Abstract:
A compact dedusting apparatus is mounted on the machine utilizing particulate material requiring contaminant cleansing to provide an economical and effective decontamination of particulate material immediately before utilization of the material. The dedusting apparatus includes a downwardly sloped infeed chute having an opening at the bottom thereof. A metering device in the form of a rotatable finned hub blocks the opening to constantly meter the flow of particulate material through the dedusting apparatus. The metering device is formed with flexible blades oriented at a slight angle to the slope of the infeed chute to provide a constant flow of material through the opening. A flow of air is directed through a wash deck positioned below the infeed chute to cleanse the particulate material. The air flow is directed along multiple paths including a path defining an air knife associated with the wash deck to facilitate the cleansing of the material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims domestic priority on U.S. Provisional Patent Application Serial No. 60/312,967, filed Aug. 16, 2001, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention disclosed in this application is directed generally to the cleaning and handling of particulate materials, such as plastic pellets, grains, glass, and the like, and particularly to the cleaning of particulate injection moldable materials as close to the actual molding process step as possible to significantly reduce contaminants. 
     It is well known, particularly in the field of transporting and using particulate materials, commonly powders, granules, pellets, and the like that it is important to keep product particles as free as possible of contaminants. Particulates are usually transported within a facility where they are to be mixed, packaged or used in a pressurized tubular system that in reality produces a stream of material that behaves somewhat like a fluid. As these materials move through the pipes, considerable friction is generated not only among the particles themselves, but also between the tube walls and the particles in the stream. In turn, this friction results in the development of particle dust, broken particles, fluff, and streamers (ribbon-like elements that can “grow” into quite long and tangled wads that will impede the flow of materials or even totally block the flow). The characteristics of such a transport system are quite well known, as is the importance and value of keeping product particles as free as possible of contaminants. 
     The term “contaminant” as used herein includes a broad range of foreign material as well as the broken particles, dust, fluff and streamers mentioned in the preceding paragraph. In any case, contaminants are detrimental to the production of a high quality product, and in some situations a health risk to employees of the producer and possibly even a source of danger in that some contaminants can produce a dust cloud which, if exposed to an ignition source, may explode. 
     Considering product quality, and focusing on moldable plastics as a primary example, foreign material different in composition from the primary material, such as dust, non-uniform material of the primary product, fluff, and streamers, does not necessarily have the same melting temperatures as the primary product and causes flaws when the material is melted and molded. These flaws result in finished products that are not uniform in color, may contain bubbles, and often appear to be blemished or stained, and are, therefore, unsellable. It is important to note that since these same non-uniform materials often do not melt at the same temperature as the primary product, the unmelted contaminants cause friction and premature wear to the molding machines, resulting in downtime, lost production, reduced productivity, increased maintenance and thus increased overall production costs. 
     Since dust and other contaminants are generated mostly by the transport system, it is of primary importance to not only provide apparatus for thoroughly cleaning the particles, but to do so as close to the point of use of the particles as possible so as to avoid the generation of contaminants through additional transport. Dedusters have been used for several years to clean materials in this application; however, the instant invention provides a large improvement over the prior art. Applicants identified the need for a smaller more compact deduster, capable of handling smaller volumes of product, yet also capable of thoroughly cleaning the product. Importantly, that the instant invention significantly reduces size and costs over prior similar machines and permits installation in the material handling process immediately before final use of the products rather than at an earlier stage after which re-contamination can occur. 
     In the past, larger dedusters were used to clean product that was then stored in bulk for later use in molding. The stored material was then often sent through a dryer to eliminate moisture just before injection molding. Moisture on the plastic pellets becomes steam in the molding machine, resulting in bubbles or discoloration in the final product. The more significant problem faced under the old system was that after cleaning and bulk storage, the particles had to be transported to the dryer, creating new dust and picking up new contaminants inherent in transport-so when the product reached the dryer, the dust and other contaminants would be “baked” on the pellets due to the high temperatures required for drying. Such problems make evident the value of cleaning just prior to drying and molding. With this new design, manufacturers will experience reduced scrap, improved end product quality, decreased maintenance on machinery, increased productivity, and short investment paybacks. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to overcome the disadvantages of the prior art by providing a compact dedusting apparatus that is capable of handling volumes of particulate material for feeding to a molding machine, while thoroughly cleaning the material before being used by the machine. 
     It is another object of this invention to provide an effective compact dedusting apparatus that can be thoroughly clean a flow of particulate material of dust particles and other contaminants immediately prior to the particulate material being used. 
