LU87282A1 - Refractory sleeve for rollers for transport - of high temperature metal products - Google Patents

Abstract

A composite roller for conveying hot metal has an inner metal structure supporting an outer refractory sleeve, and coaxial frustoconical contact surfaces between the structure and the ends of the sleeve with summit within the sleeve, each forming an angle with a radius of the sleeve whose tangent is equal to the ratio of the length of the sleeve to its mean dia.

Description

~~ Q 7 9 Û O GRAND-DUCHY OF LUXEMBOURG

Patent N ° ... O - / _ “*„. , w. . . BL 4136. July 15, 1988 -MoteurleMmistre * to ------------------------------------------- ---- · Economy and Average Classes Tïtr <= s HélivrA Intellectual Property Service

_e (= 1¾¾ LUXEMBOURG

Invention Patent Application -------------------------------------------- ------------_- (1) I. Request

Metallurgical Research Center-Centrum Voor Research In De ^ ^

Metallurgie, Association non-profit-Vérënïging zonder winstoogmerk ~ 47, rue Montoyer Β ^ ΜΟ ^ ΈΤ ^ ϋΧΕΣΠΕΒ '......... Rep.cêsentée ... par ..: ..- E-.X. -ERE.yj_LMGER. £ c._E _____ MEYERS _, _ Lng. "„ JC.o_ns ........ eO-R - .. i .. · _ (3) ----------- ---------------------------------------------------------- -------------------. 4.6, ..... r.ue ... du .... Clrn.et] .. èr.e, .. LU.XEMBQU.BG ....... MANDATA IRES___ deposit) this ........... Fifteen July one thousand nine hundred eighty eight________________________________________________________ (4) at .... 15 ,,, 00____________hours, to the Ministry of the Economy and the Middle Classes, in Luxembourg: 1. this request for obtaining a patent for invention concerning: .................. .................................................. .................................................. .................................................. ....................................: ............. .................................................. ...................................... (5) '' Refractory sleeve for a roller for transporting a metallic product at high temperature and method of manufacturing such a sleeve '' 2. the description in language _________________________ of the invention in triplicate; 3. _______________3____________________________ drawing sheets, in three copies; · 4. the receipt of the fees paid to the Registration Office in Luxembourg, on _______ 15ju | J [and __. 1.988 ________; 5. the delegation of power, dated. „.. Br.UX.eJJ.es __________________ on_____11. July 1988 · 6. the successor document (authorization); declare) assuming responsibility for this declaration, that the inventor (s) is (are): (6) PI RET Jacques Quai de Rome, 6_l / 034 B-4ÖÖÖ- LIEGE BELG1QLJÉ _ ....... ................

claims (s) for the above patent application the priority of one (or more) application (s) of (7) T 6 Ju] £ ($ ôr ............ 1.6., July 1.987 ..... and .._ 0.ZAo.Ût.J..9.8.2 ______________________________________________________________________________________________________________________________________ under N ° (10) ..................... ... Q.8..ZQ.Q.Z9.8 .....-... Q.8.ZQ.Q.8.QQ.- HSZQQflflfi_____________________________________________________________________________________ on behalf of (11) Metallurgical Research Center ____________________________________________________________________________________________________________ elitfelise) domicile for him / her and, if designated, for his / her representative, in Luxembourg________________________________________ ................................. .................................................. .46, rue du Cimetière __________________________________________________________________________________________________________ (12) requests) delivery rance of an invention patent for the subject described and represented in the abovementioned appendices, with postponement of this grant to ........................ ....— - s ........................ / .................. .................................................. ...........— month. (13)

The deputy / representative: ............................................. .................................................. ............................................. (14) (H Deposit Report

The above application for a patent for invention has been filed with the Ministry of the Economy and the Middle Classes, Intellectual Property Service in Luxembourg, on: -jg July 1988 ^ fv Pr. The Minister of the Economy ^^ t of the Middle Classes, I; \ / _ "1 The head of the intellectual property service, A 68007_1_ Y" · ’EXPLANATIONS RELATING TO THE FORMOSAife / DEFÔÎrjr / [7 Γ.

