This invention relates to bulk material handling systems and, more particularly, such systems having a static container and means to move material from such container.
Bulk-solid metering systems are used to feed finely divided (powdered or granular) material into processing equipment. The processing equipment fed by the metering system (or plural metering systems) uses the material as the sole constituent or as one of the constituents in the intermediate or final product to be made. For reasons that will become apparent, it is important that a bulk-solid metering system deliver a precisely-measured amount of material for each unit, e.g., minute or hour, of operating time. Sophisticated gravimetric and volumetric measuring systems have been developed to help assure the bulk-solid metering system performs in this way. Examples of bulk-solid metering systems are disclosed in U.S. Pat. Nos. 4,804,111 (Ricciardi et al.); 4,983,090 (Lehmann et al.); 5,201,473 (Pollock); 5,215,228 (Andrews et al.) and 5,301,844 (Ricciardi et al.) while hoppers and mass flow bins which might be used in such systems are disclosed in U.S. Pat. Nos. 4,958,741 (Johanson) and 5,361,945 (Johanson).
As but one example of how bulk-solid metering systems are used, a commercial bakery may employ several bulk-solid metering systems to feed one or more types of flour and other ingredients into a large machine for mixing bread dough. It is not unusual to automate the installation so that the operator can program which metering systems are to be operated and the feed rates therefor in order to make a particular type of bread.
As another example, a manufacturer of pharmaceutical products, e.g., cold tablets, may use plural bulk-solid metering systems to feed active and inert ingredients to a powder mixer. In turn, the powder mixer feeds what might be termed a pelletizing machine, the final output product of which is tablets.
Conventional bulk-solid metering systems are characterized by a support structure to which is secured a cone-like, wide-mouth feed hopper. At what might be termed its lower apex, such hopper has a conveyor embodied as a screw or auger rotating in a duct. The auger feeds the material in the hopper outwardly through the duct and the hopper spout to the processing equipment. The hoppers may be made of rigid or flexible substance and, if made of the latter, the system also includes paddles to agitate the hopper and help assure continuous flow of material in the hopper.
Very commonly, there is an extension hopper mounted to and above the feed hopper. The extension hopper increases the overall hopper capacity and where the hoppers are filled by batch filling from, e.g., an overhead crane, using two hoppers is significantly more efficient.
And while perhaps less common, it is not at all unusual to find a bulk-solid metering system in which the extension hopper is connected by a large tube to a bulk storage silo not unlike those found on farms. The silo holds a very large quantity of the material being metered by the system and is used to periodically xe2x80x9crechargexe2x80x9d the hoppers so that the bulk-solid metering system can run continuously for long periods of time.
While these earlier systems have been generally satisfactory for their intended purposes, they are not without disadvantages. Inevitably, repairs or other maintenance must be performed. In a conventional arrangement, the extension hopper must first be detached and lifted away from the system. Then the nozzle leading to the process equipment (such nozzle being connected to the feed hopper spout) is disconnected. Then the feed hopper auger and, depending upon the specific configuration, the auger drive are disconnected. Finally, the feed hopper is detached from and lifted upwardly out of the support structure for service. Disconnection and disassembly time is very substantial; the point, of course, is that during downtime, the user is not being availed of the value of the system.
Another disadvantage of certain known systems is that to a certain degree, the feed hopper is configured with ease of system fabrication and ease of hopper sidewall agitation in mind. These considerations are evidenced by hopper shape which, in horizontal cross-section, is rectangular along substantially the entire hopper height. Fabrication is easy since the feed hopper support frame is, itself, likely to be rectangular. And flat hopper sidewalls are or may be easier to make than curved sidewalls. Further, external agitation paddles work well against flat sidewalls. Considered from an ease-of-fabrication standpoint, a rectangular-section hopper is very easy to xe2x80x9ctransitionxe2x80x9d from a wide rectangular mouth to the narrow slot-like opening in which the conveying auger is mounted.
However, rectangular hoppers work somewhat poorly at promoting what is known as xe2x80x9cmass flow.xe2x80x9d Finely divided material in the hopper tends to xe2x80x9chang upxe2x80x9d along the straight-line seams formed at the junction of two contiguous flat sidewalls. This can impair the feed-rate accuracy of the system.
And that is not all. Where a rectangular extension hopper is used with a rectangular feed hopper, the xe2x80x9ctransitionxe2x80x9d joint between the two hoppers is difficult to seal. Further, rectangular extension hoppers are susceptible to side wall buckling due to high xe2x80x9chydrostaticxe2x80x9d pressure from the finely divided bulk material therein. (The study of the mass flow characteristics of finely divided materials and of hoppers used to hold them is no trivial matter. Numerous, highly complex technical papers have been written on the subject.)
And in the manufacture of certain food and pharmaceutical products, it is highly preferred to have the feed hopper substantially free of material from the previous batch before the next batch is xe2x80x9cchargedxe2x80x9d into such hopper. Some types of food and pharmaceutical materials deteriorate over time; xe2x80x9cfirst in, first outxe2x80x9d material management helps avoid incorporating deteriorated material into the product being made.
An improved bulk-solid metering system which addresses disadvantages of earlier systems would be a significant advance in this field of technology.
An object of the invention is to provide an improved bulk-solid metering system which addresses problems and shortcomings of earlier systems.
Another object of the invention is to provide an improved bulk-solid metering system which simplifies certain aspects of system repair and maintenance.
Another object of the invention is to provide an improved bulk-solid metering system which better promotes mass flow.
