US2330542A - Dewatering of suspended solids - Google Patents

Description

Sept. 28, 1943- A. J. BARNEBL ET AL DEWATERING OF SUSPENDED SOLIDS Filed Dec. 26, 1940 3 Sheets-Sheet 2 SePf- 28, 1943 A. J. BARNEBI. ET Al. 2,330,542

DEWATERING 0F SUSPENDED SOLIDS Filed Dec. 26, 1940 5 Sheets-Sheet 5 Patented Sept. 28, 1943 DEWATERJNG F SUSPENDED August J. Barnebl, Chicago, Howard D. Grant, Flossmoor, and August C. Barnebl, Chicago, Ill., asslgnors to Swenson Evaporator Company, Harvey, Ill., a corporation of Illinois Application December 26, 1940, Serial No. 371,818

(Cl. 21u- 62) 3 Claims.

Our invention relates to the dewatering of suspended solids.

It will be shown and explained as employed to recover sand in a casting cleaning system wherein a high pressure blast of water and wet sand is used to remove adhering molding sand from the castings and to disintegrate cores and remove the core sand.

This application is a continuation in part of our co-pending application Serial No. 257,922 filed February 23, 1939.

'I'he principal object of the invention is to provide a process and apparatus which will effectively and economically dewater and dry the sand resulting from the blast, molds and cores so that such as may again be used for making molds and cores, as distinguished* from that sand which may again be diverted to the blast, will be reduced to a so-called bone dry condition (i. e., containing not in excess of 2% of moisture) which is generally considered to be the best condition for delivery to molders and core makers, or to those who,` by adding bonding material, prepare the sand for the molders and core makers.

Further to explain the aim of and results obtainable by our invention, a brief explanation of the environment will be helpful. pressure blast cleaning of castings, such for example as set forth in United States Letters Patent No. 2,200,587, granted May 14, 1940, is employed, what may be termed the waste product resulting therefrom is a water borne mixture or conglomeration made up largely of sand, but also containing nails, wire and other objects used to strengthen cores and molds, scale, clay used as a binder for the foundry sand, fines, coke and other coarse materials, such as gates and sprues. Various methods may be employed to separate the useful sand-i. e., proper particle size ranges-from the other solid materials and to clean it and remove the lines, but with such steps this invention has nothing to do. For the purpose of our invention it can be considered that proper treatment has been employed to provide a magma of water and sand particles of a known size distribution suitable for re-use in the making of molds and cores if only its moisture content can be reduced to the necessary minimum.

In practice, however, even after such treatment, the magma of water and sand is of a continuously varying concentration. This varying concentration is inherent to the blast cleaning because, although the proportions of wet When' a high sand and water of the blast can be regulated to a. nicety and kept substantially constant, the quantities of sand removed from castings and derived from core disintegration vary over a wide range. Thus, different castings have different amounts of sand adhering thereto and require different sizes of cores and, other things being equal, the amount of sand removed at the beginning of a cleaning operation is, in general, much more than that removed during the later stages of cleaning.

Experience demonstrated that this magma of ever varying concentration could not be satisfactorily dewatered and dried. No method and means were found which could satisfactorily remove the continuously varying amounts of water in proportion to sand to produce a sand of the necessary uniformity of dryness. Nor was it found possible continuously to remove varying quantities of excess moisture to produce a magma of a uniform concentration suitable for effective filtering.

In general, our invention contemplates the reduction of the variable concentration magma to a magma of a uniform concentration too great for effective filtering and then the addition of water to transform the uniformly too concentrated magma into a magma of uniformly less concentration suitable for effective filtering by what may be termed the bridging method. This method of filtering contemplates the employment of a filter medium with interstices for the passage of water which are larger than substantially all-or at least a substantial majority-of the suspended particles, the escape of an excess quantity of particles being prevented by their tendency, under proper conditions, to wedge and interlock into masses or groups which arch or bridge the openings and thereby arrest the movement not only of particles forming the bridges or arches, but also those particles coming behind. And. because of the somewhat loose or porous character of the deposit thus formed and of the reduction of the liability of particles becoming wedged in the interstices of the filter medium to blind it, moisture may be eiectively withdrawn from the magma.

