CLIAMS:1. An improved method of maintenance of a hot metal ladle comprising the steps of:
laying of a false bottom under condition that 80 – 90% of the top bottom lining of the ladle is washed off;
laying of false working wall under condition that ~ 60-70% of the side working lining walls is damaged; and
laying of false offset at approximately 120°on one off-set and 600 on the other under condition that ~ 60-70% ladles have been heavily eroded along belly lining portion.

2. An improved method of maintenance as claimed in claim 1, wherein the laying of false bottom is carried out comprising the steps of:
ramming the irregular surface of the ladle bottom is with castable up to roughly 2” thickness to develop a planar surface;
laying of 4.5” thick 45% Al2O3 brick this on the surface;
Ramming the false bottom with 60% HA castable on all sides where the Bottom meets the ladle wall.

3. An improved method of maintenance as claimed in claim 2, wherein the ramming provides the necessary locking of the bottom.

4. An improved method of maintenance as claimed in claim 1, wherein the false working wall is made by laying 50mm/40mm straight bricks on the wall of the ladle, longitudinally, impinged into 60% HA castable.

5. An improved method of maintenance as claimed in claim 1, wherein the sides are carefully laid to remove any joint gaps and also to avoid collinear joints instead the joints are staggered.

6. An improved method of maintenance as claimed in claim 1, wherein the laying of false offset includes step of laying 39% Al2O3 bricks (end arch) along the original off-set.

7. An improved method of maintenance as claimed in claim 1, wherein the layering of the false bottom, false side working walls, and false offset contributes for lesser abrasion of mother lining.
,TagSPECI:FIELD OF INVENTION
The present invention relates to an improved method for maintenance of hot metal ladle. More particularly the present invention relates application of ground-breaking maintenance practice in Hot Metal Ladle thereby causing the saving of energy, reduction of CO2 and also enhancing the hot metal ladle life.
BACKGROUND ART
In the prior art the maintenance practice was based on a rule based on experience that ladle is put down for maintenance when the remaining working lining thickness is at least 60 mm. In another method of maintenance, the ladle is put down for relining. Before the implementation of the disclosed novel maintenance method, the ladle was patched with 2” - 2.5” thick HA-50 castable. On completion of the patching exercise, the ladle was left for natural drying for twenty four hours and then for heating for next twenty four hours before putting into circulation. The said maintenance practice had a Schematic schedule (given below for example) which was to be strictly adhered to making the regime too rigid.:

Schematic schedule:
Last T/D-heat Present-heat Heat limit Max. heat Deviation Energy Req. (Gcal)
0 200 200 200 0 177
200 430 200 400 30 59
430 620 200 630 -10 59
620 800 200 820 -20 59

Where,
(a) Last T/D-heat = the number of heats on which the ladle was last time put temporarily down for maintenance.
(b) Present –heat = the present life of the ladle.
(c) Heat limit = maximum allowable heats taken between two consecutive T/Ds.
(d) Maximum heat = the maximum life up to which the ladle can go before being put down for maintenance.
(e) Deviation = Difference between present heat and the maximum heat.

This maintenance practice was effective till third repair i.e. 600 heats after this the ladle was at risk as much of the original working lining had been receded by this time and hence it was difficult to maintain the prescribed minimum allowable thickness of working lining, due to which very few ladles gave life beyond 800 heats forcing majority of the ladles down for relining in the range of 750-800 heats. As a result the year 2009-10 saw 44 HM ladles down and relined. Each relined ladle requires two extra days of pre-heating vis-à-vis repaired ladles (one day for repaired ladles whereas, three days for relined.). It was due to this low life and higher number of down HM ladles resulting in higher energy consumption on account of pre-heating, annually that this innovative method was devised and implemented.

Refractories are widely used as working linings and secondary (safety) linings in the metal processing and related fields. These ladle linings contain molten metal and slag in metal processing and transfer vessels. Some ladle linings also are used to contain the heat and gases associated with metal processing operations within the vessels. As used herein, a "metal containment" application is one in which containment of molten metal and slag is of primary or even sole importance, while a ''metal/heat containment" application is one in which both heat containment (insulation) of the vessel and containment of molten metal and slag are of interest.

Cracking of a ladle lining results when a bonded, brittle ladle is subjected to thermal and mechanical stresses. These stresses commonly result from expansion and contraction of the lining as a result of changes in the thermal environment. Cracking allows molten metal and slag to infiltrate into the lining, resulting in an isolated failure area in the metal processing or transfer vessel. Failure of a ladle lining due to cracking is much less predictable than erosion. Cracks often do not occur in an exposed area of the ladle lining so visual inspection usually is not helpful in identifying cracking. The nature of the cracks that form in a ladle lining also may vary with the ladle composition and the thermal conditions. Ladle linings characterized by weaker bonds tend to form micro
cracks under stress while ladle linings characterized by stronger bonds tend to form macro cracks under stress. Macro cracking is particularly undesirable because it results from the failure of high strength bonds.

In addition to being unpredictable, cracking failures can be catastrophic. A macro crack that extends completely through the lining from the hot face to the cold face (e.g., the steel shell side of a metal processing vessel) may allow molten metal and/or slag to reach the outer shell of the vessel by travelling through the crack. When this occurs, the molten materials can burn through the shell, which may result in extensive damage to equipment and/or injury to personnel. A burn-through of this type can cause long, Unscheduled delays in the operation to make repairs to the lining, steel shell and structure, and any surrounding equipment.
SUMMARY OF INVENTION
In view of the disadvantages of the prior art, a need exits for a hot metal ladle for metal containment applications that provides greater resistance to crack propagation, exhibits less brittle behaviour when bonded, and has a longer service life.

