US 3871628 A
The present invention relates to a mobile conveying and mixing arrangement, particularly for powdered and/or particulate masses, which comprises two conveyors which are driven by a power source and convey components to be blended together into a mix from respective component containers. The arrangement is basically characterized in that the components are brought together in the lower portion of a mixing screw whose longitudinal axle is inclined relative to the horizontal plane and which is substantially enclosed by a casing. The diameter, pitch, r.p.m. and angle of inclination of the mixing screw are so mutually adapted to the volume of the combined components that said components only partially fill said mixing screw. The components are imparted a rolling, tumbling movement on their way through the mixing screw towards an outlet in order to produce an effective blending of the components.
Description (OCR text may contain errors)
United States Patent [191 Pulk et a1.
[ Mar. 18, 1975 CONVEYING ANDMIXING ARRANGEMENT, PARTICULARLY F OR POWDERED AND/OR PARTICULATE MASSES  Inventors: Elgas Pulk, Stockholm; John Paul Noren, Upplands Vasby, both of Sweden  Assignee: Stabilator AB, Bromma, Sweden  Filed: Dec. 5, 1972 ] Appl. No.: 312,385
 Foreign Application Priority Data Dec. 10, 1971 Sweden 15876/71  US. Cl. 259/165  int. Cl. B28c 7/06  Field of Search ..259/l61, 165,168,178 R, 259/7, 22, 97, 154, 164
FOREIGN PATENTS OR APPLICATIONS 1,296,354 5/1962 France 259/7 Primary Examiner-Robert L. Bleutge Assistant ExaminerPhilip R. Coe Attorney, Agent, or Firm-Pierce, Scheffler & Parker  ABSTRACT The present invention relates to a mobile conveying and mixing arrangement, particularly for powdered and/or particulate masses, which comprises two conveyors which are driven by a pow-er source and convey components to be blended together into a mix from respective component containers. The arrangement is basically characterized in that the components are brought together in the lower portion of a mixing screw whose longitudinal axle is inclined relative to the horizontal plane and which is substantially enclosed by a casing. The diameter, pitch, rpm. and angle of inclination of the mixing screw are so mutually adapted to the volume of the combined components that said components only partially fill said mixing screw. The components are imparted a rolling, tumbling movement on their way through the mixing screw towards an outlet in order to produce an effective blending of the components.
7 Claims, 11 Drawing Figures CONVEYING AND MIXING ARRANGEMENT, PARTICULARLY FOR POWDERED AND/OR PARTICULATE MASSES The present invention relates to a conveying and mixing arrangement, particularly for powdered and/or particulate masses, which arrangement includes conveyors driven by a power source, the components to be intermixed being conveyed, and combined, from individual containers.
When working with concrete it is normal that the powdered and/or particular masses in the concrete mix are blended together with or without the addition of water (wet and dry mix, respectively) at a mixing plant,
and thus not at the job site. This mix is then distributed, usually in a vehicle, to where it is to be used. A significant drawback with this system is that the mix must be used within a certain period of time so that the consistency of the concrete will not be jeopardized. The reason for this is that binding begins as soon as the binder (cement) comes in contact with the moisture that is usually found to a greater or lesser degree in the ballast material. Another drawback is that is it difficult to deliver just the right amount of the mix for a particular job and as a result, spillage may be considerable.
For certain uses, particularly the spraying of concrete, it is desirable for numerous reasons to vary the composition and water content of the concrete mix according to the degree of moisture of the foundation or bed on which the concrete mix is to be sprayed. The wrong amount of water will cause, inter alia, the worsening of the adhesion on the foundation with increased spillage and uneven strength of the finished concrete resulting. A varying degree of moisture in the ballast used will also mean that the addition of the same amount of water at different times will result in mixtures having different properties depending on the raw material used. It is desirable that the mix used has an optimum composition for a particular job.
For certain jobs it is desirable that an accelerator for increasing the rate of setting be mixed into the concrete mix. The present state of the art requires the accelerator to be admixed at an early stage, thus further complicating the time factor problem with the use of the concrete mix. Moreover, the accelerator often has to be added in larger quantities than is required so that an unnecessarily large amount of accelerator is used up. As mentioned above, it may even be desirable to temporarily change the proportions between the binder and ballast in the concrete mix. This is also difficult to achieve with present methods and equipment. Thus, it is obviously advantageous to be able to vary the proportions between the components between the components in the mix and to be able to make ready the mix immediately prior to its use in as large a quantity as is required.
