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DESCRIPTION

Field of the Invention

The present invention relates to a sleeve for foundries or steel plants, and in particular relates to a sleeve of the type used to make risers in foundries or ingots in steel plants.

State of the art

One of best known processes used by humans to obtain metallic objects consists in casting molten metal into molds in which there is a cavity having shape corresponding to the piece to be obtained. Once the metal has cooled sufficiently, the mold can be opened or destroyed, depending on whether it is a permanent or expendable mold, and the piece can be extracted.

For example, the classic foundry process is sand casting: the molten metal is cast into a mold composed of a special sand called foundry sand, which at the end of the process is disrupted in order to extract the manufactured item, also named cast. The following video shows the melting of complex parts of a Ferrari engine made of aluminum: https://www.youtube.com/watch?v=iBnOKOAfLnY.

During casting the temperature of the metal must always be higher than the melting point thereof or higher than the liquidus temperature in the case of metal alloy. It is essential that the casting temperature remains sufficiently high in order to prevent the molten metal from starting to solidify during the relative travel to the shaped cavity defined in the mold; a possible solidification, even partial, of the metal during the casting could compromise the quality of the obtained manufactured item.

Only when the mold has been completely filled by the liquid metal, the latter is allowed to cool until complete solidification. With this technique, the solidified metal takes the definitive shape of the manufactured item to be obtained.

During the solidification, namely during the phase change from liquid to solid, all metals are subject to volumetric shrinkage, i.e. reduction of volume. The extent of this shrinkage is proportional to the temperature gradient undergone by the metal. Technicians working in the foundry industry are very familiar with this phenomenon and take it into account for the correct sizing of the mold. In other words, the molds are slightly oversized with respect to the manufactured item to be obtained, for example 0.5% more voluminous, precisely because it is necessary to provide sufficient volume to the metal in the liquid phase, before it shrinks due to cooling.

The solidification process of metal inside the mold is complex and is often subject of study in the academic world. Metal solidification always starts at the walls of the mold, i.e. the outer part of the manufactured item cools down more quickly with respect to the inner part due to heat exchange with the mold itself. Therefore, before opening the mold, it is always necessary to wait until also the inner part of the manufactured item is solidified.

The time T _m required to obtain the complete solidification of the manufactured item is expressed by the following formulas:

where K _m is a constant depending on the used metal and the material of the mold and

Mm is the thermal modulus of the manufactured item, in turn expressed by the ratio of the volume V _m of the manufactured item to its surface S _m .

It is clear that, for the same volume V _m , if the surface S _m of the manufactured item increases, i.e. the surface exchanging heat with the mold, the time required for cooling until solidification proportionally decreases.

Manufactured items characterized by low thermal modulus are particularly subject to the so-called pipe or shrinkage cavity phenomenon. Metal layers progressively solidify starting from the surface of the manufactured item thereby generating a sort of funnel in which the molten metal drains off; in practice, the last portion of metal remaining at the center of the manufactured item, accumulates in the funnel when solidifies.

In order to prevent the pipe or shrinkage cavity from excessively growing, thereby ruining the manufactured item, risers are usually used. They are reservoirs of molten metal to be arranged in special sleeves on the mold, above the sprues or else directly on the cast. Sleeves are also known as feeders.

Risers have double function:

- increasing the molten metal pressure in the manufactured item, i.e. increasing the riser content (molten metal column) which applies pressure on the molten metal in the mold; - moving the thermal center of the cooling metal into the riser and thus outside the manufactured item, so that the pipe or shrinkage cavity can never extend into the manufactured item, but at most can involve the risers.

The thermal center is the last point where metal solidifies.

In order for a riser to be effective, it is necessary that the metal solidification ends in the riser, and for this reason the sprue connecting it to the manufactured item must be suitably sized so as to not solidify before the riser.

At the end of the process the sleeves are destroyed, the manufactured article is extracted from the mold and the solidified risers are cut, i.e. detached from the article. Part of the metal of the risers is recycled. It is not possible to recycle all the metal in the risers exactly because in the risers there is the pipe or shrinkage cavity.

