Improvement of refractory life and performance

Improve your Refractory Life and Performance by following 3 steps

Nothing counts like the 'performance'. Getting or giving a better performance is one thing which everyone tries to do. Reasons obvious! For getting better performance of refractories from an installation (lining) i.e. an improved refractory life, one must take care of the following three simple but very important things:

1. Proper Selection of Refractories.
2. Proper Installation - Laying of Refractory Bricks.
3. Proper Operation Practice.

Selection of Refractories

Though there are specific refractories for different applications, operation practices lead to certain criteria on which, depends the refractory life. As such these need to be properly considered. Customers should disclose the actual operating practices and conditions so that some important properties, required to such conditions can be taken care during the selection of refractories as well as during the manufacturing stage of such refractory bricks, castables, and mortars. Among various physical, chemical, thermo-chemical and thermo-mechanical properties of Refractories, there are a few properties which can change significantly performance of refractories. These are called Key Properties. For ensuring better performance, quality and of course, refractory life these key properties should be tested.

Installation - Laying of Refractory Bricks

Depending on the method of application or installation there has to be a set of guidelines in respect to laying of refractory bricks, their dimensions, selection of mortars, expansion joints and many other minute but very important things. So from case to case basis the supplier of refractories should specify this properly and also ensure that the methods are actually being followed. Transportation, handling, timely arrival of refractory bricks, mortars, skill of masonry work, proper equipment for application e.g. mixer machine for castable, vibrator for installation, forma etc. are very important. Maintaining proper expansion gaps, correct dimension (size) of bricks and monolithics, fixing anchors etc. all are very important to achieve better life of refractories. Once the laying job and other installation of refractories are over, the initial heating of the lining before starting the actual operation is of prime importance. Customers should demand the initial heating schedule from the refractory supplier.

Operational Practices

Proper operation is not only important for getting right quality output but also, help in getting the optimum refractory life, less downtime, maximum availability of the furnace and thus, the benefit of lower cost of refractories per tone of finished product. Customers must be aware of the reasons which can damage the refractories arising because of improper operations. During the training of the furnace operators, apart from the method of the furnace operation etc. they must be given some knowledge regarding the proper usage and importance of refractories also.

how to minimize/stop the erosion in high alumina bottom pouring sets, without much cost increase.

One can try magnesia - carbon refractory coating over the high alumina bottom pouring sets. The coating can be applied using carbonaceous adhesives.

Using BP set manufactured by small companies then probable cause of this erosion can be lower alumina content than specified or using a low melting clay as binder to reduce firing temperature. Total alumina can be checked by sending sample to any reputed lab for chemical testing. However for checking low melting matrix, you have to test hot MOR or RUL property of the sample. In case of low melting matrix, it will fuse at steel temperature and will not hold the grains, so more erosion. So buy only from manufacturers who have high temperature kilns to make fire proper grade of BP sets.

 Reduced oxygen content in the steel will be better for the refractories. I recall a case where the customer "killed" the steel in the ladle with some aluminum prior to casting. It is costly to measure oxygen but will give good information if you can do this.

what's the difference between fused zirconia and chemical grade zirconia,

The term fused zirconia refers to the zirconia grains which are melted by heating above their melting point therefore the surface of these grains is in a fused state and it is nearly theoretically dense. One would expect better thermo mechanical properties from fused grains. Where as chemical grade is generally refered to zirconia prepared by chemical precipitation or decomposition of zirconium salts and such grains show high surface porosity hence they are prone to liquid metal wetting.


 Refractoriness is all about purity. A fused grade will contain fewer of the glass forming impurities which reduce the refractoriness of high melting point materials like zirconia. Hence you will have cleaner grain boundaries less prone to chemical attack, high temperature creep etc. In extreme applications, go for fused grade every time. Of course there are grades of fused materials as well, so you have to go by the quantities and types of impurities present in the chemical analysis to be sure that you're getting a quality product.


