US3458046A - Screening elements for high speed screening machines - Google Patents

Description

July 29, 1969 R. c. PAS$AVANT 3,458,046

SCREENING ELEMENTS FOR HIGH SPEED SCREENING MACHINES Filed April 10, 1967 N [72 0622 Z01 1? uddU J CPa/SSavan/Z 5 6 7M 9* {MM 5%- United States Patent 3,458,046 SCREENING ELEMENTS FOR HIGH SPEED SCREENING MACHINES Rudolf C. Passavant, Michelbach, Germany, asslgnor to Passavant-Werke, near Michelbach, Nassau, Germany, a cor oration of Germany P Filed Apr. 10, 1967, Ser. No. 638,681

Int. Cl. E02b 5/08 US. Cl. 210-160 Claims ABSTRACT OF THE DISCLOSURE A screening element for a high speed moving band type liquid screening machine. The screemng element is curved and extends outwardly into the stream of unscreened liquid from its operating position on the screen machine. A portion of its extending surface comprises a solid wall to resist recirculation of screened liquid back into the unscreened portion of liquid, as it moves therethrough, thus increasing the screen efficiency.

The invention relates to screening elements for drum or belt screening machines for cleaning fluids such as waste or sewage-containing water and, in particular, to screening elements including improved structure for more effectively removing or screening the waste from the water.

The screening elements of prior art screemng machines generally have a triangular, trapeze-shaped, seml-clrcular or bell-shaped section, and such screening elements are arranged to move upwardly through the water head. One or only a few separate screening elements are needed to cover the total drum width or belt length.

An object of this invention is to provide an improved and more efficient screening machine without modifying the basic surface frame or design of the screen elements of known machines.

Prior art screening machines deliver satisfactory flow rates at low or average screening belt speeds; however, when the drum or belt in prior art machines is operated at higher speeds, the flow rate does not increase in the theoretically expected proportion.

Accordingly, it is another object of the invention to provide screening elements having a portion constructed with a solid wall to thus effect a more eflicient screening operation.

In prior art screening elements, because of differential pressures effective on opposite sides of the screening elements, backflows occur along sections of the screening elements. Accordingly, some of the already screened and cleaned water will flow or return through the screen to the waste-containing water, thus reducing the flow rate. Also, clean water which backflows through the screen flushes part of the waste already accumulated at the screen surfaces back into the waste water.

Accordingly, it is another object of the present invention to provide a screening element constructed with a solid wall along a portion thereof to eliminate the effect of differential pressures on the screen to prevent backflow.

It is another object of the present invention to provide a screening machine wherein the screening elements are operable at a higher rate of speed than the known screening machines.

3,458,046 Patented July 29, 1969 'ice In the present invention the screening surface available for the liquid flow remains relatively large in spite of the fact that a portion of what previously has been a screening surface is now a solid wall. This advantage is obtained since the prevention of backflow compensates for any loss in the area of the screening surface.

Thus, screening machines according to the invention, and particularly when operated at high rates of speed, are superior to prior art screening machines as regards their flow rate, even though the prior art machines of equal size are provided with a large theoretical screening surface than the screening machines according to the invention.

The invention further discloses a modification of the screening elements which protrude or extend from the surface of the screen supporting frame in a direction upstream of the direction of flow.

Accordingly, it is a further object of the present invention to provide a screening element having the intake side protruding upstream and having the downstream side connected to a supporting frame having a portion of the screening elements constructed as a solid wall. The solid wall surfaces have little effect on the total screening efficiency, provided the operation is maintained at other than low speeds.

The screening elements according to the invention are further improved to be, in cross section or profile to the shape of, about one-half of the tear-shape. The screening elements are constructed such that the steeper part of the element, i.e. the oval part of the tear-shape or the outline part, is substantially perpendicular to the direction of movement of the screening element. The foregoing construction is utilized when the protruding portion is downstream of the screen frame. It has also been found advantageous to construct the screening elements to have the steeper portion in the opposite direction with respect to movement of the screening element, when the protruding portion is upstream of the screen frame. The tear-shaped design also reduces the pressure differentials on the two sides of the screening element, without substantially reducing the size of the screening surface. The backfiow developed when using the teardrop design is greatly reduced, as compared to backflow developed when using screening elements of conventional crosssectional design.

