US3519130A

US3519130A - Apparatus for classifying of finegrained solids in wet condition

Info

Publication number: US3519130A
Application number: US667515A
Authority: US
Inventors: Waclaw Jachna
Original assignee: Individual
Current assignee: Individual
Priority date: 1966-09-21
Filing date: 1967-09-13
Publication date: 1970-07-07
Anticipated expiration: 1987-07-07
Also published as: NL141406B; NL6712888A; CS161833B2; SE325542B; NO120930B; GB1198835A; BE704168A; FR1553777A; DE1301226B

Description

y 7, 1970 w. JACHNA 3,519,130

APPARATUS FOR CLASSIFYING OF FINE-GRAINED souns IN WET CONDITION Filed Sept. 13, 1967 2 Sheets-Sheet 1 INVENTOR WACLAW J ACHNA BY W] mwwJiwwQfiu em we ATTORNEYS y 7, 1970 w JACHNA 3,519,130

APPARATUS FOR CLASSIFYING OF FINE-GRAINED SOLIDS IN WET CONDITION Filed Sept. 15, 1967 2 Sheets-Sheet 2 Fig.2

INVENTOR WAC. LAW T HNA W CL$UILJ& Mum,

ATZ'O/ZNEYS United States Patent US. Cl. 209-234- 5 Claims ABSTRACT OF THE DISCLOSURE Apparatus for classifying by size of fine-grained solid aggregates in wet condition using several sieves disposed one after the other, carried out in two or more steps and means for applying a washing liquid characterized in that material being classified in fluid or powdered state is supplied to the rotating ring of a washing liquid on the entire periphery thereof or on the part of this periphery in order to set this material in motion. Because of a centrifugal force the material being classified is readily mixed with a liquid and as a result of a comparatively great overspeed of a liquid mixed with solid particles the layer of this mixture is very thin which helps in drawing-off finest particles together with the liquid.

Classification of finest aggregates is especially diflicult, particularly in the case of aggregates containing grains being near colloidal size or being of fibrous character.

Many known methods of classifying solids have been proposed for the attainment of an increase in the accuracy of the classification. The most widely employed methods for this purpose are those employing the use of screens or sieves. In an attempt to increase the efficiency of the classification, partitioning of the sieve surface into three zones is proposed. The zones comprise a first zone for internal classification, a second zone for washing by using showers or sprays and a third zone for final classitfication. The drawback of this method consists in that the screens are usually heavy and the machines expensive.

On account of this fact, methods employing statical devices are more and more broadly used in this field. One of the first such methods employs a conical sieve known as Radialsiebanlage. The sieve used in this method is also divided into a plurality of zones in the same manner as the previously discussed device. The suspension is preliminarily deprived of liquid and finest grains in the upper part of the sieve and is then washed in the second zone on the conical surface of the sieve by means of showers or sprays.

Unfortunately, the devices for practicing this method and device do not have sufiicient accuracy of classification at full capacity of the apparatus. These inconveniences were mainly caused by the low speed of movement of the product to be classified.

The most modern and broadly propagated method of classification consists in using of an apparatus known as an arcuate sieve. In this case the partitioning of the apparatus into classification zones is impossible, as opposed to the above-discussed methods. However, this apparatus gives a low accuracy of classification although it has a great ability in drawing-off the liquid, together with finest particles, from the working surface unit. This imperfection in accuracy is caused by a low efiiciency in draining-off the liquid. For this reason the upper product from arcuate sieves is finally classified on Vibrating screens provided with showers in order to obtain an accurate classification. Another method in which arcuate sieves are used employs several arcuate sieves each of which is fed material at an equal rate.

It is possible to obtain a little more accurate classification by using sieves of the type shown and described of Polish Pats. Nos. 46,606 and 47,474. Sieves of the type shown in the forementioned Polish patents are generally referred to by those skilled in the art as being of the 080 type.

