US3021952A - Classifying apparatus - Google Patents

Description

Feb; 20, 1962 K. R. POWELL CLASSIFYING APPARATUS Filed May 29. 1958 FIG.

INVENTOR.

KEITH R. POWELL BY WJZQ; a M

ATTORNEY United States 3,021,952 Patented Feb. 20, 1962 3,021,952 CLASSIFYING APPARATUS Keith R. Powell, Minneapolis, Minn, assignor to General Mills, Inc., a corporation of Delaware Filed May 29, 1958, Ser. No. 738,872 9 Claims. (Cl.'209-339) "by suitable reciprocation r vibration of the sifting unit.

Problems have been encountered in such sifters, particularly those in which the sifting surface is enclosed in an outer box or frame, and particularly when the sifter is subjected to rapid vibratory reciprocation to convey the stock across the sifting surface. One of these problems is that of irregularity, or surging, in the sifting and conveying action of the stock on the surface. It is believed that such surging may be due to variations in the instantaneous pressure differentials above and below the sifting surface caused by rapid vibrations of the enclosure in'which the sifting surface is mounted.

With these problems of the prior art in view, it is one object of the present invention to provide improved classifying apparatus of the reciprocating type. 7

Another object is to provide an improved reciprocating or vibratory sifter having novel means for equalizing or neutralizing pressure differentials above and below the sifting surface.

Other objects and advantages will be apparent from the following specification, in which certain preferred embodiments of the invention are described. In general, the above objectives are accomplished according to the present invention by the use of suitable partitions, which are at least partially flexible, at appropriate locations in the sifter body. Such flexible partitions are particularly useful in sealing the upper chamber above the sifting surface and can be used either at the inlet or discharge end of the sifter, and are particularly useful at the inlet end.

In the drawings forming a part of this application:

FIGURE 1 is a side view, partly in section, of a vibratory reciprocating sifter embodying features of the present invention;

FIG. 2 is a sectional view on the line 22 of FIG. 1;

FIG. 3 is a partial perspective view, with certain portions cut away for clarity, to show the details of one form of flexible partition as used in FIG. 1; and

FIG. 4 is a partial perspective view of a modified form of partially flexible partition.

As shown in FIG. 1, the invention is disclosed in connection with a reciprocating vibratory sifter designated generally at 10. This classifying unit includes a body portion having a bottom Wall 12, a top wall 14, side walls 16, and end walls 18 -and 20. The stock to be sifted is shownat 22 and is introduced through a suitable inlet 24 at one end of the sifter near end wall 18; The stock is received on a conveying surface 26 which carries the stock along to a sifting or classifying screen 28. The stock is adapted to be fed across this screen 28 while desired particles are sifted through the surface 28 to the bottom 12 of the housing. The particles thus sifted are discharged through an outlet 36, while the particles which do not pass downwardly through the sifting surface 28 are carried over the tail surface 32 and discharged through an outlet 34 adjacent end wall 20.

The sifter is supported for suitable vibratory reciprocation on hangers 36 having their lower ends 38 pivoted to the sifter body and their upper ends 49 pivoted to a suitable frame member 42. The hangers may be inclined as shown in FIG. 1 to provide both an upward lifting and a horizontal conveying movement to the stock as shown by the two-headed arrow 43, which extends perpendicularly to the intermediate or rest position of the hangers 36.

The desired vibrations of the sifting unit are provided through a drive shaft 44 having one end secured at 46 to the sifter body and having its other end driven by a suitable eccentric 48-or other vibratory power sources. This eccentric, in turn, is driven by a suitable motor and gear box indicated generally at 50 and the frequency of vibration may be controlled by a suitable speed control handle 52.

The stock 22 is fed into the inlet 24 through a flexible connection 54 from a supply spout 56. Similar flexible connections 62 and 64 connect the discharge spouts 30 and 34 to appropriate subsequent apparatus; thus thespout 30 is connected to a further conveying tube 66 which feeds the material to a receiving hopper or other processing unit 68, while the outlet 34 is connected by its sleeve 64 to a suitable further processing unit or hop per 70.

