INDUSTRIAL A N D ENGINEERING CHEMISTRY
August, 1928
ing the number of grams of carbon disulfide determined iodometrically by the factor 1.14, which was derived by dividing the weight taken by the weight recovered in a large nnmbcr of laboratory tests. ALCOHOLAND U'ATm-Small quantities of alcohol and water caniiot be readily determined quantitatively in miscible carbon disulfide. The appearance and action of the finished product is a fair index of the proper proportions of these
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ingredients. If there is too much water, the miscible carbon disulfide will be translucent; if there is too much alcohol, crystals will be formed in the transparent. solution; if the proportions are correct it will remain transparent without the formation of crystals. The approximate total quantity of these ingredients can be estimated by deducting the percentage of carbon disulfide from the percentage of the total volatile constituents.
Chipping and Abrasion Tests for Paint Coatings on Metal' A. D. Camp RBSBAACX BURBAV. ALVMINUX COIIP&NY OP A I B I I C ~ BOPPILO, , N Y.
IIE selection of paints and varnishes for the finishing of furniture made of strong aluminum alloy has p r c sented problems of a somewhat different nature fnim those connected with their use on articles composed of other metals and wood. Aluminum, being a silvery white metd, shows B very great color contrast between finish and metal, if the finish is scratched or worn off. Therefore, in addition to considering the color and beauty of finish, the manufacturer of aluminum furniture must select extremely tough and durable paints, which are as resistant as possible to abrasion and chipping. A diligent search did not disclose any tests for determining those qualities which were exactly suited to our needs, so the methods in this article were developed for the purpose. These tests hare been found very serviceable in studying the comparative qualities of paints obtained irom different sources and a.pplied to aluminum by different processes.
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Nale-since this paper v a s prepared an article by Vogt [IND. ENO. Cxnar.. PO, 303 (1828)l has appeared, which describer a machine for testing the abrasion resistance of rubber. The operation of the paint and rubber teesting mechiner is quite similar except thst the abrading media and the test specinlens eichange positions. Some of the mathematical relationships walked out for the rubber machine m k h t be applied t o the abrasion testing of paint fiims. The chipping test is hardly cract enough to become a standard test for u s c b y operators working under dieerenf conditions, but it i s so simple iii its a.. ~ ~ l i c a t i othat n it rhotiid become B vrluabie nieans of aiiictlv . . f e r t i n ~the comparative tovzhneri and adherion of paint films. The abrarion test. on the other hand. i s subject t o quite exact ~onirol,and with further refinement might well become a standard test fordetermining the wearing guaiities of cpdied w i n t r . Sumeriions from paint users and manufacturers will be welromrd by t h e author.
varnish, it is necessary in most instances to test, the complete finish, in order to determine the durability of the finished article, as each coat added has an effect upon those immediately above and below it. In teatin:: finishing varnishes all samples of varnisli are sprayed upon unifomily applied backgrounds of primer and gruund color. The comparative tests of ground colors are ucually applied to primed sampleprepared under standardized conditions. It is also desirable to have all paints applied, dricd. and tested at t l e same time, since it is not always possihle to duplicate condition9 in different series of tests. The thickness of all panels is measured to 0.0001 inch with Yernier mirrometer caliprs in a t least ten spots before and after painting, and the readings are recorded on the hacks of the specimens, so thst the thickness of the paint filii1 at the point of chipping can be obtained. Tlie total thickness of the paint film for tlie chipping test has a very great influence o n the character of the chip, and for these tests it is maintained between 0.0025 and 0.0030 inch. Other thiiigs being equal, tlie heaiier the paint film the greater is the tendency to chip. Another factor which affects the test is the liardness or temper of the metal composing the sample panel; increasing softness of the metal greatly derrenees the tendency to chip.
Chipping Test
The chipping test is made by dropping on the test panel under standardized conditions R series of standard tools, and observing the extent and character of the impression made on t,he coating. PREPARATION OF TEST SPEcrmNsSince the adhesion of paint to metal surfaces is greatly influenced by their condition before the application of paint, it is of prime importance that a standardized surface condition be adopted for all chipping tests. For aluminum a sand-blasted surface has been found to offer the best foundat.ion for paint, so the test samples are uniformly sand-blasted on both sides. Specimens 4 inches wide by 8 inches long are amply large for both chipping and abrasion tests. I n testing paint films it is desirable to test, each element of the finish separately, but since most finishes for aluniiniim furniture arc compounds of primaries, ground coats, and I
Received April 30, 1928.
