US2303902A - Mixing concrete - Google Patents

Description

De. 1, 1942. c. F. BALL MIXING CONCRETE '2 sheets-sheet 1 Filed April 17, 1941 Charles 5 Ball INVENTOR.

ATTORNEY.

Dec. 1, 1942. c, F BALL 2,303,902

MIXING CONCRETE Filed April 17, 1941 ZSheets-Sheet 2 Chcz rles E'Bczll mvsmon BY fia 2 A ATTORNEY Patented Dec. 1, 1942 UNITED STATES PATENTOFFICE MIXING CONCRETE Charles F. Ball, Wauwatosa, Wis., assignor to Chain Belt Company, Milwaukee, Wis., a corporation of Wisconsin Application April 1'7, 1941, Serial No. 389,058

4 Claims. (Cl. 259-446) This invention relates to an improved method of preparing concrete mixtures from fines. coarser aggregates, cement and water, and is particularly directed to improving over prior procedures in more speedily and uniformly preparing well-mixed batches of ready-mixed concrete in a perimetrally-bladed mixing drum which has its axis of rotation fixedly inclined to the horizontal, so that its rear discharge-end is high above its closed front end;and thereafter effecting such high-level discharge of the batch without reversing the direction of rotation of the drum.

In the industry, ready-mixed is the conventional designation of concrete which, having been duly worked in a truck-mounted drum while in transit from the materials-yard to the construction-site, is delivered at said site in finished, ready-to-pour condition; and the advantage of its discharging the batch at a point high enough above ground-level to accommodate gravity-distribution thereof, via an inclined chute, to such convenient point or points of deposit as may be somewhat elevated or at quite a distance from the truck, is widely recognized industrially.

The present application, setting forth said invention is a continuation-in-part of my prior application Serial No. 359,844, filed October 5, 1940.

Prior to my present invention it had been uniform practice, so far as I am aware, in preparing ready-mixed concrete in the bladed drum of a truck-mixer, to require that during the mixing operation said drum be rotated in such direction that its spirally-disposed mixing-blades would propel perimetral portions of the concrete toward the forward, closed end of the drum; while for effecting high-level discharge of the concrete mixture it is requisite to stop the drum and then reverse its direction of rotation about its inclined axis, so that the same spirally-disposed perimetral blades would propel the mixed mass rearwardly and upwardly to the high level of the discharge opening at the drums rear end.

I have discovered that by my novel method of mixing-(to be more fully described hereinafter, but in which the materials, after a conventional shrinking, are admixed under drum-rotation that constantly propels perimetral' portions of the ingredients toward the high end of the drum)greater speed and certainty in effecting fully-adequate mixing is attained; subsequent delivery of the batch from the drum is adequately facile and rapid and saves one manual operation by the truck driver; and tendency of the mate-/ the drum (which robs other portions of the batch of their proper cement-content and is quite frequently encountered in mixing toward said closed end) is so greatly diminished that even its incipient occurrence is unusual.

In general, the object sought and attained by the present invention is to'provide a novel meth- 0d of Working the concrete-materials in a mixing drum of the inclined-fixed-axis type, which method will insure notably thorough and uni-' form mixing of the ingredients accomplished in minimal time and (as compared with the customary method of working concrete ingredients in such a mixer) with production of equally good, or even improved concrete; all at lower cost both in man-hours and in power expenditure by virtue of the shortening of the requisite mixing time, and all with the maintenance of discharge at high level, insured Icy employing an inclination of the drum axis at about as steep an angle, preferably in the order of 10 to 20 to the horizontal, as will give the larger and smaller drum-sizes approximately the same discharge-height, and be conductive, to safe truck-mounting.

