CA1191322A - Bearings for continuous casting roller aprons - Google Patents

Abstract

BEARINGS FOR CONTINUOUS CASTING ROLLER APRONS

ABSTRACT OF DISCLOSURE

Rollers used in roller aprons, which support and guide the metal strand formed in a continuous casting mold, are made of a fixed shaft and elongated roller sleeve sections which are rotatably mounted upon the shaft. The shafts are fastened upon spaced apart rails secured to support plates. Bearings are arranged between the ends of each sleeve section and its shaft. Each bearing comprises a journal type bearing part and a thrust type bearing part. The journal type bearing part includes a cylindrical bronze sleeve non-rotatably fitted within its roller section end. A "Teflon", bronze impregnated, thin wall liner bushing is fitted within a wide recess formed in the interior wall of the outer end of the bronze sleeve to thereby form about one-half of the journal bearing inner wall surface which is arranged in rotatable contact with its shaft: A bored support member, through which the shaft is extended and which connects the shaft to a rail, has a cylindrical part fitted into an endwise opening channel in the adjacent roller sleeve end. A transversely arranged, disk-like thrust bearing plate mounted on the inner transverse surface of the cylindrical part, engages with the co-planar, annular surfaces forming the outer ends of the bronze sleeve and its teflon liner bushing to provide the thrust bearing part.

Description

~89.146 BACKGROUND OF INVENTION

The invention herein relates to a bearing construction for rollers used in supporting and guiding the metal strand formed ;n a continuous casting process. The process itself and the apparatus used therewith is generally described in the patent to Jackson, U.S. Patent No. 4,023,612 issued May 17, 1977.

In general, the continuous casting process involves the gravity pouring of molten metal, such as steel, into the upper end of a box-like mold which has an open bottom. The mold is cooled, such as by water flowing through its walls.

As the metal cools, it forms a strand or slab having an outer, solidified skin that forms where the molten metal contacts thè interior, cooled walls of the mold, and an inner molten core. This strand emerges downwardly through the open lower end of the mold. Then the strand is curved into a horizontal direction. The elongated strand is guided and supported between roller aprons which comprise a large number of support rollers. Meanwhile, water sprays are directed, between the rollers, upon the outer surface of the strand to continue the cooling process so that the strand ultimately becomes completely solidified.

As the slab or strand moves in the horizontal direction, supported upon rollers, it i5 cut into lengths. The cut slab lengths are then removed for further processing, such as for rolling into sheet steel or the like.

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The st:rand or slab :is typi.c~:Lly rectcl.ngular :in cross sect:ion, as for e~amp.l.e fou:r t.o ni.ne inches in thlckness and about -three to five feet .in width. The support and guide ~ollers engage the wide opposi-te Eaces of -the strand. Because of the intense heat, substantial loads due to -the we.igh-t of the metal and -the tendency of the strand to bow outwardly under -the internal ferrostatic pressure of the molten core, and the water and steam atmosphere surrounding them, the bearing constructions and supports for the rollers tend to wear out or fail relatively quick:Ly. When this happens, this requires shut-downs of the operation, replacement of damaged or disabled parts and then start-ups which are time consuming and difficult because of the continuous nature of the casting operation.
The rollers are formed oE an inte.rnal, non-rotatable shaft whose opposite ends are secured to end rails. Each shaft may be additionally secured between its ends to intermediate rails. Tubular roller sleeve sections are rotatably mounted upon each shaft. These roller sleeve sections engage the adjacent metal strand face. Thus, bearings are arranged between the rotatable sleeve sections and their shafts upon which they are mounted ~or rotation.
The i.nven-tion herein relates to an improved bearing con-struction for the rollers, which construction substantially increases the life of the bearings, as compared to prior bearing constructions.
SUMMARY OF INVENTION
The invention herein contemplates an improved bearing construction for use between the fixed shaft and the surrounding rotatable roller sections carried by the shaft. The bearing con-struction is formed in two parts, namely, a journal type bearing part and a thrust type bearing part. I'he journal part comprises a bronze type bearing sleeve press-fitted within the roller sections, at each end thereof, for a non-slip~ frictional engagement with the interior wall of the roller sec~ion. The inner wall of the bronze bearing sleeve is rotatably or slip-fitted upon -the shaft.

