Tapered=Hole Disk Penetrometer for Determining Consistency of Semifluid Greases D. H. BIRDSALL AND B. W. HOTTEN California Research Corp., Richmond, Calif.
EMIFLUID gxeases have consistencies midway between
determine if some t l p e of cone or disk fitting this instrunicnt could be adapted to the semifluid consistency range. The Potter-McLennan disk ( 7 ) appeared to offer the most promise, but it has definite limitations in the softer greases, in which it sinks to the bottom of the penetrometer cup in less than 5 seconds.
S lubricating oils and consistent greases. They contain highly dispersed thickeners in concentrations of from about 1 to 9%. As a result, they are too viscous to be measured by normal viscometric means and yet are too fluid to be graded by conventional penetration methods. They are characterized by nonSewtonian shear-stress-shear rate relationships and possess a structure so fragile that measurements a t low shear rates are required if the consistency of the thickener-oil system rather than the viscosity of the base oil is to be measured. -4variety of methods are now used by manufacturers for grading these products, but there has been no standardization because no one instrument is satisfactory for all manufacturers and consumers. A tapered-hole disk penetrometer has been designed which provides a satisfactory method of grading semifluid greases.
E W A L L I SPACED.
.
10 0.292' DIAMETER EQUALLY SPACED.
PRESENT METHODS
Semifluid grease consistency is, a t present, determined by one of several different methods, depending upon the product and the manufacturer's choice of instruments. The various methods are tabulated in Table I, together with their advantages and disadvantages. Each method suffers from one or more disadvantages. In general, the penetration methods are too limited in range, and it is necessary to use a combination of disks or cones to measure the desired range of consistencies. The Gardner Mobilometer, and its modifications such as the S.I.L. hlobilometer ( 6 ) , although satisfactory for the analysis of paint products, are not adaptable for use with greases; they are inconvenient t o use because the variety of disk and weight combinations needed to cover the desired range makes it difficult to compare samples of various consistencies with one another. The rotational viscometers (4, 6, 8) used for the purpose are expensive and inconvenient to operate. The results, holyever, may be expressed in conventional viscosity units, which is a distinct advantage, These instruments have a definite place in research work, but they are not suitable for grease product control. The simplified pressure viscometer of Brunstrum and Steinbruch (3) is a compact, well designed instrument which provides data over a wide consistency range, but the lack of response in the Bourdon-type gage, owing to pressure drop in the Bourdon tube when a semifluid material is present, complicates its use.
.U A. C I
DESIRE DURALUMIN (ALUMINUM ALLOY 2457) WEIGHT 102.5 G.
-7J
1
,+
SHAFT PRESS FIT TO DISC.
-Y SECTION
Figure 1. Tapered-Hole Penetrometer Disk
Attempts were made to extend the range of the Potter-1IcLennan disk by two methods:
-4disk was made from Duralumin (aluminum alloy 24ST) in place of steel to decrease the weight. This attempt was unsuccessful because the more fluid greases still permitted the disk to sink t.0the bottom. A disk was fabricated from Duralumin with 0.25-inch holcs drilled on the same centers as the 0.5-inch holes in the original disk. This disk was satisfactory in soft reases, but was insufficiently sensitive for the stiffer greases, T%e holes were increased to @/32 inch and various combinations of weights were tried, but in every case an improvement a t one end of the desired range resulted in a sacrifice in sensitivity or coverage on the other end.
DISK,TYPE PENETROMETERS
Because the ASTM penetrometer ( 1 ) is the most universally used instrument for grading greases, an investigation was made to
Table I.
*k"
Summary of Present Methods for Determining Semifluid Grease Consistency
Method
Type of Apparatus
Light weight cone (3) Potter-McLennan perforated disk ( 7 ) Gardner mobilometer (6)
Used in SST-M penetrometer Used in ASTM penetrometer Falling perforated disk or cone under various loads Rotational viscometer
Convenient. low cost Convenient. low cost Wide range Wide range
Insensitive floats in soft greases Range limiked to harder semifluid greases Inconvenient t o use, hard t o clean, specifications complicated Expensive, complicated operation and specifica-
Rotating spindle mounted on torsion head Grease forced through capillary b y gear pump Torque measured on paddle immersed in rotating cup of grease
Wide range
Expensive, complicated specifications
Wide range, fixed shear rate rlutomatic recording, wide range
Expensive operation complicated because of Bourdoi gage, hard t o clean Expensive. complicated speclfications a n d operation
hlcMichae1 viscometer (6)
.4dvantages
Disadvantages
t7nn. y.y..u
Brookfield viscometera Simplified pressure viscometer (3) Brabender viscometer ( 8 ) a
Brookfield Synchro-electric viscometer, Rlodel LV, Brookfield Engineering Laboratories, Sharon, Mass.
892
V O L U M E 2 4 . NO. 5, M A Y 1 9 5 2
893 method are lower than these obtained when the container overflows, because grease must be forced up through the annular space between the container wall and the disk as the disk submerges.
Table 11. Cornarsition of Greases Oil vboosity,
Designation A
Sodium
B C
Sodium Csloium
D E
F G H I
S.S.U..
