EP0088733A1

EP0088733A1 - High-efficiency device to cool rolled bars

Info

Publication number: EP0088733A1
Application number: EP83830023A
Authority: EP
Inventors: Alessandro Facchini
Original assignee: Danieli and C Officine Meccaniche SpA
Current assignee: Danieli and C Officine Meccaniche SpA
Priority date: 1982-03-05
Filing date: 1983-02-03
Publication date: 1983-09-14
Also published as: IT8283339A0

Abstract

Device (10) to cool bars which is located at the outlet of the finishing stand in hot-rolling mills and comprises an outer container (11) in which there is positioned lengthwise a plurality of cooling units (12) separated from each other through which the bars to be cooled pass, said device being characterized by the fact that each cooling unit (12) consists of a plurality of conduits (13) placed in line, whereby the mating ends (213-413) of the conduits forming each cooling unit (12) are conformed so as to create between themselves an annular nozzle (14) which narrows in the direction of the feed of the bars, and whereby a chamber (17) for diffusing cooling liquid under pressure is located inside said outer container (11) and around each annular nozzle (14) and is connected to means (19) which feed cooling liquid under pressure and which are positioned outside said outer container (11).

Description

This invention concerns a high-efficiency device to cool rolled steel bars leaving the rolling stand, said device being able to obtain a desired, even temperature along the bars.
To be more exact, this invention concerns a device for the controlled cooling of hot-rolled bars moving at a high speed by means of a cooling liquid such as water or water containing mineral salts and/or surface-active agents, whereby said device is located downstream from the hot-rolling stand and has the purpose of bringing the temperature of the rolled products passing through down to a desired temperature quickly.
It is known in the art that the steel bars leave the hot-rolling stand with a temperature of about 1000-1100°C and are made to pass through cooling devices which have the task of bringing this temperature down to a minimum within a given time, whereby said time and minimum temperature depend on the mechanical properties required of the bars, such as the breaking point, fatigue strength, ductility and weldability.
To be more exact, the cooling time and minimum temperature of the bars are selected to suit the destination and end use conditions of the bars, for this cooling determines the microstructure of the material, and the microstructure in its turn determines and governs the aforesaid mechanical properties cf the bars.
Moreover, the carbon and manganese content of the bars ha: to be reduced to improve their weldability and ductility; bu this lessens the tensile strength of the bars.
It was proposed a short time ago, among other things, thai immediately after leaving the finishing stand of a rolling mill for bars said bars should undergo surface quenching witt a suitable cooling liquid and that the conditions of said cooling should be regulated in such a way that, on leaving tt cooling zone provided by the liquid, the core of the bar should have a temperature of about 850°C while the bar stayec in the cooling device; this condition permits, on the one hand, a tempering of the hardened surface layer consisting oi martensite and bainite and, on the other hand, an assurance that the austenite in the central part of the bar is converts into ferrite and pearlite.
Said quenching has to take place in a very short time of the order of fractions of a second.
Said cooling also has to permit the aforesaid mechanical properties to be as even as possible along the rolled bar.
Moreover, it is known that such evenness is linked to the uniformity of the cooling process itself.
Devices employing a cooling liquid are known into which tt rolled bars to be cooled are introduced while the latter are travelling at a high speed in a liquid environment, normally water, which is either running or static.
Patent BE 826.199, for instance, proposes a device to cool rolled steel bars which consists of a cylindrical conduit within which the bars pass, whereby the upstream end of the conduit is provided with an annular funnel which narrows in the direction of the feed of the bars and which serves to guide the bars, whereas the downstream end of the conduit is equipped with a guide ring.
According to this solution the conduit is fed with a continual flow of cooling water under pressure, said water being introduced through an opening provided in the middle of the wall of the cooling conduit so as to create substantially a cooling bath in which the bar to be cooled is momentarily immersed.
So as to slow down the cooling water leaving from both ends of the conduit, a jet of water directed towards the inner part of the conduit is introduced into said conduit through each of said funnels.
Furthermore, so as to complete the cooling according to this solution, the bar has to pass through a series of cooling conduits located separately, so that said cooling operation is performed with alternate phases of cooling with water in the conduit, then with static air between one conduit and the next, and then with water in the next conduit, and so on.
This lay-out is of necessity hard to regulate and requires the employment of many cooling conduits arranged very near to each other, so that each conduit makes its own contribution with a rather limited lowering of the temperature.
Moreover, this reduces the cooling efficiency and unhelpfully makes more difficult the formation of martensite on the surface and, in the case of thin bars, also reduces the speed of the passage of the bar itself.
The solution of patent BE 826.199 is further improved by patent BE 844.183. The improvement in the latter only concerns the annular narrowing funnel located at the upstream end of the cooling conduit, whereby said funnel is now equipped circumferentially with a series of holes which are sloped in the direction of the feed of the rolled bars and which act as nozzles to direct towards said bars the water under pressure coming from the supply conduit opening into the annular space created between the narrowing part of the funnel and the inner wall of the cooling conduit.
Even though this latter solution makes the cooling more regular within the cooling conduit, the aforesaid problems are still not overcome satisfactorily.