Cowlesy of Roszvrli Allen
Abrasion Teeflng Machine
For testing tlie finishes of aluminum furniture, 16 gege 51 SW alloy is selected for t,lie sample panels. This alloy has a composition of 0.1 per cent silicon, 0.6 per cent magncsium, balance aluminum, and in tlie heat-treated and quenched condition, denoted by the initial (W), it has a t,rnsilc strength
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INDUSTRJAL A N D ENGINEERING CHEMISTRY
of 30,000 to 40,000 pounds per square inch, and a Brinnel hardness number of 55 to 70. The thickness of the sheet also affects the results, so that uniformity in this respect should be maintained. EQuIrMEm-The only special equipment required for the test, outside of that already mentioned, is a piece of metal tubing 24 inches long and‘[/i inch internal diameter, and three tools Z1/2 inches long, made of case-hardened 3/g inch diameter steel drill rod. The end of one section of drill rod is ground to a sharp edge having a face 1/4 inch lung an& ataper angle of 77 degrees. The second tool is pointed in the same way as the first except that the edge is rounded on a I/sd-inch radius. The third tool is ground to a ball point 3/a2 inch in diameter. Each tool weighs approximately 1.5 ounces (43 grams), and the shapes of the points were arbitrarily selected. Some other shaped points might work better, but since the ones described above have given satisfactory results no attempt has been made to improve them. OPERATIoN-After ascertaining that the thickness of the paint film on the sample to be tested is between 0.0025 and 0.0030 inch, the panel is placed flat upon a firm metal or stone table top, in such a way that the spot being tested is in perfect contact with the support. The 24-inch section of l / ~ inch diameter tubing is then erected vertically upon the sample, and the three tools are dropped through it in succession on different portions of the surface of the panel. The impact of the “sharp” tool is naturally the most severe test, and marks or chips the paint film more or less severely in proportion t o the brittleness and adhesion of the paint. The most durable paints show only a slight dent, while very brittle films show chip marks a/16 inch in diameter. The ball-pointed tool gives the least severe test, and it breaks through the films of only the most friable paint materials. By studying the marks made by the three tools under a magnifying glass, it is possible after some practice to detect rather fine differences in the resistance to chipping of different paints. INTERPRETATION OF RESULTS-In order to obtain the best results from the chipping test, the writer has found it desirable to grade, by means of an arbitrary scale, the degree of chipping produced by each tool. It has been found thati the marks can be readily divided into six grades, roughly designated as follows: Slight dent (best) Deep dent but no chip Cut through paint but no chip as large as 1 / m inch diameter Cut through paint and slight chip between l / a and 1/18 inch diameter Cut through paint and medium chip between ‘/16 and I/g inch diameter Cut through paint and large chip greater than inch diameter (worst)
total number of points scored by a given sample in all three tests is an indication of its toughness and adhesion, and the number is called the “chipping value.” When this test is used repeatedly, it is best for judging purposes to select permanent standard samples representing each grade with which each test specimen can be compared. Abrasion Test
The abrasion test is made by determining the number of revolutions of the panel under a standard abrading disk which are required to wear through the paint film. PREPARATION OF TEST SPECIMENS-If a sample 8 by 4 inches is prepared as described for the chipping test, one half can be cut off and used for the abrasion test. The sheet should be as nearly flat as possible and the film to be tested should be between 0.0020 and 0.0035 inch in thickness, preferably 0.0025 inch. The exact thickness of the film should be determined within 0,0001 inch. A l/a-inch hole is drilled
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in the center of the sheet for the purpose of fastening it by means of a threaded post and thumb screw to the revolving table of the testing machine shown in the accompanying photograph. EQIJIPMEST APJD METHODOF ’TEsTIxG-The apparatus has a plate 5 inches in diameter, which is rotated at an approximate rate of 30 r. p. m. by means of a 1/6-horsepower 1400 r. p. m. motor, to which it is connected by a 40: 1 Boston Gear Company speed-reducing unit. Resting upon the plate, and frw% revolve upon an axis, is an abrading disk 15/8 inches in diameter and l/4 inch thick, made of a standard ink-eraser rubber composition. The revolving abradipg disk is,a,tbached to a hinged lever arm 3 inches from the hinge-or fulcrum, and it is pressed upon the test specimen under a load of 19 ounces (540 grams) consisting of a steel weight sliding upon the lever arm. In most of these tests the weight was fixed a t a point 8 inches from the fulcrum. The rubber disk is set a t an angle of 45 degrees to the radius of the plate, so that as the plate revolves the abrading disk sweeps across the inch wide. surface and wears a path about The plate is supplied with a revolution counter, and the abrasion resistance of the finish is determined by the number of revolutions of the rubber disk required to wear through the paint or varnish film. For comparative purposes the observed number of revolutions is always corrected proportionally to correspond with the standard film thickness of 0.0025 inch. I n order to relieve the operator of the necessity of constantly watching the test, there is attached to the machine a copper trailer wheel, which follows in the path of the abrading disk and is connected to a transformer, a circuit-breaking relay, and a standard motor starter (not shown in photo), so that when the wheel makes contact with the exposed metal a t the conclusion of the test it automatically stops the motor. This attachment is not necessary to the proper working of the apparatus, but it greatly conserves the attention of the operator. Tests can be checked on the same sample within about 500 revolutions when the total number amounts to between 5000 and 8000, so that it furnishes comparisons of satisfactory accuracy on the abrasionresistance qualities of different paints. A fresh disk is always started with each sample, and the disks are changed at the end of each 5000 revolutions.2 IKTERPRETATION OF REsuLTs-when a number of paint samples are being subjected to different tests for the purpose of selecting those of greatest merit, the writer has found the point system most convenient for grading the samples, and it is suggested that the abrasion test be evaluated by giving one point for each 500 revolutions which the paint film withstands. I n selecting the most desirable finishes for furniture and other articles, the abrasion or wear resistance of the paints is a very important factor. Differences in the abrasion quality of paints of the same class and applied under identical conditions have been found ranging from 2000 to 46,000 revolutions, and the writer believes that this test furnishes extremely valuable information to the manufacturers and ’ users of protective surface coatings. 2 The disks were furnished on special order b y the Eberhard-Faber Co., Brooklyn, N. Y., and the compound used is known as No. 1071.
British Low-Temperature Carbonization Project It is announced that the British Benzole and Coal Distillation, Ltd., has been formed to take advantage of the preference given by the current budget t o domestic motor fuel, that is, the tax of 4 d. per gallon which was imposed on April 25 on imported light oils. The new company proposes to install a coal carbonization plant a t Bedwas, Wales, on a site leased from the Bedwas Navigation Colliery Co., Ltd., the plant to include extensive benzene and coal distillation works, as well as a benzene rectification plant and tar distillation plant.
