GB2176210A

GB2176210A - A method and apparatus for cooling an advancing elongate metal product

Info

Publication number: GB2176210A
Application number: GB08609000A
Authority: GB
Inventors: Pierre Simon; Marios Economopoulos
Original assignee: Centre de Recherches Metallurgiques CRM ASBL
Current assignee: Centre de Recherches Metallurgiques CRM ASBL
Priority date: 1985-04-12
Filing date: 1986-04-14
Publication date: 1986-12-17
Also published as: ES8704361A1; ES553902A0; ES8706488A1; GB2176210B; ES557214A0; GB8609000D0

Abstract

The product 1 is introduced into a tubular cooling unit 3 through a liquid screen in a lock 8 preventing air from entering the cooling unit 3. At least part of the cooling liquid forming the screen flows in the opposite direction to the direction of advance of the product. <IMAGE>

Description

SPECIFICATION A method and apparatus for cooling an advancing elongate metal product The invention relates to the cooling of an advancing elongate metal product, such as a steel bar leaving a hot rolling mill.

Usually a long product coming out of a hot rolling mill is at a high temperature, e.g. of the order of 950 to 1100 C, and has to be cooled. The cooling operation can inter alia form part of a heat-treatment, more particularly in the case of the quenching and selftempering process previously developed by the present applicants.

In most cases, inter alia when cooling forms part of a heat treatment, it is important for the product to be cooled in an identical manner in each section, i.e. along its entire length.

At present, this kind of cooling is frequently brought about in installations comprising a number of successive tubular units in which the cooling liquid and the product to be cooled move, usually in the same direction.

This feature has been adopted to ensure contact between the hottest product and the freshest cooling liquid, thus obtaining a maximum rate of cooling, at least at the inlet of each unit.

Recently, however, it has been found that the head of the product, i.e. the initial portion of the product which first enters the cooling installation, sometimes has a lower hardness and less mechanical strength than the rest of the product. The difference may be such that the initial portion of the product has to be scrapped, thus reducing the productivity of the cooling installation. The cause of this sometimes considerable variation in properties has not yet been precisely established, but it appears due to an inadequate rate of cooling in this portion of the product.

What is desired is a method of improved cooling of an elongate metal product in an installation of the aforementioned kind, so as to obviate the aforementioned disadvantage.

The present invention provides a method of cooling of an advancing elongate metal product, in which the product travels through at least one tubular cooling unit, in which a screen of cooling liquid is formed at the inlet of the tubular unit so as to prevent air entering it, the metal product is conveyed through the liquid screen so as to insert it into the cooling unit, and at least part of the cooling liquid forming the screen is made to flow in the opposite direction to the direction of advance of the metal product.

The liquid screen may be formed by a number of jets of cooling liquid, preferably directed towards the longitudinal axis of the cooling unit, the jets being inclined to the axis in the opposite direction to the direction of advance of the metal product.

Alternatively, the cooling unit is equipped with an inlet lock connected to it in an airtight manner, the inlet lock is permanently supplied with cooling liquid, at least part of the cooling liquid in the lock is made to flow in counter-current with the product through the orifice through which the product enters the lock, and the supply rate of cooling liquid is adjusted so that the lock is permanently filled with liquid.

The invention also provides apparatus for cooling an advancing elongate metal product, comprising at least one tubular cooling unit, means for forming a permanent screen of cooling liquid at the inlet of the tubular unit, and means for causing at least part of the cooling liquid forming the screen to flow in the opposite direction to the direction of advance of the metal product.

In a first embodiment, a number of coolingliquid ejection ducts are preferably uniformly distributed around the metal product to be cooled and directed towards the longitudinal axis of the tubular unit in the opposite direction to the direction of advance of the product.

In a variant of this embodiment, the ducts can be formed in the inlet portion of the tubular unit.

In another variant, the ducts can be mounted on a hollow transverse ring surrounding the product to be cooled and disposed upstream of the inlet of the tubular unit and connected thereto in an airtight manner.

In that case the ducts can simply be orifices formed in the hollow ring and disposed so as to give the desired direction to the jets of cooling liquid.

