2452
INDUSTRIAL A N D ENGINEERING CHEMISTRY
ptwluc~c~sexcellrtit lulJi5a:iting oils. Reactmionconditions are (i00" t o G O " F., rc&knct. t.itnc: :tt)out, 10 hours, and pressules of 2.50 t o 5 0 0 pounds per s q u : t i ~inch g a g . Under such condit>ions I-tloccwc has given as muc*h:ts (5% by weight of an f3.A.E.-10 oil iii :I siti~lrpass, with produc:t irispections as follows: viscosity iiicies, 140; pour test, - I O " h'.: color (Lovibond), 0 . 5 ; carbon rcwiclue, nil. T h e p r i ~ f ~ w wrnnge l nf 1-olefins is from n-hexene t o rr-dodecene., Sudi ole4ns froin utiy source, as cracked p:traffirl NXS or Fisch'er-Tropscfih pi,oduc*t*, ran used for synthesis. If suit.:ible olefinic chnrgc' stlocks lx~conireconomically :~v:~il:hl~+ t h : oils can be :tcc:omconversion t80finished high g i ~ h lutwicating plished in conventional refinery equipnimt consistink of niotlified th(.t~in:tIcrackina and dist,ill:tt,ion unit,s. ACKNOWLEDGMENT
hpprt&ition is rspre-;secl t80G. (:. Slirewshry, 11. S. . \ I o i i t c . niore, Lois B. Buseni:in, :md other inembers of tho lat)orutory st,aff for their valuilhle sssistaricv? in the experimentd work. The Hydrocol product wiis supplied through the courtwy o f thc II!drocarhon Rrsiwch, Inc~orporitted. LITERATURE CITED
Huriiham, H. O., and Pease, I < .
S . . J . .lm. ot the c.h:ti acterktics that are most desirath in a lubricant. Such ploperties as high flash points, low free7ing points, extremely flat viscosity-temperature slspes, arid R high degree of rcktancse to oxidation and thermal decwniposition ale a few of theii m:my excellent physical attributes. Greaaes formulated from these materials exhibit ni:rri> of the pioprities of the basr fluidh m(*h a relative indifference to extreme temperature r h a n g ~ s ,low wlidification points, and :t reni:trknhle heat stability. In ball aiid roller bearings whwr rolling frwtion is encountered, l m t h the J o s a n e fluids and greases have performed remarkably well ( 4 , 8 ) . I n marked contrast to the suwessful use of these materids in ball bearings under actual wrvice cwiditions, the prcr,ent organopolyYiloxanes fail to provide :w :itlcbclu:itr lubricating filii1 between
T
sliding ferrous surfaces under boundary ronditions. Because of this failure, there is a reluc,tance to use the organopolysiloxanes wherever sliding friction is envountered regardless of the metal combinations involved. This reluctance can be traced directly to the dearth of information roncerning the performancue of these materials as luhic-ants for hearing combinations other than steel rubbing against steel. Although data have been published on the methylpolysiloxaries as lubricants between various metal combinations (6) no effort has been made to confirm these data other than the work done by %isman and his associates (1,2 ) . The authors have, therefore, undertaken a study of' ~ e v e r dpolysilosanrs as lul)ric*nnts for various pairs of bearing mrzterials.
December 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY APPARATUS AND TEST METHODS
The Falex lubricant test machine was chosen for this work be(-aweit permits a high degree of flexibility in test methods. Thci results obtained with the Falex machine are, of course, open to some critirism. No machine yet devised for evaluating lubricants will give a complete picture of their behavior under actual service ronditions. It is possible that some of the metal pairs which failed in the tests will be found satisfactory in actual use. Conversely, some of the recommended metal romhinations may be found unsatisfactory. ThL tests reported here were conducted under boundary or extreme pressure conditions, however, and the authors feel the results obtained with the Falex machine furnish a valuable guide in selecting the correct bearing combinations to use with organopolysiloxane lubricants. The Falex machine is a commonly aacepted device for measuring lubricity under boundary conditions and it permits determination of wear and torque while the machine is running. The essential parts of the apparatus shown in Figure 1 consist of a shaft, A , rotating between two V-shaped blocks, B, a t a constant speed. The V-blocks and shaft are immersed in the oil being evaluated. The blocks are recessed in self-aligning holders and pressed against the shaft by means of two lever arms, C. Load is applied by means of a ratchet take-up wheel, D, which turns shaft E and pulls the levers closer together. The action resembles that of a nutcracker. Applied load is measured by gage F . The whole system can rotate on its axis against point G, and the resistance of Sylphon gage H to this rotation is a measurement of torque. Wear, expressed in terms of teeth, is indicated by the number of units take-up wheel D is moved t o maintain a given load. Actual wear in inches can be determined by multiplying the number of teeth the ratchet wheel has been advanced by the factor O.ooOo218. -4ctual pressure on the bearing surfaces