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OS9.146 A thin wall liner bushing of a low coefficient of friction material, such as a "teflon"-bronze impregnated material, is inserted within the bronze sleeve. The liner flts within a recess in the interior of the bearing sleeve andoccupies roughly half of the interior wall surface thereof. Thus, the inner wallsurface oE the thrust bearing is formed of roughly one-half low coefficient of friction "teflon"-type material and the other half of bronze bearing material.
The bronze bearing material, being of higher compressive strength, handres more of the compressive loads while the frictional drag and wear is reduced considerably by the teflon liner~

In addition to the journal bearing, the thrust bearing part is arranged to handle the lateral or endwise shifting of the roller sections which occur in operation. Such thrust bearing is formed of a bored support ring-like member which is connected to a support rail and through which the shaft passes.
One end of the member is telescopically fitted within an end channel or recess formed in the roller sleeve. A bronze disk thrust bearing member is arranged wlthin the recess between the end of the member and ~he adjacent annular end surface of the bronze hearing sleeve and exposed "teflon" liner. Hence, movement of the roller section towards the support member results in a bearing engagement between the disk, the bronze sleeve; the exposed end of the "teflon"
liner, and the adjacent interior wall of the recess formed in the roller section.
This arrangement provides the necessary strength and slippage for rotation of the roller under the load of the metal strand.

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r[~he :Lmproved bear:i.ncJ const:t-uct:i.on herein appears to g:i.ve a much longer liEe than conventional bear:incJ arrangemenks and more particularly, permi-ts -the use oE smaller diameter rollers than tha-t permitted by prior conventional bearing arrangements. Consequent].y, it is possible to use more rollers on the rol.ler apron, which is a considerable advan-tage in improving the equipment. That is, with smaller diameter rollers and with more rollers formed on the roller aprons, there is less space between -the rollers and more lines o-f pressure to contain and guide the continuously formed slab, particu-larly in the areas where the skin is thin and the molten core pres-sure is still high enough to bow or bulge the slab skin outwardly.
The use of a low coefficient of friction material such as Teflon* or the Teflon*-bronze impregnated material would ordinarily not be considered feasible in the environment of roller apron con structions. That is, the loads, heat, and destructive atmosphere normally would be expected to rapidly destroy such material and prevent its use. However, with the constructions as described in this application, the bearings are unexpectedly stronger and able to sustain the pressures and loads better -than conventional journal bearings.
Further objects and ad~antages of this invention will become apparent upon reading the following description, of which the attached drawings form a part.

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08~.146 DESCRIPTION OF DRAWINGS

Fig. I is a schematic view of the continuous casting process.

Fig. 2 is an enlarged, end view9 schematically showing a pair of opposed roller apron sections with the continuous cast strand between them.

Fig. 3 is a perspective view of the apron plate or roller support plate.

Fig. 4 is an enlarged plan view of a two section roller mounted upon the support plate.

Fig. 5 is a cross sectional, elevational view, of one end and the middle of the roller illustrated in Fig. 4.

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Fig. 6 is an enlarged, partly cross sectional, perspective view showing the disassembled parts which make up the end connection and bearing construction.

Fig. 7 is an enlarged, partly cross sectioned, perspective view showing the disassembled parts which make up the middle bearing construction of a roller.

DETAILED DESCRIPTION

Fig. 1 schema~ically illustrates the continuous steel casting process. The equipment begins with a ladle 10 which carries molten steel 11 from the furnace to the continuous casting equipment. The mslten steel gravity drops downwardly from the ladle either through a nozzle 12 or by tipping the ladle for pourin~ into a tundish 13. A rese~voir of molten steel in the tur,dish provides the continuous flow of molterl metal downwardly, by gravity, into the upper, open end of a water cooled continuous casting mold 14.

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0~9.146 The water cooled mold is conventionally made of opposed side ~alls and end walls, connected together to form a box-like construction with open upper and lower ends. An example oE this type of mold construction is shown and described in the patent to Floyd R. Gladwin, U.S. Patent No. 3,964,727issued June 22, 1976.

The particular mold used here is imrnaterial to the bearing construction which is the subject matter of this application. However, the mold typically forms a continuous strand or slab which is on the order of about four to nine inches in thickness and three to five feet in width, although the dimensions may vary considerably from that given above.

