US3480261A - Process of mixing - Google Patents

Process of mixing Download PDF

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Publication number
US3480261A
US3480261A US720043A US3480261DA US3480261A US 3480261 A US3480261 A US 3480261A US 720043 A US720043 A US 720043A US 3480261D A US3480261D A US 3480261DA US 3480261 A US3480261 A US 3480261A
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Prior art keywords
mixing
water
cement
speed
concrete
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US720043A
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English (en)
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Wilhelm Eirich
Gustav Eirich
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28C—PREPARING CLAY; PRODUCING MIXTURES CONTAINING CLAY OR CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28C7/00—Controlling the operation of apparatus for producing mixtures of clay or cement with other substances; Supplying or proportioning the ingredients for mixing clay or cement with other substances; Discharging the mixture
    • B28C7/02—Controlling the operation of the mixing
    • B28C7/022—Controlling the operation of the mixing by measuring the consistency or composition of the mixture, e.g. with supply of a missing component
    • B28C7/026—Controlling the operation of the mixing by measuring the consistency or composition of the mixture, e.g. with supply of a missing component by measuring data of the driving system, e.g. rotational speed, torque, consumed power

Definitions

  • the disclosure relates to a process for the intensive mixing of the ingredients in the preparation of construction materials such as concrete, calcium silicate brick or the like and includes the steps of varying the speed of a mixing element and/or adding of water so as to maintain the energy input substantially constant at the rated capacity of the power operated drive.
  • the mixer is initially operated at a speed to produce the rated capacity and water is gradually added simultaneously with a gradual increase in speed to maintain operation at rated load.
  • all the remaining water required is added at one time and the speed of operation of the mixing element is correspondingly increased.
  • the specific energy absorption of the mixture is, for example, so low that the desired advantage cannot be achieved.
  • a further consideration of this k-ind of preparation is that a slight variation of the mixing procedure must be made for different concrete formulations.
  • the binder content also influences the energy absorption of the mixture so that, for example, mixtures having a relatively low cement content produce an almost constant energy absorption whereas mixtures high in cement with an increasing proportion of water produce a sharp decrease in energy absorption.
  • the object of the invention is to provide a process for the preparation of construction materials in which a relatively large amount of energy can be introduced into a mixture in a short period of time and the binder content can be made more useful; and one in which the drive system for the mixer used in the preparation can be driven at its nominal or rated load dur-ing most of the entire mixing procedure so that a greater amount of energy 3,480,261 Patented Nov. 25, 1969 ice is employed than when a batch is prepared by conventional methods.
  • the present invention resides in the ⁇ discovery that by the further introduction of energy after the achievement of a completely homogenous mixture, the quality of the material, particularly its compressive strength, can be considerably increased, or if the same compressive strength is to be produced, a saving in binder of up to twenty percent can be achieved.
  • the intensive preparation of materials such as concrete, with strength and/or saving in binder is accomplished by mixing a binder and aggregate with quantity of thinner, such as water, and in such a manner that the mixer operates near its rated load and the mixing continued after the achievement of a homogenous mixture until further mix-ing work produces no further increase in the quality of the construction produced from the mixed product.
  • the achievement of this ultimate condition is determined by a series of tests involving a variation in Water/cement ratio, the duration of mixing, and the speed of the rotating element or elements of the mixing apparatus.
  • cement and aggregate materials are initially combined with a fractional portion of the total amount of water required, and the mixing procedure is carried out during a period of operation of the mixing apparatus at a speed at which the maximum output of the drive for the mixer is introduced into the mixture.
  • the remaining water is then introduced with a simultaneous increase in the speed of rotation of the mixing apparatus so that the mixer continues to operate at its nominal or rated load and the energy input into the mixed materials remains at the same value.
  • the aggregate (stone and/or sand) functions in the process as a grinding medium and produces silica powder by abrasion.
  • the mixer can be driven during the preparation of the materials so that the drive motor runs at its nominal or rated capacity during the entire course of the work.
  • the fractional amount of water used in the introductory step of the process, as well as the remaining Water added in the second step carried out with an increased speed of the mixer, can be adapted to a variety of different concrete compositions so that the energy input into the mixture during the entire preparation of concrete remains at substantially the same value.
  • the mixing procedure is begun near the maximum energy input which the drive can safely utilize, which is a function of the water/ cement ratio on the decreasing portion of the curve, and the addition of water follows continuously with a corresponding continuous increase in the speed of the rotating elements of the mixer to maintain the energy input substantially constant.
