EP0742561A1 - Cast iron container with lid sealed by spraying molten lead and method for sealing the lid on the container - Google Patents

Abstract

An open topped container (2) for contaminated waste has a lid (4), the walls of the lid and container each being of double walled construction with a metal envelope enclosing an interior space which is filled with cast material, pref. lightly contaminated metallic waste. The lid fits into a recess round the container mouth, where the opposed peripheral edges of the container and lid are machined to form an upwardly open annular groove (3). Also claimed is a method of sealing the container wherein the groove is cleaned of solid debris and then filled with molten Pb, which cools to make a permanent seal.

Description

Technical area

The invention relates to a cast iron container and its lid sealed together by projection of molten lead; it further relates to the method for carrying out this sealing of the cover on the container.

The invention finds applications in the field of treatment and conditioning of waste and, more particularly, contaminated or nuclear waste.

State of the art

When nuclear installations are dismantled, the aim is most often to reduce the volume of metallic waste that comes from this dismantling. For this, it is known to carry out, in an arc furnace, very slightly contaminated metal elements in order to obtain cast iron.

This cast iron can be used, for example, to make containers intended to contain irradiating waste. These cast iron containers therefore have the double advantage, on the one hand, of being made from recycled metal and, on the other hand, of allowing the packaging of waste which is not recyclable.

The manufacture of such cast iron containers is described, for example, in "Preparation and use of recycled material for the nuclear industry", by D. BRUNING et al., Communication to the EEC, Krefeld, Germany, October 1993. However, if the cast iron makes it possible to produce containers intended to contain contaminated waste, it must be ensured that the closure of the container is just as tight to contamination than the container itself. For this, it is known to close the container with a cast iron cover produced by a process identical to the process for manufacturing the container. However, no effective method is known for sealing the lid on the cast iron container.

Indeed, the weldability of cast iron parts is only possible under very specific conditions which are very often difficult to comply with.

For example, sealing by homogeneous hot welding has been envisaged. However, this type of welding requires preheating of the entire cast part to a temperature in the region of 600 °, which would cause differential expansion of the container and the lid. In addition, in such a case, the constraints would be unacceptable for the nuclear waste contained in the container.

Sealing by "construction welding" is just as difficult to envisage for the sealing of these cast iron parts because the depth of the welding is limited to 6 mm. However, in this case, the operations should be done to a depth of 120 mm, which explains why construction welding cannot be used to close the cast iron container.

These welding methods usually used to seal a lid on a container cannot therefore be used in the case of cast iron containers containing waste because of the induced thermal stresses which are unacceptable for nuclear waste and because of all the other criteria mentioned above.

Statement of the invention

The object of the invention is precisely to remedy the drawbacks mentioned above.

To this end, it offers a cast iron container on which a cover is sealed by projection of molten lead. It also proposes the method of sealing the lid on the container by a technique of thermal projection of a lead wire.

More specifically, the invention relates to a cast iron container intended to contain waste, on which is placed a cover, the cover and the container each comprising a metal envelope filled with cast iron, characterized in that the cover and the container are separated, over part of the height of the cover, by a lead-filled groove produced by machining the metal casing and the cast iron part of the container and the cover.

Advantageously, the container has an inner wall inclined relative to the vertical, towards the top of the cover forming an acute angle α. The lid of said container comprises at least one inclined wall e forming with the wall b of the container, an acute angle θ ensuring the adhesion of lead between the walls of the lid and of the container. It also includes several different inclination planes ensuring better adhesion of lead to the wall.

• a) à déposer un couvercle sur le conteneur, tous deux préalablement usinés de façon à former entre eux une rainure ;
• b) à nettoyer la rainure des poussières et éléments nuisibles présents ;
• c) à déposer par projection thermique du plomb fondu dans la rainure, sur tout le contour du couvercle.

The invention further relates to the method of closing the cast iron container with a cast iron cover. This process consists of:

• a) depositing a cover on the container, both previously machined so as to form a groove between them;
• b) cleaning the groove of dust and harmful elements present;
• c) to deposit by thermal spraying of the molten lead into the groove, over the entire contour of the cover.

Advantageously, the lead is in the form of wire.

According to the method of the invention, the container, prior to step a), is placed on a turntable, driven by a motor to ensure regular deposition of the lead wire.