In order to minimize the cooling rate of the metal in the risers, sleeves specially designated for this purpose have been proposed, the sleeves being either insulating to limit the heat loss of the riser, or exothermic, i.e. reacting with the molten metal cast inside them, thus generating heat.

ASK CHEMICALS, FOSECO, ASHLAND and LUNGEN companies are some of the best known sleeve manufacturers.

The following video shows examples of exothermic sleeves: https://www.youtube.com/watch?v=tC4q5xMrY08.

Sleeves according to the known art are described for example in WO 01/15833, WO 2014/083155, EP 2815819, EP 1868753.

EP 2489449 describes a hybrid solution: a sleeve having an exothermic inner body and an insulating outer jacket.

The sleeves currently available are made by using, for example, mixtures of aluminum oxides, microbeads, organic binders, iron oxides, ground quartz, potassium aluminum fluoride, metallic aluminum, oxidants, organic fiber, ceramic fiber, or biosoluble fibers.

The formula (1) can also apply to sleeves in order to calculate the solidification time of the risers:

(3) T _f = k _f · M _f

(4) M _f = V _f / S _f ,

where Mf is the sleeve modulus, in turn expressed by the ratio of the volume Vf of the sleeve (and therefore the maximum possible volume of the riser) to the surface Sf therein that the molten metal can wet; the constant kf, called modulus extension factor (MEF), is:

(5) k _f = a · b,

where a is a factor depending on the metal cast into the sleeve and where b is a factor depending on the thermal characteristics of the material of the sleeve and the shape thereof, and the shape of the riser.

Sleeves are designed so as to provide a MEF factor as great as possible and maximize the cooling time Tf of the risers, so as to always meet the condition:

(6) M _f > M _m .

The sleeves may be perforated, to allow the molten metal to be cast into the mold through the sleeve itself, or blind if the purpose is to feed an inner area of the mould.

Sleeves for foundries currently available have the same inner geometry: the cavity intended to contain the initially molten metal, and thus the riser, is substantially cylindrical. This is because the sleeves are always designed as a sort of extension of the sprue outside of the mould. At most, the known exothermic sleeves are provided with a wedge-shaped portion projecting into the inner cavity by a negligible length. This portion has the function of triggering the exothermic reaction in the sleeve.

The Applicant found that current sleeves for foundries may be improved. In recent years, research has focused on materials for sleeve construction, but although investments have been made by manufacturers, there has been no substantial increase in performance.

One of the ways used in the steel plants to obtain steel ingots is to solidify the molten steel in special moulds. These moulds are called precisely "ingot moulds".

The drop casting technique consists in bringing the ladle above the ingot mould and casting the molten metal therein. The bottom casting technique provides for the casting of steel in a column connected to underground channels leading the metal to emerge in the mould from the bottom.

After casting the ingot moulds are brought to the stripping department, i.e. the just solidified ingots are extracted from the ingot moulds. The latter are turned upside down and, through two side spouts, the ingot is removed from the container by two special tongs.

Even in manufacturing steel ingots, ingots are used in combination with sleeves, even if in steelworks these elements are usually referred to using the term "hot-top" . The task of the hot -tops is to create corresponding metal accumulations above the ingot being formed.

Physical phenomena ruling the steel solidification are not significantly different from those described above in relation to foundry casts. Therefore, the above described drawbacks in relation to sleeves can also be found in the use of hot -tops.

Summary of the invention

In order to simplify the description of the present invention the term sleeve will be used more frequently than the expression hot top, still referring to the element to be combined with either the mould or the ingot mould, but the field technician must bear in mind that the use of the term riser in steel industry is actually erroneous.

Similarly, for the sake of simplicity, the term riser will be used to refer both to the solidified metal portion in the foundry sleeve and to the solidified metal portion in the steelworks hot top.

It is therefore an object of the present invention to provide a sleeve for foundries or a hot top for steel plants having improved performances with respect to a traditional sleeve / hot top, the material used for the construction thereof being equal.

In particular, it is an object of the present invention to provide a sleeve for foundries or a hot top for steel plants that, with respect to a traditional element, either allows risers or ingots having smaller volume to be obtained, or allows greater riser modulus Mf to be obtained with equivalent riser volume.