Yet another object of the invention is to provide an improved bulk-solid metering system which lends itself well to feed hopper agitation. How these and other objects are accomplished will become apparent from the following descriptions and from the drawings.
The invention involves a bulk-solid metering system of the type having a support structure and a feed hopper mounted with respect to the structure and having an upper edge. In the improvement, the structure includes an upper member and the upper edge of the feed hopper is below the upper member. The structure defines a lateral opening sized and shaped to permit the feed hopper to be withdrawn laterally through the opening.
A significant advantage of the arrangement is that the feed hopper can be serviced without removing any extension hopper which may be attached thereto. Another advantage is that if the feed hopper needs to be removed, the nozzle between the feed hopper spout and the process equipment being fed by the system need not be moved or, at most, needs only minimal time and effort to disconnect such nozzle from the hopper.
In more specific aspects of the invention, the support structure extends along a substantially vertical axis. The feed hopper includes a spout which extends from the hopper body along a first axis away from the vertical axis. The lateral opening is positioned to permit withdrawal of the feed hopper away from the vertical axis and along a second axis. Most preferably, the spout and the lateral opening are positioned with respect to one another so that the first axis and the second axis are about 180xc2x0 apart. An advantage of this arrangement is that work can be performed at what might be termed the xe2x80x9coperator sidexe2x80x9d of the bulk-solid metering system rather than from its xe2x80x9cprocess sidexe2x80x9d where service-obstructing downstream process equipment is located.
In yet other aspects of the new system, the feed hopper may be made of a flexible material or of rigid sheet metal. In either instance, it is preferred that the system include a feed hopper agitator or stirring system, respectively. With a flexible feed hopper, two such agitators are usually used and they periodically xe2x80x9cjarxe2x80x9d or push against opposite sides of the body of the feed hopper to help keep the material therein from xe2x80x9cbridgingxe2x80x9d or xe2x80x9cratholingxe2x80x9d and impairing smooth flow. The agitators are mounted for reciprocating movement along an agitator axis angled with respect to the second axis. In a specific embodiment, the agitator axis and the second axis are substantially perpendicular to one another.
Yet other aspects of the new system relate to the ability to remove the feed hopper without removing the extension hopper. An extension hopper mounted in material-feeding relationship to the feed hopper and the hoppers are joined to one another at a hopper joint. The hopper joint is below the upper member of the support structure. The feed hopper includes an upper or first flange, the extension hopper includes a second flange and a securing device is in overlapping relationship to the flanges, thereby fastening the hoppers to one another. In a highly preferred embodiment, the securing device is a circular hoop which overlaps with and engages both flanges.
For optimum mass flow characteristics and agitation capability, the body of the feed hopper is made of a flexible material. The first flange is made of a rigid material and is secured to the hopper body by such flexible material. That is, the rigid first flange is molded into the material which permanently bonds. A resilient sealing ring is compressed between the flanges and the extension hopper has a mounting member, e.g., a circular ring, removably affixed to the upper member of the support structure. When the system is so configured, the feed and extension hoppers can be easily joined to one another and, just as easily, the extension hopper can be removed from the support structure, if necessary.
Yet other aspects of the invention relate to hopper configurations. The extension hopper has an upper edge and a lower mouth and at any one of plural section planes taken between the upper edge and the lower mouth, the cross-sectional shape of the extension hopper is circular. In the feed hopper, its upper flange and its spout are spaced from one another with the conduit being below the upper flange. The feed hopper body has a first cross-sectional shape adjacent to the upper flange and has a second cross-sectional shape intermediate the upper flange and the spout. In a specific embodiment, the first cross-sectional shape is circular, thereby availing the user of very good mass flow characteristics. The second cross-sectional shape is other than circular in that it has a longitudinal axis and a lateral axis perpendicular to and shorter than the longitudinal axis. A specific cross-sectional shape is xe2x80x9crace-track-likexe2x80x9d in that it has rounded or half-circle ends joined by parallel straight sides. In a preferred embodiment, the longitudinal axis of the second cross-sectional shape is substantially parallel to the spout first axis.
Yet another aspect of the invention involves other components of the bulk-solid metering system. In a specific embodiment of such a system, the feed hopper includes a driven conveyor such as an auger. A conveyor drive unit, e.g., electric motor and speed reducer, is supported by the structure and mounted for movement between a conveyor drive position and a hopper-removing position.
In another embodiment, the feed hopper is made of a rigid material, e.g., stainless steel, rather than of a flexible material. In this embodiment, free flow of material in the feed hopper is promoted by a stirring mechanism within the hopper rather than by agitators outside the hopper. Such stirring mechanism is supported by the extension hopper and includes a drive unit, a stirring device and a power shaft extending between the drive unit and the stirring device. The power shaft is mounted for movement with respect to the feed hopper, thereby permitting the stirring device to be removed from the feed hopper.
In a more specific version of this embodiment, the drive unit and the power shaft are coupled to one another by a coupling. When the system is in use, the preferred coupling holds the stirring device at a predetermined location in the feed hopper and yet permits sliding movement of the power shaft in the drive unit.
But when it is desired to laterally withdraw the feed hopper for maintenance (or for other reasons), the sliding coupling also permits the power shaft to move upwardly through the drive unit. The system user can thereby raise the stirring device to the elevation necessary to xe2x80x9cclearxe2x80x9d the feed hopper as such hopper is withdrawn.
Other details of the invention are set forth in the following detailed description and in the drawings.