FIELD OF THE INVENTION:
The present invention is directed to a method of replacement of slew bearing used in the heavy-duty turret designed to support two teeming ladles in continuous slab caster in steel plants. The replacement becomes imminent when such bearing gets worn out. Due to continuous operation of such slab caster plants round the shifts, the slew bearing supporting the turret is subjected to wear and tear, especially where the teeming ladle carrying the liquid metal is of very heavy weights for example 300 tons and gross carrying capacity of turret of about 920 tons. Due to the presence of such worn out slew bearing in the system in continuous caster, the turret turning motor draws very high starting current in the range of about 140-142 Amp as compared to the normal value of 79 Amp. The present invention is directed to a method of replacement of slew bearing wherein the ladle supporting top frame with turret jacked-up with hydraulic jacks at selective support points and lifted vertically by about 120mm to facilitate said replacement without use of Electrical Overhead Traveling (EOT) cranes.; additionally, temporary supporting structure is built along side the slew bearing and maintaining advantageous relationship with the foundation frame such that the slew bearing is pulled out from below the top frame over the said supporting structure, without continuous involvement of the (EOT) cranes. The present process takes less time of around 8-10 days as compared to about 20 days time in conventional method of total dismantling engaging EOT cranes. Present method also involves less down time/manpower idling and more importantly the production can continue with the unaffected caster even during the replacement operation. The invention has immense potential to be adapted in any of the steel plants under similar operating facilities, with significant economic advantage.
BACKGROUND AND PRIOR ART:
The present invention relates to a new method of replacement of the slew bearing and in particular worn out slew bearing due to continuous casting operation by the two numbers slab casting machines. Such slew bearings for Top frame and Turret, supporting two teeming ladles, normally exhibit a working lifetime of about 7-8 years while in continuous regular operation on load. These machines are supported by heavy-duty turret weighing 390 tons and top rotating frame with arms capable of handling two full teeming ladles with gross carrying capacity of 920 tons. The turret with top frame is supported on the slew bearing mounted with holding down bolts with top frame and the foundation frame. It was
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observed during the regular shift operations of slab casting that the starting current of the Turret Motor in one of the caster, after long use, was of high value in the range of 140-142 Amp in place of a normal value of about 79 Amp in one of the slab casting machines. The reason for this was identified and attributed to the worn out slew bearing because all the actions usually recommended for eliminating such high starting current e.g. tightening of loosened holding down bolts or adjusting the disc-brake directed to reducing the starting torque of the turret motor to normal level, failed to yield satisfactory result.
The conventional methods of replacement of Slew bearing of such heavy duty turret with carrying capacity of about 920 ton and the total weight of turret with top frame being about 390 tons, as recommended by the maintenance manual provided by the machine manufacturer, needs to be carried out by completely dismantling of the top frame with arms, the hydraulic cylinders etc., to facilitate safe change over of the huge Slew bearing that is having an OD of 5.232 meter, ID of 4.44 meter, a height of 225 mm and weighing 8 tons approximately. The difficulty in this method suggested by the manufacturer of the original equipment was that the process of dismantling the top frame and turret would involve two numbers EOT cranes of 450/110T/20T capacity and a tackle. The complete dismantling and the change over process of the Slew bearing would have taken approximately 20 days and the production in one casting machine was going to be affected seriously when the replacement of the slew bearing was undertaken for the other machine because of the involvement of the two EOT cranes in the same production bay for the dismantling work.
It was thus the need for devising a method such that the worn out Slew bearing could be replaced with a new one for the turret of a heavy duty continuous slab caster, without much complexity and with minimum breakdown time avoiding use of EOT cranes and involving minimum manpower. Use of hydraulic jacks as an alternative way of lifting the top frame and turret, thus came into consideration for the present invention.
OBJECTS OF THE INVENTION:
Thus the basic object of the present invention, is to provide a method of replacement of the worn out slew bearing which would be simple and convenient to carry out and would favour reducing the high starting current of turret motor, and thereby facilitate simple, cost-effective change over of the said bearing with much reduced man- machinery involvement.