The degree of accuracy is defined, in one system of measurement, by the ratio of the 50% graduated grain to the graduated grain. The higher this ratio, the more efiicient the apparatus. For arcuate sieves, this ratio averages 0.55 and for sieves 080 this ratio is within the range of 0.6O .7.

The improvement of the classification index by the use of showers in 080 sieves provides only a slight efficiency increase as in the case of the use of such in Radialsiebanlage sieves or with arcuate sieves.

Furthermore, when using sieves 080 or Radialsiebanlage it is possible to divide the mixture into only two grain-classes. The division into more grain classes in the superposed or tandem system requires a second system sieve of the same type construction.

The classification accuracy on Raidialsiebanlage sieves, arcuate sieves and 080 sieves is also limited by the relatively high content of liquid in the upper product.

Moreover, in radial sieves of the type illustrated in German Pat. No. 800,223 and in arcuate sieves of the type shown in Polish Pat. No. 46,037, the flow of the mixture is parallel or nearly parallel to the surface of the sieve which causes the outflow of the liquid together with the dry product to take place when a flow disturbance occurs. On the other hand, in CS0 sieves, due to the change of the path of motion of the mixture fr m a direction perpendicular to the sieve surface to a paralllel direction with respect to the sieve surface, the change of the apparent width of the slit from 0.6 s into 1.0 s takes place, where s means the real width of the slit. This defect is also found in the device referred to as screen hydrocyclone in German Pat. No. 903,681.

This invention relates to apparatus for classifying finegrained solid aggregates in wet condition by the employment of a method using several sieves disposed one after the other. The inventive method is carried out in two or more steps and is characterized in that material being classified in fluid or powdered state is supplied to a rotating ring of washing liquid on the entire periphery of the ring in order to set the material in motion. The action of centrifugal force on the material being classified rapidly mixes the material with the wash liquid and as a result of a comparatively great overspeed of the liquid, the layer of liquid and solid particles is quite thin so that the fine grains are drained 01f with the liquid.

The product partially deprived of fine grains can then be reintroduced into the next rotating washing liquid stream and flows onto the sieve surface of the second stage where nearly all fine grains are carried off.

The apparatus for carrying out the method described above is represented on accompanying drawings, in which:

FIG. 1 is section of one embodiment of the apparatus according to the invention, in which sieves are disposed in series.

FIG. 2 is section of another embodiment of the apparatus according to the invention.

The apparatus of FIG. 1 for classifying according to the inventive method comprises one or more sieving stages of frustro conical form and with each conical sieve disposed upside down. In order to obtain an optimum separation of the liquid together with the finest solid particles, the conical sieving elements of the lowermost stage or of the individual stages, near their largest diameter or base portion in area 1 are made of profiled bars disposed in parallel to the generating line of the 3 conical sieve. Near the smaller diameter end or base they are provided with slits in area 2 disposed almost perpendicularly to the generating line of the conical sieve.

Experiments have proven that the liquid separated from the mixture on a conical sieve with slits parallel to the generating line in area 1 is kept between the bars forming the slits and is enabled to flow in a small quantity along said slits toward the top. Considerably greater amounts of liquid may flow out together with the solid particles in consequence of faults in the screen surface having bars being parallel to the generating line. Among the defects are numbered individual bars projecting above the surface of the sieve, or recesses at the places where the sieve elements are connected.

The employment in the process of this invention of conical sieves having their upper parts formed with slits extending nearly parallel to the generating line in area 1 and in the lower part of area 2 nearly perpendicular to the generating line provides the possibility of conveying to the filtrate together with the liquid remnants the finest particulate grains since the liquid dropping down can move only extremely slowly since it has to overcome the transverse slits in area 2. However, the mixture movement on the surface of the individual sieve stages in area 1 is in the form of a free vortex about a vertical axis. Movement of the mixture below the top of area 1 changes into a helical path and then in a lower portion into a radial flow path.

