Lubricants & Lubrication

Complexing of Lithium Soap Greases – A New Approach

2011-11-07T03:41:00.000-08:00

ABSTRACT

Manufacturing of lithium complex greases require skilful attention. Process parameters and sequence of additions of ingredients need to be followed carefully. Globally, Lithium complex grease is prepared by co-crystallization of two or more mono or dicarboxylic acids and or their esters with Lithium hydroxide. While manufacturing lithium Complex greases through such multi-components system requires extra time, close monitoring the process and inventory of various ingredients and resulting extra cost and occasional failure of product. To avoid undesired failure of grease, extra manufacturing steps & hidden energy loss and raw material inventory reduction, we attempted a simple method of complexing simple lithium based greases. In this study lithium based greases are prepared in conventional ways. A multifunctional additive system prepared separately, which contains self complexing agent, EP/AW additive, rust & corrosion inhibitor and antioxidant. This complete additive was added to simple lithium soap grease after getting desired NLGI consistency to enhance all desired properties of grease in addition to enhancement of working limit without increasing the extra cost of final grease. The developed grease properties were compared with conventional lithium complex grease fortified with rust & corrosion inhibitor, antioxidant and EP/antiwear additive. The structure stability of new grease were comparable or better than conventional complex grease as evidenced by extended working upto 3,00,000 stroke worked penetration, high temperature roll stability tests and series of EP load carrying tests. Various physico-chemical properties and performance details have been revealed in this study.

KEY WORDS

co-crystallization, dicarboxylic acids, multifunctional additive system, EP/AW additive, self complexing, Lithium complex grease

INTRODUCTION

Manufacturing of Lithium based greases is well known and well established. Due to upper temperature usage limit of 120^oC of simple lithium based greases, complexing of greases is essential for various high temperature industrial applications. This complexing improves the structure/mechanical stability, drop point, and resulting upper working temperature limit. To meet other requirements i.e. water washout resistance property, Thermal and oxidation stability, rust & corrosion resistance and EP/AW properties, addition of other additives is inevitable. This makes the lengthy process and increases the cost of complex grease. To simplify the complexing process we attempted a new way of complexing of simple lithium based grease. After achieving encouraging results in laboratory, a pilot batch of product was made and finally large scale production commenced. Extensive field trials were conducted in various industries and established the performance of product in various high temperature and extreme working conditions applications. Based on laboratory test results and good performance in industries, it can be concluded that the life of this grease will be comparatively longer than the complex grease manufactured in conventional method.

EXPERIMENTAL DETAILS

Following two greases were prepared.

1. Lithium based grease was prepared by conventional method by using 12-hydroxy stearic acid and lithium hydroxide. ISO VG 220 base oil was selected as a base fluid. After getting the desired NLGI consistency the multifunctional additive system prepared separately, was added i.e. Containing complexing agent, rust & corrosion inhibitor, antioxidant and EP additive.

2. A Lithium complex grease was prepared in a conventional method for comparative study. This grease was fortified with commercially available additive package to meet other requirements i.e. water washout resistance property, Thermal and oxidation stability, rust & corrosion resistance and EP/AW properties. The prepared greases were tested for the all desired tests of lithium complex grease i.e.drop point, mechanical stability, oxidation stability, rust & corrosion test and series of EP tests.

RESULTS AND DISCUSSION

The test results of new lithium complex grease vis-à-vis conventional lithium complex grease are provided in Table 1. The drop point of new lithium complex grease is nearly same with conventional lithium complex grease. The difference between 60 stroke worked penetration, 100,000 stroke, 200,000 stroke and 300,000 stroke worked penetration of both the greases show that the structure stability of new complex grease is comparatively better than the conventional lithium complex grease. The results of roll stability of both the greases at elevated temperature indicate that new complex grease has better structure and mechanical stability. The tribological results of greases indicate that the new complex grease has lower wear scar diameter, higher load wear index, higher four ball weld load and higher Timken OK load compared to conventional complex grease. These higher values of four ball weld load and higher Timken load indicate that structure stability is comparatively better in new grease and additive response is better in new grease.

CONCLUSIONS

The drop points of both the greases are nearly equal.

The complex grease prepared by new method of complexing has comparatively better structural and mechanical stability as evidenced by extended worked penetration test results. This fact is supported by elevated temperature roll stability test.