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A further aspect of the present invention is to provide for a simple and convenient replacement of the worn out slew bearing maintaining/continuing partial production in slab casting utilizing the unaffected machine/s and avoiding complex replacement procedures.
Yet another aspect of the present invention is to build up a temporary bearing supporting structure maintaining favorable relationship with the foundation frame such that the slew bearing could be pulled out from below the top frame and turret lifted by means of hydraulic jacks, sliding over the said temporary supporting, structure and replace with a new one with the help of the same supporting structure.
A further object of the present invention is to reduce the total breakdown/dismantling and bearing replacement time from around 20 days following conventional method by engaging EOT cranes, to about 8 to 10 days for the total activities relating to replacing the worn out slew bearing with a new bearing.
Yet another object of the present invention is directed to substantial financial saving by reducing breakdown time, man-hours loss and production loss in order to achieve economy in the slew bearing replacement method.
A further object of the present invention is to carry out the entire activities related to replacement of the slew bearing of the turret of continuous slab caster in a safe and secured way despite the huge size and heavy weight of the related top frame, turret or the bearing itself being handled /moved during said replacement.
SUMMARY OF THE INVENTION:
The basic aspect of the present invention is thus directed to a method for replacement of slew bearing of ladle turret, of continuous steel slab casting machine comprising:
lifting the top frame alongwith slew bearing vertically upward to desired height, using jacking means, support structure and stool means of requisite capacity;
providing a bearing support structure and channel such as to facilitate lowering and releasing the damaged slew bearing ;
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providing new slew bearing on said support structure and disposed below the said top frame;
loosening and releasing the jacking bolts such as to lower the top frame on said bearing and securely fixing the bearing to said top frame;
releasing and removing said jacking means, support structure and stool arrangement;
restoring all operative connections including putting the disc brake in position to thereby complete the replacement of the slew bearing.
According to another aspect of the present invention, the method for replacement of slew bearing of ladle turret comprising placing said lifting jacking means preferably hydraulic jacks at selective locations to apply jacking force through fabricated brackets adapted for requisite strength and welded to the top frame at pre-determined locations to facilitate the said desired lift.
According to another aspect of the present invention, said hydraulic jacks used are four in numbers, each 500 ton capacity, to lift the turret with top frame up to a height of about 120 mm to facilitate said replacement.
According to another aspect of the present invention, said selective location of the four numbers jacking points are marked on the welded brackets with respect to the 20° axis, and are located at equal centre distances on either side of the non-casting axis and equally distributed total centre distance across the casting axis of turret.
According to yet another aspect of the present invention, the method for replacement of slew bearing of ladle turret comprising providing a temporary bearing supporting structure fabricated and erected with two numbers ISMC 150 at top, maintaining preferred relationship with the foundation frame to facilitate pulling out of the worn out bearing by sliding the bearing over the said temporary structure and replacing with new one, the said bearing weighing about 8 tons, free of any required continuous engagement of EOT cranes.
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According to yet another aspect of the present invention, the method of replacement of slew bearing of ladle turret, said turret with top frame is placed at 20°position from non-casting axis for ease of bearing handling by crane.
According to a further aspect of the present invention directed to replacement of slew bearing of ladle turret wherein the soft point on inner race of the new bearing correspond to an axis at 90°to the casting axis with Soft point of outer race maintained at 90° to the 20° axis.
According to a further aspect of the present invention directed to replacement of slew bearing of ladle turret wherein said replacement of slew bearing is carried out to replace any damaged slew bearing causing consumption of high levels of starting current of the turret motor and achieve a normal starting current of 79 Amp and running current range between 51-26 Amp, resulting in energy saving.
According to another aspect of the present invention, said method of replacement of slew bearing associated with one slab casting machine, advantageously facilitate uninterrupted production by the other unaffected continuous slab casting machine unit, supported by the same top rotating frame and turret.
