Rapid Exposure Tests on Finishes H. A. GARDNER, Institute of Paint and VarnishResearch, 2201 New York Ave., Washington,D. C.
A
CCELERATED testing cabinets have been constructed a t this laboratory and experimented with for several years. These cabinets include quartz-tube mercuryvapor lamps, Weather-0-Meter carbon-arc lamps, and highamperage carbon-arc lamps. The lamps have. usually been placed in metal cabinets of sufficient size to hold from 20 to 50 test panels 5 by 10 inches (12.7 by 25.4 em.) in size, and provision is made for spraying the coated surfaces with water from time to time. As a result of several hundred tests it is believed that such cabinets may prove useful in securing comparative results on such products as lacquers and some types of enamels. Results on varnishes do not always check with exterior exposure tests. Oil paints usually show very rapid chalking, but it has been difficult to secure such defects
as checking, alligatoring, and scaling which are shown on exterior surfaces under practical conditions. For this reason, it is the writer’s opinion that accelerated cabinets have only a limited field of use, and that actual exposure tests should accompany all cabinet tests. Because of the varying climatic conditions in most parts of the country during the different seasons of the year, the exposure of panels out of doors for quick breakdown tests (three months or less) is not practical a t all seasons, as the same results would not be obtained in the winter as in the summer months. For this reason, some manufacturers have found it advisable to restrict their exposure tests to a period extending from May to October, a period of the yea.r when the sunlight is most intense. During the balance of the year it is probably desirable for manufacturers to have their tests exposed in a section of the country where climatic conditions do not vary greatly. The southern Florida peninsula, where there is sunshine for 359 days of the year, affords an ideal place for such work. Moreover, the atmosphere a t that point is practically free from smoke. A site may be selected for test within a mile of the ocean, and racks erected. The panels should preferably be exposed a t an angle of 45 degrees to the vertical, facing south, although one observer has indicated that exposures to the east, west, or south all weather w i t h a b o u t the same degree of rapidity because of the intense sunlight conditions. Exposure tests on house paints, enamels, varnishes, sign colors, automobile finishes, and other industrial products may be made on such racks. As a rule, a period of three months will give some information on many types of finishes. A period of four weeks is usually sufficient to break down inferior varnishes or coatings which are not properly designed. An exposurefor one year will often afford some information on the durability of oil paints.
RACKSFOR OUTDOORTESTS
FIQUREI
From time to time manufacturers desire tests on marine compositions which are to be employed on the exterior skin of ships, especially a t the water line where the most severe service is shown. For instance, at the water line of navy vessels, a paint known as “boot-topping” is employed. This paint is subjected to alternate exposure to salt water and air. Such coatings often break down very rapidly, and to date but few products have proved entirely satisfactory for the purpose. For this reason, boottoppings must be renewed frequently, especially on battleships where a trim appearance and freedom from corrosion must be maintained. Where tests of this sort are contemplated, it is; suggested that racks be built in the ocean a t a point near the shore, where they will be available for inspection. Such racks are shown in Figure 1. At low tide the water recedes to such an extent that the panels may be inspected if the observer will wade out to his
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INDUSTRIAL AND ENGINEERING CHEMISTRY
95
