US2383045A - Method and apparatus for sand reclamation - Google Patents

Description

A. DEN BR Aug. 21, 1945.

EEJEN ETAL 2,383,045

METHOD AND APPARATUS FOR SAND RECLAMATION Filed March 30, 1942 WATEE 6. FIN ES Patented Aug. 2l, 1945 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR SAND REULAMATION poration of Illinois Application March 30, 1942, Serial No. 438,760

8 Claims. (Cl. 22-89) The present invention relates to a method for reclaiming or cleaning sand and to apparatus for carrying out this method. More particularly, the present invention is concerned with the provision of a. method and suitable apparatus for cleaning and otherwise reclaiming used foundry sand, particularly foundry core sand, so as to make this sand suitable for use in forming new foundry molds.

It is common foundry practice to use what is known as core sand for making cores for interior and exterior surfaces. This core sand usually consists of a mixture of sand and any one of several green binding agents which retain the sand in place until the core is baked and a binding agent which gives the core strength and rigidity after baking and during the pouring operation. The binding agent most frequently used for the latter purpose is core oil, although cement or pitch or other materials are sometimes employed.

A typical core may be formed by mixing proper proportions of sand. core oil and a green binder, molding the material to the desired shape and then baking the core to oxidize the core oil After the baking step, the core thus made and used has considerable strength and should adequately resist damage until it can be used and further should resist the hydrostatic head and the erosive action of the flowing metal poured into the mold.

Shortly after the metal has started to set, the heat from the molten metal accomplishes a burning of the core oil i'llm sufficiently to permit easy disintegration of the cores'. ThusI after the metal has solidiiled and the mold is broken open, the core sand should flow out of the mold in a more or less granulated form. Core sand containing a core oil residue is black after the pouringv operation and is composed largely of sand grains, each of which is substantially completely coated with a deposit consisting of carbon and partially carbonized core oil. This deposit adheres to the sand grains with great tenacity and renders the sand practically useless for further use in the formation of foundry cores, since cores formed fromsuch sand will have little strength.

In the past, the problem of reclaiming core sand for reuse has received considerable attention, but so far as we know, no attempts to reclaim foundry core sand have been commercially successful.

Since, under ordinary conditions, core sand can be used but once as such, it will be appreciated that the cost of new sand, together with the freight charges on this new sand, are a considerable item in the cost oi' castings. In addition, the used core sand must be removed from the foundry and frequently must be hauled a considerable distance to a. dump. In fact, in many of the larger foundries, several freight carloads of used sand must be hauled from the foundry te a dump each day and several carioads of new sand must be brought in to take its place.

When cement, pitch, or other core binding agents are used instead of core oil, the problem is substantially the same in that because the used sand grains are covered with a tenacious substance which renders the sand unfit for further use, it must be discarded and replaced by new sand.

It is one of the objects of the present invention to provide a. novel method and suitable apparatus for treating used foundry core sand so that the sand after treatment is Suitable for use in forming new core and synthetic molding sand.

A further object of the present invention is to provide a novel method and apparatus fortreating used foundry sand in such a manner that the treated sand will normally form mold parts of greater :strength than mold parts formed from new sand.

Still another object of the present invention is to provide a novel method and apparatus for cleaning sand which provides clean send et extremely low cost.

Yet another object of the present invention is to provide a novel method and apparatus for removing tenacious surfsce deposits from sand grains in a commercially feasible manner and at low cost.

Yet another obiect of the present invention is to provide a novel method and apparatus for cleaning sand which eliminates the necessity for iarse foundry sand"dumps and, in addition, permits foundries to reclaim discarded sand already placed in dumps.

Still another object is to provide a novel method and apparatus for treating sand to fulfill the above objectives continuously rather than in batches.

Other objects and advantages will become apparent from the following description of a preferred embodiment of our invention taken in con- Junction with the accompanying drawing in which:

Fig. 1 is a diagrammatic representation of suitable apparatus for performing the present invention: and

Fig. 2 is an end view of a roller which forms a.

portion oi' the apparatus used in performing the present invention.

At the upper portion of Fig. 1 in the drawing will be seen a hopper lli which serves as a receptacle in which the used foundry sand is placed. This receptacle is comprised of a bin or tank of adequate capacity to contain the sand to be treated. If desired, it can be comparatively small. in which case itwill necessarily have to be filled continuously during operation of the process, or it can be comparatively large and can be illled at less frequent intervals. The sides of the hopper at its lower portion are inclined inwardly at i2, so as to provide sloping side walls to guide the sand toward an outlet opening near the bottom at the point indicated by the numeral I4.