- The improved method aforesaid may be practiced, in either of the two commoner forms of fixed-axis high-discharge truck-mixer; that is to say, in either an endcharger or top loader,

as those terms are commonly used in the ready-' mixed concrete industry; and each said type has its proponents; Top loading,--done through a hatch in the side wall of the drum, which will be tightly, closed and sealed before the mixing starts-is practically a safeguard against overloading of the drum, and introduction of the whole load practically at once either obviates shrinking or minimizes the time of that operationwhich' is done by propelling the materials toward the bottom of the drum; while 'end charging through the discharge-orifice requires drum rotation in direction to move the materials tion of the water content of the mixture until after the dry ingredients have been charged. And in mixing according to my novel practice, it is not uncommon for a truck-mixer, which has had its dry concrete-forming materials loaded at the supply yards, to have its drum started in normal rotation in due time for its permissively short, adequate mixing operation, as the requisite water content is just being admitted by the operator, en route to the job, and continue such unidirectional drum rotation uninterruptedly until the mixed batch has been fully discharged at the construction site.

Of course it is important during the mixing in transit that the materials propelled upwardly to the level at which discharge may subsequently occur shall be safeguarded against unintentional discharge and be free to return from the end zone back into the bladed portion of the mixer under the influence of gravity, for recirculation in furtherance of the adequate mixing; but I have deemed it sufiicient to indicate this generality to those skilled in the art by specifying two of the divers ways in which the conditioning of the apparatus for discharge, as distinguished from maintaining conditions for return of materials into the mixing space, is under the control of the operator.

In the accompanying drawings, diagrammatically illustrating the mixing operation, two types of machines are shown, one being a top loader and one an end charger, the latter having a suitable charging hopper arrangement cooperating with the end opening. Referring specifically to the drawings:

Figure 1 is a diagrammatic view, shown partly in section, of an inclined axis machine which is being utilized in accordance with my invention. This machine is provided with two openings, one at the side for charging, and one at the rear for discharging;

Fig. 2 is a section taken on the line 4-4 of Figure 1; and.

Figure 3 is a diagrammatic View, also partly in section, illustrating the operation of the invention and the disposition of the batch in a machine having end-charging facilities.

In all of the figures, like numbers will be used to designate like parts throughout and the arrows will show the direction of rotation.

The mixing drum or container II illustrated in the several views has two frusto-conical sections with the larger portions of each abutting, said drum being rotatable about a fixed inclined axis through the center of the conical sections. The drum-supporting means are not shown except in Figure 3, as it will be understood by those familiar with the art how the forward end may be supported on an axially disposed bearing, whereas the rear portion, which is provided with a flange or ring I2 having a cylindrical outer surface, may rest on rollers disposed a short distance in front of the discharge opening.

In the drum illustrated in Figures 1 and 2, a lateral opening 13 is provided in the frustoconical section adjacent the discharge portion, and this opening is provided with a quick opening door I4, which may be removed while materials are being charged into the drum. During mixing, this opening is closed, and the door forms part of the wall confining materials inside the drum.

Attached to the inside of the drum are suitable spiral blades -l5 (and in the present embodiment two such relatively shallow blades are shown) which are set at an angle of approximately 70 to the axis, to promote rapid and clean discharge. With the top-loading arrangement shown in Figures 1 and 2, the higher end of the mixing receptacle is provided with a closure l6 which is so mounted on the drum that it may, during mixing, close the discharge opening, and during discharging, be removed a suificient distance to afiord a large, unobstructed space for discharge commensurate with the rate of upward propulsion of materials by blades [5.

In Figure 3, the same drum II is illustrated, but instead of a charging hatch disposed in the side wall, a charging hopper I1 is arranged in cooperating relation to the opening at the rear of the drum, said hopper when in contact with the drum affording'means for end-charging, and when drawn back from contact with the drum affording a space for discharge similar to that afforded by the removal of closure IS in Fig. 1.

In both illustrations, it will be understood that the drum may be mounted longitudinally of the frame of a motor truck, with the discharge end disposed above the rear of the truck where it is most easily accessible. The forward end is in proximity to the cab and is solidly closed except that it is desirably entered axially by a properly packed water-supply pipe of future reference.

The fixed angle of inclination of the drums axis, as shown in the drawings, is approximately 18 from the horizontal, this angle being one which assures sufficient height to the rear opening for high discharge without increasing too greatly the over-all height of the machine or, what is worse, rendering the machine top-heavy when materials are distributed therein in the manner effected by the present improved method of mixing. And different sizes of drums may have somewhat different angles of axial inclination, to give approximately equal dischargeheight.

