GB2088764A - Rolling steel bar or rod - Google Patents

Abstract

In a rolling mill for making steel bars or wire rods by continuous rolling a loop of at least one turn is formed in an accumulator disposed at any suitable position in a mill train or between two trains. **ERROR**< AR>The thus looped workpiece is used either for temporary accumulation to adjust rolling speed, or to provide a long path of travel necessary to cool the workpiece to a desired temperature. The accumulator may incorporate burners or electrical heaters. <IMAGE>

Description

SPECIFICATION Methods of and apparatus for rolling steel billets This invention relates to methods of and apparatus for rolling steel billets. In more particular, this invention relates to methods of and apparatus for temporary accumulation of in process steel billets in the form of a loop or loops. More particularly, it relates to the methods of and apparatus for accumulation of inprocess steel billets which enables accumulation of the lengths of in-process steel billets in a rolling line by means of forming at least one loop or a plurality of loops of the steel billet thereby enabling rolling of the steel billets in their best condition.

Generally, when making rods or wires from steel blooms slabs or billets, it is a usual practice that an ingot or billet made by ordinary ingot making process or cast billet prepared by continuous casting process is divided into smaller section billets of a desired dimension at a blooming mills and then transferred to subsequent rolling operations after having been finished and heated to a desired temperature in a heating furnace.

Rods or wires reduced to a desired cross sectional area having undergone roughing, intermediate and finish rollings, are transferred to a cooling step and then prepared as the final product of rods or wires after having been subjected to inspection and various types of testing in the finishing step for diemensional accuracy, shape and required properties.

Studies of rolling work on rods or wires currently being carried out show that the rolling work can be broken down into three major rolling steps following the order of roughing, intermediate and finish rolling and the entirety of which, at the present stage, is being carried out in a completely continuous manner.

That is, speaking of the rolling of high quality slender rods or wires, for instance, roughing and intermediate rolling steps in many cases are performed by passing through a horizontal mill with a plurality of strands, while the finishing rolling is done by using horizontal and vertical roll stands with single strands.

As to the rolling of larger size rods, all of the steps from roughing mill upto the finish rolling are carried out through a combination of horizontal and vertical roll stands with a single strand and with no twisting.

The length of the billet being rolled, in the rolling of rods or wires as mentioned above, will rapidly increase as it moves forward from roughing mill to the finishing stage due to the decrease in the cross sectional area of the material stock.

Naturally, the rolling speed of the finishing mills must be increased up to a very high rate.

Accordingly, in order that completely continuous rolling operation can proceed throughout the entirety of the mills, it is required not only to secure optimum speed adjustment between each mill, by also to carefully control the sectional area of the starting billet material to be introduced into the roughing mill. In other words, the difference in rolling speed between the roughing mills and finishing mills increase as the cross sectional area of the billet as a starting material becomes larger.

However, there exists some restriction with respect to the minimum practical rolling speed of the roughing mills and maximum speed of the finishing mills which makes it impossible to roll starting billets having excessively large sections.

As to the rolling mills currently used, the lower limit of the rolling speed of the first pass through the roughing mill line is 0.08m/sec, while the upper limit of the final pass in a finishing mill is 75m/sec, accordingly, the section of the starting material to be passed is limited to 1 50mm square at most.

According to the conventional billet mill layout, if there exists any discontinuity, namely, from continuous to step-wise multistrand rolling all the mills are arranged in a straight line or lines without effecting any bending or looping to the billet to be passed.

Consequently, where the rolling temperature of the billet is to be controlled during and after the intermediate rolling lines, a very long distance is required for such layout.

Accordingly, for blooms or billets having larger cross sections than the said upper limit, it is difficult or impossible to introduce them into the rolling line and they have to be previously rolled down to the desired cross section.

Moreover, in completely continuous rolling work of roods or wires, the former stage of roughing is performed at relatively low speed and this is accompanied by a undesirable temperature drop during the later stage of roughing and thus the material under rolling is liable to be cooled down below Ar3 transformation point, unless it is maintained at a considerably high temperature, thereby the quality of the material is impaired.

On the other hand, the temperature of the material under finish rolling is apt to remarkably increase due to its high speed rolling, which results in both increase of cooling cost and undesirable effect on the quality of the rolled products. The constitutional feature of the present invention resides in the methods and the apparatus for carrying out the method which is capable of forming at least a single turn loop of a running billet or a plurality of loops of several turns and further disposed in stages and/or arrays at any suitable position between or subsequent to the rolling opera tion.

It is already known in the rolling mill layout of this field of art to dispose in a billet rolling line at least a repeater which functions to change or reverse the direction of advance of the billet or rod by an angle of 180 .

In this kind of arrangement, length of, namely, the size of such loop expands as rolling proceeds on, finally, the length of the loop will become largest at a moment when the tail end of the billet passes through the preceding roll stand.

In the past, no particular demand existed from customers for more than normal lengths of coiled wire. However recently, short length or under weight coiled wire has become unacceptable in the market.

Thereby it becomes indispensible for the steel maker to maintain the weight of the material in a unit coiled product pack as much as possible.

