Complexing of Lithium Soap Greases – A New Approach

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, @ 25oC 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, @ 100oC, 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 @ 80oC, % loss wt.	4.66	4.98	ASTM D 1264
Roll Stability, % change @ ambient, after 16 hrs @ 82oC, after 48 hrs.	7 21	9 23	ASTM D 1831
Oxidation Stability, @ 100oC 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