According to another aspect of the present invention, said method of replacement of slew bearing associated with one slab casting machine, involve removing all M 42 bolts 96 numbers each on the outer and inner races, used to hold the slew bearing with top frame, except for six numbers equispaced bolts selectively left out on PCD on outer race of bearing to facilitate lowering of the bearing on two ISMC 150 on said bearing supporting structure.
According to yet another aspect of the present invention, said six numbers jacking bolts are disposed at selective equispaced holes on the outside race of new slew bearing to raise it by about 10mm, to favour removal of channel support and lowering of the bearing on foundation frame.
According to a further aspect of the present invention, the total time for replacing the slew bearing by the present method takes about 8-10 days time as compared to about 20 days required by following the conventional method for similar such replacement of slew bearing.
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According to yet another aspect of the present invention, the method of replacement of the slew bearing of the turret for continuous slab casting machine is a safe and secured way despite the huge size and heavy weight of the related top frame, turret or the bearing itself being handled /moved during said replacement.
According to yet another aspect of the present invention, it is directed to substantial financial saving by reducing breakdown time, man-hours loss and production loss in order to achieve economy in the slew bearing replacement method.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES:
Figure 1: Bearing supporting structure with top frame - arrangement view from front. Figure 1A: View of turret top frame of continuous slab casting machine.
Figure 2: Bearing supporting structure- arrangement view from top.
Figure 3: Illustration of orientation of turret in relation to crane for bearing handling.
Figure 4: Illustration of location of Soft Point of inner race of existing bearing.
Figure 5: Illustration of location of jacking points for lifting of top frame and turret through welded brackets.
Figure 6: Illustration of jacking arrangement of the turret with top frame Figure 7: Illustration showing removal of old slew bearing. Figure 8: Illustration showing the new slew bearing placed in position. DETAILED DESCRIPTION WITH REFERENCE TO ACCOMPANYING FIGURES:
Reference is first invited to figure 1 that illustrates the bearing supporting structure(BSS) for replacing the worn out slew bearing(SB) according to the present invention along with the turret and top rotating frame(TF) with arms. The total scheme of the bearing
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replacement work according to the present invention was developed and activities were charted out in sequence maintaining interdependence thereof, so that the total execution time can be minimized with less manpower and without continuous involvement of EOT cranes, during the entire sequential activities involved. There were two phases of the activities involved - the preparatory activities and the Shut down activities.
As already discussed, that the present invention involves lifting of the top frame(TF) of turret(TR) using hydraulic jacks (HJ) instead of conventional deployment of two numbers of EOT cranes for entirely dismantling the elements of the total superstructure for the said replacement work. Thus the preparatory activities include fabrication of top jacking plate with stiffeners, two numbers of brackets(BKT) for jacking point(JP), bearing supporting structure(BSS) with star frame, stools(ST) of requisite numbers and sizes etc. and arranging the necessary equipments and tools viz four numbers 500 ton hydraulic jacks(HJ), eye bolts , jacking bolts, chain pulley block, welding machine etc., all moved to the work site where the replacement of the slew bearing has to be carried out. The next phase involves the Shut down activities in a number of steps. In the step-I, activities involve dismantling of the auxiliary mountings and bolts such that the turret(TR) with top frame(TF) as viewed in figure 1A, is made ready for the subsequent stage. Both the arms(AR) of turret(TR) were placed in the lowest position. The connections of hydraulic, grease, air and electricity, provided for the functions of various gadgets of the concerned continuous slab casting machine are disconnected. Three numbers disc brakes along with discs were removed. The side fire protection cover and the rotary joint inside turret were dismantled and lifted/removed. One number lownder for the affected machine was also removed.
Figure 2 illustrates the bearing supporting structure(BSS) provided with star frames for enough rigidity, temporarily fabricated and erected in step-I, to facilitate the bearing replacement without engaging the EOT cranes. The top of this supporting structure is at the same level as that of the foundation frame so that the bearing weighing about 8 tons can be moved or pulled by sliding over it by chain pulley or wire rope and winch in a safe manner.