The invention described in FR-A-2.394.337 proposes in its turn the use of a plurality of cooling pipes positioned in series underwater in a container provided with holes for the passage of rolled products.
According to this lay-out each cooling pipe has a constant inner diameter and a diameter-to-length ratio of between 1:5 and 1:15 and is equipped at its end with a circumferential series of holes to feed cooling water under pressure, said holes being sloped in a direction opposite to that of the feed of the rolled products. _;
So as to complete the cooling cycle in this device, it is necessary to position a consecutive series of cooling containers separated from each other.
This solution has the drawback of being very costly to construct because of its size and therefore entails a great deal of space and a heavy consumption of water under pressure.
The fact that the ratio between the inner diameter and the length of the pipe is between 1:5 and 1:15 means that, if this cooling plant is to work well, it will have to have a great number of small cooling pipes and therefore a great number of cooling containers.
A further drawback of the invention is found when the bar to be cooled is thin, for the bar undergoes, as we said, a braking action owing to the jet of water flowing in the opposite direction to that of the movement of the bar.
In the field of production of metallic wires the patent US 2,756,169 proposes a device to cool the rod before it is drawn, said device being able to cool the rod quickly from 982°C down to 482-704°C in 0.75-1.5 seconds.
Said device, however, consists of an inner pipe perforated peripherally and located inside another outer pipe, which is closed at its end and fed with cooling water that passes through the peripheral perforations into the said inner pipe, within which the rod to be cooled passes. The cooling water leaves from the ends of the inner pipe.
Said device also requires a group of water traps and a device to cool the rod by means of air as it passes along.
Besides the fact that this device is designed to carry out a heat-treatment of the rod which eliminates the need to perform heat-treatment of said rod before the drawing process, said device involves substantially the same problems as those described with regard to the aforesaid FR-A-2.394.337.
There exists another device for cooling bars which is described in GB-A-2,021,998; this device is substantially like that of US 2,756,169 except that the cooling water introduced into the inner pipe also leaves through diverging radial conduits opening outside the outer pipe.
Amongst other things, said device entails the drawback that the bubbles of steam forming on the surface of the bar being cooled adhere to the bar and form a boiling film which causes a considerable exchange of heat between the bar and the cooling liquid, thereby lessening the overall efficiency of the cooling device.
Standard Search Report No. RS 65507 IT, as drawn up by the European Patents Office after submission of our application for a patent in Italy and on the basis of said application, has brought forward other patents regarding the subject.
FR-A-2.231.440 (Hoogovens) shows a cooling device consisting of nozzles which are wholly immersed in water held in a tank. The cooling pipes are formed with two walls, of which the inner wall comprises a plurality of radial holes through which the cooling fluid flows.
This lay-out does not allow the cooling value to be regul ated as wished unless a great number of tanks are employed, but in this latter case the device becomes very costly and complicated. Moreover, the quantities of water cannot be varied in the lay-out of this patent.
In FR-A-2.453.689 (British Steel) the device described is very complex and consists of various stages of which each is composed of a set of nozzles spaced apart; between said nozzles there are inserted some auxiliary nozzles which spray water onto the bar in the opposite direction to that of the feed of the bar. But said solution is wholly different from that set forth in our application.
_ US-A-3,044,098 (Stalson) deals with a pickling device whic has nothing to do with a cooling device such as that of our invention.
The article taken from "La Metallurgie" examines the problem of pickling, which has nothing to do with the cooling device proposed by our invention, nor anything to do with the problems linked thereto.
Our invention has the purpose of-eliminating the aforesaid drawbacks. A further purpose of our invention is to interrupt continuously the growth of bubbles of.steam and also the formation of the boiling film on the surface of the bar and to carry out forced removal, towards the outlet of the device, o the bubbles of steam generated by contact between the cooling liquid and the bar passing through.
Another advantage of our invention is to be able to regulate at will the speed and intensity of the cooling.
Yet another advantage of our invention is that it obviates further heat-treatments aimed at the improvement of the microstructure and therefore of the mechanical properties of the bars, especially their weldability, ductility and strength.
A further advantage is the development of an even and uniform microstructure throughout the length of the bar, thereby obtaining bars with constant and uniform mechanical properties.
Our invention is therefore embodied with a device for cooling bars which is located at the outlet of the finishing stand in hot-rolling mills and which comprises an outer container within which a plurality of cooling units is arranged lengthwise and separated one from another, the bars to be cooled passing along inside said units, whereby the device is characterized by the facts that each cooling unit consists of a plurality of conduits positioned in line, and that the mated ends of the conduits forming each cooling unit are conformed so as to create between them an annular nozzle which narrows in the direction of the feed of the bars, and that within said outer container and around each annular nozzle a chamber is located for diffusing cooling liquid under pressure and is connected to adjustable means which feed cooling liquid under pressure and which are positioned outside said outer container.
We shall describe hereinafter a preferred embodiment of the invention as a non-restrictive example and shall refer to the attached tables, wherein:-

