Evaluation of a Surface Active Agent for Metal Cleaning 0. AI. MORGAN AND J. 6. LANKLER National Aniline Division, Allied Chemical and Dye Corporation, New York, N. Y-
A surface active agent, in this case an alkyl aryl sodium sulfonate with a long alkyl chain possessing wetting and detergent properties, has been shown to exert a definite improvement in the metal cleaning efficiencies of alkalies and mixtures of alkalies. Through the use of this product cleaning time, operating temperatures, and operating concentrations can be reduced. Cleaning ability is not affected by the hardness of the water.
T
HE cleaning of metal surfaces has depended for many years on the use of alkaline solutions. The popularity of alkalies for metal cleaning has been founded on their low unit cost, their widespread distribution and easy availability, as well as on their versatility in removing undesirable films from metal surfaces. Alkalies are highly reactive chemically and may clean by saponifying surface oils. I n certain types of metal they may clean by etching the surface. Etching is an important preparatory step in many metal processing operations and is well illustrated in the alkaline etching of aluminum surfaces prior to welding or painting. The purpose of the present work is to establish the scientific and commercial importance of a surface active agent in the removal of oil films from metal surfaces. The action of the surface active agent is studied in conjunction with alkaline metal cleaning compounds as --ell as by itself. Since alkaline cleaners remove practically all of the mineral oil from the metal surface, it is obvious that any improvement in cleaning must be limited t o accelerating the removal of oil and to the removal of the last traces of oil from the metal. It is highly important that these last traces of oil be removed prior to the application of any superficial coating. For example, metals t o be plated, enameled, melded, or babbitted must have their surfaces clean if proper adhesion of the coating is to be obtained. It was found necessary to develop a new method of accurately measuring the amount of oil remaining on metallic surfaces after they had been submitted to cleaning operations. A detailed explanation of this method appears in another article'. Briefly, this method depends upon the fact that some oils, particularly those of mineral origin, exhibit a bright fluorescence under ultraviolet light. Other oils, such as the animal and vegetable types, do not possess this characteristic in their own right, but fluorescence may be imparted to them by the addition of an oil-soluble fluorescent dyestuff. This fluores-
ceiice may be observed or photographed, and since it is proportional to the amount of oil adhering to the metal, a rapid and convenient method of judging the efficiency of metal cleaning compounds is provided. Photographs taken under ultraviolet light are referred to as luminograms, By means of the new analytical method it was possible t o hhovi that the use of a surface active agent with alkaline cleaners did indeed make possible the removal of traces of oil which are often left by ordinary alkaline cleaners, The laboratory results obtained by using the surface active agent have been correlated and confirmed by plant practice in a large number of commercial establishments, and m e the subject of a pending application for patent. The surface active agent used in preparing the data was Nacconol S R . Chemically it is an alkyl aryl sodium sulfonate having a long alkyl chain. It is representative of those surface active agents which have high stability and solubility in alkaline or acid solutions and are powerful surface active agents when used in very l o ~ vconcentrations
Method of Cleaning The cleaning method used in this work involves no mechanical action. The oiled metal plate is simply hung in a beaker of the solution being tested, a t the desired temperature and for the required period of time. This soaking method was selected because it is widely used and most clearly s h o w the chemical cleaning ability of any metal cleaning compound.
1IvIorgan and Lankler, IND. ENQ.CEEM.,ANAL.ED., 14, 726 (1942)
FIGURE
1.
COhfPARIJON OF CLEAN
(left)
STEEL STRIPS
AND OIL-TREATED
Weight of mineral oil, 113 grams/sq. om. (XIO-6)
1156
October, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY Clean Steel
Alkali:
FIGURE 2.
2
4
6
-
Concentration of Cleaner, % 8 10 2 4
d .
