V O L U M E 2 0 , N O . 6, J U N E 1 9 4 8 (25) (26) (27) (28) (29) (30)
hfuller, R.H., IKP EXG.CHEY.,- ~ L L ED., . 13, 718 (1941). Novak, J., and Check, V., I n d . Eng. Chem., 24, 1275 (1932). Rochow, T. G., I K D .EKG.CHEM., ANAL.ED.,11, 629 (1939). S a w , R.O., J . Am. Chem. S O L ,68, 954 (1946). Saylor, c. p., 1.Research AVutl.Bur. Standards, 15, 277 (1935). Smith, W.H., and Saylor, C . P.,Ibid., 13, 453 (1934): RllbbLr
Chem. Technol.. 8 , 214 (1935). (31) Smith, W.H., Saylor, C. P., and Wing, H. J., J . RGsearch,\rail.
Standards, 10, 479 (1933); Rubher C h e m , Technol,, 6 , 351 (1933). ( 3 2 ) Spencer, R. S., personal communication. (33) Btafford, R. W., IXD. ENG.CHEY.,-&SAL. ED.,14, 696 (1942). (34) Straat. H. W., and Forrest, J. JV., J . ~ ~ tsot.f A~ ~ ~,29, , l240 (1939). (351 ‘rilton, L.\T., Ibid., 32, 371 (1942). BUT.
523 (36) Vieweg, K., Kunststoffe, 27, 213 (1937). (37) Wagner, A. F.. “Experimental Optics,” New York, John miley and Sons, 1929. (38) Wahlstrom, E. E., “Optical Crystallography,” p. 37, New York, John Wile>-and Sons, 1943. (39) Warrick, E. L., J . Am. Chem. sot., 68, 2455 (1946). (40) West,, C. D., IND.EXG.CHEM.,,4r;a~.ED., 10,627 (1938). (41) Wile>-,R. H., I n d . En!=?.Chem., 38, 959 (1946). (42) WileY, R. H., -7. Polymer sei., 2, 10 (1947). (43) V p y , R . H., and co-workers, unpublished observations. (44) Wood, L. A., J . Oplical Physics, 12, 119 (1941); Rubber Chem. Technol., 15,23 (1942). (45) Wood, L. A., Bekkedahl, N.,and Peters, C. G., J. N u t l . B u r . Sfandards, 23, 571 (1939). RECEIVED September 5 , 1947.
Measurement of Adherence of Organic Coatings to Metal Surfaces H E N R Y G R E E N ’ A ~ TDH E R E S A P. LAM4TTINA, Znterchemical Corporation, ,Yew York,
2%’.
I-.
This paper describes an instrument and a method of measuring the adherence of organic coatings to metal surfaces. The property of adherence, as used here, is not synonymous with the term “adhesion.” Adherence is derived from a number of factors, of w-hich adhesion is but one. The other factors include plastic resistance to flow, tear resistance, and mechanical entrapment of the coating in the rouphness nf the metal surface.
T
HE iiirasurement of hdherenct! (usually called “adhesion”) has never been easy. Rork and Leigh (3) the methods of adherence measurements into five categories: (1) tensile methods, ( 2 ) scratching or gouging tests, (3) base deformation tests, (4) impact tests, and ( 5 ) miscellaneous tests The history and development of these methods have been reviewed by others (4). I t is the authors’ desire to describe their own development of one method that, they feel has possibilities for ready application to plant and laboratory work. That method is a “scratch test,” but because the scratch is madc with a knife edge 4 mm. wide the result is a band and ncrt a narrow groove such as would be made with a needle point. Koenig ( I ) , Koole ( Z ) , and Rossmann (6) investigated the possibilities o f the knife-edge scratch tester; each approarhed thc subject from a viewpoint differing somen-hat ’ from the others. The present authors’ development, while basically the same as the others. differs substantially in many essential details. ~~
ADHERENCE TESTER
The tester consists of a plate, E (Figures 1 and 2), on Ll-hich is fastened the metal base plate, V, containing the coating to be sested. By means of the motor, A , the plate moves in the direction of the arrow, pulling the base plate under a weighted knifeedge, G, which is connected by means of the beam, P , and the wire, &, to the pendulum, L. E is supported by the carriage, F , which is moved forward by means of the n-orm screw, C, and the threaded supports, D , D . P is supported by the device, X, which rotates about the axis, I . .Is G moves forward with the base plate containing the coating, the pendulum weight, M , is raised. This procedure produces a backward pull on G. At the moment t,he backward pull equals the forward thrust exerted by the coating, the knife begins to remove t,he coating. From here on G and M remain stationary while E -.
__ 1
Deceased.
cvntmues to advance. When this happens a reading is taken on a n hmes scale, K , which has a sliding arm, Tt’, resting on and activated by an eccentric, X. The scale reading is a function of the distance through TvhichM has been raised. As the knife is on a beam pivoted at S,and swings freelv on this
.G.)
t f I T
Figure 1.
idherence Tester
pivot, a pressure weight, H , is necessary to keep the kiiift:-edge down in contact with the base plate. This produces friction, which must he subtracted from the original reading. To do this a blank is run. The base plate is, therefore, returned to its original position and a run is made on the base metal strip-that area previously occupied by the coating. Both readings are converted t o dynes and the second reading is subtracted from the first. The difference is the stripping force, SF. In order to convert llmes reading to dynes, it is necessary to know the position of the center of gravity, CG of the pendulum, t,he pendulum weight, and t,he horizontal distance, H D , between CG and the vertical, 5”. The pendulum is composed of a bar and a number of weights that can be fastened to it in various combinations. The equation that gives the distance, D , from the lower end of the bar to the center of gravity is (densities of the bar and weight are assumed equal) D =
a2bc 2(ahc
- dlef
+ def)
(1)
ANALYTICAL CHEMISTRY
524 The weight is flush with the lower end of the pendulum bar,
a ' b and c (not marked in Figure 1) are the dimensions of the deiiht a being the length of the edge parallel to the length of the bar. & i s the ''length'' of the bar and e and f are its other linear
..
thepend"iumweight.,, I f Qisfpund to be .positiGe; . CGisabovehhe
Because W,, in Equation 5, oantains the force necessary to overcome thefriction of the knife-edge against the plate, this factor must he eliminated in order to obtain the true stripping force of the coating. This cannot he done by subtracting the Ames scale reading of the blank from the scale reading of the test run because the Ames g q e reading does not hear a linear relationship nith ED. The H D corresponding to the Ames gage readings is obtained from the
