Patent Number: 044997086
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 1-5 illustrate an extrusion die 10 in a schematic representation of how it is made with an electric discharge machine 12. The die 10 has a wall 14 through which a slot 16 (FIGS. 3-5) is to be formed so that a thin ribbon can be extruded from the slot. The slot 16 thus can be in excess of 1 inch in length, but less than 0.01 inch in width; and the wall 14 initially is generally in excess of 0.1 inch thick. The die will typically be formed of a structural material like steel. In order to form the slot 16 in the wall 14 of the die or work piece, a carbon electrode 18 formed to a very thin rectangular cross section is used, connected to frame 20 of the electric discharge machine 12. The electrode 18 is slightly wider than the length of cut (approximately the length of the slot 16), is slightly thinner than the width of the cut, and is longer than the thickness of the wall 14. The normal techniques of using the electric discharge machine is to mount the electrode normal to the work piece and then to move the electrode 18 straight into the work piece 10. The electrode 18 is generally at ground potential and the work piece 10 is held at a high potential (for example 250 volts) relative to the ground. Arcing thus occurs between the electrode 18 and the work piece 10 as they approach sufficiently close together or even touch; and this arcing is done in a bath of oil 22. The oil thus flushes away the material of the work piece 10 as it is eroded away by the arcing. With the extremely thin electrode 18 described herein, there was insufficient oil flushing of the slot during cutting. The invention provides drilling two holes 24 at the opposite ends of where the slot 16 is to be formed so that the oil can be circulated through these holes and the slot as the slot is being cut in the work piece 10, upon the electrode 18 being advanced toward and into the work piece. The holes 24 are larger than approximately 0.1 inch and possibly even as large as 0.5 inch, depending in part on the thickness of the wall 14. After the slot is cut in the work piece, the holes 24 are closed by metal plugs 26 (FIGS. 3-5) welded as at 28 to the die wall 14. This thereby leaves only the narrow slot 16 as a through opening in the die 10. The interior walls 30 and 32 of the die 10 are preferably tapered toward the slot 16, and each plug 26 can also be tapered at the inner end to match up flush with the wall 30. Another aspect of the invention is to extrude a solid material, even a material such as sodium or lithium that is highly reactive to air or moisture, through the die slot 16 to form a thin ribbon or foil 36. Specifically, the material is melted in a vessel 38 on a hot plate 40 and the molten material is then poured into cylinder 44 of a press 46, confined by plunger 48 in the cylinder by shifting the plunger from that illustrated in solid to that illustrated in phantom, and allowed to cool to a solid. The press is then actuated to shift the plunger 48 to the left in FIG. 1 beyond that shown in phantom to extrude the solid material as the very fine ribbon or foil 36 out the slot 16. If the material is reactive, this is all done in an inert atmosphere of argon, nitrogen, helium, etc. such as in a glovebox 42. Thereafter, separate slugs 52 of the foil are stamped from the ribbon 36 in a fixture 50. The slugs 52 are shaped and sized as needed, but typically might be cylindrical discs between 0.5 and 1.0 inch in diameter. The fixture 50 has a frame 54 with a moving punch 56 sized and shaped like the desired disc, a bed 58 to support the underside of the ribbon 36, and an opening 60 in the bed under the punch to receive the disc as it is severed from the ribbon. The punch 56 can be hand actuated by striking head 62, and spring 64 returns the punch to the up position as illustrated. This stamping operation preferably also is performed in the inert atmosphere of the glovebox 42, particularly if the ribbon material is reactive. Each formed disc 52 is then sandwiched between two larger foil-like sheets 68, 69 of aluminum preferably each between 0.05 and 0.2 inch thick. The meeting peripheral edges of the aluminum sheets outwardly beyond the disc 52 are then cold formed together between press heads 70, 71 of hydraulic press 72 by moving the heads initially against the sheets and then with a force sufficient to generate pressures of perhaps up to 20,000 psi. The rounded faces of the press heads not only form the cold weld seam 74 annularly of the disc to seal the disc in a sample pouch 76, but also sever the sheets sufficiently along line 78 to allow the resultant sample pouch 76 to be separated from the remaining annular scrap piece 80. The sample pouch 76 thus encapsulates the disc 52 of material of extreme purity and of very thin cross section in isolation from the air atmosphere for durability and extended shelf life. This packaging of the disc in the protective pouch 76 also is preferably performed in the inert atmosphere of the glovebox 42, again particularly if the material is reactive. The thin disc sample as formed herein of highly reactive material of laboratory grade purity can be used in very sophisticated tests involving a thermal reactor and the bombardment or radiation by neutrons in a selected environment. The sealed sample pouch 76 maintains the disc isolated from the atmosphere for long shelf life, but also can be examined by accurate weight charges, etc., for analyzing the reaction with, attraction to or release of any component from the disc. A specific use for such a sample is outlined in Argonne National Laboratory Report ANL/NDM-55 entitled "Thermal Neutron Calibration of a Tritium Extraction Facility Using the .sup.6 Li(n,t).sup.4 He/.sup.197 Au(n,.gamma.).sup.198 Au Cross Section Ratio for Standardization" by M. M. Bretscher and D. L. Smith.