Abstract:
The invention is a device for conditioning a comminuted light alloy feedstock to heat and remove impurities from the feedstock. The conditioner device includes a reaction chamber having a substrate feed port for feeding the comminuted light alloy feedstock into the reaction chamber and a discharge port for allowing the conditioned feedstock to exit the reaction chamber. A scrubber gas baffle is positioned at one end of the reaction chamber and coupled to a scrubber gas injector which is configured to inject a scrubber gas through the scrubber gas baffle at a volume and rate of flow sufficient to fluidize the feedstock in the reaction chamber. A scrubber gas heater is also provided for heating the scrubber gas to a temperature sufficient to condition the feedstock as desired.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. provisional patent application Ser. No. 60/935,561 filed Aug. 20, 2007 and regularly filed application Ser. No. 12/098368 filed Apr. 4, 2008, the entirety of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates generally to methods and devices for scrubbing and conditioning particulate feed stock for use in metal casting. 
       BACKGROUND OF THE INVENTION 
       [0003]    Processing light metal alloys in a conventional way involves one of the two well know processes, namely cold chamber or hot chamber die-casting methods. These processes use melting furnace to melt light alloy at superheated temperatures and than inject the molten metal into a re-usable mold. Recycled material is also re-melted in the same furnace. In the process of melting magnesium cover gas is used to prevent magnesium from evaporation and burning. The cover gas used is often SF 6  Sulfur hexafluoride. A report by the US World Resources Institute reported that the global warming potential for SF 6  is 23,900 relative to CO 2 . This means that 1 kg of SF 6  in the atmosphere gives approximately same contribution to green house effect as 24 tonnes of CO 2  per tonne of the magnesium smelted. This gas is the dominant greenhouse contributor for magnesium smelters and die-casters. The life time of SF 6  in the atmosphere is estimated to be 3200 years. Due to these environmental problems, new processes that do not require potent SF 6  gas are being searched for worldwide. 
         [0004]    Feedstock is often contaminated with organic and inorganic inclusions coming from various contamination points in a life cycle of the feedstock. These inclusions are often introduced by the chip manufacturer unintentionally due to poor process quality control. Organic inclusions could be dust or lint, for example. Some of the contamination is sourced back to exposure to environment and handling from start of the chip manufacturing to end use location. Recycled magnesium chips are often too contaminated by the oil, water, wax, mold release etc. If used in a casting process, these chips would make poor quality parts unsuitable for demanding automotive industry. 
         [0005]    During processing, these inclusions and foreign material end up in the part and are seen in the castings, by metallurgical evaluation, as voids or are often converted with help of high melt temperature into oxides with very high re-melt temperature. The water molecules, on the other hand, and entrapped air or other gasses from the air get attached to the highly stressed surface of the comminuted particle due to known physical principles mostly in acute curvature of the chip. This causes in-homogeneity in melt and subsequently affects part quality. The water affects processing of the magnesium (not exclusive to magnesium) by creating explosive conditions where water is cracked into O 2  and H 2 . The hydrogen H 2  could create explosive mixture and unsafe processing. Humidity is undesirable within the feedstock. Attached molecules of other elements or gasses like oxygen and nitrogen to the chips are also undesirable input to the casting process. 
         [0006]    All current, environmentally friendly, light metal casting processes could benefit from fine feedstock that is clean, free of all contaminants, oxygen and nitrogen free. When this feedstock is then pre-heated to 150° C., preferably up to 200° C. or even up to 250° C., or even more preferably up to 400° C. (for magnesium) it can significantly improve part quality and metallurgical properties of the casting. All processes using granulated feedstock may benefit from the current invention by receiving down stream clean, conditioned and tempered feedstock that is scrubbed from all contaminants and dried from moisture as well as purged from inclusions of air contaminants like chemically unattached oxygen and nitrogen molecules. Heating metallic feedstock is not being currently practiced in industry. Heating uniformly shaped feedstock is a challenge, but heating chips of non-uniform and random shapes is very difficult with any conventional heating means. 
