Tubular element to transfer abrasive materials, in particular concrete, and method to make it

Abstract

A method to make a tubular element to transfer abrasive materials such as concrete, inert materials or suchlike, where the tubular element includes an external tubular component made of steel and an internal tubular component, coaxial to the external tubular component, where the internal tubular component is made of chromium carbide, or other similar material resistant to wear.

Claims

1. A method to make a tubular element to transfer abrasive materials, comprising: providing an external tubular component made of steel; rotating the external tubular component around a central axis at a determinate angular speed; simultaneously casting a material comprising chromium carbide, in a pure form or in the form of an alloy or mixture thereof, into said rotating external tubular component, in a melted condition in order to mold in-situ an internal tubular component; wherein the internal tubular component is made of a material having a greater resistance to wear than that of the external tubular component, wherein said external and internal tubular components are formed coaxial to the central axis; and wherein the external tubular component delimits a centrifugal mold for molding the internal tubular component.

2. The method as in claim 1, wherein said material comprising chromium carbide is conveyed toward an internal surface of said external tubular component by distribution means, while a corresponding translation is made between said external tubular component and said distribution means in a direction parallel to said central axis.

3. The method as in claim 2, wherein said translation occurs at a determinate translation speed that is advantageously comprised between about 7 m/min and about 11 m/min.

4. The method as in claim 1, wherein said determinate angular speed is advantageously comprised between about 200 rpm and about 250 rpm.

5. The method as in claim 1, wherein the temperature of said material comprising chromium carbide, when it comes into contact with an internal surface of said external tubular component, is advantageously comprised between about 1,950° C. and about 2,000° C.

6. The method as in claim 1, wherein said external tubular component, at least during a first sub-step, is heated by external heating means so that it reaches and maintains a temperature advantageously comprised between about 1,000° C. and about 1,100° C.

7. The method as in claim 1, wherein in a zone of said external tubular component, in which the contact occurs with said material comprising chromium carbide in its melted condition, a local micro-fusion occurs, at a temperature advantageously comprised between about 1,450° C. and about 1,500° C.

8. The method as in claim 1, wherein during solidification of said chromium carbide, a thin interface layer is formed between said external tubular component and said internal tubular component.

9. The method as in claim 8, wherein the thickness of said interface layer is advantageously comprised between about 0.2 mm and about 0.4 mm.

10. The method as in claim 1, wherein the abrasive materials comprise at least one of concrete and inert materials.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other characteristics of the present disclosure will become apparent from the following description of some embodiments, given as a non-restrictive example with reference to the attached drawings wherein:

(2) FIG. 1 is a schematic longitudinal section view of a tubular element according to the present disclosure;

(3) FIG. 2 is a front view of the tubular element of FIG. 1;

(4) FIG. 3 is a schematic longitudinal section view on an enlarged scale of a step of the method to produce the tubular element of FIG. 1;

(5) FIG. 4 is a detail of the step of the method of FIG. 3.

(6) To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings. It is understood that elements and characteristics of one embodiment can conveniently be incorporated into other embodiments without further clarifications.

DETAILED DESCRIPTION

(7) With reference to FIGS. 1 and 2, a tubular element 10 to convey abrasive materials, such as concrete, inert materials, or suchlike, according to the present disclosure, comprises an external tubular component 11 and an internal tubular component 12, coaxial to a central axis X. In particular, the internal tubular component 12 is substantially made with centrifugation technology, and with some new and inventive characteristics, which will be explained later in detail.

(8) It should be noted that, although in the example provided here the central axis X is rectilinear, so that the tubular element 10 is cylindrical, the central axis X can also be curved, or comprise at least one curved segment, therefore the shape of the tubular element 10 can be curved, or comprise at least a curved toroidal part, although the two tubular components 11 and 12 remain coaxial to each other.

(9) In this particular case, the external tubular component 11 is made of metal, for example steel, advantageously not tempered, while the internal tubular component 12 is made of pure chromium carbide, for example Cr3C2, Cr23C6, Cr7C2. It is also possible to use both an alloy or a mixture of chromium carbide called Cr HARD, which is practically a chromium white cast iron, and also Cr3C2-NiCr. According to the different supply techniques, the composition of the carbides can vary, also according to the base material used.

(10) According to possible solutions, the internal tubular component 12 is made of a material resistant to wear, with a hardness higher than that of the external tubular component 11.

(11) According to possible solutions, the material resistant to wear has a hardness greater than or equal to 66HRC.

(12) Although the centrifugation technology to obtain tubular elements, or pipes, has already been known for a long time, the present disclosure proposes a new and very innovative solution, which provides to use, as a mold of the rotating centrifuge, the same external tubular component 11, made of steel, and to cast the material comprising chromium carbide in a melted condition inside it in order to produce the internal tubular component 12 and obtain the final product, that is, the tubular element 10, in a single step.