In the drawings:

Fig. 1 is a somewhat diagrammatic view of equipment for practicing our invention in the recovery of mold and core sand:

Fig. 2 is an enlarged longitudinal vertical section through apparatus for preparing a variable concentration magma of sand and water for nltering and for filtering out and drying the sand;

Fig. 3 is an enlarged partial vertical section at a right angle to that of Fig. 2, showing more in detail the equipment for concentrating and then thinning the variable magma and delivering it to the filter;

Fig. 4 is a vertical section on the line'4-L4 of Fig. 2.

Referring iirst to Fig. 1, the broken lines indicate a typical high velocity water and sand blast casting cleaning system from which a portion of the resultant sand is dewatered and dried in accordance with our invention so that it may be returned to the foundry for re-use by the molders and core makers. The full lines show a typical embodiment of the apparatus for carrying out our invention.

In the utilization of our invention for re-claiming the mold and core sand, the variable concentration magma of water and sand originates at the casting cleaning location 5 where the castings are freed from adhering mold sand and cores and the cores are disintegrated by means of .a high pressure stream of water and wet sand projected at high velocity from one or more guns 6. The wet sand is supplied to the gun from a sump 1 and the high pressure water is supplied to the gun from a suitable source 8. For further details of such a casting cleaning system, reference may be had to the previously mentioned Patent No. 2,200,587. The floor of the cleaning room may be sloped to a grated drain 9 through which all but the largest of the solid materials removed from the castings may flow to a screening device i which is designed to remove such objects as nails, Wire and other solid accessories commonly employed to strengthen molds and cores and also sand particles and agglomerates of adhering particles which are larger than desired for re-use in making molds and cores. The good sand, water, fines and other materials which flow through the screen are passed to a classified Il where, by the action of upwardly directed Water currents, the more buoyant fines, clay and soluble materials may be segregated from the good sand particles and flowed off through a spillway Up to this point, which involves no part of our invention, the resultant magma of good sand and water, although it has been largely freed from what may be generally termed impurities, is of a constantly varying concentration because of the very nature of its inception at the cleaning room as hereinbefore explained. It is such a variable concentration magma that, before the advent of our invention, deiied efforts at effective and rapid dewatering and drying to the degree required for ie-use in the making of molds and cores.

We have found, however, that this variable magma may be satisfactorily treated for recovery of good sand at the proper dryness by iirst concentrating the magma to a substantially uniform concentration too great for satisfactory filtering, and then by the addition of a substantially uniform volume of Water, to lower the concentration of the resultant magma to a substantially uniform concentration such as is satisfactory for fiowing to the filter medium and filtering. And we have found that filtering can be most effectively carried out by a rotary-drum type filter in which the interstices through the filter medium are somewhat larger than substantially allstead of passing through the openings in the filtermedium, wedge together and interlock into masses or groups which arch or bridge across the openings and thereby prevent in large measure the free passage of particles through the lter medium. We have found that the deposit or filter cake built up in this manner is suiciently loose or porous to permit effective dewatering and drying and the filling of the interstices or blinding of the filter medium is reduced to a degree such that filtering may continuously proceed over long intervals of time.

or at least a substantial majority-of the sus- Now to a detailed description of equipment for producing the magma of uniform concentration su-itable for filtering by the bridging method and for filtering it by that method.

The variable concentration magma which is too thin is flowed or pumped from the sand classifier Il to a settling tank l of the decanter type. In the decanter there is a gravity concentration of sand at the bottom, which may be and in the practice of our invention is carried to the point where .the concentration at the bottom approaches the upper limit of viscous flow and is uniform, and an overflow at the top of excess water and the less buoyant fines which the classifier has not removed. 'I'he magma of this concentration is too viscous either for proper now to and distribution over the surface of the filter, or for the production of the most effective bridging action over or across the interstices of the lter medium. However, by the addition of water in proper quantity and at a uniform rate to the too concentrated magma in the region of its emergence from the bottom of the decanter, the concentration may be lowered and the flow accelerated so that by means of an elongated chute I6, a magma of substantially constant con-- centration may be uniformly fed to and distributed over the surface of the drum l1 of the rotary filter IB.