Due to these aspects, the length of the loop in a unit coiled product pack naturally increases as consumer's demand for heavier weight material wire stock increases more and more, such change in the requirements gives rise to a widening of the temperature difference during rolling due to the extended period of time for rolling required for the length of the billet between the guiding front end and the trailing end of the billet.

Such lengthened rolling time, eventually, makes it impossible to conduct normal rolling time due to the material characteristics as well as to the quality of dimensional accuracy, shape of the products and the like.

The inventor of the present invention has carefully studied the rolling of the billet as mentioned above and considered that speedup of the rolling in the roughing mill train could be accomplished if a large amount or number of in-process steel billet or billets could be temporarily accumulated midway in the running rolling line, thereby material of larger cross section such as continuously cast billet which it has long been considered impossible to directly introduce into the rolling, would become practically possible without having been undergone the blooming mill operation.

Based on this concept, he conducted various experimental work on the method of how to accumulate such billet(s) as a loop or loops as well as the apparatus for carrying out such an aimed method.

As a result, the inventor accomplished the methods and the apparatus as explained later which have proved to be superior in perfor mance.

According to the conventional billet mill layout, rolling mills were arranged in straight lines so as not to move the billet along curved path(s) by a repeater(s) or the like such as when there is any portion of discontinuity, that is, continuous rolling to subsequent stepwise work exists in the roughing mill and the intermediate rolling.

When is is required to control the rolling temperature of the billet in the intermediate or final rolling or subsequent to the final rolling of continuous rolling, a rolling line of very long distance was required for such rolling mill layout.

Technical concept of the present invention in which at least a coil of loop or loops of billets having a turning angle of more than 360 is provided in a single turn or in a plurality of turns and in single array or in plurality of arrays in a plane and further in a single layer or in a plurality of vertical layers, is believed to be novel and which has not yet been thought of in any other part of the world.

An object of the present invention is to provide the methods of and apparatus for temporary accumulation of in-process steel billets in the form of one or more loops which obviate pending problems experienced in the conventional billet rolling operation by feeding billets of larger section such as cast billets or slabs produced by continuous casting method without subjecting them to a blooming mill, thereby enabling both speed-up of the roughing mill train and improvement in product quality.

In other words, the present invention aims to provide the methods and apparatus which permit temporary accumulation of a large amount or number of in-process steel billets and at the same time remarkably reduce floor space in a rolling mill required for such accumulation.

Another object of this invention is to provide means for the temporarily accumulation which can be readily installed at any desired portion in the billet rolling line.

A further object of the invention is to provide apparatus for temporary accumulation of steel billets which can be supplemented with either one or both of heat maintaining and/or cooling means.

A feature of the apparatus for temporary accumulation of in-process steel billets for achieving above-mentioned objects of the present invention resides in that two reverser blocks are opposedly placed to constitute an accumulator unit, wherein each of said reverser blocks is formed with at least one curved groove along which a running billet can be guided thereby the assembled accumulator unit is able to receive and accumulate at least one loop of an in-process steel billet, that the accumulator units can be arranged to constitute a plurality of arrays in a plane but also to constitute a plurality of vertically arranged stages of accumulator arrangement, and that it comprises means for introducing a steel billet into the groove(s) of through bores, such as pinch rolls disposed between each of the reverser blocks.

A further feature of the present invention is that a wall surrounding the path of a billet between the two opposing reverser block can be arranged wherein means for heating or cooling the billet therein is provided for the purpose of compensating for temperature changes during the accumulation.

The accumulator unit used for the temporary accumulation of a billet loop(s) of the present invention may be of a pair of horse shoe shaped semi-circular reverser blocks opposedly disposed being spaced each other or disposed in proximity to constitute a round chamber.

Embodiments of the methods and apparatus of the present invention will now be explained by referring to the accompanying drawings in which: Figure 1 is a layout showing an example embodying the present invention; Figure 2 is a layout showing the typical entire billet rolling line for carrying out the method of the present invention; Figure 3 is a diagram indicating changes in rolling temperature and rolling speed that take place during the rolling along a rolling trains; Figure 4 is a plan view showing arrangement of loop accumulators and the manner of actual working; Figure 5 is a side elevational view showing a vertically arranged multi-stage loop accumulator; Figure 6 is a cross-sectional view taken along line VI-VI of the Fig. 4; Figure 7 is a cross sectional view taken along line VII-VII of Fig. 4;; Figures 8a, Sb, Sc and 8d are explanatory pictures showing the manner of accumulating a steel billet using the loop accumulator; Figure 9 is a plan view showing a unit loop accumulator; Figure lOis a cross sectional view taken along line X-X of Fig. 9; Figure ii is a perspective view showing a cooling trough applicable to the present invention; Figure 12 is a perspective view of another embodiment of the present invention; Figure 13 is a sectional plan view of the apparatus shown by Fig. 12; and Figure 14 is a sectional elevation view of the apparatus shown in Fig. 12, and Figures 15a and 1 sub are elevational view and plan view showing another embodiment for guiding the coiled billet to the next rolling step.

