SOME CRITERIA UNDER VARIOUS M.

FOR THE EFFICIENCY

OF G R E A S E S

CONDITIONS

M. G e r a s i m o v

and

I.

T. Z a k h a r i e v

UDC621.892.5

Most of the existing standards for the greases produced in the Bulgarian People's Republic (BPR) do not correspond to modern requirements. In this connection, one of the most important trends in research work is the development and evaluation of new methods for determining the physicochemlcal and service properties of modern greases. Within the framework of the Council for Mutual Economic Aid (CMEA) of the BPR there is specialization in the development and introduction of new methods of studying greases, which facilitate the evaluation of their service properties. There are dozens of criteria for the properties of greases and hundreds of different methods of determining them [1, 2]. However, until now the standard requirements for greases of the same type and application in different countries have included a great variety of property criteria, and in fact there is a dearth of unified and generally accepted characteristics which can be used as the basis for evaluating different types of greases. Numerous observations and a wealth o f practical experience in greases testify to the fact that the generally acEepted standard criteria are not adequate for predicting the true behavior of greases in service, and are evidently of little importance as means of controlling the production of greases. In the BPR many of the important criteria characterizing the behavior of greases have so far not been standardized, while other criteria have not been defined. In this connection, the most important service properties of greases are: the antiwear and adhesional properties, the stability to oxidation, the water resistance, and the theological properties [3]. This article presents the results obtained in evaluating certain important properties of greases which provide a means of more completely characterizing their efficiency under certain conditions of use. The effect of various factors involved in the manufacture and application of complex barium, calcium, sodium, and lithium greases on their adhesional and viscosity properties is studied. The adhesional properties of greases, which include their power to adhere to and be retained by metal surfaces, are very important for greases used for various applications, for example antifrictional, protective, and packing greases. In order to obtain a clearer and more accurate impression of the adhesional forces (as far as possible excluding the cohesional effect), a method and the appropriate equipment have been developed which provide a means of operating with very thin layers of grease [4]. The effects of temperature and rate of rotation on the changes in adhesional properties of the greases investigated (test sample not more than 1.0 g) have been studied. Test on complex barium greases have shown the marked relation between the adhesional properties and the formulation of the grease. The best results were obtained with greases which used technical stearic acid, bone fat, and synthetic fatty acids (SFA) with more than 22 C atoms as the fat base. Grease loss under test conditions was completely absent, and the adhesional properties were expressed in terms of the percentage of grease remaining on the disc. Different results were obtained with greases using technical oleic acid and Ct9-C22 synthetic fatty acid fractions as the fat base (Table 1). It can be seen from Table 1 that the use of technical oleic acid as the fat base of complex barium greases !cads to a rapid deterioration of adhesional properties. The best results were obtained by using Ct9-C22 SFA frac-

Higher Chemical Technology Institute, Sofia. Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 7, pp. 47-49, July, 1970.

I 9 1971 Consultants Bureau, a division of Plenum Publishing Corporation, 227 West 1 7th Street, New York, N. Y. 10011. All rights reserved. This article cannot be reproduced for any purpose whatsoever I without permission of the publisher. A copy of this article is available from the publisher for $15.00.

539

TABLE 1. Adhesional Properties of Complex Barium Greases Manufactured on the Basis of Technical Oleic Acid and C~9-Czz SFA Fractions (data within braces) Rate of rotation, rpm 1800 2000 2200 2400 2600

Grease loss at the temp., % PO ~

40 ~

lOO(lOO) 93(lOO) 78(lOO) 6O(lOO) 3O(lOO)

100(100) 89(100) 71(98) 51(88) 21(66)

60 ~

46(100) 41(100) 33(93) 21(81) 11(63)

TABLE 2. Adhesional Properties of Calcium Greases Manufactured on the Basis of Bone Fat and Technical Stearic Acid (data within braces) Rate of

Grease Ioss at the temp,, %

rotation, rpm

20 ~

1800 2000 2200 2400 2600

lOO(lOO) 93(1oo) 87(98) 79(92) 60(86)