The turret was placed at 20° position from non-casting axis for ease of bearing handling by crane, particularly for removing old slew bearing(SB) from or placing the new bearing on the supporting structure. Figure 3 illustrates the orientation of the turret with respect to the crane to facilitate bearing handling ( for example, crane bay between A and Bl row of
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columns). Soft pomt(SP) of the existing bearing, as illustrated in figure 4, was located and noted for matching of the same position during mounting of new bearing. Usually, both the inner and outer race of the slew bearing(SB) is fastened to the top frame each by 96 numbers of M 42 bolts. All these bolts, except for six numbers selectively left out on outer race at equispaced locations on the outer PCD, are removed at step-I. The jacking plate (JP) with stiffeners and the jacking brackets(JB) are welded in right position on to the turret(TR) with top frame(TF).
In step-II activities involve lifting and supporting of rotating frame(RF) during shut down; At this step, two numbers base slab are placed, leveled and locked with the foundation frame. The four numbers jacking point(JP) centers were marked with respect to 20° axis as detailed in figure 5, at a longitudinal center spacing of 2625mm and a transverse center spacing of 2 x 2828mm, measured from the casting and non-casting axes respectively, accordingly four numbers of hydraulic jacks with stools atop were installed to support the turret top frame(TF) at the marked points, at virtually no load. Next the hydraulic jacks(HJ) were operated for loading top frame(TF) gradually and evenly at four points and jacking it up along with the slew bearing(SB) by about 120 mm. Figure 6 illustrates the jacking arrangement of the turret(TR) and top frame(TF) with existing slew beanng(SB), prior to dismantling.
In step-III, involve activities related to removal of old bearing the six numbers bolts on outer racing were loosened so that the slew bearing was gradually lowered and rested on the two numbers of ISMC 150 installed on the bearing supporting structure. The bolts were subsequently removed along with the nuts. The worn out old slew bearing(SB) was taken out from below the top frame(TF) by pulling the bearing and sliding over the channel and removed by crane. The figure 7 illustrates the removal of old bearing along the supporting structure.
Step-IV relates to installation of new bearing; at first the new slew bearing was put on the supporting structure by means of crane. Next, Soft point(SP) of the new bearing was located and the bearing seating surface was inspected and cleaned. The new slew beanng(SB) was pulled below top frame by sliding it over the supporting structure. The outer holes of the bearing were matched with those on top frame and six numbers of jacking bolts were mounted at equispaced locations on the PCD of 4980mm at outer race(OR). The bearing was lifted by about 10 mm advantageously by tightening these
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jacking bolts such that the supporting channels are released and removed now. The Inner race(IR) was now rotated to match the soft pomt(SP) of inner race(IR) with an axis at 90° to casting axis. Next, all the 96 numbers 045 bolts were mounted in the holes of the inner race at a PCD of 4540mm, with the nuts at top side and keeping 40mm thread length above each nut. The six jacking bolts were simultaneously loosened to lower the bearing and finally it rested on the foundation frame. These six bolts are now removed. The soft pomt(SP) of outer race(OR) was kept at 90° to the 20° axis. Next the holes on outer race(OR) are matched and all 96 bolts inserted and nuts placed as of the inner race. Now the top frame is lowered on the bearing gradually, resting on the supporting structure. The inside and the outside bolts were tightened as per the sequence such that uniform bearing sitting is ensured. Figure 8 shows the mounting and assembly of the new slew bearmg(SB) on the turret top frame(TF).
Step V involves recommissiomng of the turret; all jacks, stools and supporting structures removed/dismantled. The connections for hydraulic, grease, air and electricity are restored. The Disc brakes put on position. The Fire protection covers are again erected. The system is tested and put to trial run both at no load and on rate load capacity and the performance was found satisfactory. The range of the above programmed activities was completed by 8 days time. After replacement of the worn out slew bearing with new one, the starting current for the turret motor came down to its normal value of about 79 Amp and the operating current on load was found to be 51-26 Amp, without any abnormal signal.
