Lubrication of Girth Gears in Sponge Iron Plants

B S Nagarkoti

Email: bhagwat@hpcl.co.in

Hindustan Petroleum Corporation Ltd., R&D Centre,

Navi Mumbai - 400 705, India

Synopsis

In sponge iron plants girth gears are preferred for the rotation of furnaces over the gearless drives due to their lower initial cost, simplicity to install, operate and maintain. In coal based sponge iron technology, the furnace (rotary kiln) fulfills various functions. It is used as a conveying, mixing and charring unit, as a heat exchanger and as a reactor for coal gasification and iron ore reduction. These furnaces are moved by girth gear driven from a pinion gear. The girth gear is the heart of most mills and kiln  drive system.  They have high efficiency and the overall life of these gears depends upon proper lubrication and alignment.  For successful operations of  these furnaces,  proper lubrication of girth gear and pinion gear play vital role.  In our study we have attempted to develop a gear lubricant for girth gear. The developed product is of NLGL  0 consistency. The developed product was tested for series of EP tests and other regular tests of grease for suitability in the lubrication of girth gear. The laboratory results reveal the the product has outstanding load carrying capacity,  antioxidant property, rust & corrosion protection and adhesive property to remain on contact surfaces. Due to good adhesiveness on gear surfaces the  consumption of lubricant is less and  will reduce  maintenance and disposal cost. The specially developed load carrying lubricant does not contains ozone depleting chemicals.

Introduction

World over iron ore is the major feedstock in steel making for BF-BOF processes. About 60% of world crude steel is made by this process. But it requires various types of treatment of raw materials and involves high costs. It Integrated Steel plants are based on the conventional  route of iron making, using blast furnaces. It also leads to environmental problems. As in these steel plants, the main polluters are sinter plants and coke ovens where emissions of CO2 is very high. Secondly,  The increasing trend in scrap prices in the nineties and its short supply led to the use of sponge iron / Direct Reduced Iron (DRI) for use in the charge-mix for steel making. At present, there are no alternative coke free iron ore reduction technologies capable of fully replacing the modern high performance blast furnaces. Due to deteriorating quality as well as limited reserves of metallurgical coking coal, the essential feed material for blast furnaces has necessitated a need of raw material for secondary steel making[1]. Very high quality of coking coal is needed for making the coke as redundant in the blast furnaces. The coking coal reserves in the world are decreasing. In view of this, technologies have to be developed to use non-coking coal as redundant for the Iron Ore. Additionally, the charging of sponge iron into blast furnaces does reduce coke consumption and increases hot metal productivity. Therefore, sponge iron is being preferred as a raw material for secondary steel making.

Sponge Iron

Sponge Iron powder is produced by the direct reduction of high grade magnetite  iron ore at temperature just below the fusion point of iron. This product has derived the name "Sponge Iron" due to its porous nature. It is also called as Direct Reduced Iron (DRI). This process results in spongy particles which have good compressibility, exceptionally good green strength.  It  is a substitute of steel scrap for steel making through the secondary route i.e. DR/EF route. DRI is a high quality metallic product produced from iron ore, pellets etc. as a feed stock in Electric Arc Furnaces (EAFs), Blast furnaces and other iron and steel making processes. Hot Briquetted Iron (HBI) is a denser and compacted form of DRI designed for the ease of shipping, handling and storage. The global steel industry is using about 22 per cent of alternative iron like DRI/HBI, merchant pig iron and hot metal to produce high quality steels in the EAFs. DRI is now recognized as a high purity, top quality charge material the world over. In comparison with scrap, the use of sponge iron / HBI offers the benefits like consistency in composition, low trace elements due to its porous nature and environment–friendliness [1].