         [0007]    There are number of apparatuses claiming successful treatment of granular feedstock, but it is not known to these inventors, any application where randomly shaped light metal alloy chips are successfully and uniformly heated in temperature range 100° C. to 460° C. Heating granular substances other than light metal alloys has been used in industry for a long time. One form of the device for treating particulate product is U.S. Pat. No. 6,367,165 B1 where a granular product for generic pharmaceutical application claims the benefit of the baffle plate to distribute air in the fluidized chamber. Substantially horizontal input of air is claimed as main feature of this apparatus. Another disclosure U.S. Pat. No. 4,967,688 to Yoshiro at al., discloses powder processing apparatus with a rotating air permeable blades used to apply thin coating to chemical powders, treatment of food products and ceramic powders by liquid to apply thin coat of film to the particles. Both above disclosures are batch type structures. No cleaning and scrubbing features are mentioned or claimed in these disclosures. 
         [0008]    In U.S. Pat. No. 4,372,053 Anderson et al. relates to a method of drying particulate material within an enclosed chamber. Heating and cooling fluids are introduced in particular zones of the dryer to accomplish particular moisture content of the various grains, like corn prior to storage. 
         [0009]    In another U.S. Pat. No. 4,346,054 a fluidized bed apparatus is used for temperatures &gt;700° C. processing iron ore where fluidizing medium is under high pressure and is CO 2 , N 2  and or air. This also is a batch type fluidization apparatus. There seems to be a plethora of applications of the fluidized bed for efficient burning of organic matter and extracting heat from the burning medium. The U.S. Pat. No. 6,139,805 issued to Shuichi at al. using solid material containing a combustible and non-combustible material. Heat energy extracting plates are within fluidized bedchamber in a singular or multiple arrangements. 
         [0010]    None of the prior art describes the apparatus for heating metallic particles in a continuous process where fluidization and energy input transfer is done by the same fluidizing medium and/or by the recycled heat from other processes. So, there is a need for heating and scrubbing light metal particles from environmental contaminants and gases in a continuous manner with no adverse environmental impact and Greenhouse Gas Emissions. 
       SUMMARY OF THE INVENTION 
       [0011]    In accordance with one aspect of the present invention, there is provided a device for conditioning a comminuted light alloy feedstock to heat and remove impurities from the feedstock. The conditioner device includes a reaction chamber having a substrate feed port for feeding the comminuted light alloy feedstock into the reaction chamber and a discharge port for allowing the conditioned feedstock to exit the reaction chamber. A scrubber gas baffle is positioned at one end of the reaction chamber and coupled to a scrubber gas injector which is configured to inject a scrubber gas trough the scrubber gas baffle at a volume and rate of flow sufficient to fluidize the feedstock in the reaction chamber. A scrubber gas heater is also provided for heating the scrubber gas to a temperature sufficient to condition the feedstock as desired. 
         [0012]    In accordance with another aspect of the present invention, there is provided a device for conditioning a comminuted light alloy feedstock by scrubbing the feed stock with a heated inert scrubber gas sufficiently to drive off impurities such as water vapor, O 2  and other impurities. The device includes a reaction chamber having an upper end and a lower end. A substrate feed port for feeding the comminuted light alloy feedstock into the reaction chamber is positioned adjacent the upper end of the reaction chamber and a scrubber gas baffle is positioned adjacent the lower end of the reaction chamber for releasing a scrubber gas into the reaction chamber. A scrubber gas injector is provided for adjusting the volume and rate of flow of the scrubber gas released through the scrubber gas baffle sufficiently to fluidize the comminuted light alloy feedstock in the reaction chamber. A scrubber gas heater is provided for heating the scrubber gas to a temperature sufficient to condition the comminuted light alloy feedstock as desired, and a discharge port is provided for allowing the conditioned comminuted light alloy feedstock to exit the reaction chamber. 
