Abrading – Work rest – For centerless abrader
Reexamination Certificate
2002-06-04
2004-05-04
Hail, III, Joseph J. (Department: 3723)
Abrading
Work rest
For centerless abrader
C451S177000, C451S190000, C451S194000, C451S406000
Reexamination Certificate
active
06729948
ABSTRACT:
In a first aspect, the present invention provides a method of rectifying (i.e. adjusting the size of) cylindrical articles, in particular nuclear fuel pellets. The invention also provides apparatus for rectifying such articles, by implementing said method.
The present invention proposes a novel method and apparatus for confining and collecting the dust produced by rectifying cylindrical articles.
BACKGROUND OF THE INVENTION
Said invention is more particularly positioned and described below in the context of rectifying nuclear fuel pellets, however it is not limited in any way to said context. The person skilled in the art will readily understand that it is applicable to any context involving rectification (adjusting the dimensions) of circularly cylindrical pieces, in particular metal pieces and ceramic pieces.
In said context of rectifying nuclear fuel pellets, the method used at present is described below with reference to FIG.
1
. This description of the prior art is made with reference to said
FIG. 1
to facilitate understanding thereof and likewise to facilitate subsequent description and understanding of the invention, which invention can be considered as constituting an improvement over that prior art.
In the nuclear fuel fabrication process, the pellets obtained after compressing powders (generally UO
2
or PuO
2
+UO
2
) are the subject of uncontrolled shrinkage during a sintering operation which is performed at high temperature (at around 1700° C.).
It is therefore necessary to pass these pellets through a rectifier so as to obtain pellets of very accurate dimensions, prior to grouping them together in cladding in order to form rods.
The rectifier used at present by the Applicant mainly comprises two grind wheels
1
and
2
which are rotated in the same direction:
a working grind wheel
1
which is based on abrasive powder bonded by a metal or organic binder; and
a driving grind wheel
2
which is likewise based on abrasive powder bonded by a metal or organic binder.
The cylindrical pellets
3
that are to be rectified are conveyed in a prone position by sliding on a horizontal chute. Rectification is performed by the abrasive action of the working grind wheel
1
against said pellets
3
which are guided one after another on an alignment strip
4
over the entire width of said working grind wheel
1
. Said pellets
3
turn under the action of the working grind wheel
1
and they are moved in translation along the axis Oz under the action of the driving grind wheel
2
. The abrasive action of the working grind wheel
1
is thus properly distributed over the entire periphery (outside surface) of said pellets
3
. The translation direction (along the axis Oz) is determined by appropriately tilting the driving grind wheel
2
.
Said two grind wheels, the working grind wheel
1
and the driving grind wheel
2
are rotated in a common direction so that said working grind wheel
1
develops its abrasive action on the pellets
3
in a downward direction. The rectification dust is thus generated mostly in the downward direction and best advantage is thus taken of the “skin effect” due to the rotation of said working grind wheel
1
.
The entire assembly is confined in a glove box
6
. The confinement in question is both static and dynamic.
The rectification dust is sucked in by suction nozzles
7
,
7
′, and
7
″:
the first nozzle
7
is positioned at the bottom, beneath the alignment strip
4
and slightly offset towards the working grind wheel
1
;
a second nozzle
7
′ is positioned at the top, vertically above said alignment strip
4
; and
a third nozzle
7
″ is provided to suck directly from the protective casing
5
′ of the driving grind wheel
2
.
The protective casings
5
and
5
′ originally fitted around the grind wheels
1
and
2
are in the form of rectangular parallelepipeds whose faces are spaced apart to a greater or lesser extent from the surfaces of said grind wheels and form between them corners in which dust tends to accumulate. Said casings
5
and
5
′ provide incomplete static and dynamic confinement. A large fraction of the dust that is generated is ejected from said casings
5
and
5
′ and pollutes the glove box
6
, insofar as it is not taken up in full by the suction nozzles
7
,
7
′, and
7
″.
These drawbacks make it necessary to provide powerful suction and thus to overdimension the dust suction apparatus and the apparatus for treating the gaseous effluent from the glove box.
It has also been observed that some of the walls of said casings
5
and
5
′ can act as “impact filters”, i.e. they become contaminated by projected dust particles becoming encrusted within them. It is practically impossible to decontaminate them
OBJECTS AND SUMMARY OF THE INVENTION
It is thus in this context and with reference to the technical problem of managing the dust that is generated, that the Applicant proposes and improved rectification method and apparatus. The Applicant seeks to minimize the pollution that is generated without imposing excessive constraints on the suction.
The method of the invention is a method of rectifying cylindrical articles by the abrasive action of a working grind wheel on the outside surface (the periphery) of each of said articles. In said method:
the articles are moved continuously in translation under the action of a driving grind wheel over the entire width of said working grind wheel, with this taking place on an alignment strip positioned between said working and driving grind wheels;
said working and driving grind wheels are rotated in the same direction, which direction causes said working grind wheel to act on said articles in a downward direction; and
operation takes place in an open protection device (under static and dynamic confinement) with the generated rectification dust being sucked away.
To do this, the method of the invention is a rectification method of the type that is in use at present, in a rectifier of the kind shown diagrammatically in FIG.
1
.
In characteristic manner, in the context of said method of the invention, the following take place in succession:
the generated rectification dust is confined statically and dynamically close to the surfaces of said working and driving grind wheels; this limits the volume subjected to contamination (a volume defined by surfaces without sharp edges) and also the gas flow rate that needs to be treated (as sucked in); this imparts a maximum speed to said dust;
practically all of said rectification dust as generated and confined beside the working grind wheel and the driving grind wheel is entrained towards the bottom of said working grind wheel in a flow of gas set up firstly by the rotation of said working grind wheel and secondly by implementing forced suction; said dust is captured by suction (of a minimum volume of gas given the confinement) in a single flow of gas, and for the purpose of this capture (or trapping), advantage is taken of the “skin effect” generated around the working grind wheel; and
said rectification dust as generated, confined, and entrained (in a single gas flow) is taken away and recovered by said forced suction.
In characteristic manner, in the context of said method, close static and dynamic confinement is implemented so that the dust produced by rectification is trapped with optimum recovery efficiency (thereby minimizing pollution) and with a minimum suction flow rate (thus limiting the power of the compressor needed to provide the suction and the size of the filter device that needs to be provided downstream to recover the dust).
To ensure that the dust confined beside the driving grind wheel is entrained towards the bottom of the working grind wheel, it is necessary to provide for said dust to be transferred from beside the driving grind wheel to beside the working grind wheel. Said dust as generated and confined beside the driving grind wheel is advantageously transferred in order to be entrained beside the working grind wheel:
via at least one passage provided through th
Engelvin Pascal
Marchand Michel
Masson Serge
Cohen & Pontani, Lieberman & Pavane
Compagnie Generale des Matieres Nucleaies
Hail III Joseph J.
McDonald Shantese
LandOfFree
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