US2278729A - Apparatus for screening pulp - Google Patents

Description

April 1942- A. D. MERRILL 2,278,729

APPARATUS, FOR SCREENING PULP Filed Dec. 2, 1937 2 S heets-Sheet 1 awe/who'l flat/era Maze/2.4

April 7,' 1942.

A. 0.] MERRILL APPARATUS FOR SCREENING PULP Filed Dec. 2, 1957 2 Sheets-Sheet 2 gjwuwrvtom v 3 Hazard/7:04am W7 Patented Apr. 7, 1942 I 7 "UNITED STATES PATENT OFF-ICE APPARATUS FOR scaaanmo. PULP Albert n. Merrill, Water-town, N.- Y, Application December 2, 1931, Serial No. 177,195

1 Claim. ((1192-32) This invention relates to pulping apparatus, moreparticularly to an improved apparatus for screening of pulp, I

A typical pulp screening apparatus, employed at the present time, comprises a screen member on which the stock to be filtered or screened is fed and below which a flexible diaphragm is positioned. The diaphragm is associated with mechanical means to efiect its vibration. In use the pulp which is to be screened is forced or ,drawn through the screen plates by the pulsating movement of the body of pulp or liquid, estab.-

lished by the vibratory movement of the diaphragm. The body of liquid is normally main- 'tained at a predetermined levelby utilizing an outlet seal so that a suitable depth of the stock is maintained over the diaphragm. ,In the operation of this type of structure, the pulsating movement of the, body of liquid causes the finer fibers to be forced or, sucked throughthe' interstices in the screen while withholding or screening out the larger particles.

In the past, a number of different methods of efiecting the vibration ofthe diaphragm have been'proposed. Amonglsuch methods is the socalled positive drive that is to say adrivlng mechanism which is connected to the. resilient" diaphragm so that theidiaphragm is positively movedin each direction of its reciprocating motion. 7 t

the screen, as is known, are quite small. When the diaphragm is given a positive upward stroke by means of a non-resilient connecting rod, the body of liquid similarly tends to pulsate upwardsimple and efficacious method-of preventing such l breakage, but also to a methodof increasing The present invention relatesx not only to a production of'a screening apparatus. The broad concept ofthepresent niethod'involves the elimination of such breakage by providing a special type of outlet such that the liquid below the screen may be caused to flow outwardly of the screenon each reciprocation'ot the diaphragm. thus relieving the undesired dangerous pressure.

tion, as will be seen, the operation increases the production by reason ofan increased; flow of stock through the device. ',An additional and novel feature ofjtheinvention-is effectually -to adapt the screening unit to difierent types of fiber stock'- so as to correlate the speed ofthe ular characteristics of that stock.

discharge of stock with respect to the partic- With this fundamental concept-in view, it will be appreciated that'a'ziumberbfldifierent'speciflc'mechanical structures may-belutilized to V the accompanying 7 drawings, inwhich:

1y. In some circumstances, the fibers may clog the interstices in the screen, thus establishing a hydraulic hammer or rain; In other words.

when the interstices of the screen areplugged,

the upwardly moving body of liquid is suddenly arrested and a considerablepercussive pressure-- is. applied to the screen in consequence of the upward momentum of the'liquid magmas In many circumstances, this is of such a magnitude Figure l'is'a transverse section oi a pulp screen according to the invention;

of construction.

Figure 3 is a similar view of another modification of the invention. V

Figure 4 is a detailed view illustrating the 7 Figure 2 is a similar view of a modified form 'utilization of a' positively controlled flow of :screened pulp in the type of apparatus shown inFiguresland 2. V 5 Figures 5 and 6 illustrate, similarly, methods of positively controlling the new irom 'screen boxes 01' the type shown in Figure 3.

