United States Patent 3577648

A mixing method and apparatus wherein rock aggregates of graded sizes are stored in separate storage bins and conveyed separately through a heating zone, simultaneously heated, and combined together in predetermined portions. A heated bituminous liquid is added to the combined aggregates in predetermined proportions, and the aggregates and bituminous liquid are mixed together to form a hot asphaltic composition.

Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
34/60, 432/65, 432/86, 432/128, 432/130, 432/145
International Classes:
E01C19/05; E01C19/10; (IPC1-7): F26B3/00
Field of Search:
34/9,60 263
View Patent Images:
US Patent References:
2161354Method for lubrication of artificial silk1939-06-06Imray, Jr. et al.
1778515Art of treating shale or the like1930-10-14Hampton

Primary Examiner:
Camby, John J.
I claim

1. A method of preparing a bituminous mix comprising:

2. The invention of claim 1 wherein the step of separately conveying aggregates of dissimilar characteristics through a drying zone comprises moving the aggregates through the drying zone at rates which allow the aggregates to be dried to a predetermined moisture content.

3. The invention of claim 1 wherein the step of separately conveying the aggregates of dissimilar characteristics through a drying zone comprises controlling the volume of the aggregate being conveyed to control the quality of the bituminous mix.

4. In a method of preparing a bituminous mix of aggregates and bituminous liquid wherein aggregates of dissimilar size are dried and combined, the bituminous liquid is heated, and the aggregates and bituminous liquid are mixed together, the improvement therein comprising drying the aggregates before combining them.

5. Apparatus for preparing a bituminous mix comprising a multiple chamber storage bin for separately storing aggregates of different characteristics, a drying chamber, a plurality of conveying means communicating with the chambers of storage bin and arranged to separately convey aggregate from each of the chambers of the storage bin through the drying chamber, and mixing means arranged to receive the aggregates from the plurality of conveying means and mix bituminous liquid with the aggregates.

6. The invention of claim 5 wherein said plurality of conveying means comprise a plurality of wire belt conveyors each arranged to carry the aggregate through the heating chamber, and means for separately varying the bed thickness of the aggregate carried by each conveyor.

7. The invention of claim 5 wherein said plurality of conveying means comprise a plurality of wire belt conveyors each arranged to carry the aggregate through the drying chamber, and drive means for separately driving each of said conveyors.

8. The invention of claim 7 wherein said drying chamber comprises air heating means, blower means arranged to urge air in a downward direction through each of said wire belt conveyors, and damper means for regulating the flow of air through each of said wire belt conveyors.

9. The invention of claim 8 wherein said heating chamber includes duct means for recirculating the air through said wire belt conveyor.

10. The invention of claim 5 wherein said mixing means includes a rotatable tank for storing bituminous liquid and defining at least one opening in its upper portion, and means for rotating said tank to move its opening to a lower position and discharge its bituminous liquid through its opening.

11. The invention of claim 10 and further including weighing apparatus connected to said rotatable tank for determining the weight of the bituminous liquid in said rotatable tank.


When asphaltic concrete is used to build roads certain requirements specified by the local and national governments must be met by the contractor, These requirements usually include the size of the rock aggregate used in the asphaltic mix in the various layers of the road and the proportions of the bituminous liquid and the aggregates. Usually a larger sized aggregate is suitable for the lower layers of the road while the surface layers of the road are formed with smaller sized aggregates. Also, the graded aggregates are frequently mixed together so that a controlled mixture is used in the various levels of the road. The contractor can either screen his own aggregate or buy sized aggregate to mix with the bituminous liquid.

In the past, the typical procedure for creating the hot asphaltic or bituminous mix comprised storing graded lots of aggregate or a mixture of aggregate, mixing the graded aggregates together or blending the mixtures of aggregates in the approximate proportions that were to be ultimately mixed together, drying and heating the aggregates, elevating the dried aggregates through an elevator, screening the aggregates for separation into known sizes, combining predetermined quantities of known sizes of the aggregates together again and mixing the bituminous liquid with the aggregates, and storing or dispensing the bituminous mix into a vehicle for transporting to the construction site. It was necessary to initially separately store and feed the aggregates to the system in graded sizes or in properly proportioned mixtures so that the ultimate bituminous mix would contain the proper sizes of aggregates, and it was necessary to combine or blend the different sizes of aggregates together in order to economically dry the aggregates. This required the subsequent separation of the aggregates in graded lots so that the bituminous liquid was mixed with the exact weights of properly graded aggregates. Thus, the contractor was forced to initially combine different sized aggregates in order to properly heat them to economically dry and heat the aggregates, and after the heating step had been accomplished, the aggregates had to be separated or screened immediately before they were deposited into a batcher. This procedure required that the screening equipment be positioned vertically above the batcher, and that aggregate storage bins be positioned below the screening equipment, which created a relatively tall and expensive structure.