The series of four ball EP tests and Timken Ok load test reveal that the complex grease prepared through new way has similar and even better additive response and high load carrying capacity compared to complex grease prepared through conventional method.

Based on these test results, it can be concluded that new complex grease will have comparatively longer service life.

ACKNOWLEDGEMENT

Authors are thankful to the management of Hindustan Petroleum Corporation Limited for granting permission to publish this work.

REFERENCES

[1] William J. Mertz, Investigating the Influence of New Complexing Agents in a Lithium Complex Grease Formulation, NLGI Spokesman, Vol. 66 No. 9, December 2002

[2] Denis Smit & Sam Lane, High Performance Products from InvistaÆs C12 Business, Tribology & Lubrication Technology, pages 36-39

Table 1. Test Results of Developed Complex Grease vis-à-vis Conventional Complex Grease

Characteristics	New Lithium Complex grease	Conventional Lithium Complex grease	Test Method
NLGI Grade	NLGI 2	NLGI 2	NLGI
Consistency, @ 25^oC Worked, 60 X Worked, 100, 000 X Worked, 200, 000 X Worked, 300, 000 X	280 276 298 310 326	276 270 294 308 327	ASTM D 217
Drop Point,^oC	284	288	ASTM D 566
Copper Corrosion @ 100 ^oC, 24 hrs	1 a	1a	ASTM D 4048
Heat Stability, @ 100^oC, 30 hrs % loss	2.64	2.88	ASTM D 6184
Wheel Bearing test, Leakage by mass, gm Slump test	2.03 Pass	2.35 Pass	ASTM D 1263
Water washout @ 80^oC, % loss wt.	4.66	4.98	ASTM D 1264
Roll Stability, % change @ ambient, after 16 hrs @ 82^oC, after 48 hrs.	7 21	9 23	ASTM D 1831
Oxidation Stability, @ 100^oC Drop in psi, @ 100 hrs. Drop in psi, @ 500 hrs.	5 18	5 21	ASTM D 942
Emcor Rust Test, rating	0,0	0,0	IP 220
EP Properties Load wear Index, kg Four ball weld Point,kg Four ball Wear scar dia, mm Timken OK load, lb	46 315 0.44 45	41 250 0.48 40	ASTM D 2596 ASTM D 2596 ASTM D 2266 ASTM D 2509

Tribology of 2-Mercaptobenzothiazole in Lithium Complex Grease

2011-11-07T03:25:00.003-08:00

Abstract

Globally, extreme pressure greases are prepared by incorporating sulfurized fats, fatty acids, esters, sulfurised olefins, dialkyl polysulfides, organo-sulphur compounds and antimony dialkyl dithiocarbamate. A mixture of amine phosphates or Zinc dialkyl dithiophosphate types of compounds are used in combination with above EP additives to reduce the wear. The load carrying capacity of these EP additives is limited. Additionally, these additives contribute corrosion to yellow metals. In order to protect yellow metals, certain metal passivators are incorporated in grease, which contribute additional cost. Normally, derivatives of tolutriazole, benzotriazole or Mercaptobenzothiazole are incorporated to protect yellow metal corrosion. There are various automotive and industrial applications, where very high shock load and high temperature is encountered by bearings. For such severe applications a high performance grease with high load carrying capacity is required. Normally, solid lubricants i.e. Molybdenum di sulphide or graphite is used in combination with antiwear additive for such applications. To meet the requirements of such applications, very high treat level of such solid lubricants required. Higher particle size of such solids may also cause abrasion/wear in bearings. For prolong use at high temperature these solids tend to lead cake formation. Considering the severity of such applications, we have attempted to study the tribological properties of 2-Mercaptobenzothiazole (MBT) in lithium complex grease. The EP properties of MBT were studied in lithium complex grease alone and in combination with amine phosphates type ashless anti-wear compound and Zinc dialkyl dithiophosphate. Load carrying properties were checked by conducting series of Extreme pressure tests by four ball method and Timken method. Frictional property was studied by universal tribometer. The developed Lithium complex grease has shown very high four ball OK load, Timken OK load and lower wear scar diameter. The grease has shown very low coefficient of friction. The developed complex grease was tested for other regular characteristics in addition to tribological properties.