(1) if applicable "Request for certificate ja main patent application Ko ............ <3r ....... ...” - (2) enter the surname, first name, profession, _ n address of the applicant, when the applicant is a registered office, legal form, address of the registered office, when the applicant is a legal person - (3) enter (/ Λ M the name, first name, address of the authorized representative, industrial property attorney, with special powers, if applicable: "represented by ............ acting as representative ** LA / J * - (4) date of filing in full - (S) title of the invention - (6) write the names, first names, addresses of the inventors or the indication "(see) separate designation (will follow)", when the desi gnation is done or will be done in a separate document, or the indication "not to mention", when the inventor signs or signs a non-mention document to be attached to a designation "BL 4136 <r *

Claim to the priority of patent applications filed in Belgium on July 16, 1987 No. 08700798 July 16, 1987 No. 08700800 07 August 1987 No. 08700886 Description filed in support of an invention patent application for: "Sleeve refractory for a roller for transporting a metallic product at high temperature and process for manufacturing such a sleeve ”

RESEARCH CENTER

METALLURGICAL

Centrum Voor Research in de Métallurç

Nonprofit organization

Vereniging zonder winstoogmerk 47, rue Montoyer

B-1040- BRUSSELS

C 2404E Bis / 8807.

Refractory sleeve for a roller for transporting a metallic product at high temperature and method of manufacturing such a sleeve.

The present invention relates to a refractory sleeve for a roller for transporting a metallic product at high temperature.

In the field of the development of metal treatment, there are many situations where the transport of metal products at high temperature must be ensured. Such situations arise in particular in the context of steel manufacturing, where it is common for the temperature of the transported products to reach or exceed 1000 ° C. This is particularly the case in hot rolling mills and in continuous casting plants. Another frequent situation is the continuous heat treatment of the steel strips, in ovens where the temperature is usually between 700 ° C. and 1000 ° C. approximately, where rollers are used in particular for guiding the strip. The description which follows will essentially refer to this application, but it goes without saying that the invention also extends to rollers of this type used in other fields such as the transport of rolled products or of continuously cast products. , whether the product is ferrous, for example steel, or not.

20

In a continuous annealing furnace, the cold rolled steel strip generally enters at room temperature and it is brought, under a protective atmosphere, to the required temperature which is frequently above about 700 ° C. It undergoes this heating 25 progressively by traversing a sinuous trajectory defined by 2 a series of rotary guide rollers. During the last part of this trajectory, the strip is maintained at the desired temperature and it is the seat of metallurgical phenomena, in particular a recrystallization of its structure, before leaving the furnace towards the later stages of its treatment.

Under certain conditions, the temperature of the strip may be higher than the temperature of the guide rollers. This difference can be due to various causes, for example the arrival of a hot strip on a colder roller when the width of the strip changes, or heterogeneities in the transfer of heat between the strip and these rollers. As a result, the strip undergoes local cooling and consequently localized contractions in areas which are thus subjected to the whole of the tensile force which ensures the progression of the strip. The elastic limit of steel can be exceeded in these zones which are then the seat of plastic deformations resulting in "thermal undulations" (heat buckling) during cooling of the strip.

20

In addition, it often happens that particles of scale or steel coming from the surface of the strip are deposited on the guide rollers where they end up forming clumps. When these clusters have reached a sufficient size, they damage the surface of the strip; they can even detach from the rollers and adhere to the strip, the surface quality of which they seriously deteriorate.

Various proposals are known for guide rollers using refractory materials in an attempt to reduce these thermal effects. GB-A-1,389,852 describes a roller for a continuous heat treatment oven, which consists of a metal core surrounded by a sleeve of refractory material based on fused silica. Patent application EP-A-35 0090428 raises a roller for a continuous annealing installation, consisting of a metal core coated with a layer of 3 niobium cermet.

The present invention relates to a refractory sleeve for a roller for transporting a metal product at high temperature, in particular in a continuous annealing furnace, which has certain advantages over already known devices; it makes it possible inter alia to avoid the appearance of local thermal deformations and surface defects in the transported product, while having a long service life thanks to a mechanical strength sufficient to prevent its cracking and a high resistance to abrasion.