40 ~

99(100) 69(100) 58(95) 52(87) 46(78)

60 ~

95(100) 48(100) 31(9i) 21(81) 13(65)

tions. However, on increasing the temperature and rate of rotation by 37%, the grease w a s e j e c t e d from the test unit. The investigaEons on c a l c i u m greases also i n d i c a t e d the marked dependence of the adhesional properties on the composition of the fat base from which they were manufactured. It should be noted that c a l c i u m greases have adequate adhesiveness, which as with other types of greases is inversely related to the temperature and to the rate of rotation of the test unit. Table 2 gives data on the adhesional properties of greases manufactured on the basis of t e c h n i c a l stearic acid and bone fat. Greases manufactured on the basis of SFA fractions and t e c h n i c a l oleic acid were tested similarly. In contrast to the complex barium greases, the worst results (under the most stringent test conditions, 60 ~ and 2600 rpm) in the case of the c a l c i u m greases were obtained with those manufactured on the basis of SFA fractions with more than 22 C atoms, while somewhat better results were obtained with the C19_22 SFA fractions, and even better results with greases manufactured on the basis of t e c h n i c a l oleic acid, The adhesive powers of these greases were 5.12 and 24%, respectively. The very marked relation between the criteria of the adhesional properties and temperature in the case of the c a l c i u m greases manufactured on the basis of bone fat should be noted (see Table 2). This provides a basis for the assumption that the results of the given test method can be used, in combination with other criteria, for selecting the optimum temperature range for using a particular grease. The adhesive properties of lithium and sodium greases manufactured on various fat bases were studied. The greatest adhesion was exhibited by greases manufactured on the basis of t e c h n i c a l stearic acid and bone fat. At 60 ~ and 2600 rpm they exhibited adhesion powers of 52 and 40%, respectively. Considerably inferior results were obtained by using t e c h n i c a l oleic acid and SFA as the fat base. Thus, for example, in the case of a CIg.z2 SFN fraction the adhesion power under the most stringent test conditions was 16%, which was approximately the same as the value obtained with SFA greases containing more than 22 C atoms. In contrast to lithium and sodium greases manufactured on the basis of SFA fractions at all the temperatures and rates of rotation studied, grease losses (due to lack of adhesion) were c o m p l e t e l y absent. Adequately high a d hesion power (60*, 2600 rpm) was also o b s e ~ e d with sodium greases manufactured on the basis of bone fat, while in the case of t e c h n i c a l oleic and stearic acids the adhesive powers were 65,45 and 74%, respectively. The viscous properties of greases are very important in their selection and application. The first serious investigations in this field were carried out 30 years ago [5]. Up to the t i m e of writing some detailed studies have been reported on the effect of certain basic factors on the properties of different greases [6-8].