Introduction

There has been no much difference in usage pattern of EP/antiwear additive chemistry of additives in greases and other lubricants like cutting fluids and gear oils. These additives perform very well in some greases but not able to perform up to desired level in other applications. Due to high active sulfur content, they need supplementary additive with them for non-ferrous metal corrosion protection. Additive chemistry plays a vital role in performance of greases, none the less base fluid and thickener play an important role. These additives though are in liquid states, seems well mixed in greases but not able to perform up to desired level in actual operating conditions. As the greases is worked and churned in bearing, the grease is required to liberate some oil to lubricate race way surfaces. Some of the additives also released with oil but not able to go back in grease’s jell structure. As a result depletion of additive takes place gradually and performance level of grease decrease. Thus the life of grease and bearings reduced. In view of this, the usage of solid additives with nano particle size is increasing in high performance greases in recent times. The biggest advantage of solid additives with nano particle size in greases is it provides the structure to grease by working as the thickener/fillers and support the development of lubricating film on friction contact surfaces. Thus reduces the chances of depletion of additives with oil due to break down of grease structure due to high temperature and high load during operation. Analyzing the properties of 2-Mercaptobenzothiazole, we have attempted to study the performance of this additive in lithium complex grease. We have evaluated this additive in wide perspective of tribological behaviour in different combination with antiwear additives. Though the primary use of 2-Mercaptobenzothiazole is vulcanization accelerator for rubber, fungicide, copper corrosion inhibitors in various lubricants and coolants at a very low treat level. 2-Mercaptobenzothiazole has very high sulfur content hence it can also be used as an excellent EP additive. Due to presence of two nitrogen atom in MBT, it is slightly basic in nature which helps to neutralize the acidic components formed in application thus increases the life of grease. Additionally, due to solid nature it can work as a filler in greases and subsequently increases the yield of greases.

Experimental Details

Lithium complex grease was prepared by conventional method by using 12-hydroxy stearic acid and lithium hydroxide. Dodecanedioic acid was used as complexing agent in Lithium soap grease. An ISO VG 220 mineral oil was selected as a base fluid for better lubricity at high temperature application. The grease consistency was kept in NLGI 2 range. This grease was fortified with commercially available antioxidant, rust inhibitor to meet other requirements i.e. Thermal and oxidation stability, rust & corrosion resistance, water washout resistance property. Series of extreme pressure properties of Lithium complex grease were checked in following combinations of EP and antiwear additives.

1. Lithium complex grease without any EP and antiwear additive

2. Lithium complex grease with only 2.5% 2-Mercaptobenzothiazole (MBT)

3. Lithium complex grease with combination of 2.5% 2-Mercaptobenzothiazole and 1.0% Zinc dialkyl dithiophosphate antiwear additive

4. Lithium complex grease with combination of 2.5% 2-Mercaptobenzothiazole and 1.0% ashless antiwear additive

5. Lithium complex grease with combination of 2.5% conventionally available sulfur-phosphorous chemistry based EP additive and 1.0% Zinc dialkyl dithiophosphate antiwear additive.

The coefficient of friction was tested by universal tribometer in following combinations of EP and antiwear additives.

1. Lithium complex grease with combination of 2-Mercaptobenzothiazole and Zinc dialkyl dithiophosphate antiwear additive

2. Lithium complex grease with combination of 2-Mercaptobenzothiazole and ashless antiwear additive

The testing conditions were as under.

