US2764359A - Treatment of liquid systems and apparatus therefor - Google Patents

Description

A. SZEGVARI Sept. 25, 1956 TREATMENT OF LIQUID SYSTEMS AND APPARATUS THEREFOR Filed May 24. 1950 5 Sheets-Sheet l I N V EN TOR. ANDREW 5256 V4)?/ Ffi ATTORNEY Sept. 25, 1956 szEGvAR: v 2,764,359

TREATMENT OF LIQUID SYSTEMS AND APPARATUS THEREFOR Filed May 24, 1950 3 Sheets-Sheet 2 IN V EN TOR.

ANDREW 52 56 mm m WM A T TORNE Y A. SZEGVARI Sept. 25, 1956 TREATMENT OF LIQUID SYSTEMS AND APPARATUS THEREFOR Eiled May 24 1950 3 Sheets-Sheet 3 INVEN TOR. ANDREW Sztamm United States Patent TREATMENT OF LIQUID SYSTEMS AND APPARATUS THEREFQR Andrew Szegvari, Akron, Ohio Application May 24, 1950, erial No. 163,837

11 Claims. (Cl. 241-15) The containing attritive or grinding elements, and agitating I means adapted to be moved through these elements.

In particular the process is carried out by bringing about an activated condition of the attritive elements characterized by at least a partial random distribution of their momentum. It is not necessary that themovement be entirely random, and in the preferred operation more particularly described herein there is a superimposed drift of the elements in a circular and axial direction. The average momentum of the elements at the point of contact is large enough to overcome the resistance of the particles to subdivision.

' The invention includes the grinding of solids to reduce their geometrical or physical particle size, the mixing of two or more different solids, and the suspension of one or more finely divided solids in a liquid.

The process and apparatus have particular value. in fine grinding, especially in the presence of a liquid. By fine grinding is meant grinding to a particle size smaller than 50 microns, and approaching and extending into the colloidal range; for instance as far as to an average particle size of 2 microns, or 0.5 micron, or less.

An attritor is a vessel which contains a large number of attritive elements which may be flint pebbles, balls of metal, etc. The attrition is produced by the movement of an agitator through the bulk of the attritive elements. The relation of the essential components of the apparatus and other processing details, in particular of the agitator to the mass of attritive elements is such that the movement of the agitator maintains a condition of relative unrest between the adjacent attritive elements through- 4 out the greater part of the mass of elements. There may be little or no movement around the edges and the bottom of the vessel, but the number of elements which are not maintained in continual motion is small. The movement of the elements is produced not only by contact with the agitator but the kinetic energy imparted to the elements contacted by the agitator is transmitted by them to adjacent elements, maintaining substantially the entire mass of the attritive elements in continual motion having a certain random distribution of the momentum of the contacted elements. Each of the activated elements repeatedly and continuously bounces from contact with one element into contact with another element and with the agitator, and remains in suspension in the system; The most efiicient operation is that in which the number of contacts or collisions between adjacent attritive 'elements leading to subdivision of the material being treated approaches, or reaches, the largest possible statistical probability.

The more rapid the movement of the agitator the larger the number of contacts. Furthermore, the'greater 'ice the amount of energy transmitted to the contacted elements, for subsequent transmission to adjacent elements, the larger the number of contacts. The grinding action to which this invention relates is dependent upon the contacting interaction between the attritive elements. The attrition between the elements and both the agitator shaft and the walls of the vessel is preferably minimized to prolong their life.

The number of contacts is dependent upon various other factors. For instance, the number of contacts depends upon the type of agitation and the nature of the movement of the-agitator. A very efiicient type of agitator for use in an upright cylindrical vessel is one formed of a central shaft and agitating arms. This is preferred for wet grinding. For dry grinding two such agitators may be used spaced farther apart than the length of the longest agitator arm, so that the agitator arms overlap.

It was found that under certain conditions the movement of the agitator arms through the body of attritive elements kinetically activates them and maintains such a condition. Kinetically activated by the agitating device, means to imp-art continuously sufficient mechanical energy to a large enough number of the elements so that a random distribution of the momentums coupled with an incipient free path develops. This condition is related to that underlying all natural phenomena based on behavior of a multitude of elements having mechanical energy as in the case with gas molecules in free space. The activated elements are kept out of static contact with one another and continually interact with one another, with resultant subdivision of the material which is being acted upon.

