US2199847A - Centrifugal mechanism - Google Patents

Description

T. A. BRYSON CENTRIFUGAL MECHANISM May 7, 1940.

Filed Aug. 26; 1930 /NVEN7'DR 75nq A. Elys /7 MW ATTORNEY Patented May 7, 1940 UNITED STATES CENTRIFUGAL MECHANISM Tandy A. Bryson, Troy, N. Y.

Application August 26,

3 Claims.

While my invention is not limited thereto, it is particularly applicable to the treatment of paper pulp or other fibrous material.

In the removal of heavy and light impurities 5 from an impure mixture of fluent material in centrifugal machines, and especially in the treat- 'ment of paper-pulp, it is desirable to maintain a relatively thin wall of material undergoing treatment along the inner surface of the centrifugal drum. The reason for this requirement arises from the fact that impurities are required to move radially inwardly and outwardly through the wall of compacted, material held within the drum, in order to be caught by devices placed in the drum to retain them. A thin wall of material may be. more thoroughly impregnated with im-.

purities than a thick wall, and when it becomes necessary to stop the machine and discharge the collected impurities, the proportionate loss of material is relatively less when it is highly charged with impurities.

The result of the foregoing condition is that, of the entire volumetric capacityof the centrifugal drum, only a small portion at its periphery is employed forseparating purposes. Hitherto, efforts to increase the output and capacity of centrifugal machines of the foregoing character have been in the direction of increased diameter of drum. Since the difficulties of cleaning, emptying, and otherwise manipulating the machines increase greatly as the depth of the drum is increased, it isimpracticable to extend the area-of the drum wall to any great extent by the :use of increased depth. It is therefore apparent that the utilizable capacity of the drum in standvard practice is closely proportional to the first power of the drum diameter.

Again, it is clearly apparent that the floor space required for the -machine increases with the square of .the drum diameter, and experience in the manufacture and operation of machines of this character indicates that the weight, construction costs and power requirements increase at a rapid rate when increased output is sought I by increasing the drum diameter.

In the application of such machines to the purification of paper pulp, a serious drawback arises from the excessive cost of an installation of sufficient capacity for the usual paper making machines. Furthermore, aside from normal cost of the floorspace required to house the centrifugal machines, existing mills are already so cramped for room that the problem of providing sufficient space where it is desired, is a serious, handicap to the introduction of this 1930, Serial No. 477,965

method of treatment. Furthermore, experience has clearly proved that many advantages of the centrifugal treatment of paper pulp are lost if the centrifugals are located at a considerable distance from-the paper making machines.

One of the functions ofthe centrifugal is to break up the bundles of fiber in the pulpffluid and, in a sense, to'homogenize the mixture which is to be spread upon the wire. Stock so prepared makes a sheet of greater uniformity, not only improving its appearance, or look-through, but increasing its strength. However, the time and distance of travel of the stock from the centrifugal to the paper machine has a marked effect upon the centrifuged stock, the tendency to re-coagulate being very strong, and the homo-. genized condition is rapidly dissipated. So necessary it is, then, to locate the centrifugals closely adjacent the wire that the floor space required for the centrifugals 'is an important factor from this consideration alone. By producing a given volume of clarified pulp in one half the usual floor space, the centerof production can be placed approximately one-half the usual distance from the wire. A saving of a few feet of travel between the centrifugal and wire is of major importance in improving formation.

My present invention is based upon the use of that portion of the centrifugal drum inside of the present thin wall of material being treated and which is now noteffectively employed. By nesting or positioning a second drumco-axially within the usual separating drum, spaced therefrom radially only-so far as 'may not interfere with the action of the outer drum, and employing the innerdrum as a separator in exactly the same manner as the outer drum, thecapacity of the machine is practically doubled with no increase-in over-all size. The cost, weight, and power-required to drive the double drum machine are, with the possible exception of the last item, obviously. much less than twice the amount of the corresponding items in a single drum machine.