Fig. 1 shows basic method of the present invention to form only a single turn loop of a steel billet in single array and in single stage, namely, a single loop of a steel billet is formed at a position midway of the finish rolling line where rolling temperature of the billet rapidly increases.

In the drawing Symbols V, H, W, R denote a vertical roll stand, a horizontal roll stand, a billet to be worked and a pair of reverser blocks which constitute an accumulator unit to be disposed between adjacent two roll stands.

The accumulator R is composed of a pair of reverser blocks of the same shape construction being opposedly arranged so as to form a single turn steel billet loop by reversing twice the running steel billet thereby giving it full one turn 360 .

Symbol P denotes a pinch roll arranged at the entrance of each reverser block for taking up the running steel billet.

When even a one turn loop is formed in the process of a continuous rolling train, it is effective for temporarily lowering the rolling temperature of the billet after it has passed through the preceding pass but before it enters into the subsequent rolling pass, thereby enabling a rolling temperature of the steel billet to be controlled at its optimum level.

In order to further strengthen the cooling effect cooling means such as cooling trough can be installed between the repeater and pinch roll, alternative spray means can be arranged.

Further, such single staged one turn coil as mentioned above can be formed not always in the finishing train by at any other location in the intermediate rolling line or subsequent to the finish rolling train.

Next, another embodiment of this invention will be explained which permits discontinuous rolling by means of accumulating a large amount or number of steel billets by applying the present invention to actual steel billet rolling.

Fig. 2 illustrates an exemplified layout suitable for carrying out the method of the present invention.

In the drawing, numeral 1 is a heating furnace into which large size cast slabs or billets which have been cast and transferred to the furnace are charged and heated up to a predetemined temperature and numeral 2 is a device such as a pinch roll which takes up the heated billets.

Other numerals 3, 4, 5, 6, 7 and 8 denotes, respectively, a descaling means, roughing roll stands consisting of horizontal roll stands and vertical roll stands, a flying shear, a material stock (billet) to be rolled, a flying shear and a selector which appropriately distributes the material to be rolled having been paid off from the roughing roll stand 4 to each of a plurality of loop accumulator which will be explained hereinafter.

Numeral 9 shows a plurality of loop accumulators for temporary accumulation of inprocess steel billets which have passed roughing mill stands and are constructed such that they are capable of accumulating the in-process billets in the form of a loop or loops and further being arranged in a plurality of vertically stacked stages. In Fig. 2, four loop accumulators 9 are transversely aligned such that a single strand billet can be sheared and then branched into four strands after and including intermediate rolling train, that is, after having passed through the roughing mill train and these accumulators are disignated, for convenience sake, as 9a, 9b, 9c and 9d, respectively.

In this embodiment, the number of strands was selected to be four but any other suitable number of strands can be optionally used as required.

In the drawing numerals, 10, 11, 12, 1 3 and 14 designate a snip shear, descaling device, intermediate rolling line or block, snip shear and finish rolling line or block, respectively.

The intermediate rolling lines 1 2 and finish rolling lines 1 4 are positioned in alignment with and at the down stream side of each corresponding loop accumulator 9a-9d.

As can be seen from the layout of Fig. 2, the train of the rolling mills becomes discontinuous at this portion and hereinafter due to these plurality of loop accumulators, consequently, rolling train and trains at upstream side and downstream side, respectively, constitute a separate rolling line wherein mass flow of the billet becomes independent from each other. In other words, roughing mills in the drawing becomes discontinuous with respect to both the subsequent intermediate rolling mills and finishing mills.

At the same time, loop accumulators installed at the portion of discontinuity are able to accumulate large lengths of in-process steel billet although each loop accumulator is of compact floor space, thereby the entire rolling mill is able to deal with the rolling operation even if the length of the billet in the roughing train or trains 6 is very long.

It is to be noted further that the location of the loop accumulator 9 is not limited only between the roughing train 4 and the intermediate rolling train 1 2, but it is a basic concept that it is to be installed at a place where rolling temperature of the billet material to be rolled becomes lowest in its rolling line.

The rolling temperature in the usual billet rolling line sharply decreases in roughing train as shown by solid line A of Fig. 3, while it rises up again following its faster rolling speed and due to working heat as it moves toward the intermediate rolling and further to finish rolling where rolling temperature rapidly increases.

In such case, of course, the loop accumulator(s) 9 is arranged at midway between the roughing mill train and the finishing mill train, while it is arranged between the intermediated rolling train and finish rolling train when the rolling temperature becomes lowest at that portion.

Turning now to another embodiment where loop acumulators 9 can be installed to accumulate steel billets in a plurality of vertically stacked layers or stages.

As shown in Fig. 4, a unit loop acumulator of this type 9 consists of a pair of reverser blocks each one of which partly utilizes the principle of "repeater" but it is formed with a plurality of grooves and the two reverser blocks are placed such that each flat side face is opposed to the opposite side face to constitute a unit loop accumulator.