Owing to the fact that in its upper part the sieve is made of bars parallel to the generating line in area 1 and in its lower part of bars perpendicular to the generating line in area 2, the suspension passes the slits at a right or oblique angle which is advantageous in that it greatly lessens the possibility that the slits will become clogged.

The wearing rate of the lower sieve with openings perpendicular to the generating line will be unsymmetrical however, the small amount of centrifugal force and the low speed of motion of solid parts in this area causes the wearing rate to be smaller than that of the upper sieve having slits parallel to the generating line. For these reasons, the lower sector of the sieve in area 2 with slits perpendicular to the generating line gives smaller graduated grain than that from the upper sieve area 1 with parallel slits. This property can be put to a good use in various assemblies of sieve constructions.

In certain cases it may be of advantage or necessary to remove the finest grains from the feed prior to its introduction into the washing liquid. This occurs when according to the method of the present invention the mixture of solid parts contained in the liquid is to be divided. This is performed on the apparatus being described hereabove, but which is additionally provided with a sieve 12 with slits parallel to the generating line and mounted in a first stage guiding element or trough and also being provided with additional mixture inlets '11 for introducing the mixture to be classified.

To enable the sieve to be mounted and the rotational motion of the mixture to be maintained, the guiding element 4 is partitioned by means of a horizontal ring 10 into an upper part for the mixture to be classified, and into a lower part for the washing liquid.

In order to protect the apparatus against overcharging, the present invention includes a sieve 14 around the upper opening in a cover 13 of the first stage guiding element.

The apparatus of this invention for carrying out the accurate classification or for classifying the liquid feed into several grain classes with the use of a washing liquid, includes one or more sieving stages connected with one another by means of

circular troughs

3, 4 having one or more

tangential feedings elements

5 and 6 for feeding the washing liquid. An additional stage may be constituted by a circular trough 4 having uniform cross section and provided with a sieve 12 and by a tangential feeding element 11 for feeding the mixture 4 to be classified as Well as the washing liquid through inlet pipe 6.

Each washing liquid circular trough is provided with conical deflecting rings 8 and 9 which have only their lower portions illustrated for directing the material to be classified into a rotating liquid stream, and the Whole is placed in a housing constituting a collecting tank for the filtrate. The material can be fed from element 11 or in some cases may be gravity fed from a position above and axially in line with the axis or

conical rings

8 and 9.

The said collecting tank may be common for all screening stages or it may be inwardly positioned by horizontal and vertical ring shaped or cylindrical surfaces 15 into several separated tanks for collecting the filtrate from beneath the individual screening stages or from parts thereof.

The last-mentioned construction is of advantage in cases when the division of the feed into several classes of grains is required, because apart from the difference in the width of the slits, the size of the grains carried off can be influenced by creating in the individual tanks a defined pressure either above or below the atmospheric pressure.

The apparatus for accurate classification with washing liquid may also be adapted for superposed screening with or without washing liquid. In order to obtain such a system, the collecting tanks of the screening stages except the uppermost one, are connected to the outlet nozzle of the next above stage, in this case the collecting tanks constituting feeding and swelling reservoirs as shown in FIG. 2.

The superposed system is of great value due to the fact that it provides a classification accuracy degree which is higher than that obtained with a simple tandem system. The individual screening stages have of course to be provided with separate means for draining off the upper product.

An advantage of the screen arrangement shown in FIG. 2 consists, among others, by the inclusion of removable partitions 15 between the screen stages and outlets 18. After supplying to the inlets 19 of the second and subsequent stages of the mixture to be wet classified, a parallel work of a series of screen stages is obtained. Another advantage of this arrangement is the small area occupied by the equipment.

In order to facilitate the exchange and the change of position of worn out screening elements operating in a medium having a great corrosive power, such are connected with supporting structure, housing and circular troughs through a simple labyrinth system.

