A METHOD FOR COOLING ROLLING MILL STOCK

Abstract: A method for cooling rolled stock downstream of a given roll pair of a rolling mill having connected thereto a stock cooling section comprising at least one cooling tube (2), a liquid-coolant jacket (3) surrounding the tube, an external guide tube (8) leading from a given roll pair to the at least one cooling tube (2), and an internal guide tube (4) located in the cooling tube. The method comprises the steps of forcing the liquid coolant from the jacket into the external guide tube (8) in countercurrent with the direction of stock movement and into the internal guide tube (4) concurrently with said stock movement. In accordance with the novel features of the invention, immediately the stock leaves the nip of the given roll pair it is passed into the external guide tube (8) of a first cooling tube in line, this guide tube being placedin direct connection with said roll nip. The arrangement is such that liquid coolant can be forced from the jacket (3) into the external guide tube (8) in a controlled manner and from there into the roll nip while, at the same time, forcing liquid coolant from the jacket (3) in a controlled manner into the internal guide tube (4).

Description: A METHOD FOR COOLING ROLLING MILL STOCK FIELD OF INVENTION The present invention relates to a method for cooling stock in rolling mills of the kind which have connected thereto a cooling section comprising at least one cool¬ ing tube, a liquid-coolant jacket surrounding the tube, a guide tube leading from a given roll pair of the mill to the cooling tube, and a second guide tube located in the cooling tube, in which method the liquid-coolant is forced from the jacket into the first guide tube leading to the roll pair and into the second guide tube located within the cooling tube. It will be understood that by "stock" is meant here and in the following any hot roll¬ ed work thus cooled. BACKGROUND PRIOR ART Thermomechanical Treatment (TMT) is a novel technic rec¬ ently introduced into rolling mill technology. TMT is actually a composite term for several different process¬ es, such as controlled rolling, air-blast quenching and direct hardening. TMT was initially introduced into sheet- metal rolling mills since such mills are readily adaptable to the process of TMT in view of the fact that the mill layout permits the sheet to be air-cooled bet¬ ween roll passes, such as to attain a low final rolling temperature, in addition to which the sheet speed down¬ stream of the rolling mill is also low, which means that the cooling sections used are short and ineffective. In recent times the TMT-process has also been used in rod and wire mills. Since these mills are often fully cont- inuous, there is no opportunity for the stock to be air-cooled between passes, and hence it is necessary to cool the stock with liquid coolant, e.g. water between the individual passes through the mill. Since the travel distance between the roll pairs is often short and the stock travels at high speed, highly effective cooling must be effected in the cooling section between passes. This also applies to the cooling section down- 5 . stream of the rolling mill. The distance or space bet¬ ween the final roll pair and the cooling bed is often very short and the stock speed very high (up to 150m/s) , which places great demands on the cooling section even in order to achieve some degree of cooling. Since the 0" cooling sections are often ineffective it has not been possible to direct harden the steel, i.e. to cool the stock, bar etc. down to Tmean = 100 - 211°C before the stock reaches the cooling bed or section. Because of this other material technical processes of the type Te - 5; core have been applied, as described in Belgian Patent Specification No 790867, where the outer layer is cooled to form martensite, this outer layer being annealed by the heat conducted outwardly from the centre