     It is an advantage of this invention that the particulate material is not subjected to subsequent contamination after being cleaned through storage and handling operations. 
     It is a feature of this invention that the compact deduster can be mounted on a plastic molding machine to cleanse plastic pellets of contaminants as the pellets are being fed into the molding machine. 
     It is still another object of this invention to provide a metering apparatus that is effective to constantly meter the flow of particulate material through the dedusting apparatus. 
     It is another feature of this invention that the metering apparatus is formed as a rotatable finned hub that blocks an opening through the dedusting apparatus to control the flow of particulate material through the opening. 
     It is still another feature of this invention that the finned hub is rotated at approximately one revolution per minute. 
     It is another advantage of this invention that the finned hub utilized flexible blades that will deflect when encountering a material clog to maintain a uniform constant flow of particulate material through the deduster apparatus. 
     It is yet another object of this invention to connect the dedusting apparatus to a remote dust collector apparatus that provides a flow of clean air through the dedusting apparatus. 
     It is yet another feature of this invention that the air flow through the dedusting apparatus is directed in multiple paths, including a path that creates an air knife to help dislodge contaminants from the particulate material being cleansed by the deduster apparatus. 
     It is a further feature of this invention that the infeed device directing particulate material through the dedusting apparatus is formed as an angled chute with an opening at the lower portions of the chute to direct the flow of particulate material through the dedusting apparatus. 
     It is still another advantage of this invention that the metering device is rotatably mounted at a position over the opening at the bottom of the infeed chute directing the flow of particulate material through the dedusting apparatus. 
     It is still a further feature of this invention that the angle of the blades on the finned hub is oriented at an angle to the slope of the infeed chute to facilitate the flow of particulate material into the opening in the infeed chute. 
     It is yet another advantage of this invention that a magnetic flux field can be utilized to disrupt the electrostatic bond between the particulate material and the contaminants clinging thereto. 
     It is a further object of this invention to provide a compact dedusting apparatus that is durable in construction, inexpensive of manufacture, carefree of maintenance, facile in assemblage, and simple and effective in use. 
     These and other objects, features and advantages are accomplished according to the instant invention by providing a compact dedusting apparatus that can be mounted on the machine utilizing particulate material requiring contaminant cleansing to provide an economical and effective decontamination of particulate material immediately before utilization of the material. The dedusting apparatus includes a downwardly sloped infeed chute having an opening at the bottom thereof. A metering device in the form of a rotatable finned hub blocks the opening to constantly meter the flow of particulate material through the dedusting apparatus. The metering device is formed with flexible blades oriented at a slight angle to the slope of the infeed chute to provide a constant flow of material through the opening. A flow of air is directed through a wash deck positioned below the infeed chute to cleanse the particulate material. The air flow is directed along multiple paths including a path defining an air knife associated with the wash deck to facilitate the cleansing of the material. After passing through the dedusting apparatus, the particulate material is fed directly to the machine utilizing the material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The advantages of this invention will become apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein: 
     FIG. 1 is an elevational view of an injection molding machine having a dedusting apparatus incorporating the principles of the instant invention operably mounted on the feed hopper to remove dust particles from the particulate material being fed into the hopper; 
     FIG. 2 is a right, front perspective view of a first embodiment of a deduster incorporating the principles of the instant invention; 
     FIG. 3 is a left, front perspective view of a second embodiment of a deduster incorporating the principles of the instant invention; 
     FIG. 4 is an exploded right, front perspective view of the second embodiment of the deduster depicted in FIG. 3; 
     FIG. 5 is a front elevational view of a third embodiment of a deduster incorporating the principles of the instant invention; 
     FIG. 6 is a right side elevational view of the third embodiment of the deduster shown in FIG. 5; 
     FIG. 7 is a left side elevational view of the third embodiment of the deduster shown in FIG. 5; 
     FIG. 8 is a rear elevational view of the deduster depicted in FIG. 5; 
     FIG. 9 is a top plan view of the deduster depicted in FIG. 5; 
     FIG. 10 is a right front perspective view of the third embodiment of the deduster shown in FIGS. 5-9; 
     FIG. 11 is a left side elevational view of the deduster similar to that shown in FIG. 7, but depicting internal structure of the deduster; 
     FIG. 12 is a right side elevational view of the deduster similar to that shown in FIG. 6, but depicting internal structure of the deduster; 