The creation of this activated condition of the attritive elements by the activating device, such as the agitator, is very significant and described in the following. It is very different from the action of the grinding elements in a ball mill which is the equipment which is most widely used for fine grinding at the present time. In the first place, the grinding elements used in equipment of the type here described are much smaller than those generally employed in a ball mill. This is advantageousbecause the smaller elements produce a larger number of grinding contacts or collisions than thesame volume of larger elements. In the second place, in a ball mill the grinding action is greater or as great at the inner surface of the mill as in any other place, whereas in the preferred equipment of this invention the maximum activity is concentrated away from the walls of the vessel and this prolongs the life of the vessel. The agitator transfers mechanical energy to the attritive elements and maintains a condition of activated motion and relative unrest between the adjacent elements throughout the greater part of the mass of the elements.

The activated condition of the elements and therefore the number of effective contacts between'the elements and their attritive action on the material to be ground, is dependent on the depth of the bed of the attritive elements, the specific gravity of the liquid if any be present, the speed of the agitator, the size of the attritive elements, the distribution of the size of these elements, the shape of these elements, and on the viscosity of the liquid.

The influence of the depth of the bed of the attritive elements is such that as the settling tendency is increased a larger momentum has to be transferred to the elements to keep them in an agitated state; this requires an increased speed of agitation. If the agitator must be o'perated at an optimum speed in any given vessel operating on a given material, the depth of the bed of attritive elements will have a practical optimum.

The specific gravity of the liquid counteracts the influence of depth; in other words, the higher the specific gravity of the liquid, the greater the depth of the bed of attritive elements that can be kept in an activated condition with the same R. P. M. of the agitator.

The R. P. M. of the agitator has a direct influence on the amount of mechanical energy which is transmitted to the attritive elements from the agitator arms. The higher the speed, the greater the energy transmitted, and the more effective the random distribution of momentum to the elements leading to attritive action. However, an increase in the R. P. M. of the agitator beyond a certain limit, increases the motion of the attritive elements without producing a corresponding increase in their random action and causes their impinging on the side of the tank with increased wearing action. The wearing of the tank depends on the clearance between the agitator arms and the side of the tank, thus this clearance has a direct relation to the most practical agitator speed.

As to the size of the grinding elements, the smaller these elements, the larger the fine grinding capacity of a given volume of the elements. It was found that the geometric probability factor of the number of effective contacts between the attritive elements and thus the fine grinding capacity of a given volume of attritive elements is inversely proportional with the square of the diameter of the attritive elements. However, a decrease in the size of the elements decreases the random momentum imparted by the agitator to the elements. This decreases the I attritive action on the material to be ground. While this can be counter-balanced by an increase in the R. P. M. of the agitator, the condition is such that there is an optimum size of the attritive elements which depends on the other conditions mentioned.

As to the distribution of size of these attritive elements, it is significant that they should be substantially uniform in. size with little deviation. One or a few larger elements mixed with smaller elements are not activated as much as the smaller elements, and prevent optimum performance. Likewise, they interfere with the free movement of the smaller elements and cause the whole bed to jam, leading to destructive action on the attritive components. Such larger elements also prevent maintenance of calculated clearance conditions between the ends of the agitator arms and the inner wall of the vessel.

As to the shape of the attritive elements, it is preferred that they have the same dimensions in all directions. If they are much larger in one direction than in the other, they will greatly interfere with the random distribution of the momentum imparted to the elements. Also, they will cause jamming of the attritive elements much as larger elements mixed with smaller elements cause it to jam. Non-uniformity in the size of the elements and the presence of elongated elements greatly reduce the maximum possible R. P. M. at which the agitator may be operated in a given machine. This reduces the output of any given equipment due to the decreased attritive action between the grinding elements far below what can be obtained under optimum conditions. It should be added here that the clearance between a rotating activating device and the walls of the vessel has a definite relationship to the controlling factors mentioned above; in other words, to obtain the optimum conditions, the clearance must be varied with changes in the speed of rotation. It should be increased for higher grinding speeds.

Finally, it should be added that the size of the material to be ground has an influence on the most efficient speed to be used in any set of conditions. If the size of this material is initially large, a certain minimum momentum of the attritive elements is required to subdivide it. This is larger than the minimum required for a starting material of smaller particle size. The space-time concentration of binary contacts (collisions) between attritive elements operating on materials of smaller particle size can be increased over that required for eflicient action on larger particles.

The attritive elements will ordinarily be no larger than inch in diameter. They will usually be larger than 7 inch in diameter, although smaller elements may be used in low viscosity liquids and possibly in other operations. For an attritor of small size, for example one having a capacity of one pint to one gallon, smaller grinding elements of A to A inch in diameter will ordinarily be employed, the size of the elements depending upon the size of the vessel. In commercial units having a capacity of 60, or gallons, elements i /2 or W inch in diameter will generally be used, the smaller units being employed with smaller vessels and the larger ones with the larger vessels.