Therefore, the present invention relates to a sleeve for foundries or a hot top for steel plants according to claim 1.

In particular, the sleeve / hot top comprises an outer side wall delimiting an inner volume intended for accommodating molten metal to be solidified as a riser. Unlike traditional solutions, the inner volume is subdivided in two or more chambers so that the ratio of the surface the molten metal can wet to the corresponding volume is maximized.

The concept underlying the present invention is to subdivide the inner volume of the sleeve in multiple cavities, i.e. the inner chambers; this choice causes substantial increase in the ratio of the heat exchange surface, in practice the inner walls of the sleeve wet by the molten metal, to the volume of the molten metal cast into the sleeve. This facilitates the increase of the modulus extension factor (MEF).

The expression "surface the molten metal can wet" means the inner surface of the sleeve/hot top that can come into contact with the molten metal as the latter is cast therein. Usually, sleeves are filled to the brim.

The proposed solution provides several advantages.

A first advantage is that the sleeve promotes the increase of the time the riser requires to completely solidify. The proposed solution allows longer solidification times of the risers to be achieved, with the same dimensions of the sleeve with respect to a traditional sleeve.

As explained above, in order to obtain a good manufactured item, namely properly made and not to be wasted, it is essential that the riser solidifies after the manufactured item itself or the manufactured item portion with which the riser is combined. Therefore, the increase in the time required to complete the solidification of the riser and the increase of the riser modulus are two extremely important factors to ensure the quality of manufactured items.

A second advantage is given by the fact that the sleeve according to the present invention operates with significantly smaller amount of molten metal with respect to a traditional sleeve having the same dimensions. In practice, the sleeve according to the present invention not only ensures longer solidification time of the riser and greater thermal modulus, but is also characterized by the ability to create risers having volume with up to 50% reduction and even more, compared to a traditional sleeve. Clearly, this results in reduced consumptions of molten metal and less waste: since the risers are smaller than what could be obtained by traditional sleeves, other conditions being equal, there is also less metal to be discarded near the pipe or shrinkage cavity.

In other words, the sleeve according to the present invention either allows a smaller volume of molten metal to be used with respect to a traditional sleeve having the same capacity and overall dimensions or, by using an equal volume of molten metal, it provides a greater riser modulus Mf.

The above described advantages can be found both in foundries and steel plants.

The sleeve may be either insulating or exothermic; in any case the above described advantages are obtained.

The base of the sleeve is open to allow the molten metal to be cast into the mould or the ingot mould, or to rise again in the sleeve from the mould or the ingot mould. On the contrary, the top of the sleeve can be open, for example to allow the molten metal to be cast from outside, such as from the ladle, or if allowed by the position in the mould, or closed if the volume to be fed is in the interior and is thus covered by moulding sand.

The sleeve according to the present invention can be used with various metals, for example cast iron, steel, alloys.

Preferably, the chambers are divided from each other by one or more inner walls of the sleeve.

In the preferred embodiment, the inner walls and the outer wall are made in one piece, namely they constitute a single monolithic structure. Alternatively, the inner walls are defined by an insert that can be inserted in the inner volume of the sleeve.

Preferably, the inner walls and the outer wall are made of the same material. In the preferred embodiment, the chambers extend in height for at least 50%, and preferably for at least 70%, of the height of the inner volume of the sleeve. In other words, the chambers have significant and not negligible height extent with respect to the height extent of the sleeve itself. Preferably, the sleeve comprises a base intended for being leant on a mould, at a sprue or at the cast to be fed or else against an ingot mould, and a top. The top, in turn, can be open to allow the molten metal to be cast through the sleeve, otherwise closed for feeding an inner part of the mould in foundry. In an embodiment, the chambers join at the base to form a single lower chamber, for example a chamber having a height extending only to 25% of the height of the inner volume of the sleeve. Alternatively, the chambers extend from the base to the top of the sleeve, along the whole height available inside.

Chambers can have various geometries. For example, they can be conical with diameters decreasing towards the top of the sleeve, or have parallel generatrices.

For example, the chambers may have circular, or oval, or polygonal cross section.

