Description

ROLLED-SECTION BRAKING DEVICE IN ROLLING-MILL PLANTS AND METHOD OF REDUCING THE ADVANCING SPEED OF A STEEL ROLLED SECTION

Object of the invention 5 The invention refers to a rolled-section braking device for rolling-mill plants, method and plant according to the characteristics of enclosed claims.

Technical Field of the invention

The invention concerns braking devices, for the production of metallic rolled-sections in rolling-mill plants. 0 Definition

In this invention, the term rolled-section is intended as any type of shape, bars, sections rods, round bars or wire, not excluding strips.

Prior art and problem to be solved

Most braking devices, able to reduce speeds particularly of rolled metal bars, are based 5 on the friction generated with the contact of the same rolled-section with an auxiliary surface.

The friction can be rolling or sliding.

The limits of this process are:

A- Limited braking capacity due to the maximum friction coefficient between the 0 surfaces, above all at high speeds and with hot bars.

B- Contact between the rolled-section and the device which generates friction, with consequent loss of quality of the rolled-section, wear of the braking device, rollers or braking surfaces.

C- For the rolling braking devices (bar-break with rolls), considerable energy 5 expenditure for the braking of the masses in rotation belonging to the braking machine itself. This all results in lower efficiency.

Aim of the invention

The aim of the invention is to solve the abovementioned problems and furthermore

improve the performance of the plant in order to allow greater rolling speeds by means with greater braking efficiency without the risk of deforming the bar, without substantial wear of the braking means and in decidedly shorter times and spaces. Solution of the problem and explanation of the invention The problem is solved with the characteristics of the main claim. The sub-claims represent preferred solutions. Advantages

In this way there is the advantage of having a plant with greater braking efficiency of the advancing bar allowing the plant also to function at a greater speed without the risk of damage to the rolled-section.

A greater braking efficiency involves the possibility to: a) use greater speeds, and/or b) reduce the braking space and/or c) reduce the braking time d) maintaining the best quality of the material.

All these characteristics obviously participating for a better performance of the plant, with greater productivity evident at lower costs and with the quality unchanged. Description of the invention The invention is now described with the help of the enclosed figures in which the inventive concept is schematically represented wherein:

Fig.1 represents a side view of a rolling line in the section concerned with the braking operation before the insertion of the bar into a known channel device (or other type of known roller device with sliders) for the receiving of the bar in longitudinal advancement, stopping of the same and discharge transversely into a known underlying cooling plate which, at the same time, provides the respective transfer transversally towards packaging systems of known art (not illustrated).

Fig.2 represents the enlarged detail of the side view of the bar braking device according to the invention.

Detailed description of the invention with the help of the attached figures As disclosed by the attached figures, therein is indicated: with 1 , the cooling tank or tunnel, that can be with an air jet or water jet or other cooling liquid, - with 2, a bar guide with opposite idle rollers; with 4, the bench moveable in height with respect to the magnets or electromagnets (6), constituting the magnetic braking device with eddy currents, adjustable in the braking force by means of the allowing of greater or less approaching of the advancing bar to brake to the respective magnets (6), the movement obviously being reciprocal

(bench/magnets) also inverse; with 3, a second bar guide with opposite idle rollers as in 2, but downstream of the magnetic bar-breaking device; with 5, an auxiliary tail brake device of known art with opposite rollers, to allow a sure final stopping in the exact position.

Functioning system

The rolled metal bar, hot or cold to brake goes along its line at a nominal speed. Longitudinally to it, at a suitable and variable distance, a series of permanent magnets or electromagnets (6) are placed. Such magnets/electromagnets (6) will be of a number, size and polar combination suitable for the weight and speed of the metal bar to brake.

Such magnets/electromagnets (6) on the basis of Lenz's law, will generate eddy- currents in the bar to brake, which, to this aim, will be in ferromagnetic conditions. Such currents in their turn generate a magnetic field which, interacting with that of magnets/electromagnets (6), aims to brake the bar.

The bar to brake that is moved at a nominal speed, is advantageously cooled by a water-cooling tank or tunnel (1 ). This cooling is useful not only for the heat treatment of the rolled-section, but also to check that the temperature of the rolled-section has

sufficiently lowered so that it is influenceable by the forces of the subsequent braking magnetic field.

At the exit of said tank (1 ), the bar is guided through the idle roller devices (2) and (3), devices which have the function to keep the distance of the bar from the group of subsequent magnets/electromagnets (6) constant.

The group of magnets/electromagnets is kept at an adjustable distance from the bar, by means of the device (4), in this case with hydraulic jacks, but obviously being able to be also of other types, for example mechanic with eccentric cams or levers, sliding or other. Such device is also able to make the same group of magnets/electromagnets (6) disappear.

Exiting from the idle roller device (3), an auxiliary braking device (5) is placed, such device being able to be with rolling or sliding friction. Process The bar comes from the rolling mill at a nominal speed, enters the cooling tank (1 ) and is guided by the bar guide devices (2) and (3). When the braking must be carried out, electromagnets will be electrically supplied for a suitable time and will regulate the distance from the bar (device 4), in case of permanent magnets, only the distance will be regulated. When the speed reaches a suitably low value, the residual speed will be further reduced by means of the auxiliary brake (5). Applicability

Obviously the device of the present invention refers to magnetic bars, therefore metal bars (iron and its alloys) with the exclusion of nonmagnetic bars, for example with high nickel content (e.g. austenite steels, austenitic stainless steels with nickel-chromium 18/8 and higher, etc).

With regard to their temperature (the temperature of the passing from the magnetic/non-magnetic state - Curie temperature), the plant will obviously be regulated so that the temperature at the moment of braking is such that the rolled-

section is magnetic. For this purpose, the presence of the front cooling system (1 ) is useful, which accomplishes the double function both of heat treatment and also controlling that the temperature is not too high. Since the temperature in such a phase, namely before the plate entry, is substantially lower than the non-magnetic phase, most ferrous rolled-sections can be treated with this system and therefore also martensitic stainless steels, obviously excluding austenites for their non-magnetic nature.

The man skilled in the art therefore understands that such device is applicable to the majority of steel bars whose resistance to magnetic forces is effective at temperatures present in the bar in this phase, normally <500°C.

Great advantages are obtained particularly for the production of ribbed rods for use in constructions in concrete, and/or for products with strict finishing tolerances, said ribbings and respective known markings which are impressed on the upstream rolling cylinders are not damaged by this braking device which brakes the bar without touching it. The tail brake intervening only in the final phase can act gently without any damage.

The advantages of this solution are evident: By means of the bar-break with eddy currents the following are obtained:

- Braking limit not related to the friction coefficient. - No contact between the brake and the material to brake, better quality of the rolled- section.

- Absence of wear of the brake.

- Absence of wear for the braking of the inertial masses in rotation.

- The device can be used alone, or combined with other braking devices. - The device can be used alone, or in combination with in line cooling devices.

The device can use permanent magnets or electromagnets indifferently, alone and/or also jointly.

Obviously the magnets/electromagnets are polarized in a suitable way to the braking

cycle, the same can vary their position with respect to the bar during the braking cycle. So, for example a device with lower magnetic bench has been illustrated, but an upper magnetic counter-bench could also be provided or even a tunnel with an annular magnetic field.

Naturally the device can be applied to systems both for hot-rolling and cold-rolling. Advantageously said magnetic field generator means are cooled with appropriate cooling means, in this way the braking system is made more efficient, without involving or impairing said magnetic field generating means which advantageously for example can be electromagnetic.