can be calculated by multiplying the gage pressure by 1.4142 and dividing the product by the width of the scar on the V-blocks. A complete discussion of the performance and theory of this instrument has been presented elsewhere (3, 11). Three techniques were employed in using this machine to evaluate the lubrirating qualities of v:trious organopolysilosane fluids : Method I, v hich is designed t o 1neasut.e wear under boundary conditions, consists of applying a gage load of 50 pounds for 30 minutes while the machine is running. This is termed the breakin period and no measurements of wear are taken. The load i s then increased to 100 pounds, and readings of torque and oil temperature are taken. After 10 minutes the pressure, tor ue and temperature are again noted. The take-up wheel is b a a e d off until a gage load of 70 ounds is obtained. Load is reap lied and the number of teeth t i e wheel must be advanced beyon$ the original setting to obtain again a pressure of 100 pounds is noted as wear. This operation is repeated a t 10-minute intervals until the test is stopped or until failure occurs. Method I1 is designed to measure the load carrying capacity o f various fluids. This technique consists of a plying loads of 100-pound increments until failure is indicated y! a sudden rise in torque-for example, the system ir, run for 5 minutes at a gage pressure of 100 pounds. At the .end of this period the torque, temperature, and teeth wear are noted, and the pressure is incoreased to 200 ounds. This process is repeated with successively increasing loa& until failure takes place. Method 111 is a combination of methods I and 11. It is a rapid means of evaluating both wear and mild extreme-ptessure properties. The machine is run for 10-minute periods a t increasing loads. The starting load is 20 pounds and is increased in 20-pound increments. Measurements of wear, torque, and tem erature are taken aftei. each period, and the test is continued) for 50 minutes to a maximum gage pressure of 100 pounds. EXPERIMENTAL RESULTS
The chemistry of t,he polysiloxanes has been discussed in another paper (6). Details of their structure, therefore, will not be given here, except to explain the meaning of the term “phenyl
245 3
rontent.” A variety of organic, radirals can be attached to the silicon atom, but the two groups most commonly used are the methyl and phenyl radirals. I t is possible to synthesize polysilosanes rontaining all phenyl or all methyl groups. The latter type is represented by fluid A in Talde I. It is also possible to prepare polymers containing both phenyl and methyl radiwls in by B, C , and D in Tahlc I. variable proportions as repr~~heiitc~l
Figure 1.
Falex Lubricant Machine
Both the methylpoly’siloxanc.: ~ n dthe niethylphenylpolysiloxarlc~ Huids of varying degrees of phr~i.vI:ttionwere tested. In addition to these fluids, an S.A.E. 30 petroleum oil was also evaluated. The S.A.E. 30 was a premiuni commercial motor oil and probably vontained additives. This permitted a comparison of test results with an oil of known perfornianve under actual operating conditions. Zisnian and his co-workers ( 8 ) found that the methylpolysiloxane fluids were excellent lubricants, under certain conditions, for a steel journal rotating in R hronee bearing. Furthermore, sinre additional information was :it hand concerning this conibination of metals a steel-bronze pair was tested first in the Faley apparatus to see what correlation there might be with perforniancr undw :cc*tiinloperating conditions.
Table
1.
Fluids Evaluated with Falex Machine
Flash Viscosity Point Type Pheiiyl nt 25O C.. Minimilin. nntion Polysiloxane Content Cs. V.T.C.“ F. A ,Methyl None 101 0.60 600 B Methylphenyl Low 42 0.61 525 C Methylphenyl Medium 11.3 0.78 600 1) Methylphenyl High 482. 0.88 000 a Viscosity at 210’ F. and viscosity at 100” F. are taken from A.S.T.N. viscosity-temperature chart, the viscoPity-temperature coefficient is calculated according to the forii;nla Fluid
neliig-
,-
&2100 ?I
000
F.
r,-.
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
2454
T h e first series of tests were performed by method I at a bearingpressure of approximately 4500pounds per square inch. Each test was run for a period of 2 hours with bronze shafts rotating between two steel V-blocks. The results of these tests are summarized in Table 11.
22
20
Vol. 42, No. 12
I n order to test this hypothesis, several V-blocks and bronze shafts were lacquered by heating them in a methylpolysiloxane fluid for 24 hours a t 500" F. The treated parts were then used as the test pieces in several Falex tests. The duration of the test, method I, was 120 minutes at a gage load of 100 pounds. T h e results are summarized in Table 111. I n no instance did this lacquer treatment result in any pronounced reduction in wear. Wear was much greater with fluid A than i t was on untreated bearings, but this may have been an isolated instance.
I8 L 16
Table
IY
I
111.