The invention aims at producing a conveying and mixing arrangement which makes possible the mixing of the solid components in the concrete mix right at the job site at the rate corresponding to the rate at which they 'are used up. Another goal is to make possible the mixing of the solid components in accurately balanced proportions which can be mutually varied in a simple manner. The invention also intends to produce a robust, simple and mobile conveying and mixing arrangement.
These desiderata are accomplished by combining the components in the bottom portion of a mixing screw which is driven by a power source and whose longitudinal axle is inclined relative to the horizontal plane. This mixing screw is placed in a casing which substantially encloses it. The diameter, pitch, rpm. and angle of inclination of the screw are mutually adapted to the volume of the combined components so that these compo nents only partially fill the mixing screw. In addition, the components are imparted a rolling or tumbling motion on their way through the mixing screw towards an outlet so that they will be effectively blended together.
Other characteristics of the invention will be revealed in the rest of the description and the enclosed sub-claims.
The invention is elucidated below with the help of an embodiment shown on the enclosed drawings.
FIG. 1 is a schematic view of a concrete spraying unit.
FIG. 2 is a vertical projection of the conveying and mixing arrangement shown in FIG. 1 and mounted on a vehicle.
FIG. 3 is a side view of a primary conveyor and mixing screw with accompanying details.
FIG. 4 is a top view of what is shown in FIG. 3.
FIG. 5 shows a section along the line VV in FIG. 3.
FIG. 6 shows a section along the line VI-VI in FIG. 3.
FIG. 7 is a side view ofa secondary conveyor with accompanying details.
FIG. 8 is a top view of what is shown in FIG. 7.
FIG. 9 shows a section along the line IXIX in FIG. 7.
FIG. 10 shows a section along the line XX in FIG. 7 and FIG. III shows a portion of a longitudinal section through the primary conveyor and mixing screw.
FIG. 1 schematically shows the essential parts of a unit for spraying concrete. A conveying and mixing arrangement 2 is mounted on a vehicle 1. A conventional concrete sprayer 4 is fed from the outlet 3 of the conveying and mixing arrangement. The powdered and/or particulate masses which were blended together in the conveying and mixing arrangement 2 are conveyed in fluidized state from the concrete sprayer 4 by means of compressed air to a spray nozzle 5 where water under pressure is supplied. Thus, a ready-mix concrete is sprayed out of the spray nozzle 5 and its water content is controlled by the person handling the spray nozzle. As a result the advantage is gained of being able to easily alter the amount of water in the concrete mix to conform with the actual needs. By combining the components at such a late stage, there will be no problem with a concrete mix that has become too old for use. Moreover, it is quite simple to mix together precisely the amount of concrete required for a particular job. In the case illustrated here, it is preferable that the capacity of the conveying and mixing arrangement is equally large as the capacity of the concrete sprayer.
As is evident from FIG. 2, the conveying and mixing arrangement 2 includes pockets for the solid components in the concrete mix. Here, the pockets are placed side by side. One of them, the ballast-containing pocket 6, holds sand or the like while the other one, the binder-containing pocket 7, holds cement or the like. Both pockets open at the bottom at their respective screw conveyors, a primary conveyor 8 and a secondary conveyor 9, respectively. The primary conveyor 8 in communication with the ballast-containing pocket 6 turns into a mixing screw 10 at its upper end, the feed-out end, which screw extends to the outlet 3. The primary conveyor 8 and the mixing screw 10 share a common shaft 11 which forms a defined angle with the horizontal plane. Thus, the outlet 3 is higher than the primary conveyor 8. The secondary conveyor 9 in communication with the binder-containing pocket 7 opens with its feed-out end 12 closely above the bottom portion of the mixing screw 10. The primary conveyor 8 and the mixing screw 10 are enclosed in a common casing 13 whereas the secondary conveyor 9 is placed in a separate casing 14. The upper part of the casing 13 is fixed at the pocket 6 by means of bars 15.
In the example shown, the shaft 11 i.e., the primary conveyor 8 and the mixing screw 10 is driven by a separate power source 16 (see FIG. 3). The conveying capacity of the mixing screw 10 is preferably equal to the capacity of the concrete sprayer 4. The secondary conveyor has, as is shown in FIG. 7, its own power source 17 whose rpm. is made variable by a variator 18. It is hereby possible to vary the capacity of the secondary conveyor 9 thus also making possible a change, in a desired manner, of the proportions between the ballast and the binder. There are of course a number of other possible embodiments. For example, the shaft 11 and the secondary conveyor 9 can be interconnected via a gear with a fixed or variable ratio and, by varying the speed, within certain limits, of a common power source, it will be possible to change both the mixing proportions and the amount of the mix.