1. Load - 300 N

2. Temperature - 60⁰C

3. Frequency - 50 HZ

4. Time - 120 minutes

5. Contact - Pin-on-disk mode

Results and Discussion

The test results of Lithium complex grease with 2- Mercaptobenzothiazole and ZDDP vis-à-vis Lithium complex grease with conventional EP additive and ZDDP are provided in Table 1. The various regular properties of grease with new additive combinations i.e. combination of 2-Mercaptobenzothiazole and Zinc dialkyl dithiophosphate antiwear additive are similar with Lithium complex grease with combination of conventional EP additive and Zinc dialkyl dithiophosphate. This reveals that 2-Mercaptobenzothiazole has compatibility and good additive response in lithium complex grease. The series of extreme pressure properties of greases with different combinations of 2-Mercaptobenzothiazole with Zinc dialkyl dithiophosphate, ashless antiwear additive and grease with commercially available extreme pressure additive in combination with Zinc dialkyl dithiophosphate are provided in table 2. The four ball weld load of lithium complex grease 2 ( only 2.5% MBT) has 500 kg weld load. The wear scar dia is 0.78 mm. After addition of 1.0% Zinc dialkyl dithiophosphate and 1.0% ashless antiwear additive respectively in this grease the wear scar dia has come down to 0.30 mm in grease 3 and 4 respectively. Additionally, the weld load is increased by 50 kg. Whereas, the grease with conventional EP additive & antiwear additive has shown a weld load of 315 kg and wear scar dia 0.42 mm. The Timken OK load is also slightly higher with MBT compared to conventional EP additive. These higher values of four ball weld load, higher Timken load and lower wear scar diameter indicate that 2- Mercaptobenzothiazole has shown better response with lithium complex grease. The results of coefficient of friction of grease 3 (Lithium complex grease in combination of 2-Mercaptobenzothiazole and Zinc dialkyl dithiophosphate antiwear additive) and grease 4 (Lithium complex grease in combination of 2-Mercaptobenzothiazole and ashless antiwear additive) are provided in Figure 1. The coefficient of friction of 2-Mercaptobenzothiazole in combination with Zinc dialkyl dithiophosphate and ashless antiwear additive is very low.

Figure 1.

Conclusions

2-Mercaptobenzothiazole has shown better compatibility with Lithium complex grease and resulting good additive response.

Due to solid nature of 2-Mercaptobenzothiazole the yield of grease has increased marginally.

The series of four ball EP tests and Timken Ok load test reveal that 2- Mercaptobenzothiazole has exceptional load carrying capacity compared to conventional EP additives.

This is supported by low coefficient of Friction of greases compared to conventional EP additives.

The Based on these test results, it can be summarized that 2- Mercaptobenzothiazole has exceptional load carrying capacity compared to conventional EP additives.

References

[1] Avery , et al. Organosulfur adducts as multifunctional additives for lubricating oils and fuels and as multifunctional lubricants, United States Patent, April 9, 1991

[2]Denis Smit & Sam Lane, High Performance Products from Invista C12 Business, Tribology & Lubrication Technology, pages 36-39

[3] Wilfried J. Bartz, The Importance of Synthetic Greases for Future High Performance Applications. ELGI Annual Meeting 2005, Edenburgh

[4] [4] Kavin J. Chase & Gaston Aguilar, R.T. Vanderbilt Co., Inc. metal Dithiocarmates: A New Approach to Old technology, NLGI Spokesman, Vol. 71 No. 4, July 2007

[5] William c. ward jr., Richard A. denis, Morey Najman & Carlos L. Cerda de Groote: EP Additive Response and Tribochemical film formation in Lithium and lithium complex Grease, NLGI Spokesman, Vol. 71 No. 7, October 2007

[6] Polish, A. F. , & farmer, H.H. Dithiocarbamate additives in Lubricating greases, NLGI Spokesman, pg 200-205, 1979

Table 1. Test Results of Lithium Complex Grease with 2 - Mercaptobenzothiazole and ZDDP antiwear additive vis-à-vis Lithium Complex grease with conventional EP additive and ZDDP antiwear additive

Characteristics	Lithium Complex Grease with 2 – Mercaptobenzothiazole and ZDDP	Lithium Complex grease with conventional EP additive and ZDDP	Test Method
NLGI Grade	NLGI 2	NLGI 2	NLGI
Consistency, @ 25^oC Worked, 60 X Worked, 100, 000 X	281 305	283 309	ASTM D 217
Drop Point,^oC	272	272	ASTM D 566
Copper Corrosion @ 100 ^oC, 24 hrs	1 a	1a	ASTM D 4048
Heat Stability, @ 100^oC, 30 hrs % loss	1.85	1.76	ASTM D 6184
Wheel Bearing test, Leakage by mass, gm Slump test	2.63 Pass	2.66 Pass	ASTM D 1263
Water washout @ 80^oC, % loss wt.	4.66	4.98	ASTM D 1264
Roll Stability, % change @ ambient, after 16 hrs @ 82^oC, after 48 hrs.	6 16	7 18	ASTM D 1831
Oxidation Stability, @ 100^oC Drop in psi, @ 100 hrs.	6	6	ASTM D 942
Emcor Rust Test, rating	0,0	0,0	IP 220