The most efiicient depth for a bed of elements will depend upon the size of the elements, the R. P. M. of the agitator, and the difference between the specific gravity of the elements and the liquid in which they are immersed. For instance, in the case of a grinding tank 30 inches in diameter, using flint elements A inch in diameter, with the agitator operating at 65 R. P. M. in liquid with a specific gravity of 1.0, the most efficient depth for the bed of elements is 22 inches. Using similar equipment with a liquid having a specific gravity of 1.6, a bed 26 inches deep is most eflicient.

The speed of rotation of an agitator is dependent on its diameter, i. e., th length of its arms, because the longer the arms, the faster their ends move, and the greater the agitation produced. Thus, in a laboratory style attritor with agitator arm's 1 1 inch long (i. e., 2 /8 inches in diameter), elements inch in diameter are recommended and 350-450 R. P. M. will give etficient operation. In a production attritor containing elements inch in diameter with arms 13 inches long (i. 'e., 26 inches in diameter), 65 R. P. M. has been used.

Suflicient clearance should be provided between the ends of the agitator arms and the wall of the vessel. The amount of clearance required will vary with the speed of the agitator. At 60 R. P. M. a minimum distance equal to three element diameters is recommended if the elements are inch in diameter; therefore a clearance of 1 inches is recommended at the end of each arm. If the speed is 80 R. P. M. using the same size of grinding elements a clearance of five element diameters or 2 5 inches is recommended. Thus, in a vessel 36 inches in diameter, using elements W inches in diameter, operating at 60 R. P. M., agitator arms should be about 16% inches long. Operating at 80 R. P. M. in this vessel agitator arms of about 15%; inches will be recommended.

Although for most effic'ient operation, a vessel with a dished bottom might be recommended, from an engineering standpoint it is most practical to construct the vessel with a flat bottom. Usually a cylindrical wall will be provided. The agitator will be mounted such a distance above the bottom that there is no movement, or substantially no movement of the elements at the bottom of the bed. The bottom arm is preferably somewhat shorter than those above it. Those 'arms above the bottom arm will advantageously be arranged in pairs and spaced sufficiently to permit the liquid to pass between them. Such arrangement of the arms in pairs provides efiicient agitation with minimum hydrodynamic resistance. The resistance is much lower than that of an arm with a diameter equal to the combined diameter of the pair plus the space in between them. Such a large arm would also be expensive and heavy. Of the two arms in each pair, one is preferably located at a slight angle to the other so that "as the agitaator is rotated the arms produce a lifting tendency at the periphery of the tank which decreases to zero as the central shaft of the agitator is approached. Thus, the action of this agitator assists the natural tendency for the liquid in a rotating Cylindrical system to circulate outwards at the bottom, upwards at the sides, inwards at the top, and downwards at the center.

The maximum activity is concentrated away from the wall of the vessel to minimize wear. The elements adjacent the wall are subjected to minimum movement. The activity is greatest around the ends of the arms and decreases as the center of rotation is approached. To prevent excessive wear it is desirable to coat the arms with a very hard alloy, such as a tungsten alloy, etc.

The invention will be further described in connection with the drawings which show more particularly an attritor designed for use in production. It may have a capacity of, for example, 50 gallons to 100 or 150 gallons. An attritor for laboratory use may have as small a capacity as a pint and may have a capcity of a gallon or two. The smaller rattritors, whether for laboratory use or for production, may be constructed on a base plate which is designed to slide on rails. in the rails through which there is a rod which is fastened to each edge of the base plate it is possible not only to slide th vessel in and out from under agitator driving means, but by thus mounting the vessel it may be tilted readily when desired. The lateral relation of the vessel and base plate to the rails should be maintained constant so that when the vessel is slid under the agitation driving means the drive shaft and the agitator shaft are in lateral alignment.

Whether in a laboratory size attritor or a larger one for production use, the drive shaft is advantageously operated from a worm gear. This prevents manual rotation of the drive shaft. Manual rotation of the agitator shaft is also prevented by the resistance afforded by the presence of the attritive elements around the agitator blades. Therefore, the coupling means must be such as to permit union of the agitator shaft to the drive shaft regardless of the angular relation of the one to the other, or the angle of rotation at which the agitator is located in the vessel. For production equipment such coupling means must hold the agitator shaft to the drive shaft firmly enough to prevent slippage in spite of the fact that the rotation of the agitator must overcome the resistance afforded by the presence of the attritive elements.

