Patent Application
20150314482
This invention relates generally to concrete mixers, and more particularly to mobile concrete mixers that make concrete on a volumetric basis, rather than on a batch basis.
Concrete is an important and well-known structural material. It is used primarily as a paving material, but also to provide foundations, and other structural components. Concrete is a mixture of cement and aggregates. The most common cement is Portland cement, but other binding materials are also well-known and commonly used. The aggregates include rocks, sand, and other similar materials of varying sizes. The dry cement is mixed with water and the aggregate to form the concrete. Additionally, various other chemicals and admixtures may be included in the mixture depending upon the intended use of the concrete, as well as environmental factors such as temperature and relative humidity at the time the concrete is being mixed and poured.
Traditionally, concrete has been mixed in relatively large stationary mixing plants, and then loaded on to a truck with a rotating barrel to be transported to a job site. The rotating barrel keeps the concrete mixer flowable and mixed, until the truck can arrive at the job site.
Recently, mobile concrete mixing units have been developed that mix and dispense the concrete at the job site as it is needed. This is advantageous as it eliminates the need for transporting the wet concrete mixture. Additionally, it takes a lot of the guesswork out of trying to get the proper mixture to match the conditions at the job site. Moreover, many concrete mixtures begin deteriorating after they are mixed, and are subject to spoilage before they reach the job site. Some of these mobile concrete mixtures are of a volumetric nature, as opposed to a batch nature. That means that the stream of concrete leaving the mixer should be uniform at each time the mixture is being dispensed. In other words, the ratio of components in any given volume of the mixture should be uniform. In a batch system it is only necessary to assure that the ratio of ingredients in the entire batch matches a set standard.
The present invention is directed to overcoming challenges associated with volumetric mobile concrete mixers. Such mobile volumetric mixers commonly use hydraulics to mix the various components of the concrete. Because a concrete is relatively bulky and heavy the hydraulic systems can generate a lot of heat in the hydraulic fluid that needs to be dissipated. This can require a large volume of hydraulic fluid.
In cooler climates, as the air temperature approaches and drops below the freezing point of water, it can be difficult or impossible to mix and pour concrete that is structurally sound. In some climates this can significantly limit the number of days the mobile mixing unit can be used. Using warmer water can help in some cases, and will permit the mixing and pouring of concrete in colder temperatures; however, the water can quickly cool if its container is not insulated or heated.
Commonly, the volumetric mobile mixers include an aggregate bin situated above a moving belt. The belt is used to deliver the aggregate to a mixing area where it is mixed with the dry cement powder and water. It is known to divide the aggregate bin into separate chambers above the belt such that two types of aggregate may be included in the bin and mixed into the concrete. In these divided chambers, occasionally the weight of the aggregate upon itself can cause it to pack tightly enough to form a bridge between the divider and the sidewall of the bin once the belt starts moving, such that the aggregate stops freely flowing onto the belt. This can cause non-uniform mixtures. The bridging issue can be especially acute in cold temperatures when moisture within the aggregate can cause the aggregate to freeze together.
Another difficulty with mobile volumetric mixers is that the large volume of water can cause the unit to be unstable, especially when the water sloshes from side-to-side of the water storage tank during transportation, and also if the unit is on a significant side grade.
Another difficulty with using mobile volumetric mixers during cold weather is maintaining the water at a sufficiently high temperature to properly activate the cement.
A further issue related to mobile concrete mixers is the stability of the vehicle when cornering or driving on a side grade. The water tank can make the vehicle top heavy, and can cause the center of gravity to shift laterally as back and forth as the water sloshes within the tank.
Therefore, an objective of the present invention is to provide an improved volumetric concrete mixing system that includes a water tank within the aggregate bin.
It is another object of the present invention to provide a hydraulic fluid reservoir within the water tank in order to remove heat from the hydraulic fluid and warm the water.
It is a further objective of the present invention to provide a water tank within an aggregate bin of a volumetric mobile concrete mixer, such that the water tank serves to divide the aggregate bin into two separate compartments while also reducing the likelihood of bridging occurring within the aggregate.
It is a further object of the present invention to provide a mobile volumetric concrete mixer that has improved performance in cold temperatures.