         [0013]    In accordance with another aspect of the present invention, there is provided a feed stock conditioning device as described in the above paragraphs wherein the scrubber gas injector comprises at least one gas amplifier contained within a scrubber gas accumulation chamber positioned adjacent the scrubber gas baffle. The gas amplifier is oriented such that the scrubber gas is made to flow through the scrubber gas baffle. 
         [0014]    In accordance with another aspect of the present invention, there is provided a feed stock conditioning device as described in the preceding paragraph wherein the discharge port is formed on a discharge tube mounted within the reaction chamber, the discharge tube being movable within the reaction chamber such that the position of the discharge port relative to the bottom of the reaction chamber can be selected. 
         [0015]    In accordance with another aspect of the present invention, there is provided a feed stock device as described in the preceding paragraph further including a cowl mounted within the reaction chamber, the cowl surrounding the discharge tube. 
         [0016]    In accordance with another aspect of the present invention, there is provided a feed stock device as described in the preceding paragraph further including a first and second temperature sensor for reading a first and second temperature corresponding to the temperature of the feed stock adjacent the substrate feed port and adjacent the scrubber gas baffle, respectively. 
         [0017]    With the foregoing in view, and other advantages as will become apparent to those skilled in the art to which this invention relates as this specification proceeds, the invention is herein described by reference to the accompanying drawings forming a part hereof, which includes a description of the preferred typical embodiment of the principles of the present invention. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1 . is a perspective view of a structure for particulate scrubbing and conditioning immediately before use in the downstream processes. 
           [0019]      FIG. 2 . is a exploded view of the preferred embodiment for this invention. 
           [0020]      FIG. 3 . is a schematic enlarged view of the reactor chamber according to embodiments of the present invention. 
           [0021]      FIG. 4 . is a schematic isometric view of the lower part of a fluidized bed reactor shown with amplifiers for fluidizing medium and pre-heater plate. 
           [0022]      FIG. 5 . is a perspective view of one form the conditioner assembly with heater plate. 
           [0023]      FIG. 6 . is a schematic vertical elevation view of plasma heater for feedstock heating up to 460° C. 
       
    
    
       [0024]    In the drawings like characters of reference indicate corresponding parts in the different figures. 
       DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    New processing techniques for casting light metal alloy that does not require use of SF 6  is described in co-pending U.S. Pat. No. 1,209,836, the entirety of which is incorporated herein by reference. In this previous application to Stone at al., U.S. Pat. No. 1,209,836 we describe a method of processing magnesium by using, as a input to the process, cold mechanically comminuted chips or rapidly solidified granules which both possess unique micro structural features that facilitate transformation of the solid particles into semi solid slurry by heating it only. In the totally enclosed process, chips or granules are, by way of adding heat only, transformed into a semi liquid state that is then pushed into a closed mold and quickly solidified without need for cover gas. During the melting process it was observed that localized magnesium burning occurs during the processing cycle. While it occurs inside the totally enclosed confines of the melt containing barrel, it was observed by metallurgical analysis of the cast part. It was discovered that molecules of oxygen and CO 2  mixed with water mist and humidity from air remains entrained in the feedstock and at the suitably high melt temperature, mixture of these compounds in contact with molten metal starts an intense oxidation process. While effects of N 2  cause deterioration of the melt containment vessel, oxidation causes poor part quality. In this application scrubbing refers to the process of removing unwanted substances from the feedstock by the method and apparatus disclosed herein. Conditioning refers to a process of matching feedstock properties to the process input requirements. In this application, we will discuss effects of the oxidation caused by humidity and oxygen on the magnesium melt; however aluminum or other light metal alloys are susceptible to a similar phenomenon as well. In the case of magnesium melting, localized oxidation flare-ups, result in creation of the MgO structure that in the solidified parts can create high stress concentration and start material cracks. This is a disadvantage for high integrity castings used for automotive and other industries. Slightly different source for this kind of material contamination can be found when we use recycled magnesium alloy. 