In an embodiment, the chambers have star-shaped, hemispherical, petal-shaped, squared or indented cross-section having three or more points or hollows to maximize the surface the molten metal can wet.

Generally, all the chambers have the same height extent, otherwise the chambers which are more centrally arranged in the sleeve are higher than those exposed at the outer side wall.

Preferably, the sleeve is made in one piece but, as an alternative, it can be realized in at least two portions, a lower portion constituting the base intended for being leant on a mould at a sprue or cast or ingot mould, and an upper portion comprising the chambers. In this embodiment, the lower portion and the upper portion are constrainable one to another, for example can be interlockingly or shape coupled, or glued together.

The lower portion may be itself internally subdivided in separate chambers, or it defines in its own inside a single lower chamber.

In an embodiment for foundries the sleeve is provided at the bottom with a metal insert, or an insert made of sand or chromite, at the opening through which the molten metal is cast into the mould or rises again from the mould. The insert may be fixed or slidable with respect to the sleeve, e.g. in a telescopic way, or it can be bellows-like, so as to allow the riser to be easily cut from the cast after solidification. If exothermic sleeves are used, a further function of this insert is to space apart the cast and the exothermic sleeve. If the exothermic reaction of the sleeve is in contact with the cast, the characteristics of the cast to be fed could be changed.

The Applicant reserves to file a divisional application for an alternative embodiment of the sleeve in which the inner volume is not subdivided in a number of chambers as in the cases previously described; in this embodiment, the inner chamber is a single chamber laterally delimited by the inner wall of the sleeve. If observed in cross section (horizontal section), the inner wall is polygonal or otherwise indented, with a plurality of hollows, that can also be pointy. For example, the section is shaped as a multi-pointed star or is provided with radial niches or lobes (concave or convex).

This alternative embodiment has greater capacity with respect to the previously described variations.

It should be considered that the sections shown in figures 31 -34 may be also used to make the lower chamber 8 shown in figures 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23-30, i.e. the lower chamber 8 can be made with polygonal or indented section, as shown in figures 31-34.

Brief list of the figures

Further characteristics and advantages of the invention will be more evident by the review of the following specification of a preferred, but not exclusive, embodiment, which is depicted for illustration purposes only and without limitation, with the aid of the attached drawings, in which:

- figure 1 is a vertical section of a sleeve for foundries according to a first embodiment;

- figure 2 is a horizontal section of the sleeve shown in figure 1 ;

- figure 3 is a vertical section of a sleeve for foundries according to a second embodiment;

- figure 4 is a horizontal section of the sleeve shown in figure 3;

- figure 5 is a vertical section of a sleeve for foundries according to a third embodiment;

- figure 6 is a horizontal section of the sleeve shown in figure 5;

- figure 7 is a vertical section of a sleeve for foundries according to a fourth embodiment; - figure 8 is a horizontal section of the sleeve shown in figure 7;

- figure 9 is a vertical section of a sleeve for foundries according to a fifth embodiment;

- figure 10 is a horizontal section of the sleeve shown in figure 9;

- figure 11 is a vertical section of a sleeve for foundries according to a sixth embodiment;

- figure 12 is a horizontal section of the sleeve shown in figure 11;

- figure 13 is a vertical section of a sleeve for foundries according to a seventh embodiment;

- figure 14 is a horizontal section of the sleeve shown in figure 13;

- figure 15 is a vertical section of a sleeve for foundries according to an eighth embodiment;

- figure 16 is a horizontal section of the sleeve shown in figure 15;

- figure 17 is a vertical section of a sleeve for foundries according to a ninth embodiment;

- figure 18 is a horizontal section of the sleeve shown in figure 17;

- figure 19 is a vertical section of a sleeve for foundries according to a tenth embodiment;

- figure 20 is a horizontal section of the sleeve shown in figure 19;

- figures 21 to 30 are vertical sections of further corresponding embodiments of the sleeve for foundries according to the present invention;

- figures 31 to 34 are horizontal sections of corresponding embodiments of the sleeve, for which the Applicant reserves to file a divisional application;

- figure 35 is a diagram showing the bottom-casting technique for ingots in steel plants;