In Figures 1 and 2 an internally-bladed drum is shown as being operated in accordance with the present invention, in what has always been considered the proper manner for discharge but not for mixing. Rotation of the drum in both of these illustrations may well be at the commonly accepted speed of approximately 10 R. P. M. With my improved method of operation, the blades will effect distribution of the materials longitudinally of the drum throughout substantially the entire mixing space, in which event blade propulsion combined with gravitational action induced thereby maintains a semi-equilibrium condition as regards quantitative distribution throughout the normal mixing period. The top surface of the ingredients-mass will not be horizontal when viewed in section, as in Figure 2, but will slope laterally and also downwardly from the high end to the low end of the container-drum, due to the rotation of the drum and the lifting action of the blades.

If transverse sections were taken at other points along the rotative axis, such sections would appear somewhat similar to that shown in Figure 2, although there will be some material clinging to the blades or dropping from them at any given instant. With this condition, however, it is possible to utilize the entire longitudinal axis for mixing and to have available space at any cross section to permit the tumbling action or cascading which is sought.

When the present method of mixing is employed, little or no difliculty is encountered by reasonabledeviations from the best conditions for its performance; and its flexibility in such re gards is of advantage. Variations in the specifications of the concrete required on a particular job may be met, covering a substantial range of difference in dryness or wetness of the finished batch. And variations in the precise manner, time and place of introducing requisite water are accommodated with but relatively small effect on the goodness of the mixing performance or its celerity. But, under the preferred conditions schematically represented in Figure 3, the water is supplied, as from a tank or reservoir 22 upon' the mixer, through a pipe 23 to the nozzle 24, which is located in the end zone of the drum adjacent to the closed end and which has provision for directing the water against said head. Under such water-supply arrangement, starting the water flow concurrently with the starting of the drum in its mixing cycle to propel the materials toward the discharge end of the drum insures that sufficient water is immediately transported upwardly, by virtue of the blade-arrangement and by materials that are in upward transit, to effect a thorough wetting of the longitudinally-distributed mass. And further, the stated manner of introducing the water insures thorough wetting of the drums head, which wetting is a substantial deterrent to balling up of materials on said head, additional to deterring effect of the minimization of materials pressure against the head that I have heretofore adverted to.

The efficacy of the mix is reflected in the power requirement. Although it takes more power at a given instant to rotate adrum in a direction to propel the perimetral material to its high end than to force it downward, it is possible to effect a much more rapid commingling of the different ingredients due to cascading in a crosswise as well as in an endwise direction throughout the entire length of the drum, with the result that the total power consumption is less than under the former practice. In other words, saving of energy is a by-product of using more power for a suficiently shorter interval of time.

In order to prevent. the perimetrally propelled material from being moved through the discharge opening and out of the end of the drum during mixing, some provision for retention must be employed, but this provision is one that may take numerous forms, of which I herein show but two. In Figure 1, closure I6 serves this purpose, said closure having a dished or concave shape and providing an axial extension space which.

while exterior to the drums bladed mixing space, may be regarded as a bladeless extension of the mixing area suitable for receiving material passing through the drum opening, and from which space material may be constantly returned to the drum by gravity until the operator establishes conditions to permit of discharge. Thus the closure forms an external chamber through which material which is chuted off the end of a blade may circulate prior to return through the drum opening at a point below or behind the aforementioned blade. Or in the case of rearcharging as illustrated in Figure 3 of the drawings, a dish-shaped plate 18, disposed between the hopper and drum, but rotatable with the lat ter, forms an extension of the drum for this purpose, and the lower portion of hopper I! forms, in effect, an extension of the containers space available for gravity-return circulation of the ingredients.

