by hydraulic shear. The two aforementioned surfaces may each be generated by movement of a horizontal line which makes a right angle with'the direction of said wire travel. Said horizontal line is made to follow, in part during its travel, a curve which preferably is an involute, so that stock passing along the resulting surface is accelerated towards a center, thereby producing a vortex or violent eddy in the swirl-chamber. Stock passing through the passageway is thus subjected to the mixing or dispersing effects of large velocity changes as well as to the violent stirring action of a vortex. Where the walls make a sudden reversal of direction it is preferable to have corners or edges as sharp possible rather than rounded so that the washing effect of the flowing stock will keep them clean and prevent clumps from collecting. This is especially important in the case of all edges facing downstream with respect to the stock flow. The upstream and downstream ends of the passageway aforementioned obviously are left open for the admission and emission respectively of the stock flowing therethrough. The two sides of the passageway may be closed by plane surfaces. The path defined by the passageway is rather thin or shallow, but tortuous, and extends longitudinally from a position somewhat removed from a web-forming screen where stock enters said path, to a position adjacent said screen where the path terminates. Laterally the path extends from one side of the paper-making machine to the other, i. e. it is substantially of the same width as the paper-machine wire. A vertical section taken through the passageway in the longitudinal direction at any point in the width of the passage is substantially identical with any other parallel section.
The passageway, including swirl-chamber, entrance, and outlet, will henceforth for convenience be referred to as a. dispersion slice. The portion including the swirl-chamber or chambers and adjacent passages up to but not including the outlet may be called the dispersion-section of the device. The configuration of the dispersionsection and the clearances between the walls thereof must obviously be so designed that velocity and turbulence within said section aresumcient to bring about the desired substantially complete dispersion of the stock. To make the capacity of the device sufiiciently variable to ensure optimum results with widely varying conditions of machine speed, paper weight, stock density and the like, it is obviously desirable that provision be made to adjust the positions relative to each other of the top and bottom plates or walls forming the dispersion-section of the dispersion slice. Preferably the plates should be adjustable vertically with respect to each other as well as horizontally in the direction parallel to the length of the paper-machine.
While, as stated, there must be turbulence in the dispersion section, on the other hand the outlet of the slice should be stream-lined so that the stock issuing therefrom will exhibit substantially no turbulence. The outlet serves as a dampening chamber to absorb eddies resulting from the last swirl-chamber, and at the same time it ensures a continuously changing velocity in the stock to prevent recoagulation or agglomeration therein.
Said outlet may be in the form of a nozzle extending from a preceding swirl-chamber. The opening of said outlet should, of course, be capable of easy and exact adjustment completely across the width of the paper-machine upon which it is mounted. Advantageously at least one lip of said outlet nozzle may be of flexible material, so that the outlet may, if desired, be warped into the shape of a diverging nozzle. In
such case, the fibers when moving through the narrowest part of the nozzle throat tend to align themselves in the direction of flow; as the nozzle diverges, however, the velocity decreases and the fibers tend to swing out of alignment, so that a majority may even be more or less across the direction of flow and may be deposited upon the cally perfect formation in the finished web.
Moreover this desirable effect may be achieved without use of a shake or vibration imparted to the wire. A shake may be used if desired, however, and in some cases may be advantageous in preventing flocculation in the stock while it is still on the wire before excess water has drained away, as in the case of highly hydrated stocks.
Obviously if the objects of the invention are to be met, the stock must be completely dispersed within the dispersion slice. Complete dispersion may be accomplished in a single vortex or swirlchamber within the slice provided the velocity of the stock and resulting turbulence are suiiiciently great. However, since the velocity of the stock issuing from the slice must be governed by the speed of the wire-forming device and in consequence may have to be variable over a considerable range it follows that at times it may be difiicult or even impossible to maintain sufficient turbulence for complete dispersion in a single swirlchamber while still controlling the outlet velocity at the required value. Accordingly it is greatly preferred to provide a plurality of swirl-chamhers or vortices within the dispersion slice so that aggregates that may pass one chamber still intact may be dispersed in a succeeding chamber. There is usually little advantage in having more than three swirl-chambers in succession, but three such chambers are very satisfactory.