- figure 36 is a diagram showing the drop-casting technique for ingots in steel plants; - figure 37 is a horizontal (cross) sectional view of a first hot top according to the present invention to be used in manufacturing steel ingots;

- figure 38 is a vertical (elevation) sectional view of the hot top shown in figure 37;

- figure 39 is a horizontal sectional view of a second hot top according to the present invention to be used in manufacturing steel ingots;

- figure 40 is a vertical sectional view of the hot top shown in figure 39; - figure 41 is a horizontal sectional view of a third hot top according to the present invention to be used in manufacturing steel ingots;

- figure 42 is a vertical sectional view of the hot top shown in figure 41 ;

- figure 43 is a horizontal sectional view of a fourth hot top according to the present invention to be used in manufacturing steel ingots;

- figure 44 is a vertical sectional view of the hot top shown in figure 43.

Detailed description of the invention

Figures 1 and 2 show a sleeve 100 according to the present invention. In particular, figure 1 is a vertical sectional view, i.e. considered on a vertical and diametrical plane; Figure 2 is a cross sectional view taken on the horizontal plane A-A depicted in figure 1.

Similar views are proposed for the sleeves shown in figures 3 to 20.

Turning back to the figures 1 and 2, the shown sleeve 100 is of the exothermic type, but an insulating sleeve can be made by using the same geometry.

The sleeve 100 is made in one piece, i.e. is monolithic, and is provided with a base 2, a top 3 and a side wall 4 that delimits an inner volume 5 inside the sleeve 100 itself intended to contain the molten metal that must solidify to form a riser. The base 2 is intended to be positioned in abutment on the cast to be fed or against a sprue of a foundry mould, typically a mould for sand casting.

As can be noted, most of the inner volume 5 of the sleeve 1 is divided in two separate spaces, or chambers 6 and 7. The chambers 6 and 7 only join at the base 2 so as to form a single space 8. It could also be said that the separate chambers 6 and 7 merge at the base 2 into a single lower chamber 8.

However, in general, the lower chamber 8 can be absent and the chambers 6 and 7 may extend throughout the height of the sleeve 100.

An inner wall 9 of the sleeve 100 keeps separate the chambers 6 and 7; the inner wall 9 is joined to the side wall 4 and in particular is integral therewith.

As can be seen by observing figure 1, the height extent of the chambers 6, 7 is about 70% of the overall height H of the sleeve 100. In fact, the lower chamber 8 extends in height only for 30% of the height H. In the example shown in figures 1 and 2, the sleeve 100 has general circular section and is cone-shaped, but the chambers 6 and 7 have oval section constant throughout the vertical extent of the chambers 6 and 7 themselves.

Then the chambers 6 and 7, at the top of the sleeve 3, open to the outside in order to allow the molten metal to be cast into the mould just through the sleeve 100. Therefore, the chambers 6 and 7 are designed as extensions of the sprues of the mould on which the sleeve 100 is positioned.

Considering the section of Figure 2 and bearing in mind that the drawings are not to scale but are only illustrative, the area of the section is about 13.70 cm ² and the area intercepted by each of the chambers 6 and 7 is about 3.91 cm ² .

Figures 3 and 4 show a different sleeve 200 which differs from the first sleeve 100 because the chambers 6 and 7 are closed at the top, i.e. they can not be accessed from the outside at the top 3. This embodiment can be used when the molten metal is not required to be cast through the sleeve 200, but the sleeve has only the function of allowing the molten metal to rise again from the mould. In practice, the sleeve 200 is positioned on the mould, aligned with an open riser, so that the molten metal flowing out of the mould along the open riser enters the sleeve 200 up to at least partially fill the chambers 6 and 7, where solidification starts.

Figures 5 and 6 show a third embodiment. The inner volume 5 of the sleeve 300 is divided in three chambers 10, 1 1 and 12, which are arranged at 120° from each other with respect to the center of the horizontal section of figure 6. The chambers 10-12 are slightly conic and have circular cross section.

In practice, the inner wall 9 occupies the whole cross section of the sleeve 300 except precisely at the chambers 10-12.

Also in the sleeve 300, the chambers 10-12 open upward and merge into the chamber 8 at the base 2 of the sleeve.