         [0026]    Additionally, during processing, we have unexpectedly noticed, that feeding granular alloy into the melting barrel heated at 600° C. causes sudden increase in thermal gradients, resulting in stress in the containment barrel causing premature barrel failure. When a slower granulate feeding approach was adopted by experimentation, it was discovered that thermal gradients are sustainable but the rate of production is reduced by more than 25%. The water content in the feedstock can cause uneven heating due to latent heat of water that tends to slow down heating of the feedstock, as was observed with our experiments. To increase material throughput, it was necessary to pre-heat the granular material to at least 200° C. We have observed significant improvement in the integrity of the cast parts and high integrity casting was possible with this process. 
         [0027]    In order to solve the above problems, it is an object of the present invention to provide an apparatus and structure to scrub the magnesium feedstock from organic contaminants, moisture, oxygen O 2  and nitrogen N 2  etc. that could be present in the feedstock material in a batch and/or continues flow. It is further object of this invention to uniformly preheat the feedstock to preferably 250° C. and or most preferably up to 425° C. for magnesium alloy. It is further, object of this invention to control feedstock temperature in a closed loop with variation of the set point temperature not more than +/−1° C. and provide cycle to cycle uniform and consistent temperature of the feedstock that is demanded by the type of the light alloy processing. 
         [0028]    Further, another object of the present invention is to provide an apparatus that could effectively mix additives and modifiers to the feedstock for enhancement of casting properties of the part. 
         [0029]    Another objective of this invention is to recover at least 45% of the heat from the downstream casting process or heat from hydraulic oil or other cooling medium from the process. Or, most preferably accomplish high rate of energy recovery from downstream processes and recover up to 75% of the heat from the process by putting it back into pre-heating feedstock. 
         [0030]    Finally it is possible to have a process where energy input into the feedstock, and melting the feedstock and then injection of the feedstock into the mold, and then by removing heat from the casting and use that removed heat to pre-heat new feedstock and achieve closed energy balanced casting process. 
         [0031]    It is understood that once volatiles and gasses molecules are removed from the feedstock reactor, these volatile compounds O 2  and N 2  as well as humidity can be removed by suitably placed upstream equipment well known in the industry that will not be described in this application. Angled section (see  FIG. 1 , top right) of material feedstock in feed system can also be used for O 2  and N 2  and humidity removal and or argon (fluidized cocktail) recycling and/or refining for re-use and usage conservation. Volatiles would be preferably removed at the intake point of the feedstock where is lowest temperature and O 2 , N 2  and humidity can be condensed absorbed from the system. 
         [0032]    In order to achieve the above set goals of the invention let us review  FIG. 1 . Referring now to  FIG. 1  is a vertical cross-sectional view of the feedstock-conditioning reactor according to the preferred embodiment of the present invention. A feedstock-conditioning reactor has a substantially tubular reaction chamber  10  made from cylindrical structure  11 , located centrally along the axis of the conditioner. Reaction chamber  10  has upper and lower portions. The bottom of the chamber is mounted into a structural scrubber gas heater plate  14  where inert scrubber gas is preheated prior to injection into a reactor chamber  10 . A suitable scrubber gas, preferably inert gas like Argon (Ar) is heated by heater plate  14  and then passed trough gas chamber  20  and through scrubber gas baffle  50  by scrubber gas injector  30 . Preferably, gas injector  30  comprises one or more gas amplifiers, similar to one made by company BRAUER™ from England and sourced in North America from NexFlow™. The gas amplifier is used to enhance scrubbing gas volume required to fluidize the feedstock with minimum argon consumption. Gas amplifiers  30  are used to provide a simple, cost effective means of using small amount of heated pressurized argon to accelerate a large amount of returned argon in the gas chamber. It uses the low volume of high pressure inert gas to produce a high velocity, high volume lower pressure gas flow necessary to create fluidization of the feedstock in the reactor chamber  10 . 
         [0033]    Conditioned substrate exits the reaction chamber via discharge port  55 , which forms an opening in axially located discharge tube  40  passing from the reactor chamber through the perforated baffle plate  50  into gas accumulation chamber  20  and then centrally passing through the base plate housing structure and therefore creating an output passage  60  for pre-heated and conditioned feedstock that can be further conveyed to the down stream process. 