According to one embodiment of the invention, the cleaning of dust and noxious elements is carried out by spraying a jet of compressed air into the groove then suctioning of this dust and noxious elements.

Brief description of the figures

• Figure 1 schematically shows the device for sealing the cover by thermal spraying of molten lead;
• Figure 2 schematically shows an enlargement of the area around the lead-filled groove, located between the cover and the container;
• FIG. 3 represents a functional diagram of the method for closing the cast iron container of the invention.

Description of embodiments of the invention

In Figure 1, there is shown schematically the device for sealing the cover on the container.

In this Figure 1, there is shown the entire waste container with its cover, referenced 1. This assembly 1 comprises the container itself, referenced 2, and the cover 4, both made of cast iron. This cover 4 is placed on the container 2 and has a gripping hook 6 which allows it to be lifted to be placed on the container 2. According to the invention, this hook 6 is removable and can be removed when the cover is in square.

The container / cover assembly 1 is then placed on a turntable 8 which is driven by a motor (not shown in the figure for the sake of simplification of the figure) so as to effect a regular rotational movement. This turntable can be, for example, a positioner as used in the field of welding. Thus driven by the turntable 8, the container 2 and its cover 4 are subjected to a rotational movement relative to the sealing means 10 of the cover on the container. These sealing means 10 consist of a spray gun 12 and a system for cleaning dust and harmful elements 14.

More precisely, and as will be described in more detail later, the container 2 is separated from the cover 4 by a groove 3 in which it is sought to project the lead wire so as to seal the cover 4 with lead. container 2.

In order to ensure good adhesion of the lead to the walls of this groove 3, a cleaning system 14 is used to remove any dust and noxious elements which would be present in this groove 3. The cleaning system 14 therefore comprises a hose air supply 14a which provides a projection of compressed air inside the groove 3 to bring out all the dust and all the foreign bodies which may be there. In addition, to improve the elimination of this dust and harmful elements, a suction hood 14b sucks the dust and foreign bodies which have flown away under the effect of the pressure of the compressed air jet.

When the groove 3 is cleaned, the lead wire can then be deposited there by means of the projection gun 12. This gun 12 comprises a lead projection nozzle 12a, a supply of lead wire 12b and the supply pipes in fluid 12c. According to one embodiment of the invention, the lead wire 12b has a diameter of approximately 3 mm. For example, a device which would project a lead wire at a rate of 7.5 m / min would make it possible to project approximately 36 kg of lead in 1 hour.

Advantageously, the lead spray gun is oriented at an angle of about 9 ° relative to the vertical, so that the jet of lead covers the bottom of the groove 3. Preferably, the spray gun is oriented by means of a robotic arm 16.

Such a lead spray gun is already known and used in the nuclear field, for example for coating glove boxes or for coating accelerator chambers or even for covering elements emitting significant radiation; for example, this gun is used to eliminate a source of irradiation which is too large to allow the source to be blocked by human action. This projection gun which makes it possible to implement the technique of thermal projection of lead will therefore not be described in more detail since it is already known.

It is specified however, that this technique of thermal projection of lead is very affordable, both in investment and in use.

In Figure 2, there is shown the detail of the groove 3 located between the cover 4 and the container 2. Typically, the container 2 is made by means of an envelope 2a, which can be, for example, steel and which is filled with cast iron obtained from recycled metallic materials. The cast iron part of container 2 has been referenced 2b.

Similarly, the cover 4 is produced by means of a casing 4a, for example of steel, filled with cast iron 4b.

As can be seen in this figure 2, the groove 3 was obtained between the cover 4 and the container 2 following machining of the cover and the container. It is filled with lead 12b represented by speckles in FIG. 3. The container 2 has in fact been machined so as to have a relatively deep groove on the bottom (a) of which the cover comes to rest, at least in part. 4. More precisely, the cast iron part of the container 2 has been machined so as to have a horizontal surface (a) which constitutes the bottom of the groove 3. The inner wall of the container 2, referenced b, has been machined from so as to form an angle of about 2 ° to 5 ° from the vertical, closed towards the opening of the groove 3 (i.e. the surface of the groove). The angle that this wall b forms with respect to the vertical is referenced α. The inclination of this wall b made of cast iron allows, when the groove 3 is filled with lead, to ensure that the lead flow cannot come out of the groove. In addition, the steel casing 2a of the container 2 is machined on its surface, at the edge of the groove 3, so as to form with respect to the vertical an angle of around 45 °. This angle is referenced β and the edge of the envelope 2a bordering the groove 3 is referenced c.