Price wise:
It can expected the fused grade to be more expensive. But there are different grades of fused zirconia, as with any other fused material. The fused material obtained from the centre of the melted mass is expected to contain the least contaminants and companies will often sell this material at the highest price whilst sell the material obtained from the outside of the melt at a lower price.
Whether it's better depends upon what use of it and how essential the place it is. That is, it could be cost effective to use the lower grade of zirconia in certain applications. Usually any containment vessel is zoned and the highest grade, fused materials only used in the high wear areas.


Crystal Size :
Cristal size is a major difference. Fused ZrO2 is slowly cooled, thus allowing for better formed and larger crystals than chemical ZrO2.


Lattice Size: 
There can not be major difference in the lattice parameters of the fused and chemical grade calcined zirconia but it may vary by from 5to 6% because the chemical grade is expected to have high vacancy or interstitial concentration hence it may show larger lattice parameter.Since in the fused zirconia the imputities are segregated to the surface of grains during solidification therefore it show lattice corresponding to that of pure zirconia crystal.

how Manganese cause Magcarbon refractory erosion?

1) Rich MnO slags can lead to Mn-rich metallic particles and solid solution with Mg (and, indeed, carbon oxydation) at the interface between slag and lining. 
Anyway, this is seldom the first cause of erosion: it generally occurs after the lining has been weared for some other reason (i.e. slags unsaturated in MgO or rich in FeO).


2) Mn presence in converter causes erosion faster, as it behaves acidic, makes the liquid less viscous, penetrates the pores and joints and reacts with MgO at the contact point. For Mn steel, different of configuration of MgC brick is used.


3) it is observed that after a low grade ore(high impurity i.e Mn,Si) converter life is almost reduced and high erosion profile is being observed. 
as my observation high Mn slag is very fluid and do not cover the converter lining after slag splashing. reducing use of iron ore as coolant may help.


MnO + SiO2 = very low melting and corrosive liquid. 

I suppose primary wear area limiiting converter life will be the trunnions. Trunnions can be zoned with higher quality MgO containing bricks - MgO purity should be 97.5 minimum and of largest MgO crystal size available. Graphite should be 10-20% and have coarse flaked quality -- exact amount of graphite is function of sracp charge; hot metal chemistry; gunning practice; slag viscosity etc. A good start would be 15% C. Metal additions should be aluminum and silicon metal which will form carbides for added strength and corrosion resistance. 

Turkish fused MgO is superior to Chinese fused MgO especially for corrision resistance - crystal size is larger and grain chemistry is more homogeneous. 

Some other thoughts: 

The operator should be adding enough lime/limestone/dolomitic lime to maintain slag basciity at a > 3:1 lime:silca ratio and some MgO is helpful to reduce slag liquidity and reactability. 

Reblows will be especialy harmful as added FeO can result and FeO+MnO+SiO2 is a refractory solvent that is very aggressive. So effort should be taken to control reblowing to minimum. 

Overblowing such that temperature is overheated should be controlled. 

Corriosive slag should be slagged off shortly after tap. 

A high purity MgO gun mix and laser readings to identify low spots for added gunning maintenance will extend service life. 

Do practice slag splashing; a special lance is used to inject nitrogen after tap - the slag is made more refractory prior to the nitrogen splasing by addition of dolomitic lime. 

A good strategy would be to plan for Continuous Improvement over several linings rather than thinking that one design change can be a silver bullet. Key is to study the wear profile, identify the wear mechanism and develop new lining design that addresses the wear area and wear meachanism; this should be repeated in several iterations over several linings as in "chaisng the hole". As one area is upgraded the weak link might move to another area of the vessel. EX: An upgrade of trunnions might shift the limiting zone to the cone or the slagline or the charge pad or the tap pad...

phenomenon of Alumina pick up by the liquid mould flux during Continuous Casting and how it affects the quality of cast strands?

The pickup of alumina in the mold causes the formation of calcium aluminates. Since there are a variety of different calcium aluminate morphs(each one with a higher melting temp.) over time the mold flux can and will begin to thicken up and the fluid lubrication on the strand mold faces can be interrupted causing surface defects & breakouts. Old timers used to throw Calcium flourides (spar) into the mold to liquify it but each time you do that you also increase the CA content which in turn will eventually thicken back up. Spar is a bad actor in the mold. In order to stay fluid there is a delicate chemical balance between CA & Al.