         [0034]    Similarly, inputting feedstock into the reactor chamber  10  is accomplished via the centrally positioned substrate feed port or tube  9 , which is 30-60 mm in diameter and enters through the reactor cover plate  7 . Just beneath the lower outlet of the in-feed tube is positioned cowl  8  which is formed as an inverted, right circular cone flange which surrounds or covers discharge tube  40 . This immersed, circular cone flange (see  8  on  FIG. 2 ) may force the feedstock to follow a more defined path on its way to the outlet tube  40 . The purpose of the cowl is to spread incoming feedstock uniformly around the reactor chamber and to act as a separator to divide the reaction chamber into first portion  10   a  located outside the cowl and second portion  10   b  located inside the cowl. A secondary purpose of the cowl is to guide pre-heated feedstock into an outgoing tube  40  such that the feedstock travels as indicated by arrows  51  and  54  which is in part counter to the flow of scrubber gas shown by arrow  53 . The outgoing tube  40  is threaded into a housing structure  14  (heater plate) and adjustable in height relative to the assembly. The reactor cover plate also houses two thermocouples  100  and  101  that each provides temperature feedback to controls system mounted elsewhere. Thermocouple  100  (T/C# 1 ) is positioned to measure temperature of the feedstock adjacent where the feedstock enters the reaction chamber. Thermocouple  101  (T/C# 2 ) is placed to detect temperature of the feed stock adjacent the vicinity of the baffle plate  50 . The volume and pressure of the hot inert gas will be controlled by the differential temperature of these two set points to ensure that the differential temperature is minimal. Minimum differential temperature translates into uniform heating from bottom to top of the feedstock in the reactor chamber. 
         [0035]    The reactor chamber is filled by feedstock up to 5-30 mm below port  55  of the outflow pipe  40 . This is done to ensure that reduced volume density of the feedstock during fluidization will get up to the rim of the outflow pipe and with fine regulation of the volume of the inert gas cocktail (mixture of inert and functional gasses) and at the correct temperature feedstock will leave the reactor chamber trough the outflow tube  40 . Incoming feedstock material will be replenishing outgoing heated feedstock, by directed flow to the side of the reactor chamber absorbing heat from the heat exchanger coils  80  so that continues flow of pre-heated and preconditioned feedstock will be maintained. By using argon with higher specific density than Oxygen and Nitrogen, it will naturally displace O 2  and N 2  attached to particles of feedstock and push water vapor, contaminants and residuals out trough the incoming supply pipe  9  and vent it in the containment vessel or be absorbed by upstream equipment out of the feedstock. 
         [0036]    Surrounding the reactor containment tube  11  is external containment tube  204 . There exists a space between inner reactor tube  11  and outer containment tube  204  to facilitate return of the hot inert gas accumulated in the area of the cone  8 . The gas amplifiers are suctioning return gas and combining it with heated inert gas and continually repeating this cycle. Return gas is therefore flowing between two cylinders. The space between cylinders  11  and  204  forms a mantle  70  which houses heat recovery coils  80  of the energy heat exchanger tubes within, which will return energy from the downstream process and deposit it into the feedstock. Additionally, thermal insulation is provided in the co-axial cavity between cylinders  202  and  204  to increase overall energy recovery efficiency 
         [0037]    Referring now to  FIG. 2  shows reactor structure in an exploded view with basic display of components and their functional relationships. Finally, external to the feedstock conditioner is coaxially located an external steel tube  202  covering over level of heat insulation not shown. Further we can see the bottom structural heater plate  14  broken down into its functional elements. At the top of the cover plate  7  is mounted the incoming feedstock supply tube  9  with side opening  222  for adding additives and alloy enhancing elements like additional metals, alloys, ceramics, oxides, whiskers, colorants etc., simply called functional additives. 
         [0038]    The bottom structural heater plate is a sandwich made of gas heater plate  217 , gas amplifier base plate  218  and, at the bottom of the conditioner, the gas heater cover plate  215 . This plate also has an insulating plate  216 . Gas heater plate  217  contains from the bottom side grooves for cable heaters. At the top side are gas grooves made to allow for fast heating of the inert gas or gas cocktail. 