According to one embodiment, the present invention is directed to a mobile concrete mixing unit that has a mobile frame with an aggregate bin mounted to the mobile frame. The aggregate bin includes a front wall, a rear wall, and sidewalls that span between the front and rear walls. Each of the sidewalls slopes downwardly and inwardly towards each other at a lower portion. A water tank is located within the aggregate bin. The water tank spans between the front wall and the rear wall of the aggregate bine. The water tank divides an upper portion of the aggregate bin into a first storage area and a second storage area, the first and second storage areas being open at a lower end. The water tank includes a water outlet for dispensing water. A conveyor belt is mounted to the frame below the lower ends of the first and second storage areas. A hydraulics system provides power to the mixing unit. The hydraulics system includes a reservoir of hydraulic fluid. The reservoir of hydraulic fluid is located at least partially within the water tank. A cement bin is mounted on the mobile frame. A control system controls operation of the conveyor belt, hydraulics system, and water outlet to mix aggregate from the aggregate bin, cement from the cement bin, and water from the water tank to form a concrete mixture, whereby heat from the hydraulics system is transferred into water within the water tank to cool the hydraulics system and warm the water. A lower portion of the water tank may slope downwardly and inwardly to prevent aggregate within the aggregate bin from bridging. A first baffle may be included within the water tank. The first baffle may be a plate spanning across a width of the water tank, including a plurality of openings to permit flow of water through the first baffle. A second baffle including a second plurality of opening to permit flow of water through the second baffle may also be provided in the water tank. A divider flange may extend downwardly from the lower portion of the water tank towards the belt. A resilient separator may be mounted to the divider flange and extend below the divider flange into close engagement with the belt. The reservoir of hydraulic fluid may include a hydraulic fluid inlet connected to an outlet of the hydraulics system and a hydraulic fluid outlet connected to a suction line of the hydraulics system, and the reservoir of hydraulic fluid may include a divider plate separating the hydraulic fluid inlet and the hydraulic fluid outlet to cause a flow of hydraulic fluid within the reservoir to thereby increase heat transfer between the hydraulic fluid within the reservoir and water within the water tank. A support rod may be mounted between one of the sidewalls of the aggregate bin and a sidewall of the water tank. The mobile frame may include a plurality of ribs that support the aggregate bin on the mobile frame, and the support rod may be aligned with one of the ribs.
According to another embodiment, the present invention is a mobile concrete mixing unit with a mobile frame and an aggregate bin mounted to the mobile frame. The aggregate bin includes a front wall, a rear wall, and sidewalls that span between the front and rear walls, with each of the sidewalls sloping inwardly towards each other at a lower portion. A water tank is located within the aggregate bin. The water tank spans between the front wall and the rear wall, with the water tank dividing an upper portion of the aggregate bin into a first storage area and a second storage area. The first and second storage areas are open at their lower ends. The water tank includes a water outlet for dispensing water. A conveyor belt is provided below the lower ends of the first and second storage areas. A lower portion of the water tank slopes inwardly away from the sidewalls of the aggregate bin to prevent aggregate within the aggregate bin from bridging. A first baffle may be provided within the water tank. The first baffle may be formed by a plate spanning across a width of the water tank with a plurality of openings to permit flow of water through the first baffle. A second baffle may also be provided within the water tank, including a second plurality of opening to permit flow of water through the second baffle. A divider flange may extend downwardly from the lower portion of the water tank towards the belt. A resilient separator may be mounted to the divider. A hydraulics system may be provided for providing power to the mixing unit. The hydraulics system can have a reservoir of hydraulic fluid, the reservoir of hydraulic fluid being located within the water tank enclosure. A control system may control operation of the conveyor belt, hydraulics system, and water outlet to mix aggregate from the aggregate bin, cement from the cement bin, and water from the water tank to form a concrete mixture, whereby heat from the hydraulics system is transferred into water within the water tank to cool the hydraulics system and warm the water. The reservoir of hydraulic fluid may include a hydraulic fluid inlet connected to an outlet of the hydraulics system and a hydraulic fluid outlet connected to a suction line of the hydraulics system. The reservoir of hydraulic fluid may include a horizontal divider plate separating the hydraulic fluid inlet and the hydraulic fluid outlet to cause a flow of hydraulic fluid within the reservoir to thereby increase heat transfer between the hydraulic fluid within the reservoir and water within the water tank. A support rod may be mounted between one of the sidewalls of the aggregate bin and a sidewall of the water tank. The mobile frame may include a plurality of ribs that support the aggregate bin on the mobile frame. The support rod may be aligned with one of the ribs.