(13) FIG. 3 shows schematically a functional diagram of the method to produce a tubular element 10.

(14) The external tubular component 11 is both made to rotate at a high speed around the central axis X, for example at an angular speed W advantageously comprised between about 200 rpm and about 250 rpm, and also made to translate longitudinally, that is, parallel to the central axis X, as indicated by the arrow F1, for example at a translation speed V advantageously comprised between 7 m/min and about 11 m/min.

(15) At the same time, by means of a chute 13 disposed inside the same external tubular component 11, a material comprising chromium carbide in a melted condition, coming from an external crucible, of the known type and not shown in the drawings, is cast onto the internal surface of the external tubular component 11, as indicated by the arrow F2. The temperature T1 of the material comprising chromium carbide at exit from the crucible is advantageously comprised between about 2,100° C. and about 2,200° C., while the temperature T2 of the material comprising chromium carbide when it comes into contact with the internal surface of the external tubular component 11 is advantageously comprised between about 1,950° C. and about 2,000° C.

(16) Furthermore, in order to guarantee the correct compromise between the fluidity of the cast material, that is, of the chromium carbide, and the maintenance of the fluid state, and therefore guarantee the correct workability of the material, it is necessary to maintain the external tubular component 11 functioning as a mandrel at a given temperature T3, advantageously comprised between about 1,000° C. and about 1,100° C., during the whole step of the method. This is obtained by suitable heating devices, of a known type and not shown in the drawings, which radiate heat, as indicated by the arrows F3.

(17) According to a variant, not shown in the drawings, but easily understandable for a person of skill in the art, the external tubular component 11 rotates, but does not translate longitudinally, while it is the chute 13 that is translated parallel to the central axis X toward the inside of the same external tubular component 11.

(18) A method of this type allows the perfect adhesion of the two tubular components 11 and 12, since the internal tubular component 12 literally conforms to the external tubular component 11 according to the actual geometry of the latter. This is allowed by the presence of a thin interface layer 14 (FIG. 4) which is automatically created between the two tubular components 11 and 12 during the solidification of the chromium carbide. In fact, in a zone 15 of the external tubular component 11 made of steel, where contact with the chromium carbide in a melted condition occurs, a local micro-fusion occurs, at a temperature T4 advantageously comprised between about 1,450° C. and about 1,500° C.

(19) The interface 14 between the two materials, that is, the steel and the chromium carbide, is characterized by the dispersion of the chromium carbide inside the metal external tubular component 11, for example made of steel, following the simultaneous co-fusion of the two materials.

(20) With an external tubular component 11 having a thickness comprised between 1.5 mm and 2.0 mm, advantageously 1.8 mm, the interface 14 between the two materials guarantees the correct adhesion of the parts and its thickness is advantageously comprised between about 0.2 mm and about 0.4 mm.

(21) The internal tubular component 12 made of chromium carbide is able to ensure a duration, that is, a resistance to wear, considerably higher than a known component in tempered steel. In fact, chromium carbide allows to reach higher levels of hardness compared to those of tempered steel, for example greater than or equal to 66HRC, compared to 63HRC of tempered steel.

(22) The advantages of the present disclosure are many and at least the following.

(23) The final product, that is, the tubular element 10, made using the method described above is much more economical than that obtained with known methods, since with the present disclosure it is possible to reduce manufacturing costs and times, as some operations have been eliminated, including the movement of the sub-parts and the flaring processes, which on the other hand are necessary in known methods.

(24) Another advantage of the present disclosure is the repeatability of the method, which is decidedly greater than that of known methods and this provides a greater reliability and stability of the final product. In particular, the known method which provides both the flaring step and also the tempering step is instead affected by a whole series of uncertainties linked to the state of the semi-finished products, including the ovalization and the curvature of the components, which go to the detriment of the quality of the final product.

(25) The productivity of the method according to the present disclosure is decidedly high; in fact, the method according to the present disclosure is of the continuous type, therefore it can be industrialized for decidedly significant volumes. On the other hand, the production of the tubular elements with known methods has significant productivity limits and must also deal with the stand-by steps and the constant presence of the operators.

(26) Furthermore, the method according to the present disclosure can be completely automated, so that it also allows to reduce the physical presence of the operators, also with advantages in terms of safety.

(27) Furthermore, the tubular element obtained with the method according to the present disclosure is advantageously suitable to withstand an internal working pressure, therefore continuous, typically equal to 85 bar.

(28) It is clear that modifications and/or additions of parts may be made to the tubular element 10 to transport abrasive materials, in particular concrete, and to the method to produce it as described heretofore, without departing from the field and scope of the present disclosure.

(29) It is also clear that, although the present disclosure has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of tubular elements to transport abrasive materials, and of the corresponding methods to produce them, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.