Also, in accordance with the invention the steeper parts of the teardrop are constructed as a solid wall. Any backflow which might otherwise tend to be developed cannot become effective, so that the total remaining tear-shape curved screening surface is available for screening without the destructive influence through backflows.

Other screening elements with different cross-sectional designs can have solid wall parts formed thereon, as separately or individually determined according to the water pressures formed in the particular system.

Accordingly, it is a further object of the invention to provide a screening element for screening machines which is operable to move the associated screening-band at a speed of 12 cm./ sec. At such speeds the full advantages of the individual are utilized.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawlngs.

FIG. 1 is a cross-sectional view of a basket band screening machine according to the invention.

FIG. 2 is a cross-sectional view of a modification of a basket band screening machine according to the invention.

FIG. 3 is a cross-sectional view of a drum screening machine according to the invention.

Referring to FIG. 1, semi-circular shaped screening elements 2 and 3 are mounted on a screen supporting frame 1 of a basket band screening machine. Screening tissue or material of any suitable known type, not numbered, covers the screening elements 2 and 3. The individual elements 2 and 3 of the screen supporting frame 1 are flexibly connected between each other by means of a flexible coupling 4, and are moved upwardly (as oriented in the figures) in the direction of the arrow 5. The water level 6 to the right (as oriented in FIG. 1) of the wastecontaining water is higher than the water level 7 of the cleaned water to the left (as oriented in FIG. 1) of the screening machine; the flow of water through the screen is in the direction of the arrow 8. The water is cleaned as it passes through the screen and the waste matter, indicated by the numeral 9, accumulates as a layer on the upstream side or inside surface of the screening elements 2 and 3. As is known, the higher pressure on the intake side of the screening elements 2 and 3 relative to the downstream side thereof causes the water to flow through the screening elements. It has been found that the passage of water through the screening elements 2 and 3 causes a low pressure zone to be formed along a portion of the screening elements on the intake or upstream side of the screening elements which tends to cause water to backfiow or flow through the screening elements in a relatively opposite direction.

While backfiow may not present a problem if the screen movement is at a low rate of speed, rapid screen movement may give rise to turbulences which interfere with the pollution or waste accumulation.

To eliminate the effects of backfiow, the top parts 10 and 11 of the screening elements 2 and 3 are constructed with a solid wall. When the screening elements 2 and 3 pass through the clean water, a water pressure occurs accordingly, as indicated by the arrows 14. If the portion of the screening element 3 on which the water pressure occurs, indicated by the arrows 14, were to be covered with screening tissue or material, a backfiow of clean water, as described above, would result and the accumulation of a layer of waste on this part of the screening element would not be permitted. Thus, when part 10 is constructed as a solid wall, there is no change in the waste accumulation. Further, the elimination of a backfiow of clean water increases the theoretical screening capacity.

At the bottom side of the screening elements 2 and 3 a low pressure zone is formed in the area labeled 15, and depicted by the stippled area, which actually encourages the screening effect. At higher screening speed, however, turbulences can occur in area 15, which may cause a decrease of the flow rate. When this is the case, the lower part 15 of the screening elements 2 and 3 can be partially constructed as a solid wall.