Said system is in principle sufficient to prevent grains of defined size to pass to the filtrate and the filtrate to the main product. To obtain a better tightness, a flexible sealing pad is located in the labyrinth trough and pressed down by the dead load of the screening element.

Taking advantage of the flexible pad supporting the screening element or using additional resilient supporting elements if necessary, it is possible to impart to the sieve an oscillating motion of small amplitude.

As it has been found in the course of tests, in case of classifying a mixture containing a considerable quantity of grains having a size approaching the width of the slits, clogging of slits may occur and make worse the classification results. In the present practice declogging of slits was performed by periodic hand hammering the surface of the sieve by means of a wooden or rubber hammer which required a continuous attendance and increased the Wearing rate of the sieve.

FIGS. 1 and 2 show an example of mounting a vibrating motor 20 for creating axial oscillations of the sieve elements. In case of sieve assemblies disposed in superposed, tandem or parallel system, one of several vibration drives may be used, making use of the idea shown in FIGS. 1 and 2.

An additional advantage of the use of a vibration drive is the increase of the rate of draining off the liquid and preventing the upper product to collect in the lower part of the sieve. The excitation of oscillations may be a continuous or a periodic one.

Having regard to the fact that different kinds of materials may be employed in the device, the virbation drives are adapted to change the amplitude of the excitation force and of its frequency as required by the dilferent materials.

Outlets 16 are provided in the embodiment of FIG. 2 for the purpose of discharging drained products in a manner analagous to the operation of outlets 16 in the FIG. 1 embodiment.

What is claimed is:

1. Apparatus for classifying by grain size friable material comprising an inverted conical sieve, a plurality of profiled bars disposed in a first area of said sieve adjacent the upper part thereof corresponding to the base of the conical geometric configuration of the sieve and oriented in parallel relationship to the generating line of the sieve so as to provide slots also oriented parallel to the generating line of the sieve, a second area of said sieve forming the lower portion thereof comprising bars essentially perpendicular to the generating line of the conical sieve and providing slots oriented essentially perpendicular to said generating line of the sieve, a circular trough oriented above the sieve and coaxial therewith, and a plurality of tangential fluid inlets providing means associated with said circular trough for providing a rotating ring of washing liquid in said circular trough for gravitationally receiving material to be classified and for subsequently gravitationally depositing said material and said washing liquid into the upper portion of said sieve for enabling classification of said material as to size.

2. The invention of claim 1 wherein a plurality of said sieves are positioned in axial vertical alignment with respect to each other with said sieves having different slot widths for providing varying classifications of materials so that material deposited from an upper conical sieve is subsequently fed into the trough of a lower conical sieve for subsequent depositing into said lower conical sieve.

3. The invention of claim 2 wherein each of said troughs comprises an outer peripheral wall and a downwardly inclined slanted floor portion.

4. The invention of claim 2 additionally including a conical deflecting ring having its base spaced inwardly adjacent said troughs for feeding friable material to each of said troughs.

5. The invention of claim 4additionally including a cylindrical sieve mounted above said conical sieve for receiving material injected radially inward through said cylindrical sieve for subsequent deposit on said conical member.

' References Cited UNITED STATES PATENTS 170,471 11/1875 Crocker 209397 X 527,860 10/1894 Kayser 209-304 1,774,644 9/1930 Gesnel 209-306 X 2,974,796 3/1961 Jung 209-300 X 2,998,137 8/1961 Vane 209-305 X 3,045,823 7/1962 Fontein 209274 X 3,061,098 10/1962 Brezinski 210304 X 3,247,965 4/ 1966 Braun 209-304 X 3,232,436 2/1966 Nilsson 210304 X FOREIGN PATENTS 546,647 4/ 1956 Belgium.

9 45,755 4/ 1962 Poland.

678,037 1/1964 Canada.

823,828 11/ 1959 Great Britain.

r FRANK W. LUTTER, Primary Examiner R. HALPER, Assistant Examiner US. Cl. X.R.