The sand to be treated is placed in the hopper l and is Well covered with water if it is not already wet, so that the spaces between the sand grains are substantially completely taken up by the water. Such a mixture flows with diiliculty and therefore the wet sand is fed from the hopper I0 through the opening indicated by the numeral I4 and down a chute I5 by means of water jets not shown but located opposite the openings at I4. Ihese jets are fed through a pipe line I8 and the velocity of the water through these jets can be controlled by a valve 2D connected in this pipe line. Since the use of Water jets for the purpose of causing sand or like material to ow through a passage is Well known, no detailed description of these jets need be given here.

'I'he mixture of sand and water ilows down the chute i6 and upon a dehydrating shaker screen 22. The screen 22 normally is considerably longer than it is wide and is inclined so as to have the end which receives the sand and water mixture from the chute IB higher than its opposite end. This screen is kept in constant vibration during operation of the process so as bo cause the wet or damp sand to move over its surface toward its lowenend. Since the use of vibrating mechanisms for generally similar purposes is well known. no special description of this vibrating apparatus need be given. We have found, however, that a vibrating mechanism which gives a frequency of aproximately 3300 cycles per minute of comparatively short amplitute is suilcient for this purpose.

The rapid vibration of the screen, together with its downhill slope, causes the sand grains to move toward the discharge end, while a large portion of the Water mixed with the sand runs through the screen thereby materially reducing the moisture content of the sand before it is discharged from the lower end of the screen. We have found that with such an arrangement as Just described, the water content of the sand and water mixture can be reduced to approximately 16 to 18 per cent by weight. Such a mixture of sand and water will neither ow as a liquid nor will it now as does dry sand, but it can be caused to move over a vibratory screen in the manner described.

In general, the mesh of the screen 22 should be suiflciently small to retain the major portion of the sand grains upon its upper surface. It is not advisable. however, to make it sumciently small to retain al1 of the fines that it ls desired t0 include in the nal sand mixture, since a screen of this degree of fineness does not easily permit the flow of water therethrough because of the capillary action of the water.

Since the water which flows through the screen contains a portion of the fines which are desired to be included in the final sand mixture. this water is collected from beneath the screen in a large funnel 24 and is passed downwardly through a chute 26 to a sump 28 from which it is pumped through a pipe 3l) by means of a centrifugal type pump 32 or suitable apparatus back into the hopper I 0. Thus the usable fines are not lost from the system. It should be appreciated that only a comparatively small portion of the fines pass through the screen 22 and have to be returned to the hopper l0. At least per cent of the nes ordinarily will stick to the larger sand particles and be carried over the surface of the screen 22 and will be discharged directly with the larger particles from the lower end of the screen.

The sand dehydrated to aproximately 16 to 18 per cent moisture will slide substantially continuously from the lower end of the screen 22 and will fall into a sharply downwardly sloped chute 34, the lower of which empties into a rotating barrel 36.

In one embodiment of our invention which is adapted for cleaning sand upon a comparatively small scale, that is. at the rate of approximately two tons per hour, the previously described screen 22 is approximately 18 inches wide and 48 inches long, while the barrel 36 is approximately 5 feet long and 30 inches in diameter.

This barrel 36 is mounted to rotate about a slightly downwardly inclined axis upon anged rollers 38 which engage tracks 4l) secured to the exterior surface of the barrel. This barrel is driven by means of a motor 42 through a speed reducing gear box 46 and chain 4B, the chain 48 engaging a sprocket 50 attached to the exterior surface of the barrel. In the embodiment shown which is adapted to have the cleaning capacity previously mentioned, we have found that the barrel works efhciently in a manner to be described, when rotated at a speed of from 20 to 60 revolutions per minute.

Both ends of the barrel are partially enclosed by caps 52, each of which has an opening in the center. Thus, sand will be continuously discharged from the discharge end of the barrel so long as the barrel rotates and so long as sand is fed into the inlet end of the barrel. It will be appreciated, however, that the barrel will always contain a quantity of sand suilcient to cover the lower portion of the interior of the barrel to a, substantial depth.

