Oil Removal by Alkaline Cleaners J
’
Effect of Surface Condition of Metals SAMUEL SPRING AND LOUISE F. P U L E Frankford Arsenal, Philadelphia, Pa.
A study of the effect of variations in surface condition on ease of oil removal from metal surfaces has shown that mineral oil is readily removed from cold-rolled surfaces but this removal is sharply diminished after niiltl pickling operation. Buffing of pickled surfaces or, in the case of steel, passivation with concentrated nitric acid, results in restoration of a high level of cleaning efficiency in mineral oil removal. Removal of this oil is also efficient with steel surfaces covered with oxide (mill scale). This efficiency is greatly reduced on pickling. As the surfaces become rougher, the effects due to pickling and passivation are re-
dueed. There is evidence that these trends are reversed when oils rich in free fatty acid are removed. In these instances the unpickled or the pickled and passivated surfaces giie lower values for cleaning index than the pickled surfaces. It is hypothesized that these phenomena are associated with metal-oil adherence in the presence or absence of an appreciable oxide film. The effect due to free fatty acid may be caused by soap formation. Another factor may be the abnormal properties of flowed surface metal. In general, ease of oil removal is decreased as surface roughness is increased by severe etching or mechanical means.
A
i. the average value obtained for ten observations-i.e., both sides of five panels. Although this method was discussed previously, some data are given in Table I to indicate the reproducibility of the values for cleaning index.
RECENTLY developed method of evaluating metal cleaners has bcen applied to a study of the effect, of the surface condition of metals on the ease of removal of oils from t’hese surfaces. The importance of maintaining uniform surface conditions in this method was pointed out) in a previous description of the method ( 5 ) . It was based on the observation t h a t aluminum surfaces with a mirror finish gave high values for cleaning index, which were sharply reduced upon abrasion with fine steel wool. This investigation has disclosed that large variations in cleaning efficiencymay be observed as a result of changes in surface condition. Therefore, d a t a on this factor should be important in the evaluation and use of alkaline metal cleaners. There is apparently little literature on this subject, and the relatively complete bibliography on aluminum metal cleaners of Harris and Mears ( 2 ) does not make any reference to this factor. The procedure used here for evaluating the cleaners was similar to t h a t previously reported ( 5 ) . hi general, this consists of coating metal panels by immersion in various oils, followed by drainagc under st,andard conditions, particularly with regard to temperature. The panels are cleaned by a cont’rolled procedure. in which time, concentration, agitation, and temperature are uniform. After a prescribed rinsing operation, the panels are sprayed wit,h water. This results in a uniform water film over the cleaned areas wher’eas discrete droplets condense over the areas t h a t have not been thoroughly cleaned. These delineated areas are sketched on graph paper having one hundred squares, and the. percentage of the panel area t)hat has been cleaned is thus estimated. The cleaning index
EFFECT OF ACID TREATMENT
Table I1 shows t h a t panels in the cold-rolled condition were far easier t o clean of medium-viscosity mineral oil when untreated than after pickling. “Untreated” means the condition after removal of the original soil by an alkaline cleaner or petroleum other. A mild pickling treatment at room temperature in -50% hydrochloric acid was sufficient to cause a rcduction in cleaning index from 97 to 47. This was the case even for a 5second trc:it ment under these mild conditions, which could scarcely rrsult in appreciable roughening. Continued pickling to cause a mild etch (2 minutes in 50y0 hydrochloric acid a t 60” C.) had little effect, but more severe etching by treatment with 50% hydrochloric acid at 75’ C. for 5 minutes resulted in 8 further decrease in cleaning index to 17. Pickled panels n w e treated with concentrated nitric acid to effect passivation, and the excess was removed by wiping with a cloth