Sodium Metasilicate
6
8
1159
10
Y
Cleaner No. 1
EFFECTOF NACCONOL NR ON CLEANINQ EFFICIENCY OF SODIUM METASILICATE AND CLEANER No, 1 AT 140” F. AND 10-MINUTECLEANING TIME
Cleaning experiments were conducted on the following metals: Steel: 20-gage cold-rolled sheet Galvanized steel: aO-gage, hot-dip-galvanized Tin-plated steel: 24- age dairy plate Aluminum: Alloy 38 (1.2 per cent manganese), aO-gage, mirror finish Brass: Soft brass sheet, 0.032 inch thick, Rockwell F hardness 61-62, annealed at about 550’ C. For manv metal cleaning and etching DurDoses . it is feasible tor’use indihdual alkalies accomplish a desired result. For other purposes “team work” is more desirable and mixtures of various alkalies are prepared to serve these needs more effectively. Through these mixtures of alkalies the manifold needs of the metal processing industries have been met with a wide variety of proprietary alkaline cleaning compounds. I n order that the evaluation of the surface active agent in alkaline cleaning compounds might be conducted on as simple a basis as possible, single alkalies were generally used in the present work; the results with individual alkalies should not be regarded as representing the effects obtained with mixtures containing the individual alkalies tested.
of Nacconol NR required with different alkalies t o obtain improved results. The effects of hard water, time, and temperature on the steel cleaning process are also portrayed. Figure 2 shows that when sodium metasilicate and cleaner No. 1 are compounded with 5 per cent Nacconol NR, there is complete oil removal a t 2 per cent concentration. The
Clean Steel
0.5
Concn. of Cleaner, % 1 2 3
5
Cleaner, of Compn. %
Nacconol N R
95 Nacconol NR 5 Na metasilicate
+
Experimental Results The evaluation of Nacconol NR as a metal cleaner and also as a metal cleaning assistant when used in conjunction with alkalies is presented in Figures 1 to 7 . Figure 1 compares the appearances of clean and oiled steel, respectively, when viewed under ultraviolet light. The clean steel appears black while the oiled steel glows with a brilliant fluorescence. This picture illustrates the extremities of the visual scale which is established by this test method. Figures 2 to 6 illustrate the effect of the more common variables which are of importance in a steel cleaning process. Methods of effecting complete or partial removal of the mineral oil composition are studied as well as the amounts
--
90 Nacoonol NR 10 Na metasillcate
+
3. EFFECT OF NAccoNoL NR, AND WITH SMALLAMOUNTS OF ALKALI,ON OIL REMOVAL AT 140’ F. A N D ~O-MINUTE CLEANING TIME FIGURE
1160 Clean Steel
---
INDUSTRIAL AND ENGINEERING CHEMISTRY -4
-- Concentration of Cleaner,
yo
-
Vol. 34, No. 10
silicate to Nacconol NR, lower concentrations of the mixtures are indicated to achieve the Alkali alone desired results. Figure 4 shows that Nacconol KR exerts a greater boosting effect on the cleaning efficiency of some alkalies 95 alkali + than it does on others. 5 Xacconol N R An addition of 5 pcr cent Xacconol NR t o sodium orthosilicate p ~ o duces a cleaner which is efficient a t a 2 per 90 alkali + cent concentration for 10 Iiaoconol N R the cleaning of mineral oil from steel. Addition of 20 per cent Sacaonol NR to caustic soda pro80 alkali + duces a cleaner which is 20 Nacconol X R inefficient below 8 per cent c o n e e n t r a t i o n . Hence the amount of Alkali: Sodium Orthosilicate Caustic Soda Nacconol NR required FIGURE 4. EFFECTOF KACCONOL NR ON CLEANING EFFICIENCY OF SODIUU ORTHOSILICATE depends on the choice of alkali. ASD CAUSTIC SODAAT 140' F. AND 10 MITUTECLEANIXG TIME Figure 5 indicates that a cleaner containing 5 per cent compound referred to here as cleaner No. 1 was composed Sacconol NR is more efficient than one containing 5 per cent of 10 per cent caustic soda,, 55 per cent trisodium phosphate, rosin soap when used under hard mater conditions. Further and 35 per cent soda ash. Sodium metasilicate alone effects work has shown