From the foregoing it should be evident that the dispersion section must be so designed that it offers no opportunity for reflocculation of the stock after it has been dispersed. In practice this means that there must be no stagnant or dead spots at any place in the whole dispersion slice. In other words, the velocity and/or the rate of change in velocity of all portions of the stock must be kept sufficiently high so that no flocculation or agglomeration can take place. The volume of stock moving through the disper sion slice is governed by the quantity required to make a paper web of the particular weight being manufactured, which in any case is comparatively small per unit of machine width. Consequently it follows that all passages of the dispersion slice, including the swirl-chambers, shall also be comparatively small; else sufficient turbulence cannot be attained therein. In fact the passages are so small that they cause considerable resistance to the flow of stock and make necessary the use of considerably more pressure head, frequently more by several times, applied to the intake of the dispersion slice than would be necessary with a slice of conventional design in making the same weight of paper. In fact the device under consideration makes possible the use of a high pressure head behind the slice even on a paper-machine which operates at low speed, which has not heretofore been possible. This in itself, though wholly incidental to the chief object of the invention, is nevertheless advantageous, in that slight variations in the high pressure head have no appreciable effect at the outlet of the slice whereas variations of equal magnitude in a low head cause serious variation at the outlet of a conventional slice.
The passages in the dispersion section of the slice are so small and the resistance to fiow therein is so considerable that said dispersion section cannot serve as an equalizing chamber to distribute or equalize the flow of stock across the width of the machine. On the contrary, to ensure a uniform flow from the slice outlet completely across the paper machine wire it is pre ferred that the stock shall approach the intake to the dispersion section across its entire width at substantially uniform pressure and velocity; for the dispersion section is not sufficiently voluminous to allow large irregularities to be completely evened out by cross-flow. To increase the size of the dispersion'section to the extent required to ensure complete equalization of flow would entirely defeat the purpose of the present invention, because the increase in size would automatically reduce the velocity of flow and resulting turbulence to such an extent that hydro dynamic dispersion would not take place. A large distributing chamber may, if desired, be employed behind the dispersion section but a well-designed conventional flow-box generally is capable of supplying a, sufiiciently uniform flow of stock to the intake of the dispersion section.
The surfaces of the inner passages of the dispersion-s1ice should obviously be very smooth so that there shall be no opportunity for fibers to be caught by projections from said surfaces. Various materials may be used in constructing the passages; preferably the material chosen should be strong and light in weight. Heavily lacquered wood may be used with good results, though uneven absorption of water by the wood may in some cases cause distortion of the structure. Sheet metal, such as copper. is satisfactory but synthetic resins either thermosetting or thermo plastic are preferred. It is likewise advantageous to have the passages made of transparent material, such as glass or synthetic resin, so that visual observation can be taken of the condition within the dispersion-section.
very satisfactory material from which to construct the device.
In one satisfactory device having three swirlchambers roughly cylindrical in shape, good results were obtained when the outlet of the slice had a vertical opening of about inch and the maximum vertical clearance in the dispersionsection was about 3 inches. The overall horizontal distance from the point where stock en tered the device to the point where it flowed from the outlet was 21 inches. The width of the device Was equal to the width of the paper-machine wire. Normally this would be of the order of from about 5 to about 20 feet or more.
A embodiment of the invention is illustrated in the accompanying drawings, in which:
Fig. 1 is a side elevation with a portion broken away to reveal the interior in section, of a paper making machine showing the flow box, the dispersion slice of the present invention, and a portion of the web-forming wire;
A transparent thermoplastic resin of the Plexiglas type is a 1 rubber or other suitable flexible strip 8.
} edge of the upper frame 9 of the slice is connected to the panel ||l which in turn is connected.
1 to the upper edge "-01? the opening in the flow box by the flexible strip l2.
. panel l0, also, although this does not appear in 1 the drawings, are connected to the ends of the Fig. 1a is a side elevation of the broken away 3 portion of Fig; 1;
Fig. 2 is a partial vertical transverse section 1 on the line 2-2 of Fig, 4;
Fig. 3 is a front elevational view of the slice and Fig. 4 is an enlarged vertical sectional view of Fig. 5 is a broken transverse section through the dispersion slice with portions of the adjoining flow box and web-forming wire, and
Referring to the drawings, I is the flow box, 2
It will be noted that the flow box I is of considerable height in order to provide the necessary hydrostatic head for operating the slice. The
flow box is provided with the conventional gate 4 and operating mechanism 5 and its width is,
6 of the opening in the flow box is connected to the edge of the lower frame I of the slice by the The The ends of the opening in the flow box by flexible strips and the bottom edges |3 of the end portions H of the 1 panel In (see Fig. 2) are connected to the edge 6 I of the opening in the flow box by a continuation 1 of the same strip of flexible material 8 which 1 connects the edge of the frame I of the slice to the edge 6 of the openings in the flow box. As a. matter of fact, the strip of flexible material runs all the way around the opening in the flow box and forms a liquid-tight joint between the flow box and the edges of the panel l0 and the edges of the slice inlet.
