US3353674A

US3353674A - Apparatus for the wet-screening of particles

Info

Publication number: US3353674A
Application number: US385224A
Authority: US
Inventors: Jan N J Leeman
Original assignee: Stamicarbon BV
Current assignee: Stamicarbon BV
Priority date: 1963-08-01
Filing date: 1964-07-27
Publication date: 1967-11-21
Anticipated expiration: 1984-11-21
Also published as: OA01007A; NL296114A; BE651275A; ES302687A1; GB1025619A

Description

Nov. 21', 1967 J. N. J. LEEMAN 3,353,674

APPARATUS FOR THE WET-SCREENING OF PARTICLES Filed July 27. 1964 United States Patent APPARATUS FOR THE WET-SCREENING 0F PARTICLES Jan N. J. Leeman, Heerlen, Netherlands, assignor to Stamicarbon N.V., Heerlen, Netherlands Filed July 27, 1964, Ser. No. 385,224 Claims priority, application Netherlands, Aug. 1, 1963, 296,114 6 Claims. (Cl. 209-440) The present invention relates to a screening apparatus for the wet-screening of particles and more particularly to improved apparatus of the tangentially fed, fixed bar screen type. Apparatus of this type, which is sometimes designated a sieve bend, comprises a stationary, cylinrically curved screening deck provided with .a supply end, a discharge end, and a screening surface extending between them and being provided with a large number of transversely extending screen openings. The particles and the liquid to be separated are fed tangentially, as a layer, on to the concave side of the screening deck at an initial rate high enough to make an overflow fraction move from the supply end to the discharge end. As the layer travels over the screening surface, successive thin laminae of a thickness considerably less than the width of the screen openings are peeled off; the liquid and the particles which have a diameter smaller than the width of the openings pass through the openings as undersize.

A preferred embodiment of the sieve bend apparatus has a screening surface which consists of a large number of parallel bars set transversely t0 the direction of flow. These bars may be generally rectangular in transverse cross section. Accordingly they are mounted so as to have faces which are presented towards the supply end of the screening deck and which split oh the successive thin laminae to produce the sieve bend effect. If the particles in the liquid being screened are somewhat abrasive, the bar face edges become somewhat rounded in the course of time, which results in a decrease of the screening elliciency. Usually, to increase the useful life of the screening deck at a reasonably high screening efficiency, the bars and the deck are made symmetrical, so that upon reversal of the screening deck the desired lamina splitting can be effected by the faces of the bars which were originally presented towards the discharge end. The length of the period between reversals depends on the material of which the screening deck is made and on the abrasiveness and volume of the influent particle-liquid mixture to which it is subjected.

The width of the inlet of most currently used sieve bend installations is generally made so large that it equals three times the maximum grain size of the raw product supplied thereto. By using a slot width of this size, obstruction of the slot is effectively prevented. However, this often causes the coarser particles flowing along the upper surface of the raw product to be delivered to the screening deck so far below the supply end of the deck that not only will these particles fail to hit the screening deck at a tangent to the deck resulting in the discrimination being shifted to a larger particle size than is-desired, but also there will be additional wear of the screening deck at the point where these particles hit the deck. As a consequence, the life of the deck is shortened.

To alleviate this shortcoming, it has been suggested, for instance in US. Patent 3,007,574, to provide a b-aflle system as a part of the inlet to the screening device. However, such a system has not been found to he acceptably satisfactory in many instances because the baflles rapidly become Worn and thus ineffective and they substantially increase the overall height of the screening installation.

It is therefore an important object of the present in- 3,353,674 Patented Nov. 21, 1967 vention to provide a sieve bend installation which does not possess the above mentioned drawbacks and is particularly suited for handling coarse particles.

It is another object of the invention to provide screening apparatus of the type described wherein the feeding arrangement for the screening deck consists of a feeding launder at one end of the bottom of which is a downwardly opening slot-like spout which is inserted in a throat defined between a fixed downwardly sloping wall tangentially leading into the screening surface and by a flexible movable wall for varying the width of the throat passage. The vertical distance between the said slot-like spout and the upper end of the screening surface according to the invention is large and adjustable to ensure the desired screening effect.

