TECHNICAL LIELD

The invention relates to a cell for the collection of slag samples which comprises a containment body preferably in the form of a tube or a ring; and a bottom which can be inserted/is inserted removably on one end or inside the containment body defining in the inserted state together with said body a container. This cell can be mounted on a lance to take slag samples from an oven. The slag samples can then be analysed to evaluate the trend of the melting process.

STATE QL THE ART

The slag is a product that is formed during the melting process in an oven. It is characterized by the formation of a lighter foam layer compared to the metal (steel) bath and contains the unwanted elements that are to be removed from the scrap mixed with different chemical additives (e.g, lime), injected specifically for this purpose.

The melting of scrap and lime leads to the separation of the metal phases from the non-metallic phases (different refractory oxides) that float above the metal phases forming the slag layer, which brings different benefits, provided that it is formed in the desired quantity and quality. One benefit among all acts as a shield between the molten metal and the surrounding oxygen; other benefits are the protection of furnace refractories with respect to the electric arc, the elimination of acid oxides and inclusions from the metal, the dephosphorization and desulfurization of the bath, the impairment in the absorption of hydrogen and nitrogen, and the thermal insulation of the metal bath. The composition and physical characteristics of the slag are important for obtaining a metallic bath with the desired characteristics and the benefits illustrated above. It is therefore necessary to control the slag during the various steps of the bath production process.

According to the state of the art, during the melting, the operators proceed with the taking of samples of metal and slag, in order to determine if the fusion is proceeding as desired. Such samples are taken, for example, through suitable disposable probes, which normally are provided in the tip with a capsule having a cylindrical container of ceramic material and two circular metal "caps", in which one of the two caps is perforated in a conical manner for to allow an easy entry of the liquid to be taken into the sampling chamber. Such a conventional probe is described later with reference to Figure 1.

The probe with the sampling cell is inserted in a special lance and immersed in the bath, or as in the present invention, in the slag layer, filling with metal or slag the chamber between the two metal discs. After a few seconds the lance is extracted. Given the small amount of material taken, its hardening is very fast.

Generally, at this point the probe containing the cell with the material is beat to the ground to make the ceramic break and the sample emerge, which is cooled and brought to the laboratory for analysis. It is readily apparent that very often in this passage the sample is damaged.

Moreover, this system can be quite good in the case of liquid slag, but not with foamy slag composed of a part of liquid slag, precipitated solid particles and a gaseous portion, mainly composed of carbon monoxide in which the solid particles act as sites of nucleation for the development of gas bubbles. Slags with high foaminess indexes (and therefore a large number of small bubbles) are disadvantageous, as illustrated by E.B. Pretorius and R.C. Carlisle in “ Foamy Slag Fundamentals and their Practical Application to Electric Furnace Steelmaking at the 56 ^th Electric Furnace Conference in 1998 in New Orleans (published in Electric Furnace Conference ,, vol. 56, p. 275-292, 1998). In fact, a highly foamy slag is very difficult to enter in sufficient quantity in the sampling cell and often the taken samples are not representative, however it is still necessary for shielding the bath from oxygen and reducing the electrical consumption of the oven thanks to its insulating power.

Very complex probes for the sampling of metal and/or slag are described, for example, in US documents US 7,621,191 B2, US 9,176,027 B2 and US 7,832,294 B2. Samples taken with these probes must all be destroyed in order to be analysed.

DISCLOSURE OF THE INVENTION

The object of the invention is to overcome the aforementioned drawbacks and to propose a cell, or a sampling probe for the collection of slag samples, particularly during the melting process of a metal bath, which is suitable for collecting samples, even significant ones, of very foamy slag. A further object of the invention is to propose a system that allows cooling of the sample, but at the same time makes it possible to obtain a sample which is not damaged by extraction from the cell and/or which does not require its destruction in order to be analyzed, a problem apparently not yet considered in the state of the art. Another object is to provide cells for the collection of slag, which are not of the single-use type but which are at least partially reusable. The object is achieved by means of a cell for the collection of slag samples, comprising:

(a) a containment body, preferably in the form of a tube or a ring; and

(b) a bottom which can be inserted/is inserted removably on one end of or inside the containment body defining in the inserted state together with said containment body a container, in which at least one area of the surface of the bottom, which in the inserted state of the bottom faces the inside of the container (i.e. which is facing the sample), is made in such a way as to have a roughness Ra less than or equal to 1.6 pm, preferably with a roughness Ra from 0.05 to 1.6 pm, more preferably with a roughness Ra of about 0.8 pm.