         [0039]    Let us now turn to  FIG. 3 , representing the inner reactor cylinder  11 . Inner reactor cylinder  11  is made from highly thermally conductive material that will conduct heat from outside from the energy exchange tubs and also maintain uniform temperature along inner reactor wall. The inner reactor cylinder has a perforated floor  310  to facilitate inner gas passage from the gas amplifiers at the bottom gas accumulation area. Cylinder wall  11  is carved to facilitate feedstock containment and gas return passage. Inverted cone  8  is mounted with three standoff pins  320  to support the cone is extended axially to form preferred flow of the feedstock 
         [0040]    Referring now to  FIG. 4 , represents inert gas heating plate  217  that accepts supply of the inert gas at inlets  410  and  420 . Heating plate is shown without sealed cover plate. At the bottom of the heating plate is a resistive or inductive heater. Grooves shown represent gas paths. Two independent gas flows are shown to improve heating efficiency. 
         [0041]    Let us now see  FIG. 5 , representing the fully assembled view of the feedstock conditioner without bottom insulating plate and gas heater cover plate. The bottom side of the heater plate  217  shows heaters installed into grooves. The feedstock conditioner works by creating fluidized feedstock that will uniformly heat and burn all contaminants. O 2  and N 2  molecules mixed with humidity and water molecules will move up from the reactor and only clean feedstock at uniform temperature is discharged via exit pipe  60 . Firstly, feedstock material is supplied into the input supply tube  9 . Feedstock material is then uniformly distributed into a fluidizing bed. Once heated, feedstock material is dropped through the central out flowing pipe  60  to the plasma chamber as partially schematically shown on  FIG. 6 . It is anticipated that other sources of heating like direct heating of fluidizing medium is envision by using plasma source of heat. Plasma heaters could be easily incorporated in at least one-gas amplification devices  413  or elsewhere in the inert gas-feedstock path. Any type of the plasma heating is acceptable as long as temperature of the inert gas or fluidizing medium does not exceed 425° C. for case of processing Magnesium. The microwave activated plasma, induction plasma, gliding arc discharge plasma etc could be used in this specification. The type of plasma used could be DC but preferably three phase. AC (Alternating Current) plasma is most optimal for this application. 
         [0042]    It is envisioned that plasma generating system uses three electrodes inside a gas flow chamber creating synchronizing three phase plasma moving with frequency of supply around electrodes. It is not necessary to heat only fluidizing medium, it could also be possible heat mixture of inert gasses with feedstock in a plasma chamber. In operation, plasma is generated by application of electromagnetic field upon ionized inert gas, the applied field induces Eddy currents in the ionized medium and by means of Joule heating, and stable plasma is sustained. The operation of the electromagnetically sustained plasma in a plasma chambers, including ignition of plasma, is believe to be otherwise within the knowledge of one of ordinary skill in the art and does not need to be further described in the present specification. 
         [0043]    The plasma chamber contains:
         610 : Plasma housing—ultra high frequency energy transparent or absorbent material.     620 : Insulator     630 : Electrode—Electromagnetic energy source conduit.       
 
         [0047]    Energy could be electrical high frequency or micro wave to facilitate arc establishment and plasma maintenance. Plasma reactors and its benefits to the processing materials is well known and disclosed in patent to Hollis, Jr. et all U.S. Pat. No. 4,745,338. The secondary heating is used as an optional means of heating. It is preferable that only recovered heat is used for feedstock re-heating and scrubbing. 
         [0048]    Once pre-heated, feedstock material is dropped through the plasma chamber and finally feedstock material reach process feedstock delivery pipe (not shown on  FIG. 6 ) that is connected to injection casting machine (not shown) for further processing. 
         [0049]    A specific embodiment of the present invention has been disclosed; however, several variations of the disclosed embodiment could be envisioned as within the scope of this invention. It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.