SOW
%
TYDe ~~
Sodium
Caloium Calcium Sodium Sodium Sodium
7 7 O F. 1,950
12
.
4.7 5.6 9.1 4.6 5.1
3,304
12.000 1.800
6,000 1.600
7.3
1,500 1,500 1.350
6.8 4.5
.
Gen+
Description Medium fiber. buttery, NLGI Grade 0 Long fiber Short fiber. v e r y s t r i n g y Medium fiber, buttery Short fiber, stringy Short fiber. stringy Medium fiber, buttery Medium fiber, buttery Medium fiber, buttery
.
TAPERED-HOLE DISK PENETROMETER
From experience gained in the variations of the Potter-Meh n a n disk, i t was decided to make a thicker disk having large holes a t the bottom, which tapered to a smaller diameter a t the top and were drilled on the same centers as in the previous disks. Sensitivity of the new disk should thus be approximately the same a8 that of the Potter-McLennan disk in the harder semifluid greases, while its travel would be impeded in the softer greases by the tapering holes, with a consequent broadening of range. .
.
. .
.
The effect of loading the disk was studied, and i t was found that reasonably good sensitivity could be obtained over a very broad consistency range if the disk was used with a total moving weight of 150 grams. The effect of additional weight wa8 also studied by testing the same greases with total weights of 200 and 250 grams. The results of these experiments are tabulated io Table I11 and plotted in Figure 3. The abscissa of the plot is an arhitrmy scale and has no relation t o the absolute consistency of the greases under test, because no suitable standard is available from which to set up a scale.
~
'O
i
=- 210 0
E2
200
B 110
ID0
A
B
C
D
L
r
C
"
,
GREASE
Figure 3.
Figure% Tapered-Hole Disk Penetrometer
For provision of a reasonable gradient it was decided t o make the disk 0.5 inch thick with the top opekng of the holes 9/8* inch in diameter and the bottom slightly over 0.5 inch in diameter or approximately the diameter of the holes in the Potter-McLennan disk. A Greenfield No. 233 spiral fluted burring reamer was found t o have about the desired taper. T h e final disk was fabricated from Duralumin and had holes tapering from 0.281 inch in diameter on thetop to 0.585 inch on the bottom. The disk weighs 102.5 grams so that a total moving weight of 150 grams is used with the standard ASTM penetrometer shaft. When fully submerged, the disk displaces 2.34 cubic inches of grease as compared to the 2.27 cubic inches displaced by the ASTM cone at full penetration.
A drawing of the new disk is shown in Figure 1 and a photograph in Figure 2.
Effect of Load on Tapered-Hole Disk Penetrometer
It can be seen from Figure 3 that increasing the weight increases the sensitivity of the instrument, hut there is a slight sacrifice in range. It remains to he decided from experience in use what the optimum weight for the disk should be. Grease I was a very fluid laboratory preparation, undoubtedly softer than the vast majority of semifluid greases marketed. It may thus be desirable to weight the disk and take advantage of increased sensitivity in the harder semifluid greases rather than attempt to obtain the widest range. The disk was a180 tried with the aluminum penetrometer shaft (aluminum counterpart of the standard steel ASTM shaft), and i t was found that an extremely fluid grease (1300 S.S.U. a t 100" F.) could be graded by this method. However, this would not he a. desirable test in most cases, hecause i t would involve changing the penetrometer shaft when changing from ASTM to disk penetrations. Table 111. (Penetrations in deoirnillimeters)
Grease
Designation
30-Gram PlaStie Cone
Tapered-Hole Diak 200 g. 250 g.
150 g.
PotterMoLennan Disk
EXPERIMENTAL RESULTS
Nine semifluid greases were used to test the tapered-hole disk and to compare i t with other penetration methods. The types of greases and their compositions are shown in Table 11. Eightounce tins (3 inches in diameter and 2 inches deep) were used as sample containers because they have the =me diameter as COMPARISON W J n l OTHER METHODS
fourths full. They do not flow over and permica greater depth of travel, hut are nondispossble. Penetrations obtained by this
The 30-gram plastic cone (2)anp the Potter-MeLennm disk were also used to test the same nine greases. Figure 4 is a plat of
894
ANALYTICAL CHEMISTRY
these two methods, together with one of the tapered-hole diJk a ithout added load. The Potter-McLennan disk gives good sensitivity up through grease E, but strikes bottom on all the softer greases. The 30gram cone measures all the greases, but owing to bouyancy, its sensitivity is low compared with the disk methods. There i3 a total spread of only 108 points over the nine greases tested, and there is a definite tendency for the sensitivity to decrease among the soft gremes. The data spread with the tapered-hole disk without load i J 233 points over the same range of consistencies. Its sensitivity is substantially tbe same as that of the 30-gram cone in the harder greases, and it is increasingly sensitive in the more fluid range. The Precision penetrometer timer was used for all data presented in this paper. Reproducibility was greatly improved over manual timing in the soft greases, wherein the disk moves continuously over the 5-second period. It was also found essential that the penetrometer cup be level full (except when the beakets were used) for each determination, in order to obtain good reproducibility with any of the instruments. The new disk-type penetrometer having tapered holes ha3 proved useful for grading semifluid greases. It is used in (>onjunction with the ASTM penetrometer, and it can be fabricated simply and cheaply. Its use requires no special skill or training other than that required for operation of the ASTJI penetrometer. LITERATURE CITED
A
B
C
D
E
F
C
~
I
GREASE
Figure 4.
