Particle Wetting Process and Apparatus

This invention relates generally to mixing of calcareous cement particles or powders, and water, for use in making concrete; and more particularly it concerns an unusually useful and efficient process, and associated apparatus, for performing the steps of the process, to effect efficient cement and water mixing, i.e. batching.

Problems associated with present dry cement, water and aggregate batching procedures, as in truck mounted rotary containers to which such ingredients are supplied, include: excessive cement dust formation and escape into the atmosphere; "balling" of cement particles and water (i.e. formation of unwetted cement agglomerates in partially wetted balls; and build-up of unwetted cement powder, as well as slurry, on rotary mixer surfaces). These also contribute to production of concrete mixes characterized by out-of-proportion ingredients, leading to reduced strength concrete. There is need for a precise, controlled, and otherwise highly efficient cement and water mixing or batching process that overcomes such problems and difficulties.

It is a major object of the invention to provide an improved and highly efficient process, and controlled system, that meets the above needs. Basically, the process of the invention involves use of a primary mixing vessel in which a cement and water slurry is produced, the process including the steps:

(a) introducing a measured quantity of water into the vessel,

(b) introducing a measured quantity of particulate cement into the vessel,

(c) agitating the water and cement in the vessel to form a slurry;

(d) and, while continuing said agitating, pumping slurry from the lower interior extent of the vessel and delivering the pumped slurry to the upper interior of the vessel, at high velocity,

(e) removing slurry from the vessel for flow to an auxiliary mixing vessel for mixing with aggregate,

(f) and employing wash water to wash remanent slurry from surfaces in the primary mixing vessel and removing the wash water and remanent slurry from the primary vessel for flow to the auxiliary vessel.

Typically, multiple rotary agitators are employed in the vessel, and operated to create streams of slurry which impinge upon one another in that vessel; also, the agitators advantageously include upper and lower bladed agitators rotated in a direction or directions so that the upper agitator drives slurry in a stream toward the lower agitator, and so that the lower agitator drives slurry in a stream toward the upper agitator, whereby the two streams impinge upon one another. Enhanced wetting of cement particles can be obtained by evacuating air from the interior of the primary vessel after mixing of the water and cement, then rapidly re-admitting air to the primary vessel, thereby enhancing wetting of the cement particles in the slurry.

Further, a wash water holding tank is typically provided, and the method includes adding to that tank a fixed fraction of said predetermined amount of water, for use as said wash water. The water in the holding tank is pressurized, as by application of air pressure, for delivery of pressurized water streams to the vessel interior to wash down said surfaces in the primary mixing vessel.

The same pump as is used in a first mode for recirculating slurry to the vessel interior, at high velocity, can also be employed in a second mode to rapidly pump the slurry from the cement and water batching vessel to an auxiliary vessel (such as the rotating container on a "ready-mix" truck), for mixing with aggregate (sand or rock) delivered to that auxiliary vessel; and the amount of water added to the batching vessel can be reduced (under computer control) in proportion to the amount of water that is carried by wet sand in such aggregate, so as to arrive at an ultimate concrete mix with correct water content.

The batching apparatus of the invention basically comprises:

(a) a primary mixing vessel having cement and water inlet means, and slurry outlet means,

(b) means for introducing measured quantities of water and cement into the vessel,

(c) agitation means for agitating the cement and water in the vessel, thereby to form the slurry,

(d) means including a pump for removing a stream of slurry from the lower interior of the vessel and flowing said stream into the upper interior of the vessel, at high velocity, and for removing slurry from the vessel for flow to an auxiliary mixing vessel for mixing with aggregate,

(e) and washing means including a wash water holding tank for supplying wash water to the interior of the vessel so as to wash remanent slurry from surfaces in that vessel for flow out of the primary vessel and to the auxiliary vessel.

Also provided is apparatus to produce agitation in the vessel, without need for rotating blades, and for removing cement dust from the vessel upper interior, to be re-introduced in a slurry re-circulation stream that acts to produce agitation.

These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following specification and drawings, in which:

FIG. 1 is an elevation showing apparatus in accordance with the invention;

FIG. 2 is a right side elevation taken on lines 2--2 of FIG. 1, and partly broken away to show interior construction of the primary mixing vessel;

FIG. 3 is a plan view taken on lines 3--3 of FIG. 1;

FIG. 4 is a left side elevation taken on lines 4--4 of FIG. 1;

FIG. 5 is a block diagram showing computer control of actuators and valves associated with the apparatus,

FIG. 6 is a block diagram showing operation of an auxiliary mixing vessel.