It is conceivable that a third, oreven a fourth drum, may be employed; the consecutive drums being progressively smaller in diameter. There is a practical limit however to the reduction in size of the added drums, since,-as is well known, the effectiveness of a centrifugal machine varies with the distance between the axis of rotation and a particle undergoing treatment. In the construction shown, however, the separating force in each drum is proportional tothe first power of the'radius thereof and, with materials of the type under consideration which must be treated in thin layers, the difference in diameter between two adjacent drums, and hence the difference in separating efficiency is so small as to be practically negligible. It is well within the range of possibility to provide in each drum of a double drum machine a centrifugal effect varying not more than five percent from the average.

It is well known to those skilled in the art of centrifugal separation that variation of a few percent in centrifugal force, except in very rare instances, can not be observed in its effect upon eiiiciency of separation. Many other variable factors, much more marked in their effect upon separation in the practical application of the art. For instance, a factor markedly affecting centrifugal separation is the time during which a given particle is subjected to treatment within the drum. This factor is measured by the volumetric capacity of the zone of treatment and the rate of feed and discharge'of material. In the present invention this factor may be employed wholly to offset the effect of any variation in centrifugal force between the different drums by controlling the relative rates of feed to the respective drums. Adjustable orifices, or other suitable means, are provided for maintaining desired rates of feed to the various drums.

As pointed out above, the efliciency of'separation of impurities by centrifugal sedimentation is dependent upon (1) the magnitude of the separating force applied thereto, and (2) the duration of time this force is permitted to act thereupon.

It has been shown that the separating force generated in a series of nested drums,'all operated at the same relative speed, is in each drum proportional to the diameter (or radius) thereof. It has further been shown that the time a given particle of fluent material remains within the drum, for a given rate of feed, is proportional to the volume of treating capacity thereof; this volume in a drum of applicants type being proportional to the diameter. 7

It follows that'the measure of the purifying or treating capacity of any one of applicants series of drums; that is, its force-time effect upon the material for a given feed rate, is a function of the square of its diameter. Since it is desirable, if not essential, to obtain comparable purifying effects in the different drums of the series, it is necessary to feed the drums substantially in accordance with their purifying capacities, or in other words, in accordance with the square of their respective diameters (or radii) To determine by experiment the acceptable rate of feed for any particular single drum centrifugal machine, and to supply it thereafter at this rate is a simple procedure, but determining the proper rate of feed for each of a plurality of nested drums, receiving feed from a common source and delivering their product to a common receiver presents a very different and difhcult problem. This is so because it is comparatively easy to judge the efiiciency of operation of a single drum machine by inspection of the treated material flowing therefrom, and the rate of feed necessary to provide the desired force-time effect may be simply adjusted. However, with a series of nested drums, each providing a different force and time effect, and having a common feed and outlet, only the average effect of all drums may be inspected.

"My invention will best be understood by reference to the accompanying. drawing in which I have illustrated the preferred embodiment of my invention, and in which Fig. 1 is a side elevation, partially in section, of a centrifugal machine appropriate for carrying out my invention; Fig. 2 is a sectional view taken along a plane of the line 22 of Fig. 1; Fig. 3 is a fragmentary plan view of the baffles; and Fig. 4 is a fragmentary section showing drums of modified form.

Like reference characters indicate throughout the drawing.

Referring now to the drawing, I is a spindle preferably provided at its lower end with a tapered portion 2 on which ismounted a support 3, preferably held in position by a nut 4 secured like I parts -on the lower end of the spindle I. The support 3, which comprises a hub 5 surrounding the tapered portion 2 of the spindle, is provided with a plurality of radially extending arms 6,, connected to a funnel shaped annular member I. A space baiilesmay be supported by suitable brackets (not illustrated), which brackets may be similar to those illustrated in my Patent No. 1,828,096,. The baffles II are preferablyprovided at their intermediate portions with a plurality of annularly arranged openings III). The drum I0 also supports at its upper end a top ring I2, which may also be similar to that illustrated in my said'patent. Each of the arms is also preferably pro vided with a projection I3, said projections providing supports for the inner drum I4, which is preferably arranged concentrically with respect to the outer drum and spaced therefrom.