Sponge iron is produced from iron ore by using low quality coal. In these plants big rotary kilns are used where the iron ore, coal and limestone are fed from one end of kiln. The hot air is injected in the kiln from various zones, which heat the raw materials, and a temperature is reached where the iron ore gets reduced leaving solid contents along with gange material. The hot reduced material is discharged from the other end of kiln, which is cooled. The gases emitted from the Kiln have high calorific value containing Carbon Monoxide, methane and ethane etc. These are used for generating Power and in rehearing furnaces of rolling mills [2]. The global supply of sponge iron is expected to reach 55 MTPA in 2010 as against about 40 MTPA at present, liquid hot metal and solid pig iron would also be used to a large extent.

Raw materials for sponge Iron

The major raw materials required for production of sponge iron are oxides of iron in the form of lump iron, pellets, non-coking coal and fluxes (limestone and dolomite). Use of high purity of lump ore, pellets with low phosphorus at an economic price helps in the cost effective production of sponge iron.

Iron Ore

The iron ore used is hematite with an Fe content of 62-66% having low decerepitation characteristics. This has resulted in reducing the cost of iron ore fed to the kiln. The consumption of iron ore has also decreased from about 1600 KG per tonne of sponge iron to 1500 KG levels mainly due to a better understanding of the process, improvements of the equipment and increased levels of automation.

Coal

Non-coking coal is being used having certain important parameters considered necessary for the direct reduction of iron ore viz. reactivity, ash softening temperature, caking and swelling indices and sulphur content etc.

Dolomite

Dolomite is mainly used as a desulphurising agent to prevent the pick up of sulphur by the sponge iron from the sulphur released by the burning of coal inside the furnace.

Evolution of the sponge iron industry in India

The first  coal based sponge iron plant was set up at Paloncha in Andhra Pradesh in 1980, which had a capacity of just 0.039 million tones per annum. In the next nine years, five more coal-based were set up and to-day there are 19 coal-based plants in India using various technologies like SL/RN, ACCR, Krupp, Codir, TDR, Jindal etc. the present estimated capacity is nearly 4.5 million tones. presently operating in eight different States of India. India became the largest producer of sponge iron with a record production of 7.7 million tons in year 2003. At present it is about 12.77 MT[3]. The India is the highest producer of coal-based DRI in the world. sponge iron can be utilized in iron making for two main applications  reduction in coke rates and  Increase in hot metal productivity. Coal based sponge iron technology has gained higher economic viability by its ability to generate a considerable quantity of electricity through use of hot waste gases and kiln waste (char) materials.  In coal based sponge iron technology, the furnace (rotary kiln) fulfils various functions. It is used as a conveying, mixing and charring unit, as a heat exchanger and as a reactor for coal gasification and iron ore reduction. In coal based sponge iron kilns, depending on the quality of reductant (coal) used, about 60% of the total heat input is utilized in the reduction process. About 40% of the heat input is discharged with the kiln waste gases and the kiln materials in the form of chemical heat. The hot waste gas and char produced thus contain considerable energy saving potentials. By burning coal fines, coal washery rejects and the non-magnetic kiln discharge (char) in a fluidized bed boiler, steam can be generated which can in turn be used for power generation[4].

Experimental Details

(A) Preparation of Base  Grease (Aluminum Complex)

The main ingredient for open gear lubricant  is  Aluminum complex grease. The aluminum complex grease was prepared in the laboratory in a well established method. The grease was prepared to get LNGI 3 cnisistency. The grease was tested for following characteristics in addition to other regular grease tests.

1. Consistency test (STM D 217)

2. Drop point (ASTM D 566)

3. Four Ball Extreme Pressure Test using method ASTM D 2596 series of EP tests conducted i.e. Weld load, load wear index and wear scar diameter.

4 Timken OK load test using ASTM D 2509.

5.Oxidation stability test ( ASTM D 942)

(B) Open Gear Lubricant - 

Formulations were developed using this base grease and various other additive components.  The open gear lubricantÆs consistency was maintained at NLGI 0 range to get good spreadability and adhesiveness on gear teeth. The developed open gear lubricant was tested for following parameters. The formulation with best results was selected for field trials.