The roughness is defined according to the equation (1)

in which Ra is the roughness expressed as the arithmetic mean deviation of the absolute values measured within the length L, expressed in pm of the evaluated profile, L is the base length of the section subjected to measurement, Z is the height of an element of the profile (sum of the height of a peak and the depth of a valley of the an element of the profile) and x is the length of an element of the profile. The parameters are illustrated later with reference to Fig. 6. Preferably, the roughness is detected on the section of a plane normal to the surface and transverse to the orientation of the major grooves. As a measure of roughness, the parameter "Ra" is assumed to be advantageous, i.e., the arithmetic mean value of the absolute ordinates of the profile measured with respect to its average line (length of the section subjected to measurement), expressed in pm. Preferably, the roughness Ra is determined following the indications of the standards (UNI EN) ISO 1302 {Geometrical specifications of the products ( GPS ) - Indication of the state of the surfaces in the technical product documentation) and (UNI EN) ISO 4287 ( Geometric specifications of the products (GPS) - Surface condition: Profile method - Terms, definitions and parameters of the surface status.).

The presence of an area or surface with a very low roughness, that is a very smooth surface, creates a corresponding surface of small roughness of the sample that can be placed directly in a spectrometer and subjected to an analysis of its composition without requiring further sample preparation steps (e.g. its pulverization and its dissolution in specific solutions). Samples obtained with the cell according to the invention are particularly suitable for LIBS spectroscopy (Laser Induced Breakdown Spectroscopy).

A preferred material for the bottom is the metal that is particularly suitable for obtaining very smooth surfaces and which allows to easily work the roughness of the surface. Obviously, variants of the substrate are conceivable, which do not have only a surface area of low roughness, but in which the entire surface which comes into contact with the sample has a roughness with values as defined above.

Variants of the bottom comprise, for example, a flat disc or a disc with the edges curved upwards, i.e. a flared disc, creating a bottom with a C-shaped section. Inside the containment body a narrowing of the wall can be provided, in such a way as to reduce the inner circumference, i.e., one or more protrusions may be provided, for example an annular step. Shrinkage and projection(s) allow the support of the sample after inserting the bottom, avoiding its escape from the containment body from the side corresponding to the bottom. In another preferred variant of the invention, the bottom may have an area larger than the opening of the containment body and may be welded with some easily breakable points on the edge of the containment body. Bottoms screwable on the edge of the containment body are also conceivable, having respective threads. In this case, it is possible to hypothesise to create a double bottom, in which the screwable bottom comprises inside in a loose form a disc with a low roughness zone according to the invention such as to reduce the risk of scratching the smooth area by unscrewing the bottom from the containment body. In another variant, the bottom has a through channel hole which is aligned with two opposite holes made in the wall of the containment body when the bottom is inserted in the containment body; with a pin or a key passing through all three holes, the bottom is then fixed in the containment body.

In a particularly advantageous variant of the invention, the cell further comprises

(c) an insert in the form of a tube or ring that can be inserted/is inserted removably inside the containment body and suitable to hold the bottom in its position if it is placed inside the containment body. A more preferred cell is therefore a combination of a containment body, a bottom, for example a preferably metallic disc, and an insert as a blocking element for fixing the bottom in its position. In a further variant, the insert can also be divided into two or more components, so as to be easily separated from the sample once extracted from the containment body.

A suitable material for the insert and also for the containment body is the ceramic, which is not subject to thermal expansion. Materials that are not subject to thermal expansion are generally preferable.

In the case of the presence of the insert, the sample is collected in the space delimited by the insert and the bottom and can, after solidification, be easily extracted together with the insert from the containment body and detached from the bottom. Thus the containment body becomes reusable. The cells known in the state of the art are instead mainly of the disposable type, i.e., can be used only one time.

The sample with a smooth base deprived from the bottom, still contained in the containment body or in the insert can be analyzed without the need to break the element that contains it. Preferably, in the absence of the insert, the inner wall of the containment body is at least partially covered with protrusions.