To this end, the present invention provides a refractory sleeve for a transport roller having a small contact surface with the product transported.

In accordance with the present invention, the refractory sleeve for a roller for transporting a high-temperature steel product is characterized in that its external lateral surface has a plurality of gradations defining an "alternation of raised zones and zones in relief. hollow and in that the radially culminating points of said raised areas define a cylindrical surface coaxial with said sleeve.

According to a particular variant of the invention, the sleeve is constituted by a hollow cylindrical part made of a first refractory material, furnished with a plurality of bodies made of a second refractory material, partially embedded in the outer surface layer of said hollow cylindrical part .

30

These bodies are therefore projecting with respect to the external lateral surface of said hollow cylindrical part and they thus form the raised zones and the hollow zones which constitute the external lateral surface of the sleeve.

Said bodies can have any shape without departing from the scope of the present invention. It is however preferable that their shape is regular, in particular spherical or cylindrical.

In the case of cylindrical bodies, the end surfaces 5 of the cylinders can be planar or curved and in particular spherical.

If the bodies are spherical balls, they are preferably contiguous and arranged either in squares or in staggered rows; 10 if they consist of cylinders, these are preferably aligned along external generatrices of the sleeve, with their end surfaces contiguous or spaced, said cylinders also being able to be offset transversely relative to the other between two lines of neighboring cylinders.

15

In the context of this variant, said first refractory material, constituting the hollow cylindrical part, is advantageously a concrete with a high alumina content (A ^ Û ^) and preferably of so-called "tabular" alumina.

20

Also in the context of this variant, said second refractory material, constituting said bodies, is advantageously a ceramic material having a high abrasion resistance, preferably composed of very pure alumina (A ^ O ^), pressed iso-25 statically and sintered.

According to another variant of the invention, said raised zones are constituted by portions of the external lateral surface of said sleeve, while the hollow zones are constituted by cavities cut in said external lateral surface. These recessed areas may be separate cavities hollowed out in the surface of said sleeve and therefore surrounded by a single raised area; these recessed areas can also be formed by a network of grooves, which surround a plurality of individual raised areas forming part of the external lateral surface of said sleeve.

5

In this variant, it is advantageous that at least the outer surface layer of said sleeve is made of a refractory material having a high resistance to abrasion.

It is further advantageous that said raised areas and therefore also said hollow areas, and in particular said bodies, are distributed in a regular manner in the external lateral surface of the hollow cylindrical part. Such a distribution makes it possible to offer a support as homogeneous as possible for the product such as a steel strip, transported by the roller equipped with said sleeve.

Other features and advantages will appear on reading the description given below, by way of example, of preferred embodiments of a refractory sleeve according to the invention. In this description, reference is made to the accompanying drawings, in which FIG. 1 represents, in longitudinal and transverse sections, a refractory sleeve of the prior art; FIG. 2 shows, also in sections, a fragment of a sleeve according to a variant of the invention, the lateral surface of which carries spherical balls; FIG. 3 shows, also in sections, a fragment of a sleeve according to another variant of the invention, in which the side surface carries cylindrical bodies; Figure 4 shows, in longitudinal section and in perspective, a fragment of a sleeve carrying a network of grooves; and Figure 5 shows, also in longitudinal section and in perspective, a fragment of a sleeve carrying a plurality of discrete cavities.

These figures are schematic representations, in which only the elements necessary for understanding the invention have been reproduced. In particular, the metal support has not been shown on which the sleeve of refractory material * 6 is normally mounted. In addition, identical or analogous elements are designated by the same reference numerals in all the figures.

FIG. 1 shows a refractory sleeve 1 intended for a transport roller of the prior art. The outer lateral surface of the sleeve 1 is substantially smooth and gives rise to the drawbacks mentioned above.

Figures 2 to 5 show fragments of refractory sleeves 1 10 made in accordance with different variants of the present invention.