     FIG. 13 is a cross-sectional view of the housing taken along lines  13 — 13  in FIG. 5; 
     FIG. 14A is an enlarged end elevational view of a first embodiment of the agitator member; 
     FIG. 14B is an enlarged end elevational view of a second embodiment of the agitator member; 
     FIG. 14C is a side elevational view of the agitator member orthogonal to the view of FIG. 14B; 
     FIG. 14D is a detail view of a fin forming part of the agitator member shown in FIGS. 14A and 14B; 
     FIG. 14E is an enlarged elevational detail view of the hub forming the central part of the agitator to which the fins of FIG. 14D are mounted to form the second embodiment of the agitator; 
     FIG. 14F is an enlarged detail view similar to that of FIG. 14E, except corresponding to the first embodiment of the agitator shown in FIG. 14A; 
     FIG. 14G is an elevational detail view of a portion of the deduster depicting the mounting of the agitator; and 
     FIG. 15 is an enlarged detail view of the chute member cooperatively positioned beneath the agitator to guide particulate material to the agitator for feeding into the deduster. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a practical application of the deduster of the instant invention can be seen. An injection molding machine  1  has a feed hopper  2  at the input into which is fed a controlled amount of raw material in the form of plastic pellets. The molding machine may be of any form or type, and is not part of the instant invention. Generally depicted affixed to hopper  2  is the deduster  10  of the instant invention through which the plastic pellets must pass on their way to hopper  2 . The embodiment of the instant invention shown here is intended to be part of a closed loop air circulation system, so there is a hose  12  feeding clean air to the deduster from the dust collector  14 , and a return hose  16  directing contaminated air from the deduster to the dust collector. The dust collector creates a vacuum in the return hose  16 . The instant invention permits the development of a deduster that is much smaller in physical size than ever before possible, and thus the insertion of such device in a location in the overall molding process that is immediately at the molding machine input. In this way, contaminants are substantially eliminated, saving considerable losses, reducing wear within the molding machine itself and reducing maintenance costs, and providing for the production of a more consistent looking and salable final product. 
     For purposes of explanation, FIG. 2 is provided as a simplified perspective of a first embodiment of the overall machine  10  of the instant invention, though it should be noted that the embodiment shown in FIG. 2 is somewhat different from that shown in the remainder of the drawings (however, there is no significant difference between the embodiments shown). Product (in this example, plastic pellets plus the usual contaminants associated therewith) is fed into inlet  15  where it enters a flux field generated by the primary magnetic flux field generator  20 . As more fully explained in earlier U.S. Pat. No. 5,035,331, issued on Jul. 30, 1991, which is incorporated herein in its entirety by reference, this magnetic flux field disrupts the electrostatic bond between dust and pellets. 
     The product then encounters agitator  25  that drops the pellets in a measured, consistent flow onto a wash deck where they are fluidized by wash air that lifts the lighter contaminants above the main product stream. The pellets then pass through a venturi chamber that regulates updraft air velocity, via an air knife (to be discussed further below), to a sufficient level to remove even difficult contaminants. The dust, fluff and streamers are carried out of the deduster through air outlet  30 . The air is filtered at the air inlet  35  and either recirculated to the wash deck through a dust collector, or discharged to the atmosphere. The cleaned pellets are then discharged through outlet  40  at the base of the unit  10  and into the utilization process, in this example, a plastic molding machine, as depicted in FIG.  1 . 
     The flux field serves to disrupt the static charge attraction of dust and other contaminants adhering to the primary particulate product, thereby allowing this unwanted material to be separated and removed from the product flow path. The magnetic field is varied in strength and frequency to vary the level and intensity of the flux field in order to more effectively cause separation of the contaminants and the primary product. Primary separation is achieved by airflow through the product by means of a perforated screen or wash deck to both remove the unwanted material from the flow path and to accelerate the primary product along that path. Prior art machines generally required multiple wash decks to achieve acceptable levels of product cleaning. Due to the ergonomic design and unique utilization of the instant invention it accomplishes acceptable levels of product cleaning with a single deck. A venturi zone creates high relative velocity counter-airflow to more effectively promote separation of the contaminants. Secondary cleaning and magnetic fields can also be provided. The discharged air is treated to trap the removed contaminants, preventing it from returning into the flow path. The subject apparatus preferably has a slight negative internal pressure to assure collection of the separated contaminants. 
     The magnetic flux generator  20  is not necessary in every application. If the dust particles to be removed are less than 100 microns in diameter, the generator should be used; however, for removal of dust particles greater than 100 microns in diameter, a magnetic flux generator  20  may not be necessary or essential. 