  • the maxing procedure is begun at an energy level approaching the maximum energy input to the mixer as a function of the water/cement ratio, and the remaining water is added in one portion with a simultaneous increase in the speed of the mixer in a single step.
  • the number of revolutions is adjusted so that the drive motor of the mixer is operated at about its rated load in both mixing phases.
  • the throughput of the above described preparation method can be increased by heating the concrete in the mixture.
  • the strength of the early set concrete can be so increased that molds, frames and forms may be quickly removed from concrete bodies of large dimensions.
  • molds can be used three times within a twenty-four hour period.
  • Such heating preferably takes place during mixing by the introduction of saturated steam at a pressure of 2.5-3 kg./cm.2, in a conventional manner.
  • the temperature of the concrete should not exceed 60 C., however.
  • Portland blast-furnace cement is particularly suitable.
  • the mixing procedure may be carried out in a countercurrent mixer with a main mixing system continuously rotating at uniform speed and a variable speed mixing element or agitator.
  • the high speed mixing element strongly promotes the intensive preparation of mixed materials.
  • Mixing shovels are principally necessary for emptying the machine.
  • By the use of a barrier wall it it possible to avoid the use of ywide-area mixing shovels, so that all rotating systems can operate with a relatively high rate of speed and thereby noticeably increasing the overall effect.
  • FIG. 1 is a plot of several curves showing the energy requirement of a rotating type mixing element of a countercurrent mixer at different speeds of rotation of the element and for mixtures of diiTerent consistencies;
  • FIG. 2 is a further plot of curves showing the continual increase in the speed of rotation of the mixing element with a continuous addition of water during the second process step of the present invention
  • FIG. 3 is a schematic view of an apparatus suitable for carrying out the process of the invention.
  • FIG. 4 is a schematic plan view of the apparatus.
  • FIG. 5 shows a drive mechanism for the mixing apparatus of FIGS. 3 and 4.
  • the curves of FIG. 1 were determined from using a countercurrent mixer having a rotary mixing element and loaded with a mixture comprising 750 liters of aggregate, 175 kg. of cement, and 140 liters of water.
  • the rotating element had the form of an H.
  • Lower curve I was determined at an agitator revolution of 200 ⁇ r.p.m.
  • upper curve II was determined at an agitator revolution of 400 r.p.m. Both curves clearly show the very different total energy input of the drive motor of the mixer for different numbers of revolutions and different consistencies of the mixture.
  • Curves I and II of FIG. 2 were plotted from data obtained from the same machine when filled with the same material as in FIG. 1.
  • the rotative speed of the [cyclone type] mixing element was continuously raised from 200 r.p.m. to 400 r.p.m. at point 2 with continuous addition of water until a desired water/cement ratio of 0.75 was reached.
  • the maximum energy input to the machine can be held at a substantially constant value, here shown as 40 kw., despite an increase in the rotative speed to 400 r.p.m.
  • a tine reduction of the binder is brought about from the very beginning and then is further increased in the second step of the process upon increasing the number of revolutions of the rotating mixing element and upon addition of the remaining quantity of water until the water/ cement ratio is about 0.65, for example.
  • the first step of the intensive preparation requires only a very short period of time (for example 40-70 seconds), whereupon the addition of the remaining water follows and the number of revolutions of the rotating mixing element is increased. The latter is raised from time to time as the consistency of the mixture softens upon the addition of water, so that the drive motor is kept near its nominal or rated load.
  • the mixture can be discharged after as little as an additional '20-40 seconds of operation.
  • the maintenance of the energy demand of the drive motor at a constant value is accomplished for different concrete formulations on the one hand by graduated water additions and, on the other hand, by varying of the speed of rotation of the mixing elements. It has been found that the energy demand of the drive motor for a rotating mixing element increases almost proportionally with the increase in the number of revolutions thereof, and that this ratio is Variable within certain limits depending on the consistency of the material being mixed. Concrete mixtures having a low cement content, for example, show an almost constant, relatively high, specific energy demand over the entire range of consistences conventional in concrete technology. Concrete mixtures having a high cement content, in contrast, have a steeply decreasing specic energy demand with increasing water/concrete ratio.
  • the process of the invention can also be used for maintaining a certain constant concrete consistency, particularly when the consistency lies in the region of the steeply decreasing Ibranch of the energy requirement curve. In this case, the addition of water is stopped as soon as the energy input of the mixer has reached a value corresponding with the desired linal consistency.
  • the rotative speed of the mixing element is adjusted to the maximum permissible load and the intensive preparation is completed.
  • a first quantity of water can be added depending on machine load, that is, the addition of water is discontinued when a value in the neighborhood of the energy maximum is reached.
  • any residual portions of water still lacking can be quickly introduced with a water meter and the mixing continued, or the step of adding the remaining water may be eliminated if the smaller drive demand corresponding with the desired region of consistency is reached.