FIG. 2 shows such a sleeve carrying it spherical balls 2, preferably contiguous, partially embedded in the refractory material of the sleeve. The penetration depth of the balls 2 in the refractory material is advantageously between 1.2 times and 1.8 times the radius of said balls, so as to guarantee the stability of their positioning in the sleeve.

The diameter and the number of balls are in principle arbitrary. However, the number of balls should be sufficient to offer uniform support to the moving steel strip; this number should not however be too high, otherwise the sleeve would in practice approach the conventional sleeves of FIG. 1.

25

According to the invention, it appeared that a number of balls between 5 balls / dm2 and 500 balls / dm2 makes it possible to offer the strip sufficient support without inducing the aforementioned risk of deformation of the strip. These numbers of balls per unit area correspond roughly to ball diameters of 5 mm to 50 mm and assume that the balls are contiguous. A diameter of beads of the order of 10 mm to 25 mm has proved to be interesting. In the case of 10 mm diameter beads, their number is approximately 115 beads / dm2.

The spherical balls 2 can be arranged in any desired manner; the most frequent arrangements, however, are the 7 square arrangement and the staggered arrangement.

FIG. 3 illustrates another variant of refractory sleeve 1b in accordance with the invention, in which the bodies are constituted by the cylindrical elements 3, of a length between 10 mm and 50 mm and of identical diameter with shaped ends of spherical caps. Similarly to Figure 2, these cylindrical bodies penetrate to a depth between 1.2 times and 1.8 times the radius of their cylindrical part. These cylindrical elements are aligned with their longitudinal axis parallel to the longitudinal axis of the sleeve. They are preferably contiguous in the same line and two adjacent lines are preferably contiguous, while possibly being offset longitudinally by a fraction of the length of one of said cylindrical elements.

15

FIG. 4 shows, in longitudinal section and in perspective, a cylindrical sleeve the whose lateral surface is divided into zones 4, preferably regular, by means of a network of grooves 5. A network of substantially square meshes has been shown here , 20 which also leads to substantially square zones 4. It is however obvious that the meshes of this network can have any shape and orientation. They can be wide.

In Figure 5, there is shown, also in longitudinal section 25 and in perspective, a refractory sleeve ld whose side surface 6 carries a plurality of cavities 7. The dimensions and shape of said cavities 7 may be any; similarly, their distribution can be arbitrary, although it is advantageous to produce a regular distribution in a square or staggered fashion.

30

In the sleeves according to the invention, the contact zones with the strip are different depending on the variant envisaged. Punctual in the case of balls 2 and linear with the cylindrical bodies 3, these contact zones are two-dimensional in the case of surfaces 4 and 5.

8

The distribution of these contact zones is in principle arbitrary; it is nevertheless advantageous for this distribution to be uniform over the lateral surface of the sleeve. It would not, however, depart from the scope of the invention for this distribution not to be uniform and for it to be different, for example, in the central region and in the end regions of the sleeve. It is obvious, moreover, that the contact zones must be distributed over a length of sleeve which is at least equal to the greatest width of strip to be transported.

10

The present invention also relates to a method of manufacturing a refractory sleeve; this method, which uses the centrifugation process, is particularly applicable to the production of sleeves comprising bodies partially embedded in the outer surface layer of said sleeve, as illustrated in FIGS. 2 and 3.

According to the present invention, the method of manufacturing a refractory sleeve is characterized in that bodies of a first refractory material are introduced inside a rotary cylindrical mold, in that one rotates said mold about its longitudinal axis and distributes said bodies on the interior surface of said rotating mold, in which at least one second refractory material is poured into said rotating mold, so as to form a layer which coats said molds body and whose total thickness is greater than the radial dimension of said bodies, in that said layer is maintained by support means, in that the setting of said layer is effected, in that one immobilizes said cylinder mold, in that said support means are removed, in that said layer is demolded in the form of a sleeve whose surface area contains said bodies, in that it is removed minus part of said second material a refractory located between said bodies in the outer lateral surface of said sleeve and in that said sleeve is subjected to a drying operation, respectively to baking.