For facilitating end-to-end circulation and tumbling action, utilizing blades which are relatively shallow with respect to the diameter of the drum (regardless of what cross section'is considered) is essential since a relatively large, substantially unobstructed, axial core-space is thus provided, for uninterrupted cascading of materials. So, too, provision of an axial open space at the discharge opening permits faster charging, when end-charging is employed, and promotes circulation through the free upper zone above the blades. Although a dished or concave member is desirable for utilizing the entire upper end of the drum, and for flushing the ends of the blades, various other restraints against accidental discharge may be employed provided the present method of mixing is not restricted, and action by the operator is necessary toobviate the normal restraint, and thus cause the discharge to be under the operators control. I

A more complete description of hopper i! may be obtained by reference to my prior Patent No. 2,265,751, granted December 9, 1941; or for modifications thereof reference may be made to my prior Patent No. 2,265,752, granted December -9, 1942, in each of which patents I disclose suitable structures and operating mechanism'for this type of charging device. Whether the restraint against discharge be provided by a closure, a charging hopper, or'some other means, it is important that such means be capable of withstanding the weight of the material propelled thereagainst without leakage during the mixing period.

The operation of the invention as herein described may be briefly summarized as follows: Materials may be charged into the empty'drum through either the side opening M as shown in Figure 1 or through the hopper ll shown in Figure 3. In either case, the raw materials may be charged to occupy considerably more than half the drums capacity, in keeping with usual practice; and when end-charging is employed, the drum may be rotated to propel the dry ingredients downwardly and forwardly in the drum to facilitate the loading and effect preliminary shrinking of said ingredients.

After charging. the drum is rotated so that the blades propel perimetral portions of the materials rotatively and longitudinally with respect to the axis up to the high discharge end, thereby distributing the materials throughout substantially the full length of the drum. and promoting tumbling of the materials transversely to the axis as well as longitudinally toward the closed bottom end. Material reaching the high end of the drum is restrained from discharge and returns, under the action of gravity, for end-to-end recirculation during the mixing period. In both illustrations of practice of the invention shown in the drawings, the discharge opening communicates with an extension space which affords a free zone for facilitating recirculation. In this way the in gredients are thoroughly dispersed and commingled during the mixing period.

Water may well be introduced into the mass near the lower end of the drum, as shown in Figure 3, prior to the period of upward propulsion, and consequently the water is worked upwardly with the dry ingredients and any serious balling or packing at the drum head is obviated, even under conditions that are highly conducive to that malign effect. When water and cement come in contact, a paste will be formed provided there is suflicient agitation to hydrate the-paste forming components of the cement particles. By the method herein described, mixing action is considerably hastened, for there is relative move.- ment between the drum and large portions of the mass and an opportunity for cascading ,of free surface-materials for substantially the full length of the drum. Once a paste is formed, it works through the materials as a lubricant, under the movement and scouring action of the solids, coating the sand and coarser aggregates and forming therewith a sticky mixture. Thereafter, mixing proceeds rapidly due to the mechanical action between solids within the batch as well as surface tumbling, the former being facilitated by the .cement-water paste just described.

When the batch is suffic-iently worked to produce substantially uniform concrete of the desired consistency, discharge may be effected at the high end of the drum :by further propulsion of the perimetral portions of the batch into the discharge zone, such propulsion being in the same manner and direction as in the case of mixing.

One of the advantages resulting from this invention which has not been heretofore mentioned is that, in utilizing the same propelling forces for mixing as for discharge, it is possible, if toploading is employed and shrinking of the dry materials is therefore not a necessity, to eliminate the reversing mechanism in the drum drive transmission, thereby saving a considerable item of cost and simplifying the present truck-mixer structure. Where end-charging is employed, this saving would not be considered practical, because the drum is normally rotated during charging to shrink the materials and enable larger batches to :be produced in a given drum.

Since it is realized that those skilled in the :art may vary the precise steps and combinations of steps constituting the method here described Without departing from the spirit of the invention, the invention is not to be limited to details of the above disclosure except as expressed by the following claims.