In order to allow even better adhesion of the lead in the groove 3 and in particular on the walls of the cover 4, this wall has also been machined so as to comprise several inclined planes, of different inclinations. The side d produced in the casing 4a and partly in the cast iron 4b of the cover 4 forms, with respect to the vertical, an angle γ of about 15 °, open towards the surface of the groove 3.

The side e of the cover is machined so as to be substantially vertical in order to produce an angle between 2 and 5 ° with side b. This angle, between side e and side b, is an acute angle, referenced θ. It ensures a retention of the lead bead between the container 2 and its cover 4 by producing a "jamming" effect in the event of the cover being torn off, in other words, in the case where the cover 4 is subjected to a tensile force. The lead sealing bead thus produced therefore has a substantially frustoconical section.

The side f of the cover 4 is machined in an inclined manner and forms, with respect to the vertical, an angle δ of approximately 45 °, closed towards the bottom (a) of the groove 3. The side g adjacent to the side f and opening out on the bottom (a) of the groove 3 is machined so as to be generally inclined at an angle ε, relative to the vertical. This angle ε, closed towards the bottom (a) of the groove 3, is approximately 15 °.

It will be understood, of course, that the machining of the side wall of the cover 4 and the machining of the interior wall of the container as shown in Figure 2 are only examples; the lengths of the sides and the values of the different angles may obviously differ from the values which have been given previously by way of example.

Still by way of example, it can be specified that the height of the groove 3 from its surface s to its bottom a is at most 116 mm.

The cover 4 further comprises, at its lower base, a machining operation which substantially forms a right angle between the side h and the side i of the cover 4. This machining allows the cover to be able to be introduced along the interior wall of the container 2, while by being supported, by its side g, on the bottom (a) of the groove 3.

The container 2 can also include an additional machining on its internal wall, forming the side j and allowing the side i of the cover 4 to fit along the side j of the container 2.

Thus, the cover 4 can be inserted very easily inside the container 2; the side h of the protrusion 4c of the cover rests on the bottom (a) of the groove 3; the side i of the cover which forms the right angle with the side g ensures the centering of the cover along the side j of the inner wall of the container.

The different planes of the walls of the cover 4 and of the container 2 ensure good adhesion of the lead and allow easier introduction of the spray gun and the cleaning system.

Advantageously, the side wall of the cover and the interior wall of the container are rough so as to allow even better adhesion of the lead.

In Figure 3, there is shown the functional diagram of the different stages of the process for sealing the lid on the container.

In this functional diagram, the block 110 represents the fitting of the cover 4 on the container 2. This fitting of the cover is done by means of the gripping hook 6 shown in FIG. 1. The cover is centered in the opening of the container. Preferably, the accuracy of the centering of the groove is less than 1mm.

When the container is provided with its lid, the container-lid assembly is deposited on the turntable during a step 120.

Block 130 represents the step of setting up the sealing means, that is to say setting up the spray gun, as well as the extractor hood, the air jet projection pipe. tablet, etc. All the elements constituting the sealing means are placed in the most suitable position for sealing the lid on the container.

Block 140 represents the step of rotating the turntable on which the container and its cover has been placed.

Block 150 represents the operation for cleaning dust and noxious elements which would have remained in the groove 3. More specifically, this cleaning consists in blowing in the groove a jet of compressed air to remove all the cast iron dust, the abrasive elements and all foreign bodies which could adversely affect the good adhesion of lead to the walls of the groove. More specifically, the air nozzle which provides this projection of compressed air is placed inside the groove at a height of approximately 70 mm relative to the bottom of the groove.

When the cleaning of dust and harmful elements has been carried out, the position of the spray gun is refined and the wire and fluid supply of the gun is checked. More specifically, the fluids which supply the gun 12 are oxygen, acetylene and compressed air. For example, oxygen can be at a flow rate of 1,500 l / h, acetylene has a flow rate of 750 l / h and compressed air at a flow rate of 30 m ³ / h. This adjustment improvement is carried out in the step represented by block 160. This block 160 represents the step of projecting the lead which therefore comprises a sub-step of positioning the gun in the groove at a height of approximately 75 mm by relative to the bottom of the groove and at an angle of about 9 ° to the vertical so that the jet of lead sent by the gun covers the bottom of the groove.