The inner drum I4 is also provided with baffles if:

II provided with openings I") of the same character as those with which the bafiles supported on the outer drum are provided. The drum I4 is also provided with a top ring I5. An inwardly extending flange I6 is supported on the bottom of the inner drum I4 and serves as the bottom for said drum. It is necessary for the retention of the cylindrical wall of treated material therein that this flange extend inwardly further than the inner edge of the top ring I5.

A stationary pan I1 is provided for receiving the material to be treated from the supply or feed pipe I! I. An inner tube I9 and an outer tube 22 spaced therefrom, are secured to'the pan I1 and are preferably formed integral therewith. An adjustable weir I3, preferably threaded on its outer periphery, engages screw threads formed on the upper inner surface of the inner tube I9. The material flowing over the pan from the adjustable weir I8 falls through the inner tube I9 onto an outwardly extending flange 20 on the bottom portion 3. By reason of the rapid rotation of the bottom, and the attached drums, the material is thrown outwardly, is caught by the portion 1 which is also rotating, and is'directed into the radially inwardly and outwardly disposed layers 1 or sections of the liquid wall which contain the lighter and heavier impurities, respectively, are restrained from. axial fiow by the inner and outer portions respectively of the baflles I l. The axial flow of the relatively pure intermediate layer or stream takes place in a series of steps, said stream being passed through a series of compartments in the hollow cylinders of material, and in each compartment a further purification takes place.

When the hollow cylinder of material has beenbuilt up as described, it will :be maintained by continuing the feed of material through the inspecific gravities, the heavier particles finding their way to the periphery of the drum, and the lighter impurities remaining on the inner sur-' face of the hollow cylinder. The intermediate particles of fluent material, which in the case of paper pulp are the purest, will occupy a radially intermediate portion in the liquid wall. Since the orifices IHJ are located at this radially intermediate portion, the particles which escape ax. ially into the vertically adjacent compartment will be those of maximum purity, while the outer and inner portions of the bafiie II will retain the heavier and lighter impurities, respectively, and prevent their axial escape.- It will be evident that the corresponding operation takes place in each compartment, the intermediately located and, therefore, purest fluent particles being forced into the compartment above.

By virtue of the narrowness of the orifices H0, the escape of material from one compartment to the next higher compartment takes place in a very thin stream and at a-relatively high velocity. As this stream. moves into the comparatively quiet zone of the compartment above, it flares or mushrooms radially, due to the rapid reduction in velocity. Due to this sudden change in axial velocity, the centrifugal action, in the compartment is promoted. v

Further advantages of the, particular process and structure described result from the passage of the pulp througha plurality of restricted orifices, as more fully set forth inmy application above referred to.

In the purification of the axially flowing stream of material, the separationof impurities is also promoted by the action set up by the frictional contact of the particles in the radial borders of the axial stream with the fibrous masses retained on either side thereof. There is thus a combing or brushing action by the relatively stationary masses of fibrous material upon the borders of the stream and sets them free for further centrifugal action.

' The pan I! is provided with perforations 2|, communicating with the space between the inner tube l9 and outer tube 22. The material-falling through the outer tube is directed onto an annular plate 23, supported on posts 23!. A certain amount of clearance is provided between the annular plate 23 and the inner tube l9, as indicated at 24, and a rib or section 25 is preferably formed on the inner tube, as indicated at 25, for directing the falling material over the clearance space 24. From the plate 23, the material is thrown into the lower compartment of the inner drum l4, and thence proceeds upwardly under treatment in the same manner as the layer of material in the" outer drum, and is finally discharged over the ring IS. The discharge from the top ring l2 of the outer drum, and from the top ring l5 of the inner drum, is caught in an annular receiv-- ing trough or gutter 26, whence it may be led to any 'desired location.

In the embodiment of my invention illustrated, the relative volumes or amounts of material which are supplied tothe inner and outer drums may be controlled by adjusting the position of the ring I8 up or down, and this is accomplished by screwing it in its threaded seat inthe tube l9. Raising the ring l8increases the head on the holes above the openings 2|, thereby increasing the relative feed to the inner drum and correspondingly decreasing the feed to the outer drum.

