Q. How do you calculate the amount of electrical energy in amps-hr. required to deposit one gallon of epoxy electrocoat feed? Will this electrical energy be constant during the entire coating cycle or variable? —P.L.
A. The amount of energy required to deposit electrocoat material is directly proportional to the amount of solids, by weight, of electrocoat material deposited.
In order to calculate the amount of electrocoat by weight in one gallon, you first need to know the percent solids by weight and the density or specific gravity of the supplied ecoat. Since that information is not provided, I will assume that this particular electrocoat feed material is 30 percent solids by weight and with a specific gravity or density of 1.05. Remember that the percent solids above are not the percent solids in your bath but the percent solids in the electrocoat feed material.
By multiplying the specific gravity 1.05 x 8.34 you can obtain that one gallon of feed weighs 8.8 lbs. At the 30-percent solid level, the weight of electrocoat solids available for deposition is obtained by multiplying 8.8 x 0.3, or 2.6 lbs. of electrocoat solids per gallon of feed.
The next calculation step requires that you know the electrochemical equivalent of the specific electrocoat material used in the operation. This is a number that is readily known and available from your electrocoat supplier. It typically ranges between 11,000 and 15,000 coulombs/lb., and I will use 12,000 coulombs/lb for the calculation.
Since one coulomb is equivalent to 3,600 amps-hr., we can then calculate that to deposit one gallon of ecoat feed material requires 2.6 x 12,000 and then divide the resulting number by 3,600, or 8.7 amps-hr. This calculation is total energy for the entire gallon cycle.
The above result of 8.7 amps-hr. is a theoretical calculation, so reality will be a little different. Real consumption will always be slightly higher than theoretical consumption. The difference between theoretical consumption and real consumption is the system efficiency.
The amount of energy required for deposition will not be constant through the coating cycle, because of different coating deposition rates and inefficiencies in contact points and grounding. Electrocoat material deposits faster at the beginning of the cycle when there is only uncoated metal, and slower as the film deposits and introduces additional resistance. Additional resistance translates into slower deposition rates.
Measure the real electrical consumption during a coating cycle and divide this number by the theoretical calculation to obtain the coating system electrical efficiency in percent.
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