Patent Number: 051981823
Section: description

DESCRIPTION OF EXAMPLES EMBODYING THE BEST MOST OF THE INVENTION A neutron-absorbing tube according to the invention is shown generally at 10 in FIG. 1. Preferably, as will be described in greater detail immediately below, the tube 10 is formed of a pair of thin, rigid neutron-absorbing sheets 12 and 14 which are identical to one another, one of which is shown in FIG. 3, after rolling, trim and prior to bending. Each of the sheets 12 and 14 is formed from a metal ingot 16, as shown in FIG. 2. The metal ingot 16 is formed in an elongate, generally rectangular fashion from aluminum, therefore having aluminum faces 18 and 20, and opposite aluminum side edges 22 and 24. The ingot can be formed in accordance with the disclosure of incorporated U.S. Pat. No. 4,027,377, or in accordance with any other process for formation of a similar ingot. Once the ingot has been formed, at least one elongate, metal divider 26 is installed in the interior of the ingot to form the ingot into at least two chambers 28 and 30. The divider 26 shown in FIG. 2 is actually formed of one or more metal elements, and preferably is made of the same material as the metal ingot 16. Alternatively, the divider 26, side edges 22 and 24, and aluminum faces 18 and 20 can be formed as a single unit. Also, each metal divider 26 may, alternatively, be formed of a single length of metal, and as explained above, more than one metal divider may be installed in the hollow interior of the ingot 16, in order to form additional chambers. For example, if two metal dividers are installed, the dividers, in combination with the metal ingot, would form three chambers, three dividers would form four chambers, and so forth. Once the ingot has been thus-formed, the chambers 28 and 30 are filled with a substantially uniformly dispersed mixture of a finely divided neutron-absorbing compound and a finely divided metal powder. The mixture preferably is in accordance with that disclosed in detail in incorporated U.S. Pat. No. 4,027,377. Other similar materials, however, may be formed as well so long as they exhibit the neutron-absorbing capacity after a sheet has been formed. Once the ingot has been formed and filled, it is soaked to an elevated temperature which is below the melting temperature of the metal powder. In accordance with the preferred form of the invention, the ingot 16 is soaked for a period of time sufficient to raise the temperature of the ingot to between 800.degree. and 850.degree. Fahrenheit throughout, for rolling. In the rolling operation, the ingot 16 is hot rolled to reduce its thickness. The thickness is preferably reduced in a series of passes through a rolling mill. During that process, the mixture of boron compound and metal powder become metallurgically bonded together or sintered to form the sheets 12 and 14. The resulting sheet has thin, rigid neutron-absorbing areas 32 and 34, opposite metal edge portions 36 and 38, and an elongated metal spacer portion 40 at the location of each metal divider 26 in the ingot 16. The edge portions of the sheet 12 are trimmed as necessary so that preferably the combined widths of the edge portions 36 and 38 approximates the width of each spacer portion 40, although the combined widths can be wider or narrower, as well. After the sheet 12 has been formed, it is longitudinally bent at each spacer portion 40, preferably to an L-shaped cross section, as illustrated for each of the sheets 12 and 14 forming the tube 10 of FIG. 1. At the same time, the wider edge portion 36 is also bent to an L-shaped cross section. The two sheets 12 and 14 are then longitudinally joined at their edge portions 36 and 38 by welding, as shown at welds 42 in FIG. 1. It is preferred that the welds 42 not be located at the bends of the edge portions 36, but rather be formed on an unbent portion of the edge portion 36 to assure the greatest possible strength for the formed tube 10. Alternatively, if the edge portion 36 is not bent, the edge portions 36 and 38 can be abutted and welded where they abut. The tube 10 is therefore formed with neutron-absorbing areas 32 and 34 of the sheets 12 and 14 being unbent, but with bends in the spacer portions 40 and edge portions 36 being wholly within solid metal areas. The bends therefore do not affect the integrity of the neutron-absorbing core portions or areas of the sheet. Although the tube 10 is preferably formed of two sheets 12 and 14 formed and welded in accordance with the process set forth above, the tube 10 can also be formed from a single sheet having three metal dividers 26 installed in a metal ingot 16 forming four chambers in the ingot. After the ingot is filled and soaked, it is hot rolled in the same manner as described above, resulting in a sheet having opposite edge portions 36 and 38 similar to the sheet 12, but having three of the metal spacer portions 40 dividing adjacent neutron-absorbing areas. The thus-formed sheet is bent at each of the spacer portions to an L-shaped configuration, and also the edge portion 36 is bent to an L-shaped configuration, forming a tube appearing the same in cross section as the tube illustrated in FIG. 1. Since the tube is formed from a single sheet, only one longitudinal weld 42 is required to weld the edge portions 36 and 38 together to complete the tube. Although the tube 10 is shown in its preferred form as being generally square in cross section, the tube can be formed with a rectangular cross section. In addition, the tube can be formed with more than four sides, in a pentagonal, hexagonal or other configuration. However the tube is formed, it is important that the tube be formed with longitudinal bends being located wholly within a metal spacer portion dividing adjacent neutron-absorbing areas of the sheet or sheets forming the tube. Each of the metal dividers 26 may be formed of a single length of metal, or may be formed of one or more lengths of metal. However the dividers are configured, the ultimately-formed sheet is as illustrated in FIG. 3, with one or more spacer portions 40 being formed of metal, so that the sheet 12 may be bent at the spacer portions. It is also preferred that the sum of the widths of the edge portions 36 and 38 equal that of the spacer portion 40, so that when each of the sheets 12 and 14 is bent, the resulting formed tube 10 is essentially symmetrical. Again, however, that relationship is not critical, and the sum of the widths can be greater or less than the width of the spacer portion 40. A square tube 10 is illustrated in the drawing figures, manufactured from two of the sheets 12 having a central spacer portion 40. If a rectangular tube is desired, it will be evident that the metal divider 26 can be offset in the ingot 16 toward one or the other of the side edges 22 or 24 so that one of the chambers 28 or 30 is larger in the other, resulting in a sheet 12 with the spacer portion 40 offset toward one or the other of the edge portions 36 or 38. It will be evident to one skilled in the art that other shapes can be effected as well by simple location of the ultimate spacer portion or portions 40 and bending of the sheet or sheets 12 thereat. The width of the spacer portion 40 is formed to the minimum extent necessary so that the sheets 12 and 14 can be bent without bending or affecting the integrity of the neutron-absorbing areas 32 and 34. The width of the various spacer portions 40 will be evident to one skilled in the art, given the disclosure of the present application. Various changes can be made to the invention without departing from the spirit thereof or scope of the following claims.