In the drawings Fig. 1 is a front elevation, partly broken away, of the attritor;

Fig. 2 is a section on the line 2-2 of Fig. 1;

Fig. 3 is an enlarged detail of the clamping means taken on the line 3-3 of Fig. 1;

Fig. 4 is a detail showing the operation of the clamping means;

' Fig. 5 is a side view of the attritor with the vessel turned through an angle of 90;

Fig. 6 is a detail on the line 66 of Fig. 5 showing means for locking the attritor in an upright position;

Fig. 7 is a detail on the line 77 of Fig. 5 showing the screen clamping means;

Fig. 8 is an enlarged section of the outlet valve from the attritor;

Fig. 9 is a section on the line 99 of Fig. 8;

Figs. 10a, 10b, and 100 are elevations on the line 1010 of Fig. 8 showing the valve in open, partly open, and closed position, respectively; and

Fig. 11 is an exploded view showing the three essential parts of the valve, each partly broken away.

The drawing illustrates an 'attritor of the type which may be used to advantage in production, particularly for the dispersion of finely ground solid particles in a liquid. The vessel 1 provided with the jacket 2 is supported at each side on trunnions 3 and 4, which in turn are supported in hearings in the triangular side plates Sand 6 respectively. These side plates are in turn supported on grooved wheels 10 which are adapted to be rolled back andforth on :the'track 11. Thus the vessel 1 is mounted- By providing slots to be rolled back and forth on the track to bring the agitator under the drive means or to bring the vessel forward for dumping. A flexible conduit is fastened to the opening 13 to supply cold (or, if required, hot) water or other liquid to the cooling jacket 2 to provide tern.- perature control. The jacket may be drained through the valve-equipped hose 14 into the receiver shown, or to other suitable discharge means.

The agitator is formed of the central shaft 15 and the arms 16, 17, 18, 19 and MP. It is supported only by the coupling which holds it to the drive shaft 22. The motor 23 drives a worm gear (not shown) in the housing 24, which in turn rotates the shaft 22 in the diredtion indicated by the arrow in Fig. 2. The shaft 15 is clamped to it and driven by it. I

The four upper arms 17, 13, 19 and 20 are arranged in pairs. The lower arm of each pair is slightly forward of the upper arm so that when the agitator is rotated in the direction indicated by the arrow the arms tend to facilitate movement of any liquid in the attri tor upward around the outer surface of the vessel, then inward across the top of the vessel, downward around the shaft 15, and outward at the bottom. The space between the arms of each pair is not more than three element diameters. (For instance, using attritive elements /2 inch in diameter it will not be more than 1 /2 inches.) However, the space between the arms of each pair is such as to permit the flow of liquid between them together with any matter suspended in the liquid.

To facilitate circulation of the liquid in the vessel the attri to-r is equipped with a pump 39 driven by the motor 31. This draws off liquid from the top of the vessel through the intake pipe 32 and discharges it through the flexible conduit 33, back through the valve 34 into the vessel. During any grinding operation all of the liquiddrawn off through the intake pipe 32 is returned to the vessel through the conduit 33. Opposite the inlet 36 of the valve to which the conduit 33 is connected is a discharge opening 37 to which is connected a hose or other type of conduit (not shown). This latter conduit is provided with a valve and when the operation of attrition is completed, on opening this valve thecontents of the attritorare discharged into any suitable receptacle. Alternatively, the vessel may be discharged by being dumped, as illustrated in Fig. 5. Likewise, the'vessel may be discharged through the valve 34 by reversing the pump 30 and either pumping the liquid through the conduit 32 which may be of flexible construction, or providing a T in the conduit 32 and suitable valves to convey the liquid from the pump away from the vessel.

The motor 23, housing 24, rails 11, pump 39 and motor 31 are all supported by the sturdy frame 40. If the vessel is to be dumped instead of being discharged through the valve 34, the screen 41 is fastened over the top of the vessel by the dogs 42 (of which only one is shown). The screen may be in two halves and fit snugly The lock which holds the vessel" around the shaft 15. upright is then unlocked. The handle 44 .(Fig. 1) is fastened to the rod 45 which is fastened to the link 46 at the rear of the attri tor. clockwise condition lowers the outer end of this link 46, lifting the opposite end of the adjacent link 47, lifting bolt 48 out of its hole in plate 49. When the bolt 48 is lifted the vessel can be moved forward on the track 11. The crank handle 50 is turned, and this in turn rotates the worm 51 which is meshed with the gear 52 which is fastened to the side of the vessel. By rotating the handle 50 the vessel is dumped. The spout 53 directs the material discharged from the vessel.