Also in the sleeve 300 the chambers 10-12 extend for about 70% of the height H of the sleeve itself.

Considering the section of Figure 6 and bearing in mind that the drawings are not to scale but are only illustrative, the area of the section is about 13,70 cm ² and the area intercepted by each of the chambers 10-12 is about 2.83 cm ² .

Figures 7 and 8 show a fourth embodiment 400 similar to the previous one, but different in that the chambers 10-12 are closed at the top.

Figures 9 and 10 show a fifth embodiment 500 of the sleeve. The sleeve 500 is similar to the sleeve 300 but there is the fourth chamber 13. The four conical chambers 10-13 are arranged crosswise around the center of the section shown in figure 10.

Also in the sleeve 500 the chambers 10-13 extend for about 70% of the height H of the sleeve itself.

Figures 11 and 12 show a sixth embodiment 600 similar to the previous one, but different in that the chambers 10-13 are closed at the top.

Figures 13 and 14 show a seventh embodiment 700 of the sleeve. The sleeve 700 is similar to the sleeve 500 but different in that there is the fifth chamber 14. The five conical chambers 10-14 have pentagon-like arrangement around the center of the section shown in figure 14.

Clearly, also in the sleeve 700 the chambers 10-14 extend for more than 50% of the height H of the sleeve itself.

Figures 15 and 16 show an eighth embodiment 800, similar to the previous one, but in which the chambers 10-14 are closed at the top.

The Applicant carried out comparison tests by using the sleeves 100-800 and a standard sleeve according to the known art, by making iron castings, thereby obtaining results that are summarized in the following Table 1, where the modulus is expressed in centimeters, the sleeve volume is expressed in dm ³ , the volume reduction with respect to the reference sleeve of the known art is expressed in percentage, quantities of cast iron are all expressed in kilograms and the capability of volume settling with respect to the reference sleeve of the known art is expressed in percentage.

TABLE 1

Reference

sleeve of

2.74 0.80 reference 6.250 4.700 1.550 25% the

known art

Sleeve

2.74 0.33 59% 2.543 1.170 1.373 54% 100

Sleeve

2.74 0.24 70% 1.781 0.850 0.931 52% 200

Sleeve

2.74 0.33 59% 2.588 1.440 1.148 44% 300

Sleeve

2.74 0.28 65% 2.593 1.310 1.283 49% 400

Sleeve

2.74 0.27 66% 2.056 0.987 1.069 52% 500

Sleeve

2.74 0.26 68% 1.916 0.881 1.035 54% 600

Sleeve

2.74 0.26 68% 1.898 0.968 0.930 49% 700

Sleeve

2.74 0.25 69% 1.838 0.845 0.993 54% 800

Carried out tests show that, with unchanged modulus compared to a traditional sleeve without the internal subdivision in separate chambers, i.e. a sleeve with a not- divided internal volume, the sleeves 100-800 according to the present invention allow substantial reduction of the amount of cast-iron, both that used in the liquid phase and the amount that solidifies in the sleeves turning into risers. Furthermore, the sleeves 100-800 are smaller.

Thus, tests proved that the subdivision of the interior volume 5 of the sleeves in separate rooms, laterally divided from each other, has beneficial effect on the ratio of the available volume of molten metal to the surface the latter can wet.

Similar results have been obtained also for the steel.

Further embodiments will be now described.

Figures 17 and 18 show a ninth embodiment 900 of the sleeve. The sleeve 900 is similar to the sleeve 300, but the three chambers 10-12 have cross section shaped as a five-pointed star. In general it is clear that the number of the points can also be different. Advantageously, at the star points the molten metal in the sleeve 900 will wet a greater surface of the sleeve. In other words the star-shaped, hemispherical, petal- shaped, squared or anyway indented cross-section allows the heat exchange surface for exchanging heat between the metal and the sleeve to be maximized, thereby increasing the modulus extension factor (MEF).

Clearly, also in the sleeve 900 the chambers 10-12 extend for more than 50% of the height H of the sleeve itself.

Figures 19 and 20 show a tenth embodiment 1000, similar to the previous one, but in which the chambers 10-12 are closed at the top.