Why mag-c bricks is mostly prefer for ladle and EAF, why not spinel refractory?

EAF is all mag-carbon. Why it works well and zoning is done based on carbon level, anti-oxidant, graphite quality and magnesia grain quality. In steel ladles, however, mag-carbon is the solution in the slagline only. If the shop is in an alumina killed process, the common is alumina/magnesia carbon for the barrel and bottom. For silicon killed shops, the norm is dolomite (carbon bond normally) or magnesia carbon. The selection comes down to what works in the application and which technology is most cost effective. The later takes on a regional aspect. In fact one shop in ---- (blastfurnace not EAF) is using a bottom and barrel that is alumina magnesia castable with a mag-carbon slagline, why? Simple they maintain the barrel profile with shotcrete and recasting through many slaglines. In fact they only reline the barrel and bottom from the shell once a year!


MgO-C is more compatible with high lime fluid slag. Spinel is more neutral and performs well in molten metal contact.

In basic steel making process, the slag is high in lime. So the brick need to be compatible with the slag. So MgO.C is one of the brick suitable for ladle metal line & only brick suitable for slag line. Graphite addition provides nonwetting character, spalling resistance and additional corrosion resistance especially against FeO. Other bricks Al2O3-MgO-C (Al killed) & Dolo-C (Si-Killed) bricks are used mostly on metal line of ladle. Some ultra low-C, Al-killed steel customers use Al2O3-MgO castable & Spinel bricks in ladle metal line, prefab/precast ladle bottom depending on their plant practices. In EAF also basic slag & hot spots suits MgO.C bricks. It is also economic against spinel brick.

Benefits of using Steel Fibers and Organic Fibers in Refractory Castables and Monolithics

One of the most effective ways of improving the mechanical and thermal properties of refractory castables and other monolithic refractories is adding in suitable proportions of stainless steel fibers and organic fibers to the castable respectively.

Steel Fibers

Steel fiber reinforced refractory castables are very resistant to the tendency of the material to fall apart on thermal cycling. Stainless steel fibers greatly improve the flexural strength of the castable. And this added increase in ductility contributes significantly to the thermal shock and spalling resistance of the material. The fibers generally used are in size varying between 0.1 to 0.4 mm2 in cross-section & 20-40 mm in length. For monolithic SS is used either high chrome or high chrome nickel steels available in the market with different grades. One reason commonly reported that the thermal shock resistance of castables is greatly increased through addition of SS fibers because these fibers act as crack arresters, preventing cracks propagating. This is also possible that the microcracks caused by a mismatch in thermal expansion coefficients of matrix and fibers dissipate energy from larger cracks propagating as a result of thermal stress. However percentage of these fibers added becomes important because of two reasons as it has a direct impact on the fluidity of the castable, then it may also cause mixing difficult due to fiber-balling when added beyond 3% by volume. Another critical factor will be the maximum application temperature for the castable that those fibers present in the castable can resist oxidation (since these fibers can not perform beyond their melting temperature).

Organic Fibers

An effective means for improving the explosive spalling resistance of a castable is to add organic fibers to the formulation. It has been reported that the composition & concentration of fibers are not as important as melting temperature of the fiber, since these fibers after melting increase permeability at certain temp. & thereby reducing the explosive spalling tendency of the castables. The fibers generally used for this purpose are Polypropylene fibers, Polyester staple fibers, etc.
Because of these different advantages it have been found that both organic and SS fiber reinforced refractory castables provide substantial increase in service life and therefore, a considerable reduction in refractory maintenance cost and furnace down-time.

Ladle Slide Gate

 refractory slide gate plates used, in pair, as a valve at the bottom of the ladle in order to control molten metal flow during casting. Highly sliding surfaces of these plates are necessary for easily opening and closing operation as they slides on each other. 
My question is whether these refractory plates required tar impregnation treatment, because i found this treatment in most of the articles regarding refractory slide gate plates, or it also not necessary require tar impregnation likewise magnesia carbon bricks and can be use directly after curing.