Indeed, the adjustment of the gun must be refined so that the jet of lead is well centered so that a minimum of lead is deposited on the walls of the groove. During deposition, it is almost constantly checked that the shooting distance is between 70 and 100 mm. This is done in periodically lifting the gun. A check is also carried out during the operation to check whether the whole operation is being carried out continuously since any untimely stopping could hinder a good sealing of the lid on the container. Also, the stops necessary for checking and for changing the bobbins of lead wire are as short as possible; in addition, a mechanical densification of the lead is carried out during the process, by knurling.

The block 170 therefore represents a test step during which it is checked whether the filling of the groove is finished and carried out correctly. If not, step 160 is repeated until the groove is completely and correctly filled. On the contrary, if this is the case, the projection of lead is stopped, as well as the rotation of the turntable. This is represented by block 180.

It is then the end of the container 2 closing operation; we can then proceed to the closure of a second container.

As explained in Figure 2, the adhesion of lead to the walls of the groove can be further improved if these walls are rough. Also, to make the different sides of the cover 4 and of the container 2 even more adherent, it is possible to strip these walls by means of an abrasive jet to make them rough. The abrasive dust which remains inside the groove after the walls have been stripped off, is cleaned either by blowing with a jet of compressed air, or by suction. According to the preferred embodiment and described in FIG. 1, the groove 3 is cleaned both by blowing a jet of compressed air and both by suction of the dust propelled by the air jet. This step has not been shown in the diagram of FIG. 3, because it can be carried out either between steps 120 and 130, or at the time of machining of the container and its cover.

When the sealing is finished, the quality of the lead seal can be checked by infrared thermography measurements. This quality control consists in checking the absence of internal cracks or detachment at the seal / cover interface or at the seal / container interface. More specifically, the control technique consists in transmitting a heat flux to a so-called "hot" source, which is the cover or the container (depending on the case) and observing the propagation of this heat up to the cold source, namely respectively the container or the lid, via the lead seal.

If the seal adheres perfectly to the interface on the cover and container side, then the heat propagates homogeneously from the hot source to the cold source and the thermal image obtained by infrared camera is then perfectly uniform.

Otherwise, that is to say if the seal has a bonding defect at one of the seal / cover or seal / container interfaces, the infrared image is characterized by a dark trace in the middle of the assembly. with a clear surface.

Claims (8)

Cast iron container intended to contain waste, on which a cover (4) is placed, the container and the cover each comprising a metal casing filled with cast iron, characterized in that the cover (4) and the container (2) are separated, over part of the height of the lid, by a groove (3) filled with lead produced by machining the metal casing and the cast iron part of the container and the lid. Cast iron container according to claim 1, characterized in that the container has an inner wall (b) inclined relative to the vertical, towards the top of the cover, forming an acute angle (α). Cast iron container according to claim 1 or 2, characterized in that the cover of said container comprises at least one inclined wall (e) forming with the wall (b) of the container, an acute angle (θ) ensuring the adhesion of lead between the sides of the lid and the container. Cast iron container according to any one of Claims 1 to 3, characterized in that the cover has a side wall comprising several inclined planes (g, e, f, g, i), of different inclinations, ensuring adhesion of the lead on the wall. Method for closing a cast iron container containing waste, characterized in that it consists of: a) depositing (110) a cover (4) on the container (2), both previously machined so as to form between them a groove (3); b) cleaning (150) the groove of dust and harmful elements present; c) depositing (160), by thermal spraying, molten lead (12b) in the groove, over the entire contour of the cover. Method for closing a container according to claim 5, characterized in that the molten lead is introduced in the form of a lead wire. Method for closing a container according to either of Claims 5 and 6, characterized in that the body of the container, prior to step a), is deposited (120) on a turntable (8), driven by a motor to ensure regular deposit of the lead wire. Method for closing a container according to any one of Claims 5 to 7, characterized in that the cleaning of dust and harmful elements is carried out by spraying a jet of compressed air (14a) into the groove then suction of this dust and harmful elements.

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