As shown in the drawings, a series of slotted screen Plates I are supported in a traminf dicated generally at 2, which framing serves as a container for the pulp to be "treatedJA dia- The screen is suitably secured to the framing in any desired manner, as for example by being locked between the shoulders 2' and the removable plate fasteningi'rames 4. Obviously, any

enmmmmaa tcumu us o yard;

metal plate i ,on which is formedan apertured shoulder I to which the connecting rod I is pivotally connected. At its other end the connecting rod is associated with any suitable mech which functions to impart a predetermined reciprocating motion to the .eonnectins rod and thence to the diaphragm.- ,-Such connection is shown as comprising the driving e. t6 themain'drive'shait:

imlconmneri-aibmmed use man with a passageway or duct l i, thrcugh which screenedstockpasses to thetroughdi. As will l which is keyed screened stock .by those 'skilledjin th'eart,lthe passes fromthetrough I! through usual outlet seal (not shown'i, which is operative to maintains body. ofthe liquid pulp at a predetermined depth in screening; chamber. .It'wlll be understood that, in the operation of suchmeehanism, the vibratory movement of .the diaphragmstransmits a corresponding pulsatingmovement to the liquid mass in the-screen- ;ing" This pulsating movement at the :one time tends. to draw the liquid and the finer Jlbers through the screen apertures, and by rea- "of the agitation. due to pulsaticn in the liquid body, to prevent immediate 1-1odgment in the screen apertures. ,In actual-practice, however. itjis-found that 1-2 g Pulp which. under the action of the diaphragm,

.someffibersyattach to. the sides 'oithe apertures,

or slots; in thefplates. and tend .progressivelyjtog stroke oi the diaphragm. In other words, on the downstroke of the diaphragm, the now of the suspended finer particles down through the screen is induced. On the up-stroke of thediaphragm, since the pressure oi the liquid adjacent the screen increases considerably above that in the sealing tube il, a predetermined amount of the screened pulp flows outwardly through the tube. This now of' liquid obviously relieves the impact pressure on the bottom of the screen and thus eliminates the possibility of'such pressure building up to the danger point, that is, to the extent or breaking the screen plate.

It will also be seen that this type of operation considerably increases the output of the machine, as well as serving to clean the screen. As will be observed {mm the figures, the flow of liquid through the auxiliary outlet 2| tends to be substantially parallel the bottom'of the screen, in contradistinctionto the main movement of the is substantially vertical or reciprocatory. In these thereiore,'the flow of liquid h ou h tube :0 tends to shear away fibers which may have adhered to the underside of the screen. It will also be appreciated that; in the older type of structure, under the pulsating action of the diaphragmron the up-stroke, -a consider-,

able amount of liquid was forced upwardly through the screen apertures and effective now of pulp through the machine was dependent largely on the down. or suction stroke of "the diaphragm. In the present type or structure,

however, the diaphragm incombination with the two outlets II and 2| functions essentially as'a' double acting pump. 0n the down-stroke,'liquid is drawn through the screen and overflows into the trough to be discharged in the usual man,-

her. On the upstrokefas explained, not an inconsiderable quantityof the pulp is forced outwai'dly through the seal 20. It will thus be observed that the output from this type of machine 7 veis iz'eof theaperturesandultimatelyblocking f 5 r vi us y explained the ll itself 1 ynence; when the screen I p a-certain;point,-the-upl V .ffi ifl fnqi d-body issuddenlyf;

thereby -applyinrapressure or con--" 1 magnitude underside ,ofthe v'iewof' large of :the liquid,j.=this percussive force may reach such I ,Ea magnitude {as to fracture the screen.

i sa w er in ention,.; such danger oi breaking the screen is' This is done by providing 1 the principles-of the present ""ai seri'essoi: safety outlets for the liquid and-prefof this potential water-v hammeractlon, that is to say, adjacent the undersidefroflthescreen. shown imfigure 1," thisben'eiicial result may. be achieved by the.

simpleexpedient or empioyinaxa seal outletjadjacent the'underside of the plate. Such'outlet .may comprise the-usual form of suchasthernemberll.v

Ll-tube seal, It will be seen that sums structure establishes a new mode. of operation for the screening devicein that it provides for what in function may is 'considerabiy greater than from one which is not'soconstrucied.