In the modification of the invention shown in FIG. 2, the teardrop-shaped screening elements 2, 3 of the screening band machine both protrude in the direction of flow; that is, downstream from the screen frame 1'. The flow of water passes through in the direction of the arrow 8. The screening elements 2' and 3 are moved through the water layers 6' and 7 in the direction of the arrow 5. As mentioned, the screening elements 2 and 3 are provided with a cross-sectional or profile shape which corresponds more or less with one-half of the outline of a teardrop. In the embodiment shown, the steeper (relative to the direction of movement) or oval parts 16 and 17 of the teardrop are formed in the front or in the direction of movement of the screening elements. These steeper parts 16 and 17 are constructed with a solid wall while the flatter parts 18 and 19 of the screening elements are provided with screening tissue. The teardrop shape of the screening elements will reduce the turbulence along parts 18 and 19. The flow direction 8' is about perpendicular to the parts 18 and 19 of the screening elements 2 and 3 covered with screening tissue. The latter is desirable because the fiow resistance will then be at a minimum. Further, the differential pressure along the parts 16 and 17 of the screening elements 2 and 3 is ineffective and unable to cause a backfiow, because here, as with the structure of FIG. 1, the screen parts 16 and 17 are constructed with a solid wall.

In the embodiment of FIG. 3 the water flows through the screening elements 2" and 3" of a drum screening machine in a relatively opposite direction to that shown in FIGS. 1 and 2, as indicated by the arrow 8". The waste water level which in this case is to the left of the screening elements 2" and 3" (as oriented in FIG. 3) is indicated by the numeral 6"; and, the clean water level is indicated by the numeral 7". In this embodiment the high pressure provided by the water level 6" tends to cause the water flow to be in the direction indicated by the arrow 8". The solid wall parts 18' and 19' of the screening elements are here provided at the back of the screening elements with respect to the direction of movement 5". These parts 18 and 19' are relatively steeper with respect to the direction of movement. The waste collecting parts 16 and 17' which are relatively flat with respect to the direction of movement are covered with screening tissue and provide a large surface through which water can flow to thereby enable the movement of the screening element to tend to increase the flow speed. Note that the direction of water flow, indicated by numeral 8, is also about perpendicular to the parts 16' and 17 covered with screening tissue.

As mentioned above, little or no waste tends to accumulate along parts 18 and 19, since a backfiow from the inside of the screening element is prevented. Accordingly, in the present invention the screening elements are constructed to have a solid wall along the parts labeled 18' and 19' to avoid a backfiow of water for purposes described above.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A screening element for a high speed multiple screening element band or drum screening machine of the type used for cleaning waste water and other waste containing liquid flowing through said screening element wherein,

(a) said screening element has end portions and an intermediate portion and is formed in a curvilinear shape, the ends of said screening element being positioned adjacent an associated supporting frame, and the intermediate portion of said screening element protruding outwardly from the supporting frame;

(b) said screening element is arranged to move in a direction transverse to the water stream to screen the waste water passing therethrough to clean said water; and

(c) a substantial part of said screening element is constructed with a solid wall exposed to the flow of water to prevent unwanted backfiow through said element due to the shape and movement of said element.

2. A screening element as in claim 1 wherein the front part of said screening element, relative to the direction of movement of said screening element, is constructed with a solid wall.

3. A screening element as in claim 1 wherein the crosssectional shape of said element is a semi-circle.

4. A screening element as in claim 1 wherein the screening element protrudes downstream from said frame.

5. A screening element as in claim 1 wherein the cross-sectional shape of said element corresponds to about one half of a tear-shape.

6. A screening element as in claim 1 wherein the screening machine is movable at a screening band or screening drum circumferential speed of over 12 cm./sec.

7. A screening element as in claim 4 wherein said element has its steeper part, relative to the direction of movement of said element, of the teardrop-shape in the front thereof relative to the direction of movement of said screening element.

8. A screening element as in claim 4 wherein the screening element protrudes in a direction opposite the direction of flow and wherein the cross-sectional shape is such that the steeper part of the teardrop-shape is in References Cited UNITED STATES PATENTS 1,799,299 4/1931 Johnston 2l0-400 2,804,209 8/1957 Carlton et al 210-160 X REUBEN FRIEDMAN, Primary Examiner FRANK A. SPEAR, JR., Assistant Examiner US. Cl. X.R. 210-330, 400, 402

Images