And two or more of these unit accumulators can be vertically arranged one on another as a plurality of stages (four stages) as shown in Fig. 5 together with pinch rolls 1 6 and 1 7 arranged at the inlet of each reverser block which has several grooves 1 8 formed on the surface depend upon the required number of turns as shown by Fig. 6 (shows four grooves).

A portion or space between two reverser blocks 1 5 where the billet takes a straight path and usually is maintained as long as possible, is preferably constructed for heat insulation or positive heat compensation as shown by Fig. 7.

In Fig. 7, numeral 1 9 is a refractory cover surrounding the entire portion of the aforesaid passage-way for billets. 20 denotes side guides vertically and length wisely disposed at a predetermined distance with respect to the movement of the billets so as to separate adjacent moving billets from each other. 21 denotes a plurality of base plates attached along the side guides 20 and swingably movable for a disposed position and for a withdrawn position. 22 are the burners for heating arranged at the upper portion of the cover 1 9.

23 denotes power cylinders for moving the base plate 21. 24 is an exhaust opening. As the billet having gone through roughing mills is accumulated as a loop or loops of very long length with increased surface area, there exists a fear of appreciable temperature drop, and it is practicably effective to provide heat compensation device in said accumulator unit as shown in Fig. 7. In the illustrated example, a burner heated heat compensator chamber is explained, but it is not limited to this type, but any other suitable means such as direct electric heating type or high frequency induction heating system may also be used.

The base plate 21 is disposed in position when the billet undergoes normal running, while it is withdrawn when the billet is guided at the initial loop making or for paying off of the billet toward subsequent operation.

Now, explanation will be made by referring to Fig. 2 on the method of rolling billets according to the present invention applied to the aforesaid rolling mill.

A continuously cast billet or billets casting are charged into a heating furnace 1 and heated upto a predetermined temperature having gone through finishing steps such as inspection for defects. Then the heated billets are taken up by a pinch roll 2 and are descaled by a descaling device 3. Thereafter each billet is passed through roughing mill 4 (a continuous H-V rolling mill is depicted but reversible type one also can be used) and is rolled down to a desired section.

The billet having finished the roughing step is directed, by means of the selector 8, to any one of the desired loop accumulators, where it is accumulated in loops of a plurality of turns and further in a plurality of vertically piled layers or stages, if necessary.

When supply of the billet to any one of the loop accumulator has finished, the billet is cut away by a flying shear 7 and the subsequent billet is supplied to and accumulated by the next accumulator.

By repeating this work in a manner as mentioned above, the rolled and cut billets are succesively accumulated in the four loop accumulators 9a-9d. The billet within the accumulator is heated, for instance, by suitable burners to maintain the billet temperature so as to prevent the billet from cooling below the necessary rolling temperature.

Now, explanation will be made by referring to Fig. 8 to show in what manner the billets can be acumulated in each group of related loop accumulators 9.

Assume, in this instance, that accumulation of the looped billets is to be performed one on another from the bottom stage to its next upper stage, a loop of the billet on the first stage is formed as shown by Fig. 8a from the outermost end toward the innermost end by using corresponding pinch rollers and accumulator, while a second loop of the billet is formed from the innermost end toward the outermost end as shown by Fig. 8b.

Similarly, a third and fourth loops from the bottom are formed alternatively in reversed way as shown by Figs. 8c and 8d.

The leading end of each looped billet is taken up by a succeeding intermediate rolling line.

The length of the looped billet in each stage is almost constant, thus the amount of the accumulated steel billet in one stage is kept almost constant. Fig. 4 indicates in what manner the steel billets are fed from these loop accumulators 9a-9d to the respective intermediate rolling train 1 2.

The drawing indicates the loop accumulator 9a in the process of taking up an in-process steel billet from the roughing mill train 4, wherein a part of an previous billet is still moving and remains within the loop accumulator 9a, while the remaining portion of that billet is running through the succeeding intermediate and finish rolling lines 12 and 14.

During the period when a certain loop accumulator is taking up a billet, pinch rolls 1 6 and 1 7 are driven in synchronization with the rolling speed at the outlet of the roughing roll stand.

The travelling speed of the previous billet at the inlet of the intermediate rolling train 1 2 is maintained slower than that of the pinch rolls 1 6 and 17, accordingly, the distance between the previous billet and the succeeding billet is gradually shortened.

The other loop accumulators 9b, 9c and 9d are releasing their accumulated billets, respectively, toward their corresponding intermediate rolling trains and further to the finish rolling trains.

Taking up of the billet can be made not only from the top stage but can be taken up from any desired stage.

An in-process billet fed from an accumulator or a group of accumulators 9 to the succeeding intermediate and finishing roll trains are rolled down into a final section and wound up into a coil per each strand, and transferred to any suitable cooling step for cooling and then finished into a product of final rod or wire.

Pinch rolls 1 6 and 1 7 are shown in the drawing as each pair of rollers drive each of the looped billet of a plurality of turns, and in this instance, if these looped billets are driven by a common driving means, pinch rolls in each stage cannot be slowed down to the rolling speed of the roughing train until the tail end of the last billet has completely passed therethrough, this results in excessively long distance between two successive billets to be rolled, thereby obstructs productivity of the rolling mill.

