FR2642512A1 - CONTINUOUS SINTER FURNACE - Google Patents

Abstract

The invention also makes it possible to dismantle the heating elements 18 from a section without dismantling the latter. The furnace comprises an external enclosure inside which is placed a refractory core with a horizontal axis, provided with heating means 18 distributed inside the core. It consists of several sections attached to each other in a sealed manner. The heating means 18 are mounted inside the refractory core by passing through the external enclosure 17 by sealed feedthroughs 20 placed on the end faces 25, 26 of the sections. The heating means 18 consist of electrical resistors placed laterally on the internal walls of the refractory core. The latter is of square section and consists of refractory elements 11 assembled by interlocking by means of tenons and mortises. The soles 13 and the edges 23 are made in the form of monobloc parts in the shape of an elongated I, symmetrical and reversible. Application to the firing of refractory powders used as nuclear fuels.

Description

CONTINUOUS SINTER FURNACE

DESCRIPTION

  The invention comes from the field of high temperature sintering furnaces and controlled atmosphere. This type of oven is mainly used for cooking preformed parts by cold pressing of refractory powders, such as

  used as nuclear fuel.

  The present invention relates more exactly

  the internal structure of the sintering furnaces.

  The sintering of pellets involves during the shaping, the addition of organic binders which must be removed and collected during a thermal operation called "preheating", which precedes sintering itself. Since thermal operations must be carried out under a controlled atmosphere, it is necessary to take measures to ensure that the unbound binders or byproducts can not diffuse into the sintering zone and exert an influence therein. In addition, any work on materials, for example such as plutonium, involves a waterproof material to avoid alpha contamination. Other materials used to make such pellets may be refractory metals, such as

  molybdenum, silicon, tantalum, tungsten.

  Metal oxides, such as uranium oxide or uranium-plutonium mixed oxides, may also be used, as well as metal borides, carbides, nitrides and silicides. Finally, refractory ceramics such as thoria and zirconia are also likely

  to be used to form such pellets.

  With reference to FIG. 1, this type of tunnel-shaped furnace is usually formed of several sections, each consisting of a core of refractory bricks. This one is surrounded, on the whole periphery, of unrepresented insulating bricks. The core contains a set of pieces of refractory materials, such as soles 3, banks 4, and support parts 5 and 6 forming a flow path of the containers containing the products to be sintered. All is mounted in a steel body

  which ensures the mechanical strength of the entire oven.

  The heating is obtained by means of solenoid-shaped electrical resistors 8 arranged inside the body. They provide heating of the tunnel thus formed in the middle of the core at a temperature which is between 1600 and 1800 C, in

usual applications.

  FIG. 1 shows the manner in which the solenoid-shaped electrical resistors 8 are positioned relative to the circulation path constituted by the soles 3, the banks 4 and the support pieces 5 and 6. This circulation path is surrounded by the turns of the solenoids, the latter coming to fit into the base 10 of the circulation path

containers.

  This design - presents many

  disadvantages, the main ones of which are the following.

  The replacement of an electrical resistance 8 is possible only after the uncoupling of two firmly coupled sections and after the removal of the refractory bricks 1 and insulation bricks that surround

The heart of the oven.

  Adjusting the height and alignment of the sole 3 also requires uncoupling of the sections. Due to the position and shape of the resistors 8, control and regulating thermocouples 9 are placed at the periphery of the inner wall of the tunnel, hence in the immediate vicinity of the resistors 8. This results in an imprecision of the temperature of the the sintering zone being further away from the resistors 8. Finally, a sector of electrical resistances is located below the soles 3, which causes the existence of an area which is not swept by the protective gases which circulate in the tunnel. It follows a risk of overheating and accelerated corrosion resistances 8 may lead to the rupture thereof, but also the melting of some refractory materials that may cause disorders among the soles 3, the banks

4 and the support pieces 5 and 6.

  The object of the invention is to overcome these disadvantages by providing a sintering furnace

having a different structure.

  For this purpose, the main object of the invention is a continuous sintering furnace comprising an external enclosure inside which is placed a refractory core with horizontal axis, provided with heating means distributed inside and along refractory core, the furnace consisting of several sections fixed to each other in a sealed manner by two end faces. The oven according to the invention is characterized in that the heating means are mounted inside the refractory core by passing through the refractory core and the outer enclosure by sealed passages placed on the end faces.

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  sections. This makes it possible to change an element of the heating means without dismantling the section to

  inside which this heating element is mounted.

  The heating means consist of electrical resistances placed laterally on the internal walls of the refractory core, on either side of the soils constituting the paths of

  circulation of products to be sintered.

  Preferably, the heart

  Refractory thus formed has a square section.

  According to one aspect of the invention, the refractory core consists of refractory elements assembled by interlocking by means of tenons and mortises. According to a technical feature of the invention, the soles and the banks are made in the form of elongated I-shaped pieces

symmetrical and reversible.