As described up to this point, the sifter 10 is essentially conventional. It has been observed, however, in connec' tion with such sifters, that the stock 22 does not always feed evenly along the sifting surface 28 and may, in fact, bunch up or collect at certain portions of the surface, while leaving other portions of thesurface essentially bare. The present invention is based on the belief that these difliculties in feeding and sifting of material may be due to the failure of prior Workers to recognize that an enclosed vibratory sifter of this type inherently creates variable instantaneous pressure differentials above and below the screen. Thus, when the sifter is moved to the right in FIG. 1, the closed inlet end 18 of the sifter body tends to push the column of air below sifting surface 28 toward the right to cause an increase in pressure along this 'air column or slug of air. The increase in dynamic pressure at various points beneath the sifting surface 28 appears to depend on the total length of the air column involved bet- ween walls 18 and 20 and on the relative distancefrom end wall 18. Above the siftingsurface 28, there is less tendency to generate dynamic pressures in the longitudinal column of air because the inlet opening 24 may dissipate some of the pressures generated by end wall 18 above the screen. Thus, an instantaneous pressure differential may be created as the sifter is moved upwardly and to the right and this pressure differential, particularly near the inlet end, may lift the stock upwardly from the surface 28 just at the point when it should be in contact withsuch surface to obtain the desired conveying'movement. Conditions may be reversed on the return stroke, when movement of end wall 18 to the leftin FIG. 1 may tend to pull the respective air columns to the left and create instantaneous decreases in dynamic pressure. Similar phenomena are believed to occur at the discharge end of the, sifter with respect to end wall 20 and the various wall portions of the discharge outlets 30 and 34.

According to one feature of the present invention an effort is made to equalize the pressure variations in the air slugs or columns above and below the sifting surface by the introduction of suitable flexible partitions at appro' priate points in the sifter body. In connection with the inlet of the sifter, it has been found particularly helpful to introduce a flexible partition 72 above the initial receiving surface 26 which receives the stock 22. This partition 72 may be made of rubber, plastic, cloth, or other relatively flexible material, having its upper portion secured to a suitable cross member 74 secured to thetop I wall 14 of the sifter body. This upper portion 76 of the flexible partition hangs generally vertically from its support 74.

The total vertical length of the flexible partition is somewhat greater than the vertical spacing between the top wall 14 and the surface 26. Thus the lower end of the flexible partition at 78 is inclined away from the inlet toward the outlet end of the sifter, as shown in FIG. 1,

' to permit the stock 22 to pass beneath this partition. The

flexibility of the partition, and its owninherent weight, tend to hold the trailing end 78 of the partition in contact with the stock and thus seal oft the inlet end of the air column above sifting surface 28 and effectively isolate it from the inlet opening 2 4.

In operation the partition 72 serves in a manner similar to end wall 18 and is believed to generate dynamic pressures above the sifting surface which are in phase with reciprocation of the sifter and which can effectively equalize or neutralize the pressures generated below that surface by end wall 18. Thus the contact of the stock 22 with sifting surface 28 and the action of that surface on the stock will be essentially the result of the desired vibration of the sifting surface and will not be substantially affected by undesired air pressures and differential pressures generated by the reciprocating movement.

According to a further feature of the invention it is possible to utilize a similar flexible partition 80 supported on a cross member 82 near the discharge end of the sifter and above the sifting surface 28. In some cases it may be desirable to utilize a similar flexible partition 84 beneath the sifting surface 28 and between the end of that surface and the discharge outlet 30. Such a partition may be mounted on a cross member 86 to provide essentially identical end wall conditions at the discharge ends of the respective longitudinal air columns above and below the sifting surface 28.

FIG. 4 shows a modified form of partially flexible partition for use according to the present invention. Here the partition 88 includes a relatively rigid upper portion 90, which may be secured to a suitable cross member 92 in the sifter body by bolts 94. This portion 90 provides a solid wall portion throughout a. major part of the cross section between the sifting surface and top of the sifter. The lower portion of partition 88 is made of flexible material 96, secured at 98 to the portion 90.

Just as in the case of the completely flexible partition of FIGS. 1 to 3, the flexible portion 96 of partition 88 in FIG. 4 will tend to accommodate itself to the surface of the stock received by the sifter. These flexible portions will thus maintain a suitable air seal regardless of variations in the rate of feed of the stock beneath the partition. At the same time the angular orientation of these flexible portions toward the discharge end of the sifter will permit them to increase or decrease their spacing above the sifting surface in accordance with the rate of stock feed.

According to the. foregoing description, this invention contemplates the use of at least partially flexible partitions at appropriate locations to equalize the variations in dynamic pressures above and below a sifting surface in a vibratory sifting unit. While these partitions have particular utility in connection with vibratory reciprocating sifters of the type shown in FIG. 1, they are believed to have applicatiton to certain other types of sifters in which similar surging problems may be encountered. The foregoing specification includes a description of the principles which are believed to be involved in the present invention, together with some of the ways in which the" invention may be practiced.