If the above-mentioned pair of pinch rolls are arranged as separately driven rollers, the preceding billet in the accumulator can be adjusted to the rolling speed of the intermediate and finish rolling trains and when the tail end has passed through the outlet pinch roll, the pair of pinch rolls can be placed on standby at the speed of the roughing train.

By means of this separate driving system, not only the length of each loop can be correctly controlled but the distance between two successive billet and the point of discontinuity from the preceding billet to the next billet can be minimized as compared with the former type group driving.

In case of separate driving rollers, it is also possible, if necessary, to perform rolling down operation within this step and further control loop formation in accordance with the present invention.

In the method of the present invention shown in Fig. 2, a loop accumulator or a lineup of loop accumulators which form a loop of a plurality of turns and further a plurality of stacked billets enable speed-up of the rolling spaced at a desired rate, consequently, there exists no appreciable lowering of rolling temperature in the roughing mill train which permits discharging of the material billet from the heating furnace at considerably lower temperature.

This corresponds to the status as shown by the dash-dotted line B shown in Fig. 3, which indicates a dramatically lower temperature discharging as compared with the temperature change in the roughing mill train of the conventional method shown by line A of the same drawing.

This gives rise to such merits as saving of energy in furnace heating, lowering of a primary scale loss caused by oxidation during heating at higher temperature, extension of roll life due to prevention of decarburnization of the heated billet and the patterned cracks on the surface of the roll body from occuring.

Total number of loop accumulators 9, location to be installed, number of turns in one stage and the number of stages to be laid one on another are not restricted to those shown in the drawings but can be optionally aitered depending upon such factors as the length and cross sectional area of the material billet to be used and the speed of rolling and so forth.

In the description of the invention made heretobefore, the loop accumulator of this invention has been explained with respect to the examples arranged for the purpose of temporary in-process accumulation of the billet, but it can also be disposed between the intermediate rolling line and finish rolling line and also at the down stream side of the finish rolling train as a means for long distance cooling in lower temperature rolling for imparting toughness to the rolled wire product.

In case of this lower temperature rolling, the heat compensation device arranged in the accumulator explained in Fig. 7 can be replaced with a cooling device which can be of either one of water cooling or air cooling systems.

The present invention permits disposition of a plurality of groups of continuous rolling trains each performs different "mass flow" from each other, so it is able not only to readily adopt rolling system which is able to maintain total sum of the heating energy and rolling energy at minimum level but also to optionally combine controlled rolling and controlled heating with each other for the purpose of obtaining a metal structure of the rolled billet feasible for spheroidization.

Recently several methods of rolling continuously cast billet by utilizing the stored heat after it has solidified have been attempted, in view of these attempts, the present invention indicates that the present invention is able to contitute a rolling process which enables rolling operation most economically within the same rolling process without allowing the rolled billet(s) to be completely cooled down, particularly when the rolled product is required to undergo cooling down to below its transformation point before it has been finally rolled.

The unit loop accumulator in the foregoing examples are shown and explained as one having a construction consisting of a pair of opposedly disposed reverser blocks having a straight intermediate portion between the two blocks, alternatively to two blocks can be placed being in close contact with each other as will be explained later in detail by referring to Fig. 12-14 so as to constitute an annular sealed body like a doughnut within which a billet can be accumulated spirally to constitute a plurality of turns and further in a plurality of stacked loops.

Next, apparatus for temporary accumulation of the in-process billet according to the present invention will be explained by referring to the following drawings.

Fig. 9 shows a loop accumulator which partly utilises the principle of a repeater which has been used for turning and guiding a running in-process steel billet.

A pair of reverser blocks 31, 31 are opposedly placed being spaced apart to constitute a loop accumulator unit and several of these accumulators can be laid one on another in vertical direction, if necessary, to constitute a plurality of stages as shown in Fig. 10 (shown as four stages) in the drawing).

Adjacent to the inlet of each opposedly arranged reverser block 31, a pair of pinch rolls 33 and 34 are disposed for introducing the billet into respective reverser block the surface of which is formed with a plurality of grooves dependent upon the number of turns per one face of the unit loop accumulator.

As shown in Fig. 10, aforesaid pinch rolls 33 and 34 drive the billet as a pair and forcedly feed it into respective block to constitute a looped billet of a plurality of turns per one stage.

These pinch tolls 33 and 34 can be driven either by group driving means throughout the entire stages or can be separately driven as already explained in the foregoing method.

As already explained, straight portion between the two opposing reverser blocks forming passage ways of the billet, when constructed as having a compensation device, will prevent lowering of the temperature of the billet during its accumulation.

In addition to the use of the present invention for temporary accumulation of the inprocess billet thereby enabling rolling by discontinuous method, the apparatus of the present invention can be utilized with minimum floor space as a long distance cooling path for the billet indispensible for imparting desired toughness to the rolled product.