A moregeneral object of the invention is the provision of an extremely simple, easily accessible, and conveniently arranged sieve bend construction, in which the screening deck is subjected to uniform wear and the overall height is minimized owing to the elimination of the necessity of providing a feeding trough with baffles in such installations to ensure the desired separation.

The invention will now be elucidated with reference to the illustrative embodiment shown in the attached drawing.

In the drawing:

FIGURE 1 is a vertical longitudinal sectional view of the sieve bend installation according to the invention;

FIGURE 2 is a fragmentary vertical longitudinal sectional view of the sieve bend showing a modified arrangement of the feeding launder.

Now with more specific reference to the drawings the open feeding launder 1 is provided near one end of the bottom thereof with a spout 2 communicating with a throat 3 of the sieve bend, generally indicated at 4. The throat 3 is defined by a fixed, sloping wall 5 tangentially leading into the uper end of the curved screening deck 6 of the sieve bend 4 and by a movable wall comprising a resilient rubber plate 7, in such a way that the wall-5 and the plate 7 converge downwardly towards the sieve bend 4. In order to take advantage of the increased efficiency provided by the flexible plate 7 and more smoothly tangentially transfer the influent particle containing liquid to the screening deck 6, the wall 5 is preferably set at an angle in the range of 60 to from horizontal.

Instead of being made of rubber, the plate 7 may alternately be made of other tough, flexible wear resistant material such as synthetic plastic sheet material. By preference, the upper edge of the plate 7 is clamped at an angle to the vertical, although a hinged attachment is also within the purview of the invention. The plate 7 effectively ensures that liquid and solid particles which might otherwise detach themselves from the layer flowing along wall 5 will be tangentially supplied to the screening deck 6. Furthermore the generally rectangular throat end at the lower end of the fixed sloping wall 5 and the lower end of the plate 7 will always adjust itself to the minimum area which will pass the influent particle containing liquid owing to the resilience of the plate material. The just mentioned feeding throat never being unnecessarily wide, the liquid will always be supplied in a direction more nearly tangential to the screening deck than was heretofore practicable thus promoting a more even wear of the deck and more effective separation of the particles by size. As the rubber plate 7 is deflectable, obstruction of the feeding throat by coarse particles contained in the material supplied will not occur.

The screening deck 6 is preferably mounted so as to be reversible by turning it end for end to extend the life thereof. The underflow fraction of the sieve bend 4 which passes in laminae between the bars thereof is collected in a collecting reservoir 8, which is communicated freely with the atmosphere along an upper portion of a side thereof. The collected underflow fraction is discharged from the reservoir 8 through a suitable conduit (not shown). The overflow fraction of the sieve bend 4 carrying the larger diameter particles is discharged via the sloping overflow plate 9. The plate is preferably positioned at a delivery angle of about 30 from horizontal.

The bottom of the feeding launder 1 may slope towards the sieve bend at a small angle (a few degrees) in order to facilitate movement of the raw product therein. As illustrated, launder 1 including the spout 2 is suspended over the throat by means of a detachable connection shown including a plurality of relatively long bolts 10. By means of these bolts the launder 1 can be leveled to obtain a supply fiow which is properly distributed across the width of the spout. The bolts 10 additionally enable the chute to be adjusted vertically. The vertical distance between the opening 2 and the upper end of the screening surface 6 being adjusted empirically to ensure the desired screening effect. In practice, this distance may be about 0.5 meter.

If space limitations or other circumstances so demand, the launder may alternately be connected to the sieve bend installation the other way round as shown in PEG- URE 2. This can be done in a simple way by releasing the bolts 10, lifting the launder spout out of the throat and turning it through 180 in the horizontal plane with respect to the throat. The performance of the screening device according to the invention does not depend on the direction in which the material is supplied, because of the sloping wall 5 and the convergence and cross sectional area adaptability of the throat 3.

The walls of the launder, the spout 2, and the fixed sloping walls 5 and 9 are lined with wear-resistant material.

