EP0299944A2 - Method of making a multilayered cylinder, and cylinder so obtained - Google Patents

Abstract

A multilayered cylinder is manufactured by forming the layer(s) by deposition of one or more metals or metal alloys in the form of fine liquid droplets under a controlled atmosphere. The liquid droplets are obtained by dispersion of a molten metal or metal alloy with the aid of a cold fluid. The deposition is carried out on the surface of a cylinder which is in rotation and in translation relative to the flow of droplets. The layer(s) deposited may be subjected to a thermomechanical densifying treatment. <IMAGE>

Description

The present invention relates to a method for manufacturing a multilayer cylinder and to the cylinder obtained, more particularly to a metallurgical rolling mill cylinder.

At present, there are two main groups of rolling mill cylinders which are classified according to their method of manufacture.

The first group includes the cylinders obtained by forging. These have a fine and resistant metallic structure which responds well to the mechanical stresses of rolling mills. However, the aforementioned shaping, that is to say forging, greatly limits the composition of the alloy used because the ability necessary for forging restricts the additions of alloying elements possible to increase the hardness. It follows that this type of rolls must undergo a heat treatment step subsequent to shaping, in order to give it sufficient hardness to limit wear during its use in the rolling mill.

In contrast to the first group of cylinders, the second comprising the cylinders obtained by casting, does not pose any problem as to the chemical composition and is not limited in addition elements. However, these cylinders often have a coarse structure due to the shaping means, that is to say the casting and the core of the cylinder is not always able to withstand high stresses by shocks that the cylinder undergoes during its work at the rolling mill.

In addition, there are also cylinders made up of separate elements, the different elements being assembled by shrinking to form a cylinder. In theory, this solution seems ideal because each element of the cylinder can be best adapted to its work at the rolling mill.

In practice, it is found that problems of wear and longevity arise from the fact that there is no real connection or metallic continuity between the various constituent elements of the cylinder.

The method of manufacturing a multilayer cylinder of the present invention has the great advantage of eliminating the drawbacks mentioned above linked to the type of production of the cylinder.

The term "multilayer cylinder" must be taken in the sense of a cylinder of which at least one element, for example the envelope surface of the cylinder, is formed of at least one layer of deposited material.

The process for manufacturing a multilayer cylinder, object of the present invention, is essentially characterized in that the layer or layers are formed by depositing one or more metals or metal alloys in the form of fine liquid droplets under an atmosphere controlled.

According to a first method of implementing the process of the present invention, the controlled atmosphere is of the neutral type in the metallurgical or chemical sense of the term.

According to a second method of implementing the method of the invention, the liquid droplets are obtained by dispersion of a metal or of a molten metal alloy using a cold fluid.

This production technique allows the deposition of any metal or metallic alloy without limitation in its composition and gives the deposited layer a structure with remarkable mechanical properties, linked in particular to the absence of coarse dendritic structures for casting and to the absence of solidification macrosegregations.

According to a preferred embodiment of the method of the present invention, the deposition is carried out on the surface of a cylinder which is in rotation and in translation relative to the flow of droplets.

It is therefore understandable that this technique makes it possible to combine the properties of a forged core with the wear resistance of a highly alloyed envelope by producing the cylinder by depositing the envelope on a forged cylinder which constitutes its core. .

According to another embodiment of the process of the present invention, one proceeds to the deposition of one or more successive layers on a worn cylinder, that is to say that one proceeds to the operation of reloading said cylinder, said cylinder being of the cast or forged type.

The fact of using a used cylinder leaving the rolling mills as the basis for the deposition allows the appreciable economy of the casting and / or forging of this cylinder and the complex rectification of the pins.

The process of the invention gives rise to multilayer rolls whose thermomechanical resistance properties can be selected according to their working location in the rolling mill and which are more reliable from the point of view of wear than the conventional cast envelopes obtained by disgorging or centrifugation.

According to another preferred embodiment of the process of the invention, the deposition of a layer forming part of a series of successive layers is controlled both from the point of view of thickness and chemical composition, so that after wear of the outer layer The cylinder is able to be used again, but upstream from its initial position in the rolling mill.

The previous method defines a remarkable advantage of multilayer cylinders compared to conventional cylinders: a multilayer cylinder after wear of its outer layer can be used again on a rolling mill, but in an upstream location, that is to say towards the beginning of the rolling mill train from the place where it previously worked.

We know on the one hand, that the rolls of rolling mills "go up in the train", that is to say that the more their wear increases and the more their working location moves upstream of the rolling mill train and on the other hand, that "the rolling gap", that is to say the distance between the rolls at work, increases.

It is easily understood that in the case of a multilayer cylinder, this raising of the train by the cylinder can be prepared in advance during the development of the cylinder, by controlling the composition and the thickness of the deposit forming each layer as a function of the location of the cylinder in the rolling mill and its future development.

In addition, such a multilayer cylinder further simplifies inventory management of rolling mill rolls by establishing a unique relationship: outside diameter of the cylinder = position in the train = surface layer with properties suitable for its work.

According to yet another embodiment of the process of the present invention, the deposited layer or layers are subjected to a thermomechanical densification treatment.

The present invention also relates to the cylinders obtained by applying the method described above.

The multilayer cylinder obtained by implementing the method which is the subject of the present invention is essentially characterized in that it consists of at least two elements, in that the first element constitutes the core of the cylinder and that it supports the latter during its assembly in a rolling mill train and in that the outermost element with respect to at the longitudinal axis of the cylinder is formed by at least one layer deposited on the whole or only part of the surface of the core or of the previous layer.

