US2237043A - Method of manufacturing oxidized lead powder - Google Patents

Description

H. D. WILSON April 1, 1941,

METHOD OF MANUFACTURINQ OXIDIZED LEAD POWDER 1 Filed Oct. 23, 1936 2 Sheets-Sheet l N Inventor, HARLAND D. WILSON April 1, 1941. H n wlLsoN 2,237,043

METHOD OF MANUFACTURINQ OXIDIZED LEAD POWDER Filed Oct. 23, 1936 2 Sheets-Sheet 2 f2" l.l

Y r IO N u N a S l Inventor: HARLAND D. W/LSON Attofneu.

Patented Apr. 1, 1941 METHOD OF MANUFACTURING OXIDIZED LEAD POWDER Harland D. Wilson, Indianapolis, Ind., assignor to Prest-O-Lite Storage Battery Corporation, Speedway, Indianapolis, Ind., a corporation of Indiana Application October 23, 1936, Serial No. 107,2Q5

4 Claims.

My present invention relates to a continuous process of manufacturing oxidized or partially oxidized lead powder, and more particularly to a process in which lead pieces are subjected to attrition by rumbling them in a rotatable vessel or mill in the presence of a controlled current of air or other oxidizing gas and under controlled temperature conditions.

In carrying out such a process, the product is obtained by first forming a brittle coating of oxide on the surfaces of the metallic lead pieces by bringing the current of air or other oxidizing gas into contact with the metallic lead pieces at an elevated temperature. The coating thus formed is abraded off in the form of an extremely fine powder, either by attrition of the lead pieces or by the rubbing action of the interior surface of the rotating vessel with that portion of the lead mass with which it is in contact. Thus new surfaces of metallic lead are being continually exposed to the action of the oxidizing agent, and, in turn, will be oxidized and abraded. The product thus formed may be removed from the mill by the current of oxidizing gas or by any other suitable means.

The frictional heat produced within the mill, plus the heat liberated by the oxidation reaction, will be more than sufficient to maintain the interior mill temperature at the desired elevated value without the addition of heat from external sources.

I have found that in practice the process may be carried out more efiiciently, and a more nearly uniform product obtained by maintaining the interior mill temperature constant and at as high a value as is possible without causing the lead pieces to melt.

In processes heretofore used (as, for example, that disclosed in U. S. Patent No. 1,584,150 issued May 11, 1926, to Genzo Shimadzu) it has been proposed to control the temperature within the mill by varying the speed of the mill, the amount of oxidizing gas passing through the mill, or the amount of charge in the mill. In practice, however, it has been found desirable to maintain the mill speed and the volume of air constant, with the result that temperature control has been effected solely by varying the amount of charge. However, because of the period of time required for a variation in the amount of charge in the mill to effect a change of temperature Within the mill, this method has not been entirely satisfactory. Also, the efiiciency of the process has been somewhat impaired, by reason of the. fact that in order to lower the mill temperature it has been necessary to reduce the amount of charge, thus reducing the area of the lead surface available for oxidation.

One object of my invention is to provide a process of the type referred to above in which the temperature within the mill, including the temperature of the lead masses undergoing attrition, may be controlled within narrow limits by a novel method and without the necessity of varying the operating conditions of the mill.

A further object of my invention is to provide an improved method of the foregoing type having a greater opera-ting efficiency and producing a greater yield of product than similar processes heretofore used.

Another object of my invention is to provide a method of producing an oxidized lead powder of a more nearly uniform character than has heretofore been possible.

A further object of my invention is to provide an improved method of producing oxidized lead powder by the attrition process which is independent of changes in climatic conditions to a greater degree than processes heretofore used.

A further object of my invention is to provide a novel'apparatus for carrying out the herein described method.

Other objects, features and advantages will be apparent as the description proceeds.