In such case, the heat compensation device is replaced with a cooling means such as water spray cooling shower from the upper and or side portion of the device, alternatively a box-shape trough can be installed at the straight passageways of the billet as shown in Fig. 11 and cooling water or any other cooling media is sprayed down through shower means 43 for cooling the billet.

Next, operation and function of the forego ing loop accumulating apparatus or device will be explained.

In Fig. 10, each reverser block in a pair is designated, from the bottom to upper ones, as 1 a-2a, 1 b-2b, 1 c-2c and 1 d-2d, respectively, similarly, pinch rolls in each stage designated as 3a-4a, 3b-4b, 3c-4c and 3d to 4d, respectively.

The material billet 6 is introduced into the reverser block 1 a at the bottom and then fed through the pinch roll 4a into the first groove of the grooves of the next reverser block 2a; next the steel billet advanced outward from the reverser block 2a is fed again into the reverser block la. In this manner, a looped billet of a desired number of turns is completed.

In case where the looped billet in the first stage is formed as shown in Fig. Sa from the outermost turn toward the innermost turn, the looped billet in the second stage from the bottom is formed from innermost turn toward outer one as shown in Fig. 8b, then that formed in the third stage will be formed again from the outermost to the inward as shown in Fig. Sc and the fourth one as shown in Fig.

8d. The direction of the travel of the billet in each stage is shown by dashed lines in Figs.

8 and 10.

Formation of such a looped billet of a plurality of turns and further in a plurality of stages will enable accumulation of in-process billet in large amount or numbers without requiring excessive floor space.

The number of turns of the loop and the number of stages can be optionally selected and the paying off of the accumulated billet can be made from a plurality of stages.

It is also possible to heat the billet, for example, by heating burners 22 of Fig. 7 or to cool it by the device as shown in Fig. 11.

The apparatus as shown in Figs. 12, 1 3 and 1 4 is another type of loop accumulating device according to the present invention, in which there exists no straight passageways between the two opposing reverser blocks as in the embodiment shown in Fig. 9, thereby the steel billet can be formed into a looped form of a plurality of turns and further in a plurality of stages one on another in the form of substantially cylindrical configuration.

As shown in Fig. 12, a suitable portion in the rolling line between the two rolling mill trains is surrounded by an enclosure wall body 55 of sealed construction having annular cylindrical configuration, wherein annular reverser blocks are laid one on another to form a plurality of layers as desired. The enclosure wall body 55 is composed of a heat insulating material such as used for making a heating furnace.

At a suitable portion on the exterior surface of the wall body an inlet opening 56 and an outlet opening 57 for the billet are provided.

As shown in Fig. 13, pinch rolls 58 and 59 for effecting introduction and spiral looping of the billet are disposed transverse to the path of the billet and in a pair in each stage of the accumulator ring as shown in Fig. 14 and the bearings and driving means 60 are disposed outside the side wall of the wall body through which a respective drive shaft passes from one side to the other side.

The steel billet 6 fed from the rolling mill train at the upstream side into the loop accumulator through said billet inlet opening is forcibly guided and driven by the pair of pinch rolls 58 and 59 along or through the grooves or bores formed in a continuous spiral into a spirally formed loop having a plurality of turns of desired number.

When the billet has been formed into the loop of desired number of turns by the pair of pinch rolls, the billet is further driven to the next stage by the pinch roll in the next stage and is driven into a next loop of a plurality of turns by following the same operation as mentioned above by one dotted dash line in Fig. 1 3 which indicates the part of the billet being shifted to the next stage.

When all of the billet loops in all of the stages have been formed, the billet 6 is taken out through the outlet opening and fed to the subsequent rolling mill train.

Taking out of the billet can be done from any stage at option and the direction of the taking out is not necessarily in the same direction as that for introducing the billet but any other direction such as one normal to that used for introducing or feeding the billet can also be used.

Though not illustrated in the latter embodiment, any suitable heating means or cooling means can be arranged as shown in the first embodiment so as to utilize the apparatus for heating or cooling the in-process billet.

It is also possible as a means for converting the mode of rolling into a discontinuous one, to wind up the looped billet around a pawling reel or a laying reel then reduce the speed and stop the rotation of the reel while holding the tail end of the billet, and then feed the tail end of the billet to the next rolling train by reversing the rotation of the reel while guiding it by a selector.

When the billet becomes slender to a certain extent, it is also possible to wind it up around a bobbin and feed it, by uncoiling, to the next rolling step.

A type of this modified mode of embodiment will be explained by referring to Fig. 1 5.

As shown in Fig. 15, continuous billet loops formed in the loop accumulator of the present invention are successively laid one after another by means of loop layer 61 on the moving conveyor 62, the laid billet in the form of large number of continuous coils or rings 63 are arranged to be packed in overlapped state as densely as possible, then the thus densely packed billet corresponding to one unit coiled product is transferred to the next rolling mill train.

Preferably, the leading end and the tail end of the loops or rings of such densely packed continuous loops could be reversed by the end of this packing and transferring step such that the tail end of the loop left the accumulator can be fed to the subsequent rolling step.