540

Since greases have to be used at various temperatures and at various speeds of the lubricated components, the factors generally studied are the viscosity-temperature and the v i s c o s i t y - v e l o c i t y characteristics (VTC and VVC). In our investigations we studied samples of barium, lithium, c a l c i u m , and sodium greases of high adhesive power. The tests were carried out on a type "Reotest RV" rotating viscometer, which enables the v i s c o s i t y - t e m p e r a ture characteristics of greases to be determined over the temperature range - 3 0 to +150", and at absolute viscosities of I0-I0 -7 cP. The results obtained in studying complex barium greases showed that the viscosity-temperature characteristic deteriorates on increasing the rate of deformation. In evaluating VTC and VVC greases at the m a x i m u m permissible speeds (i.e., 243 rpm) and temperatures, the viscosity was found to depend more on the rate of rotation than on the temperature. In this respect the best grease was the c o m p l e x barium grease obtained by using t e c h n i c a l stearin. With this grease, increasing the speed from 0.28 to 243 rpm at - 3 0 ~ reduced the viscosity by a factor of 49, and at +150 ~ by, a factor of 70, whereas in the case of greases based on bone fat the viscosities were reduced at these t e m peratures by factors of 48 and 246, respectively. Raising the temperature from 40 to 120 ~ at constant velocity of rotation reduced the viscosity of the grease based on stearic acid approximately by a factor of two, while in the case of greases based on bone fat, those based on oleic acid, those based on Cm_22 SFA, and finally those based on SFA with more than 22 C atoms, the viscosities were reduced by factors of 11.4, 7.9, 4.2, and 6.2, respectively. In the case of c a l c i u m greases it has been established that the greases with the m a x i m u m effective viscosity are those manufactured using bone fat, while those based on SFA exhibit the m i n i m u m effective viscosity. The best results with respect to the viscosity as a function of temperature and v e l o c i t y gradient were obtained with greases manufactured on the basis of bone fat and oleic acid. Thus, e.g., with oleic acid based greases this r e l a tion, at constant temperature, rises from 48 to 124 over the range of rotation velocities studied, while with greases based on stearic acid this change is spread over the range 38-75. Of the lithium greases, those with the m a x i m u m effective viscosity were the ones manufactured on the basis of oleic acid and bone fat, and those with the m i n i m u m effective viscosity, those manufactured on the basis of SFA. The l i t h i u m greases e x h i b i t e d the best viscosity-temperature characteristics, this being especially characteristic in the case of lubricants based on t e c h n i c a l stearic acid and bone fat, for which the VTC (over the temperature range 30-70 ~ were expressed by the values 2.3 and 2.9, respectively. The relation between the viscosity of these greases and the v e l o c i t y gradient is more c l e a r l y apparent, while for the range of velocities studied the change in the viscosity ratio (at constant temperature) is within the range 164-202. This indicates that the lithium greases are more suitable for use under conditions where the characteristic feature is a change in temperature for r e l a t i v e l y constant rates of movement of the lubricated surfaces. In contrast to the lithium greases, the sodium greases having the m a x i m u m effective viscosity are those manufactured on the basis of SFA, while the ones with the m i n i m u m effective viscosity are those based on oleic acid. tn the case of the SFA greases, on raising the temperature the viscosity fails to a less extent than with the lithium and sodium greases. A c o m m o n factor with all the samples of sodium greases is the high values obtained for the viscosity ratio at e x t r e m e temperatures, this behavior being more marked with the SFA based greases than with those based on stearic a c i d A n o t i c e a b l e change in the viscosity of greases is observed over a l i m i t e d range of variation of rotation rate. In the case of greases based on bone fat, the velocity temperature characteristic has the value 63, whereas for greases based on stearic acid, oleic acid, and those manufactured using Ct0_22 SFA and SFA containing more than 22 C atoms the values are 150, 100, 191, and 225, respectively. This indicates that the sodium greases manufactured on the basis of fats of natural origin have better viscosity characteristics than those based on SFA. LITERATURE I.

2. 3. 4. 5. 6. 7. 8.

CITED

K. D. Boner, Manufacture and Application of Greases [in Russian], Gostoptekhizdat (1958). V. V. Sinitsyn, Foreign Greases [in Russian], Gostoptekhizdat (1963). M. M. Oerasimov and L T. Zakhariev, Annual Publication of KhTI, Book 2, 9 (1962), pp. 128-125. L T. Zakhariev, New Types of Greases and Methods for Their Thorough Investigation [in Bulgarian], Candidate's Dissertation, VKhTI, Sofia (1968). N. H. Arvenson, Ind. Eng. Chem., 24, No. 1 (1932); 26, No. 6, 628 (1934). V. V. Vinogradov, Uspekhi Khim., 20, No. 5, 533 (1951); 21, No. 6, 756 (1952). V. V. Sinitsyn and K. I, Klimov, Kolloidn. Zh., 22, 469 (1960). V. V. Sinitsyn, Viscous Properties and Boundary Sliding of Greases [in Russian], Candidate's Dissertation (1954).

541