Abstract:
An on-line moisture analyzer and method of analyzing the moisture content of an ore concentrate. A sample conveyor moves a sample of the concentrate to be analyzed to an aluminum pan that receives and holds the sample of the concentrate. A horizontal linear slide having a pneumatic vertical lift mounted to rotary arm is detachably connected to the aluminum pan by gripping fingers that detachably engage the pan. A scale is accessible by the conveyance member for weighing the sample. An oven also accessible by the conveyance member has a door that has a complimentary shape relative to a cross section of the sample container and conveyance member is used for heating the sample. A programmable logic controller controls the conveyance member and the oven door. A data processing unit receives data from the scale and determines a moisture content based on the data.

Description:
TECHNICAL FIELD 
     The invention relates generally to the field of on-line testing of moisture content of processed material. In particular, the invention relates to an on-line moisture analyzer for testing the moisture content of ore concentrates. 
     BACKGROUND OF THE INVENTION 
     The moisture content of material being processed can be an important factor in assuring the quality of final product and in controlling manufacturing parameters to obtain an optimal moisture content. For example, in the iron ore industry raw ore is ground and mixed with water to form a slurry that is processed to remove undesired constituents such as sand. After processing, the slurry is filtered to remove the bulk of the moisture and the resulting “filter cake” is rolled in a drum to form pellets. The filtering process is controlled to produce a filter cake having a desired moisture content and the rolling process is optimized based on filter cake moisture content. The rolling process requires a relatively constant moisture content in the filter cake for proper processing. Deviations from the desired content can compromise the quality of the pellets. Therefore, it is critical to have real time information about the moisture content of the filter cake to achieve consistent high quality pellets. 
     Numerous techniques have been developed to test the moisture content of filter cakes and other ore concentrates. A reliable and relatively simple way to determine moisture content is to take a sample, weigh the sample, bake the sample or otherwise remove the moisture from the sample, and then weigh the sample again. The difference in the weight of the sample before and after baking corresponds to the amount of moisture that was present in the sample. This weighing technique is typically done manually in a laboratory environment due to the relatively involved process of obtaining, weighing, and baking the sample. Taking the sample to a separate location increases the delay between the taking of the sample and the availability of useful moisture information to process controls. In addition, the introduction of technicians into the measurement process means that human error may affect the accuracy of the results and that measurements can only be taken when a technician is on duty. 
     Existing on-line testing techniques monitor filter cake characteristics that are related to moisture content. These characteristics include electrical conductivity, dielectric properties, microwave absorption, and radio frequency transmission. Because the characteristics are affected by properties other than moisture content, such as the precise mineral content of the ore or ph of the water, they are unreliable and may only be accurate to about +/−0.50% (industry standard is +/−0.10%). Infra-red reflectance has been used as an indication of moisture content, but this method has proven unsatisfactory in a factory setting because it is susceptible to errors caused by water vapor or reflective surfaces in the optical path. Neutron activation principles have been employed that determine the hydrogen content of the concentrate from which moisture content is inferred. The devices used in this technique are bulky, complex, and require extensive shielding to diffuse the emitted radiation. One other technique involves correlating moisture content to the drag forces exerted on a probe by the concentrate moving on a conveyor. This method depends on a uniform distribution of concentrate on the conveyor, which is not realistic in a manufacturing environment. 
     SUMMARY OF THE INVENTION 
     According to the present invention, an apparatus is provided for measuring the moisture content of a concentrate, such as an iron ore concentrate. According to an embodiment of the invention, a sample container receives and holds a sample of the concentrate. A conveyance member has a plurality of conveyance devices that are connected to the sample container that each move the sample container about a single axis. A scale is accessible by the conveyance member for weighing the sample. An oven having an oven door accessible by the conveyance member heats the sample to remove the moisture. A controller controls the conveyance member and the oven and a processing unit receives data from the scale to determine a moisture content based on the data. 
     In an embodiment, the conveyance member is a sliding carriage, such as a horizontal linear slide, having a rotatable arm for rotating the sample container about an axis of rotation. A pair of opposing fingers apply a gripping force to the sample container and may have at least one pin insertable into the sample container. A pneumatic vertical lift lifts the arm and the arm features a torque limiting brake. 