Another particularly advantageous embodiment comprises an inlet lock disposed upstream of the tubular unit and connected to it in an air-tight manner, means for supplying the lock with cooling liquid, and means for causing at least part of the cooling liquid in the lock to flow in counter-current to the product, through the orifice through which the product enters the lock.

The inlet lock preferably has axial symmetry and is disposed so that its axis of symmetry coincides with the longitudinal axis of the tubular unit to which it is fitted.

The cooling-liquid supply means may comprise at least one opening formed in the side wall of the lock and connected by a suitable pipe system to a source of cooling liquid.

More particularly the cooling-liquid supply means may comprise a number of openings formed in the side wall of the lock and uniformly distributed around its periphery, each opening being connected by a suitable pipe system to a source of cooling liquid.

Preferably, the diameter of the outlet orifice of the lock is at least equal to the inner diameter of the tubular unit.

The diameter of the inlet orifice of the lock is preferably at most equal to the inner diameter of the tubular unit. The inlet orifice of the lock preferably has a coaxial cylindrical duct extending at least partly outside the lock and having a convergent inlet. The inner diameter of the cylindrical duct is preferably at most equal to the inner diameter of the tubular unit.

In a preferred embodiment, the apparatus has means for checking that the lock is in fact completely filled with cooling liquid. The checking means advantageously comprise a small-diameter tube, e.g. a flexible metal tube, one end of which is connected to the top part of the lock whereas the other end is left free and held at a level higher than the highest point of the lock.

The invention will be described further, by way of example, with reference to the accompanying drawing whose sole Figure is a diagrammatic axial section through part of an apparatus for cooling steel bar leaving a hot rolling mill.

A bar 1, travelling at high speed in the direction of arrow 2, moves through a cooling installation which comprises a number of successive tubular units 3, only one of which is shown (partly). The tubular units 3 have an inner diameter , suited to the diameter of the bars to be cooled. As a simple example, the drawing shows a tubular unit 3 supplied with cooling liquid through an annular slot 6. The slot 6, which is formed between the actual unit 3 and a head 4, is itself supplied from a source 5 of cooling liquid. In known manner, the head 4 has a bevelled portion 7 facilitating insertion of the bar 1.

The tubular unit 3 is equipped with a lock 8 disposed upstream of the head 4 and preferably pressed in sealing-tight manner against its inlet surface. For reasons of symmetry, the lock 8 preferably has a circular cross-section and is centered along the longitudinal axis of the unit 3. In the embodiment illustrated lock 8 has two diametrically opposite supply ducts 9, 10 connected to a suitable source of cooling liquid. The upstream and downstream surfaces of the lock 8 are formed with respective inlet and outlet orifices 11, 12 for the bar, the orifices being centered along the longitudinal axis of the lock 8. The inlet orifice 11 has a cylindrical duct 13 extending mainly outside the lock 8 and having a convergent inlet 14.

The inner diameter d of the cylindrical duct 13 is equal to or less than the inner diameter o of the tubular unit 3, so as to product a pressure drop and thus offer suitable resistance to the flow of cooling liquid.

Finally, the lock 8 has a small-diameter tube 1 5 connected to a top point of the lock 8 and used to check that the lock 8 is filled (by observing that liquid leaks from the upper end of the tube 15).

The above-described apparatus operates as follows.

The lock 8 is supplied with cooling liquid through the ducts 9 and 10. The cooling liquid flows from the lock 8 through the inlet orifice 11 and the outlet orifice 12 and also to a much smaller extent through the pipe 15. The supply flow rate is adjusted so that the lock 8 is permanently filled with cooling liquid, which is checked by observing the presence of a flow in the narrow tube 5. Next, a bar 1 from a rolling-mill (not shown) is inserted in the direction of arrow 2 into the inlet 14 of the duct 13, through which the cooling liquid escaping from lock 8 flows in counter-current to the bar. The bar 1 thus successively travels through the lock 8 (filled with cooling liquid from the ducts 9 and 10) and then through the head 4 and the tubular unit 3, which are filled with cooling liquid supplied through the annular slot 6.