It should now be apparent that the screening apparatus of the invention just described effectively accomplishes all of the objects set forth hereinabove. However, inasmuch as the specific embodiment shown and described to illustrate the principles of the invention may be considerably modified without departing from these principles, the present invention should be understood as encompassing all modifications Within the spirit and scope of the following claims.

I claim:

1. In an apparatus for the wet-screening of solid particles comprising a sloping concavely curved sieve bend screening surface and a feeding device suprajacent said sieve bend an adapted to direct a downwardly falling layer of particle containing liquid tangentially onto said sieve bend, the improvement wherein said feeding device includes:

(a) means defining a throat comprising a fixed position sloping wall and a movable wall spaced outwardly from and sloping downwardly toward said fixed wall, said movable wall being composed of a plate of resilient flexible material fixedly clamped at the upper end thereof at a substantial angle to the vertical; and

(b) a feeding launder for receiving particle containing fluid, said launder being mounted above said throat, said launder having, a transversely elongated spout communicated thereto, said spout depending downwardly from said launder toward said throat.

2. Apparatus as set forth in claim 1 wherein the improvement further includes connector means on the apparatus for vertically adjusting said feeding launder with respect to said throat to provide means for empirically adjusting the separation provided by said sieve bend.

3. Apparatus as set forth in claim 1 wherein the sloping angle of said fixed position sloping wall is in the range of to to a horizontal plane.

4. Apparatus as set forth in claim 1, the improvement additionally, including an overflow plate leading tangentially from the lower extent of the sieve bend screening surface and positioned at an angle of about 30 to a horiozntal plane.

5. Apparatus as set forth in claim 1, the improvement additionally including an underflow collecting reservoir mounted beneath said curved sieve bend screening surface, said reservoir being communicated to the atmosphere.

6. Apparatus as set forth in claim 1 wherein the improvement further comprises connector means on the apparatus detachably mounting the feeding launder therefrom; said connecting means further allowing the rernounting of said feeding launder on said apparatus in a position rotated degrees in a horizontal plane from the predetachment position thereof.

References Cited UNITED STATES PATENTS 1,333,127 3/1920 Nall 209262 X 2,916,142 12/1959 Fontein 209274 2,995,245 8/1961 Titelboorn 209243 X 3,007,574 11/1961 DeKoning 209281 K 3,116,237 12/1963 Fontein et al. 209242 3,145,164- 8/1964 Jonkman 209254 FOREIGN PATENTS 128,815 7/1959 Russia. 566,362 4/ 1958 Belgium.

HARRY B. THORNTON, Primary Examiner. R. I-IALPER, Assistant Examiner.

Claims

1. IN APPARATUS FOR THE WET-SCREENING OF SOLID PARTICLES COMPRISING A SLOPING CONCAVELY CURVED SIEVE END SCREENING SURFACE AND FEEDING DEVICE SUPRAJECENT SAID SIEVE BEND AN ADAPTED TO DIRECT A DOWNWARDLY FALLING LAYER OF PARTICLE CONTAINING LIQUID TANGENTIALLY ONTO SAID SIEVE BEND, THE IMPROVEMENT WHEREIN SAID FEEDING DEVICE INCLUDES: (A) MEANS DEFINING A THROAT COMPRISING A FIXED POSITION SLOPING WALL AND A MOVABLE WALL SPACED OUTWARDLY FROM AND SLOPING DOWNWARDLY TOWARD SAID FIXED WALL, SAID MOVABLE WALL BEING COMPOSED OF A PLATE OF RESILIENT FLEXIBLE MATERIAL FIXEDLY CLAMPED AT THE UPPER END THEREOF AT A SUBSTANTIAL ANGLE TO THE VERTICAL; AND (B) A FEEDING LAUNDER FOR RECEIVING PARTICLE CONTAINING FLUID, SAID LAUNDER BEING MOUNTED ABOVE SAID THROAT, SAID LAUNDER HAVING A TRANSVERSELY ELONGATED SPOUT COMMUNICATED THERETO, SAID SPOUT DEPENDING DOWNWARDLY FROM SAID LAUNDER TOWARD SAID THROAT.