• Le schéma de la figure 1 illustre une unité d'atomisation (U.A.). On y distingue en 1 le cylindre ou l'âme à traiter, en 2 et 3 les moyens respectifs pour mettre en translation longitudinale et en rotation le cylindre précité, en 4 le métal en fusion qui doit être déposé, en 5 le fluide qui assure la dispersion du métal précité, en 6 le flux de gouttelettes qui est déposé sur le cylindre 1 et enfin en 7 le cyclone assurant le dépôt sous atmosphère contrôlée.
• Le schéma de la figure 2 montre une installation de recouvrement à deux unités d'atomisation (U.A.) pouvant travailler en continu. On y dis­tingue en 1 l'atelier où arrivent les cylindres usés (2), le four de préchauffage ou de traitement thermique (3), les deux U.A. (4 et 5), et le retour (6) des cylindres après rechargement.
• La figure 3 schématise une ligne continue de rechargement à plusieurs unités d'atomisation (U.A.).

According to a preferred embodiment of the multilayer cylinder, object of the present invention, the layer or layers constituting the external element of the cylinder comprise at least one or more of the following elements: Fe, Si, Mn, C, Ni, Co, Nb , Cr, Mo, V, W.

• The diagram in Figure 1 illustrates an atomization unit (UA). We distinguish in 1 the cylinder or the core to be treated, in 2 and 3 the respective means to put in longitudinal translation and rotation the aforementioned cylinder, in 4 the molten metal which must be deposited, in 5 the fluid which ensures the dispersion of the aforementioned metal, in 6 the flow of droplets which is deposited on the cylinder 1 and finally in 7 the cyclone ensuring the deposition under controlled atmosphere.
• The diagram in FIG. 2 shows a covering installation with two atomization units (UA) which can work continuously. There are 1 in the workshop where the used cylinders (2) arrive, the preheating or heat treatment oven (3), the two AU (4 and 5), and the return (6) of the cylinders after reloading.
• Figure 3 shows schematically a continuous line of recharging with several atomization units (UA).

We can see the cylinder (1) to be recharged; arriving via an airlock (2), it undergoes preheating (3) then three successive operations (4, 5, 6) of recharging, it passes via an airlock (7) in a heat treatment oven (8) and leaves in ( 9) towards possible further processing.

By way of nonlimiting example, the results of various practical embodiments will be presented below by application of the method of the present invention.

Table 1 defines the chemical composition and the type of production of the elements forming the core of the cylinders.

Table 2 defines the chemical composition of the layers deposited by implementing the method of the present invention. TABLE 2 No. Composition (in% by weight) Yes Mn VS Or Cr Mo V 1 0.2 0.3 0.8 - 1.7 0.2 0.1 2 0.43 0.95 2.84 1.41 17.8 1.07 0.21 3 0.95 0.98 3.37 4.42 1.88 0.31 4 0.49 0.69 1.35 0.76 11.8 2 0.13 5 0.53 0.79 1.95 0.7 13 3 0.3 6 2.2 1 3.3 4.4 4.7 2 -

Table 3 defines the combinations chosen for a total deposited thickness of 60 mm.

Table 4 gives the values of the hardnesses HV 50 kg obtained. TABLE 4 Deposited metal HV 50 kg 1 757 2 783 3 661 4 752 5 762 2 + 1 657 + 779 2 + 6 + 1 661 + (± 715) + 776

Wear tests were then carried out in the laboratory, under defined conditions, in order to obtain relative wear values using conventional forged steel as a reference; Table 5 shows the values obtained.

The advantage of the process of the invention is obvious from the figures in Table 5, because it allows a wear efficiency of 1.4 to almost 5 times higher, therefore increasing the longevity of the cylinders in the same proportions .

In the last two examples, the wear resistance varies according to the nature of the layer, in order to allow the latter maximum performance taking into account other stresses that can be envisaged.

It goes without saying that this description was deliberately focused on the rolls of rolling mills, but it is not beyond the scope of protection of the invention to apply its working principle to the production of other rolls such as those of grinders, with grooves, for rolling back, continuous casting or even heat treatment.

Claims (9)

1. A method of manufacturing a multilayer cylinder, characterized in that the layer or layers are formed by depositing one or more metals or metal alloys in the form of fine liquid droplets under a controlled atmosphere. 2. Method according to claim 1, characterized in that the controlled atmosphere is of the neutral type in the metallurgical or chemical sense of the term. 3. Method according to claims 1 or 2, characterized in that the liquid droplets are obtained by dispersion of a metal or of a molten metal alloy using a cold fluid. 4. Method according to claims 1, 2 or 3, characterized in that the deposition is carried out on the surface of a cylinder which is in rotation and in translation relative to the flow of droplets. 5. Method according to either of claims 1 to 4, characterized in that one proceeds to the deposition of one or more successive layers on a worn cylinder, that is to say that one proceeds during the reloading operation of said cylinder. 6. Method according to one or more of claims 1 to 5, characterized in that the deposition of a layer forming part of a series of successive layers is controlled both from the point of view of thickness and chemical composition, so that after wear of the outer layer the cylinder is suitable for being used again, but upstream from its initial position in the rolling mill. 7. Method according to either of claims 1 to 6, characterized in that the deposited layer or layers undergo a thermomechanical densification treatment. 8. Multilayer cylinder obtained by implementing the method according to one or more of claims 1 to 7, characterized in that it consists of at least two elements, in that the first element constitutes the core of the cylinder and that '' it supports this when it is mounted in a rolling mill train and in that the outermost element relative to the longitudinal axis of the cylinder is formed by a layer deposited on the whole or only part of the surface of the core or the previous layer. 9. Multilayer cylinder according to claim 8, characterized in that the layer or layers constituting the external element of the cylinder comprise at least one or more of the following elements: Fe, Si, Mn, C, Ni, Co, Nb, Cr, Mo, V, W.

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