     In an exemplary embodiment, the oven door has a complimentary shape relative to a cross section of the sample container and conveyance member and is adapted to open in response to a signal from the controller. The processing unit determines the moisture content of the sample by finding a difference between a first weight of the sample container before the controller causes the conveyance device to move the sample container into the oven and a second weight of the sample container after the controller causes the conveyance device to remove the sample container from the oven. A plow mechanism in communication with the sample container may be provided for distributing the sample in the sample container. According to a feature of the invention a sweeping mechanism removes sample residue from the sample container after the analysis is complete. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an on-line moisture analyzer constructed in accordance with an embodiment of the present invention; 
     FIG. 2 is an enlarged perspective view of the sliding carriage shown in FIG. 1; 
     FIG. 3 is a side view of the sliding carriage and support structure shown in FIG. 1; 
     FIG. 4 is a perspective view of the gripping member shown in FIG. 1; 
     FIG. 5 is an enlarged perspective view of the sample plow shown in FIG. 1; 
     FIG. 6 is an enlarged perspective view of the scale and oven shown in FIG. 1; 
     FIG. 7 is a perspective view of a sample pan sweeper constructed according a feature of an embodiment of the present invention; 
     FIG. 8 is a fragmentary view of a support plate for the analyzer shown in FIG. 1; and 
     FIG. 9 is a perspective view of an enclosing structure constructed in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While it is to be understood that practice of the present invention is suitable for moisture testing of any concentrate, the following description will focus on an analyzer constructed in accordance with the present invention adapted for testing of iron ore concentrate. FIG. 1 depicts an on-line moisture content analyzer  10  that can be located in an ore processing facility. Operation of the various components of the analyzer is controlled by a controller shown generally within a housing  12 . The analyzer  10  has a supporting structure shown generally as  20  that supports a sliding carriage  30  that rides on rails  32 . The supporting structure  20  also supports a laboratory grade scale  60  and a sample plow  41 . An oven  50  is located in proximity to the supporting structure and is accessible by a sample holding arm  35  that releasably grips a sample pan  40 . The sample pan  40  has a handle  145  with several docking holes (not shown) that engage corresponding pins  132  (FIG. 4) on a gripping member  37 . According to the invention, the sliding carriage moves the arm  35  from a sample conveyor  92  (such as a Roach Model 350 SB Conveyor equipped with a variable speed drive motor assembly), where it receives an ore concentrate sample in the pan  40 , to the scale  60  where the sample is weighed. After the sample is weighed, the arm  35  moves the sample into the oven  50  for drying and back onto the scale to be reweighed. A processing unit (shown generally within the housing  12 ) determines the moisture content of the sample by finding the difference between the two weights. 
     FIG. 2 depicts the sliding carriage  30  in more detail. The sliding carriage is driven by a GE FanucTwo Axis Digital Motion Control System. A rotatable shaft  71  is driven by a servo motor (such as PhD Series Ra-S550) located in a housing  73 . The shaft  71  is supported by bearing blocks  39  and protrudes into a torque limiting brake  38  (a suitable brake is Applied Robotics Model OS 400). The brake  38  limits the amount of torque that can be output by the arm  35  to prevent damage or injury if the arm encounters an obstruction when it is rotating. The gripping member  37  releasably connects to the handle  145  of the sample pan  40  shown in FIG. 1. A flexible sleeve  42  protects electrical leads that connect to the devices on the carriage  30 . FIG. 3 is a side view of the carriage  30  that illustrates a lifting feature of the carriage. A pneumatic lift  33  (such as PhD Model C7550) supports an upper carriage plate  34  on extendable legs  43 . The lift has an approximate stroke of about two inches and lifts the upper carriage plate  34  that supports the arm  35  to allow the arm to place the sample pan  40  on the scale. 
     FIG. 4 illustrates in more detail the gripping member  37 . The member features fingers  138 , one of which is moveable within a groove  131  in the arm  37 . The fingers  138  are pneumatically moved into gripping engagement with corresponding holes (not shown) on a handle  145  of the sample pan  40 . FIG. 5 illustrates in more detail the sample plow  41  that is also shown generally in FIG.  1 . The sample plow  41  is pneumatically actuated by extendable rods  45 . The plow  41  moves across the top of the pan  40  to distribute the ore evenly within the pan  40  to allow for uniform drying in the oven  60 . 