The panel I9 is adjustably supported to the flow box by the angle irons l5 provided with elongated openings |6 which receive the top screws l1 and extend into the threaded inserts |8 in the ends of the panel. Thus it will be seen that the whole slice structure is flexibly attached to the flow box so that it can be moved vertically to adjust the distance between the outlet of the slice and the permits a further adjustment of the upper wall of the slice longitudinally with respect to the lower wall thereof to vary the shape of the passageway between them. All of these adjustments are, of course, small, generally amounting to only a fraction of an inch.
The drawings do not illustrate any special means for providing a liquid-tight joint between T the downwardly projecting ends l4 of the panel I0 and the side walls of the slice. Since there is only sliding movement between these parts a suf- I the dispersion slice and 3 the web-forming wire.
ficiently tight joint may be provided to prevent objectionable leakage. It may be desirable, however, to take care of this joint as by attaching a rubber strip to the member l4 with its free edge pressed against the side wall of the slice.
The slice consists of the upper rigid frame 9 and the lower rigid frame 1 made, for instance, of
cast metal. The frames I and 9 are adapted to support the more or less flexible and preferably transparent synthetic resin walls of the slice passageway. The upper frame 9 has a downwardly extending portion l9 .to which is bolted the synthetic resin or plastic strip 2|), the contour of the lower edge of which corresponds to the shape of the upper wall 2| of the slice passageway. The strip 20 and wall 2| may be secured together as by means of adhesive and, of course, may, if desired, be molded integral with each other. The lower frame I supports the strip 22, the upper edge of which has the shape of the lower wall 23 of the slice passageway. The sides of the space between the the walls 2| and 23 are closed by the plates 24 and 25 secured to the frames 1 and 9 by means of cap screws 26 and 21. Screws 21 extend through large openings 21 in the plates 24 and 25 covered by washers 28 to permit adjustment, vertically or horizontally, of the upper wall 2| with respect to the lower wall 23.
The entire slice may be raised or lowered by adjustment of the screws 29 and 3|]. Also, by loosening the screws 29 and 30, the whole slice structure may be moved slightly toward or away from the flow box. The upper wall of the slice may be raised or lowered with respect to the lower wall thereof by means of the screws 3| to change the size of the passageway and the upper wall may be moved longitudinally with respect to the lower wall by means of the screws 32 to change the shape of the passageway. It is noted in this connection that screws 3| are connected to the upper frame 9 through the plates 33 which are secured to the frame 9 by the screws 34 which pass through elongated openings (not shown) in the plates 33 permitting an adjustment of plates 33 with respect to the frame 9.
The upper and lower walls 2| and 23 and the side plates 24 and 25 extend beyond the rigid frames 1 and 9 to provide more or less flexible lips for the slice outlet or nozzle. The side plates 24 and 25 are held in place by the screws 35 and 36 carried by the brackets 31 and 38 secured to the frame 9. Frame 9 also supports forwardly extending brackets 39 and a third pair of brackets 49 secured to the frame 9 by the screws 4|. Brackets 39 carry the screws 42 which support the transverse rod 43 which is adapted tobear against the upper wall 2|.- The brackets 40 carry the transverse shaft 44 which is adjustable with respect to brackets 49 by the screws 45. Shaft 44 carries the screw threaded rods 46 which are attached near the edge of the wall 2| and are individually adjustable with respect to the shaft 44 by means of the wing nuts 41. Thus it will be seen that the projecting end of the wall 2| may be raised or lowered with respect to the wall 23 to change the size of the slice orifice or flexed to change the shape of the channel leading to the orifice. Thus the projecting edges of walls 2| and 23 may be made parallel to each other or uniformly converging or they may be brought closer together in the vicinity of the rod 43 than at the orifice thus providing a diverging channel immediately to the rear of the orifice,
It will be appreciated, of course, that any one or more or all of the various adjustments of the slice described above may be omitted. It is entirely feasible to give the whole slicea fixed shape with its upper and lower and side walls rigidly attached to each other and to mount the slice in a flxed position with respect to the flow box and the web-forming screen. I have found, however,
in making different kinds and weights of paper that some adjustment of the slice is desirable and that even in the continuous production of the same kind of paper unavoidable variations, such as variation in the paper making stock, make some adjustments of the slice highly desirable.