and rinsing thoroughly with water. This resulted in an increase in cleaning index from 47 t o 85. However. when the passivated surfaces were given a mild acid treatment, the cleaning index reverted to the original value for pickled steel. Since passivation is probably due to oxide formation, this seems to indicate t h a t these phenomena are related t o the presence or absence of an oxide film on the metal surface. I n addition, good cleaning w a ~ obtained a i t h surfaces covered with black iron oxide. This good performance was also destroyed by removal of the oxide by treatment with acid (Table V). T.4BLE I. REPRODUCIBILITY O F DATABY THE EXPERIMENTAL I n contrast to the behavior of mineral oil, removal of a sulMETHOD furized fatty oil did not demonstrate such sharp trends. Whatever trends there were seemed to be diametrically opposed t o (Cleaner, 3% sodium orthosilicate a n d 0.15% sodium keryl benzene sulf o n a t e ; conditions, 60‘ C.. 10 revolutions per minute, 5 minutes) those observed with mineral oil. Thus, there was an increase i D R e m o v a l of Bline:al Oil R e m o v a l of sulfurized F a t t y Base cleaning index of 20 to 55 due to pickling, which was lost, upon Cleaning Standard Cleaning Standard index deviationD index deviations passivation of the surface. 56 81 The sulfurized fatty oil differs chemically from the mineral oil 53 86 in t h a t it contains fatty oil, free fattyacids, and sulfur compounds. 55 84 56 81 Since prime lard oil demonstrated trends similar to those ob53 84 63 83 served with mineral oil (Table 11), it appears t’hat the phenomena a Ten obaewations. are not due to the fatty oil content. hloreover, sulfurized fatty base from xyhich the free fatty acids were removed by trentmcnt
.
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Vol. 38, No. 10
a mild pickling operation t h a t had no visually perceptible effect on the surface. As in the case of steel, the removal of sulfurized fatty oil from brass did not give these results. 111 coiitrast with removal of mineral oil, there was an improvement after acid treatment and no improvement after buffing. Aluminum gave the same results as the other metals as far as mineral oil removal was concerned. The mild pickle t h a t . caused the first drop in cleaniiig index did not m:u the mirror finish of the panels in any way that \vas visually perceptible. Slight etching with 5Y0 hydrochloric acid further reduced the cleaning index from 66 to 19.
A hypothesis might be advanced to explain the data Dresented. In the case of t h e nlincral oil i t Figure 1. Photomicrographs of Plastic Replicas of Rolled Steel Surfaces may be collsidered that the surface oxide satisfies ( X 50) the residual valence forces of the molecules at the surface and causes the adliesion of oil to metal to be relatively weak, so that it is easier to remove the with calcium hydroxide gave the same trend as the mineral oil. oil. Removal of the oxide by pickling might change this condiOn the other hand, lard oil containing higher concentrations of tion and consequently increase the tenacity with which the oil free fatty acids exhibited the same trend as t,he sulfurized fatty adheres to the surface. On the other hand, the sulfurized fatty base. These d a t a (Table 11) indicate that the difference between oil is rich in free fatty acid that could cause soap formation or mineral oil and sulfurized f a t t y oil removal is due to the presence chemisorption on oxide-covered surfaces. Rcmovltl of the oxide of about 10% free fatty acid in the latter. by pickling in this case would reduce the adhesion of the oil to T h e trends observed with steel surfaces n-ere also found with the metal by preventing compound formation. Consequently, brass surfaces (Table 111). A mild pickling operation caused a pickling would cause improvement in cleaning efficiency. reduction in cleaning index for mineral oil from 33 to 8. Buffing The spreading of droplets of oil on metal surfaces was also the pickled brass surfaces resulted in a great improvement in found to be very dependent upon whether or not the Surfaces cleaning, the cleaning index increasing to 86. This tremendous, \\-ere pickled. Mineral oil did not spread readily on surfaces increase in cleaning due to buffing was completely nullified by B . Smooth
A . Rough
Smooth
Very Smooth
Figure 2.