Within this barrel we have placed a generally cylindrical roller |54 which can be formed of a length of heavy steel pipe with a plurality of longitudinally extending generally rectangular ribs 56 `welded to its external surface. As the drum rotates, the roller 54 will rotate therein because gravitational forces acting upon the roller 54 tend to maintain it in general toward the bottom portion of the barrel. In the embodiment of the invention shown, this roller is approximately 54 inches long, is 9 inches in diameter, the ends are closed, and it is weighted with shot so as to have a weight of approximately 500 pounds.

As the barrel Il rotates, the sand will be tumbled therein and tend to remain in the lower portion of the barrel, while the roller 5I continuously rolls through the sand. The weight of the roller should lbe so adjusted that it will sink into the sand a considerable distance, but the roller should not be so heavy that `it cuts clear through the sand and touches the inner surface of the barrel. It appears that the roller causes the sand grains to be ground against each other under considerable pressure. This interaction between the sand grains when under pressure completely breaks loose and removes all surface deposit from the sand grains excepting for the negligible portion of the surface deposit which is located in deep pits in some of the individual grains where it is not touched by other moving grains.

We have found that for the above beneficial inter-action to take place between the sand grains, several factors are of importance. In the first place, as has been mentioned, the roller should sink well into the sand but should not touch the surface of the barrel. In the second place, the water content of the sand should be suiilciently low so that the sand does not act` as a liquid. We have found, for instance, that a good scrubbing or mulling action does not take place if the water content of the sand is greater than approximately 2G per cent. On the other hand. if the water content of the sand is lower than approximately 5 per cent, the sand grains are not efficiently cleaned. In general, it may be said that the water content shouldbe between the 1mits of 20 per cent moisture and 5 per cent moisture by Weight. The speed of rotation of the drum should be suiiicient to bring about a good tumbling action and should be fast enough so that time is not wasted by permitting the sand to remain in the barrel longer than necessary. n the other hand, the speed of rotation must kept well below centrifuging speeds as otherwise the water in the sand will tend to migrate toward the axis of rotation, with the result that the sand and water mixture within the drum is no longer 'of a homogeneous consistency. As mentioned previously, for a barrel of the size given, a speed of 20 to 60 revolutions per minute is satisfactory.

In place of the single roller I, several smaller rollers may be used and if desired, these rollers, or the roller 5I can be coated with rubber. The use of rubber does not appear to affect the rate of sand cleaning to any considerable extent, but does under some conditions seem to have less tendency to crack the grains, also, rubber coated rollers operate more quietly and wear more slowly than steel or iron rollers.

The well mulled mixture of sand, water, carbon particles, and other foreign substances issues from the barrel in a comparatively constant stream and falls into a hopper 58. At this point in the process the mixture is black and has a gritty paste-like consistency. 'I'he above is true if the ycore sand was oil bonded. If cement was used as a bonding agent, the mixture will be grey instead oi' black.

Water is added to the mixture in the hopper 58 through a pipe line 6B and the slurry thus formed is pumped by means of a centrifugal type pump 62 or other suitable device, to a spreader flume 6I of a counterfiow classifier, indicated generally by the numeral B8.

This sand classier comprises the before-mentioned spreader flume 6l which causes the incoming material to be distributed evenly over the surface of a hopper 6B. This hopper in turn discharges at its lower end into one or more tapered discharge tubes Til. The openings at the lower ends of these tubes in turn discharge materia-l into a hopper 12. Annular rings Il are arranged at the lower ends of the tubes 10 to direct jets of water from a pipe line Hi upwardly into these tubesand the amount of water flowing through these jets can be regulated by valves 1B. The water from the jets flows upwardly continuously through the sand in the classifier and carries with it the soluble materials. buoyant carbon particles, cement, and other refuse materials mixed with the sand. These more buoyant particles are carried to the surface at the upper portion of the classifier and overflow into a spillway 80 which leads to a sludge settling tank 82. The openings at the lower ends of the tubes lll are so proportioned that the flow of sand and water therethrough is somewhat less than the i'low of material into the classifier, thus a substantially constant rate of overow of water and buoyant material into the splllway 80 is assured.

The water and sand mixture discharged from the classifier into the storage hopper I2 is substantially free of all carbon particles and other refuse material mulled from the sand grains in the barrel 38. This sand and water mixture is then pumped by means of a centrifugal pump B4 or its equivalent to wherever it is to be dried for re-use.