Table 2. Tribological properties of Greases

Characteristics	Grease 1	Grease 2	Grease 3	Grease 4	Grease 5	Test Method
Load wear Index, kg	66	132	166	166	112	ASTM D 2596
Four ball weld Point,kg	200	500	550	550	315	ASTM D 2596
Four ball Wear scar dia, mm	0.80	0.78	0.30	0.30	0.42	ASTM D 2266
Timken OK load, lb	15	40	50	50	45	ASTM D 2509

Lubrication of Girth Gears in Sponge Iron Plants

2011-10-03T04:29:00.000-07:00

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

Water Resistant property of Lubricating Greases – an Outlook

2011-09-30T03:36:00.000-07:00

Abstract

In rolling mills of steel plants, cold rolling oil emulsion is used as coolant and lubricant for rollers. Normally simple Lithium soap, mixed soap (Lithium and Calcium) based and Lithium Complex greases are used for lubrication of bearings. In recent time Overbased Calcium Sulfonate complex based grease is also being used predominantly as lubricant in the bearings supporting the rollers. But due to continuous high ingress of water/emulsion, in some cases this grease also gets emulsified due to absorption of water and looses its structure. Due to drop in consistency the grease is washed away from the bearings. As a result frequent re-lubrication is required in bearings. Which causes production loss and high production cost. In order to maintain its structure, the grease is required to have good water repellency in addition to water tolerance property. By making grease water repellent, the water tolerance/resistance limit can be extended and resultant water washout and water spray-off property can be improved. Thus life of grease and bearings can be increased substantially. We have attempted to study the water washout resistant property of four different soap based greases by incorporating two different types of polymers viz. high molecular weight polymer and specially designed hydrocarbon resin polymer in these greases. The water washout and water spray off tests were conducted of these greases with these polymers. The water washout and water spray off tests were also conducted in base greases (without these additives). Other performance enhancing additives like EP/Antiwear, antioxidant and rust and corrosion inhibitor were also incorporated to meet requirement of high performance grease. These greases were tested for all other test parameter also. There is a lot of improvement achieved in water washout resistant and water spray-off properties in these greases specimens. The grease specimen has enhanced high temperature thermal/oxidation stability, rust and corrosion inhibition property, good shear/ mechanical stability and high load carrying capacity as expected.

Introduction

The present work relates to study the water washout resistance and water spray-off resistant properties of two different types of polymers in four different soap type greases. The greases used in steel plants are more susceptible to water washout due to heavy water ingress in hot & cold rolling mills. Therefore selection of proper grease is very important for successful running of rolling mills. Normally simple Lithium soap, mixed soap (Lithium and Calcium) based and Lithium Complex greases are used. These greases are emulsified with huge quantity of water thus not able to withstand the force of water sprayed on bearing and washed away from the bearing. Therefore Overbased Calcium Sulfonate complex based grease is introduced and being used predominantly. But due to continuous high ingress of water/emulsion it absorbs lot of water and grease gets emulsified and deterioration of grease structure takes place. Normally 300 and 400 BN calcium sulfonate is used for making calcium sulfonate complex grease. Total Base Number (TBN) of calcium sulfonate used for making Calcium sulfonate complex grease, also play a crucial role in water resistant and water spray-off resistant property. Higher the TBN of Calcium sulfonate about 400 better the water wash out and spray-off resistant property, whereas, the calcium sulfonate with 300 TBN have less water resistance and tolerance than 400 TBN calcium sulfonate. Though the Calcium Sulfonate complex grease has good water absorption and water tolerance property at lower consistency and retaining its structure, but this tolerance limit decreases at higher consistency side, as a result break down of grease structure takes place and grease is washed away due to continuous spray/ingress of water. As a result frequent re-lubrication is required in bearings. Additionally, the water washout property and water spray off property is also related with consistency of grease and the viscosity of base oil used for making grease. Lower the consistency and higher the base oil viscosity, better the washout and spray-off resistance property. Grease in NLGI 3 range is not suitable for centralized lubrication system. But in rolling mills the grease made with high viscosity oils also not able to withstand force of water and rolling oil emulsion. Since in steel plants bearings are lubricated through centralized lubrication system, the consistency need to be adjusted at higher side i.e. between NLGI 2 and NLGI 1.5 consistency range having high water resistant and water spray-off property, good structure/shear stability and the mechanical stability even in the presence of water ingress. In order to maintain its structure and remain inside the bearings, the grease is required to have good water repellency in addition to water tolerance property. By making grease water repellent, the water tolerance/resistance limit can be extended and resultant water washout and water spray-off property can be improved. This can be achieved by use of high molecular weight polyisobutylene and specially designed hydrocarbon resin polymer (neopolymer) in these greases. The greate advantage of hydrocarbon resin is they are very good water repellant, highly hydrophobic and shear stable. Due to better water repellency they will not soften and washed away even in hot water. Thus the grease will remain in bearing and the life of grease and bearings can be enhanced substantially. They are more water repellant than polymers and penetration of water will be less in grease and retention of grease structure and water resistant will be higher. This hydrocarbon resin gives extra tackiness and embodiment to grease. Due to these characteristics they are preferably used in water resistant paint for longer life. The Performance of the grease was bench marked with respect to water wash out resistant, water spray-off resistant properties, the structure/shear stability and load carrying properties.

