Patent Number: 060834544
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, an apparatus 10 for forming uniformly sized and shaped spheres is generally shown. The apparatus 10 comprises at least one sphere generation means 12 and an enclosed controlled temperature solidification environment 14. The sphere generation means 12 generally comprises a crucible 20 and a stimulation actuator means 50. The crucible 20 has a top portion 22 which is in a spaced apart relationship to a bottom portion 24. The crucible 20 defines an enclosed space 26 which contains a supply of a low viscosity liquid material 28. In certain high temperature applications, the crucible 20 is made of a ceramic material. The temperature inside the crucible 20 is monitored by a thermocouple probe 25 and a temperature controller 27 which are operatively connected to a heating means 29. The heating means 29 maintains the material 28 at a temperature above its melting point. The crucible 20 is operatively connected to a pressure regulator means 30 by a supply means 32 at a supply inlet 34. The pressure in the crucible 20 is monitored by a pressure transducer 36 located near the inlet 34. The pressure in the crucible 20 is adjusted by the pressure regulator means 30. It is within the contemplated scope of the present invention that the pressure regulator means 30 can supply a positive pressure of an inert gas such as nitrogen to the crucible 20. The crucible 20 has an end cap 40 with a nozzle 42 detachably connected to the bottom portion 24. The nozzle 42 is attached at generally the center of the end cap 40. The nozzle 42 defines at least one orifice 44. In a preferred embodiment, the orifice 44 has an inside diameter in the range of about 12 to about 1000 microns. It is within the contemplated scope of the present invention that the nozzle 42 can have more than one orifice 44. For ease of illustration however, only one orifice will be discussed in detail. In a preferred embodiment, a sapphire nozzle is used which can be operatively attached to the end cap 40 using a high temperature ceramic material. In other embodiments, a ceramic nozzle can be used. The nozzle 42 fits into a tapered fitting at the center of the end cap 40. In a preferred embodiment, the nozzle 42 is secured to the end cap 40 using, for example, a jam nut 46. The stimulation actuator means 50 provides a periodic disturbance to the low viscosity liquid material 28. In the embodiment shown, the stimulation actuator means 50 comprises a stack 52 of piezoelectric crystals 54 operatively connected to the top portion 22 of the crucible 20. In a preferred embodiment, the piezoelectric stack 52 contains at least 5 piezoelectric crystals 54A, 54B, 54C, 54D and 54E. The bottom four crystals 54B, 54C, 54D and 54D are mechanically connected in serial and electrically conducted in parallel to a high sinusoidal voltage source 56. The top piezoelectric crystal 54A serves as a motion sensor. The output voltage of the motion sensor 54A provides an indication of the amplitude of the stimulation actuator means 50. An extender means 56, such as a stirring rod, is attached to the bottom of the piezostack 52. The stimulation of the piezostack 52 is transferred to the material 28 by the extender means 56. It is also within the contemplated scope of the present invention that the simulation actuator means 50 can comprise a monolithic multilayered piezoactuator (not shown) containing, for example, 25 to 30 and, in certain preferred embodiments 29 layers, of piezoelectric ceramic cofired together having the dimensions of approximately 5 millimeters by 5 millimeters by 5 millimeters and being capable of over 3 microns of expansion. In an alternative embodiment, the stimulation to the material 28 can be provided by using a piezoelectric ceramic material as a nozzle material. A sinusoidal voltage is directly applied on the nozzle causing a periodic disturbance in the nozzle. In certain embodiments the pressure regulator means 30 includes a vacuum pump 60 operatively connected to the top portion 22 of the crucible 20 through an inlet 61. The vacuum pump 60 keeps the crucible 20 at a negative pressure prior to the formation of the spheres. The negative pressure prevents the material 28 from escaping through the nozzle 42 prior to operation of the sphere generation means 12. During operation of the sphere forming apparatus 10, an applied constant pressure from the pressure regulator means 30 forces the material 28 out of the nozzle 42 and into the controlled temperature solidification environment 14. The material 28 forms a steady laminar jet or stream 70 of material. The stimulation from the stimulation actuator means 50 causes a periodic disturbance to the stream 70. Due to the phenomena of the Rayleigh instability effect, the stream 70 breaks up into uniformly sized and uniformly spaced spheres 72. A charging system 80 is attached to the crucible end cap 40. The distance between the charging system 80 and the end cap 40 can be adjusted depending on the desired operating parameters. In a preferred embodiment the charging system 80 can be an aluminum material. A high voltage is applied to the charging system 80 from a voltage source 82. The stream 70 breaks into