* t 9

The bodies can a priori have any shape without departing from the scope of the invention; the process is however particularly advantageous when using bodies having a shape of revolution, such as spheres or cylinders.

According to the invention, said second refractory material can be made entirely with fine-grained refractory concrete, capable of flowing in the interstices between the bodies which constitute said first refractory material. It has however appeared advantageous to use such a fine-grained refractory concrete only to fill the voids existing between said bodies and the interior surface of said mold and to use coarser-grained refractory concrete to produce the radially inner part of 15 the layer in contact with the bodies; in this case, the fine grain refractory concrete constitutes said second refractory material, while the coarser grain refractory concrete constitutes a third refractory material.

It has also been found to be advantageous to subject said mold to vibrations during the positioning of the bodies and during the casting of the second and possibly the third refractory material, in order to ensure correct distribution of said bodies, as well as of said material, in particular between and around said bodies.

25

According to a particular characteristic of the process of the invention, said support means are constituted by a quick setting material, such as quick setting plaster, which is poured inside said refractory sleeve, then which is remove after 30 taking the whole.

According to another characteristic of the invention, said support means comprise a tube, preferably metallic, the outside diameter of which corresponds substantially to the desired inside diameter of the sleeve.

t t 10

According to yet another advantageous characteristic, the operation of removing said second refractory material between the bodies is carried out by sandblasting, that is to say by spraying sand which removes the refractory material infiltrated around the radially external part of the body. The "sand" considered here includes not only conventional sand, but also a substance called "metallic sand" and made up of fine particles of metal.

The process of the present invention will be more easily understood and implemented using the description which follows and which refers to FIG. 6, where the principle of the process of the invention has been illustrated schematically.

A cylindrical mold 11 rests on a foundation 12 by the intermediate 15 of raceways 13 and bearings 14. The ends of the mold 11 are provided with annular plates 15, 16, pierced with a central opening which gives access to inside the mold. The internal diameter of the mold 11 corresponds to the diameter of the external envelope of the sleeve to be produced. The mold 11 can be rotated about its longitudinal axis 17 by means of a motor of known type, not shown. For the manufacture of such a sleeve, the mold 11 is rotated about the axis 17, then a plurality of bodies made of a first refractory material are introduced into the mold, such as balls 18 of alumina. Due to the centrifugal force applied to them by the rotation of the mold 11, these balls 18 are distributed in a layer which completely covers the interior wall of the mold 11. A second refractory material is then poured into the mold 11, namely a fine-grained refractory concrete which, also under the effect of centrifugal force, fills the voids 19 existing between the balls 18 and the wall of the mold 11. A third refractory material is then poured which is a refractory concrete with larger grain and which forms a substantially cylindrical layer 20. This coarse refractory concrete ensures the mechanical strength of the sleeve. Inside this cylindrical layer 20, a quick setting material 11 is then poured, such as plaster 21, in order to hold the assembly. When the setting of the plaster is finished, the rotation is stopped and the setting of the refractory materials 19 and 20 is allowed to take place. The radial width of the annular plates 5 15, 16 corresponds at least to the total thickness of the walls of the mold and of the refractory sleeve. The central openings of the plates 15, 16 can be closed or reduced, for casting the plaster. When this setting is complete, we unmold the assembly and then pluck the plaster, to clear the inside of the sleeve. To facilitate the removal of the plaster 21 without damaging the refractory material 20, a film of a lubricating agent or of a plastic material can be placed between them which does not disturb the support effect exerted by the plaster.

Finally, part of the refractory material which has passed through the interstices between the balls 18 is removed by sandblasting, in order to disengage the external part of these balls 18 to the desired depth.

The procedure is substantially the same when the bodies are small cylinders. Due to their cylindrical shape, these align spontaneously along generatrices of the internal wall of the mold 11 under the effect of the centrifugal force due to rotation.

25

To avoid any risk of incorrect positioning of these cylinders, the mold 11 may possibly be subjected to slight vibrations. Stronger vibrations then contribute to ensuring good distribution and good densification of the refractory concretes.