that it is necessary to use 10 per cent rosin nearly complete mineral oil removal a t 10 per cent consoap in the cleaner to equal the performance of a 5 per cent centration. Cleaner Xo, 1 does not approach complete oil Sacconol S R content. Hard water does not affect the cleanremoval even at 10 per cent concentration. The use of more ing ability of the compound containing Nacconol NR. than 5 per cent Saccoiiol N R in these mixtures does not Figure 6 (left) shows that 3 or 4 per cent solutions of a appear to be necessary for the removal of this type of oil. yo Concn. of Cleaner ( 5 Nacconol N R + 95 % Concn. of Cleaner (5 Rosin Soap + 96 Figure 3 shows that Cleaner No. 1) a t 140' F. Cleaner S o . 1) a t 180' F. Clean partial removal of oil Steel 2 4 6 8 10 2 4 6 8 10 from steel surfaces can Hardness of be conveniently effected Water (U.S Scale) through the use of Kacconol NR alone or by 00 mixtures of Nacconol NR with small amounts of alkali. K i t h a 0.5 per cent solution of Tacconol NR (top row) 30 appreciable amounts of oil are left on the surface of the steel. The use of higher concentrations of lXacconol K R reduces these oil resi7.50 dues. T h e n mixtures of Xacconol NR with 5 , 10, or 20 per cent sodium metasilicate are used, partial to complete oil removal is 200 effected with gradually increasing concentrations of the mixtures. With the larger addiFIGURE 5 . EFFECT OF HARDNESS OF WATERON CLEANIKG EFFICIENCY OF NaccosoL NR AS tions of sodium metaC O M P - I R E D WITH ROSINSOAP AT 10-YhTUTE CLE.1NISG TIME 2
~
6
8
10
2
4
6
8
i n. .
Compn. of Cleaner, yo
L
7
2
-
-
1161
INDUSTRIAL AND ENOI~NEERINGCHEMISTRY
October, 1942
Clean Steel
--
2
Time of Wash, Min. 4 6 8
10
. --------Temperature, 120 140
160
F. 180
ZOO
W
Same
Same
OF TIME AND TEMPERATURE ON CLEANING EFFICIENCY AT 140' F. FIGURE 6. EFFECT
Clean Steel
--Time 120
60
of Wash, See.-30 20
10
Steel
Brass
Aluminum
Galvanilied steel
Tinplated steel
FIGURE 7. EFFECTOF CLEANINGTIMEON CLEANING EFFICIENCY OF 95 SODIUM METASILICATE--6 N A C CONOL NR, USEDAT 4 PER CENTCONCENTRATION, ON FIVEMETALS AT 140" F
cleaning compound containing 5 per cent Nacconol NR plus 95 per cent sodium metasilicate effect complete removal of the mineral oil from steel surfaces in 2 to 4 minutes. A 1 per cent solution of this mixture effects removal of the mineraioil in 8 minutes. A 4 per cent solution of sodium metasilicate is not capable of completely removing the mineral oil from the steel in a 10-minute soaking operation. I n the experiments represented by the right-hand luminograms of Figure 6 the cleaning time was fixed a t 5 minutes and the temperature of the cleaning solution was varied between 120" and 200' F. A 4 per cent solution of a cleaner containing 5 per cent Nacconol NR plus 95 per cent sodium metasilicate effects complete removal of the mineral oil at all the temperatures tested. A 3 per cent solution cleans a t 140" F. or higher, while a 1 per cent solution requires a temperature of 200" F. A 4 per cent solution of sodium metasilicate will remove the mineral oil from the steel at 200" F. but not below. The improved results obtained with additions of surface active agents to alkalies in the cleaning of galvanized steel, tin-plated steel, brass, and aluminum are much the same as those obtained on steel with the exception of the time required to effect complete oil removal. These data are presented in Figure 7 where it will be noted that the rate of cleaning is increased more by Nacconol NR for aluminum and galvanized steel than for steel. The rate of cleaning on brass and tinplated steel is slower than on the other metals studied, but is more rapid than when alkalies are used alone in the absence of Nacconol NR.
Acknowledgment The authors wish to express their appreciation to L. H. Flett for helpful suggestions in the preparation of this paper. They also desire t o thank C. Ockler for his help in performing the tests and J. Fogel for his assistance in connection with the photographic work.