knees. During the daytime the tests receive sun exposure, and a t high tide they are completely covered by sea water. Practically all coatings are to some extent permeable to salt water. The water going through the coating causes rapid corrosion of the underlying metal or contraction and discoloration defects on wood. During the drying-out period, the water is eliminated, but part of the salt contained in the water may be retained in the film and cause disintegration. I n making tests of varnish under any of the conditions r e f e r r e d to above, it is highly important to take into consideration the length of oil and the percentage of non-volatile matter. Thus, for instance, a varnish which contains 60 per cent of non-volatile matter will n a t u r a 11y form a very much thicker film than one which may be of the same visc o s i t y b u t which contains only 40 per cent of n o n - v o l a t i l e m a t t e r . Thickness of film is a v i t a l factor in the durability of a coating material. It is usually d e s i r a b l e in making comparisons to d e t e r m i n e the thickness of film after application of the finishing system by removing a portion of the coated surface about FIGURE 2. RESULTSOF WASHINGTON ROOFSALTWATER-AIRTEST AFTER 10 DAYS’EXPOSURE 1 mm. square, and then using an instrument such as the Ames dial micrometer on the abraded surface and on the unabraded In making water exposures of varnishes which are designed surface. The film should preferably be a t least 30 microns for use upon yachts, the writer has employed oak panels a t in thickness to give good results. Miami, and prefers them to steel, as the rusting of the steel will greatly affect the durability of the varnish and give LABORATORY TESTS results which are not comparable t o those obtained on wood. For manufacturers who have not made arrangements for The writer has used oak panels 12 by 18 inches (30.4 by 45.7 the exposure of tests in Florida, and who prefer to have their TABLE I. SALTWATER-AIRTESTIN OCEANAT MIAMI tests under their own supervision so that daily inspections can (Inspection at end of 6 weeks’ exposure) be made, it is suggested that an apparatus such as is shown in STEEL WOOD the lower part of Figure 1 be experimented with. This NO. VARNISH 2 brush coats 3 brush coats apparatus has been recently designed by the writer and has 958 Phenolic resin 2540 low-cook tung Failed. 0. K.0 50%’rusted oil varnish, 44 gal. length; purbeen in service during the past three months in conducting chased tests on the roof of the laboratory. 959 Modified phenolic resin 2260 lowFailed. 0. K.= 6O%’rusted cook tung oil varnish, 44 gal. In considering the results outlined in the Washington roof length; purchased salt-water test, it is apparent that one flow coat of coating 962 Phenolic zesin 2540 low-cook tung Failed’ 0. K.5 material is entirely insufficient to produce a film which will oil varnish, 44 gal. length: made 20%’ rusted in laboratory withstand such a test for any extended period of time. On 963 Modified phenqlic resin 2260 low- Failed * 0. K.a the right side of Table I1 referring to these tests, the results cook tung oil varnish, 44 gal. 50%’rusted length; made in laboratory obtained on panels coated with three brush coats of coating Failed. Bad checking. slow-drying 30 gel. ester materials are more in line with those which are obtained by 964 Old-type gum tung oil varnish: 600’ oook 100% rustedb removed f r o d test actual exposure to the air. Figure 2 shows the rusted and 966 25 gal. tung oil-synthetio ester Failed’ Bad checking. whitened surfaces of the panels after ten days’ exposure. No. 1 varnish containing 0.01% 100% rustedb removed f r o d sulfur: cooked a t 600’ F. (315O C.) test In these tests, the low-cook phenolic and modified phenolic 967 44 gal. synthetio ester No. 1 tung Failed: Bad checking; resin-long oil varnishes gave generally satisfactory results oil varnish containing 0.05% SUI80% rusted removed from fur; low cook test as compared to the other coatings. Rapid failure was shown Failed, Bad cheoking: 968 44 gal. ester gum-tung oil varnish by sulfur-treated varnishes, lead tungate liquids, boiled linseed containing 0.1% sulfur: low cook 100% rusted removed from test oil, gloss oil, and a rubber varnish which has been recently made with equal parts Failed. 0. K. advocated as a water-resistant product. It must be pointed 969 Laoguer 3 0 d rusted nitrocellulose and glycerol ester PRX out that to date insufficient tests have been made with this Complete breakdown and covered with rust in one month. type of exposure test to warrant any general conclusions. b High gloss on wood panels a t end of one month. However, because of the speed with which results may be Note. At end of ten weeks, panels 958, 959,. 962, and 963 had.medium obtained, it is suggested for experimentation on the part of gloss. First three showed some slight grain erosion b u t were in fairly good condition, especially 962. Some mildew and water-spotting of the wood other investigators. was shown on 963 and 969. L J
96
ANALYTICAL EDITION
Vol. 4, No. 1
TABLE 11. SALT WATER-AIR TESTON ROOFOF LlBORATORY No.