Fig.1 shows a diagram of a cooling device according to the invention;
Fig.2 shows a lengthwise section of a cooling unit according to the invention;
Fig.3 shows a crosswise section of the cooling device of Fig.1;
Fig.4 shows a diagram of a cooling device according to the invention together with the feeding means.

In the figures the same parts or parts having the same functions bear the same reference numbers.
In the figures the device 10 to cool bars according to th invention consists of an outer container 11 and a plurality cooling units 12 within which the bars to be cooled pass, sa units 12 being positioned lengthwise within said outer container 11 having a round, square or rectangular section (the figures show it as being rectangular).
Said outer container 11 is equipped with an outlet pipe 1 for discharging, if necessary, the cooling liquid leaving th< cooling units 12, which are positioned separated from each other, as shown in Fig.1.
Said cooling liquid may consist of water or of water with suitable additives containing mineral salts and/or surface-active agents.
Each cooling unit 12 consists of at least two lengthwise conduits 13 positioned in line, and the bars to be cooled pas through said conduits 13 (the bars are not shown).
The mating ends of the conduits 13 are conformed so as to constitute between them an annular nozzle 14 which is sloped and faces in the direction of the feed of the bars.
Said annular nozzle 14 is formed by bevelling the outer edge 113 of the outlet 213 of one conduit 13 and bevelling t1 inner edge 313 of the inlet 413 of the next conduit 13.
This enables the cooling liquid under pressure to be directed against the bars passing along in their direction of forward movement so as to discharge, preferably towards the outlet 15 of the cooling unit, any steam generated by the contact between the hot bars and the cooling liquid, for it i known that the presence of steam inside the cooling unit lessens the efficiency and overall yield of the cooling device.
According to the invention a chamber 17 for diffusing cooling liquid through the nozzle 14 into the conduits 13 is located within the outer container 11 and around each annular nozzle 14.
Said diffusion chamber 17 has a circular section in our example, but could have another section, and comprises a nipple 117 connected by a conduit 18 to means 19 feeding cooling liquid at an adjustable pressure to each annular nozzle 14.
In the example shown said means 19 feeding cooling liquid under pressure comprise a main conduit 119 connected, at one end, to the source of cooling liquid under pressure and, at its other end, to a distribution manifold 219, to which the conduits 18 conveying cooling liquid into the respective diffusion chambers 17 are connected by individual means 118 whici regulate the flow.
The main conduit 119 is equipped with servo-controlled means 20 governing the rate of flow.
To be more exact, said servo-controlled means 20 regulatinc the flow comprise a servo-controlled valve 120 located betweer said main conduit 119 and the distribution manifold 219, and also comprise another servo-controlled valve 220 positioned between said main conduit 119 and a discharge outlet 320.
The main conduit 119 is equipped with a flow indicator 191, a thermometer 291, a pressure gauge 391 with an appropriate tap and also a main gate valve 491.
The preferred lay-out of the cooling device of the invention is shown in Fig.4, wherein the means 19 feeding the cooling liquid serve more than one cooling unit positioned in line.
The device 10 of the invention is able to cool the bars passing through from a temperature between 1100° and 1000°C down to even 80-100°C within a period of 0.5-1.5 seconds.
This'is brought about by introducing the cooling liquid into the chambers at a pressure between 12 and 16 atmospheres.
Said liquid is thrust at high speed into the respective cooling conduits 13 through the plurality of annular nozzles 14, which spray it evenly over the surface of the bars passing through and break up continuously the film formed by the bubbles of steam and drive said bubbles of steam towards the outlet 15 of each cooling unit.
According to the invention the cooling of the bars can be regulated and differentiated during their passage through the cooling device by operating by hand or automatically on the adjustable means 19 feeding the cooling liquid.
It is also possible to position several cooling units 12 or several cooling devices 10 in series on the path of the bars.
Moreover, it is possible to locate in the end part of the outer container 11 one or more cooling units 12 in which the nozzles 14 are reversed, that is, turned in the direction opposite to that of the feed of the bars to be cooled; the purpose of this is to halt the jet of cooling water at the outlet of the device and to restrict its flow out of the cooling device.
It is also possible to put an air drier at the outlet of the device so as to eliminate any residual water on the cooled bars.
We have described here a preferred embodiment of the invention, but variants are possible.
The shapes, sizes and proportions can be changed and it is possible to use the device of the invention to carry out cooling cycles and heat-treatments other than those described herein without departing thereby from the scope of this invention.