The casings 13 and 14 are U-shaped and open at the top, as is revealed in FIGS. and 6, 9 and respectively. Both casings substantially enclose the screw means placed inside them and the edges of the casings essentially reach up to a level even with the upper limits of the screw means. In addition, the end of each casing where the material is fed into respective conveyors is provided with a door 19 and 20 respectively which is openable for emptying and cleaning purposes. Moreover, the part of the casing 13 which encloses the mixing screw 10 is internally lined with a replaceable lining 21 of rubber or similar material, as shown in FIG. 6.
As is evident from FIG. 4, the diameter of the primary conveyor 8 is considerably smaller than the diameter of the casing 13 and the diameter of the mixing screw 10. Furthermore, the pitch of the primary conveyor is less than the pitch of the mixing screw 10 so that the capacity of the primary conveyor is less than that of the mixing screw. The dimensions and r.p.m. of the secondary conveyor are so adapted that the desired amount of binder is fed to the mixing screw 10.
The arrangement works as follows: The primary conveyor 8 is kept constantly filled with material from the ballast-containing pocket 6 and, because of the difference in dimensions between said conveyor and the casing 13, a stationary ballast layer is formed around the primary conveyor 8 while the ballast material in the primary conveyor is fed towards the mixing screw. The stationary ballast layer has a friction-reducing effect whereby larger particles at the outer diameter of the conveyor can be embedded in this layer instead of, as is usually the case, being squeezed against an adjacent wall.
The ballast from the primary conveyor 8 and the binder from the secondary conveyor 9 are brought together in the mouth of the mixing screw i.e., close to the connection to the primary conveyor. However, the amount of the ballast and the binder together is not enough to fill the mixing screw which is so dimensioned that the combined components, when conveyed through it, are made to roll or tumble in order to produce an effective blend of the components. The intermixed components are them emptied in an in an even flow into a concrete sprayer 4.
In order to obtain the desired rolling, tumbling movement, it is necessary, inter alia, that the components combined in the mixing screw have just the right amount of space available in the mixing screw. This is achieved, as mentioned above, by having both the pitch and the diameter in the mixing screw greater than in the primary conveyor. The ratio between the diameter D of the mixing screw and the diameter D, of the primary conveyor ought to be greater than l.20:l and less than 1.50:1, preferably about 1.35:1; the ratio between the pitch S of the mixing screw and the pitch S, of the primary conveyor ought to be greater than 1.511 and less than 2.511, preferably 2:] (see FIG. 11). The angle of inclination a of the shaft 11 towards the horizontal plane 22 (see FIG. 11) may be varied between a negative value, where the mixing screw 10 is placed lower than the primary conveyor 8, and a positive value where the mixing screw 10 is positioned higher than the primary conveyor 8. The greatest negative value for a is about -l0 and the greatest positive value is about +30". Normally, a positive value for a is chosen, preferably in the 18 22 interval to obtain the best mixing results. In order to make the duration of the blending process long enough, the mixing screw 10 ought to have a longitudinal extension corresponding to at least six times the pitch. The r.p.m. of the shaft is adapted to given data for the mixing screw so that the desired rolling, tumbling movement is obtained.
The spiral on commonly designed screws of the type used in conveyors forms a right angle with the screw shaft. In order to decrease wearing at the periphery, it is preferable that the spiral on both the primary conveyor and the mixing screw has an angle of inclination [3 relative to a line perpendicular to the axis so that the periphery of the spiral lies closer to the outlet than the spirals connection with the shaft does (FIG. 11). Angle B, which on conventional screws is 0, may be as great as about 3 but ought to be about 1.5". It has been shown to be preferable to have a plane surface rather than a curved surface on the spiral.
In order for the primary conveyor and the mixing screw to function satisfactorily, the pitch may not at any place decrease towards the outlet 3; otherwise the risk of clogging arises. The capacity of the primary and secondary conveyors ought to be variable so that it is possible to obtain a mixing ratio between 113.5 and 1:5.5 between thebinder and the ballast. Since the periphery on the primary conveyor is subjected to greater wear than the corresponding portion on the secondary conveyor, a pre-set mixing ration will gradually be altered. This is counteracted to a certain degree in that the walls of the spiral and the shaft also wear; however, it is still advantageous to regularly check for wearing and, by corresponding adjustment of the mutual conveying capacity of the primary and secondary conveyors, restore the desired value of the mixing ratio. By suitably selecting the adjustment interval, it is possible to retain substantial accuracy. When definite amount of wear is obtained, the screw e.g. may be provided with a facing which again increases the screw diameter and thereby prolongs the life of said screw. Operational reliability is further improved if the pockets are provided with means to prevent the components stored in the pockets to stick to said pockets. Therefore, these pockets can suitably e.g. be coated internally with plastics and optionally be equipped with mechanical or pneumatic vibrators which e.g. can be operated for a short period each time conveying is begun and ceased. This diminishes the risk for bridge building and the like.