Although the described apparatus includes the pipe line and the pump 32 for carrying back into the tank IB the fines that pass through the screen 22, it will be appreciated that this portion of the apparatus may be dispensed with if the user of the process is willing to add to the reclaimed sand a small amount of fines to take the place of this lost material. It will be appreciated further that the addition of the necessary small amount of lines to take the place of this lost material will be relatively inexpensive, since only a small ptrtion of the fines is lost through the screen 22 inasmuch as the major portion adheres to the larger sand particles and therefore is carried over screen 22 with these particles. It is apparent, therefore. that whether or not the fines are to be reclaimed from the water passing down the chute 26 is largely a matter of choice to be made by the process user. In general. a comparatively large installation would probably include the necessary apparatus to recover these lines, whereas in a small installation the slight expense of the lost fines might not justify the additional cost` of the necessary apparatus for reclaiming this srnall amount of material.

The process and apparatus described are capable of cleaning and reclaiming sand continuously rather than in batches and this feature has an important advantage not readily preceivable on rst impression. This advantage arises from the fact that a sand and water mixture is an extremely difficult material to handle efficiently, unless it contains sufficient water to flow readily. I! it contains sufficient water and the sand is in a substantially homogeneous suspension, the mixture can be pumped, or flowed cr otherwise treated as a liquid as long as itis kept in continuous rapid motion. In a continuous process, such as above described. such continuous rapid motion is feasible. In batch processes in which the sand and water mixture must stop flowing periodically, the sand settles out of the water and fouls the system whenever the flow ceases or decreases below a critical point. The result is that if a sand and water mixture handling system does not operate continuously, complicated conveyor systems are needed, since such a mixture cannot be treated as a liquid. It should be noted that in the system of the present invention, the sand is rapidly and continuously pumped or flowed from place 1o placa` as a liquid, excepting during the dewatering step, the mulling step, and the transfer step located between the dewatering and mulling steps. Such an arrangement would not be feasible excepting in a continuous process.

The following is a typical example of the effectiveness of this process and the apparatus shown for carrying out the process. All ilgures were arrived at by performing standard tests upon standard core parts constructed and tested in the manner recommended by the American Foundrymens Association.

A typical core in a typical foundry was found to be formed of new Manistee sand four parts and new Juniata sand one part. Test cores were made in the standard manner from this new sand in which the mixture consisted of the following: 12,000 grams new Manistee sand, 3000 grams Juniata sand, 232,5 grams linseed oil, and 600 c.c. water. This mixture had a ilowability as arrived at on the standard American Foundrymen's Association flowability meter of 88. Cores made from this material had a permeability when tested on the American Foundrymens Association recommended permeability test apparatus of 119. Five sample cores were made of this material and baked. ano1 when tested for tensile strength showed the following readings on the American Foundrymen's Association tensile testing apparatus: 43.7, 44.6, 47.7, 42.0, 45.4 or an average of 44.7. Since this tensile figure is to be multiplied by live to give the actual tensile strength, the average tensile strength of these cores proved to be 223,5 pounds per square inch.

Sand was then taken from the heap of used sand in this foundry and was treated by the before-mentioned process. This sand was then mixed for test purposes as follows: 15,000 grams of reclaimed sand, 232.5 grams linseed oil, and G cubic centimeters of water. That is, it was mixed in the proportions used for the new sand. The ilowability of this mixture was 89, or slightly better than the flowability of the mixture made from new sand. The permeability of the test core was 119, or exactly the same as the core made from new sand. Five standard cores for the determination of tensile strength were then made and these cores gave the following readings on the tensile test machine: 49.3, 45.7, 46.0, 46.5, 48.3, or an average of 47.2. When this latter gure is multiplied by ilve. it gives the tensile strength of cores made from reclaimed sand as 236 pounds per square inch, which is materially better than the 223.5 pounds per square inch obtained when new sand was used.

It is probable that sand reclaimed by the present process gives cores of greater strength than cores made from new sand because all new sand includes small amounts of impurities, such as vegetable matter, which weaken the cores made from this sand, whereas the present sand cleaning process removes these foreign substances. It has been found, for instance, that new sand treated by the present process gives approximately the same test results as used foundry sand which has been reclaimed by this process.