At any rate, in order to maintain the billet at a predetermined temperature, it is indispensable to insulate the billet from the exterior temperature or positively heat it as desired.

In case where the overlapped and compacted coils of a billet are formed by said reels, bobbin or loop layer, a longer time is required for heating or cooling such coiled billet due to the densely compacted state and to the inevitably varied extent of compactness.

Accordingly, it it is required to forcibly heat or cool the billet, such operation should be conducted at portion of the process before or after the loop forming operation where there is no fear or necessity of forming a densely compacted coiled billet.

Though not illustrated in the latter embodiment, any suitable heating means or cooling means can be arranged as shown in the first embodiment so as to utilize the apparatus for heating or cooling the in-process billet.

Working examples of the rolling operation in accordance with the methods and by using the apparatus of the present invention will be described hereinafter.

Example 1.

Material billet: 250mm X 250mm square x 5 meter length cast billet Rolling mill trains: roughing mill train (11 passes) intermediate rolling train (8 passes) finish rolling train (8 passes) Any of the trains consist of alternative succession of horizontal-vertical roll stands using a single strand in roughing mills but four strands in intermediate and finish rolling trains.

Loop accumulators: Four sets between the roughing mill train and the intermediate rolling train.

The construction is of the type having straight passageways as shown in Fig. 9 having accumulating capacity for a 400 meter billet.

In the above example, the billet in the roughing train is rolled down from 250 mm square into 30 mm square, wherein the rolling speed at the inlet stand was 0.11 m/s, while at the outlet stand the speed was 8.0 m/s.

The billet having passed the roughing step was transferred into and accumulated in successive four loop accumulators as predetermined cut lengths, thereafter these billets were fed into respective intermediate rolling trains at a rate of 3.0 m/s and rolled down from 30 mm square into 13.8 mm round.

Next these billets were reduced down in the finishing mill trains to the final size of 5.5 mm. Rolling speed at the final pass of the finish rolling was 75 m/s and the weight of the single coiled product was 2.5 tons.

It is to be noted that a longer billet of double length of 250 mm X 250 mm x 10 can be equally satisfactorily rolled by using a flying shear as shown in Fig. 2.

As already explained, it is general practice in the continuous rolling of rods or wires according to the conventional method, to layout roughing and intermediate rolling mill trains with multi-strands.

By virtue of the method of the present invention, however, it becomes possible to perform the work by a single strand passing throughout the entire stands which permits non-twist H-V rolling without being accompanied by any lowering of production capacity and thereby dramatic improvement of the product quality can be expected.

If comparison is made with a former method relying on roughing mill train of four strands pass, the present invention accomplishes a greater extent of simplification in the mill equipment such as roll stands, reduction gear mechanism and the like due to the decrease of the rolling load to about a quarter, which further contributes to the reduction of rolling torque and saving of electric power.

As explained above, according to the method of temporary accumulation of the inprocess steel billet of the present invention, rolling temperature during the continuous rolling of the billet can be controlled with ease and without requiring any large floor space.

Installation of a loop accumulator or accumulators which is capable of forming multiturned loops of a billet and further in multistages at any optional position of the billet rolling mill, enables the rolling operation performed thereafter to be converted into a discontinuous type thereby permitting selection of the optimum rolling speeds across that position as desired.

Particularly, when the roughing mill train is changed to discontinuous from other succeeding trains, a large number of billet loops can be formed at the portion of the discontinuity, thereby the rolling speed of the roughing mills can be speeded-up independent of that of the intermediate and finish rolling trains.

This enables roughing of the material slab or billet of such a larger operable section which has hitherto been considered impossible and further renders billet of longer length to be capable of being rolled and thus leads to improvement in yield rate of rolling.

While, in the continuous rolling system for slender rolled wire, a lower limit for minimum diameter reduced by rolling work has been considered to be 5 mm due partly to the restrictions for speeding-up of the finish rolling and also due to the increasing rolling temperature.

However, by introducing the novel concept of the present invention this difficulty can be obviated and it becomes possible now to roll a slender billet of down to 2-3 mm diameter.

The loop accumulating apparatus of the present invention, in spite of its compact construction and size enables accumulation of the in-process steel billet not only as a single turn loop but also as multi-turn loops and further these billet loops can be laid one on another into a plurality of floors or stages and further can be transversely disposed in a plurality of arrays, thereby the steel billet or billets can be accumulated in large quantity and in the form of longer lengths.

Moreover, the apparatus can be supplemented with means for heating or cooling the in-process billet, so it is very effective for accumulating steel billets during the process of rolling or for performing long distance cooling during and after the rolling of the steel billet.

In addition, the quantity of the steel billet to be accumulated can optionally be adjusted and the apparatus can be installed as a means for giving discontinuity of rolling within a production line of a billet rolling mill.

As a consequence, by virtue of the present invention, billets of larger section now become acceptable for billet rolling which has hitherto been considered to be impossible.

As the present invention permits lower temperature rolling in an effective manner, such meritorious effect is highly appreciated in the industry.

