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.
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 India
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
[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
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 |