of the stock. In order to cool the stock, bar etc. effectively 0 it is necessary to use a coolant capable of carrying away large quantities of heat, water being one of the most common coolants used in this regard. Other publications which disclose methods for cooling hot rollers work include US Patent No 2,856,803, EP-A1- 5 0141511, French Published Specification No 2231440, and US Patent No 4136544. One problem with water cooling is the film of vapour which forms closely adjacent the stock surface. This vapour film, which has poor thermal conductivity, pre- 0 vents fresh water from reaching the surface of the stock, therewith resulting in poor cooling. An extremely -good cooling effect is achieved, however, when it is possible to break down the vapour film so that a new vapour film can form and then quickly broken down again. If no vap- 5 our film is formed, i.e. the stock bar etc. passes through the water so quickly that heat transfer takes place solely between the stock and- the water, the cool¬ ing effect is poor, since water is a poor conductor of heat. In order to cool the stock effectively it is necessary to effect the cooling process in a manner such that while a vapour film is formed it is quickly washed away so that a fresh film can form. One method of cooling the stock is to spray the stock with water through noz- zles or sprays (vide for example Pro Conf "Mechanical working and steel processing", Cleveland, Oct. 1979, pp 107-126.) . Another method is one in which the stock is passed through a tube in which water is forced into the space between the stock and the inner wall of the tube in accordance with German Auslegschrift 1602356. The cooling tube is normally designated annular gap quench¬ ing tube,. and the space between stock and tube the mat¬ erial gap. At suitable relative speeds between the stock and the water there is generated a strong radial and axial turbulence which breaks down the vapour film, to provide effective cooling of the stock, bar etc. One effect that has previously been observed is that a rel¬ atively cold surface e.g. 600 C can be cooled more eas¬ ily than a hotter surface (e.g. 1000 C) due to the fact that the vapour film forms more slowly on the surface whose temperature is 600 C than on the surface having a temperature of 1000 C. This means that the same rate of cooling ( C/s) can be achieved with cooler surface at a lower relative speed between stock and water. Vide for example Pro Conf "resources efficiency in iron and steel" G. Elsen: "Improved roll cooling practices for roll materials" . SUMMARY OF THE INVENTION The object of the present invention is to provide a method for improved cooling of stock, bar, etc. in a rolling mill. Accordingly, there is proposed in accordance with the invention a method for cooling rolled stock downstream of a given roll pair of a rolling mill having connected thereto a stock cooling section comprising at least one cooling tube, a liquid-coolant jacket surrounding the tube, an external guide tube leading from a roll pair to the at least one cooling tube, and an internal guide located in the cooling tube, the method comprising the steps of forcing the liquid coolant from the jacket into the external guide tube in countercurrent with the dir- ection of stock movement and into the internal guide tube concurrently with said stock movement, characteriz¬ ed by the further step of passing the stock, .immediately it leaves the nip of said roll pair, into the external guide tube of a first cooling tube in line, said guide tube being placed in direct connection with said roll nip, such that liquid coolant can be forced from the jacket into the external guide tube in a controlled man:-; ner and from there into the roll nip while, at the same time, forcing liquid coolant in a controlled manner from said jacket into the internal guide tube. BRIEF DESCRIPTION OF THE DRAWINGS So that the invention will be more