  • Variable speed electric or hydraulic motors can be employed to drive the mixing element. Regulation of the rotative speed can be carried out by means of automatic control switches either automatically or by hand.
  • Example I An aggregate having a particle size of from 0-30 mm. and a suitable amount of cement, for example in a ratio of 3400 kg. aggregate to 500 kg. cement, is supplied to a countercurrent mixer having a mixing apparatus and a cyclone type mixing element. Water is then added as quickly as possible in an amount such that the drive motor is loaded to its full rated load. In practice, a wattmeter will initially indicate that the energy input exceeds the rated load of the motor during the course of water addition. So much additional water then must be added that the watt meter returns to the rated load for the motor. For this composition, intensive mixing takes about a minute.
  • the duration of the intensive mixing is dependent on the amount of cement employed and for larger quantities of cement, a longer intensive mixing is necessary in order to achieve line reduction of the numerous particles.
  • Prior test runs are used to determine which specific power consumption and in which time the optimum cement yield can be obtained, that is, the most satisfactory relationship between early strength, iinal strength and ease of workability for a particular concrete composition.
  • the remaining amount of water is added in order to bring the concrete to the desired consistency, and then the mixture is removed from the mixer.
  • Example 2 Cement, sand, and gravel are introduced as dry components into a countercurrent mixture as above and the total quantity of water desired for the nal consistency is added.
  • the variable speed mixer element or elements are then set at such an r.p.m. rate that the rated load of the drive motors is reached. Mixing is continued at rated load by varying the speed of rotation of the rotary mixing element or elements until the optimum binder utilization has been achieved, as determined by prior exploratory tests.
  • This in in distinction to the mixing techniques heretofore used in the art where the mixing machine always operates at the same rotative speed independent of the consistency and of the kind of concrete being prepared. Nevertheless, even in the preparation of concrete of a relatively soft consistency, the amount of energy necessary for an intensive preparation are not used.
  • Variable alternating current motors do develop good torque characteristics as soon as the desired number of revolutions is reached.
  • these motors in their standard form have the disadvantage of not being able to accelerate under a heavy load from a low to a high rotative speed.
  • the mixing bowl 1 may be rotated in a clockwise direction by conventional mechanism not shown in the drawings and the high speed mixing element 3 may be rotated in a counter-clockwise direction by mechanism described hereafter.
  • Positioning rod 5 is either movable vertically (FIG. 3) or rotatable within a limited angle (FIG. 4).
  • the drive for the drive shaft 6 of the rotating .mixing element 3 is shown in FIG. 5.
  • pulley 8 On each of its upper and lower faces, pulley 8 carries clutch discs '9 and 10, each of which is provided with a clutch facing.
  • the opposing clutch halves each have a pinion 11 and 12 linked to shaft 6 of the mixing element in a ratio of 1:1 or 1:4 (or 1:5).
  • the clutch discs are positioned on a stationary shaft 13 which is, however, vertically moveable.
  • the drive motor is started and brought up to a high speed of, for example, 1500 r.p.m. Then shaft 13 carrying the clutch discs is lifted and clutch 10 is brought into engagement. In analogous fashion, the upper coupling half 9 is activated.
  • the shifting of the clutch can take place manually, or by electric motor, through a small worm and wheel drive with limit switching. Continual contact pressure and maintenance of the median position is achieved by means of a spring introduced into the vertically moveable arrangement. Starting and switching of the drive motor follows from time to time from the idling position with the clutch in an intermediate position. All gears remain in mesh. It is possible to change the direction of rotation if desired.
  • the emptying blade 4 illustrated in the drawings can be omitted in mixers having bowls which can be tipped for emptying.
  • the curves of FIGS. l and 2 and the working examples pertain to mixtures containing cement.
  • the invention is also applicable to materials containing lime as a binder, for example calcium silicate brick (sandlime brick) mixtures.
  • materials containing lime as a binder for example calcium silicate brick (sandlime brick) mixtures.
  • sandlime brick calcium silicate brick
  • the avoidance of binder aggregates and the promotion of sand abrasion are critical because the presence of suiiiciently tine quartz powder s necessary for the development of the binding strength of the lime.
  • a process for the intensive mixing of the ingredients of a construction material with the aid of a mixing apparatus having at least one variable speed mixing element and a power operated drive for the mixing element which comprises the steps of supplying an aggregate, binder and thinner to the apparatus, adding thinner to the apparatus for varying the consistency of the mass, rotating the mixing element at different speeds in the materials supplied to the apparatus to mix the materials at the rated capacity of the drive, and varying at least one of the steps consisting of varying the speed of the mixing elements and adding thinner to the apparatus so as to maintain the energy input substantially constant at the rated capacity of the power operated drive for at least the time required to produce a homogeneous mixture, thereby to produce a. more intensive utilization of the mixing apparatus.