When the molten steel is poured into the upper end of the mold, the portions of the metal in contact with the water cooled mold interior walls begin to solidify rapidly and form a thin skin. Within the skin is the molten core.

Thus, as the slab or strand 15 gravity rnoves downwardly through the open lower end of the mold, it comprises a rougly rectangular shaped in cross section envelope of solidified skin within which is the molten core. The molten metal within the slab exerts a substantial outward ferrostatic pressure which tends to bulge the skin outwardly.

The strand passes through cooling plates 18 or cooling rollers or pull rollers, as ~he case may be depending upon the kind of equipment used.
Frorn that point downwardly, water spray nozzles 19 are directed upon the strandto chill it and continue the cooling of the core. Meanwhile, roller apron guide rollers 20 guide the strand downwardly and then along a curve until the strand is arranged horizontally. These guide rollers also hold the strand against bulging because of the interior ferrostatic pressure.

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38~.146 The roller aprons are forrrled in sections or units, as illustrated for exarnple in Fig. 2. These units are arranged to form curved upper units 21 and lower units 22 between which the strand 15 is guidedO

When the strand turns into the horizontal direction, it is carried upon support rollers 24 which are made in the same way as the guide rollers 20.
However, the support rollers 24 are carried upon suitable support bases or base construction sections 25. The support rollers move the strand beneath a conventional cutter 26 which cuts off pre-determined slab lengths 27. These slablengths are then moved into storage or transportation areas for later use in steel fabrication processes, such as for use in a rolling mill to make sheet material or the like.

The roller apron sections, each have an apron plate 30 (see Figs. 2 and 3) which is provided with parallel end rails 31 and one or more center rails 32 upon which the rollers are mounted. The plates are also provided with suitable lar~e openings 33 through which the water spray may be directed, between the rollers, against the metal strand.

The rollers 20 are each formed of a central steel shaft or axle 35 upon which are rotatably positioned roller sleeve sections 36. The shaft 35 is fixed against rotation and preferably is chrome plated by any suitable conventional techniqueO The opposite ends of the shafts are secured to rails 31 by rneans of end support members 38. A bored opening 39 in such member receives the end portion of a shaft.

The support member is secured to the rail first by means of a squared section 40 which snugly fits within one of the notches 41 formed in eachof the rails. In ad~ition, an end cap 42, which is cup shaped to fit over and receive the end of the shaft, is proYided with fastening ears 43 which are secured to the adjacent r~l portion. Holes 44 formed in each of the ears are aligned with corresponding holes 45 in the rail so as to receive fastening screws 46 (see Figure 6).

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089.146 Eacll end support rnember 38 inclucles a cylindricaJ end portion 47 which fits into an annular recess or groove 48 formed in the opposite ends of the roller sleeves 36. One or more conventional autolnotive engine type p;ston rings49, posi~ioned wi~hin grooves formed in the end member cylindrical portion, seals against the inner surface of the sleeve recess.

A bronze type thrust bearing disk 50 is arranged within the sleeve recess 48 adjacent the transverse end of the support member cylindrical portion 47. An opening 51 throu~h the disk receives the shaft 35.

The diame$er of the interior surface 55 in the roller sections are larger than the shafts upon which the roller sections are positioned. Moreover, enlarged bearing recesses 56 are formed at the opposite ends of the roller sleeve openings.

Bronze journal type bearing sleeves 58 are press-fitted within the bearing recesses 56 for non-rotatable, frictional mounting therein. Each bearingsleeve 58 is also provided with an end recess 59 which receives a tubular shaped"teflon" liner 60. The liner is roughly one-half of the length of the sleeve 58 so that its inner wall surface forms about one-half of the bearing or sli~fit surface of the journal bearin~ for rotatably enveloping the fixed shaft 35.

By way of example, the "teflon" liner may be on the order of about 0.125 thick and rnay be bron2e impregnated teflon tubing. This material iscornmercially available, although it has not previt>usly been thought of as a suitable bearing material f or this environment because of its relative low strength, etc.