readily understood and further features thereof become apparent an exempl¬ ifying embodiment will now be described with reference to the following drawings, in which Figure 1 is a schematic illustration of a cooling sect- section in a rolling mill which applies the method acc- rding to the invention; Figure 2 is a longitudinal sectional view of one of the cooling tubes incorporated in the cooling section acc- ording to Figure 1 ; and Figure 3 is a diagram which illustrates the relation¬ ship between water pressure, water velocity, and the cross-sectional area of the stock when carrying out the method according to the invention. DESCRIPTION OF A PREFERED EMBODIMENT The cooling section, which can be used both for cooling stock, bar or other hot work between roll pairs and af¬ ter the final or finishing roll pair 1 , comprises a number of cooling tubes 2. The number of tubes used depends on the extent of cooling desired and on the space available. The cooling tubes comprise a water jacket 3 having a guide tube arranged internally there¬ in, and a housing 5 for pressurized air having an air inlet 6. Although water is referred to as the coolant used in this embodiment, it will be appreciated that other liquid coolants may be used. The jacket 3 and housing 5 are firmly welded in a cooling tube chest 7. A guide tube 8 extending from the roll pair 1 is att¬ ached to the water jacket 3. The length of the guide tube 8 should be as short as possible, so that the hot stock is introduced into the inner guide tube 4 in the shortest time possible. Water under high pressure (20-500 bars) is delivered to the jacket 3 through a conduit 9. The water is then forced into the afore- said material gap, i.e. the space between the hot stock (not shown) abd the inner wall of the guide to to o cπ o cn cn through consecutive cooling tubes, it becomes hot and evaporates off, i.e. the cooling effect is lowered. In this event, it is beneficial to switch on the supply of air under pressure in one of the cooling tubes, so as to blow the water away from the cooling tube 2, where¬ after the process is repeated downstream of the cooling tube 2. In this case, however, the pressure employed (the velocity of the water) need not be as high as that applied in the cooling tube 2, as evident from Figure 3 since the temperature of the stock is now about 100 C as opposed to an earlier temperature of 600 C. In the case of stock of coarser dimensions, the water supplied to the cooling tubes should be under low pressure (~10 bars). The water from the cooling tube 2 is therefore replenished in the subsequent cooling tubes to compensate for the substantial loss of water, through evaporation. Since fresh water is constantly added, it is not necessary to blow the water away until the last cooling tube is reached. The speed at which stock moves through a continuous rolling mill constantly increases and when leaving the last pair of rolls in the mill the stock speed may be as high as 150m/s. This means that the intermediate time periods between passes are very short, and the rolls in the finishing pair will exert a cooling eff¬ ect on the surface of the hot stock. For example, if there is maintained a roll surface temperature of about 100 C and the stock has a temperature of 1000 C upon entry into the roll nip of said roll pair, the temper- ature of the stock at the point of contact between rolls and stock, and for a short time thereafter, will be about 650 C. This enables the surface temperature of the stock to be more readily lowered to about 100 C. to to o cπ o cπ cn tr Φ rt or s CD t rt tr D en rt o Ω rV P 13 Pi rt tr CD Z P rt- ro H • Since the stock travels at a high speed, each point on the stock is only located in the internal guide tube 4 in the cooling tube 2 for a very short space of time. Thus, only the outer surface of the stock is cooled to the aforesaid temperature of about 100 C, i.e. only a small amount of the water delivered to the cooling tube 2 is heated and evaporated off, the remaining wat¬ er is "unnecessary". By permitting the water from the cooling tube 2 to press into the next cooling tube, the water can be "re-used", thereby lowering the water con¬ sumption to a commensurate extent.