 There are mainly four types of commonly used slide gate plates.These are:

1) Cured Alumina carbon plates
2) Fired alumina carbon plates
3) Cured magnesia carbon plates
4) Fired magnesia carbon plates

Fired plates have better erosion resistance as well as better mechanical properties at high temperature.

Cured plates give 1 heat life and after polishing/coating the plate by repair may give one more extra heat life.

Fired plates can give around 4-6 heats life.

There are also zirconia based plates which are very expensive and used by reputed steel plants who targets to achieve 8-10 heats per pair of plates.

Magnesia based plates are preferable where slag corrosion rate is very high.

Tar impregnation is effective on fired products.After firing,the plates can have a porosity of about 13-14%.After tar impregnation,the porosity is reduced to around 3 %.

Tar impregnation is not much effective on cured products,as cured products already show a porositiy of about 5 %.

Purpose of tar impregnation are to lower the porosity and increase the carbon content.This results in better thermal conductivity and oxidation resistance.In case of Alumina carbon plates,tar impregnation also protects the aluminium carbide from hydration.

So,I will say,although environmentally hazardous,tar impregnation is necessary for fired slide gate plates.

applicability of fused MgO (periclase) with a grain size from 0.5 to 0.001 and the content of the MgO is not more than 95%

 1) In finer fraction of batch composition of magnesia carbon bricks for ladle free board and EAF slag door application.

2) Some quantity can be mixed with coarser grains of DBM 95 to produce wet ramming mass.

3) Can be mixed with DBM ,graphite and a binder to produce slag conditioner balls for using in converter,LF,etc.

Why does magnesia carbon brick chip out ? part -2

Perhaps we can go for more details about what the chipping out looks like.

Is every vertical and every horizontal joint being eroded?

Or are there cracks developing around the circumference of the ladle?

Or is the chipping out more prevelant in one area like in the stir quadrant?


our use of 97.5% purity fused MgO and 98% purity Fused MgO suggest best in class MgO.

Also key is the purity and crystal size of the graphite. A large coarse flake graphite of intermediate purity, not necessarily the highest purity available, should offer better oxidation resistance as the impurity in the flaked graphite is SiO2 and SIO2 will provide some protection against anti-oxidants.

The particle size and amounts of anti-oxidants will affect oxidation resistance; thermal expansion and hot strength. As your ladles seem to be going cold and empty for extended periods, I would expect some addition of Al and Si to help retard oxidation of the cabon.

Construction design can also affect joint erosion as the design affects stress distribution:

Spiral construction is quickest to install but worst for structural integrity. This is especially true for ladles with poor lip ring retainers.

MiniKeys that are keyed to cloe each ring will provide a more stable lining AND they can be run to a thinner wear profile for longer life versus semi universal construction as the semi u bricks lose structural integrity when they get beyind 50% or so of the original wear profile.

The best construction is in my opinion arch brick construction. Arches have the advantage that the greatest number of joints are in the vetical dimesnsion so hoop stresses are more uniformily distributed.

In the USA, there is a trend to lower purity 96.8% fused magnesia as a cost savings - the problem with this is that there is a resulting increase in SiO2 inthe bricks and the bricks are more prone to cracking. To combat vertical cracking that occurs about every 750mm to 1000mm around the circumference, some success has been achieved by increasing the graphite levels by 2-4%.

Vertical cracks were observed in middle of many bricks. 

However,in the current ladle,after all the steps we had taken,the over all metal zone is in very good condition except chip out in 1 or 2 pockets in the purging side. 

Yes,we had chosen best fused magnesia with C/S ratio 1.9-2. 

Natural flake graphite used was of -196 grade with about 88 % passing through the 100 mesh screen.Fixed carbon tested was about 96.20 %.So,from your suggestion,it seems,we should have used -192 or -194 grade graphite. 

I carefully note down your suggestion on anti-oxidant.We had used about 1.2 % Aluminium powder and 0.8 % Silicon metal powder in slag zone bricks as the plant makes Si : Al killed steel in the ratio of 70: 30 . 

