Metal Finishing Guide Book

2012-2013

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and one part Component B. For the time being, you will not add any thinners. From the MSDS you get the following information: Component A = 3.6 lb/gal Component B = 2.2 lb/gal Set up the same table as before and insert the given information into columns 1, 2 and 3 as shown in Table II. Following the same steps given in the previous example, you simply divide the total number of gallons of the mixture into the total Emissions. Therefore, the VOC of one gallon of the mixture is: VOC = 15.9/5 = 3.18 lb/gal Once again, if someone were to sample the coating, the VOC content would be 3.18 lb for 1 gal of the mixture. Because the VOC content of the mixture is below 3.5 lb/gal, you are allowed to add thinners, if necessary, but under no circumstances are you allowed to exceed the 3.5 lb/gal limit. CALCULATING THE VOC OF A TWO-COMPONENT COATING MIXTURE PLUS THINNERS Suppose you do want to add thinners having a VOC of 6.4 lb/gal to the coating mixture in Table II. How much can you add before exceeding the regulatory limit? There are two methods for making this determination. The first is quite simple and does not require any knowledge of algebra. The second is slightly more difficult, but a whiz for those who still remember their high school math. Here is the simpler of the two methods. Suppose you were to add only one quart (0.25 gal) of thinner, would you exceed the VOC limit? Solution Using Trial and Error The results of the first trial are shown in Table III. Following the same steps as given in the previous examples, VOC = 17.5/5.25 = 3.33 lb/gal Because the VOC content of the mixture is still below 3.5 lb/gal, you can afford to add slightly more, if necessary, but remember that under no circumstances may you exceed the 3.5 lb/gal limit. Repeat the calculations by adding another quart (0.25 gal) of thinners. In re- 868

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