Up to the present, where continuously cast billets or slabs are to be used as starting materials for high grade steel billets it has been considered, due to the required reduction ratio, harmful inclusions and the like, that such material could not been rolled down into material billets unless they have been initially cast in larger section.

Accordingly, it was indispensable for such high grade steel, that it had to be once subjected to a blooming step.

However, the present invention, by virtue of its applicability to cast billets of larger section, has brought about many meritorious effects such as elimination of the blooming step, remarkable widening of allowable material defects and simplification of finishing as well as inspection procedure.

The above mentioned meritorious effects of the present invention can be summarized that they bring about various advantages such as, saving of ingot making and subsequent blooming steps, grading up of the billet quality due to the expanded applicability to larger section material billets, a great simplification in finishing and inspection, saving of energy in the billet mills, simplification in plant layout and expanded applicability to rolling down of the billet into much more slender sectional size and so forth.

Claims (14)

1. A method of rolling a billet for making steel bars or wire rods which comprises the steps of: feeding at a predetermined position of the rolling process an in process steel billet transferred from the step at an up-stream side into a loop accumulator; forming therein a single turn loop or loops of a plurality of turns of billet at least in a single stage for temporary accumulation or for providing a long path of travel; feeding the thus formed loop or loops to a subsequent operation.

2. A method of rolling a billet for making steel rods or wires as claimed in claim 1: wherein the looped billet is continuously fed to a subsequent operation for forming a long distance path of travel to secure necessary cooling during its travel.

3. A method of rolling a billet for making steel bars or wire rods as claimed in claim 1 or claim 2 wherein the billet is formed into continuous loops of a plurality of turns in a stage which are further stacked one on another into a plurality of stages.

4. A method of rolling a billet for making steel bars or wire rods as claimed in claim 1 or 3 wherein the billet is prevented by means of heat insulation and or by positive heating or cooling, from undesirable cooling or excessive heating place, during it loop forming operation.

5. A method of rolling a billet for making steel bars or wire rods as claimed in claim 1, 2, 3 or 4 which further comprises the step of laying down the coiled billet successively to constitute a number of partly overlapped and densely compacted continuous coils to be fed to the next rolling step either from the tail end or from the leading end.

6. A method of rolling a billet for making steel bars or wire rods or as claimed in claim 1, 2, 3, 4 or 5 which further comprises the steps of: cutting up the billet when a preceding part thereof has been formed into at least a loop of single turn or loops of plurality of turns to constitute one or more of vertically stacked stage(s); feeding the leading end of the succeeding part of the billet to another loop accumulator and working it to constitute another array of a loop or loops disposed transverse to the direction of the travel of billet in rolling, repeating one after another the above mentioned feeding and working by using another loop accumulator placed on stand-by; and feeding the looped billet in each array to each subsequent rolling mill train arranged in correspondence to each array of looped billet, thereby converting single strand rolling in a previous rolling train into discontinuous multi-strands rolling with a desired number of subsequent trains of rolling mills.

7. A method of rolling billets for making steel bars or wire rods as claimed in claim 1, 2, 3, 4, 5 or 6, wherein eachf rolling train of a rolling mill which works a different mass flow can be controlled at a desired rolling temperature by varying its rolling speed, respectively.

8. An apparatus for forming a loop or loops of an improcess steel billet within a line of rolling mill trains at any desired position or positions in at least one of said rolling mill trains and/or between two adjacent rolling trains at least in a single turn, single stage and in single array, a unit of said apparatus comprises:: a unit loop accumulator consisting of a pair of reverser blocks each having a semi-circular or semi-oval cross section straight side faces of which are being opposedly disposed each other at a certain distance or juxtaposed; one or a plurality of curved grooves or bores formed on the surface or in the body of said reverser block to guide and drive the steel billet into a loop or a loops of a plurality of turns continuously and spirally formed along said groove(s) or bore(s); a pair of driving rolls disposed adjacent to each of said loop accumulator for pinching the billet at its leading end and forcibly driving it to pass through said groove(s) or bore(s).

9. An apparatus as claimed in claim 1, wherein said unit loop accumulator further comprises a means for compensating for undesirable temperature drop during it loop forming operation.

10. An apparatus as claimed in claim 1, wherein said unit loop accumulator further comprises at least a device for cooling the looped steel billet at a desired temperature.

11. An apparatus as claimed in claim 1, wherein said means for compensating undesirable temperature drop is a sealed heat insulating chamber for housing the looped steel billet.

1 2. An apparatus as claimed in claim 4 wherein said means for compensating possible temperature drop further comprises at least a burner for heating the looped billet.

1 3. An apparatus as claimed in claim 3, wherein said device for cooling is a water spray trough.

14. An apparatus as claimed in claim 3, wherein said device for cooling is an air jet cooling chamber.

1 5. An apparatus as claimed in claim 1, 2, 3, 4, 5, 6 or 7 wherein said unit loop accumulator is succeeded by a means for laying down each loop of a steel-billet successively on a succeeding conveyor means for transferring the loop as partly overlapped and densely compacted coils.

1 6 An apparatus as claimed in claim 8, wherein said means for laying down the billet is a loop layer.