After the vessel is emptied it is returned to the upright position and rolled back on the track until the agitator Thev shaft 15 is directly under the driven shaft 22. coupling of these shafts must be such as to fasten them securely together regardless of the relative angular position of the two shafts.- It is impossible to manually Turning the handle 44 in the- 7 rotate the agitator because of the presence of the attritive elements which cover the arms in the vessel. It is further impossible to manually turn the shaft 22 because it is driven by the worm gear. It is, therefore, necessary to clamp the two shafts together without adjusting them to any predetermined angular relationship.

The operation of the clamp is illustrated in Fig. 4 and the details of one clamping element are illustrated in Fig. 3. The disc fitting 55 is fastened to the shaft and the disc fitting 56 is fastened to the shaft 22. Both discs are circular and the upper disc 56 is countersunk to receive the disc 55. The fittings are keyed to the respective shafts by the keys 58 and 59. Set screws 60 prevent vertical movement of the fittings on the shafts.

Three clamps are pivotally fastened to bosses 62 on the upper fitting. An angular member 63 is pivoted to each boss by the pivot 64. The handle 65 which is swivelly attached to member 63 provides a convenient leverage for the operation of the toggle coupling.

The lower member 70 of the clamp is pivoted at 71 to the angular member 63. The lug 73 on the lower member projects inwardly and the set screw 74 is screwed through it. To clamp the two shafts together the three handles 65 are swung upwardly bringing the set screws 74 to bear against the lower surface of the disc 55. The screws are tightened in this position. The tighter the screws are drawn the more the pivot 71 is drawn inwardly and downwardly. At the interface of the discs is the fabric liner 77. This may be treated with oil or asphalt or the like to give it wearing qualities. It is preferably cemented to the upper disc but may be cemented to either disc. One such liner may be fastened to each disc. This cushions the clamps and prevents slippage.

The valve 34 is especially designed to operate successfully in concentrated liquid slurries which because of settling, will rapidly clog a conventional valve. It satisfies the following requirements:

A. There is no dead space between the inside of the tank and the closing member of the valve, so that if the valve is closed no settling of the slurry can take place.

B. The closure itself is constructed so that the operation of the valve involves automatic cleaning of the openings through which the liquid flows when the valve is open.

C. The valve body 80 itself is swept free from settled material by a built-in sweeping device which operates when the valve is operated.

The housing 80 is cylindrical. The end plate 81 is fastened onto it by the bolts 82. Gasket material 84 is held to the outer surface of the housing by the clamping ring 85. The outer end of it is located between the cover plate 86 and bosses 87 in the wall 88 of the jacket. The plate 86 is fastened into the bosses by the bolts 89. The inner end of the valve slides into the opening in the wall of the vessel 91 bounded by the ring 92. This ring is welded to the wall 91. O- rings 95, 96 and 97, located between the wall 80 and the ring 92, and also at the outer end of the valve, prevent leakage.

The'inner end of the valve housing is closed by the stationary plate 100. This is covered by the screen 101 which is likewise stationary. In close contact with the plate 100 is the rotatable valve head 102. Pins 104 in the end plate 100 fit into the circular grooves 105 in the valve plate 102. Pins 107 on the inner surface of the valve plate 102 fit into the grooves 108 in the end plate 100. The valve plate 102 is connected by the stem 110 with the valve handle 111. The webs 115 fastened to the stem 110 support the scrapers 116. As thevalve handle 111 is turned the scrapers 116 prevent the accumulation of solid matter on the wall of the housing 80. Likewise, as the valve handle 111 is turned the valve plate 102 is rotated against the surface of the end plate 100. As the valve plate 102 is rotated the pins 104 and 107 clear away any deposit of solid matter which may form in the slots 105 and 108 respectively. The screen 101-prevents any 8 of the attritive elements 120 (Fig. 8) from lodging against the slots 108. The length of the diameter of the openings in the screen is the same as the width of the valve slots 108. Thus the slots are small enough to prevent the attritive elements 120 from entering them. The purpose of the round orifices of the screen is to prevent elongated elements (such as might be formed by fracture or wear of the spherical attritive elements) from lodging in the openings 108. The screen 101 is necessarily thin so that any settling within the cavity represented by such orifice cannot take place. There is thus no possibility of these cavities becoming plugged. The plate is thick and strong enough to withstand any pressure developed within the vessel 1 and the mechanical action of the attritive elements. that suspended matter can settle in them and plug the slots. The pins 107 remove any such potential deposit when the valve is turned. Thus the valve is used in a system in which there is suspended matter of two different sizes, permits the passage of the fraction of the smaller sizes while excluding the fraction of the larger sizes, and it stays operative in spite of the tendency for deposit formation.