Brush Analyzer Tracings for Three Rolled Steels
Rough
INDUSTRIAL AND ENGINEERING CHEMISTRY
October, 1946
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rougher surfaces. Figure2shows representative Brush analyzer tracings ( 4 ) of these 'surfaces. (Cleaner, 1,5% sodium orthosilicate lu, 0.150, sodium keryl benzene sulfonate. Conditions, 60' 8.,;O r.p.m., 5 minutes) RlllS (root mean square) values Sulfurized Sulfurized F a t t y Rase (4) were obtained from the tracllediumF(1053 a r t y Base Prime Lard Oil Prime Oil w i t.\rids h Fatty ings by an approximate method Free (1,SG Free +S'%Lard Oleic ViscoPir. Ziineral Oil F a t t y Acid) F a t t y Acid) Acid R e rnoved recommendc,d by the Brush DcT r e a t m e n t o f S t e e l S u r f a c e C.I." S.D.6 C.I. B.D. C.I. P.D. C.1 P.D C.I. P.D. velopment Company ( 1 ) . These 1 . Alkali-cleaned (no arid trentn SI7 2 20 9 87 6 is ,?;% values ~verc' found t o be 6, 19, and 31, respectively. I n spite of HCI, 25' C., .j sec. 17 8 31 8 these differences, data for the 3. Same :IS 2 , 25O C . , 60 ._ 6 50 92 3 9 3 6 sec. 4i E 55 cleaning index, obtained for each 4. Same as 2. 60' C . , 2 111111. JR A 39 6 48 h of these surfaces under a num5. Fanie as 2 , i s o C.. 5 min. li 9 17 9 S 6 bcr of eoiiditions, were similar in 6. Sar:ie as 3, passivated concd. HSCIa 8.5 0 1; 5 a11 instances. Table V gives 7 . h n i e as 6. pickled as some of these data. 11: 3 36 D 23 5 The level of values (Table V) a Cleaning index. b Standaid derintion. for cleaning index dropped sharply when the cold-rolled TABLE 111. EFFECT OF ACID TREATVEST OF BRASSASD panels were pickled. These XLG~~IIX SURFACES ~U ON OILREMOVAL values were restored upon buffingthe panels, which causes surface flow of metal (Figure 3). The cleaning index again dropped (Conditions. 60' C.. 10 r.p.m.. 5 minutes) Sulfuwed when the buffed panels were pickled.
TABLE11.
EFFECT O F ,4CID TREATMENT OF S T E E L SCRF.4CES O S OIL
REMOVAL
Jlineral 011F a t n Oil -__ c.1a S D h DBra*s Cleaner (1 jC;Sodlum Orthosilicate O 12% Sodium k e r \ l Benzenesulfonater
c n
+
Alkali-cleaned (untreated) Alkali-cleaned Dirkled Alkali-rleaned: acid-etched Alkali-cleand pickled huffed Alkali-cleaned: pirbled,'huflrd, pickled
33
9 6 2
, 30
86
6 5
2i
14
i9
16
6
23
Aluminum, V i r r o r Finish Cleiner (1 5% Sodium Metasilicate 0.1570 Sodium Iieryl Benzenesulfonntej Alkali-cleaned 86 5 Alkiili-cleaned pickled 66 9 Alhali-cleaned 19 5 0
E
22
s
+
Cleaning index.
b Gtundaid de\iation
that vere in the cold rolled condition or on metal after buffing, after passivation, or when covered with black oxide (mill scale). On the other hand, rapid spreading occurred on these surfaces after they had been subjected t o a pickling process with 50% hydrochloric acid at room temperature for one minute. The data previously present,ed were obtained n.ith a single alkaline cleaner-namely, sodium orthosilicate plus an organic surface active agent of the alkyl aryl sulfonate type. Table IT. gives d a t a for a wider range of cleaners. For the alkali alone there ITas much better cleaning for unpickled surfaces than for pickled surfaccs in removing mineral oil and lard oil. Generally this difference was also obtained with a variety of surface active agents; but i n the eases in which good results were obtained Kith pickled surfaces, the values for unpickled surfaces were not much better. On the other hand, only minor improvement was obtained for unpickled as rompnred with pickled surfaces when TABLE IT. the surface active agent alone was the cleaning agent (at higher concentration than when used in conjunction n-ith alkaline salts). EFFECT O F SURFACE ROUGHNESS
I n the course of this investigation three samples of cold-rolled steel were tested. One of them had a rough appearance. whereas the others were smooth and shiny as in normal. P l a t i c film replicas (3) of ttvo of these surfaces (Figure 1) indicated t h a t the floved metal was in t h e form of larger masses in the case of the
1.