The apparatus seen in FIGS. 1-4 includes an upright primary mixing vessel 10 having a cylindrical side wall 11, a top cover 12, and a tapering lower extension 11a of wall 11. A water fill line 13 extends downwardly from a water storage tank 14, toward a water inlet 15 in cover 12. Valve V.sub.1 in line 13 controls water egress from the storage tank 14, and a control valve V.sub.2 in and at the lower end of line 13 controls water admission to the vessel 10. Calcareous cement in particle form (as for example Portland cement) is conveyed by screw conveyor 16 toward a cement inlet 17 in cover 12. A drive D.sub.1 for the conveyor is operable and controlled, as by computer 19 seen in FIG. 5, to cause a measured amount of cement to be conveyed at 16 and introduced via inlet 17 into the vessel 10 immediately after a measured amount of water is admitted to the vessel. For this purpose, the vessel is mounted via load cells 21 to frame structure 22. The outputs of the load cells, represented by weight signal W (net of tare weight of the vessel) in FIG. 5, is transmitted to the computer, as shown. Also, desired water weight K.sub.1 and cement weight K.sub.2 settings are keyed into the computer, via keyboard K, as shown. Initially, the computer opens valves V.sub.1 and V.sub.2 (via associated actuators also represented by the valve symbols) to admit water to the vessel 10. When the weight W.sub.1 of the admitted water reaches the pre-set or measured level K.sub.1 as determined by comparison of signal values K.sub.1 and W.sub.1, the valves V.sub.1 and V.sub.2 are closed by the computer. Next, cement is delivered into the vessel, for mixing with water, and for this purpose, the computer effects operation of drive D.sub.1. When the weight W.sub.2 of the admitted cement reaches the preset measured level K.sub.2 as determined by comparison of signal values K.sub.2 and W.sub.2, the drive D.sub.1 is stopped.

Also, provided is agitation means for agitating and thereby mixing the cement and water in the vessel, to form a slurry, in which the cement particles are thoroughly wetted, for optimum strength concrete production. The agitation means, generally indicated at 25 in FIG. 2 includes multiple rotary agitators in the lower interior 26 of the vessel 10, i.e. inwardly of wall lower extension 11a. As shown, the agitators includes an upper bladed agitator 27 mounted on a vertical drive shaft 28, and a lower bladed agitator 29 also mounted on shaft 28, and extending directly below agitator 27. Shaft 28 extends upwardly and to the vessel exterior above the cover. A drive D.sub.2 including a motor is connected to the upper end of the shaft, and support bearing means for the shaft is seen at 129. Suitable seals are also provided.

The blades 27a of the upper agitator are angled relative to horizontal so as to drive slurry in a downward stream 27b, and the blades 29a of the lower agitator are angled relative to horizontal and oppositely to the blades 29a of the upper agitator so as to drive slurry in an upward stream 29b toward the upper agitator. As a result the two streams impinge from one another for enhancing wetting of the cement particles, and flow outwardly and downwardly as well as outwardly and upwardly. Also, vortexing flow in the vessel is substantially reduced, which also contributes to enhance wetting of the cement particles. If desired, the two bladed rotors can be separately driven. Each agitator typically includes four blades, and the agitator shaft may be rotated at between 140 and 180 RPM--preferably about 160 RPM.

Furthermore, a pump P is carried at the bottom outlet 36 of the vessel to receive or remove a stream of slurry from the vessel and to flow the slurry via duct 38 into the mix at the upper interior of the vessel 10 and at high velocity. Drive D.sub.3 including a motor serves to rotate the pump impeller at high speed (1,000 RPM, for example), to create the high velocity stream of slurry that is caused to impinge upon the slurry in the vessel, after being jetted tangentially relative to wall 11, from duct outlet 39, (FIG. 3). Further, agitation, and enhanced wetting of the cement particles is thereby achieved. Pump P is also operable in a second mode to pump slurry from the lower interior of the vessel and via duct 40 to an auxiliary mixing vessel 41, after opening of a discharge valve V.sub.6 seen in FIG. 4. Vessel 41 is typically a rotating container on a ready-mix truck transporting concrete to a job site for pouring. Aggregate (sand and rock) is added in measured amount to the vessel 41, at 42.