The pins 104 and 107 are in line with the slots 108 and 105, respectively, and are spaced a short distance from the end thereof. When the valve is closed the two plates overlap to this extent. Fig. 100 shows the valve closed with the pins 104 moved to the end of the slots 105, and in dotted lines it shows the pins 107 at the ends of the slots 108. When fully opened (Fig. 10a) the pins 104 (which are stationary) are located in the opposite ends of the slots 105. The pins 107 on the valve plate 102 are turned through an angle somewhat less than 180 and are in the ends of the slots 108. Over the greater part of their respective lengths the slots coincide and provide an opening through the valve. Liquid and suspended solid matter are circulated through these openings by the pump 30 and connecting conduits. Fig. 10b shows the valve only partially opened. The curved slots and 108 coincide over only a portion of the distance-between the pins 104 and 107. Thus, this valve permits free flow of the liquid and suspended matter and prevents accumulation of such matter when the circulation of liquid ceases or is temporarily slowed down.

The flexible conduit 33 connects with the chamber which is open at both ends and provided with the connections 36 and 37 (Fig. 2). By plugging the opening 37 or closing a valve in the draw-01f conduit attached to this connection the liquid circulated by the pump 30 is returned through the valve head 102 into the bottom of the vessel. If the contents of the vessel are simply to be drained through the valve the opening in the conduit attached to the connection 37 will be open and the valve head 102 will be turned to the opened position so that the liquid can drain out through the valve.

The attritor can be used for a multitude of different operations. Thus, it may be used for grinding pigments which are not to be used in suspension in liquid but which, after grinding, are separated from the liquid used in the attritor. The separation may be accomplished in any usual manner. The following examples illustrate applications of the attritor:

Example I Ultramarine blue pigment which as originally processd contains particles up to 60 microns. It has to be subdivided to consist of essentially 4 microns or smaller particles. This is carried out in the form of a water slurry; and using conventional pebble mills requires 24 to 48 hours. The same or better effect can be obtained in an attritor in 2 to 4 hours. For example, a l30-gallon attritor may be used, the tank of which is 35 /2 inches in diameter and 40 inches high. This is equipped with an agitator of the type illustrated in the drawings in which the four upper arms each measure 29% inches from tip to tip, giving a clearance of 3 inches at the end of each shaft. The tank contains 900 pounds of specially processed The slots 108 are therefore necessarily so deep a? rounded flint 7 inch in diameter. This is suited for rotation of the agitator at 80 R. P. M. For more rapid rotation smaller flint elements will be used and the time required will be reduced.

A 50 per cent slurry of the ultramarine is made in water containing 1 per cent of ammonia and 0.5 to 2 per cent or" a dispersing agent, such as naphthalene sulfonic acid derivative. 75 gallons of such slurry is finely ground in this attritor and reduced to the desired particle size.

The finely ground ultramarine may be separated from the liquid in any usual manner.

Example I] The attritor is used advantageously to produce and simultaneously suspend finely divided particles in a liquid. Thus, for example, in the preparation of dispersions of compounding ingredients to be used in latex for the production of foamed rubber products or dipped goods, etc., the dispersions of compounding ingredients may be more advantageously and more cheaply prepared in the form of dispersions in an attritor than in conventional equipment. The following illustrates the preparation of compounding ingredients to be added to a rubber latex.

One hundred parts of sulfur, 50 parts of phenyl naphthylamine, 50 parts of a mercaptobenzothiazole derivative and 250 parts of zinc oxide are slurried into a water solution containing 0.5 per cent ammonia and l per cent of a dispersing agent such as either Darvan made by the Dewey & Almy Chemical Corporation, or Marasperse made by the Marathon Paper Company. Forty gallons of such slurry are ground in an attritor tank having a 75-gallon capacity and containing 600 pounds of /2 inch flint pebbles. This tank measures 28%; inches in diameter and is provided with an agitator of the type illustrated in the drawings, the four upper arms measuring 22% inches from tip to tip. Operating at 75 R. P. M. the composition is reduced to an average particle size of less than 0.5 micron in five or six hours grinding. It would take 90 hours to produce the same eifect in a conventional pebble mill.

Example III In the following example, the finely ground product will be used as a slurry without separation from the liquid medium.