+ + +
3. 4.
5. 6. 0
b
It is not desired to enter into a discussion of whether these phenomena are due to an amorphous surface layer, the presenoe or absence of oxide, or some other alteration of the surface. Nevertheless it is evident t h a t the cold-rolled and the buffed surfaces have different properties from the surfaces prepared otherwise, and i t appears that these properties affect cleaning t o a greater extent than gross differences in surface roughness, within a limited range.
EFFECTOF PICKLED AND UNPICKLED STEELSURFACES WITH VARIOUSCLEAWERS
(Conditions, 60' C., 10 r.p.m., 5 minutes) Removal of Medium-Visrmitv &liners1 o i l ~ ~ - - - ~Removal - " of Prime Lard Oil Pickled Unpickled Pickled Unpickled Cleaning Agent C.1." S.D.a C.I. S.D. (2.1. S.D. C.I. 8.D. 1.5% sodium orthosilicate 20 6 17 6 0 t 17 Same as 1 , 0.15% surface active agent .\ 47 6 86 6 50 6 87 0.15% surface active Same as 1, went B 31 3 85 6 7 5 8 8 9 4 s a g e as I , 0.15g;~surface active agent C 28 9 70 5 4 1 9 8 8 8 Same a5 1. 0.15% surface active agent D 97 3 100 o 77 . 8 96 a 570 surface active agent A 11 6 58 0 70 8 77 0 Cleaning index. Standard deviation.
+
2.
Figure 3. Photomicrograph of Plastic Replica of Surface Similar to That of Figure 1A after Buffing ( X 50)
~~
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TABLE J'.
.
~IECHASICAL A S D A C I D TREATY~NTY OF STEEL SURFACES ox EASEOF OIL R~aror.41, EFFECT O F
(Medium-viscosity mineral oil of 472 seconds Saybolt Universal viscosity a t 100' F.: cleaner, 1.5% sodium orthosilicate 0.15% of sodium keryl benzenesulfonare: conditions, 60' C., 10 r.p.nl,, 5 minutes) Cleaning St:xnd;trtl It113 Treatment of Steel Surface Index 1)eviatioii Value l a . Smooth-rolled n o t pickled 86 1 6 l b . Smooth-rolled', pickled 44 2 2s. Smooth-rolled, not pickled 88 1 19 2b. Smooth-rolled, pickled 17 3a. Rolled with rougher surface, no: pickled 97" 7 31 3b. Same as 3a, pickled 47 4 8 4. Same as 3h h u f e d Sl 1; .~ 6 ; Same as 4, pickled 67 .. 6. Panels covered R i t h black iron oxide 72 > 7. Same as 6, pickled 11 Ground n i t h fine grain grinding 8. rr heel c, J 83 Same as 8, pickled 30 9. 8 Ground with medium-grain grind10. ing a h e e l 62 9 Ground with coarse-grain grinding 11. ~"
+
A light s:iridblabting treatmciit gave aurse cleaniiig than any of the otlwr treatments. These surfaces gave neither xvorse rcsults on pickling uor better results on passivation. P u t of this may bc due to the fact that the level of results was in the range that is 1eaFt sensitive. I t seems to be established, hu\vevcsr. that pa4v:Ltioii docs iiot C:IUYC any improvemcIlt a.hen the surfaces are quiti, rorigh.
,,
[. of o i l removal from metal surfaces is grwtly inis probably metal oxide
may tic different for dif.ed far more readily wlien containing considerable quantities oE fntc fatty arid is removed more readily when it, is absent. 3. 'The I J W S ~ I ~ C Iuf : tlie cold-rolled or worked s u r f x e condition seeins t o be more iniportarit in determining cleaning performance than gross surface roughness n-ithin a limited range. 4. Ease of cleaning diminishes as the roughness of the surface iiicreascs. After a certain level of considerable roughness. the effects apparciitly clue to the oxide film are lost.