Several benefits arise from locating the water tank inside in the aggregate bin with the hydraulic tank inside water tank, including: (1) Keeping the hydraulic oil cool. Even if water is hot, the water temperature will be less than hydraulic oil temperature. This also reduces the volume of hydraulic fluid needed for the system. (2) Preventing aggregates from freezing. The aggregates absorb heat from the water tank to help keep the aggregate above freezing and free flowing. (3) Maintaining water temperature. Typically in cold temps, aggregates are heated before loading, or else the loaded unit is kept in a heated location prior to use. The sand and gravel surrounding the water tank insulates the water tank and reduces heat loss from the tank to the environment.
The stability of the mobile mixer is improved by the location and shape of the water tank within the aggregate bin which lowers the overall center of gravity and maintains it closer to the longitudinal centerline of the unit. Additionally, internal baffles reduce sloshing of water, which in turn improves stability, especially during cornering and on side grades.
A series of brackets 48 extend inwardly from the sloped lower portions 26 of the sidewalls 23. These brackets 48 are each aligned with a corresponding rib 20. In a preferred embodiment, the brackets 48 are each affixed directly to a corresponding rib 20 and extend through the sidewall lower portions 26. A corresponding set of brackets 49 are provided on the walls of the water tank 42. Tie rods 50 are provided between the brackets 48 and brackets 49 in order to help support the water tank 42. Additionally, supplemental brackets 52 and 53 may be mounted on the upper portions 24 of the sidewalls and the water tank 42 respectively. Supplemental tie rods 54 may be mounted between the brackets 52 and 53 to provide additional stability for the water tank 42 within the bin 14.
As best seen in
The water tank 42 is provided with a vent opening 62 near the top of end plate 56. This vent opening 62 prevents a vacuum from forming above the water as the tank 42 is emptied, and prevents pressure build-up as the tank 42 is filled. The rear wall of the water tank 42 also includes a water inlet and outlet 64 that connects with water conduit 32 to provide water to the mixer 30. The water inlet and outlet 64 is used to provide an inlet to fill the tank 42 and to provide and outlet for water to the mixer 30 when concrete is being mixed. A manual valve (not shown) may be connected with outlet 64 to manually turn off the water supply. The rear wall of the water tank 42 may also include an opening 66 to attach a water level gauge. The rear wall of the water tank 42 also includes a hydraulic fluid vent opening 85 to provide a vent for the hydraulic fluid reservoir 78. A hydraulic fluid filling opening 87 is provided is provided adjacent to the vent opening 85 to permit adding hydraulic fluid to the hydraulic fluid reservoir 78 from outside the aggregate bin 14 and water tank 42. A sight tube opening 89 is provided to permit attachment of a clear tube attached to the hydraulic fluid reservoir 78 to permit a visual inspection of the hydraulic fluid. As an alternative to a clear tube, a sensor may be located at the opening 89 to monitor hydraulic fluid level.