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0~9.146 Th~ fre~, annular ends of the "teflon" liner, surrounding bronze bearing slee\~e 5S, and an annulal end wall 61 formed within the roller sleeve recess 4~ provide a coplanar surface for engaging the bronze thrust bearing disk50. Normally, the disk 50 is spaced a short distance from that surface.
Engagement takes place when the roller sleeve section moves in the direction of the disk which occurs from time to time during operation, but ordinarily not continuously. Figure 5 illustrates the normal spacing between the disk 50 and the annular surface withir the roller sleeve recess 48.

The end of the shaft 35 is fixedly connected to the end cap 42 by means of threaded openings 63 formed in the shaft (see Figure 6) which are aligned with openings 64 formed in the end cap to receive fastening screws 65.
Further, an O-ring 66 arranged within a ~roove formed in the shaft 35, seals theshaft to the interior of the end cap. An automotive type piston ring of the appropriate size may be used for such an O-ring seal.

It can be seen that the chrome plated shaft 3S is non-rotatably secured to the rails so as to span a pair of spaced apart end rails. Meanwhile, a number of sleeve sections 36, rotatably supported upon the shaft, may independently rotate thereonO The number of roller sleeve sections may be varied and typically would be on the order of 2, 3 or 4 sections, depending uponthe span required. Each of the roller sleeve sections is provlded with the interior journal bearing construction descrlbed above as well as the thrust bearing construction. To form the thrust bearing construction between the ends of the shaft, that is at the middle rails 32, the end support member is slightly mod;fied to form a middle support mernber 68, as shown in Fi~ure 7. Such middle support member includes the squared section 40 and the cylindrical portion 47, but includes a second cylindrical portion 47a which also has one or more pis~on ringtypes of seals 49, as described above. Otherwise, the middle support member 68 is the same in construction as that o~ the end support member 38.

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089.146 The squared portion 40 of the middle support mernber 68 snugly fits into one of the notches 41 formed in the center rail 32. It is locked in the notch by means of a lock bar 70 which rests upon the upper surface of the rail and the upper flat surface of the squared portion 40. The lock bar is secured tothe rail by means of screws 71 extending through aligned holes 72 and 73 in the lock bar and ~he rail, respectively. The lock bar may be in the forrn of short lengths or of one long length to match the length of the central r~il. ~

Where the rollers are formed of more than two roller sleeve sections, additional middle rails 32 are moun~ed upon the apron plate 30. The rails 32, as well as the end rails 31, may be suitably welded to the plate or o~erwise permanently affixed thereto.

The space between the interior of the tubular roller sleeves and the shaft upon which :the sleeves are mounted, is packed with a suitable high temperature lubricant or grease. This lubricant is applied throu~h an axially extending hole 75 formed in each shaft. Transverse holes 76 carry the lubricant from ~e hole 75 into the spaces between the adjacent inner wall surfaces of the roller sleeve sections and the outer surface of the shaft, as well as in the small spaces between the journal bearings and the shaft. The lubricant is applied, when necessary, through a central opening 77 forrned in the end cap, which is ali~nedwith the opening 75 in the shaft. The end cap opening is normally closed by a screw type closure 78 (see Figures 5 and 6).

Although the dimensions may vary considerably, by way of illustration for the purposes of determinin~ relationships of parts, a roller rnade ln accordance with ~e construction described herein may comprise a shaft of about five feet in length with an O.D. of about 3 1/2 inches. The roller sleeve 3~

089.146 may have an O.D. of abou~ 7 1/4 inches and if three sections are used, each would be sligh~ly less than 16 inches in length with a wall thickness of about 3/4 inch. The bron~e journal bearings may be on the order of about two inches in axial len~th and about 1/4 to 3/8 inches in wall thickness. The liner of "teflon"
material may be on the order of about one inch in axial length and about 1/10 inch, e.g., .125, in wall thickness and may be made of a split ring configuration, that is, a length of sheet material which is rolled into a circular cross-sectional shape.

Conventional rollers are ordinarily of a considerably greater diameter. Thus, the bearing construction herein permits the reduction in O.D.
of the rollers, thereby permitting more rollers to be used along the length of the continuously cast strand, with a space in between the rollers being much reducedas compared ~o the conventional aprons.