  Control control thermocouples may be placed in first through-holes located in the furnace axis, at the top, at the

  bricks constituting the vault of the refractory heart.

  When the circulation of shielding gas is necessary, there are provided second gas inlet passages, located in the axis of the furnace, at the top, at the bricks constituting the vault

refractory heart.

  To adjust the plate of the soles, the refractory heart can be placed on tuning jacks

through the rest of the oven.

  A water cooling coil can be provided and brazed outside the enclosure

external metallic.

  The invention and its various technical features will be better understood

  to read the description that follows and that is

  attached figures representing respectively: - Figure 1, a perspective view highlighting a detail of realization of a sintering furnace according to the prior art; - Figure 2, a cross section of a sintering furnace according to the invention; - Figure 3, a perspective view of the positioning of the heating elements in a sintering furnace according to the invention; - Figure 4, a longitudinal section of a

  section of a sintering furnace according to the invention.

  With reference to FIGS. 2, 3 and 4, the continuous sintering furnace according to the invention is a tubular enclosure with a horizontal axis, divided into several sections. The design and structure of each section is directly related to the design of the heating means, and in particular

  as regards their fixation and their assembly.

  This design of the heating means is illustrated by Figure 3 on which the four elements

  Heaters 18 of a section are shown.

  Figure 4 is a vertical section (A-A)

  of a section of the sintering furnace according to the invention.

  - In correspondence with this figure and Figure 3, we can immediately notice notches 20

  made on the ends 25 and 26 of the section.

  These notches 20 are located at mid-height of the section and are intended to leave a passage to the heating elements 18. The shape of these heating elements 18 is symbolized in this Figure 4 by mixed lines and is such that these heating elements 18 cover any the length of the internal side walls of the section. The two ends, marked 27 and 28 in Figure 3, the heating elements through the refractory core by the notches 20 placed on the ends 25 and 26 of the section. With O-rings, not shown, placed around the ends 27 and 28 of the heating elements 18, at the outer enclosure 17, said bushings are sealed. The heating elements 18 and their ends 27 and 28 installed in the notches 20, are embedded

in a fibrous insulation.

  It is found that these heating elements 18 of a section can be removed by simple horizontal translation, once the section has been separated from the adjacent sections to which it is attached. By this mounting design, we avoid

  to dismantle the constituent elements of the section.

  With reference to FIG. 2, the heating elements 18 can be fixed by a simple suspension by means of hooks 24 planted in the side walls.

of the tunnel.

  The heating elements 18 are preferably doped molybdenum. Their electrical connections are brought back to the end faces 25 and 26 of the section,

  especially at the level of the external enclosure 17.

  It can be seen that these heating elements 18 no longer encircle the pathway constituted by

  mainly by the soles 13 and Their shores 23.

  Accordingly, a technical feature of the invention is that the soles 13 and the banks 23 are formed of one-piece pieces, I-shaped elongate, that is to say a form strictly

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  symmetrical. This has the advantage, in case of wear of these soles 13, that they are reversible and therefore

usable on both sides.

  The structure of the refractory core is such that its sintering tunnel has a substantially square section, as shown in FIG. 2. The walls of this tunnel consist of refractory elements 11, assembled to one another by interlocking by means of tenons 31. and mortises 32. The assembly constitutes a self-locking structure. More specifically, these bricks are made of an electro-cast refractory material entitled "S 5 211" supplied by the European Society of Refractory Products (SEPR). Thus constituted, these refractory bricks provide the mechanical stability of the refractory core up to temperatures of around 1800 C. This makes it possible to obtain a homogeneous temperature in the tunnel of the refractory core and thus to form a first thermal barrier. It is on the side walls of these refractory elements 11, that are placed hooks 24, now suspended the

  heating elements 18 along the walls of the tunnel.

  The second thermal barrier consists of twenty bricks 12 made of insulating material, preferably an aluminous lightweight insulator of the "IRCOR 34" type, supplied by the same company (SEPR). The assembly technology of these parts is the same as that used with the refractory parts 11, that is to say that it uses the assembly by pins 31 and mortises 32, also contributing to the same good mechanical strength of all. This set of two thermal barriers is positioned on two base parts 14 made of electro-melted refractory material, called "JARGAL PMS", this material is also provided by the company called SEPR. These two base pieces 14 thus support the refractory core. They are positioned on jacks 21, which are placed in a vertical operating position. This makes it possible to adjust the attitude of the way of travel, by varying the height of the soles 13. The refractory core is positioned laterally relative to

  to the outer enclosure 17 by means of metal guides 33.

  All this assembly is surrounded by a fibrous insulating material 15. The whole is enclosed in the cylindrical metal enclosure 17, which is fixed on a support

34 of the oven.