A divider flange 68 extends downwardly from the lower extreme of the water tank 42. The divider flange 68 may be an angle that is welded, or otherwise secured to the bottom surface of the tank 42, as best seen in
One or more baffles 74 may be provided inside the water tank 42 to prevent water from within the tank 42 from sloshing excessively, especially during transportation of the unit 10. Each of the baffles 74 may take the form of a flat plate with a plurality of openings 76 that permit water to flow through the baffles 74. Each of the baffles 74 may span between the sidewalls of the water tank 42 and may be welded in place. In
A hydraulic fluid reservoir 78 may be provided within the water tank 42. The hydraulic fluid reservoir 78 is inserted into the water tank 42 through an opening in the rear end plate 56. The hydraulic fluid reservoir 78 has a shape of a generally tapered prism that is relatively wider at its base where it connects to the end plate 56, and relatively narrower at a distal end. The proximal end of the hydraulic fluid reservoir 78 includes openings 80 that connect to suction lines 38 of the hydraulic system 36 in order to provide cooled hydraulic fluid to the hydraulic system 36. The hydraulic fluid reservoir 78 also includes an opening 82 that acts as an inlet to receive relatively hot hydraulic fluid from the exhaust (return) line 40 connected to hydraulic system 36. The openings 80 and 82 may have standard fittings attached to permit easy and sealed coupling with the suction line 38 and exhaust line 40 respectively. A horizontal divider plate 84 is provided within the reservoir 78 to encourage the hydraulic fluid to flow along the walls of the reservoir as it flows from the inlet 82 to the outlets 80. The divider plate includes a plurality of openings 86 that permit the hydraulic fluid to flow through the divider plate. These openings are especially helpful when the unit is on a slope that might cause the fluid to pool at one end of the reservoir 78. In
The water tank 42 includes a lower portion having sides 88a and b that slope inwardly. This inward slope of the lower portion 88a and b of the water tank 42 is advantageous because it permits the aggregate to spread to a cavity as it drops onto the belt 28. This prevents an impingement point between the water tank 42 and the sidewalls 26 of the aggregate bin 14, which can cause compaction of the aggregate, and disadvantageously, can lead to a bridging effect whereby a bridge is formed between the water tank 42 and the sidewall 26 such that the aggregate above the bridge does not freely flow onto the conveyor belt 28. It should be noted that one of the sides 88a of the embodiment shown is sloped more steeply than the other side 88b. This increased slope of side 88b provides a larger storage space on that side of the water tank 42 within the aggregate bin 14. This larger storage space permits the aggregate bin 14 to store the separate aggregate components in a proportion that matches the concrete recipe. According to a common recipe for concrete, more rock aggregate by volume is used as compared to sand aggregate, such that the rock aggregate might be stored on the 88a side, such that the aggregate bin 14 will hold rock and sand aggregate that will make roughly the same amount of concrete.
The stability of the mobile mixer is improved by the location and shape of the water tank 42 within the aggregate bin 14. Specifically, the water tank 42 is relatively long and narrow, such that all of its weight is located very close to the longitudinal center of the truck 12. Furthermore, the water tank 42 is mounted to extend to the bottom of the aggregate bin 14, which keeps the center of gravity of the water and water tank 42 relatively low. Additionally, internal baffles 74 reduce sloshing of water, which in turn improves stability, especially during cornering and on side grades.
In operation, the water tank 42 is filled with water using inlet 62. Aggregate is loaded into the aggregate bin 14. If desired, separate types of aggregate may be placed on opposite sides of the water tank 42 without mixing. The water tank 42 acts as a divider to keep the two types of aggregate separate from each other. Dry cement powder is loaded into cement bin 16. There may be additional additives provided in other tanks or bins (not shown) on the truck 12, as is commonly known. A control system 41 is used to control and activate the various components. Power to the various components is provided by a hydraulics system 36 including hydraulic fluid. For example, the hydraulic fluid may be used to operate the mixer 30 and the conveyor belt 28. During a mixing operation, the conveyor belt 28 will continuously rotate beneath aggregate bin 14. Aggregate within the two sides of the bin 14 will drop onto the belt 28. The aggregate should freely flow onto the belt without impingement as a result of the sloped portion 88 of the tank 42. An adjustable gate (not shown) may be used to adjust the amount of aggregate provided by each rotation of the belt 28. As the aggregate is provided to the mixer 30, cement powder from the cement bin 16 is also provided to the mixer 30 via cement dispenser 34, and water is provided from water tank 42 to the mixer 30 via water conduit 32 connected to water outlet 64.
As the system operates, the hydraulic fluid will flow from the hydraulic system 36 through exhaust line 40 into inlet 82 of the hydraulic fluid reservoir 78. The hydraulic fluid will continue to flow across and through the divider plate 84 within the reservoir 78 and will be returned to the hydraulic system working components through the outlet openings 80 and suction line 38. The hydraulic fluid will be cooled by transferring heat to the water within tank 42. As a result of the high efficiency and capacity for removing heat of the large volume of water surrounding the hydraulic fluid reservoir 78, a relatively smaller amount of hydraulic fluid will be needed than would otherwise be necessary. Additionally, the warmed water within the water tank 42 will permit the concrete mixing unit 10 of the present invention to be used in lower temperature situations where the water and resulting mixture would otherwise be too cold.
A preferred embodiment of the present invention has been described above. It should be understood that modifications may be made in detail, especially matters of size, shape, and arrangement of parts. Such modifications are deemed to be within the scope of the present invention, which is to be limited only by the language of the claims, which are set forth below.
