Miniature Penetrometer for Determining the Consistency of Lubricating Greases -
GUS KAUFMAN, W. J. FINN,
AND
R. J. HARRINGTON, The Texas Company, Beacon, N. Y.
T
penetrometer and which permits accurate consistency measureHE accepted method for determining consistencies of ments on small samples of greases-that is, about 3 to 5 grams. lubricating greases is the A. S. T. M. method ( I ) , which, With a slight modification of the design, consistencies of even however, requires that a considerable quantity of grease be smaller samples could be determined. Generally, more than available-i. e., a t least 400 to 500 grams for grease of soft or this quantity of used grease can bereadilyrecovered from antimoderately soft consistencies. Such large quantities of friction bearings of average size. The miniature penetromegrease are readily obtainable in the manufacturing plants or ter not only permits positive measurements but also allows in storage; however, it frequently happens that information check determinations with a small supply of sample, and fairly on the consistencies of very small samples of grease is desired. consistent check results are possible on the same sample of For example, after use on ball or roller bearings, such as the used grease. Furthermore, the miniature penetrometer is so antifriction bearings of motors, automobile wheels, indusconstructed as virtually to preclude any possibility of the trial machines, etc., only relatively small quantities of worked cone’s touching the sides of the special grease container used in or used grease adhere to the bearings. This amount of used this method. grease is inadequate for actual measurements of consistency The question of obtaining consistencies of small quantities by the A. S. T. M. method; hence it has been the usual cusof semisolid materials such as lubricating greases, as expressed tom to estimate consistency change in use more or less by in terms of the depth of penetration of a plunger, has been guess or by comparison with products of known consistency. given study in the past, the apparent solution being to use a The accuracy of such practice is, of course, questionable. small penetrometer needle and a small holder for the grease in Again, in the case of the A. S. T. M. method, it is difficult to place of the present A. S. T. M. grease cone (6.5-cm., 2.56 obtain accurate check determinations on the same sample if inches, in diameter) and the rather large-sized grease holder the grease is soft and the penetration of considerable mag(453.6-gram, 1-pound, tins are recommended). nitude-for example, 300 and over (units being tenths of a While various types of small plungers such as glass rods of millimeter). The large size of the A. S. T. M. penetrometer different weights have been used in earlier work, thereby recone in relation to the grease surface presented for test, which ducing the size of- the is- limited by the size of plunger cone, the chief the grease container, is difficulty encountered has responsible for this condibeen in a suitable design tion. In taking penetraof a small holder for the tions of soft greases even grease, since charging of a in the required size of consmall cylinder w i t h a tainer, the depth of penesemisolid material such as tration is such that the a lubricating grease causes original grease surface is air entrainment as well as considerably disturbed w o r k i n g d o w n of t h e and the bulk of the grease grease structure and conslightly worked. The sequent alteration in conlimited area exposed presistency, usually softenvents subsequent detering. Both difficulties are minations on undisturbed overcome by using a split surfaces, owing to the cylinder for the holder. danger of the cone’s touchEach half of the cylinder ing the sides of the grease can be charged with grease container. The only reby simply using a spatula. maining alternative, I n this manner, working therefore, is to smooth out down of the grease is the disarranged surface practically negligible and and again determine the air entrainment is reduced consistency in essentially to a minimum. the same spot. Readings With regard to the peneincreasingly higher than t r o m e t e r cone, in t h e the original value, since A. S. T. M. method the repeated working induces cone, as stated above, softening, are usually obhas a maximum radius of tained as a result of this 6.5 cm. (2.56 inches), the procedure. total weight of cone and T o circumvent the plunger being 150 g a m s . above objections to the In order to take penetraA. S. T. X I . method a tions of small samples it m i n i a t u r e penetrometer was necessary to reduce has been designed which the size and weight of the may be utilized as an adplunger, which was acFIGURE1. MINIATUREPENETROMETER ASSEMBLY junct to the A. s. T. M. 108
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FEBRUARY 15, 1939
ANALYTICAL EDITION
109
transferred into the small grease holder by means of ci spatula, filling each half of the split cylinder. The two halves are then clamped together by means of the brass collar as indicated in Figure 1 and the surface of the grease is smoothed off. In order to ensure centering of the grease holder with the plunger, a centering plate (not shown), with suitable recess to fit the base of the miniature grease holder, is affixed to the base of the A. S. T. M. penetrometer and the grease holder is placed in the recess. This prevents movement of the holder during taking of penetrations. Penetrations are obtained as in the A. S. T. M. method. After each penetration, if check results are desired, additional grease is added to the grease cup, the surface is smoothed off, and the test is repeated. For very hard greases weights can be added to the plunger.