     Referring now to FIGS. 3 and 4, a second embodiment of the deduster can best be seen. One of ordinary skill in the fabrication arts will readily recognize that the deduster  10  can be constructed in many different ways from many different materials. The construction variables are generally not part of this invention, and the structure actually described should be taken as but a single example of how one can build such an apparatus that will be fully functional. More specifically, the components, assembly and subassemblies can be made from steel or plastic and other similar materials, and may be fabricated, cast or molded. Casting the housing  100  in aluminum or, for installations requiring high quality operations, in stainless steel has proven to be an economical alternative to fabricating the housing  100  from sheet metal which has been bent and welded into shape. The housing  100  is a single assembly that can be comprised primarily of subassemblies fabricated from steel sheeting and tubes. While the fabrication of the subassemblies and housing assembly will be clear to one of ordinary skill in the art from these figures, there are a few elements and structural components that should be described in more detail. 
     A third embodiment of the instant invention can be seen in FIGS. 5-13. While the configuration of the structural components of the deduster  10  vary between the embodiments disclosed in FIGS. 2-13, the general operation of the deduster  10  is substantially the same. Particulate material, such as plastic pellets, contaminated with dust or other associated contaminants, are fed into the deduster  10  through top opening  15 . The system and controls for feeding the pellets from bulk storage is known in the art and will not be described herein. The pellets fall onto chute  102  that is angularly fixed to feed the pellets from the rear toward a feeding and regulating device  25 , to be described in greater detail below, called an agitator. The chute  102 , importantly, is shaped to have an opening therein  104  with a curved lower portion, best seen in FIG. 15. A sight window  106 , seen best in FIGS.  8  and  11 - 13 , is positioned at the rear of the deduster  10  to allow an operator to view the operation of the wash deck  120  and judge the overall operation of the deduster  10 . 
     Referring now to FIGS. 11 through 12, additional details of the invention will be described. Particulate material to be cleaned is fed through the top opening  15  and onto chute  102  where they feed angularly and downwardly toward the bottom of opening  104 . As can perhaps be seen best in FIGS. 11 and 12, an agitator rotor  110 , mounted to motor  112 , extends into the opening  104  and generally blocks the opening  104  with respect to the flow of the material. FIGS. 14A through 14F show the structure of the rotor  110  as being formed as a metal hub  113  with reverse threads and flexible blades  114  adhered thereto. The blades  114 , when rotated by motor  112 , feed a measured amount of material through the opening. The number of blades  114 , and, therefore, the configuration of the metal hub  113 , can vary, as depicted in FIGS. 14E and 14F, depending upon the size and type of pellets being fed; however, for most situations three blades have been found to be acceptable and provide satisfactory results. 
     A critical component of this structure is the use of flexible material for the blades  114 . If the blades  114  are rigid, it has been found that the pellets tend to clog and jam the opening  104  and/or between the blades  114  and the chute  102 , resulting in an interruption of the flow of pellets to the wash deck  120  and in a breakage of the pellets. On the other hand, flexible blades  114  provide a continuous measured flow with no breakage or interruption. If a blockage is encountered, the blades  114  flex and thus pass enough material into the opening  104  to automatically and quickly restart the desired flow. The flexible material used for the blades  114  must be flexible enough to deflect when an obstruction is encountered, yet rigid enough to last a reasonable period of time. Polyurethane has been found to be a very acceptable material. 
     The angle of the blades  114 , i.e., the angle between the flight with the hub as seen in FIG. 14D (the acute angle to the left in FIG. 14D) is different than the angle of the chute  102 , as seen best in FIG.  14 G. This relationship, which can vary with the size of pellets being fed, tends to “walk” pellets that are caught down the flight toward opening  104 . The motor  112  is set to operate at about one revolution per minute, though can be modified, or made variable, depending upon the parameters mentioned above. The blades  114  are triangular-shaped to fit the opening  104 . 
     Immediately below the opening  106  is the wash deck  120  that is also an angled surface running from just below the rotor  110  downwardly toward the circular output  40 . Though designs corresponding to operation with different particulate materials or pellets may differ, the concept of an air wash deck  120  is known in the art and shown, for example, in U.S. Pat. No. 4,631,124. In general, however, wash deck  120  is a flat sieve-like member with holes or slots therein to allow air to flow through as part of the cleaning process. It has been found that the air is passed through and is properly directed by using a perforated directed material for the screen—the perforations are “louvered” to give better directional air flow. As best seen in FIG. 3, an optional air filter  122  can be located within the air flow immediately adjacent the wash deck  120 . In this second embodiment, a closed air inlet fixture  128  can be added that includes inlet and outlet openings  124  and  126  to direct the air flow through the deduster  10  in the desired manner. 
