Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating
Patent
1996-04-02
1998-03-03
Derrington, James
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
264 121, 264 123, 264325, 264332, B29D 1100
Patent
active
057230765
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention applies to the technology of manufacturing inorganic optically transparent and scintillation plates of large size by pressure treatment, and to the manufacture of large scintillation detectors and optical screens.
U.S.S.R. Author's Certificate No. 340,441 describes a process for obtaining large plates from optical and scintillation materials. The process employs large, high-quality single crystals, without defects and cracks. The crystals are cut either perpendicularly to the crystal axis, such as for manufacture of discs, or in parallel to or at an angle to the crystal axis for manufacture of large plates. Subsequently, the discs or plates are ground and polished to the necessary size and quality. The process has several shortcomings. More particularly, the process cannot be used to manufacture large products having arbitrary configurations. Additionally, monocrystalline scintillation plates have low resistance to the effects of mechanical handling and heat. As a result, the plates often crack during cutting, making the plates unusable. Moreover, the large single crystal plates are characterized by a non-uniform dispersion of dopant, such as thallium, resulting in inhomogeneity of light output along the area of the detector that is based on monocrystalline scintillation plates.
U.S. Pat. No. 3,933,970 describes a method of producing polycrystalline plates of large size from optical and scintillation materials through the use of thermomechanical axial pressing. According to this process, a cylindrical crystalline blank is cut out of a large ingot grown from the NaI(T1) single crystal melt. The cylindrical size of the blank is approximately 50.8 mm (millimeters) in diameter and 152 mm in height. The blank is placed between graphite coated plates of a 750 ton hydraulic press and is heated in an electric furnace to 500.degree. C. One of the press plates includes a thermocouple for recording the temperature of the press plates. When reaching 500.degree. C., the upper plate is moved at a rate of 9 mm/min, and the crystalline blank is deformed by axial pressing without radial restriction perpendicular to the cylindrical blank bottom. The 9 mm per minute rate is used when pressing crystalline blanks of small size.
When reaching a thickness of 31.75 mm between pressed plates, the upper press plate is removed and the resulting flat crystalline disc is removed. The resulting disc has a diameter of 127 mm and a height of 28.57 mm. To obtain discs of larger size, it becomes necessary to use starting blanks of larger starting diameter and height.
The method described in U.S. Pat. No. 3,933,970, does not permit production of polycrystalline optical and scintillation plates of various geometric shapes, for example, rectangular. More particularly, the blanks employed with the process are in the shape of discs and when deforming by axial pressing without radial restriction, the crystalline structure will seek a shape with minimal surface area, resulting in a disc-shaped product. To obtain other geometric shapes, such as rectangular, the pressed disc must be cut into the desired shape, resulting in a significant amount of waste material (about 36.4%). The high amount of waste decreases the efficiency of the process such that the process has not received wide commercial application.
The process described in U.S. Pat. No. 3,933,970, also requires coating the press plates with graphite to avoid interaction between the press and the pressed material. As a result, it is necessary to remove a layer of the resulting disc that is contaminated by the graphite. The removal of the contaminated layer results in additional waste of base material, and additional steps are required to complete the disc. As an example over 9,000 cc (cubic centimeters) of starting monocrystalline material is required to obtain plates having dimensions of 550 mm by 600 mm by 10 mm thick.
U.S. Pat. No. 4,044,082, describes a method of producing polycrystalline plates of large size from optical scintillation material
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USSR Author's Certificate No. 340,441, with English summary, Jun. 1972.
Chernyshov Aleksandr Antonovich
Gordienko Lyudmila Sergeyevna
Ilyukha Aleksandr Ivanovich
Onoprienko Pyotr Nikolayevich
Osadchii Fyodor Antonovich
Amcrys-H, Ltd.
Derrington James
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