I claim:

1. In preparing a batch of ready-mixed concrete from fines, coarser aggregates, cement and water in, and effecting high-level discharge of the mixed batch from, a closed-bottom, spirally-bladed container rotatable about an axis of fixed inclination to the horizontal and having a substantially unobstructed central core-space: the method of rapidly and thoroughly mixing said ingredients which comprises subjecting relatively-shallow perimetral portions thereof to propulsion by said bladed-container, both rotatively with respect to the inclined axis and upwardly into the high end-portion of said container, while restraining said ingredients against discharge from said high end-portion; thereby effecting and maintaining, during an adequate, permissively-short mixing period, distribution of the ingredients-mass downslopingly from said high end-portion to the lower end-portion of the axial core-space, thereby inducing gravitational surface-cascading of ingredients from higher portions of the long slope toward its lower portions; and after such mixing period conditioning the high end-portion of the container for discharge of the batch therefrom, and efiecting ,such discharge by further propulsion of perimetral portions of the batch up to the high .discharge-level upon further rotation of said container in the same direction as in mixing the batch.

2. In the preparation of a batch of concrete from fines, coarser aggregates, cement and water in, and effecting high-level discharge of the mixed batch from, a spirally-bladed container having a transversely-closed bottom and a substantially unobstructed axial core-space, and which is rotatable about an axis of fixed inclination to the horizontal of the order of 10 to 20: the method of expediting and facilitating thorough mixing of the ingredients in amounts substantiaily exceeding, when duly mixed, half the volumetric capacity of the container, which comprises introducing water into the dry ingredients while subjecting relatively-shallow perimetral portions of the resultant mass to propulsion by said bladed containers revolution, both rotatively with respect to the axis and upwardly into the high end-portion of said container, so freeing part of said containers closed bottom from ingredients andrcducing the pressure of the ingredients-mass on the remainder of the closed bottom, while engendering end-to-end circulation of the ingredients and disposing the ingredients-mass downslopingl from the high end of the container to the low end of said core-space, thereby inducing surface-cascading toward the bottom of the core-space; restraining discharge of the materials from the high end of the container during mixing; and thereafter removing said restraint and effecting discharge of the batch upon continued propulsion of perimetral portions thereof up to said high-discharge level.

In the mixing of a batch of concrete from materials including fines, coarser aggregates, cement and water, in a container which is closed at its lower end, is perimetrally and shallowly bladed spirally, provides a relatively-broad, substantially-unobstructed axial core-space, and is rotatable about an axis fixedly inclined to the horizontal; and thereafter eifecting high-level discharge of the mixed batch from said container: the method of facilitating and expediting the thorough commingling of said materials prior to discharge thereof, which comprises introducing water into the lower portion of the said materials while perimetral portions of the latter are being propelled upwardly together with a portion of the water so introduced; continuing the stated propulsion of said materials for an adequate mixing period after the waters introduction, thereby to dispose the moistened materials-mass downslopingly from the upper end portion of the container to the closed end thereof, so creating a free space above the materials from end to end of the container and inducing free surface cascading of the materials, while simultaneously therewith effecting an end-to-end circulation of the materials-mass; and thereafter conditioning the high-end portion of said container for high-level discharge of the batch upon further propulsion of perimetral portions there.- of up to the discharge-level by further containerrotation in the same direction as in mixing the batch.

4. In the preparation of a batch of mixed concrete from the ingredients thereof in a closedbottom, spirally-bladed container rotatable about an axis fixedly inclined to the horizontal and having a substantially unobstructed corespace which communicates at its upper end with an extension-space provided by a dischargerestraining element: the method of facilitating and expediting the mixing of said ingredients, which comprises rotating said bladed container during a mixing period in such direction as to propel perimetral portions of said ingredients both rotatively and longitudinally-upwardly with respect to said axis into said extension-space, from which they cascade by gravitation to lower portions of the container for recirculation; said upward propulsion of the ingredients from, and

gravitational return thereof to, the lower portions of the container producing a distribution of said ingredients downsloping from the highend portion to the low-end portion of the container which provides a free working space above the ingredients from end to end of the container in which said cascading takes place; and, after the mixing period, disrupting communication between said core-space and extension-space and further rotating the container in the aforesaid direction, whereby the upward propulsion of perimetral portions of the mixture resulting therefrom will effect high-level discharge of the batch from the upper end of the container.

CHARLES F. BALL.

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