Figure 21 shows a further embodiment 2000 provided with dome-shaped top 3 and chambers 10, 11 closed at the top.

Figure 22 shows a further embodiment 3000 characterized by having a central chamber 15 higher than the other chambers 10, 11 positioned around it. Moreover, in this sleeve 3000 there isn't the lower chamber 8.

Figures 23 to 26 show further embodiments, all referred to by the number 4000. The lower chamber 8 has different shape with respect to the above described versions. In particular, the lower chamber 8 is conical, with section decreasing towards the base 2, and the other chambers are parallel.

Figures 27 to 30 show further embodiments, all referred to by the number 5000. These are sleeves similar to the sleeves 4000, but realized in three pieces that can be coupled to each other preferably in a modular way. In particular, a base portion 20, a top portion 30 and a central portion 40, which can be interlockingly joined, are shown. This is an advantageous solution because it allows a sleeve 5000 to be composed as desired, by assembling the different parts 20, 30, 40 according to the needs, thereby simplifying the management of the foundry stock.

However, the sleeve 5000 can be realized with only the two modular portions 20 and 30.

Figures 31 to 34 shows a different variation of the sleeve, for which the Applicant reserves to file a divisional application.

In particular, figure 31 shows a sleeve 100' provided with the single inner chamber 10 whose cross section defines a multi-pointed star 101. In the specific case the points 101 are twelve, but the number may be different, for example eight, ten, sixteen, etc.

Figure 32 shows a sleeve 100' provided with the single inner chamber 10 whose cross section is circular with a plurality of radially-arranged polygonal niches 102 projecting towards the outer wall of the sleeve 100'. In the specific case the niches 102 are eight, but the number may be different, for example ten, twelve, etc.

Figure 33 shows a sleeve 100' provided with the single inner chamber 10 whose cross section is circular with a plurality of circumferential lobes 103 projecting towards the outer wall of the sleeve 100', like flower petals. In the specific case the lobes 103 are twelve, but the number may be different, for example eight, six, ten, etc.

Figure 34 shows a sleeve 100' provided with the single inner chamber 10 whose cross section is circular with a plurality of arrow-shaped points 104 projecting towards the outer wall of the sleeve 100'. In the specific case the arrows 104 are twelve, but the number may be different, for example eight, six, ten, etc.

Figure 35 schematically shows the way bottom casting is carried out in steel plants to manufacture ingots. The molten metal 6001 is cast from a ladle 6000 into the column 6002 connected, in turn, to the ingot mould 6003 by means of lower runners 6004. Then, the metal rises again in the ingot mould 6003 from bottom, i.e. from the base.

Figure 36 schematically shows the way drop casting is carried out in steel plants to manufacture ingots. The molten metal 6001 is cast from a ladle 6000 directly into the ingot mould 6003 from above.

In figures 35 and 36 a hot top according to the present invention is schematically depicted by the reference 100".

Figures 37 and 38 show a first example of hot top 100" according to the present invention. Figure 38 is a section taken on the plane B-B of figure 37. Unlike conventional solutions, the inner volume of the hot -top 100" is divided in several chambers 10, 11, etc., as explained above in relation to the sleeve for foundries.

Figures 37 and 38 show an example with circular chambers extending for almost the entire height of the hot top.

Figures 39 and 40 show a second example of a hot top 100" divided into chambers having a six-pointed star section. Figure 40 is a section considered on the plane C-C of figure 39.

Figures 41 and 42 show a third example of a hot top similar to the first one shown in Figures 37 and 38, but comprising the single lower chamber 8 which extends in height to not more than 30% of the height of the hot top. Figure 42 is a section taken on the plane D-D of figure 41.

Figures 43 and 44 show a fourth example of hot top similar to the second one shown in Figures 39 and 40, but comprising the single lower chamber 8 which extends in height to not more than 30% of the height of the hot top. Figure 44 is a section taken on the plane D-D of figure 43.

As understood by the field technician, according to the concepts of the present invention, also the hot top can be subdivided in more than two chambers having circular or polygonal cross-section and possibly tapering at the top or the base.

Although not shown in Figures 37-44, also the hot top for steel plants can be made in several pieces that can be coupled to each other as described above for the sleeve for foundries.