     Referring primarily to FIGS. 5-13, a vacuum draws air through the wash deck  120  via the return hose  16  interconnecting the outlet  152  and the dust collector  14 . A curved baffle  136 , best seen in FIGS. 11-13, helps prevent the pellets themselves from being pulled through the outlet tube  152 . A pressure gauge  140  may be conveniently added to provide a visual representation of the pressure in the deduster  10 . 
     For improved clarity, particular reference is made to FIGS. 11 and 12. Clean air from the dust collector is drawn into the inlet  150 , from which the air may flow along three different paths: (1) directly through the wash deck  120  (and through a filter if provided), and then through outlet stub  156  to outlet  152  back to the dust collector for cleaning; (2) directly across the housing  100  to the return conduit  158  and back to the dust collector via outlet  152 ; or (3) through the slot  160  below wash deck  120 , up into the semi-circular venturi chamber  162  and eventually out through outlet  152 . In the second embodiment shown in FIGS. 3 and 4, the inlet and outlet  150 ,  152  are completely separated by a fixed closure  164 ; however, in the preferred third embodiment, the inlet and outlet are not structurally joined except via the paths defined above. A pressure relief valve  166 , that is adjustable by manual movement of a thumbscrew working against a spring representatively shown at  167 , will provide a relief against excessive pressures. In the second embodiment shown in FIGS. 3 and 4, the relief valve  166  is incorporated into the closed air inlet fixture  128 . In the preferred embodiment of FIGS. 5-13, the pressure relief valve  166  is mounted vertically in the front face of the deduster  10 . 
     An adjustable damper  168  is fitted into outlet conduit  158  to further control the direction of the flow of air through the housing  100 . The adjustable damper  168  includes a rotatable baffle  169  mounted within the outlet conduit  158  and connected to an external actuator lever  169   a  to manually control the orientation of the baffle  169 . The actuator lever  169   a  can be disposed on the side of the return conduit  158 , as shown in FIG. 3, or more conveniently placed on top of the return conduit  158 , as is depicted in FIGS. 5,  7 ,  9  and  11 . The positional orientation of the baffle  169  varies the amount of air that can be passed through the outlet conduit  158  and, therefore, varies the amount of air passed through the wash deck  120  and the venturi chamber  162 . One skilled in the art will recognize that different particulate material, particularly different sized pellets of particulate material will require different air flow rates to provide effective cleansing of the pellets before being fed into the processing machine  1 . 
     In operation, pellets are dropped periodically or constantly depending on the product into opening  15  where they engage chute  102  and are fed to opening  104  and agitator  110 . Upon entering the deduster  10 , the pellets are subjected to the flux field created by the flux field coil  20 , and the powders, dust particles and other contaminants are thereby separated from the pellets. As the rotor  110  turns, pellets are released in a constantly metered flow onto wash deck  120 . The constant airflow created by the vacuum in outlet  152  is drawn through the openings in the wash deck  120 , fluidizing the stream of pellets and removing the contaminants from the deduster  10 . 
     Within the venturi chamber  162  the air taking what was described above as the third path is adjusted to create an “air knife”, i.e., the air flows within the system are adjusted so that the air flow upwardly through venturi chamber  162  almost supports or suspends the pellets falling from the wash deck  120 , thus moving the maximum amount of dust and contaminants upwardly to the outlet stub  156 . This air adjustment is done by the operator as he views the activity through sight window  106 . More specifically, the operator adjusts overall flows, including the damper  168  and valve  166  to control the activity he sees in the window  106 . Finally, the pellets fall through the outlet  40  into the molding machine. 
     The deduster  10  is of such size and construction to handle relatively small volumes of primary product. Generally, volumes less than 500 or 600 pounds per hour make up the best range for this apparatus  10 . Other practical applications for this invention will be apparent to one of skill in the art. Wherever it is critical that the primary material be as free from contaminants as possible, this compact deduster will find use. 
     It will be understood that changes in the details, materials, steps and arrangements of parts, which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles of the scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description may be employed in other embodiments without departing from the scope of the invention. Accordingly, the following claims are intended to protect the invention broadly, as well as in the specific form shown.