Experimental Details

Four different soap type greases were prepared by conventional method. The fatty acids for all the three types of greases were kept same. In first experiment the base oil viscosity of all the three grease types were kept in ISO VG 150. The consistency of all the four types different soap types greases were kept in NLGI 3 consistency range between 244 to 246. The water washout tests were conducted on these four greases. In second experiment the consistency was raised from NLGI 3 to NLGI 2 with consistency range between 274 to 276. Water washout test was conducted of these greases. In third experiment the base oil viscosity was further increased from ISO VG 250 to ISO VG 220 but consistency of the greases were maintained between 274 to 276. Water washout test was conducted of these greases. In fourth experiment the base oil viscosity was further increased from ISO VG 220 to ISO VG 320 but consistency of the greases were maintained between 274 to 276. Water washout test was conducted of these greases. In fifth experiment water wash out test was conducted for greases having different base number of over based calcium sulfonates used for making calcium sulfonate complex greases. Because Total Base Number (TBN) of calcium sulfonate used for making Calcium sulfonate complex grease, also play a crucial role in water resistant and water spray-off resistant properties. The base oil viscosity of both the greases was maintained in ISO VG 320 and consistency in NLGI 2 at 275. Since in steel plants water ingress is very high, the grease need to have very good water washout and water spray-off resistant properties, therefore the losses due to water washout and water spray should be minimal. In order to achieve this two different types of polymers viz. high molecular weight polymer and specially designed hydrocarbon resin polymer were tried at same treat level in these greases to enhance the water washout resistance and water spray-off resistant properties. Again water washout tests were conducted in all four different soap types greases. Other performance enhancing additives like EP/Antiwear, antioxidant and rust and corrosion inhibitor were also incorporated to meet requirement of high performance grease. These greases were tested for all other test parameter in addition to water washout resistance and water spray-off resistant tests. The water resistant properties were checked for all the four grease specimens before addition of these polymers. The details of types of greases are as under.

1. Simple Lithium soap grease

2. Lithium/Calcium mixed soap grease

3. Lithium Complex grease

4. Calcium Sulfonate complex grease

Results and Discussion

The test results of water washout and water spray-off properties of base greases prepared in NLGI 3 are provided in Table 1. The water washout value of simple lithium grease, Lithium/calcium mixed soap, lithium complex greases are about 5 to 6%, whereas in case of calcium sulfonate complex grease it is 3.6%. With rise in consistency of all the greases the loss due to water washout has almost doubled in all the greases. The results are provided in Table 2. It is clear that with increase in consistency the water wash out loss increase due to less adhesive property of grease as water can penetrates easily in thinner grease. However, when viscosity of base oil in grease is increased from ISO VG 150 to 220, the losses due to water wash out can be improved about 15 to 20%. The results are provided in Table 3. And when the base oil viscosity was further increased from ISO VG 220 to ISO VG 320 the losses due to water wash out could be further reduced from 16 to 20% in different soap type greases. The results are provided in Table 4. In recent time Overbased Calcium Sulfonate complex based grease is also being used predominantly in steel plants. As the Total Base Number (TBN) of calcium sulfonate used for making Calcium sulfonate complex grease play a crucial role in water resistant and water spray-off resistant properties. The Water washout test was conducted of two calcium sulfonate complex greases having 300 and 400 TBN. The results are provided in table 5. It can be observed that calcium sulfonate used for making grease having high base number i.e. 400 TBN has shown better water washout resistant property than lower base number i.e. 300 TBN calcium sulfonate. The grease having 400 TBN has water washout loss 4.28% whereas grease is having 300 TBN has shown water washout loss 5.33%. But these losses are also very high. And grease will be washed away from the bearing shortly. Therefore this limit need to be reduced minimal level. In order to make grease more water washout and water spray-of resistant two different types of polymers viz. high molecular weight polymer and specially designed hydrocarbon resin polymer were tried at equal treat level in these greases to enhance the water washout resistance and water spray-off resistant properties. The water washout resistance of simple lithium soap grease come down from 8% to 5% with both the polymers. In lithium calcium mixed soap grease from 6.4% to 2% and 2.1% with polymers with P1 and P2 respectively. In lithium complex from 6.5% to 4.4% and 4.5% with polymer P1 and P2 respectively. And in calcium sulfonate complex grease it has come down from 4.29% to 1.97% with polymer P1 and 2.1 with polymer P2. The results are provided in table 6.