ONE FLOW COAT THREEBRUSHCOATB TYPEOF CLEAR Condition Condition COATINQ USED Failure of film Failure of film Days 4 50% rust
Day8 124-
4
50% rust
12+
Few tiny blisters, slight rust under film
9
Slightrust
124-
Few tiny blisters slight rust unde; film
4
50% rust
12
Small blisters at top, slight rust under film
4
50% rust
12
Tiny blisters slight rust under hlm
967 44
2
70% rust
3
Large blisters oonsiderable ruiting
965
4
50% rust
5
Fairly large blisters, considerable rusting
9
Very slight rust
12
Tiny rust spots, dull
4
50% rust
12
Tiny blisters, slight rust under film
958 Phenolic resin 2540 low-cook tung oil varnish, 44 gal. length: purchased 959 Modified phenolio resin 2260 low-cook tung oil varnish, 44 gal. length: purohased 962 Phenolio resin 2640 low-cook tung oil varnish, 44 gal. length. made in laboradory 963 Modified phenolic resin 2260 low-opok . tung oil varnish, 44 gal. length: made in laboratory 966 25 gal. tung oilsynthetio ester No. 1 varnish, containing 0.01% sulfur. oooked a t 600' F:
969
972
975 976
(316"C.) gal. synthetio ester No: 1-tung oil varnish containing 0.05% sulfur: low-cook 44 gal. ester gumtung oil varnish oontaining 0.1% sulfur; low-cook Lacquer made with equal parts nitrocellulose and glycerol ester P R X Phenol resin 5000tung oil varnish 50 gal. length: made a t laboratory: slow drying Viscous lead tungate liquid oontaining 32% non-volatile matter Commercial kauri spar varnish
4
100% rust
4
30% rust
Few tiny blisters slight rust undei film
1
Badly whitened and rusted
10
Tiny blisters, oonsiderable rust under film
em.) in size, the backs and edges of which are sealed with two or three coats of protective paint. Even under these conditions the face of the panels may sometimes show absorption of sea water to such an extent as to cause slight raising of the grain and black spots which resemble mildew. It was interesting to observe that in the salt-water test, linseed oil (which, when exposed to the air, is of greater durability than most varnishes) failed with extreme rapidity. This was due to the fact that linseed oil films are very porous and allow salt water to go through and quickly attack the iron, causing corrosion which rapidly disrupts the film. This is a further indication that coatings for exposure-under water should be formulated with resins or in other fashion to produce relatively impermeable films. COMPARISON OF WASHINGTON AND GAINESVILLE TESTS In considering the other tests reported in Tables I, 11, and 111,it would appear that normal exposure of panels to the air at Washington and at Gainesville showed the superiority of low-cook phenolic or modified phenolic resin varnishes as compared to those made with ordinary resins. It is probable that the former types are a t least 100 per cent more durable than the latter. Apparently great improvement has been effected in the production of long-oil varnishes for exterior use. However, it should be pointed out that the durability of varnishes made from the newer synthetic resins may to some extent be due to the fact that they are of great oil length and are cooked at low temperatures (approximately 450' F. or 232' C.). This may possibly limit their use in some fields.
ONE FLOW COAT THREEBRUSHCOATS TYPE OF CLE.4R Condition Condit,ion COATINQ USED Failure of film Failure of film Days Days 977 Lacquer contain- 9 Very slight 10 Tiny blisters, dull ing equal parts by rust weight nitroaellulose and glycerol phthalate plasticized resin 990 Combination phe2 50% rust 10 Tiny blisters, rust nolio phthalio anlower half under film hydride glycerol ester-tung oil varnish, 50 gal. length 991 Ester gum-tung oil 2 60% rust 10 Tiny blisters oonvarnish 50 gal. siderable rus't under length" cooked a t film 460' 6. (232' C.) 993 Same as 991 except 2 50% rust LO Tiny blisters very contains 21/& suldull, muoh ;ust unfur added as disder film persion in oil previous to cooking 994 Commercial 4-hour 9 50% rust 10 Tiny blisters slight varmsh extended lower half rust under hlm with 20% bodied . tung oil 995 Commeroial 4-hour 9 50% rust 10 Tiny blisters slight varnish extended rust under hlm with 20% bodied tung oil containing 1% sulfur 996 50%. rosin, 50% 1 100% rust 5 Entirely rusted mineral spirits 997 Boiled linseed oil 2 100% rust 1 Entirely rusted and disintenrated 995 B l p w,n t u n g , o i 1 2 70% rust 10 Many small blisters, hquid containing considerable rust 33% non-volatile matter 999 50% vinyl acetate, 2 60% rust Not inoluded 50% ioluene 9 20%rust 12 Tiny blisters some 1000 S y n t h e t i o e s t e r N 1-tung oil varrust under dlm nish 60gal. length. tun; oil first treated t o -induce formation of @-eleostearin by irradiation and iodine treatment 2 Entirely rusted and 1039 M o d e r n r u b b e r v a r n i s h (GH), disintegrated baked
No.