Preferably, in the case of the presence of the insert, the inner wall of the insert is at least partially provided with protrusions.

The protrusions present on the wall, or of the containment body or of the insert, which delimit laterally the space in which the sample is received, catch it and retain it even in the liquid state. Advantageously, the outer wall of the insert and the inner wall of the containment body are shaped in a complementary form, so as to allow a tight fit between the containment body and the insert. Preferably, this shaping are sectors of the two aforementioned walls inclined in complementary form. Advantageously, the shaping or inclination is dictated by a wedge-shaped section of the parts of the walls that are coupled, in particular in the case of the insert. In the case of a flared bottom, the wall shapes adapt if necessary to the inclination of the edge of the bottom. This shaping of the insert complementary to the relative shaping of the containment body (and possibly of the bottom edge, if present) allows a simple operation of the insert as a reversible block element of the bottom. Solutions are also conceivable in which the insert is screwed within the containment body by providing relative threads on both elements.

In a preferred embodiment of the invention, the protrusions are a thread. The thread inside the containment body or the insert allows the slag sample once solidified to be easily unscrewed from the same, which can subsequently be reused. Advantageously, the opening of the containment body and, if present, of the insert, is chosen so as to represent an entrance area for the sample of at least 4 cm ² . Advantageously, this area corresponds to the opening defined by the inner tubular or annular circumference of the containment body and/or of the insert. Preferably, covers of the opposite end to the bottom of the containment body or of the insert (as, for example, the second metal disc of the cell of the state of the art described above) are not provided. The advantage of this solution consists in having a wide mouth to receive the slag, which despite being foamy and viscous, can enter the cell in sufficient quantity to be analysed. The cell according to the invention is therefore suitable for collecting slag with high foaminess indexes, which correspond to the maximum value of the foaminess index which is reached as a function of the effective viscosity and of the fraction of precipitated solid particles.

The section of the tube or ring forming the containment body or the insert is preferably circular (in this case the body and the insert are cylindrical), but sections of other geometries are also conceivable, such as, inter alia, hexagonal and octagonal sections. The circular section allows the presence of threads that guarantee the unscrewing of the sample.

A further aspect of the invention relates to a probe for the collection a slag sample, which comprises a cell according to the invention and a lance on which the cell is mounted. The lance allows the operator or robot to introduce the cell into the liquid slag. The cell is advantageously placed with its bottom laterally of the lance.

A further aspect of the invention relates to a process for the collection and the analysis of a slag sample, comprising the following steps:

(a) providing a cell with the bottom inserted or a corresponding probe according to the invention;

(b) collection of a slag sample which is received in the space inside the containment body or, if present, in the space inside the insert;

(c) waiting for the solidification of the sample and preferably the cooling of the sample;

(d) separation of the bottom from the sample; and

(e) sample analysis.

The process, thanks to the use of the cell according to the invention, provides a sample which, after being detached from the bottom, provides a slightly rough surface of the sample. Preferably, the analysis is performed directly on the surface of the solidified sample that was in contact with the low roughness surface area or surface of the bottom, making it unnecessary to destroy the sample having a smooth surface suitable for the LIBS analysis ( Laser Induced Breakdown Spectroscopy).

Advantageously, the slag sample has at the time of collection a high foaminess index.

In a particularly preferred embodiment of the method, the cell comprises said insert and the solidified sample is extracted after step (c) together with the insert from the containment body. With a thread inside the insert it is also possible to simply unscrew the sample from the insert allowing the reuse of the insert.

The features described for one aspect of the invention may be transferred mutatis mutandis to the other aspects of the invention.

The embodiments of the invention described reach the objects of the invention. In particular, they allow the collection of very foamy slag, the reuse of the containment body and the insert after use, and the attainment of a sample with a very smooth surface directly suitable for the LIBS analysis.

Said objects and advantages will be further highlighted during the description of preferred embodiment examples of the invention given, by way of example and not of limitation.

Variants of the invention are the object of the dependent claims. The description of preferred exemplary embodiments of the cell, the probe and the process for the collection and the analysis of slag samples is given by way of example and not of limitation, with reference to the attached drawings.

DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS

Fig. 1 shows a cell for the collection of slag samples according to the state of the art.

Fig. 2 shows in an exploded view and in the cross-sectional mounted state a first exemplary embodiment of a cell for the collection of slag samples according to a first embodiment of the invention.

Fig. 3 shows in an exploded view and in the cross-sectional mounted state a second exemplary embodiment of a cell for the collection of slag samples according to a second variant of the invention. Fig. 4 shows a cross-sectional view of the preparation of the probe filled with slag of the exemplary embodiment of Figure 3 for the LIBS analysis.

Fig. 5 shows an enlarged and cross-sectional view of the empty and assembled cell of the exemplary embodiment of Figure 3.

Fig. 6 shows in an exploded view and in the cross-sectional mounted state a third exemplary embodiment of a cell for the collection of slag samples according to a second variant of the invention.

Fig. 7 illustrates the parameters of equation (1) for the determination of roughness values according to ISO 1302 and 4287 standards.

Fig. 1 shows a cell 2 for the collection of slag samples according to the state of the art. The probe 2 is composed of a ceramic cylinder 4 in which a compartment 6 is enclosed on the lower part by a first metal disc 8 and on the upper part by a second metal disc 10 provided with a hole 12 serving as an input for the sample.

Fig. 2 shows in an exploded view and in the cross-sectional mounted state a first exemplary embodiment of a cell 102 for the collection of slag samples according to a first embodiment of the invention. The cell 102 is composed, as can be clearly seen in the exploded view at the top, of a ceramic containment cylinder 104, a lower metal disc 108 with a C- shaped section and an insert in the form of a ceramic block wedge 114. In the empty assembled state it can be seen that the lower metal disc 108, which has a plate-like shape, is inserted into the ceramic cylinder 104 forming its bottom. The C-shaped section prevents the disc 108 from coming out of the containment cylinder 104. The wedge 114 holds the disc 108 fixed. The wedge 114 has protrusions 116 on its inner side wall, preferably a thread, which serves to retain the sample in the initial liquid state and then to unscrew it once it has solidified. Inside the cell 102 there is therefore a compartment 106 which resembles a glass with an opening whose perimeter corresponds to the inner perimeter of the wedge 114. In this way a sample, also very foamy, can easily enter and fill the compartment 106 where it is stopped by the protrusions 116 inside the wedge 114. The cell 102 therefore has no coverage. In the image below in Fig. 2 the cell 102 comprises in its compartment 106 a slag sample 118. The inner walls of the body 104, or containment cylinder, and the exterior walls of the insert or wedge 114 have complementary inclinations therebetween and compatible with the inclination of the edges of the bottom 108 to create a sealed insertion.

Fig. 3 shows in an exploded view and in the cross-sectional mounted state a second exemplary embodiment of a cell 202 for the collection of slag samples according to another embodiment of the invention. According to the same principle of the probe of the previous figure, the probe 202 is composed of a ceramic containment body or cylinder 204, a bottom in the form of a lower metal disc 208 and a ceramic wedge-shaped insert 214. The containment cylinder 204 comprises a stepped shaping 205 therewithin, which allows the support of the metal disc 208 without this being able to exit downwards from the containment cylinder 204. The disc 208 is held by the ceramic block wedge 214 against the step 205. Inside the wedge 214 there are also protrusions 216 in the form of a thread for retaining the slag 218. The inner walls of the containment body 204 and the exterior walls of the insert or wedge 114 have complementary inclinations therebetween to create a sealed insert. In this exemplary embodiment the bottom 208 is not flared.

Fig. 4 shows a cross-sectional view of the preparation of the cell filled with slag of the exemplary embodiment of Figure 3 for the LIBS analysis. Once the cell 202 is filled with the slag 218 and the slag 218 is solidified, the cell 202 is turned upside down i.e. rotated in the direction of arrow Xi. The ceramic block wedge 214 and the metal disc 208 emerge, which can easily be detached from each other. The wedge 214 comprises solidified slag 218, which has a smooth surface 220 where it was in contact with the metal disc 208 and in particular with its low roughness surface 209. The ceramic cylinder 204 is turned according to the arrow X2 and can be reused by recomposing the cell 202 with the recovered metallic disc 208 and with the recovered wedge 214 (the thread allows the unscrewing of the solidified slag) or in case of breakage with a new wedge. The insert 214 with the slag 218 contained is inverted and inserted into a LIBS instrument (not shown) which analyses the composition of the slag 218 directly on the smooth surface 220 without requiring the destruction of the sample or insert 214.