It requires 24 to 48 hours in a conventional pebble mill to reduce a titanium dioxide alkyd paste containing 50 per cent titanium dioxide to a particle size of 7.5 to 8 North Gauge reading. When 400 grams of such a crude paste is placed in a laboratory size attritor using its inch stainless steel balls, an agitator with arms measuring2 /2 inches from tip to tip with inch clearance between the end of each arm and the wall of the vessel, and rotating the agitator at 400 R. P. M., the paste will be reduced to the above fineness in 20 to 30 minutes.

Such an operation may be carried on efiiciently in a larger attritor, such as those referred to in Examples I and II. In a laboratory attritor the arms are not usually arranged as shown in the drawings but may be placed individually, and at right angles to one another. A wide choice in the arrangement of the arms is possible.

Thus it is seen that the action of the attritor and the factors influencing the effect of the attritive action of the elements is quite difierent from the action of the grinding elements in a conventional ball mill and the effect of their action. The attritor offers various advantages over the ball mill, both from the standpoint of construction and convenience of operation and from the standpoint of efficiency. Thus, on one hand an attritor may be made several times as efficient, e. g., 20 times or more, as the most eflicient ball mill, thereby reducing the time required to complete a certain action. On the other hand, the convenience of its operation is of greatest practical significance.

A ball mill is mounted horizontally and is charged and discharged through an opening in its cylindrical wall.

iii This opening must be brought to the top of the mill when the mill is to be charged and it is brought to the bottom of the mill to discharge the mill. While operating the cover must be tightly sealed on the mill. A particualr advantage in the construction of the attritor is that the attritor need not be covered and there is no danger of building up explosive pressure inside of an attritor as there is Within a ball mill. Whether the attritor is covered during an operation or not, it is relatively easy to charge it. Further, it may conveniently be provided with means for dumping the entire charge when an operation has been completed. Furthermore, in various operations it is desirable to add some reagent a little at a time. To conduct such an operation in a ball mill it is necessary to stop the mill and open it and then close it again for each addition. In the operation of an attritor, particularly if the top of the attritor is open, the addition may be made even without stopping the agitator. A further advantage over ball mill operations is that the attritor may be conveniently jacketed for cooling and heating, whereas the jacketing of a ball mill is impractical, or at best exceedingly expensive.

What I claim is: I

l. The method of treating a heterogeneous liquid system in an enclosure in which are a large number of relatively spherical attritive elements, which method comprises continuously moving an agitator through the elements thereby displacing the elements in its path, all of the elements being substantially the same size, and the speed of movement of the agitator being sufficient to impart to at least most of the elements a movement having at least a partially random distribution causing each of said elements to repeatedly and continuously bounce from contact with one element into contact with another element and with the agitator, and remain suspended in the system.

2. The method of treating a heterogeneous liquid system in an enclosure in which are a large number of relatively spherical attritive elements, all of substantially the same size, which method comprises rotating an agitator through the elements at a speed between substantially 450 and 60 revolutions per minute thereby displacing the elements in its path and imparting to at least most of said elements a movement having at least a partially random distribution causing each of said elements to repeatedly and continuously bounce from contact with one element into contact with another element and with the agitator, and remain suspended in the system.

3. The method of treating a heterogeneous liquid system in an enclosure in which are a large number of relatively spherical attritive elements with a diametric measurement between substantially and W inch, but all of substantially the same size, which method comprises rotating an agitator through the elements at a speed between 450 and 60 revolutions per minute thereby displacing the elements in its path and imparting to at least most of said elements a movement having at least a partially random distribution causing each of said elements to repeatedly and continuously bounce from contact with one element into contact with another element and with the agitator, and remain suspended in the system.

4. The method of treating a heterogeneous liquid system in a vessel in which is a rotatable agitator immersed in the liquid and at least partially covered with relatively spherical attritive elements with a diametric measurement between substantially 7 and W inches in diameter, but all of substantially the same size, which method comprises moving the agitator through the attritive elements at a speed in the range of substantially 60 to revolutions per minute, thereby displacing the elements in its path and imparting to at least those elements located away from the bottom and cylindrical wall of the vessel a movement having at least a partially random distribution causing each of said elements to repeatedly and 11 continuously bounce from contact with one element into contact with another element and the agitator, and remain suspended in the system.

5. The method of treating a heterogeneous liquid system in an upright cylindrical vessel provided with a'central agitator having substantially horizontal agitating arms, the vessel being filled with attritive elements to a height such that at least the bottom arm of the agitator is covered by them, the elements being relatively spherical with a diametric measurement of substantially 73 to inches, but all of substantially the same size, with the end of each arm at least three times the diametric measurement of the elements away from the cylindrical wall, which method comprises rotating the agitator at a speed of substantially 60 to about 450 revolutions per minute depending upon the size of the elements, the smaller the elements, the higher the speed of rotation of the agitator, and by such rotation imparting at least a partially random distribution to the elements located away from the wall causing each of them to bounce from contact with one element into contact with another element and with the agitator, and remain suspended in the system.