It will'readilybe understood'that, with the broad concept in mind, a number of specifically different types of'structures may be provided, particularly in 0,1 the typ of seal used.

An example of such alternative construction is shownin Figure 2, in which the special double bend seal- I. is employed. As will have been appreciated this sealfunctions essentially in the same manner as seal II, shown ingFigure 1.

Since the essential offthe seal is that iof a valve, allowing amaintenance of suction on the" down str'oke; and an outward flow of'pulp on -theupstrokeit is clear that other ".*types may beused. The auxilia y outlet t fore, need' notbe a seal of the typelshown, but

may be of any other typeof structure in which these essential functions are performed. In the 'type of structure shown, the size of the seal 2| for SI' will, oicour'se, depend uponthe relative of the screening chamber, the depth of the ,stock; the-speed of vibrationfof the "diaphragm, .andthe like. 'lln typical installations, .such a 'seal may be of the order 0! from 2 to18 inches. inany'. ev'ent, [as explainedpthe seal'is so conbe considered a check valve, allowing a now of -theliquid from-the area subiacent the screen,

under, predetermined pressure-conditions, and

preventing;this now imder certain different pressure conditions. During operation, it will be undersmod that. the outlet tube il'iss'ealed and hence does not break the suction on the downstream, to insure a maintenance of the suction orvacuum on the ldown stroke and a positive outward now of liquidjontbe upstroke, thus preventing the application] of anyconsiderable impact pressure on the screen.

Sincea' salient feature of the invention'is the establishment of a outward flow of screened stock on each stroke of the diaphragm while-insuring the effective suction of the downstroke, it will be appreciated that this may be accomplished by other methods. The device illustrated in Figures l and 2 show, ineflfect, the

achievementof this new functionin an existing type of machine having the usual low level discharge (I I). In such a structure the benefits of th invention may be secured by providing a secondary or auxiliary outlet 20 (Figure. 1) or III (Figure '2). The same essential functionsmay be .secured by constructing a screening device having a special single outlet such as is shown inv FigureB. In such anapparatus, asindicated, the construction of the screen box and the relative location of the screenand diaphragm may be the same as that shown in Figures 1 and 2,

and such have therefore been indicated by identical numerals. Under the invention as shown in Figure 3 a special type of single outlet 40 is provided. As shown this comprises a' substantially U-shaped portion 4|, constructed in a manner similar to that of the sealing discharge units 20 and 30 shown in Figures 1 and 2 respectively. Such a U-shaped discharge duct .serves to permit outward flow of the screened stock under predetermined hydrostatic pressure conditions and also acts as a seal to maintain the desired suction in the screening chamber. As will be noted from an inspection of Figure 3,

.the discharge tube 40 is connected to the screen box and is therefore in fluid communication with the mass of pulp in the box at relatively high point and closely subjacent the screen. In these circumstances, the discharge tube perform the functicn'of both'the low level discharge II and the discharge. tube 20 and 30 of the structure shownin Figures 1 and}. I

In operation, when the diaphragm 3 is vibrated under the action of the driving mechanism 8-40,

the screen stock is caused to flow outwardly through the tube '40 on each-stroke of the diaphragm. Due to the utilization of the U-tube section and, hence, the establishment of a liquid seal, the desirable suction on the down-stroke of the diaphragm is maintained. 0n the upstroke of the diaphragm the screened stock is caused to flow outwardly through the U-tube when the pressure obtaining in the body of pulp exceeds that established by the particular height- 013 the seal, which is chosen. In this type of structure, therefore, in accordance with the general principles of the invention, the double pump action is secured, a greater 'thruput of stock is achieved;

andthe undesirable hydraulic hammer efiect the bottom of the screen'is precluded.

As is known to those skilled in the art, a particular pulp mill may operate upon different types of cellulosic stock and may, in the course ofits normal operations, cook materials varying from a very soft to a very hard stock. It has been found that the flow of the pulp through a particular screening apparatus is greatly influenced by the particular characteristics of .the stock and, as a matter of fact, such flow is. in part a function of such characteristic of the stock.