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  • Chemical & Material Sciences (AREA)
  • Dispersion Chemistry (AREA)
  • Preparation Of Clay, And Manufacture Of Mixtures Containing Clay Or Cement (AREA)
  • Mixers Of The Rotary Stirring Type (AREA)
US720043A 1967-04-11 1968-04-10 Process of mixing Expired - Lifetime US3480261A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE1967E0033771 DE1683811B2 (de) 1967-04-11 1967-04-11 Verfahren zur intensivaufbereitung von bindehaltigen baustoffmischungen

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US3480261A true US3480261A (en) 1969-11-25

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US720043A Expired - Lifetime US3480261A (en) 1967-04-11 1968-04-10 Process of mixing

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US (1) US3480261A (de)
CH (1) CH486298A (de)
DE (1) DE1683811B2 (de)
FR (1) FR1576415A (de)
NL (1) NL152789B (de)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4335966A (en) * 1979-12-22 1982-06-22 Elba-Werk Maschinen-Gesellschaft Mbh & Co. Method of preparing concrete mixtures
WO1996000640A1 (en) * 1994-06-30 1996-01-11 Max George Hood Apparatus for cement blending
EP4299170A1 (de) * 2022-06-30 2024-01-03 Liebherr-Mischtechnik GmbH Mischverfahren und mischer

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2718236C2 (de) * 1977-04-23 1986-06-26 Hacheney, Wilfried, Dipl.-Ing., 4930 Detmold Verfahren zum Herstellen von hochkolloidalen Zement-Wasser-Gemischen
JPS55104958A (en) * 1979-02-07 1980-08-11 Ito Yasuro Preparation of green blend by hydraulic matter and application thereof
FR2539323A1 (fr) * 1983-01-18 1984-07-20 Exper Rech Etu Batimen Centre Procede et installation perfectionnes de malaxage permettant de controler la fluidite d'une charge malaxee
FR2680887A1 (fr) * 1991-08-30 1993-03-05 Cappelletto Renzo Dispositif de regulation de vitesse destine notamment aux malaxeurs, et nouveau malaxeur destine notamment a la fabrication de sable de fonderie.

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3062514A (en) * 1958-09-25 1962-11-06 Waimer Eberhard Concrete mixer or the like
US3081983A (en) * 1959-12-31 1963-03-19 Thibodeaux Clifford Concrete mixer
US3160400A (en) * 1960-09-26 1964-12-08 Liner Concrete Machinery Compa Mixing machines
US3326535A (en) * 1965-02-19 1967-06-20 Clercx Roger Johannus Henricus Methods and equipment for preparing mortar or concrete

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3062514A (en) * 1958-09-25 1962-11-06 Waimer Eberhard Concrete mixer or the like
US3081983A (en) * 1959-12-31 1963-03-19 Thibodeaux Clifford Concrete mixer
US3160400A (en) * 1960-09-26 1964-12-08 Liner Concrete Machinery Compa Mixing machines
US3326535A (en) * 1965-02-19 1967-06-20 Clercx Roger Johannus Henricus Methods and equipment for preparing mortar or concrete

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4335966A (en) * 1979-12-22 1982-06-22 Elba-Werk Maschinen-Gesellschaft Mbh & Co. Method of preparing concrete mixtures
WO1996000640A1 (en) * 1994-06-30 1996-01-11 Max George Hood Apparatus for cement blending
GB2303562A (en) * 1994-06-30 1997-02-26 Max George Hood Apparatus for cement blending
GB2303562B (en) * 1994-06-30 1997-10-08 Max George Hood Apparatus for cement blending
US5908240A (en) * 1994-06-30 1999-06-01 Hood; Max George Apparatus for cement blending capable of forming a thick slurry
EP4299170A1 (de) * 2022-06-30 2024-01-03 Liebherr-Mischtechnik GmbH Mischverfahren und mischer

Also Published As

Publication number Publication date
DE1683811A1 (de) 1971-10-07
DE1683811B2 (de) 1976-04-22
NL6804423A (de) 1968-10-14
CH486298A (de) 1970-02-28
FR1576415A (de) 1969-08-01
NL152789B (nl) 1977-04-15

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