Claims

1 - Device (10) to cool bars which is located at the outlet c the finishing stand in hot-rolling mills and comprises an out er container (11) in which there is positioned lengthwise a plurality of cooling units (12) separated from each other through which the bars to be cooled pass, said device being characterized by the fact that each cooling unit (12) consist of a plurality of conduits (13) placed in line, whereby the mating ends (213-413) of the conduits forming each cooling unit (12) are conformed so as to create between themselves an annular nozzle (14) which narrows in the direction of the fee of the bars, and whereby a chamber (17) for diffusing cooling liquid under pressure is located inside said outer container (11) and around each annular nozzle (14) and is connected to means (19) which feed cooling liquid under pressure and which are positioned outside said outer container (11).

2 - Device (10) to cool bars as in Claim 1, characterized by the fact that each annular nozzle (14) is obtained by bevelling the outer edge (113) of the outlet (213) of one conduit (13) and by bevelling the inner edge (313) of the inlet (413) of the next conduit (13).

3 - Device (10) to cool bars as in Claims 1 and/or 2, characterized by comprising in the end part of the outer container (11) at least one cooling unit (12) positioned back-to-front with its annular nozzles (14) turned in the opposite directior to that of the feed of the bars to be cooled.

4 - Device (10) to cool bars as in Claim 1 and in one or the other of the Claims thereafter, characterized by the fact that the means (19) feeding liquid under pressure can be regulated for each annular nozzle (14).

5 - Device (10) to cool bars as in Claim 1 and in one or another of the Claims thereafter, characterized by the fact that said means (T9) feeding liquid under pressure comprise a main conduit (119) connected, at one end, to the source of cooling liquid under pressure and, at its other end, to a distribution manifold (219) to which the conduits (18) conveying cooling liquid into the respective diffusion chambers (17) are connected by individual means (118) which regulate the flow.

6 - Device (10) to cool bars as in Claim 1 and in one or another of the Claims thereafter, characterized by the fact that said main conduit (119) is equipped with servo-controlled means (20) to regulate the flow.

7 - Device (10) to cool bars as in Claim 1 and in one or another of the Claims thereafter, characterized by the fact that said servo-controlled means (20) to regulate the flow comprise a servo-controlled valve (120) located between said main conduit (119) and said distribution manifold (219), and also comprise another servo-controlled valve (220) placed between said main conduit (119) and a discharge outlet (320).