I have discovered that by impinging directly upon the rumbling pieces of lead-a small but continuous supply of water, a substantially larger quantity of lead pieces may be rumbled in the rotatable vessel with the result that a substantially larger output per unit of time may be secured without a corresponding increase in temperature such as would result if no water were used. Further, I have discovered that the mill temperature is rapidly responsive to changes in the volume of water so supplied, a slight increase in the amount of water will cause the temperature to drop, and conversely, a slight decrease will cause the temperature to rise. By means of this very sensitive method of temperature control, any tendency of the mill temperature to vary from the desired operating temperature can be readily and rapidly compensated for, and the temperature maintained constant within very narrow limits, the time lag between variations in water supply and their eifect upon the temperature being of the order of two to three minutes, as compared with a lag of the order of twenty to thirty minutes where temperature control is effected by varying the amount of charge. In addition to the greater yield mentioned above, the

elimination of temperature variations results in a more nearly uniform product. As a practical illustration, I have found that the normal charge for a mill of the type disclosed in U. S. Patent No. 1,896,020, issued January 31, 19.33, to Genzo Shimadzu, having a diameter of about four and one-half feet and a length of six feet, and through which air is being passed at the rate of about 470 cubic feet per minute, is about 4,000 pounds.

temperature of the mill will normally be about Under these conditions the interior 410 F. However, by supplying small quantities of water in the manner set forth above, I have found that the amount of the charge may be increased to approximately 5,200 pounds without a resulting increase in temperature. At the same time, the quantity of oxide produced per day increased from 16,000 pounds to 20,000 pounds of product having substantially the same physical and chemical characteristics.

The quantity of water which is appropriate to be introduced is very small in comparison with the effect obtained, being of the order of magnitude of 100 to 600 cubic centimeters per minute for a charge" of 5,200 pounds. Best results are obtained by impinging the water upon the tumbling charge at a number of different points so that contact of the water with the charge is not confined to a single locality within the vessel. Small tubes discharging in different zones are a suitable means of introduction.

The amount of water required for smooth operation'will vary from time to time, so that it is essential to provide a means of securing variations in the rate of flow in accordance with practical requirements. The moisture content of the air is considerably greater at some times than at others, for example, on rainy days. It is also considerably greater during thesummer than during the winter.

The exact manner in which a small amount of water impinging upon the charge in the rotating vessel efiects such a remarkable increase in efficiency of ODEIHJtlOIl'Of an oxide producing unit, or" serves as such an extremely sensitive temperature regulator, is not fully understood". It may be that the effect is partially one of catalysis. Or it maybe that the eifect resides in the concentration of water vapor per unit volume of space within the reaction vessel. When atmospheric air enters such a vessel, it quickly becomes expanded due to the elevated temperature ofthe charge, and due to this expansion the moisture density per unit volume becomes considerably lower than in atmospheric air at roomtemperature. Experience has shown that operation of the oxide producing process becomes unsatisfactory when the moisture content of the air reach'es'unusually low concentrations as, for example, in very cold winter weather; It may be, therefore, that the function of water impinged upon the charge is to increase the moisture density per unit volume in the zone of reaction to a more efficient concentration. It is also possible that one function of introduced water is the absorption of heat at the point Where heat is liberated by friction and oxidation, the effectiveness of water in this respect being due to its large latent heat of vaporization as well as'to its relatively high specific' heat.

In the annexed drawings, wherein I haveillustrated suitable apparatus for carrying out my process; 7 Y j t Figure 1 is a'. side elevational' view partly in Section of an attrition mill;

Figure 2 is a sectional view of an air nozzle taken through the line 2-2 of Figure 1;

Figure 3 is a schematic illustration of a complete installation for carrying out my improved method, and

Figure 4 is a sectional view taken on the line 4-4 of Figure 3. I

Referring to the drawings, reference numeral l-ll designates generally an attrition mill, preferably cylindrical in form, which is rotatably mounted by means of hollow trunnions H and I2 which are supported by bearings I3 mounted on foundations M. The means for causing rotation of the mill are not illustrated as they form no part of this invention, it being understood that any suitable means may be employed for that purpose. Lead lumps or balls are fed continuously by suitable feeding mechanism 15 to a screw conveyor l6 which in turn delivers them to the interior of mill I0. Air is supplied to a header l1 positioned axially of the mill by means of a blower I8. Jets or nozzles [9 leading from the header direct a plurality of streams of air atthe lead masses 20. Outlet trunnion l2 communicates with a conduit 2| through which the escaping air passes to a cyclone separator 22, thence through conduit 23 to a dust collector 24. The dust free air is exhausted to the atmosphere through opening 25, preferably located above roof 2-6. The powder falls into drums 21 located below the cyclone and dust collector,