At the filter, which in general maybe of conventional drum type, the magma is dewatered by means of suction provided by a vacuum pump I9 acting in the usual manner with a Water trap and through a vacuum line 2| connected to the customary distributing chamber of the filter at the trunnion of the filter drum. Trap 2U may be provided with a barometric leg 22 and a sump 23. Drying of the sand is completed by hot gases which are produced in a mechanically stoked furnace 24 and forced into the lter housing through a duct 25 by a blower 26.

Referring particularly to Figs. 2 and 3, the equipment for concentrating the variable magma into a magma of uniform but too great concentration and for then uniformly thinningit and applying the magma of uniform and proper concentration to the lter drum will now be described.

The settling tank or decanter l5 has a hopper bottom in which-the sand particles may be settled. The variable magma iiows in from the classifier Il through an inlet 3l. The sand settles into the hopper bottom 3D and the excess Water, carrying with it only fines and lighter smaller particles. flows over a launder 32 and out through an overiow 33. Undue turbulence caused by the inowing magma may be obviated and proper settling of sand particles facilitated by a baiile 34 in the vicinity of inlet 3|. In such a decanter the sand will settle to the bottom of the hopper forming there a magma the concentration of which is uniform and near the upper limit of viscous ow. Its concentration is therefore too great for eective delivery Ito a filter and filtration.

The next step is to dilute this uniformly too concentrated magma by the introduction of water continuously as the magma -iiows out lof a series of spouts 35 projecting from the lower end of the hopper bottom of the decanter. Dilution to the concentration for proper flow, distribution and bridging action are accomplished by a series of water Jets supplied through a nozzle 38 in each spout 35. Nozzles 36 are connected to a. source 31'of water under pressure and preferably each is equipped with an independent control valve 38. The lower ends of spouts 35 are equipped with suitable reduction connections 39 to each of which is fitted a relatively smallapertured nozzle 40. Because the concentration of the sand precipitate at the bottom of the decanter I is substantially constant and the water projected through nozzles 36 can be regulated in amount and maintained substantially constant, the concentration of the magma discharged from nozzles 40 can be regulated and maintained substantially uniform. The result is that there can be deposited upon the sloping floor 4| of the elongated chute I6 a uniformly concentrated magma of the desired consistency for filtration. The consistency or concentration and the rate of discharge can be controlled by regulating the Water Jets and by changing the bores of the magma discharge nozzles 40 which, for this purpose, are preferably made readily removable for substitution.

The uniformly concentrated magma flows down the chute I8 onto the perforated surface 42 of the drum l1 of the rotary filter I8 through a slot 43 in the filter housing. 'Ihe direction of drum rotation is indicated by the arrows and a dam 45, tipped if desired with rubber wipers 5B, may be provided to guard against flow of the magma down the periphery of the drum in the reverse direction. A baiiie 51 may be used to level down to a uniform thickness the magma as deposited upon the drums filter surface.

In a foundry producing medium size steel casting, the core and molding sand recovery has been satisfactorily carried out with a uniform concentration at the discharge from the settling tank at about BB1/3% of water by weight.

The perforated filter surface or filter medium of drum l1 is of metal, having holes-preferably circular-therethrough to provide a mesh with interstices slightly larger than substantially allor at least a substantial majority-of the sand particles of the magma flowed thereon from chute IB-that is the particles which by screening and classification have been retained for recovery. At the magma of water and sand particles, of proper known size distribution and at a uniform consistency or concentration only slightly above the limit of viscous flow, spreads out uniformly upon the moving surface of the, filters rotary drum and is subjected to the suction existing upon the interior of the drum, the particles seeking the places where the suction effects are most pronouncedi. e., the holes in the filter medium-tend to crowd together and approach the holes in groups. Such crowding results in particles becoming wedged together around and across the holes in bridges or arches which not only prevents particles constituting arches from reaching the holes, but sets up a porous barrier against particles arriving later. 'I'he consequence is that particles do not become wedged in the interstices of the filter medium,