17. 18.
Sandblasted lightly 14 SRme a8 15.pickled 16 Same aa 19, passivated concd. "Os 9 a Removal of sulfurized fatty base, deposited from 1: 9 solution in toluene gave value of 14 for Bame conditions as 3a and 55 for same condition a d 3b:
ACKNOWLEDGJIENT
19.
20.
The effect of other mechanical variations of steel surfaces WI? also studied to some extent, and the data are presented in Table V. Surfaces that were obtained by grinding with a fine-grnirietl grinding Thee1 gave rather good cleaning-for example, a clemiing index of 83 in the removal of medium mineral oil. Surfnce!: ground Fvith a medium and Kith s coarse Ivheel gave valucLs that were worse than those ground x i t h a fine n~lieel-62 arid Zi, respectively. As in the case of the cold-rolled panels, cleaning index decreased with pickling and increased with subsequent passivation, although the changes Tere smaller with the coarse ground surfaces than with those obtained with the fine grained wheel. Surfaces prepared with a shaper using a fine fecd gave conbidcsrably worse cleaning than those ground Kith a coarse wheel. This cleaning was made tvorse by pickling. Hon-ever, cleaning of t h i ~ iurface was not improved by passivation.
Apprwiatioii is espressed t o C. C. 1;:iivcett arid E. It, Itechel of the Frankford Arsenal Laboratory for their cooperation, and to the Ordnance Department for permission t o publish this paper. Special thsiiks :ire due J. ;\Iitclic.ll for helpful review of the manuscript m d to Adele Goldsteiri fiir performing a considerable amourit of tlic: experimental work. LITERATURE CITED
( I ) Brudi Ilcvcloyiiierit Co., "Surface Finish Xomenclature", 1945. ( 2 ) Harris, J . C., and Mesrs, li. R.,A S T M Bull. 120, 33 (Jan., 1943); 121, 33 (March, 1043); 129, 21 (May, 1944). ( 3 ) Herschman, H. K., J . Research S u l l . Bur. Stondards, 34, 26 (1945). (4) Sclilesinger, G., "Surface Finish", p. 152, London, Inst. of Production Engrs., 1942; Am. SOC. Mech. Engrs., .imcricen d., 11 (1942). (6) Spring, S., Forman, II. I., and Pede, L. F., IXD.Eso. CHEM.. .\x.\I,.ED.,18, 201 (1946). PRESENTED before the Division of Industrial and Engineerine Chemistry AL Atlantic City. a t the 109th hZeeting of the AXERICAN C ~ I E M I C SOCIETY, N. J.
Correlation of Tensile Strength with
Brittle Points of Vulcanized Diene Polvrners d
A. 81. BORDERS 4x1)R. L). .JLVE The Cood3eur Z'ire & Rubber Compurrj, fhrort 16, O h i o
F
OR several years work has been carried on here to evaluate a large number of diene polymers and copolymel's as rubberlike materials. The writers have observed that changes-in polymer composition vhich result in improved tensile strength and crack-growth resistance of the wlcanizate cause an increase in low temperature stiffness and a rise in brittle point. This generalization seems to apply for tensile values measured at elevated temperatures as well as for those a t room temperature. For example, a butadiene copolymer of dichlorostyrene can be made n-hich, as a tread type vulcanizate, exhibits a tensile
strength of over 1500 pounds per square inch a t 93" C., in comparison with 800 to 1000 pounds per square inch for GR-S in the same test tread formula a t the same temperature. The brittle point of the butadiene-dichlorostyrene rubber, however, is -35" C. or higher. GR-S treads in the same test have brittle points b e t w e n -55' and -60" C. Probably of greater practical importance is the fact that the vulcanizate with the higher brittle point is stiffer at temperatures well above the brittle point. The purpose of this investigation was to determine to what extent the maximum tensile strength of tread stocks of several