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WE CLAIM:
1. A method for replacement of slew bearing of ladle turret, of continuous steel slab casting machine comprising:
lifting the top frame alongwith slew bearing vertically upward to desired height, using jacking means, support structure and stool means of requisite capacity;
providing a bearing support structure and channel such as to facilitate lowering and releasing the damaged slew bearing ;
providing new slew bearing on said support structure and disposed below the said top frame;
loosening and releasing the jacking bolts such as to lower the top frame on said bearing and securely fixing the bearing to said top frame;
releasing and removing said jacking means , support structure and stool arrangement;
restoring all operative connections including putting the disc brake in position to thereby complete the replacement of the slew bearing.
2. A method for replacement of slew bearing of ladle turret as claimed in claim 1
comprising placing said lifting jacking means preferably hydraulic jacks at selective
locations to apply jacking force through fabricated brackets adapted for requisite
strength and welded to the top frame at pre-determined locations to facilitate the
said desired lift.
3. A method for replacement of slew bearing of ladle turret as claimed in anyone of
claims 1 or 2 comprising providing a temporary bearing supporting structure
fabricated and erected with two numbers ISMC 150 at top, maintaining preferred
relationship with the foundation frame to facilitate pulling out of the worn out bearing
by sliding the bearing over the said temporary structure and replacing with new one,
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the said bearing weighing about 8 tons, free of any required continuous engagement of EOT cranes.
4. A method for replacement of slew bearing of ladle turret as claimed in anyone of
claims 1 to 3 wherein said replacement of slew bearing is carried out to replace any
damaged slew bearing causing consumption of high levels of starting current of the
turret motor and achieve a normal starting current of 79 Amp and running current
range between 51-26 Amp, resulting in energy saving.
5. A method for replacement of slew bearing of ladle turret as claimed in anyone of
claims 1 to 4 wherein the said hydraulic jacks used are four in numbers, each 500
ton capacity, to lift the turret with top frame up to a height of about 120 mm to
facilitate said replacement.
6. A method for replacement of slew bearing of ladle turret as claimed in anyone of
claims 1 to 5 wherein preferably the orientation of turret is placed at 20°position
from non-casting axis for ease of bearing handling by crane.
7. A method for replacement of slew bearing of ladle turret as claimed in anyone of
claims 1 to 6 wherein the said selective location of the four numbers jacking points
are marked on the welded brackets with respect to the 20° axis, and are located at
equal centre distances on either side of the non-casting axis and equally distributed
total centre distance across the casting axis of turret.
8. A method for replacement of slew bearing of ladle turret as claimed in anyone of
claims 1 to 7 wherein the soft point on inner race of the new bearing correspond to
an axis at 90°to the casting axis with Soft point of outer race maintained at 90° to
the 20° axis.
9. A method for replacement of slew bearing of ladle turret as claimed in anyone of
claims 1 to 8 wherein the said jacking bolts are disposed at selective equispaced
holes on the outside race of new slew bearing to raise it by about 10mm, to favour
removal of channel support and lowering of the bearing on foundation frame.
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10. A method for replacement of slew bearing of heavyduty ladle turret for continuous slab casting machine as substantially herein described with reference to accompanying figures.


Dated this 17th day of January, 2007

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A simple and cost-effective method of replacement of worn out slew bearing(SB) used in the heavy duty turret(TR) with top frame(TF) The method includes simple lifting of the top frame(TF) with turret by about 120mm, using preferably hydraulic jacks at selective support points and a temporary bearing supporting structure(BSS) maintaining advantageous relationship with the foundation frame(FM) such that the involvement of the Electrical Overhead Traveling (EOT) cranes is avoided. The present process reduces loss of manhours and production, by continuing production with unaffected caster during the replacement operation. Thus the present invention is not only faster, simpler and safe but also economic and energy saving; and has immense potential to be adopted in any of the steel plants in India or abroad, having similar facilities.