UNITED STATES DEPARTMENT OF COMMERCE. Maurice H. Stans, Secretary NATIONAL BUREAU OF STANDARDS Lewis M. Branscomb, Director 1964 Exposure Test of Porcelain Enamels on Aluminum 1964 Exposure Test of Porcelain Enamels Margaret A. Baker * An exposure test of porcelain enamels on aluminum was initiated by the National Bureau of Standards and the Porcelain Enamel Institute in 1964. The enamels were returned from the exposure sites to the laboratory at NBS to be measured for changes in gloss and color after exposures of six months, one year, and three years. Changes were found to be greatest at Kure Beach and least at Montreal and Los Angeles, with moderate changes occurring at Washington and New York. Although the boiling citric acid test is used as an acceptance test for these enamels, the correlation with color change, particularly at Kure Beach, was not as good as expected. A cupric chloride test was developed which shows an improvement in this correlation. Key words: Color; gloss; porcelain enamel on aluminum; weather resistance. 1 1. Introduction The application of porcelain enamels to aluminum is a relatively recent development in the field of porcelain enameling. A few of the early porcelain enamels on aluminum included in an exposure test initiated in 1956 [1] indicated that accelerated tests used with confidence for porcelain enamels on steel were not reliable indicators of the weatherability of the new, lower firing porcelain enamels on aluminum. Therefore the Aluminum Council of the Porcelain Enamel Institute agreed to sponsor, with the National Bureau of Standards, an exposure test consisting solely of porcelain enamels on aluminum. Nine colors used in 2.1. Enamels porcelain enamels on aluminum and enamels varying in initial gloss and thickness were tested. The enamels in this test are exposed at Kure Beach, North Carolina; New York, New York; Washington, D.C.; Los Angeles, California; and Montreal, Canada. They were inspected after exposures of six months, one year, and three years and were returned to the exposure racks for further exposure. This report is a summary of the results of these three inspections. The next inspection is tentatively scheduled after five years of exposure. 2. Materials and Procedures Sixteen enamel systems were included in this test. These enamel systems were represented by nine colors, three gloss ranges, and both one- and two-coat enamels as indicated in table 1. The enamels in this test were coded for identification. Each enamel system can be identified by the first two code letters. The first letter is always A and indicates an enamel on aluminum. This letter may seem redundant but it is included because the manufacturers recognize their enamels by the three letter code. The second letter indicates the enamel systemcolor, number of coats, and gloss range while the third letter indicates the different fabricators for each system. The differences between the enamel systems are apparent (see table 1) for all systems except AA and AZ, which were planned to have significantly different thicknesses. However, this difference was not attained during manufacture. When variations in milling and firing of the enamels by the different fabricators are taken into account, there are, in effect, 51 different enamels included in this test. 2.2. Test Specimens Each enamel was sprayed onto a 3 X 5-ft sheet of 0.064-in 6061 aluminum alloy. After the enamel was fired the sheet was cut with a band saw into a seventyeight 4716-in-square and nine 4 × 6-in exposure specimens. This was done to obtain more uniform specimens than could be obtained by spraying and firing small individual metal blanks. Also, the speci mens thus obtained would more closely simulate actual production enamels than small individually prepared specimens. 2.3. Exposure Sites Three of the 47/16-in-square specimens of each enamel were exposed on the roofs of Federal Government Buildings in New York, N.Y.; Los Angeles, California; and Washington, D.C.; as well as on the roof of the Stores Department Building in Montreal, Canada. Three of the 4 × 6-in specimens of each enamel Research Associate from the Porcelain Enamel Institute at the National Bureau of Standards, 1964 to present. 1 Figures in brackets indicate the literature references at the end of this paper. |