Briefly described, the present invention comprises a bituminous mixing method and apparatus which dries and heats graded aggregate in separate lots, and combines the separate aggregates together immediately before placing the aggregates in a batcher or mixer.

Another object of this invention is to provide a heating, drying, and conveying mechanism for use in a bituminous mixing process wherein aggregate can be conveyed separately from graded lots of aggregate, simultaneously heated and dried in varying quantities, and combined together as they are placed in a batcher or mixer.

Another object of this invention is to provide apparatus for preparing an asphaltic mix which is inexpensive to construct and maintain, convenient to operate, and which provides accurate control over the size aggregate used in the mix.

Other objects, features and advantages of the present invention will become apparent upon reading the following specification when taken in conjunction with the accompanying drawings.


FIG. 1 is a schematic perspective view of the bituminous mixing, storage and dispensing apparatus.

FIG. 2 is a schematic side cross-sectional view of the delivery end of the drier, the batcher, and the pug mill.

FIG. 3 is a schematic end cross-sectional view of the drier.


Referring now in more detail to the drawing, in which like numerals indicate like parts throughout the several views, FIG. 1 shows bituminous mixing assembly 10 which includes a multiple chamber storage bin 11, aggregate conveyor system 12, aggregate drier 13, hot aggregate storage bins 18, batcher 14, pug mill 15, mix conveyor 16, and storage silos 17.

Storage bin 11 includes a plurality of storage chambers 20, 21, 22, and 23 which converge in their lower portions and open onto conveyor system 12. Conveyor system 12 includes a conveyor for each storage chamber 20--23, which comprises feed conveyor 25 and transfer conveyor 26. Feed conveyor 25 is relatively short and positioned directly beneath its storage chamber, while transfer conveyor 26 is positioned to receive materials from feed conveyor 25 and carry the materials to aggregate drier 13. Each feed conveyor 25 and its transfer conveyor 26 is driven by a motor 27. Both feed conveyor 25 and transfer conveyor 26 are belt conveyors, and the length of transfer conveyor 26 is such that support rollers 28 are required beneath the upper flight of the belt conveyor to support the material conveyed.

As is best shown in FIGS. 2 and 3, aggregate drier 13 comprises a housing 31 that encloses heater conveyors 30, fan rotors 33, heaters 38, and forms a recirculating air flow system. Transfer conveyors 26 extend up an incline from feed conveyors 25 toward the entrance opening or hoppers 29 at the upper portion of drier housing 31. Transfer conveyors 26 are arranged to deposit the materials carried thereby onto drier conveyors 30 (FIGS. 2 and 3) which have upper flights 36 that extend through the upper portion of housing 31 and lower flights 35 that extend through the lower portion of housing 31. There is one drier conveyor 30 for each transfer conveyor 26, and each drier conveyor 30 is a wire belt conveyor. A bed thickness adjustment plate 32 is positioned adjacent each hopper 29 and vertically movable to spread the desired thickness of aggregate onto a conveyor 30. Fan rotors 33 are placed in side-by-side relationship in the lower portion of housing 31 and are driven by electric motors 34. Heaters or burners 38 extend into the lower portion of housing 31 and function to heat the air circulated in the housing. Each heater 38 comprises a cylindrical shell 39, a blower 40, and an oil feed conduit 41. A flame is created in shell 39 and the heat from radiation and convection from the flame functions to heat from radiation and convection from the flame functions to heat its cylindrical shell 39 and the air circulated within its shell. Each cylindrical shell 39 is positioned within a cylindrical housing 42 which is sized larger than its shell and defines an annulus 42a. Converging ducts 37 open at substantially a tangent into each cylindrical housing 42 and project up toward the upper flights 36 of the drier conveyors. Fan rotors 33 each function to pull air in a downward direction through the upper flights 36 of drier conveyors 30, through one of the converging ducts 37, around annulus 42a of a cylindrical shell 39, and then expel the air in an upward direction. Housing 31 guides the air back around to a position above the upper flights 36 of drier conveyors 30, so that the air is recycled continuously through conveyors 30.

Each drier conveyor 30 is separated from its adjacent conveyor by partitions 43, both above and below the upper flights 36 of the conveyors. Air flow control vanes or dampers 46 are positioned above each conveyor 30 and extend substantially the entire length of the upper flight 36 of each conveyor. Dampers 46 are arranged so that they can pivot to close off or reduce the flow of air through their respective conveyors. Dampers 46 can be manually controlled, thermostatically controlled, or controlled by various other automatic means.