No anti-oxidant was used in metal zone and bottom bricks. 

Yes,mini key bricks 7/8 and 7/30 are used in both metal and slag zone as per customer's requirement.However,our lining expert says that due to the condition of ladle shells,7/40 would have served better in place of 7/30. 


FM 96.8 with higher carbon content is very useful.I am thinking in this direction as many customers want to buy cheaper bricks and we need to find solution.Normally 8-10 and 12-14 % final carbon are retained in metal zone and slag zone bricks.So,for lower purity FM,what % of final C you wll recommend for bottom,metal zone and slag zone bricks ? 

I have one more question.What are the advantages of using +196/+195/+194( 80 % min retained on 100 mesh screen) graphite in place of -194/-195/-196(min 80% passes through 100 mesh) in magnesia carbon bricks? 
And what are the advantages of using +895 graphite in place of + 195 graphite.I mean how larger flake lengths help in magnesia carbon bricks.I am perplexed because now people are doing research and developing bricks by using Nano graphite(3 D graphite)particles. 

 Ladle insulation , Maximum continuity , control slag , using right taphole in EAF , minimize super heat before tapping , optimize treatment time between EAF and casting , and many others from steel making side are very important for ladle life.

Why does magnesia carbon brick chip out ?

I recently observed early life (30-40 heats) cracking and chip out of magnesia carbon bricks(especially in metal zone) of 50 ton capacity ladle in a steel plant where 30-40% heats are routed thru VD and alloy steel is produced. 

I have found that plant operation is intermittent and sometimes,after every 2-3 days,a ladle is kept out of circulation and in cold condition for 8-24 hours before being heated for 3-4 hrs and brought to circulation once again.This is done to accomodate some other ladle which is in circuit.This is done on rotation basis. 

So,why this chip out is happening ? 

Is it due to expansion of the bricks ? 

Is it due to spalling ? 

Is it due to very tight refractory lining ? 

Is it due to lower residual carbon % (presently residual carbon is 10% metal zone and 14 % slag zone )? 

Does it depend on purity of magnesia (presently 97.5% FM with C/S ratio 1.7-1.9 and 98 % FM with C/S ratio 1.9 are used in metal and slag zone respectively) ? 

Can it happen due to entry of any foreign element in the batch? 

Will addition of DBM reverse the trend ? 

Will using a single 2 mm thick mortar paste between two bricks in each ring to provide expansion gap help ? 

Can it happen due to size/location of the key (piece of brick which is cut out from the mother brick and inserted to tighten each ring).I mean if keys of several rings fall in the same line,or keys are too small to get eroded and come out of the lining) or keys fall on the purging side of the lining! 

Can step formation in the lining result in faster damage of the bricks ? I have observed 10-20 mm steps between two rings in few cases in a ladle which was being lined.

Can spiral lining in place of present straight lining reduce such chip outs ? 

Is chip out a quality issue of the lining or of the product? 

Ladle Preheaters

The ladle refractory lining temperature, during the production cycle, especially for basic linings, must be constantly reset and maintained at convenient temperature values higher than 1.000°C-1.200°C. A correct management of ladle heating and temperature keeping, allows to improve the main steel making parameters:

* Low liquid steel temperture changings before and after tapping

* Tapping temperature decrease at E.A.F. (5-10°C)

* Consumption reduction of expensive energy (i.e. reduction electrical energy of the E.A.F.)

* Electrode consumption reduction of the E.A.F.

* Reduction of Tap to Tap time at E.A.F.

* Increase of E.A.F. productivity

* Guarantee of casting start in the C.C.M.