J.
For instance, some very durable long-oil exterior varnishes may not be entirely satisfactory for floors or for permanently white non-skinning enamels. Similarly, certain glycerolbase resins have remarkable exterior durability but may have such poor initial air-drying properties as to restrict their use. It would appear, therefore, that the resin selected for a varnish must to a great extent depend upon the characteristic and physical properties which are desired. TABLE111. TESTS
NO.
OF CLEAR VARNISHES ON STEEL (2 BRUSH COATS),AIREXPOSURE
(Inspeotion after 14 weeks' exposure) WASHINQTON ROOF, JULY 22, VARNISH 1931
GAINEMVILLE FLA.,JULY 3d, 1931
Phenolio resin 2540 low- Few slight rust Few tiny rust spots, good gloss oook tung oil varnish 44 spots under film gal. length: 64% dongood gloss. good' good condition volatile matter oondition 962 Modified phenol resin Slight rust e ot- A few tiny rust 2640 low-cook tung oi! ting under &m spots, good gloss, varnish, 44 ga!. length, good. gloss, good good oondition 64% non-volatile matter oondition 963 Modified phenol resin Sli h t rust under Small rust spots 2260 low-oook tung oil i l m , fair oondiunder film, fairly varnish. 44 gal. length: tion good gloss, fairly 50% non-volatile maxter good oondition 958
964
965
Ester gum-tung oil var- Very pronounoed Rust below film, nish, 30 gal. length; 46% rust and checking very dull non-volatile m a t t e r . in 6 weeks: re600° F. (315O C.) oook' moved from test in 10 weeks: failed Synthetic ester No. 1- Very pronounoed Rust below film: tung oil varnish containrust and oheaking o h e o k e d very ing 0.1% sulfur, 26 gal. in 6 weeks; redull, poor 'oondilength: 58.6% non-volamoved from test tion tile matter in 10 weeks; failed
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INDUSTRIAL AND ENGINEERING CHEMISTRY
91
be slightly more rapid than a t Gainesville. At Washington
t a n k N ~ ‘ e ; h e ~ ~“ ~, ~“ ~e ~p~ ~~ ~d f~ ~d a ~ &p $3 a e~ a6 ~ $~ ~~ &~ ~~ ~ ~ ~ ~ usually indicated excellent gloss and good oondition. Pane1’963 heveloped the panels are sprayed with water every day between twelve slight rust under the Uviarc lamp. Panel 964 showed pronounced rust and one o’clock. under both lamps. White enamels prepared with 20 per cent Titanox, 20 per cent pure Exposures Of lacquer ‘Oatin@ during the last two years zino sulfide and 60 per oent of the varnishes referred to above were exposed for 14 weeis at Washington and at Gainesville. Panels 958 960 and 962 have indicated the value of two types of glycerol-base resins. showed strong lemon-yellow tints and tiny rust spots. Panei 963 kemained These two types Of resins have proved superior to others very white and free from ruet. All showed heavy chalking. A pale pink
employed in the formulation of lacquer that is to be exposed g ~ ~ i ~ P c t r ~ ~zf ~~d~~~~~~~ i , n P ~ ~ , ~n , ~O tps ~~~ ~~ $ ~$ ~ out ~ ~of doors. They have also stood up very well in the salt
product of the resins employed.
water-air exposures.
be Of interest to note that in the comparative It may exposure Of varnishes at and at Gainesville during the summer months the results a t Washington seem to
RECEIWDAugust 15, 1931. Presented before the Division of Paint and Varnish Chemistry at the 82nd Meeting of the Amerioan Chemioal Soaiety, Buffalo, N. Y., August 31 to September 4, 1931.