Common to all the metal discs 108 and 208 of the exemplary embodiments shown, respectively, is the fact that they have at least on the side that inside the cell 102, 202 is turned towards the slag 118, 218, a very smooth surface 109, 209, which allows obtaining a suitable sample for the LIBS analysis and being able to easily detach the solidified and cooled slag 118, 218 from the metal disc 108, 208. Fig. 5 shows finally an enlarged and cross-sectional view of the empty and assembled cell 202 of the exemplary embodiment of Figure 3. The containment body or cylinder 204 carries on the step 205 the metal disc 208 with a smooth surface 209, which is pressed by the ceramic wedge insert 214 against the step 205. The protrusions 216 on the inner side wall of the insert 214 catch and retain the slag (not shown). The insert 214 has projections 215 which help, being placed at a distance from the upper edges of the containment body 204, to extract the insert 214 from the latter. In contact between the outer wall of the insert 214 and the inner wall of the containment cylinder 204, inclined in a complementary shape therewith, a resin 203 can be provided, which improves the sealing of the fixed insert 214 to the cylinder 204 without making it difficult to separate them to prepare the sample for the LIBS analysis.

Exemplary dimensions include a height of the insert 214 of 20 mm, a distance of the projection 215 from the upper edge of 7 mm; in the area of the upper opening of the insert 214 an inner diameter of 45 mm and an outer diameter of 55 mm. The lower opening of insert 214 has a diameter of 46 mm and the overall lower diameter of insert 214 is 70 mm. The height of the containment cylinder 204 could be 22 mm and the overall height of the cell 202 with insert 214 completely inserted into the containment cylinder 204 30 mm.

For the elements of the cells 102, 202 made of metallic material, a steel of the type AISI 304 or 316 is particularly suitable.

Fig. 6 shows in an exploded view (to the left) and in the cross-sectional mounted state (to the right) a third exemplary embodiment of a cell 302 for the collection of slag samples according to a further variant of the invention. The containment body 314 can be seen with an inner thread 316 and the bottom 308. The bottom 308 is composed of a thick plate 311 with a smooth surface 309 facing the containment body 314 and with a channel hole 317 passing through the plate 311. In the lower part of the bottom 308 a kind of knob 313 is provided, which facilitates the manipulation of the bottom 308 which resembles a cap or a cover. In the direction of the arrow the bottom 308 is inserted in the containment body 314 and secured with the help of a pin 321 which is passed through two opposed holes 319 applied in the wall of the containment body 314 and through the channel hole 317 of the bottom, this last hole 317 having been aligned with the holes 319 of the wall of the containment body 314 with the insertion of the bottom. The pin 321 before insertion is L- shaped, once inserted the straight end coming out of the containment body 314 is slightly bent in such a way as to fix the bottom 308 preventing the pin 321 from being released. Once the sample has been collected and solidified, the bent end is "straightened" and the pin 321 is extracted to detach the bottom 308.

Fig. 7, finally, illustrates the parameters of the equation (1)

for the determination of roughness values according to ISO 1302 and 4287 standards in the current revision status at the filing date of the present application. The roughness is the complex of microgeometric errors present on a surface obtained with any processing. It is indicated with the value Ra that corresponds to the arithmetic average value of the absolute ordinates of the detected profile with respect to its average line M (length of the section subjected to measurement), expressed in pm, i.e. the arithmetical mean deviation of the absolute values detected within the length L of the bottom of the section subjected to measurement. With Zi, Z2 and Z(x), in general, is meant the height of an element of the profile, which is the sum of the height of a peak and the depth of a valley of the element of the profile. With x is meant the length of an element of the profile.

During operation, further implementation modifications or variants, not described herein, of the cell and the probe for the collection of slag samples, and of the relative procedure for the sample analysis, according to the invention, may be implemented. If such modifications or such variants should fall within the scope of the following claims, they should all be considered protected by the present patent.