  The furnace has thermocouples 19, placed at the top of the refractory core, in the refractory bricks of voote. They are more precisely placed in first orifices 35 passing through the various upper layers of the furnace in an alumina sheath,

and positioned in the axis of the oven.

  Second ports 36 can also be used for the entry of the gas to be circulated in

the refractory heart.

  A water cooling coil 37, made of copper tubes, is brazed outside the

  the outer enclosure 17 which is metallic.

  At each end 25 and 26 of a section, four plates 38 of refractory material are placed opposite the fibrous insulation 15 to ensure its

mechanical strength.

  In agreement with the presence of these end refractory plates 38, and with reference to FIG. 4, the ends 27 and 28 of the heating elements 18 may have a slightly twisted shape, so as to leave the necessary space for these refractory plates. end ends 38. The ends 27 and 28 of the heating elements 18 may also consist of electrical connection cables

  extending these heating elements 18.

  A J game exists between the base plate

  14 and the metal side guides 33 of the oven.

  This clearance J is intended to compensate for any variations in oven size due to the thermal expansion of the oven elements, and to avoid disturbances

during transport.

  The external metal enclosure 17 makes it possible to ensure the mechanical stability of the assembly and to connect the sections together by means of flanges. It also ensures the containment of the entire oven. The different sections of the furnace are assembled by means of male interlockings and

  females, at the level of the refractory heart.

  It is therefore found that the structure of this furnace allows the change of the heating elements 18, in this case resistors, without dismantling the refractory parts. The resistors can be extracted and replaced by the end faces and 26 of the section, after the disconnection of

  this one of these adjacent sections.

  Similarly, the adjustment of the height and the alignment of the sliding soles 13 does not require the uncoupling of the sections, this adjustment being provided by the cylinders 21 of the outside of the enclosure

external metal 17.

  The heating elements 18 benefit from good protection since they are located entirely in the gaseous atmosphere of the sintering tunnel, therefore

their corrosion is very limited.

  The sintering gases are entirely confined to the inside of the refractory core, thanks to the assemblies by tenons 31 and mortises 32 of the pieces of refractory material 11 constituting the sections, and O-rings located at the flanges.

  allowing the link between sections.

  The location of the temperature control and regulation thermocouples 19 located in the axis of the furnace, just above the soles 13 o circulate the products to be sintered, makes it possible to better control the sintering temperatures, since these thermocoupts 19 do not are not in the immediate vicinity of the elements

heating 18.

  Thanks to the structure of the sintering furnace according to the invention, a time limitation is obtained, and thus the cost of intervention on this type of furnace for replacements of defective heating parts. If this furnace is used for the sintering of uranium oxide fuel, or mixed oxides of uranium-plutonium, this structure makes it possible to limit the volume of radioactive waste to only

replaced parts.

Claims (10)

  1. Continuous sintering furnace comprising an outer enclosure (17) inside which is placed a refractory core (1) with a horizontal axis, provided with heating means (18) distributed inside and along the core refractory (1), the furnace being constituted of several sections, fixed to each other and each having two end faces (25 and 26), characterized in that said heating means (18) are mounted inside the refractory core (1) passing through the refractory core (1) and the outer enclosure (17) through vias (20), placed on the end faces (25 and 26) sections.   2. Sintering furnace according to claim 1, comprising a circulation path composed of soles (13), characterized in that the heating means (18) consist of electrical resistances placed laterally on the inner walls of the refractory core (1). , on both sides of the soles (13).   3. Oven according to claim 1 or 2, characterized in that the bushings (20) are equipped with O-rings at the outer enclosure.   (17) to form watertight crossings.   4. Sintering furnace according to claim 2, characterized in that the refractory core (1) is of square section.   Sintering furnace according to any one of   of the preceding claims, characterized in that   that the refractory core (1) consists of refractory elements (11) assembled by interlocking means   of tenons (31) and mortises (32).   6. Sintering furnace according to claim 2, comprising banks (23) constituting a part of the circulation path, characterized in that the soles (13) and the banks (23) are constituted by one-piece, I-shaped pieces. elongated, symmetrical and reversible.   7. Sintering furnace according to any one of   of the preceding claims, characterized in that   it comprises first through-holes (35) of thermocouples (19) located in the furnace axis, at the top, at the level of the refractory bricks (11)   constituting the vault of the refractory heart (1).   Sintering furnace according to any one of   of the preceding claims, characterized in that   it comprises second gas inlet openings (36) located in the furnace axis at the top, at the level of the refractory bricks (11) forming the vault of the refractory heart (1).   9. Sintering furnace according to any one of   of the preceding claims, characterized in that   that the refractory core (1) is placed on adjusting cylinders (21) passing through the remainder of the furnace, and   for adjusting the sole plate (13).   Sintering furnace according to any one of   of the preceding claims, comprising the enclosure   outer shell (17) being metallic, characterized in that a water cooling coil (37) is brazed   outside the outer enclosure (17).