ST€€L LOCKNUT
LUMINUM CON€
RASS COLLAR
FIGURE 2. DETAILSOF ASSEMBLY
complished by the use of a n aluminum plunger and cone with a total weight of but 20 grams. For very hard greases, provisions are made for adding weights to the grease plunger. The small grease holder and plunger are then used in conjunction with the present A. S. T. M. grease pen+ trometer indicator, thereby reducing the cost of the miniature penetrometer to a minimum.
Description of Apparatus I n Figure 1 is shown a photograph of the miniature penetrometer assembled, and in the foreground are shown the individual parts of the grease holder, plunger, and cone. Figures 2 and 3 give details of construction of the grease cup or holder, aluminum plunger, and aluminum cone. The grease cup (capacity 4 grams of grease) consists of a split brass bushing 5.715 x 0.952 cm. (2.25 X 0.375 inches) in inside diameter affixed to a suitable base. The penetrometer needle or plunger consists of an aluminum cone which fits into an aluminum plunger and is connected to the A. S. T. M. penetrometer indicator. The total weight of the aluminum cone, plunger, etc., is 20 grams. The method of obtaining penetrations follows that outlined in A. S. T. M. Designation D217-33T (1). After bringing the grease to the usual teomperature, 25" * 0.556' C. (77 * 1 F.), it is
Experimental Data I n order to determine what relationship, if any, exists between this miniature penetrometer and the A. S. T. M. penetrometer, comparative data were obtained on the most common types of greases of different consistencies, as follows: Calcium soap with oil of low and of high viscosity. Sodium soap with oil of low and of high viscosity. Mixture of sodium and calcium soaps with oil of low and of high viscosity. Aluminum soap with oil of low and of high viscosity. Results obtained are given in Table I. The range of consistencies of the greases shown is that commonly termed in the trade from No. 00 to KO.3, and penetrations have been compared on the worked sample as specified under A. S. T. M. Designation D217-33T ( I ) . As regards reproducibility of results, except for very fibrous greases the miniature penetrometer method compares favorably with the A. s. T. 111. method which permits a mean deviation of 3 per cent. With regard t o a possible correlation between the miniature penetrometer and the A. S. T. M. penetrometer, it is seen from
I
76.
OF GREASECUP, CONE,AND PLUNGER FIQURE 3. DETAILSOF CONSTRUCTION
All dimensions are in millimeters
INDUSTRIAL AND ENGINEERING CHEMISTRY
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VOL. 11, NO. 2
available is too small for the A. S. T. M. penetrometer, t h e (Penetrations of worked samples) Grease B Grease C Grease A miniature penetromeMiniaMiniaMiniater satisfactorily A.S.T.M. ture A.S.T.M. ture A.S.T.M. ture serves the purpose of Buttery texture calcium 327 208 298 111 266 84 soap, mineral bil 300 Sa 323 209 292 108 262 86 determining the rela, . , 210 ... 111 ... 84 U. a t 37.78” C. (100 85 tive change in consist., 209 ,.. 110 . . F.) ,,. 211 ... 116 ... 85 ency of a grease after ... 211 ... 118 .. ... ,,, ... 116 . . .. use compared to the Av. 325 210 295 113 264 85 original, u n u s e d Grease D Grease E product. Buttery texture, oalcium 299 167 278 104 ... ,. As an example of soap, mineral oil 100 Si 295 163 273 103 .. U. at 98.89’ C. (210 ,., 166 ... 103 . . the application of the B.) ,.. 165 ... 102 . . miniature penetromeAv. 297 165 276 103 ter in practical Grease F. Grease G e v a l u a t i o n s ,two Fibrous texture sodium 290 103a 232 57 , . . , . 288 110“ 225 57 ... .. soap mineral bil 300 8. greases having prac... 57 ... .. U. s’t 37.78’ C. (100’ 287 llla .. tically identical A. S. ... ... ... 1120 F.) ... ... Dl T. M. worked pene... ... ... 58 Av. 288 1090 229 58 .. trations were used on the same ball bearing Grease H Grease I Grease J Fibrous texture sodium 348 291 286 131 214 60 o p e r a t i n g a t 3,450 341 295 282 126 ... 61 soap mineral bil 175 S. r.p. m. After such use ... 298 ... 130 ... 63 U. dt 98.89’ C. (210’ ._ _ 294 ... 