     FIG. 6 depicts the oven  60  in proximity to the scale  50 . A laboratory scale such as Sartorius Model IS-16EDE-S with the docking plate  146  is used to weigh the sample in the pan  40 . The scale features a docking plate  146  having pins  141  and holes  140  that engage an underside of the pan  40  to positively located the pan on the scale. The weight of the pan  40  is tared out on the scale periodically so that it does not factor into the moisture determination. A data processing unit, such as an analog input card GE Fanuc Series ALG693, receives sample weights from the scale for use in the calculation of moisture content. A programmable logic controller (located within housing  12 ) can be used to manipulate the data received from the scale and also to control the operation of the slide, lift, rotary arm, and oven door. 
     The oven  50  is a convection style oven (such as Despatch Lab Oven Model 142-3) that can quickly heat the sample to temperatures ranging from 32 degrees F. to 500 degrees F. The oven  50  features a notched door  55  shown in a closed position that has a shape adapted to allow close passage into the oven of the gripping member  37  when it is supporting the pan  40 . The close fit between the oven door and the gripping member/pan assembly limits the amount of heat that escapes from the oven and minimizes the amount of work necessary to open and close the door. An actuator  53  is connected to the door  55  by a linkage  52  that translates the stroke of the actuator into a pivoting movement of the door between open and closed positions. 
     FIG. 7 depicts a sample pan broom  80  that is supported by the support structure  20 . The broom  80  moves across the sample pan  40  to remove any remaining sample material after the arm  35  rotates down to dump the sample (not shown). The broom  80  extends on rods  82  that are actuated by a pneumatic actuator  81 . A cooling fan (not shown) is located in proximity to the broom  80  to cool the pan  40  prior to loading of another sample. 
     FIG. 8 illustrates an analyzer support table  90  on which the support structure  20  and the oven  50  are mounted, making the analyzer  10  a self contained unit that can be moved as a single module. The support table  90  rests on adjustable feet  95  that adjust to level the analyzer  10  and also damp vibrations from the factory floor. FIG. 9 shows a screen enclosure  99  that encloses the analyzer  10  with the exception of an opening (not shown) for the sample conveyor  92  to protect the analyzer from airborne contaminants in the factory. 
     Referring again to FIG. 1, the operation of the moisture analyzer  10  will be outlined. When the analyzer is set up, the weight of the sample pan  40  is tared out on the scale  60 . To begin analyzing ore concentrate, a sample moves down sample conveyor  92 . The sample conveyor  92  may be accessible to any number of conveyors to allow for analysis from multiple process locations by the same analyzer  10 . The carriage  30  is located at a load location such that the sample pan  40  is beneath the end of the sample conveyor  92 . The sample dumps from the conveyor  92  into the sample pan  40  that is held by gripping member  37 . The sample plow  41  moves across the pan  40  and distributes the sample to an equal depth throughout the pan. The carriage  30  slides down to the scale  60  and the lift  35  (shown in FIG. 3) lowers the pan  40  onto the scale. The gripping member  37  releases the pan  40 . The weight of the sample is sent to the controller. 
     The gripping member  37  engages the sample pan  40  and the lift  35  raises the pan. The carriage  30  moves to the oven  50 . The oven door  55  (FIG. 5) is opened by the door actuator  53  and the carriage moves the gripping member  37  into the oven. The gripping member  37  releases the pan  40 , moves out of the oven  50 , and the oven door  55  is closed. The sample bakes in the oven  50  until its moisture is removed. This can be accomplished by leaving the sample in the oven a predetermined amount of time or by monitoring the sample and removing it once it is dry. The oven door  55  is opened and the gripping member  37  enters the oven  50  and removes the sample pan  40 . 
     The carriage  30  moves the gripping member  37  to the scale and the sample is again weighed as already described. After the sample has been weighed, the controller calculates the moisture content of the sample. This content is recorded and sent to process controls that depend on the moisture content to effectively process the ore. The carriage  30  moves to a dump station (not shown) and the arm  55  rotates approximately 110 degrees to dump the sample. The broom  80  then removes any sample residue from the pan. The arm  55  returns to its original position and is carried by the carriage  30  back to the load location to receive a new sample. The approximate cycle time of the moisture analyzer  10  is twenty to thirty minutes. 
     As can be seen from the preceding description, the moisture analyzer in accordance with the present invention provides reliable, accurate, and expeditious on-line analysis of moisture content in a factory floor setting. While the exemplary embodiment of the invention has been described with a degree of particularity, it is the intent that the invention include all modifications and alterations from the disclosed design falling within the spirit or scope of the appended claims.