According to another feature of theinvention, increased efllci'ency may be assured by providing means for regulating the discharge of pulp from the screening mechanism with respect to the character of the particular stock flowing through it. In these circumstances, the retention period in the screening device and-the quality of the product can be predeterminedand maintained.

. rection, the aperture 6| maybe moved :in and out.

of register wtih the discharge duct '41 so as to ablevalv 5 5 eflectivejcro'ss sectionaljfsize and hence-the speed ih re i us n w. b ontro d- Similar'meansare provided; tocontrol the size of the comprises the gacewalve member-50. Ihis'valve =is provided with the aperture 5] and the valve is adapted to slide, in the known manneninthe apertured guide 52.. At its'upperflportionthe gate is provided with thethreadedstem 53, on

the end of which is 'provided'the usualfoperatm handle. It will be understood thatwith this type of structure, by rotating thehandlejon the gate valve 50, the aperture 5| may be moved vertically upwardly and downwardly so as to control theefiective size of the discharge, and

thus regulate the amount of stock discharged the discharge tubes II and 20, respectively.

It will be'appreciated thatthis same type of controlled operation may be utilized with the.

single discharge screen structure of .the type shown in Figure 3. Thus, as shown in Figure 5, the screen may be provided with a gate valve of the type shown in Figure 4. This valve may comprise the gate or plate formed with the aperture. :6l. the apertured plate seat 62. The upper portion of the. gate is connected with the threaded stem at the end of which is provided theusual operating handle. In this type 'of structure,. by rotating the handle .of the stem- 63 in the proper dicontrol the effective size of the discharge tube and hence regulate'the amount ofpulp flowing therethrough.

It will be understood that the invention com prehends broadly the control of flow of the screened pulp outwardly of the screen box.

comprises a gate valve platewhich. has a plurality oforiflces of predetermined size; Sucha valve may comprise the gate plate I0, provided with l the differential size orifices 1|, I2 and .13, respec- These advantages may be secured-by the simple tively. The valve may be mounted for vertical movement in the valve seat platefl. At the upper 'end the valve may be provided with an 'apertured handle'or stud 1.5 in which the latch I6 is adapted to reciprocate. The latch 16, it willbe understood, is adapted to project through the stud I6 and engage in the detents or depressions 11. Such detents are, in the mafiner known. vto those skilled in the art, suitably vertically spaced so that they conform to the several registe ms position of the apertures ll, 12 and I3.

The gate is adapted to reciprocate in,

4 amazon In the structure shown in Figure 6, for example, the gate valve is set so that the middle sized aperture 12 is in register with the discharge line ll-Ji. By withdrawing the member I. from register with a detent, the gate Ill may be elevated or depressed, by utilizing the stud handle 15 so as optionally to register apertures II, I! or 18 with the discharge opening Hi.

The particular types of valves have been given as merely illustrative of any mechanism which functions in a similar manner to control the flow of stock through either the single discharge type of screen (Figure 3) or through the double type discharge (Figures 1 and 2).

It will be appreciated that the present invention presents a simple and effective method of eliminating a marked defect in pre-existing processes and furthermore insure the positive and additional advantage of a considerably greater thruput of stock, the flow of which may accurately be'controlled. While preferred modifications of the invention have been described, it is to be understood that these are given'to exemplify the underlying principles involved, andnot as limiting the fundamental concept to the "precise apparatus chosen for illustrative purposes.

I claim:

A pulp screening apparatus comprising a container, a screen mounted at the upper part of the container, a resilient diaphragm mounted at the base of the container, positive driving means for the diaphragm; an outlet for the container located closely adjacent thescreen, a valve in said outlet, a second outlet from the container located closely adjacent the diaphragm, a control valve in said outlet and means to eilfect a controlled flow of screened pulp through each of said outlets.

' ALBERT D. MERRIIL.

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