The process according to the invention is obviously not limited to the embodiments which have just been described and illustrated by way of example. In particular, it would not be outside the scope of the invention to produce a refractory sleeve by replacing said bodies with an appropriate profiling of the internal surface of the mold, 12 which would make it possible to produce sleeves in accordance with the variants illustrated in the figures. 4 and 5. Likewise, the refractory material could be reinforced with suitable materials, such as steel fibers or carbon fibers. One could also, still within the scope of the invention, use any material other than plaster, and in particular plastics, to support the refractory material during the molding of the sleeve. Finally, one can use a mold in several parts, known per se, to facilitate the release of the refractory sleeve.

10

The transport roller equipped with the refractory sleeve, as just described, is generally produced by mounting the sleeve on a metal structure to give it an appropriate mechanical resistance; this "composite" structure however leads to problems arising directly from the temperature conditions to which it is subjected in service.

The high temperatures in fact cause a much greater expansion of the internal metallic structure than of the external refractory sleeve; this difference in expansion rapidly leads to the ruin of the composite roll by rupture or cracking of the refractory sleeve.

Another object of the present invention is to provide a composite roller for transporting a metallic product at high temperature, which makes it possible, by simple means, to remedy the aforementioned drawback and to extend the service life to a considerable extent. 'such a transport roller.

According to the present invention, a composite roller for transporting a metallic product at high temperature, which comprises an outer refractory sleeve mounted on an inner metallic structure, is characterized in that said metallic structure supports said refractory sleeve and in that that said contact surfaces 35 are frustoconical surfaces coaxial with said refractory sleeve, the apex of which is situated inside said refractory sleeve 13 and which are inclined, with respect to a plane perpendicular to the longitudinal axis of said refractory sleeve, an angle whose tangent is equal to the ratio between the length and the average diameter of said refractory sleeve.

5

Within the meaning of the present invention, the average diameter is that which corresponds to the half-thickness of said refractory sleeve.

The invention will be more easily understood and implemented thanks to the detailed description, given below by way of example, of a preferred embodiment of a composite roll according to the present invention. This description is illustrated by the appended drawings, in which FIG. 7 illustrates in radial section the principle of the assembly 15 according to the invention; and FIG. 8 shows, on a larger scale, the behavior of such an assembly during a temperature variation.

In these figures, which are schematic representations, only the elements which are directly necessary for the proper understanding of the invention have been shown voluntarily. In addition, identical or analogous elements are designated by the same reference numerals in all the figures.

FIG. 7 illustrates the principle of the assembly, in accordance with the invention, of a refractory sleeve 1 on a metal structure in order to constitute a composite roll for transporting a metal product at high temperature. The metallic structure is partly known and will not be described in detail here. By way of example, it may consist of a cylindrical drum assembled by end flanges 22, 23 to a shaft 24. According to the invention, this structure is completed by two rims 25, 26, bolted to the aforementioned drum and extending said flanges 22, 23 outward. The rims have frustoconical surfaces 27, 28 on which the refractory sleeve rests freely by corresponding frustoconical surfaces.

14 The angle of inclination of these frustoconical surfaces relative to a plane perpendicular to the axis of the refractory sleeve 1 is such that its tangent is equal to the ratio L / D, L being the length of the refractory sleeve and D being its diameter interior.

5

FIG. 8 shows, on a larger scale, the behavior of such a transport roller during a temperature variation. The initial situation is shown in solid lines: the refractory sleeve 1 rests freely on the rim 26 by the contact surface 10 28. This situation corresponds to ambient temperature. During heating to its operating temperature, the roller expands both in the axial direction and in the radial direction. The rim thus takes position 26 'shown in phantom, while the refractory sleeve comes in position 1', also shown in phantom. The dilations are exaggerated for the clarity of the drawing; however, the expansion of the metal structure is greater than that of the refractory sleeve.

