Patent Number: 051867648
Section: summary

BACKGROUND TO THE INVENTION 1. Field of the Invention This invention relates to the treatment of apertured plates with a gas. More specifically the invention has been developed for the treatment of apertured thin steel plates with a nitriding or nitrocarburising gaseous medium to form a layer of iron nitride on the surfaces of the plates. The invention provides apparatus for such treatment, a method of treatment and a fixture on which a multiplicity of plates can be supported for treatment. 2. Description of the Prior Art It is known from U.S. Pat. No. 4,793,871 assigned to Lucas Industries plc and issued Dec. 27th 1988 to treat steel plates to provide an iron nitride layer thereon by heating the plates in an inert atmosphere in a retort and then evacuating the inert atmosphere and introducing a nitrogen-containing gas which reacts with the heated plates to form the iron nitride layer on the surface thereof. In prior apparatus used for this purpose, the number of plates that could be accommodated in the retort so as to be properly treated was limited since one relied solely on the undirected circulation of the nitrogen-containing gas through the furnace by a fan. SUMMARY OF THE INVENTION It is an object of one aspect of the present invention to provide apparatus which will allow the effective treatment of a much greater number of plates than heretofore in the process described above. It is an object of another aspect of the invention to a provide an effective treatment method and it is an object of a third aspect of the invention to provide a fixture for the plates which will conveniently accommodate them for effective treatment by a gaseous medium. According to one aspect of the present invention we provide apparatus for treating a multiplicity of apertured plates with a gaseous medium comprising a chamber defined by opposite end walls and bottom, top and side walls extending between said end walls; means to circulate gaseous medium through said chamber in a general direction from one of said end walls to the other end wall, means to support said plates in the chamber in mutually spaced relation in a plurality of adjacent rows which extend generally parallel to said end walls so that faces of the plates lie parallel to said general direction of flow; and deflector means on at least some of said bottom, top and side walls for deflecting gas flowing along said walls to flow towards and between said rows so that the gas flow across all said plates is substantially uniform. The provision of the deflector means enables a large number of plates to be contained in the apparatus for treatment in an effective manner due to the uniformity of the gas flow across the plates. Preferably said deflector means comprise a plurality of deflecting members mounted on at least some of said bottom, top and side walls to project therefrom and so that the projection of the deflecting members from the wall on which they are mounted increases the nearer said deflecting members are to said other end wall of the chamber. The deflection of the gas is thus progressively increased as it flows through the chamber and this ensures the uniformity of the gas flow across the plates. More specifically the invention provides apparatus for treating a multiplicity of apertured plates with a gaseous medium comprising a chamber defined by opposite end walls and bottom, top and side walls extending between said end walls; means to circulate gaseous medium through said chamber in a general direction from one of said end walls to the other end wall; a fixture for supporting said plates in said chamber and comprising a base having opposed sides, a plurality of vertical columns mounted on each of said sides, each column of the plurality on one of said sides being aligned with a column of the plurality on the other of said sides to form a pair, a plurality of support bars each extending between a pair of columns so that the support bars are generally parallel to said end walls and so that a number of support bars engage each such pair of columns, each bar being adapted to be threaded through the apertures in a plurality of said plates to support the latter in rows and having locating means to hold the plates threaded thereon in fixed positions and in mutually spaced relation, an apertured end fitting at the end of each support bar, each such fitting having an aperture through which a column passes, and spacers on each column between the end fittings of adjacent support bars on the column to hold said support bars in vertically spaced relation on the column; and deflector means on at least some of said bottom, top and side walls for deflecting gas flowing along along said walls to flow towards and between rows of plates mounted on the support bars so that the gas flow across all said plates is substantially uniform. The provision of a fixture as set forth above together with the deflector means enables a large number of plates to be effectively treated with the gaseous medium One of said end walls may form a door and said chamber may include means whereby said fixture can be moved into and out of said chamber through the door. Said means for moving the fixture into and out of the chamber preferably includes a roller conveyor mounted on the bottom wall of the chamber. The invention also provides a method of treating plates with a gaseous medium in a chamber defined by opposite end walls and side walls extending between said end walls and in which the gaseous medium is circulated in a general direction from one of said end walls to the other, comprising mounting said plates in said chamber in fixed positions and in mutually spaced relation in a plurality of adjacent rows extending generally parallel to said end walls so that faces of the plates lie parallel to the general direction of flow of gaseous medium through the chamber and deflecting gaseous medium which flows along said walls so that said deflected gaseous medium flows towards and between said rows and so that the flow of gaseous medium across all of said plates is substantially uniform. The mounting of the plates so that their faces lie parallel to the general direction of gas flow through the chamber, together with the deflection of the gaseous medium ensure effective treatment of the plates. The plates are preferably apertured and are mounted in said rows with their apertures aligned, so that said deflected gaseous medium also flows into the aligned apertures of the rows of plates. The plates may be mounted in mutually spaced relation in notches on support bars which pass through the aligned apertures of each row of plates. Preferably the plates are of steel and are heated in the chamber in an inert atmosphere which is then evacuated and replaced by a gaseous medium which is a nitriding or nitrocarburising medium and is heated and circulated to form a surface layer of iron nitride on said plates. The invention also provides a fixture for supporting a multiplicity of apertured plates whilst undergoing treatment with a gaseous medium, the fixture comprising a base having opposed sides, a plurality of vertical columns mounted on each of said sides, each column of the plurality on one of said sides being aligned with a column of the plurality on the other of said sides to form a pair, a plurality of support bars each extending between a pair of columns so that a number of support bars engage each such pair of columns, each bar being adapted to be threaded through the apertures in a plurality of said plates to support the latter and having locating means to hold the plates threaded thereon in fixed positions and in mutually spaced relation, an apertured end fitting at the end of each support bar, each such fitting having an aperture through which a column passes, and spacers on each column between the end fittings of adjacent support bars on the column to hold said support bars in vertically spaced relation on the column. The locating means on the support bars may be notches, preferably of Vee-shape, to receive the edges of the apertures in the plates. The support bars may be of upwardly open Vee-section with said notches provided in opposed sides of the Vee. At least one tie bar may connect together the columns of each plurality adjacent the tops of the columns and may have apertures to receive the columns whilst being of angle section between said apertures. Each of said columns may consist of a plurality of separate parts which mutually and telescopically interfit. This enables the fixture to be built up as the plates are being mounted on it.