Measurement of Slow Gas Flow D. H. KILLEFFER, 50 East Forty-Jirst St., New York, N . Y. EASURENIENT of very slcw gas flow often presents serious difficulty, for standard metering equipment is inaccurate outside rather closely defined limits. Since such problems may arise to plague other investigators from time to time, it has been thought worth while to present here for their benefit a method employed by the writer. It is neither new in principle nor in detail, but rather belongs among those things whose simplicity has allowed them to be generally forgotten. A method quite similar in principle is applied to measurements in the manufactured-gas industry. The particular problem had to do with variations in flow of carbon dioxide by convection in a closed flue system. Because of the limitations of anemometers and the problem in hand, it was impractical to use them. The velocities to be measured were too small to give satisfactory readings with a Pitot tube, and the use of an orifice (which also would have given a reading too small for accuracy) would have restricted flow to an unpermissible extent. It was finally decided to use the thermal characteristics of the gas as a means of measurement. Two methods suggested themselves for this purpose: (1) measurement of the change of temperature of a radiator supplied with constant heat with changes of gas velocity; and (2) measurement of the change of temperature of the gas when supplied with a measured heat input. The first method offered several difficulties not readily overcome, largely involved in the radiation characteristics of the radiator itself and the difficulty of standardization. The second, although involving possible sources of error, seemed to be simpler to utilize. The results were probably accurate to 10 per cent as used, and under the other conditions of the experiment this seemed fairly satisfactory, The equipment required was extremely simple and easy to install. It consisted of a heating coil, a voltmeter, an ammeter, and two thermometers carefully compared for accuracy. The heating coil consisted of a length of ordinary resistance wire wound on a non-conducting form. This was suspended in the gas stream in such a way as to give maximum contact between the wire and the gas. The form is merely an open frame designed to reduce flow resistance and is sufficiently smaller than the duct in which it is suspended to prevent high radiation loss to the duct. The duct itself is best lined for a short distance on either side of the radiator with sheet asbestos or other non-conducting material to avoid the error introduced by conduction of the duct wall.
The two thermometers are placed with their bulbs as nearly as possible in the center of the duct, a t some distance on each side of the radiator, with shields so placed as to reduce errors in their readings caused by radiation. There were about five diameters between each thermometer and the radiator, which proved satisfactory. It is, of course, essential to be able to read very accurately the difference in temperature between the two thermometers, as this is a limiting factor in the accuracy of the method. Mercury thermometers that can be read to a tenth of a degree serve quite well. In operation, a measured amount of current is passed through the resistance unit which is kept a t a relatively low temperature, and the difference in temperature of the gas before and after passing it is carefully measured. It is, of course, necessary t o know the specific heat of the gas for this method to be applicable, but having that, it yields fairly close results. The calculation of rate of flow from the observed data is easily made by the following formula: (V X A X K) = (Sp. H. X (T - To)
where F = rate of flow V = impressed voltage A = amperage Sp. H. = specific heat of gas To = temperature of gas before passing heater T = temperature of gas after passing heater K = constant for convertingwattage to calories or B. t. u. per unit of time
If temperature is expressed in centigrade, K = 0.860, and gives F in kilograms per hour. If temperature is expressed in Fahrenheit, K = 3.412, and gives F in pounds per hour. There are several fairly obvious errors in this method of measurement, but if care is taken in the installation of the resistance and thermometers, and if readings are carefully made, low velocities can be determined with greater accuracy than by any other simple method. The installation of such a device in pipes carrying gases is relatively simple. The precautions to be especially observed are as follows: 1. Carefully isolate heater from the pipe walls to reduce heat losses by a conduction and radiation. A small loss by convection cannot be avoided. 2. In applying heat to‘the radiator, care must be exercised to prevent its becoming red hot, and its temperature should be kept as low as possible. It is preferable to use a long resistance wire which can be heated to a low temperature rather than a
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