14
4
k! w
2
12 IO
C 4
= 0
Falex Tests with Methylpolyriloxane Lacquered Bearings Temp., Tor ue Total Fluid c. Lb.-?noh Teeth P 95 8 33 B 95 9 14 C 95 14 26 D 95 12 59
6 4
2 0
20
0
40
60
80
120
100
TIME -MIN
Figure
2. Wear Characteristics with Increasing Time for Several Organopol ysiloxanes
These data indicate that temperature has little effect on the results obtained. Furthermore, as the phenyl content of the organopolysiloxane is increased, the lubricating properties of the polymer decrease. This is in contradiction to the work of Kauppi and Pedersen (9)who used a different test apparatus, but agrees with the results obtained by Brophy el al. ( 1 ) . Finally, fluid B appears equal to S.A.E. 30 in the prevention of wear whereas fluid A is definitely superior. A summary of the wear data is shown graphically in Figure 2. Each curve represents a composite of all the wear data obtained b y method I for a given lubricant. The curves for the more highly phenylated fluids, C and D, indicate that there is high initial wear and little evidence that wear will decrease with increasing time. The curves for the S.A.2. 30 oil and fluid B indicate that wear increases much more slowly, but here again there is no tendency for wear to abate with continued operation. Finally, the curve drawn for fluid A shows both a lower initial wear and a definite decrease in the rate of wear with continued operation. One explanation of this phenomenon may be that a methylpolysiloxane "lacquer" is formed on those portions of the bearing surfaces where abnormal heat is generated by friction.
Even if the run with fluid A is disregarded, the fact remains that these Falex tests do not show that performance under boundary conditions is improved b y the application of a methylpolysiloxane lacquer. These results do not confirm the observations of Brophy et al. ( 1 ) who found that either a long break-in period or the deposition of a methylpolysiloxane lacquer was necessary for optimum performance of an organopolysiloxane lubricant for a chrome-plated journal rotating in a bronze bearing. This disagreement between the Falex tests and journal bearing tests is not surprising since the conditions of operation u ere much different. This disagreement does question the benefits of lacquer treatment under all conditions where methylpolysilo~anesare employed as lubricants. Some work was also done to determine the relative load carrying capacity of fluids A , B , and D as well as an S.A.E. 30 oil. Method I1 was used for this work. Again the test pieces consisted of bronze shafts rotated between steel V-blocks. 60
I
I I
c L
y
40
,
C '
' 4
30
w
? i 4
%
20
U
Table Fluid EAE 30
II.
Falex Tests with Bronze Shafts and Steel Blocks Tzms..,
33 85 155 190 90 90
A
B
45 55 70 155 220 40 180 95 100 185 100 155
C D
140 95 96 95
Torque, Lb.-Inch 6
5 9 9 6 6
10 10 7 7 5 9 7 8 11 9 9 10 10 10 15 13
10
Total Teeth
Wear, Inch
15 15 14 12 12 11 13 11 7 7 7 6 5 16 15 12 12 9 7 42 45 34
0.000327 0.000327 0.000305 0.000262 0.000262 0.000240 0.000283 0.000240 0.000153 0,000153 0.000153 01000131 0.000109 O,OOO349 0,000327 0,000262 0.000262 0,000196 0.000153 0.000916 0.000981 0,000741
n
o
100
200
300 GAGE
Figure 3.
400 LOAD
500
600
700
am
POUNDS
Load-Carrying Capacity
of Organopolysiloxanes
T h e results obtained under mild extreme-pressure conditions are shown in Figure 3. Each curve represents the composite data from two or more tests. I n contrast to the data obtained by method I, S.A.E. 30 sKows the least wear up t o the point of seizure. With the organopolysiloxanes, load carrying capacity increases with decreasing phenyl content. Wear studies made according to method I are confirmed in the case of fluid A . This methylpolysiloxane fluid carries the greatest load before seizure and i t allows the least wear under a given load. Fluid A carried a load of approximately 23,000 pounds per square inch before failure occurred. The highly phenylated fluid D carried 9000 pounds per
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Deoember 1950
2455
60
Table
IV.
Bearing Metala Graphite shafts and steel V-blocks
Effectiveness of Polysiloxaner as Lubricants (Method 111) Fluid A Fluid D Wear, Vp;, Load, Torque No. Torque, lb. Ib.-incd teeth 1b.-inch teeth 0 20 40 60 80
100 Zino-plated shafts and steel V-blocks
0 20 40 60 80
0 20 40 60
80
loa Cadmium-plated shafts and steel V-blocks
3.5 4.5 6.5
0 22 48 84
0 0.5 1.5 3.0
0
31
76 118
Load, Lb.
V.
: 5 30 I
I-
Failure
-I
.O
20 40 60 80 100
0 1.0 2.5 3 4 5
0 3 7 11 16 20
0
0 19 22 26