128 ... .. -l7) less than 10 grams of Av. 345 295 284 129 214 61 grease were available Grease K Grease L for examination, in340 300b 312 177 ... .. MiFed sodium and. calsufficient for an A. s. 335 2882, 316 167 ... .. mum soaps mineral ... 290b 315 167 , . . .. oil 200 9. U: a t 37.78’ T. M. worked pene.... ,. 275b ... 177 ... .. C. (100’ F.), very short tration. The consist288, ... 177 ... .. fibers ... ... ,.. .. ... 282) ency of the used ... ... ... .. ... 2S7b ... ... , . ... 278b ... grease was therefore Av. 338 286b 314 173 .. determined by the Grease M Grease N miniature penetromeMixed sodium and ca!296 153 270 110 ... ter and i t was found 271 110 ... oium soaps, mineral 011 293 155 ... 157 ... 116 50 6. U. at 98.89’ C. a considerable that ... 111 ... .. (210’ F.), very short ... 160 difference in consistfibers ... 155 ... 112 ... *. Av. 295 156 271 112 ... .. ency of t h e t w o greases existed after Grease 0 Buttery texture, alumi289 125 ... ... ... .. use, in spite of the num soap, mineral oil 299 122 ... ... ... .. fact that the original 300 S. U. a t 37.78’ C. , .. 121 ... ... . . . .. 122 ... ... ... .. (100’ F.) A. S. T. M. worked .. . ,. 121 ... ... ... Av. 294 122 ... ... ... .. p e n e t r a t i o n s were practically identical. Grease P Crease Q Table 111 points this 340 218 310 173 ... .. Buttery texture, alumi318 220 305 176 ... .. num soap, mineral oil out and shows that ... 217 ... 176 ,.. .. 100 S. U. at 98.89’ C. ... 218 ... 175 ,.. .. (210” F.) t h e A. S. T. M. Av. 329 218 308 174 ... .. worked penetration Fibrous texture,.difficult to obtain checks. does not necessarily b Difficult to obtain checks on acoount of texture. predict the consistency of greases after use in ball bearings, nor is it necessarily a criterion of leakage tendency. TABLE 11. GREASECONSISTEXCIES
the data submitted that the relationship, if any, varies with the texture of the grease, the particular soap used, the viscosity of the mineral oil, etc. I n Table I1 miniature penetrations are shown for greases of different soaps, different textures, and different oils, but having approximately t h e same A. S. T. M. workedpenetration of 300. For an A. 8. T. M. worked penetration of about 300 the miniature penetration varies from 120 to 125 for a lime soap or aluminum s o a p g r e a s e of a buttery texture cont a i n i n g a low-visoosity oil to about 170 to 200 for a fibrous soda soap or mixed soda-lime soap grease containing an oil of either high or low viscosity. Apparently, therefore, the fibrous texture of soda soap greases permits greater penetration of the miniature plunger than is the case with the “buttery” textured lime soap cup greases. H o w e v e r , since in studying the performance of lubricating greases in service it is desired to know primarily the relative change in consistency, and since the quantity of grease
Soap
TABLEI. COMPARATIVE CONSISTENCY DETERMINATIOKS
,
- - I
e?
. I .
.
I
.
5
Soda
Texture Fibrous
Mixed soda-lime
Very short fibers
Aluminum
Buttery
Lime
Buttery
TABLE
~~
.I
Viscosity of Oil Low High Low High Low High Low High
Miniature Penetrations for A.S.T.M. Worked Penetration of 300 175 170 200
160
125 170 120 165
111. GREASE CoNSISTENCIES
A.S.T.M. worked penetration Miniature penetration after working in ball bearing Remarks
Grease R 323
Grease S 324
345
456 Bad leakage past bearing seal
N o leakage past
bearing seal
Summary A method of obtaining penetrations of small samples of grease of the order of 4 grams is described, which gives re-
sults of reasonable reproducibility, The apparatus is inexpensive, since it utilizes the present A. S. T. M penetrometer and requires in addition only a simply constructed grease holder and an aluminum plunger and cone. It is a valuable adjunct to the A. S. T. M. penetrometer.
Literature Cited (1) Am. SOC.Testing Materials, “Standards o n Petroleum Products a n d Lubricants,” Designation 217-33T, p. 235, 1936. RECEIVED September 27, 1938. Presented before the Division of Petroleum Chemistry a t the 96th Meeting of the American Chemical Society, Milwaukee, Wis., September 5 to 9,1938.