droplets 72 while passing through an opening 84 in the charging system 80. The charging system 80 imparts a charge on the stream 70. As the spheres 72 form, the spheres 72 retain the charge. The charge in the spheres 72 exerts a force between adjacent spheres 72 and prevents the spheres 72 from merging. The charged spheres 72 pass through the enclosed controlled temperature solidification environment 14 which, in the embodiment shown, comprises a first or gaseous environment 102 and a second or liquid environment 122. In the embodiment shown, the enclosed controlled temperature solidification environment 14 includes an upper chamber 90 and a lower chamber 100. In certain embodiments the upper chamber 90 is maintained at a first temperature and the lower chamber 100 is maintained at a second temperature. The first and second temperatures define a temperature gradient within the enclosed controlled temperature solidification environment 14. In an embodiment where the spheres being formed are made of a tin/lead alloy, it is desired that the first temperature in the upper chamber 90 ranges from about room temperature to about -90.degree. C. (in certain embodiments about 0.degree. C.) while the second temperature in the lower chamber 100 ranges from about -110.degree. to about -170.degree. C. The sphere generation means 12 is mounted inside the upper chamber 90 by a support bar 92. The upper chamber 90 is sealingly engaged to the lower chamber 100. This upper chamber 90 is in communication with the lower chamber 100 such that the upper chamber 90 and the lower chamber 100 define the first or gaseous enclosed environment 102. The upper chamber 90 has at least one portion 94 which is transparent. In a preferred embodiment, the upper chamber 90 comprises an acrylic material having, for example, the dimension of approximately 12.times.12.times.24 inches. A visual observation system 98 is located adjacent to the transparent portion 94 of the upper chamber 90. The visual observation system 98 monitors the formation of the spheres 72 and measures the size of the spheres as the spheres pass the visual observation system 98. The lower chamber 100 has at least one wall 104 and a bottom portion 106. In certain embodiments, the lower chamber 100 is preferably made of a CPVC tube material and has preferably a 14 inch interior diameter. The lower chamber 100 includes a deflection means 110. In the embodiment shown the deflection means 110 includes two deflection plates 112 and 114. The plates 112 and 114 each have a repelling or charging surface 112' and 114', respectively. The distance between the adjacent plates 112 and 114 defines an opening 118 through which the charged spheres 72 pass. The attracting or repelling surfaces 112' and 114' are preferably made of a highly conductive material such as copper, aluminum, steel or the like and have a length, in certain embodiments, from about 150 to about 400 millimeters. The opening 118 between the surfaces 112' and 114' is generally about 10 to about 40 millimeters. It is to be understood that in other embodiments, these lengths and distances are dependent, at least in part, on the type of low viscosity liquid material, the size of the spheres being generated, and other operating parameters. As the spheres 72 descend, the spheres pass through the deflection means 110. A high voltage is applied across the deflection means 110 from a voltage source 116. The high voltage generates an electric field between the plates 112 and 114. Since the spheres 72 are charged, the electric field either attracts or deflects the spheres 72. The deflection distance of the spheres is a function of the charge, size and speed of the spheres. The bigger spheres 72 descend in a path close to a center axis through the deflection means 110 while smaller spheres are deflected away from the center axis of the deflection means 110. The bottom portion 106 of the lower chamber 100 contains the liquid environment 122. In preferred embodiments the bottom portion 106 includes a funnel 124 made of a stainless steel material. A cryogenic valve 126 is located at a bottom portion 128 of the funnel 124. By opening the valve, the spheres 72 in the funnel 124 can be collected and retrieved. The lower chamber 100 includes a first or upper heat transfer medium inlet supply means 130 which is located at an upper portion 132 of the lower chamber 100. The inlet supply means 130 comprises, in a preferred embodiment, a copper tubing 134 which circumferentially extends adjacent the wall 104 of the lower chamber 100. The copper tubing 134 has a plurality of openings 136 radially extending through the tubing 134. In a preferred embodiment the openings 136 are generally evenly spaced around the copper tubing 134. The openings 136 allow a first heat transfer medium 138 to be dispensed into the lower chamber 100. Since the lower chamber 100 is in communication with the upper chamber 90, the heat transfer medium 138 cools both the upper chamber 90 and the lower chamber 100. In embodiments where the heat transfer medium 138 comprises liquid nitrogen, the heat transfer medium keeps the temperature in the gaseous enclosed environment 102 below about -80.degree. C. to about -170.degree. C. In