because they are too small, andneither do they pass through in objectionable amounts because the bridging or arching eectively obstructs most of them. Thus the filter is not clogged or blinded for reasonably long periods of timeperiods long enough for feasible commercial operation-and a uniformly porous cake through which the suction may effectively operate for de watering is accumulated upon the drums periphery. Therefore, the dewatering starts promptly after the magma is deposited on the drum and progresses rapidly as the cake travels around inside of the 'llter housing. Most of the water is withdrawn by suction, which has been found to be the least expensive method of 'water removal from sand down to something like 7% moisture by weight, and the remainder, sumcient to reduce the moisture content to as low as 2% by weight, may be removed by evaporation by the blast of hot gases from furnace 24. These gases completely encircle the drum and are sucked through the sand-filter cake upon the drum because of the suction applied to the interior of the drum. The outer layers of sand dry faster than inner layers and consequently in order progressively to remove the outer dryer layers, a series of Scrapers 60 may be provided. They are arranged so that in the direction of rotation each scraper has its active edge closer to the filter medium' surface than does the one behind. The dried sand removed progressively by the scrapers falls into the hopper bottom of the filter where it may be fed out through an outlet chute 62 by a feed screw 63 (drive not shown) which serves to convey the sand to the outlet where it may be deposited upon a conveyor belt 64 for return to the molding and core room' or to storage. It is advisable to locate the conveyor-or it may be a delivery platform-close enough to the chute 62 to enable the sand flow to accumulate to a suicient extent to block the lower end of the chute suiiiciently to prevent excess air flowing therethrough under the influence of the hot gas blast supplied` to the filter housv ing by blower 26.

Although we have directed our explanation to the treatment of foundry sand, it will be apparent that the invention is applicable to the dewatering and drying of solid particles from varying concentration magma of other varieties.

Having thus described the nature and a typical embodimentof our invention, what we claim and desire to secure by United States Letters Patent is as follows:

1. The method of dewatering a variable con- A centration magma of water and insoluble granular solid particles for the recovery of the solids, comprising continuously passing the variable concentration magma to a settling region and there permitting the solids to collect to provide a magma of substantially uniform concentration greater than desired for filtration and withdrawing excess water continuously from above the concentrated magma, continuously withdrawing the too highly concentrated magma from the settling region and adding to such magma water at a uniform rate in sufllcient quantity to produce a uniformly concentrated magma of the concentration desired for filtration, and passing the resultant mixture to a filter.

2. 'I'he method of dewatering a variable concentration magma of liquid and insoluble granular solid particles for the recovery of the solids by means of a filter in which the passage of particles through the lter medium is prevented by bridging action between particles, characterized by the steps of continuously passing the variable concentrated magma to a settling region, there settling the solids at the bottom to form a magma of substantially uniform concentration greater than that which will afford proper ow, withdrawing excess water continuously from above the concentrated magma, withdrawing the too concentrated magma from the settling region and adding thereto Water at a uniform rate and in amount sufcient to pro duce a uniformly concentrated magma of the concentration which will afford proper flow` and bridging action between particles, and passing the resultant mixture to the lter.

3. The method of preparing for filtration to recover the solids therefrom a varyingly concentrated liquid suspension of granular solid particles, the lterlng being of the type wherein the passage of particles through the lter medium is prevented by bridging action among particles, characterized by the steps of continuously passing the variably concentrated suspension to a settling region and there settling the solids to a concentration which is essentially uniform but too high to ow properly to the lter medium and removing excess liquid continuously from the settling region, and withdrawing the excessively concentrated mixture from the settling region and adding thereto liquid at a uniform rate and in amount sumcient to produce a. uniform concentration which will afford proper flow to the lter medium and there produce the desired bridging action between particles.

AUGUST J. BARNEBL. HOWARD D. GRANT. AUGUST C. BARNEBL.

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