For the purpose of supplying water to the interior of the mill, I have provided conduits 28 connected with a source of supply of water (not shown). Said conduits enter through header H and terminate at a point adjacent the orifice of a nozzle 19 as shown in Figure 2. The quantity of Water passing into the mill is controlled by valves 29 and may be visibly ascertained by means of sight gauges 30. Although for purposes-of illustration, Ihave'shown but two water supply conduits, it is to be understood that, in practice-it is desirable to supply water to the lead massesat many points,.as, for example, through each nozzle.

In operation, the millll! isrotated to cause abrasion of the surfacesof. the lead pieces which have been oxidized by exposure to the air at an elevated temperature. The powder thus'formed is carried by the air current through trunnion H to the cyclone 22 where partial separation from the air is efiected. The powder remaining in the air is caught by dust coll'ecter 24 and falls into drum 21. New lead is continuously added to the mill by feedingmeans 15 through screw conveyor F6. The temperature of the mill is readily controlled by manipulation of valves 29) to increase or diminish the quantity of Water entering the mill. V

The advantages of my invention are now apparent. By the simple and economical expedient ofsupplying a small quantity of water to the lead masses in the reaction zone of the vessel, I have been able to greatly increase the efficiency of the process andto obtain a product, the uniformity of which may be more readily maintained. Also I'have completely divorced the matter of temperature control from the various other mill operating conditions, thereby permitting a more-j uniform year-round operation. I have found-that best results are obtained when the water, probably in the form of an atomized spray, is" applied directly to the surfaces of the lead masses, as by being carried by the air-streams passing through jets I9, altho any other satisfactory means for applying the water to the lead masses may be employed.

The term oxidized lead powder as used herein is intended to mean the product of the herein disclosed process which, when carried out in accordance with the preferred embodiment disclosed above, produces a product consisting essentially of an intimate mixture of extremely finely divided litharge (PbO) and metallic lead (Pb). A small percentage of finely divided suboxide of lead (PbzO) may be intermixed therewith. For storage battery purposes the desirable percentage oxidation, calculated as litharge, is 65%, but it will be readily understood that the degree of oxidation may be varied over a wide range by varying the operating conditions, such as the temperature, amount of air, speed of the mill, amount of charge, etc. The term partially oxidized lead powder as used herein is intended to mean a lead powder, some of the particles of which have been oxidized, but the total oxygen content of which is less than that of litharge.

The method and apparatus herein described are for purposes of illustration only, and are not intended to limit the scope of my invention. Many modifications will occur to those skilled in the art. It is my intention that this patent shall cover all such modifications as come within the scope of the appended claims.

Having thus fully described my invention, what I claim is:

1. The step in the method of manufacturing oxidized lead powder by the attrition process at a temperature above 212 degrees F. which consists in apply a plurality of small streams of water to the surfaces of the lead masses undergoing oxidation and abrasion to control the temperature thereof.

2. The method of manufacturing oxidized lead powder which consists in placing pieces of lead in a rotatable drum, rotating the drum, supplying an oxidizing gas to the drum to oxidize the surfaces of the lead pieces, abrading the oxide thus formed by attrition, applying water to the surfaces of the lead pieces, and controlling the temperature of the lead pieces by regulating the quantity of water so supplied, the temperature of said lead pieces being above the boiling point of the water.

3. The method of controlling the temperature of the interior of an attrition and oxidizing drum, said temperature exceeding 212 degrees F. which consists in introducing into the drum and onto the material undergoing oxidation and attrition a stream of water, and regulating the quantity

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