Now, therefore, I claim: 1. In a vibratory classifying unit comprising a sifting surface having receiving and discharge ends, a body portion having top, bottom, side and end walls enclosing said sifting surface and providing substantially closed upper and lower chambers aboveand below said surface, means for reciprocating said body chambers and sifting surface as a unit longitudinally along a desired path and thereby conveying stock from said receiving end to said discharge end while classifying the stock by said surface, an inlet for stock at one end of said upper chamber, and an outlet for stock at the other end of each chamber, the improvement comprising an anti-surging partition located .in said upper chamber between said inlet and the receiving end of the sifting surface at a point adapted to provide desired dynamic air pressures above said sifting surface, said partition having its upper edge secured in air tight relation adjacent said top Wall and its upper portion extending downwardly across the entire width of the upper chamber toward said sifting surface and secured for longitudinal reciprocation with said body and sifting surface, at least the lower portion of said partition consisting of flexible, airtight material extending toward said outlet and located to engage the top of the stock on said sifting surface and maintain a substantial air seal between the main portion of said upper chamber and said inlet.

2 A classifying unit according to claim 1 in which both the upper and lower portions of said partition consist of flexible material.

3. A classifying uni-t according to claim 1 in which said partition comprises a rigid, substantially vertical upper portion extending downwardly from said top wall to a level spaced above the sifting surface and a lower portion of flexible material extending downwardly toward said surface and longitudinally toward said outlet.

4. A classifying unit according to claim 1 having a second partition of similar construction located adjacent the outlet from said upper chamber and thereby providing a sealing wall between said upper chamber and outlet.

5. A classifying unit according to claim 4 having a third partition of similar construction located adjacent the outlet from said lower chamber and thereby providing a sealing wall between said lower chamber and outlet.

6. A reciprocatory classifying device comprising a sifting chamber enclosed by a plurality of wall members, means for reciprocating said device including said chamber and wall members along a given path, inlet means in said chamber for feeding stock to be classified thereto, outlet means for discharging the classified stock, a sifting surface intermediate said inlet and outlet means for classifying said stock during said reciprocation, a substantially imperfo-rate receiving plate at one end of said sifting surface below said inlet means, a relatively airtight discharge plate at the opposite end of said sifting surface adjacent said discharge means and flexible anti-surging partition means disposed above at least one of said plates and reciprocable with said chamber, said partition having a substantial area transversely of said path located and arranged to move the volume of air withinsaid chamber in phased relation to the reciprocation of said chamber and thereby provide improved sifting and conveying.

7. An improved classifying device, the combination comprising a rectangular sifting chamber enclosed by a plurality of Wall members, and provided with a classifying surface therein, inlet means for admitting stock to said classifying surface, means for moving said chamber and said classifying surface as a unit relative to said stock along a desired path, said stock being classified by said movement, outlet means in said chamber for discharging the classified stock, and flexible anti-surging partition means located between said classifying surface and said outlet means and extending substantially normal to said path and movablewith said chamber and surface thereby moving a'volume of air within said chamber in correlation to the movement of said classifying surface.

8. An improved classifying device, the combination comprising a rectangular sifting chamber enclosed by a plurality of wall, members, and provided with a subt nti lly horizontal classifying surface therein, inlet means for admitting stock to said classifying surface, means for moving said chamber and said classifying surface as a unit relative to said stock along a desired path, said stock being classified by said movement, outlet means in said chamber for discharging the classified stock, and flexible partition means located adjacent each of said inlet and outlet means and extending transversely of said path, said partition means moving with said chamber and moving air within the chamber thereby generating dynamic aid pressures ofi setting undesired pressure differentials resulting from movement of the volume of air within said chamber.

9. The device of claim 8 wherein each flexible partition means is positioned generally perpendicular to the direction of flow of the stock and has at least one yieldable longitudinal edge in engagement with said stock and References Cited in the file of this patent UNITED STATES PATENTS 398,692 Bittinger Feb. 26, 1889 418,587 Prinz Dec. 31, 1889 1 ,214,506 Brasack Feb. 6, 1917 1,629,244 WillcoX May 17, 1927 1,686,107 Sewell Oct. 2, 1928 2,047,713 Simpson July 14, 1936 2,903,135 Dryg Sept. 8, 1959 FOREIGN PATENTS 7 3,646 Germany Apr. 5, 1893

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