In operation, the apron sections are suitably supported upon a framework (not shown) which is conventional so as to form parallel, spaced apart, arrangements between which the strand passes (see Figure 2). The rails of each apron are curved, either concave or convex, so as to mount the rollers 20 in a similar curved path. Thus, as the strand emerges downwardly from the mold 14, it begins curving due to the guiding of the rollers. The rollers are subjected to considerable forces or loads due to the weight of the metal as well as ~e tendency of the metal to bulge or bow outwardly because of the f errostatic pressure of the molten core within the surrounding skin. However, as the skin thickens, along the downward curved path of the strand~ the core pressure is contained within the skin itself. Nevertheless, the load upon the rollers and the adverse atmosphere within which it operates would normally tend to rapidly destroy the bearing constructions. However, the bearing construction herein, J 13; 2 089.146 despite the much limited compression or load resistance o~ ~he "teflon" bearing section as compared with the bronze section, provides a much greater life than an all bronze bearing, unexpectedly. Thus, the roller apron may be used for many more continuous casting production hours than the previously known constructions. Then, when the bearings ultimately begin to fail, the operation may be shut down and the roller sleeve sections, which normally are made of a suitable steel material, may be removed from the shafts and the bearings rebuilt relatively easily because of ~heir simplified construction.

Having fully described an operative embodiment of this invention, I now claim:

Claims (9)

1. In a roller apron having spaced apart rails with elongated rollers extending between the rails and with the rollers each formed of a center shaft and with means fixedly mounting the shaft upon the rails, and a surrounding cylindrically shaped roller sleeve rotatably fitted around the shaft and having its inner circular wall spaced from the outer surface of the shaft, an improved bearing construction comprising:
a journal type bearing arranged between the shaft and roller sleeve and formed of an elongated, thin wall, generally cylindrically shaped bearing sleeve surrounding the shaft and tightly in surface to surface contact with the inner wall of the roller sleeve so as to form a non-slip, frictional engagement with the roller sleeve and to form a rotatable contact with the shaft;
an annular, cylindrically shaped recess of substantial width formed in the inner surface of the roller sleeve and a thin-wall, cylindrically shaped liner bushing being tightly and non-rotatably fitted within the recess, and the inner surface wall of the bushing rotatably engaging the shaft and forming a part of the shaft engaging wall surface of the bearing sleeve;
and said bearing sleeve being formed of a bronze-like bearing type material of relatively substantial compressive strength, and with the bushing being formed of a lower coefficient of friction, but lower compressive, material, such as a "teflon" material.

2. A construction as defined in claim 1, and said recess extending for roughly about one-half of the axial length of the bearing sleeve, and the bushing axially extending for substantially the full length of said recess.

3. A construction as defined in claim 2, and said recess being of a depth which is considerably less than one-half of the wall thickness of the bearing sleeve.

4. A construction as defined in claim 2, and said recess being open endwise at its end which is nearest to its adjacent roller sleeve end.

5. A construction as defined in claim 4, and the means for mounting at least one end of the shaft upon its adjacent rail comprising a sleeve-like support member telescopically receiving a portion of the shaft, and having means for mechanically and non-rotatably securing the member to the rail and the shaft;
said support member having an inner, cylindrically shaped end portion fitted within an annular groove formed within the adjacent roller sleeve end, so that said portion is surrounded by the roller sleeve, but fitted within its end;
a disk-like thrust bearing secured to the inner face of the member, which face is located within said end groove of the roller sleeve, with the thrust bearing normally spaced a short distance, measured axially, away from the adjacent bearing sleeve and bushing end surfaces, wherein upon axial shifting of the roller sleeve in a direction towards said support member, an endwise thrust-type slip engagement will take place between said bearing sleeve and bushing end surfaces and the disk-like thrust bearing.

6. A construction as defined in claim 5, and including a piston-type sealing ring arranged between and in contact with the stationary, outer surface of said support member portion and the rotating inner wall surface of the roller sleeve groove within which said portion is fitted for sealing therebetween.

7. A construction as defined in claim 5, and including a cup shaped end cap fitted over the end of the shaft and engaging the adjacent end of the supporting member, with said cap being mechanically fastened to the adjacent rail and to the shaft.

8. A construction as defined in claim 5, and including identical, but mirror image, bearing parts as set forth above, formed on the opposite ends of each shaft.

9. A construction as defined in claim 8, and each said roller sleeve being formed in at least two sections, with each inner end, which comprise adjacent ends of each roller sleeve section, and the shaft portion between said sections including substantially the same bearing constructions as set forth above.