Comparison of Penetration Methods
( 2 ) Brunstrum, L. C., A S T M Bull. 154, 66-7 (1948). 1 3 ) Brunstrum, L. C., and Steinbruch, R., Inst. Spokesman (Satl.
Lubricating Grease Inst.), 8, No. 8, 10 (1949).
:4) Buchdahl, R., Curado, J. G.. and Braddicks, R., J r . , Rev. Sci. Instruments, 18, 168 (1947).
6 )Combes, K. C., Ford, C. S., and Schaer, W. S., IXD. Esc. CHEY.,AKAL.ED.,12, 285-7 (1940). ( 6 ) .\lacMichael, R. F., J . Ind. Eng. Chem., 12,817-8 (1920). (7) Potter, R. -1..and McLennan, L. W.,Inst. Spokesmn?r ( S a t l . Lubricating Grease Inst.),8, S o . 9. 16 (1949). ( 8 ) JVicker, R . C., and Geddes, J. A , . dSTMBulZ. 120, 11-15 (1943).
(1) Am. SOC. Testing Materials, "Standards on Petroleum Products
Lubricants," Designation D 217-48, November 1950.
R E C E I V Efor D review M a r c h 23, 1951. A i c e p t d Soveiiiher 13, 1951.
Spectrophotometric Study of Cadmium-1,lO - Phenanthroline System COE WADELIN WITH M. G. SIELLON Purdue University, Lafayette, Ind.
X VIEW of the successful use of 1,lO-phenanthroline
as a
I reagent for the determination of iron (6),an investigation of the spectrophotometric properties of the cadmium-1,lO-phenan-
throline system was undertaken to determine the feasibility or' using it for the determination of cadmium. The possibility of such a method was indicated in the earlier work by the strong interference of cadmium in the determination of iron. The dissociation constant of the cadmium-tris-l,lC-phenanthroline complex was recently reported to be 6.4 X 10-'6 ( 4 ) . As the complex is colorless in solution, the ultraviolet region of the spectrum was scanned in order to see if any absorptive characteristics there could be used. It was found that 1,lO-phenanthroline itself absorbs radiant energy in the region from 200 to 300 mp and that the curve is modified by the presence of cadmium salts. Typical curves are shown in Figure 1. REAGENTS
Doubly distilled water x a s used throughout. I n order to ensure the absence of iron, a standard solution of cadmium chloride was prepared by electrolyzing a solution of J. T. Baker Chemical (20,'s C.P. cadmium chloride according to an ASTM method ( 2 ) , using a xeighed platinum cathode. The electrode ivas dried and rexveighed, then the cadmium deposit was dissolved in a minimum amount of reagent grade hydrochloric acid and diluted to 1000 ml. All other chemicals used wexe of reagent grade, no further puriEcation being made. APPARATUS
Measurements of the absorption of radiant energy were made with a Beckman quartz spectrophotometer, Xlodel DU. The
wave-length scale w-as calibrated frequently with a mercury arc using the lines at 546.1 and 135.8 nip. The instrument i v m operated a t a constant slit width of 2 mni. when quantitative measurements were being made. This slit width gives a hslfintensity band width of 2.5 mp at 211 mp. Matched 1-cxn. cells were used. pH measurements were made fiith a Beckman pH meter, Model G. It was calibrated several times each day with a Clark and Lubs buffet of pH 7.00 prepared from sodium hydioxide and sodium dihydrogen phosphate (3) Volumetric flasks were calibrated by M eighing. Pipets were not calibrated, exce t for a 5-ml. Nohr pipet used t o measure the cadmium chlorife solution, since all other constituents ere added both to the blank solution and to&e solution containing cadmium. EFFECT O F 4CIDITY
Consideration of the fact that 1,lO-phenanthroline exhibits basic properties attributable to the nitrogen atoms contained in pyridinelike rings indicates that changes in hydrogen ion concentration might be expected to affect the properties of the compound, including the absorption of radiant energy. In order to study the effect of acidity, a series of curves correlating transmittancy and wave length was made a t pH's ranging from 3.0 to 8.0, covering the wave-length range from 200 to 300 mp. Two curves were determined at each pH value, one using a solution which was 2 X 10-5 M in 1,lO-phenanthroline, the other using a solution which contained the same concentration of 1,lO-phenanthroline, and also 1 X 10-5 -11' cadmium chloride. The pH was adjusted with 0.02 V hydrochloric acid and 0.02 AI' sodium hydroxide. Since the system nas not buffered, the pH was again measured after the curves xere run, in order to detect any change. J\'ater was used as the blank solution in each case, it having been determined in advance that hvdrochloric acid and