In order that the dust or small particles of debris be removed from the air circulating within housing 31, an elongated recess or pocket 48 is formed in each cylindrical housing 42 and an auger or screw conveyor 49 is located in each pocket. As air flows about annulus 42a the heavier debris is thrown into a pocket 48 by centrifugal force and removed from the system by conveyor 49. In addition, a small centrifuge 50 is placed below the outlet end of the upper flights 36 of the drier conveyors 30, and includes an exhaust blower 51 to remove approximately 10 percent of the flowing air from the system.

As is shown in FIG. 2, a plurality of hot aggregate storage bins 18 are positioned below and at the ends of the upper flights 36 of conveyors 30. Each hot aggregate storage bin 55 is separated from the adjacent bin by partitions 56, and the walls of the bins converge together at their lower portions. The outlet of each hot aggregate storage bin 55 is controlled by a swing valve 58 which is actuated by an hydraulic cylinder 59. One cylinder 59 is provided for each swing valve 58, so that the aggregate flowing from each bin 55 can be individually controlled.

Aggregate batcher 14 is of conventional construction, and is positioned below the plurality of hot aggregate storage bins 18. Aggregate batcher 14 includes a pair of converging troughs 60, and the flow of aggregate through the converging troughs is controlled by pivotal gates 61. Aggregate batcher 14 is pivotally supported (not shown) below hot aggregate storage bins 18, and a weighing mechanism (not shown) is connected to aggregate batcher 14 in the conventional manner so as to determine the weight of the aggregate accumulated therein.

Liquid asphalt distributing pan 62 comprises a heated horizontal cylinder 63 having slots 64 along its curved upper portion. The cylinder is attached to bearings 65 at its ends for rotational movement. The bearings are also pivotally supported and a weighing mechanism (not shown) is connected thereto in order to determine the amount of liquid therein. Cylinder 63 is constructed so that the liquid flowing thereto flows into one end thereof. Hydraulic ram 66 is arranged to rotate cylinder 63 so that its slots 64 are moved to the lower portion thereof. With this arrangement, the liquid in cylinder 63 will flow from slots 64 when hydraulic ram 66 is actuated. If desired, cylinder 63 can be heated by flowing heated oil through passageways defined in its walls (not shown).

Pug mill 15 is of conventional construction and is located beneath batcher 14. A pair of shafts 70 are mounted in parallel side-by-side relationship and a plurality of arms 71 radiate from each shaft 70 at spaced intervals along the lengths of the shafts. Paddles 72 are connected to the ends of arms 71. The bottom wall 74 of pug mill 15 conforms to the path of travel of paddles 72, so paddles 72 generally pass immediately adjacent bottom wall 74, and sliding door 75 is movable back and forth over the opening to open or close pug mill 15.

Mix conveyor 16 extends from below pug mill 15 up toward the upper portion of storage silos 17. Mix conveyor 16 is a drag chain conveyor of conventional construction. Mix conveyor 16 delivers the mix to a distributing conveyor 78 above storage silos 17. Distributing conveyor 78 functions to deliver the mix to selected ones of silos 17.

After the hot aggregate and hot bituminous liquid are mixed in pug mill 15, the mix must be maintained at a relatively high temperature in order to prevent its hardening. Thus, mix conveyor 16, distributing conveyor 78, and storage silos 17 should be heated. For this purpose, hot oil heater 79 of conventional construction is provided to heat and supply oil to conveyors 16 and 78 and silos 17. The oil from heater 79 is circulated in the walls of storage silos 17 and in the walls of conveyors 16 and 78. Storage silos 17 are elevated by framework 80 so that trucks can pass beneath silos 17 and receive deposits of the mix from one or more of silos 17. Thus, the hot oil system functions to maintain the bituminous mix at a controlled elevated temperature until it is deposited into the truck.


The aggregate to be utilized in the bituminous mixing assembly 10 is screened or graded prior to being stored in multiple chamber storage bin 11. Each grade of aggregate is stored in a separate chamber 20--23. When bituminous mixing assembly 10 is placed in operation, heaters 38 of aggregate drier 13 are ignited and fan rotors 33 are energized. If a mix containing a small size aggregate is desired, the feed conveyor 25 and transfer conveyor 26 associated with the storage chamber having the smaller sized aggregate are energized, which causes the aggregate to pass to one of the hoppers 29 of aggregate drier housing 31. The conveyors 30 within housing 31 are continuously operated, so that when the aggregate reaches housing 31 on its transfer conveyor 26, it will be deposited onto the upper flight of a drier conveyor 30 and transported through a heating zone inside aggregate drier 13. Bed thickness adjustment plates 32 function to spread the aggregate on their respective conveyors at the desired thickness. Fans 33 function to continuously circulate air through housing 31, so that the air is blown down through drier conveyors 30. The air flows around annulus 42a about heaters 38, and heaters 38 reheat the air during each cycle through housing 31. If only a single one of drier conveyors 30 is transporting an aggregate through aggregate heater 13, the dampers 46 of the remaining drier conveyors 30 can be closed, or partially closed to insure that the proper air flow is maintained through the loaded drier conveyor 30. Also, if more "drying time" is required for the aggregate on one conveyor than the aggregate on another conveyor, the dampers can be adjusted to flow a larger volume of air through the slower drying aggregate.