From the foregoing, it will be appreciated that the present process and the apparatus for carrying out this process are material advances in the foundry art and that this process and the described apparatus fulfill all the objectives set forth for this invention at an earlier portion of this specification.

Having described our invention, what we claim as new and useful and desire to secure by Letters Patent of the United States is:

l. Th'e method of reclaiming used foundry sand made up principally of said grains coated with burned binding material which comprises mixing the sand to be treated with water to form a ilowable mixture, passing the flowable mixture over a screen to reduce the moisture content of the mixture to between 20 per cent and 5 per cent water by weight, mulling the resulting damp mixture so as to cause relative movement between the individual grains, and exerting a force upon the sand during the mulling step so as to cause the relatively moving sand grains to scrub each other.

2. 'Ihe method of reclaiming used foundry sand made up principally of sand grains coated with burned binding material which comprises mixing the sand with water to form a ilowable slurry, dewatering said slurry to reduce the water content of the sand and water mixture to such a point that the resulting mixture is mushy in consistency, collecting the water removed from the mixture in the dewatering step. said water including a portion of the ne material originally mixed with the sand to be treated. reclaiming at least the heavier solid particles from the collected water and remixing these particles with additional sand to be treated, mulling the dewatered sand mixture so as to cause relative movement between the individual sand grains, and exerting a force upon the sand during the mulling step so as to cause the relatively moving sand grains to scrub each other.

3. A device for reclaiming used foundry sand comprising means to store a quantity of the sand to be treated mixed with water, a dewatering screen, means to transfer the sand and water mixture from the storage means to the dewatering screen at a comparatively constant rate, means to cause the sand and a portion of the water mixed therewith to pass over said screen, means to collect the material passing through said screen, means to transfer at least the major portion of the larger solid particles collected by the last said means to the storage means, a rotating barrel having inlet and outlet openings, means to introduce the material passed over said screen into the inlet opening of said barrel, a roller positioned within said barrel and adapted to rotate freely therein, said roller being of considerably smaller diameter than the internal diameter of the barrel, said roller being so weighted that it sinks well into the sand in said barrel, but being insufciently weighted to bring it into contact with theinner surface of said barrel, means to rotate said barrel, and means to collect the material passing out of the outlet opening of said barrel.

4. A device for reclaiming used foundry sand comprising means to store a quantity of sand to be treated mixed with water, a dewatering screen, means to transfer the sand and water mixture from the storage means to the dewatering screen at a comparatively constant rate, means to cause the sand and a portion of the water mixed therewith to pass over said screen, a rotating barrel having inlet and outlet openings, means to introduce the material passed over said screen into the inlet opening of said barrel. a roller positioned within said barrel and adapted to rotate freely therewith, said roller being of considerably smaller diameter than the internal diameter of the barrel, said roller being so weighted that it sinks well into the sand in said barrel, but being insuiilciently Weighted to bring it into contact with the inner surface of said barrel, means to rotate said barrel, and means to collect the material passing out of the outlet opening of said barrel.

5. A device for reclaiming used foundry sand comprising means to store a quantity of sand to be treated mixed with water, a dewatering screen, means to transfer the sand and water mixture from the storage means to the dewatering screen at a comparatively constant rate, means to cause the sand and a portion of the water mixed therewith to pass over said screen, a mulling device having an inlet and an outlet, means to introduce the material passed over said screen into the inlet of said mulling device, means in said mulling device periodically to compact the material therein during the mulling operation, and means to collect the material passed out of the outlet of said mulling device.

6. A device for reclaiming used foundry sand comprising means to store a quantity of the sand to be treated mixed with water. a dewatering screen, means to transfer the sand and water mixture from the storage means to the dewatering screen at a comparatively constant rate, means to cause the sand and a portion of the water mixed therewith to pass over said screen, means to collect the material passing through said screen, means to transfer atleast the major portion of the larger solid particles collected by the last said means to the storage means, a mulling device having an inlet and an outlet, means to introduce the material passed over said screen into the inlet of said mulling device, means in said mulling device periodically to compact the material therein during the mulling operation, and means to collect the material passing out of the outlet of said mulling device.

7.- A device for reclaiming used foundry sand comprising means to mix sand to be treated with water to form a lowable mixture, dewatering means receiving the flowable mixture from the mixing means to remove a portion of the water therefrom and to leave the mixture mushy in consistency, a rotating barrel having inlet and outlet openings, means to introduce the mushy mixture from the dewatering device into the inlet opening, a roller in the barrel adapted to rotate freely therein, the roller being of substantially smaller diameter than the barrel and so weighted that it sinks well into the mixture in the barrel but insuilciently weighted to bring it into contact with the inner surface of the barrel, and means to rotate the barrel.