* Low ladle refractory lining consumption

* Increase of safety refractory lining performances

* Elimination of liquid steel infiltrations trough / behind the working lining

Ladle Preheaters Combustion Technology Should be :

* High efficiency gas – air burners

* High velocity and long flame burners

* Pulse firing burners or modulating burners

* Low NOx emissions of burners

* Burnes designed and manufactured with special refractory steel parts for long life time of operation

* Micro / PLC Automatic control of burners combustion ratio

* Automatic and efficient control of ladle temperature

* High preheating performances

* Extraordinary uniformity of ladle lining temperature

* Low gas consumption

* Shorter drying – preheating time

* Significant energy saving compared to usual technology

* High efficiency thermal recuperators (additonal energy saving 30%)

* Burners available for natural gas, L.P.G., Diesel oil, Coke oven gas

* Emission rates according to E.C.C. standards

* Exhaust fumes system and post-combustion system for dangerous and smoking emissions

KT2000 LadleSLAG

The KT500 OnLineMOMS system integrates caster variable inputs to provide a complete monitoring system for process and mechanical/control analysis of the caster. The system consists of:

main control unit with system computer and software;

four compact sensors, which are permanently attached to the mold table;

and high temperature system cables.

TYPICALLY INTEGRATED SIGNALS

• Oscillation speed

• Casting speed

• Mold level

• Tundish temperature

• Tundish slide gate position

• Tundish weight

• Ladle weight

ADVANTAGES

• Monitor real-time casting conditions

• Evaluate variables that effect cast product quality

• Provide early indication of maintenance issues

• Compare noncasting to casting conditions

• Evaluate mold lubrication practices

MEASUREMENTS AND CALCULATIONS

• Up/Down Displacement

• Left/Right Displacement

• Front/Back Displacement

• Residual Displacement

• Phase

• Rise/Fall Ratio

• Low, Medium and High Frequency Vibrations

• Negative Strip Time and Ratio

• Positive Strip Time and Ratio

• Mold Lead

• Friction Index

• Oscillation Mark Depth

Crude steel production (million tonnes):

Crude steel production (million tonnes):

Rank	Country/Region	2007	2008	2009	2010	2011
—	World	1,351.3	1326.5	1,219.7	1,413.6	1,490.1
1	People's Republic of China	494.9	500.3	573.6	626.7	683.3
2	Japan	120.2	118.7	87.5	109.6	107.6
3	United States	98.1	91.4	58.2	80.6	86.2
4	India	53.5	57.8	62.8	68.3	72.2
5	Russia	72.4	68.5	60.0	66.9	68.7
6	South Korea	51.5	53.6	48.6	58.5	68.5
7	Germany	48.6	45.8	32.7	43.8	44.3
8	Ukraine	42.8	37.3	29.9	33.6	35.3
9	Brazil	33.8	33.7	26.5	32.8	35.2
10	Turkey	25.8	26.8	25.3	29.0	34.1
11	Italy	31.6	30.6	19.7	25.8	28.7
12	Taiwan	20.9	19.9	15.7	19.6	22.7
13	Mexico	17.6	17.2	14.2	17.0	18.1
14	France	19.3	17.9	12.8	15.4	15.8
15	Spain	19.0	18.6	14.3	16.3	15.6
16	Canada	15.6	14.8	9.0	13.0	13.1
17	Iran	10.1	10.0	10.9	12.0	13.0
18	United Kingdom	14.3	13.5	10.1	9.7	9.5
19	Poland	10.6	9.7	7.2	8.0	8.8
20	Belgium	10.7	10.7	5.6	8.1	8.1
21	Austria	7.6	7.6	5.7	7.2	7.5
22	Netherlands	7.4	6.8	5.2	6.7	6.9
23	South Africa	9.1	8.3	7.5	8.5	6.7
24	Egypt	6.2	6.2	5.5	6.7	6.5
25	Australia	7.9	7.6	5.2	7.3	6.4
26	Argentina	5.4	5.5	4.0	5.1	5.7
27	Czech Republic	7.1	6.4	4.6	5.2	5.6
28	Saudi Arabia	4.6	4.7	4.7	5.0	5.3
29	Sweden	5.7	5.2	2.8	4.8	4.9
30	Kazakhstan	4.8	4.3	4.1	4.3	4.7
31	Slovakia	5.1	4.5	3.7	4.6	4.2
-	Malaysia	6.9	6.4	4.0	4.1	N/A
32	Finland	4.4	4.4	3.1	4.0	4.0
—	Others[4]	29.8 (est.)	28.3 (est.)	23.3 (est.)	25.6 (est.)