As the aggregate passes through aggregate drier 13, it is heated and dried, so that when it reaches its hot aggregate storage bin 55, it is suitable for mixing with the bituminous liquid. In order to transfer aggregate from a bin 55, its hydraulic ram 59 is actuated to swing its valve 58 away from its lower opening, and the aggregate is deposited into batcher 14. When the proper weight of aggregate is present in batcher 14, its gates 62 will open and allow the aggregate to fall into pug mill 15. Hydraulic ram 66 is actuated to pivot cylinder 63 of liquid asphalt distributing pan 62 to move the slots 64 of cylinder 63 to a lower position and flow the bituminous liquid into pug mill 15. Shafts 70 of pug mill 16 will rotate in the direction as indicated by the arrows, to thoroughly mix the aggregate and the bituminous liquid. After the proper amount of mixing has taken place, sliding door 75 will be opened, and the mix will fall into drag chain conveyor 16.

Drag chain conveyor 16 functions to carry the mix up to the top of storage silos 17, where the mix is carried to one of the silos 17 by distributing conveyor 78. Hot oil heater 79 functions to supply the walls of storage silos 17 and conveyors 16 and 78 with hot oil to maintain the mix at an elevated temperature and heat the bituminous liquid.

With the arrangement disclosed, the aggregate can be carefully screened or graded prior to being placed in a chamber of storage bin 11. This will be the only time that it is necessary to grade the aggregate. Conveyor system 12 functions to carry the aggregate through aggregate heater 15 without mixing the aggregates from different storage chambers until the aggregates are deposited in batcher 14. There is virtually no possibility of combining or intermingling the aggregates together before they reach batcher 14. Furthermore, an easy visual inspection can be made of the storage chambers 20--23 of storage bin 11 to determine the quantity and quality of aggregate present in each storage chamber and the size of each aggregate. The aggregate is heated and dried just prior to being mixed with the bituminous liquid, so that virtually no heat loss is experienced. Bituminous mixing assembly 10 is generally oriented in a horizontal direction; that is, only a small amount of vertical movement of the aggregate and bituminous liquid is required in the process, and a tall expensive structure is not necessary to practice the mixing process. Of course, storage silos 17 are relatively tall since they function to store the mix at an elevation where it is ready for delivery to a truck, which is conventional in the industry.

While drier conveyor 30 of aggregate drier 13 have been disclosed as being continuously driven and transfer conveyors 26 have been disclosed as being driven at various different speeds by their respective motors 27 in order to vary the quantity of the aggregate passing through aggregate drier 13, both drier conveyors 30 and transfer conveyors 26 can easily be arranged to be intermittently driven and driven at varying speeds by conventional means, and dampers 46 are adjustable to vary the air flow as may be desired. With an arrangement of this sort, even further control of the aggregate deposited in batcher 14 can be maintained, and the proper proportions of air flow can be applied to each aggregate to obtain optimum drying speed. For instance, if two drier conveyors are being used and their respective transfer conveyors 26 and bed thickness adjusters 32 are arranged so that one conveyor 30 is transporting twice the bed thickness or volume of aggregate as the other, the dampers could be adjusted to flow twice the volume of air through the larger volume of aggregate and the conveyors driven at equal speeds, so that both aggregates would be dry as they approach their respective hot aggregate storage bins 55, or the dampers could be adjusted for equal air flow and the conveyor carrying the smaller volume driven faster than the other conveyor. Also, if the characteristics of the aggregates are such that they have different drying times for an equal mass of aggregate, the conveyor speeds and dampers can be adjusted to compensate for these differences.

If it is desired to prepare a mix having a mixture of graded aggregates, two or more of the conveyor systems can be energized to carry the aggregates from their respective storage chambers 20--23 through aggregate drier 13 to hot aggregate storage bins 55. The mix prepared in pug mill 15 will then contain aggregates in proportion to the amount of each aggregate fed from storage bin 11. Thus, accurate control can be maintained over the mixture of the aggregates in pug mill 15 by controlling the flow of aggregates from their respective storage chambers 20--23 into the conveyor system.

While this invention has been described in detail with particular reference to preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinbefore and as defined in the appended claims.