6. The method of treating a heterogeneous liquid system in a vessel equipped with an agitator and containing a large number of relatively spherical attritive elements, all of substantially the same size, which cover at least the bottom of the vessel and embed at least the lower portion of the agitator, which method comprises moving the agitator and displacing the elements in its path, the speed of movement of the agitator being suflicient to impart to all of the attritive elements which are located away from the bottom and the side of the vessel at least apartially random distribution causing each of said elements to repeatedly and continuously bounce from contact with one element into contact with another element and the agitator, and remain suspended in the system; while providing a relatively motionless layer of the elements over the bottom of the vessel, and a relatively motionless layer of the elements adjacent the side to a depth substantially equal in height to the height of said activated elements.

7. The method of treating a heterogeneous liquid system in a stationary vessel, containing substantially spherical attritive elements all of substantially the same size which comprises imparting to at least most of the elements at least a partially random distribution causing each of said elements to repeatedly and continuously bounce from contact with one element into contact with another element and the agitator, and remain suspended in the system, while adding to and subtracting from the system within the vessel and retaining the attritive elements in the vessel.

8. An upright substantially cylindrical vessel, an agitator shaft located axially of the vessel with means for rotating the shaft, arms extending substantially horizontally from the shaft, at least some of the arms being paired and separated from any other arms longitudinally of the shaft.

by a substantially greater distance than the distance between the arms of the pair, the upper arm of each pair being angularly behind the lower arm in the sense of the.

rotation of the shaft, and relatively spherical elements with a diametric measurement between substantially and inches, the elements all being of substantially the same size, the elements filling the vessel to such a ered with the attritive elements.

9. An upright, substantially cylindrical vessel with a vertical agitator concentric therewith the outermost part of which approaches the wall of the vessel, and contained in the vessel relatively spherical attritive elements, all of substantially the same size, which elements fill the vessel to a height above the lower part of the agitator, there being a clearance between the outermost portion of the agitator and the wall nearest thereto which clearance is equal to at least three times the diameter of the elements.

10. A movable vessel equipped with an agitator on a substantially vertical shaft, and containing substantially spherical attritive elements of substantially the same size which fill the vessel to a height above the lower part of the agitator, drive means for the shaft located above the agitator, means at the top of the agitator shaft having a horizontal top surface, the bottom surface of the drive means being horizontal and in the same plane as the aforesaid surface, and toggle clamps for clamping said surfaces together when the drive means and shaft are concentric and said horizontal surfaces are in contact.

11. The method of mixing and grinding two solid components in a liquid system, in which there are a large number of relatively spherical attritive elements of substantially the same size, which method comprises moving an agitator through the system at a speed sufficiently to impart to at least most of the elements a movement having at least a partially random distribution causing each to repeatedly and continuously bounce from contact with one element into contact with another element and with the agitator and remain suspended in the system, and thereby causing the two solid materials to be subdivided and intimately admixed with one another.

References Cited in the file of this patent UNITED STATES PATENTS 441,419 Jones Nov. 25, 1890 919,112 Zinke Apr. 20, 1909 1,169,668 Merritt Jan. 25, 1916 1,192,689 Sayer July 25, 1916 1,363,620 Sellman Dec. 28, 1920 1,414,120 Fulcher Apr. 25, 1922 1,479,242 Johnson Jan. 1, 1924 1,521,891 Kleinfeldt Jan. 6, 1925 1,605,025 Hildebrandt Nov. 2, 1926- 1,652,929 Cawood Dec. 13, 1927 1,956,293 Klein et al. Apr. 24, 1934 2,019,454 Larsen Oct. 29, 1935 2,208,892 Bukacek July 23, 1940 2,212,641 I-Iucks H Aug. 27, 1940 2,218,580 Kennedy Oct. 22, 1940 2,241,848 Eckart May 13, 1941 2,292,275 Kiesskalt Aug. 4, 1942 2,297,009 Mead Sept. 29, 1942 2,577,353 Naidu et al. Dec. 4, 1951 FOREIGN PATENTS 36,858 Germany Sept. 15, 1886 160,506 Switzerland June 1, 1933 OTHER REFERENCES Hard Surfacing by Fusion Welding, by Howard S. Avery, pub. by The American Brake Shoe Co., New York. 1947. (Copy in Division 55.)

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