Therefore such as herein described there is disclosed a method of maintenance includes layering of false bottom, false working wall and false offset.

It is an object of the invention to provide a ladle for metal containment applications that is resistant to crack propagation, and particularly macro cracking.

It is another object of the invention to provide a ladle for metal containment applications that exhibits less brittle behaviour when the installed ladle has formed strong bonds in response to heat.

It is yet another object of the invention to provide a ladle for metal containment that provides a longer lining service life.

Therefore improved method for repair emphasizes at providing the ladle with a surrogate working-lining by providing a secondary working lining to the HM ladle after much of the original working lining have eroded.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrates the secondary lining as structures underwrite ladle, false working wall/ layer cross-sectional schematic repair in accordance with the present invention;
Figure 2 illustrates the false offset lining as structures underwrite ladle in accordance with the present invention;
Figure 3 illustrates the false bottom lining as structures underwrite ladle in accordance with the present invention.
DETAILED DESCRIPTION
Ladle linings for metal and heat/metal containment applications typically are consumable. They erode, crack, or otherwise are damaged by exposure to conditions within the vessel. When a certain amount of consumption of or damage to the ladle lining has occurred, repair or replacement of the lining is needed. Repair or replacement interrupts the metal processing operation, sometimes for an extended time. Some interruptions are unexpected while others are more or less predictable. Because repair or replacement of a ladle lining disrupts operations, it is desirable that the ladle lining perform in a predictable manner to allow for scheduled rather than emergency repairs.

Erosion of the ladle lining due to contact with the corrosive molten metal and slag results in a gradual consumption of the ladle lining. Erosion rates generally can be predicted by visual inspection of exposed portions of the vessel lining or other techniques. A predictable erosion rate can be established for a particular ladle lining based on the metal and thermal containment characteristics of the application and historical ladle consumption. For electric induction furnaces, the erosion rate can also be estimated by changes in electrical readings over time.
The disclosed improved process emphasizes at providing the ladle with a secondary working-lining and hence this innovative method of secondary lining was designed. Secondary lining is a method of providing a secondary working lining to the HM ladle after much of the original working lining have eroded.

It is carried out by lining the ladle with 50mm/40mm straight bricks. The bricks are laid longitudinally as shown in fig 1.
The secondary lining is a need based maintenance practice, and can be broadly divided into three categories:
(i) False Bottom: False bottom is laid when 80 – 90% of the top bottom of the ladle is washed off. To lay this first the irregular surface of the ladle bottom is rammed with castable up to roughly 2” thickness to develop a planar surface. On this surface 4.5” thick 45% Al2O3 brick is laid. The False Bottom is then rammed with 60% HA castable on all sides where the Bottom meets the ladle wall. This ramming provides the necessary locking of the bottom.
(ii) False working wall: The said wall is made by laying 50mm/40mm brick on the wall of the ladle, longitudinally, impinged into 60% HA castable. Its sides are carefully laid to remove any joint gaps and also to avoid collinear joints instead the joints are staggered.
(iii) False Offset: This is done by laying 39% Al2O3 bricks (end arch) along the original off-set the angle of laying is approximately 1200 on one off-set and 600 on the other; this practice is not so frequent and done only in ladles heavily eroded along the belly portion.
1. Application of 39% Al2O3 bricks in slag/metal zone area and 60% HA castable in top ring and spant is a new concept for maintenance of hot metal ladle.
2. Application of 45% Al2O3 bricks in bottom and 39% Al2O3 bottom conical area is also done in the given design (shown in Fig-2 & Fig-3) for the first time. In hot metal ladle.
3. The new lining design contributes for lesser abrasion of mother lining and hence enhanced life.
4. The new lining design is capable of transferring hot metal consistently more than >80 ton tare weight.
5. The new lining design has helped increasing ladle availability by reduction of frequency of repairs and higher campaign life.
6. Formulation of specifications for the following ladle for hot metal ladle.
a) 45% Al2O3 bricks. b) 39% Al2O3 bricks. c) 60% HA Castable
Prospects for utilization/commercialization of the innovation:
The implementation of this ground breaking maintenance practice for HM ladle brought about improvements as shown below:
(i) Number of relining ladles came down from 44 annually prior to this method to 32 annually after its implementation.
(ii) Number of repair ladles came down from 118 annually, prior to this method to 104 annually after its implementation.
(iii) The energy consumed in pre-heating of the ladles came down from 14760 Gcal annually prior this method to 11808 Gcal annually after its implementation, saving a total of 2952 Gcal of energy annually.
(iv) The average life of HM ladles rose from 793 heats annually, prior to this method to 984 heats annually after its implementation. ( in 2011 which has now crossed 1100 heats with highest HM ladle life over 1400 heats that is a record for 90 T ladle in SAIL.)

Economic impact:
As per data of the paper presented at International conference on EESI-2011 the commercial impact is for 12 re-linings and 14 repairs. (Refer points (i) & (ii) above.) This manifests in following three savings:
1. Rs. 70 lacks on account of Material saving for 12 re-linings (12T Bricks + 7T HA castable)
2. Rs. 7.44 lacks on account of savings of HM as 12 less relining per annum means approximately 48 T of HM savings. (on account of bottom and top jams of down ladles)
3. Rs. 1.84 Crore on account of saving of gas (Coke Oven Gas) required for heating up of ladles before putting in regular operation, i.e equivalent to 321 KL ( 2777 barrel) of Crude Oil (KLOE)

In the preceding specification, the invention has been described with reference to specific embodiments thereof. It will be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense. Therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.