Claims: co to to o cn o cn cπ Ω H P co rt P to li Hi Hi rt t-o CD Hi •XI P- ro 3 rt t-o rt P •X) ft Ω rt cQ ___, n o P- P ts • O H • o 0 li tr Pi H- P- 0 ts o ø P- 0 ø P- tr o tr P- • tr* O Λ H ft rt H li o CD Λ li < •XJ rt < tr iXJ tr Pi o O φ ¬ J < r > t-o 0 to l-h P- H Ω 3 0 H- cn ro H CD ro 0 ro CD t-* ϋ CD > H to- to- rt P- P- ts CD to- CD H- ts rt- ts ft * 3 P- -. P 0 <t t - ro 0 rt s tS ex •< en 3 Hi •XJ 3 Pi tS X i tr ro . — . Pi 0 ø S rt 3 cn •XJ Φ rt- CD •XJ tr rt- ex Ω li ro i cr •XI o li ro Ω O ø rt ro rt ft 3 ro ro Ω to¬ O o ε t 00 rt l P- rt •— - Ω tr P- o ro 0 rt ft o Mi cn tr Φ 0 tr P t-o li li 0 ri 0 t-o cn rt o D ø t- ^ rt P t-o 13 * 0 o ro o ø o t P- ro ts 0 CD -o I-* rt tr P to- 0 rt- t-o 0 t-o o cr - Ω Pi Pi rt P. ts XI P Ω to- 0 t tS t-o 3 ro P tr cn i Φ P 0 rt P * CD 0 P- t-o n rt tS J Ω cn Pi P CD ϋ J ø Φ rt J cn 13 0 li Hi P- Φ P li P- t ts •XJ P I P Ω 0 rt 0 P ^ ~. o • P Hi rt H φ O 3 Ω Pi rt •XJ rt Ω P-. P- P- o rt tr P P- ro to Ω P- O to- TJ ti Φ * Ω to- o 0 O rt li Pi ts ø o H li X •— rV li li P tS φ en P- 0 tS Ω H- Ω ts ø P- rt 0 Hi i rt- Ω •XJ P Ω Λ li ft o rt i P ts tr 3 cn 0 rt- ϋ •XJ rt ro P Ω o Ω Ω rt 0 •X) 0 Pi O O tr CD 0 ro ro P- 3 rt ro o Ω 0 o li o Hi O o rt * Φ 0 ϋ P" P- I-* φ Ω ts ro O rt li 3 o P- ø t-o o O 3 0 Pi t-o CD i t ft P ft cr rt P- rt* Pi Ω tr Ω 3 Pi ft P P- t- > P t-> TJ tr I-* to- P >X1 tr ts ii 0 ro H- ts o P- rV ro 0 rt TJ ro tr t-o iXJ to- P- P φ •< tS rt- Ω ro rt 0 cr o P li tr ϋ ro ø tS ϋ 0 ts cn • * •XJ ro O rt - CD Hi ts ct rt- 3 P- li CD P- rt •XJ P- •XJ o •XI H- ti 0 o to¬ Hi I-* o to¬ tr ro 0 ts CD en 0 P 0 . — . P. H Φ O Ω en I-* ts ϋ li ■ ε ts CD < rt- ts «_|. P- cr rt P- cn H H cn ts P" rt ft P o rt- o ts 00 Ω to¬ CD • Φ ro rt P ø ro P. Ω CD P- O Φ P O tr 0 -o ro 3 to- CD rt " * ro 3 H Ω • J t-o ro 0 Ω 0 t-o rt li Ω en ft P li TJ Pi tr X to¬ CD ø S π ^ -. ro o ft •XJ tr P P t P- ts cn to- cn rt- rt t P P- ro rt P rt I-* P- Φ φ Hi Ω P 3 P P tS Mi Ul P ro rt H ft rt tr " ' cn 0 en O 3 P rt rt t o - rt I-* to- tr li P r* li t-o • * tr CD rt cr 0 ts P- cn Φ Φ tr cn _ ~ - Pi P- P 0 to- ex 0 CD •XJ P- H ro rt t-o en rt li li CD T. •» cQ t- o 3 ex P P Ω 0 rt ø cn O o Ω t-o rt O P- ε, CD 0 l_l. φ Ω •X) I-* < tr P- tr rt rt- Ω 0 — . c_ι. o O Ω rt N tr cn CD Ω P- P *» o ft li 0 CD P Pi CD o CD P ro 00 P 3 tr Ω x 4 tr φ to- TJ Pi tr Pi Ω ts tr o P- •XJ cn ti ro TJ rt- — - Ω TJ P I Φ Pi Ω CD P CD I P rt ro H P. 0 P Pi rt cn ro Ω li <! rt tr CD ε li CD rt ϋ H ro P- rt Ω rt p- tr . o t-o Φ P- t ¬ Pi tr O σ i tr P rt rt o Pi tr rt- 0 H CD O o Φ rt * en ts o li rt •< * rt t* Ω 0 rt * P 0 rt CD CD ro tr CD Hi P- t-o en P- •X) SJ o tr tr 0 Ω rt- cr . — . tr t-o Ω H- 0 H ro Ω CD ø to¬ ex co t p 0 φ TJ CD Mi tr ro ro CO Φ ro t TJ tr rt ø P- ft X Ml ts P- •XJ Ω cn •XJ H H ϋ • — • Pi CD * * ro ø P- N .— . P- rt- o ft • J ø cn o rt tr P I-* ft to¬ P- . — . en ft tr TJ ro its. o ro li tr •XJ ø P 0 ϋ cn Ω f- tr la N >P» to- P 3 cn tr ro Pi 0 H Ω ro rt li rt 0 CD Ut 0 to- Xt ro CD —* tS 3 P ,— , ' ø ro 0 0 P- 0 Hi li CD P Φ Ω tS 0 Mi Pi • CD ts O Ω P- . — . Hi tr Ω o P t Ω tr li O I-* Ω 3 i P" •XJ P" cn H en ts >— tr- ts 00 * 0 Hi I-* •XJ 0 ro o 0 ro rt- 0 ex rt 0 cr rt * ro •XJ rt 0 0 3 ø P ro o φ rt P 0 3 Ω r* ϋ H- rt tr TJ Ω cn cQ rt H * —. Pi cn P Hi 0 tr Ω Ω o 3 ts tr J o CD P 0 ft 0 tr P- to P P- rt rt P J o X Hi P- ts ro P rt P I-* l-h cn li o P- CD 0 0 P P- rt t-o 0 • P- 3 ft t O rt P cn li Ω •XJ •XJ o P 0 t-o <! TJ 1 Pi Ω P 1 1 r ro ø M 1 1 CD 1 1 CD

Inventors: TJERNQUIST ULF, TJERNQUIST, ULF
Applicants: STIFTELSEN METALLURG FORSK, MEFOS-STIFTELSEN METALL FORSK
Application year: 1986
Main classification: B21B45
IPC codes: B21B45