Conclusions

The water washout losses of greases increase with increase in penetration/consistency of grease. The water washout losses of greases reduce with increase of mineral oil viscosity used for making greases. The base Number of over based calcium sulfonate used for making calcium sulfonate complex grease also plays a role in improvement in water washout and water spray-off resistance properties. Higher the base number of calcium sulfonate used for making grease lower the losses of grease due to water washout. Use of water repellent is essential for making grease more water washout resistant and water spray-off resistant. By making grease water repellant water tolerance limit of greases can be extended thus greases will be most water resistant. The hydrocarbon resin polymer used for making water resistant grease has also comparable water washout resistant properties with high molecular weight polymer used currently.

Table 1. Test Results of water washout properties of base greases (grease consistency NLGI 3)

Grease type	Grease consistency 60 X (NLGI 3)	Base oil viscosity @ 40°C	Water Washout, ASTM D1264 79°C % loss

Simple Lithium soap	245	150	6
Lithium/calcium mixed soap	244	150	5
Lithium Complex	246	150	5
Calcium sulfonate complex	245	180	3.6

Table 2. Test Results of water washout properties of base greases ( grease consistency NLGI 2)

Grease type	Grease consistency 60 X (NLGI 2)	Base oil viscosity @ 40°C	Water Washout, ASTM D1264 79°C % loss
Simple Lithium soap	274	150	12
Lithium/calcium mixed soap	276	150	10
Lithium Complex	275	150	10
Calcium sulfonate complex	276	180	6.8

Table 3. Test Results of water washout tests of base greases with higher viscosity base Oil (ISO VG 220 )

Grease type	Grease consistency 60 X (NLGI 2)	Base oil viscosity @40°C	Water Washout, ASTM D1264 79°C % loss
Simple Lithium soap	274	220	9.5
Lithium/calcium mixed soap	276	220	8
Lithium Complex	275	220	8
Calcium sulfonate complex	276	220	5.1

Table 4 Test Results of water washout properties with higher base oil viscosity (ISO VG 320 )

Grease type	Grease consistency 60 X (NLGI 2)	Base oil Viscosity @40°C	Water Washout, ASTM D1264 79°C % loss
Simple Lithium soap	274	320	8
Lithium/calcium mixed soap	276	320	6.4
Lithium Complex	275	320	6.5
Calcium sulfonate complex	276	320	4.29

Table 5. Test Results of water washout properties of Calcium sulfonate grease with different base number without polymer

Grease type	Grease consistency, 60 X	Base oil Vis @40°C	Water Washout, ASTM D1264 79°C % loss
			300 BN	400 BN
Calcium sulfonate complex	275	320	5.33	4.28

Table 6. Test Results of water washout tests of greases (with two different polymers)

Type of polymers

1. Hiigh Molecular Weight polymer (P1)

2. Hydrocarbon resin polymer (P2)

Grease type	Grease consistency 60X (NLGI 2)	Base oil Vis @40°C	Water Washout, ASTM D1264 79°C % loss
			P 1	P2
Simple Lithium Soap	274	320	5	5
Lithium/calcium mixed soap	276	320	2	2.1
Lithium Complex	275	320	4.4	4.5
Calcium sulfonate complex	278	320	1.97	2.1