1. Consistency test ( ASTM D 217)

2. Drop point ( ASTM D 566)

3. Series of Four Ball Extreme Pressure Test using method ASTM D 2596 conducted i.e. Weld                                    load, load   wear index and wear scar diameter.

4 Timken OK load test using ASTM D 2509

5. Oxidation stability test ( ASTM D 942)

6. Rust test ( IP 220)

Results and  Discussion

The test results of base grease are provided in table (1). The results of base grease shows good structure stability as evidenced by 100,000 stroke worked penetration and roll stability test. The grease has  high dropping point and acceptable required properties of aluminum complex grease. The grease has acceptable EP properties even without performance additive. Since load carrying capacity was very crucial for open gear lubricant. Selection of EP additives was done very  carefully to get desired EP characteristics. The test results are provided in Table 2.  The series of Four ball EP test results reveal that the developed product can withstand a high load on gear.  This is also supported by Timken OK load test. Load carrying property is witnessed by field trial results. The product has very good spreadability and adhesiveness on the gear surfaces.

Conclusions

The base grease selected for preparing open gear lubricant shows very good structure stability as evidenced by 100,000 stroke worked penetration test and roll stability test and higher drop point. The fibre structure of greases  are very short compared to lithium soap, therefore suitable for good spreadability and uniformity.  The developed open gear lubricant  has good lad carrying capacity, which is very essential for open gear lubricant particularly girth gear. The facts is also supported by good adhisiveness on gear surfaces.

References

[1]  Sanjay Sengupta, Indian Sponge Iron Industry in Global Perspective, Steel World, October 2001

[2]  Steel Making in India Technology Scenario Changes, SteelWorld, Monthly Journal

[3]  Sponge Iron - A Nerve for Steel making, SteelWorld, Monthly Journal

[4]  A Pandit et al, Coal Based Sponge Iron Industry A prime Mover  to Enhance steel making Capacities  in  India, SteelWorld, Monthly Journal

           

           

Table -1  Test  results of Base  Grease (Aluminum Complex)

Characteristics	Test  Results	Targets	Test Method
1.Appearance	Smooth	Smooth	visual
2. Colour	Light brown	-	visual
3.Consistency, NLGI   Grade	NLGI 3	NLGI 3	NLGI
4.Consistency,@ 25oC  Worked, 60 X  Worked, 1,00,000 X	243 246 258	+ 10 of 60 220-250 +30 of 60	ASTM D 217
5. Copper corrosion,     @ 100oC, 24 hrs.	passes	passes	ASTM D 4048
6. Drop Point,oC	262	>230	ASTM D 566
7.Wheel bearing   test Leakage by  mass, g	1.65	5 max	ASTM D1263
8. Roll Stability, %change	4.6	10 max	ASTM D1831
9.Water wash out  test  @ 80 oC % wt. loss	3.82	10 max.	IS:1448 P:89
10.Oxidation Stability, drop in pressure, psi	7	10 max.	ASTM D 942
11. Emcor Rust Test	0/0	0/0	IP 220
12.Four  ball  weld  load, kg	180	250	ASTM D 2596
13.Wear scar diameter, mm	0.58	0.65	ASTM D 2596
14. Timken  OK  load, lbs.	45	40	ASTM D 2266

           

                        Table -2. Test  results of Open Gear Lubricant

Characteristics	Test  Results	Test Method
1.  Colour	Dark  brown	visual
2.  Consistency, NLGI	NLGI 0	NLGI
3.  Consistency,@ 25oC      Worked, 60 X	370 362	ASTM D 217
4. Copper corrosion, @ 100oC, 24 hrs.	passes	ASTM D 4048
5. Drop Point,oC	226	ASTM D 566
6. Water % wt.	Nil	ASTM D 95
7. Rust Test	passes	IP 220
8. EP properties Load wear Index, kg Four ball weld Point, kg Four ball wear scar dia, mm	160 700 0.48	ASTM D 2596 ASTM D 2596 ASTM D 2266
Timken OK Load, lb	90	ASTM D 2509