When, after treating a sufficient volume of material to fill the drums to the extent of their dirt retaining capacity, it is necessary to discharge the machine, the feed is stopped and the drums brought to a stop. All fluid material drains through the bottom opening 8. In order to remove caked impurities which may be held between the bafiies II, the following steps are preferably taken. The feed pipe III is swung aside, and the pan I1, carrying with it the inner and outer tubes I9 and 22, respectively, is raised vertically, thus exposing and making accessible the interior of the drum M. The dirt thereon may then be scraped oif or washed with a hose down through the bottom opening 8. In like manner, the inner drum l4 may be raised or telescopically withdrawn from the outer drum Hi to facilitate cleaning the interior of the outer drum. After replacing the foregoing parts, the machine is ready for another cycle.

In themodification of my invention illustrated in Fig. 3, elongated openings III are provided instead of the circular openings of Figs. 1 and 2.

In some cases, where it is unnecessary to subject the material to a succession of purifying actions by a series of baffles, as in Figs. 1 to 3, the baffles are omitted and in place thereof skimming rings 26' and 2'! of known form are providedand may be supported Within the respective drums l0 and I4, preferably by brackets 28 and 29, respectively. The outer edges of the skimming rings are spaced from the respective drums l0 and I4, but extend outwardly beyond the inner edges of the top rings l2 and I5, respectively, while the inner edges thereof extend inwardly beyond the inner edges of the top rings l2 and I5.

From a consideration of the foregoing it will be apparent that drums which are decidedly conical in form cannot be used efficiently to purify material in the manner herein described. The

inner surface of a body of fluent material subjected to rotation about a vertical axis is a paraboloid of revolution but, at the rotative speeds normally employed in centrifugal machines, this surface, within the confines of the drum, may

be assumed to be practically cylindrical. In the device of my invention it is desirable, in order to avoid waste and sliding of the mat, to maintain on the inner surface of each drum, and throughout the vertical extent thereof, a continuous layer of fluent material of substantially uniform thickness making, of course, due allowances for the differential in head between the top and bottom of the drum which is necessary to maintain a desired rate of flow. It follows, that to attain this result the shape of the drum should be approximately cylindrical, and where the drum is coniform to the extent that the difference in diameter between the top and bottom thereof is so'great that there is a substantial difference in mat thickness at the top and bottom of the drumthis result cannot be attained and the apparatuswill not function to purify material in the manner herein described. Hence, the term approximately cylindrical as used in the claims is to be understood as covering variations from a true cylinder to the extent herein noted.

While I have described my inventionin its preferred embodiment, it is to be understood that the Words which I have used are Words of description rather than of limitation, and that changes within the scope of the accompanying claims may be made without departing from the true scope and spirit of my invention.

What I claim is:

In a centrifugal machine of the sedimentation type for the purification oiliquid materials, the combination with a plurality of rotatable, approximately cylindrical, laterally imperforate drums of different purifying capacity coaxially arranged in spaced, nested relation, one within the other, of means at the top and bottom of each drum for maintaining therein, under the action of centrifugal force, a continuous layer of substantially uniform thickness of material undergoing treatment while permitting a simultaneous discharge of purified material from ,each

taneously supplying untreatedfiuid materials to each of said drums; said last mentioned means fractionating the feed to said drums in accordance with their; respective purifying capacities.

2. The structure set forth in. claim 1 in which said drums are provided, intermediate the layer maintaining means, with annular bafiles" having openings therein confined to a restrictedannular zone but being otherwise imperforate.

.of said drums,- and-acommon means forhsimul- 3. Centrifugal apparatus for purifying paper, I

pulp, comprising a pluralityof drums mounted one within another for rotation together about a common vertical axis, a collecting trough surrounding the upper edges of said drums to receive liquid discharged therefrom, and means for supplying separate streams of liquid to said drums TANDY A. BRYSON, 7

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