The combination of axial and radial expansions results in each point on the surface of the rim 26 moving obliquely to the axis of the roller; the same is true for each point on the surface 28 of the refractory sleeve 1. By choosing the angle of inclination of this contact surface 28 in accordance with the invention, that is to say such that tga = L / D, each point of the surface 28 moves while remaining in this surface, both for the rim 26 and for the refractory sleeve 1. As a result, the contact surfaces slide freely on each other and that the heating does not induce any tensile stress in the refractory sleeve. 30

The opposite behavior manifests itself during progressive cooling of the roller and one thus returns to the initial situation represented in solid lines.

The composite roller according to the invention therefore eliminates the problem of the rupture of the refractory sleeve following the strong expansion of the metallic structure. One can of course seek to reduce this expansion, for example by cooling the metal structure by any suitable means. The free expansion assembly proposed by the present invention, however, reduces the need for such means. In addition to the aforementioned technical advantages, there is also the advantage of an economic cost price of the proposed composite roller.

Claims (12)

1. Refractory sleeve for roller for transporting a metallic product at high temperature, characterized in that its external lateral surface has a plurality of gradients defining an alternation of raised zones and hollow zones and 5 in that the points radially peaks of said raised areas define a cylindrical surface coaxial with said sleeve. 2. refractory sleeve according to claim 1, characterized in that it is constituted by a hollow cylindrical piece made of a first refractory material, furnished with a plurality of bodies made of a second refractory material, partially embedded in the outer surface layer of said hollow cylindrical part. 3. Refractory sleeve according to claim 2, characterized in that said bodies are spherical balls, the diameter of which is between 5 mm and 50 mm. 4. Refractory sleeve according to claim 3, characterized in that it comprises from 5 to 500 balls / dm2 approximately. 20 5. Refractory sleeve according to claim 2, characterized in that said shaped bodies are cylindrical elements with a length between 10 mm and 50 mm and with a diameter between 10 mm and 50 mm approximately. 25 6. Refractory sleeve according to one of claims 2 to 5, characterized in that said first refractory material, constituting the hollow cylindrical part, is a refractory concrete with high alumina content (A ^ O ^). 30 7. refractory sleeve according to one of claims 2 to 6, characterized in that said second refractory material, constituting said bodies, is a ceramic material having a high resistance to abrasion. * 17 ♦ »» 8. Refractory sleeve according to claim 1, characterized in that said raised areas are formed by portions of the outer lateral surface of said sleeve, while the recessed areas are formed by cavities cut in said outer surface. 9. Method for manufacturing a refractory sleeve by centrifugation in a rotary cylindrical mold, characterized in that bodies are introduced in a first refractory material, inside said mold, in that it is made to rotate said mold around its longitudinal axis and said bodies are distributed over the inner surface of said rotating mold, in that at least one second refractory material is poured into said rotating mold, so as to form a layer which coats said bodies and whose The total thickness is greater than the radial dimension of the said bodies, in that the said layer is maintained by support means, in that the said layer is set, in that the said immobilization is immobilized cylinder mold, in that said support means are removed, in that said layer 20 is removed from the mold in the form of a sleeve whose surface area contains said bodies, in that at least one is removed part of said second material refra ctaire located between said bodies in the outer lateral surface of said sleeve and in that said sleeve is subjected to a drying operation, respectively baking. 10. Method according to either of claims 1 to 5, characterized in that said second refractory material is poured so as to fill the voids existing between said bodies and the interior surface of said mold and in that pouring a third refractory material, with a coarser grain, so as to form the radially inner part of said layer. / 11. Composite roller for transporting a metallic product at high temperature, which comprises an outer refractory sleeve mounted on an inner metallic structure, characterized in that said metallic structure supports said refractory sleeve through of contact surfaces situated at the ends of said refractory sleeve and in that said contact surfaces are frustoconical surfaces coaxial with said refractory sleeve, the apex of which is situated inside said refractory sleeve and which are inclined, with respect to a plane perpendicular to the longitudinal axis of said refractory sleeve, by an angle whose tangent is equal to the ratio between the length and the average diameter of said refractory sleeve. 10 12. Composite roller according to claim 11, characterized in that said frustoconical surfaces are formed on rims mounted on said metal structure.