Also provided is washing means, including a wash water holding tank 43, for supplying pressurized wash water to the interior of the vessel 10, to wash remanent slurry from surfaces (such as wall surfaces and agitator surfaces) in the vessel. Such wash water and remanent slurry then flows to the auxiliary vessel via the pump P. A fixed or predetermined fraction (preferably about 5%) of the required water for the ultimate mix in vessel 41 is supplied to the holding tank 43, as via line 45 and valves V.sub.3 and V.sub.4 seen in FIG. 1, for use in washing down the interior surfaces as described. Three flushing lines 46 extend to spray nozzles 47 in the vessel upper interior, from a pipe or manifold 48 connected with lowermost interior of tank 43 as via a control valve D.sub.7 . Also, a wash water line 50 extends from pipe 48 to the pump housing for washing pump surfaces free of remanent slurry. Computer 19 is programmed to open valve V.sub.7 to flow or pass water to lines 46 and 50, after all of the slurry has been pumped from vessel 10 to flow to vessel 41, at 40. A source of air pressure is shown at 210 and connected to tank 43. After completion of wash-down, valves V.sub.6 and V.sub.7 are closed.

All of the valves V.sub.1 -V.sub.7 may be operated by computer-controlled air-operated actuators. FIG. 2 also shows lines 61-64 connected to the water inlet duct 13, for passing selected additives or other admixture agents, to the vessel interior. FIG. 4 also shows a vibrator 68 connected to a cement supply silo 69 from which cement is conveyed to vessel 10. At such time as cement inlet gate valve V.sub.5 opens, just after completion of water input to vessel 10, the vibrator is energized so as to effect gravity flow of cement to the conveyor. At that time, the agitator drive is energized and the pump drive is also energized, under computer control. Air pressure is also admitted to the holding tank. After completion of cement input to the vessel 10, V.sub.5 is closed, and the vibrator is de-energized. For initial water input, valves V.sub.1, V.sub.2, V.sub.3 and V.sub.4 are all opened simultaneously.

The apparatus and method to produce slurry (wet batching) can also be used in conjunction with dry batching. Thus, a predetermined proportion of the ultimate mix in vessel 41 can be supplied by the wet batching process as described; and also, the balance of the ultimate cement and water mix in vessel 41 can be supplied by dry batching--i.e. loading dry cement and water directly into that vessel (see arrow 70, in FIG. 6).

Even further wetting of cement particles in the slurry can be effected by evacuating air from the interior of the primary vessel after mixing of the water and cement, then rapidly re-admitting air to the primary vessel, thereby enhancing wetting of the cement particles in the slurry. See for example the air evacuation line 80 in FIG. 3, connected with the tank upper interior and leading to an evacuation pump P.sub.2. Air can be suddenly re-admitted to the tank by opening a valve V.sub.8 to 80, under control of the computer, as during the slurry mixing process.

Finally, a sensor 86 is associated with the computer for sensing the amount of water per unit volume of wet sand added to the auxiliary vessel 41, whereby the computer then calculates the diminished amount of water to be added to the vessel 10 in the first instance, as by control of valves V.sub.1 -V.sub.4, so that an ultimate correct formula mix is produced in vessel 41.

It is also possible to omit agitators 27 and 29 or drive for such agitators and instead employ the centrifugal pump P operated in such a way that is impeller inlet side, exposed to slurry in the lower interior of the vessel 11, induces rotations of the lower slurry in one rotary direction about the tank central vertical axis. At the same time, the amount of slurry recirculated to the tank upper interior, via line 38, is controlled, and the slurry outlet nozzle is directed so as to drive slurry in the upper interior of the vessel in another rotary direction (i.e. opposite to said one rotary direction, about axis 80. As a result, the two opposite rotary streams interfere with one another as in shear, and a very high degree of particle setting is achieved, as is desirable for high strength concerte. In one example, about 10% of the slurry in the tank is continuously recirculated at 38. Also, the particle wetting effect is enhanced by creating a partial vacuum in the tank interior withdrawing air from the tank upper interior. In this regard, voids adjacent cement and other particles created by loss of air are replaced by water. Operation of the pump P itself may create some of such vacuum.

In another arrangement, means is provided for aspirating cement dust particles from the upper interior of the vessel 11, and for circulating them to the recirculated slurry, as in line 38. For this purpose a line may extend upwardly from the top of the vessel, and back downwardly to discharge aspirated air. A branch line then connects to the side of the vent line to aspirate rising dust particles sidewardly from the rising air streams. The dust particles travel in the bran line under vacuum created by slurry travel in line 38, to which the branch line connects as at a venturi. Thus, no cement dust is wasted, but is recirculated and fully utilized.