The flow of cooling liquid through the duct 13 is counter-current relative to the direction of advance of the bar 1 prevents any air entrained by the bar from entering. Also, the airtight connection between the lock 8 and the head 4 ensures that no air penetrates here.

Note that the air-tightness between the head 4 and the lock 8 need not necessarily be me -chanically complete, but can be maintained by a slight leakage flow of cooling liquid resulting from the pressure inside the head 4 and the lock 8.

The bar 1 is therefore in cpntact, right from its extreme end, with the cooling liquid and not with a mixture of liquid and entrained air.

This ensures the required cooling along the entire length of the bar.

Of course, it will not be beyond the scope of the invention to provide a device such as the lock 8 on all of the tubular units 3 of an installation for cooling advancing elongate products, or to equip some of the tubular units with such a device.

It is also clear that the use of such a device is not limited to a tubular unit of the kind shown by way of example in the accompanying drawing, but also extends to any other type of tubular unit, e.g. units comprising two coaxial tubes where the inner tube is formed with orifices for spraying the bar.

Finally, the invention also covers any installation comprising a number of successive tubular cooling unit, in which at least one tubular unit (e.g. the first) is equipped with one of the devices described above.

Claims

1. A method of cooling an advancing elongate metal product, in which the product tra vels through a tubular cooling unit, a screen of cooling liquid is formed at the inlet of the tubular unit so as to prevent air entering it, the product is introduced into the cooling unit through the liquid screen, and at least part of the cooling liquid forming the screen is made to flow in the opposite direction to the direc tion of advance of the product.

2. A method as claimed in claim 1, in which the screen of liquid is formed from jets of cooling liquid inclined to the longitudinal axis of the cooling unit in the opposite direction to the direction of advance of the product.

3. A method as claimed in claim 2, in which the jets are directed towards the said axis.

4. A method as claimed in claim 1, in which the cooling unit is equipped with an inlet lock permanently supplied with cooling liquid, at least part of the cooling liquid in the lock is made to flow in counter-current to the product through the orifice through which the product enters the lock, the supply rate of cooling liquid is adjusted so that the lock is permanently filled with liquid, and air is prevented from entering between the inlet lock and the cooling unit.

5. Apparatus for cooling an advancing elongate metal product, comprising a tubular cooling unit, means for forming a permanent screen of cooling liquid at the inlet of the tubular unit, and means for causing at least part of the cooling liquid forming the screen to flow in the opposite direction to the direction of advance of the product when the product is introduced through the inlet.

6. Apparatus as claimed in claim 5, including a number of orifices and/or ducts for ejecting cooling liquid, distributed around the longitudinal axis of the tubular unit and directed towards the said axis in the opposite direction to the direction of advance of the product.

7. Apparatus as claimed in claim 5, including an inlet lock dislosed disposed upstream of the tubular unit and connected thereto in an air-tight manner, means for supplying the lock with cooling liquid, and means for causing at least part of the cooling liquid in the lock to flow in counter-current to the product, through the orifice through which the product enters the lock.

8. Apparatus as claimed in claim 7, in which the diameter of the product inlet orifice of the lock is not greater than the inner diameter of the tubular unit.

9. Apparatus as claimed in claim 7, in which the inlet orifice of the lock has a coaxial cylindrical duct extending mainly outside the lock and partly inside the lock and having a convergent inlet.

10. Apparatus as claimed in claim 9, in which the inner iameter of the cylindrical duct is not greater than the inner diameter of the tubular unit.

11. Apparatus as claimed in any of claims 7 to 10, including means for checking that the lock is filled with cooling liquid.

12. Apparatus as claimed in claim 11, in which the checking means comprises a narrow tube having one end connected to the upper part of the lock and the other end left free and held at a level higher than the highest point of the lock.

13. A method of cooling an advancing elongate product, substantially as described with reference to the accompanying drawing.

14. Apparatus for cooling an advancing elongate product, substantially as described with reference to, and as shown in, the accompanying drawing.