8. The method of reclaiming used foundry sand made up principally of sand grains coated with burned binding material which comprises mixing the sand to be treated with water to form a owable mixture, dewatering the mixture while in a flowing stream to reduce the moisture content of the mixture to between 20 per cent and 5 per cent water by weight, mulling the resulting damp mixture so as to cause relative movement between the individual grains, and exerting a force upon the sand during the mulling step so as to cause the relatively moving sand grains to scrub each other.

ADRIAN DEN BREEJEN. ROY LUCE.

JASPER JAMES AMARI. DANIEL H. PETTY. RONALD Waas ne. TOWNER K. WE i TER, JR.

CERTIFICATE 0F CORRECTION.

Patent No. 2,565,0li5.

August 2l, 19145.

ADRIAN DEN BREEJEN, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page ZQseeond column, line 19, after "lower" insert the word end; page li, first column, line 16, for "252,5" read 252.5; line '?5,'claim l, for "said" and second column, line il, same claim, before "screen" insert and that the said letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office signed and sealed this 25th day of December, A. D. 19li5.

(Seal) Leslie Frazer First -Assistant. Commissioner oi Patents.

material passing out of the outlet opening of said barrel.

5. A device for reclaiming used foundry sand comprising means to store a quantity of sand to be treated mixed with water, a dewatering screen, means to transfer the sand and water mixture from the storage means to the dewatering screen at a comparatively constant rate, means to cause the sand and a portion of the water mixed therewith to pass over said screen, a mulling device having an inlet and an outlet, means to introduce the material passed over said screen into the inlet of said mulling device, means in said mulling device periodically to compact the material therein during the mulling operation, and means to collect the material passed out of the outlet of said mulling device.

6. A device for reclaiming used foundry sand comprising means to store a quantity of the sand to be treated mixed with water. a dewatering screen, means to transfer the sand and water mixture from the storage means to the dewatering screen at a comparatively constant rate, means to cause the sand and a portion of the water mixed therewith to pass over said screen, means to collect the material passing through said screen, means to transfer atleast the major portion of the larger solid particles collected by the last said means to the storage means, a mulling device having an inlet and an outlet, means to introduce the material passed over said screen into the inlet of said mulling device, means in said mulling device periodically to compact the material therein during the mulling operation, and means to collect the material passing out of the outlet of said mulling device.

7.- A device for reclaiming used foundry sand comprising means to mix sand to be treated with water to form a lowable mixture, dewatering means receiving the flowable mixture from the mixing means to remove a portion of the water therefrom and to leave the mixture mushy in consistency, a rotating barrel having inlet and outlet openings, means to introduce the mushy mixture from the dewatering device into the inlet opening, a roller in the barrel adapted to rotate freely therein, the roller being of substantially smaller diameter than the barrel and so weighted that it sinks well into the mixture in the barrel but insuilciently weighted to bring it into contact with the inner surface of the barrel, and means to rotate the barrel.

8. The method of reclaiming used foundry sand made up principally of sand grains coated with burned binding material which comprises mixing the sand to be treated with water to form a owable mixture, dewatering the mixture while in a flowing stream to reduce the moisture content of the mixture to between 20 per cent and 5 per cent water by weight, mulling the resulting damp mixture so as to cause relative movement between the individual grains, and exerting a force upon the sand during the mulling step so as to cause the relatively moving sand grains to scrub each other.

ADRIAN DEN BREEJEN. ROY LUCE.

JASPER JAMES AMARI. DANIEL H. PETTY. RONALD Waas ne. TOWNER K. WE i TER, JR.

CERTIFICATE 0F CORRECTION.

Patent No. 2,565,0li5.

August 2l, 19145.

ADRIAN DEN BREEJEN, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page ZQseeond column, line 19, after "lower" insert the word end; page li, first column, line 16, for "252,5" read 252.5; line '?5,'claim l, for "said" and second column, line il, same claim, before "screen" insert and that the said letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office signed and sealed this 25th day of December, A. D. 19li5.

(Seal) Leslie Frazer First -Assistant. Commissioner oi Patents.

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