The primary function of the slice, as stated above, is to take a paper stock of substantially uniform composition from the flow box and by passing it at a high velocity and at a constantly changing velocity and subjecting it to turbulent flow, to break up any aggregations of fibers and uniformly distribute the fibers throughout the vehicle and deliver it uniformly to the web-forming device. As stated, the slice passageway, in order to give the furnish the necessary velocity and turbulence, must be of relatively small vertical dimension and must therefore be of substantially the full width of the slice orifice throughout its length.
,It will be appreciated that various changes may be made in the structure disclosed without departing from my invention. The slice passageway may be somewhat narrower or somewhat wider at its inlet than at its outlet, or the side walls might be so shaped as to vary the width of the slice passageway between its ends, provided stantially uniform width equal to the width ofof roughly cylindrical shape intermediate the ends of said passageway connected on one side tangentially to the smaller discharge end of a portion of said passageway and on the other side that the passageway is not called upon to accomplish too great a spreading of the stream. These possible modifications of the shape of the slice passageway would complicate the structure from the standpoint of adjustment of the top and bottom walls thereof, but would be practicable if this adjustment feature of the slice were omitted. It further appears that those portions of the passag-eway connecting ,the turbulence chambers might be of uniform cross-section and that useful results would be obtained due to the turbulent flow in the chambers and the changes in the velocity of flow as the stock turbulence chambers.
1. A slice for delivering paper-making stock from a supply thereof under pressure onto a webforming device, comprising a passageway of substantially uniform width equal to the width of the web, said passageway including at least one open and unobstructed roughly cylindrical chamber of relatively large cross section into which stock is delivered tangentially from a portion of said passageway of relatively small cross section, compared to the cross-section of said chamber, said passageway including a nozzle portion the upper and lower walls of which adjacent to the pulp discharge outlet diverge gradually to said outlet.
2. A slice for delivering paper making stock from a supply thereof under pressure onto a webforming device, comprising a passageway connected at one end to said supply of paper-making stock and at the other end to a nozzle positioned to deliver the paper-making stock onto the web forming device, said passageway being of subenters and leaves the v tangentially to the larger inlet end of portion of said passageway.
3. A slice for delivering paper-making stock from a supply thereof under pressure onto a webforming device, comprising a passageway con-' nected at one end of said supply of paper-making stock and at the other end to a nozzle for delivering the paper-making stock onto said webforming device, said passageway being defined by plane parallel side walls and by curved top and bottom walls and including a plurality of curved portions of progressively decreasing cross section in the direction of fiow of the paper-making stock therethrough, each connected tangentially at its end 01 smaller cross section to a roughly cylindrical open and unobstructed chamber of relatively large cross section.
4. A slice for delivering paper-making stock from a supply thereof under pressure onto a webforming device, comprising a passageway connected at one end to said supply of paper-making stock and at the other end to a nozzle for delivering the paper-making stock onto said web-forming device, said passageway being defined by substantially parallel plane side walls and top and bottom walls each consisting of a plurality of connected curved surfaces, said passageway being tortuous and of constantly changing and repeatedly increasing and decreasing cross section in the direction of flow of the stock therethrough and including a portion of relatively large crosssection constituting an open and unobstructed swirl chamber formed by opposed upper and lower oppositely curved walls, and means for adjusting the vertical distance between said top and bottom walls.
5. Apparatus as defined in claim 4 in which said top and bottom walls are relatively adjustable in the direction of flow oi the stock.
HARRY WIHTNEY OSGOOD. JR.
REFERENCE-S crran The following references are of record in the file of this patent:
UNITED STATES PATENTS another Number Name Date 2,028,637 Lang Jan. 21, 1936 2,241,688 Wiliams May 13, 1941 2,329,799 Thorsen Sept. 21, 1943 2,347,130 Seaborne Apr. 18, 1944 Certificate of Correction Patent N 0. 2,506,678
HARRY WHI It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:
Column 10, line 18, for the words May 9, 1950 TNEY OSGOOD, JR.
JOE E. DANIELS,
ssz'stant Commissioner of Patents.
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|Cooperative Classification||D21F1/028, D21F1/02|
|European Classification||D21F1/02G, D21F1/02|