the embodiment shown, the lower chamber 100 also has a second or lower heat transfer medium supply means 140 which is positioned adjacent, but in a spaced apart relationship, to the funnel 124. The funnel 124 is filled with a predetermined quantity of a second heat transfer medium 144. It should be understood that the first and second heat transfer media can be the same material, or can be different materials, for example a liquefied gas such as nitrogen and/or a liquid halo-carbon. The supply of the second heat transfer medium 144 defines second or liquid environment 122. The controlled temperature solidification environment 14, which, in the embodiment shown, comprises the gaseous environment 102 and the liquid environment 122, allows the spheres 72 to solidify before contacting the bottom 128 of the funnel 124. The heat of fusion is removed in the gaseous environment 102. The specific heat is removed in the liquid environment 122. The liquid environment 122 in the funnel 124 cushions the spheres 72 before the spheres 72 contact the funnel 124. In the embodiment shown, a first thermocouple 150 monitors the temperatures of the upper chamber 90 and a second thermocouple 154 monitors the temperatures of the lower chamber 100 so that the gaseous environment 102 and the liquid environment 122 remain at preferred sphere solidification temperatures. It is to be understood, however, that additional thermocouples can be used to monitor the temperature gradient in the enclosed controlled temperature solidification environment 14. Before operation of the sphere generation means 12, the enclosed controlled temperature solidification environment 14 and the crucible 20 are purged with a dry and inert gas. An oxygen content monitor 160 is positioned within the chamber 100 to monitor the oxygen content throughout the operation of the uniform size sphere forming apparatus 10. A relief valve means 162 extends from the enclosed controlled temperature solidification environment 14 to provide a desired pressure and amount of heat transfer medium in the controlled temperature solidification environment 14. In operation, the orifice 44 in the nozzle 42 is aligned with the opening 84 in the charging system 80. The charging system 80 applies a charge to the stream of material 70. As each sphere 72 is formed and breaks from the stream 70, each sphere 72 retains a portion of the charge. As the charged spheres 72 descend, the spheres pass through or adjacent the charging plates 112 and 114 of the deflection means 110. When the charging or repelling surfaces 112' and 114' are held at a predetermined desired voltage, the electrical field generated in the opening 118 provides a further charge to the spheres 72. The spheres 72 remain a predetermined distance from each other and from the charging or repelling surfaces 112' and 114'. This repelling force is generally shown by the arrows in FIG. 2. As each sphere 72 descends, the leading sphere is repelled, not only from succeeding spheres 72, but is also repelled from the sides of the charging surfaces 112' and 114', thereby preventing the like charged spheres from merging with each other. It is to be understood that various suitable materials can be used, depending upon the end use application of the spheres to be formed. The actual charge on the sphere is a function, not only of the type of metal used, but also the diameter of the spheres, and the voltage between the charging plates 112 and 114 and the spheres 72. A charge on the sphere 72 in the order of 10.sup.-7 coulmb-gram is useful; however, it is to be understood that other charges are also useful and that the charges depend on the various parameters discussed above. The charged spheres 72 solidify during the descent through the gaseous environment 102 and are completely solidified before contact with the liquid environment 122. As seen in FIG. 2, the spheres 72 first form a skin portion 172 which shields a molten portion 174. As the spheres 72 descend and solidify, the skin portion 172 thickens until the molten portion 174 disappears prior to contact of the sphere 72 with the funnel 124. It is to be further understood that the sphere forming apparatus 10 of the present invention is operatively connected to a data acquisition/control system 180 to collect and measure data and to control the sphere forming apparatus. The data acquisition/control system 180 also measures the voltage output of the thermocouples and pressure transducers. The data acquisition/control system 180 is also operatively connected to the visual observation system 98 to provide the capability of actively controlling the formation of the spheres. During operation of the apparatus 10, the size and shape of the spheres being generated are measured. The data acquisition/control system 180 varies the crucible pressure and frequency generated by the stimulation actuator means 50 so that the sphere size and shape are kept at a predetermined desired diameter. It is to be understood that only the preferred embodiments of the invention have been described and the numerous substitutions, modifications and alternations are permissible without departing from the spirit and scope of the invention as defined in the following claims.