In certain cases it is desirable to mix an accelerator into the concrete mix. The arrangement shown here provides different possibilities for mixing a powdered accelerator with the ballast and the binder. The best effect is achieved by first blending the accelerator in with the binder so that the particles which will affect each other come into as close contact as possible. This can be done e.g. by shaping a portion of the secondary conveyor 9 as a mixing screw and supplying accelerator to said portion in the desired amount, e.g. via an extra screw conveyor. Another, but less preferable possibility is to.instead add the accelerator in the mixing screw 10 in the same way as the binder. The supply of accelerator can be varied according to its need via suitable arrangements.
In order to further improve the mixing capacity of the mixing screw, it is possible to provide it with pegs, flanges or the like; however, tests have shown that this is not normally necessary. The lining 21 in the casing 13 serves as a wearing surface and impedes adhesion on the walls of the casing. It even has a certain noisemuffling effect. Because the casings 13 and 14 are open at the top, it is easy for the person handling the arrangement to control the mixing procedure. Moreover, cleaning is facilitated since easy access is provided.
The conveying and mixing arrangement 4 can be made mobile in numerous ways. This is advantageous for the effectiveness of the arrangement since a mobile unit can be moved into from one job site while the concrete is setting to another site where its use is required. If the different job sites are close to one another, it is also possible to leave the arrangement in one place and to transport only the raw materials essential for making the concrete. Normally, only one man is required to look after the conveying and mixing arrangement, and one man handles the spray nozzle. Thus, significant working capacity is achieved with a minimum of personnel. The opportunity of being able to produce an optimum concrete mix at all times results in a decrease of spillage and an improvement in the quality of the finished concrete as compared with what it is possible to produce with previously known arrangements.
The arrangement described herein can of course be used for purposes other than mixing concrete, and a number of different embodiments would be obvious to a man of art. For example, the number of components in the mix could be further increased, resulting in special demands on the embodiment.
What is claimed is:
1. An arrangement for conveying and mixing at least two different dry particulate components and including for each such component a container and a conveyor driven by a power source, said conveyors being arranged to bring together from their respective containers such components into a driven mixing screw having a feed-in end and a feed-out end;
a first conveyor for a first component being a screw conveyor joined with and changing into the feed-in end of said mixing screw, said first conveyor having a smaller pitch and smaller diameter than said mixing screw;
said first conveyor and said mixing screw being substantially enclosed by a common casing having a substantially constant inner width;
said first conveyor and mixing screw having a common shaft of constant diameter;
a second conveyor for a second component being arranged to discharge and to feed the mixing screw above the feed-in end of the mixing screw,
the ,screw surface of the mixing screw being continuous and imperforate between the shaft and a pcripheral outer edge at a constant radial distance from the shaft,
a radius to said screw surface having an angle ofinclination relative to a plane perpendicular to the lengthwise direction of said shaft and inclining away from said plane in a direction towards the feed-out end of the mixing screw,
the mixing screw having its diameter, pitch, r.p.m. and angle of inclination relative to a horizontal plane so mutually adapted to the volume of the components brought together that said components only partly fill said mixing screw and are imparted a rolling, tumbling movement on their way towards the feed-out end of the mixing screw, thus causing an effective dry mixing of the components.
2. Arrangement according to claim 1, wherein the ratio between the mixing screws diameter and the first conveyors diameter is greater than 1.20:1 and less than 1.50:1, preferably about 1.3521.
3. Arrangement according to claim 1, wherein the ratio between the mixing screws pitch and the first conveyors pitch is greater than 15:1 and less than 2.5:1, preferably about 2:1.
4. Arrangement according to claim 1, wherein said angle of inclination of the mixing screw axle relative to the horizontal plane is a value between -l0 and +30", the negative value implying that the mixing screws feed-out end lies lower than its feed-in end and the positive value implying that the mixing screws feed-out end lies higher than its feed-in end, said angle of inclination being preferably positive and lying within the +l8 and +20 interval.
5. Arrangement according to claim 1 in which the containers, the conveyors, the mixing screw and the powewr source are built together to form one unit.
6. Arrangement according to claim 5, wherein the unit is mobile.
7. Arrangement according to claim 1, in which said conveyors for the different components have a mutual variable capacity so that the components can be mixed in variable proportions.