Companies today are not in the business of making a product or supplying a service, they are in business of making money. Most companies want to make more of it. Making more money or improving profitability has become an incessant demand for virtually all companies and industries. However, today's competitive environment has made it very difficult to improve financial results through large increases in business share, and nearly impossible to do it through increasing price. In fact, it is not unusual for companies to reduce prices in order to keep or gain customers. Reducing costs and improving profitability without understanding what the costs are can be difficult. The applied cost of electrocoat is one area where all the variables need to be understood to determine the impact of changes on costs. The cost of electrocoat is usually a high percentage of the total operating costs of an electrocoater. Changes to the applied cost of electrocoat can have an impact on operating costs and profits.
Electrocoat is sold at X dollars per gallon. The price per gallon varies from supplier to supplier, and different products from the same supplier can vary in cost per gallon. Comparisons are made, sometimes, based on cost per gallon. This is not correct; all electrocoats are not created equal. There are many variables that affect the final or applied cost of electrocoat and your profits. The main variables that affect applied coating cost are percent volume solids, bake off and film shrinkage. Within each on of these variables are other variables that affect it.
Each one of these variables and its associated variables are addressed in this article. I will try not to quote lab work and extensive studies in this article; you don't coat parts in the lab. Lab work is nice to use as a guide, but do not base your decisions solely on it. I will try to supply you with procedures and formulas that can be used by the average electrocoat shop to determine the applied coating costs. One note: Bake off and film shrinkage as expressed in this article are two different variables.
Percent volume solids is the amount of paint per unit volume that can be applied to a part. Percent volume solids is not the same as percent weight solids. Percent weight solids is the amount of paint per unit weight that is non-volatile. Percent volume solids is available from the paint suppliers. If a gallon of paint has percent volume solids of 50, half of the gallon can be applied to a part. A gallon of paint with volume solids of 50 will cover approximately 800 square feet at 1 mil of thickness. The formula to determine the square feet per gallon:
% volume solids for electrocoat x 231
144 square inches x coating thickness in inches |
One sq ft is equal to 144 sq inches. The factor 231 is the amount of cubic inches in a gallon. One mil is equal to 0.001 inch.
A paint with volume solids of 50 at a thickness of 1 mil will cover:
0.50 x 231 = 802 sq ft
144 x 0.001 |
The volume solids expressed in the previous equations is the combined volume solids of resin and pigment. Resin and pigment will have different volume solids. To determine the combined volume solids the following formula is used:
Fed Ratio x Resin Vol Solids + Pigment Vol Solids
Fed Ratio + 1 |
Fed ratios are generally expressed in parts of resin to one part pigment.
The combined volume solids of a product will vary with the fed ratio. The variation of volume solids can affect the amount of sq ft a gallon of electrocoat will cover. An example of the affect fed ratio can have on volume solids is illustrated.
Example 1:
The fed ratio for a product ranges from 6.8 parts resin to 1 part pigment up to 11 parts resin to one part pigment. The resin has volume solids of 31 and the pigment volume solids are 41.
Volume Solids for a fed ratio of 6.8:1 =
(6.8 x 0.31 + 0.41)/(6.8+1) = 32.3
Volume Solids for a fed ratio of 11:1 =
(11 x 0.31 + 0.41)/(11+1) = 31.8 |
The difference in volume solids illustrated above is approximately 1.5 % or about 8 sq ft per gallon. This may not seem like much until you work the numbers. If a shop is using about 12,000 gallons a year the difference equates to 96,000 sq ft.
Volume solids vary from supplier to supplier and product to product. The above formula can be used to compare supplier to supplier and product to product. An example of the volume solids of a different product are presented below and compared with the previous example.
Example 2:
The fed ratio for a product ranges from 4 parts resin to 1 part pigment up to 7.1 parts resin to one part pigment. The resin has volume solids of 34, and the pigment volume solids are 30.
Volume Solids for a fed ratio of 4:1 =
(4 x 0.34 + 0.30)/(4+1) = 33.2
Volume Solids for a fed ratio of 7.1:1 =
(7.1 x 0.34 + 0.30)/(7.1+1) = 33.5 |
The product in example to will cover about 4 % more area then the product in example 1.
The above formula provides the theoretical coverage for a perfect electrocoat system; the amount of electrocoat deposited is equal to the amount after the system. Real world system loss from film shrinkage is not considered. When calculating the actual coverage, which takes into account the system losses, use the following formula:
Sq Ft per Gallon of Electrocoat = Actual Sq Ft
1+ System Losses/100 Gallon |
An electrocoat film will shrink when cured. Furthermore, components of the electrocoat film volatilize, or bake off, in the oven and escape out the exhaust. The components that can escape are not just limited to water and solvent but can be other parts of the electrocoat. Film shrinkage and bake off are related but not the same. I prefer to use film shrinkage. When was the last time you weighed a part to see if it had enough film?
Electrocoat film shrinkage is defined as the amount or percentage that an electrocoat film will shrink during baking. The thickness of an electrocoat film will physically shrink or reduce during bake. The amount of the shrinkage will depend on the type of electrocoat and the bake temperature. The higher the bake, the greater the film shrinkage. Values for film shrinkage are generally not available from the supplier. There are many factors that influence film shrinkage, making it hard to quantify for general use. The film shrinkage experienced at a particular plant can be quantified using in-plant procedures. The procedures are discussed below.
Electrocoat bake off is defined as the percent weight loss of the electrocoat film during the cure process. During the cure process, crosslinker blocking agents, solvents, and lower molecular weight components are driven off in the bake oven. The weight of the cured film is less than the weight of the uncured deposited film.
The bake temperature affects the amount of bake off and film shrinkage. The higher the temperature, the greater the bake off and film shrinkage. Higher bake off and film shrinkage increase the amount of electrocoat that has to be applied in the tank to achieve a film build. Increasing the amount of electrocoat applied, increases the usage. Bake off and shrinkage losses can impact usage significantly.
Higher bake off and film shrinkage usually occur in ovens where parts of different masses are processed. The oven is set up to cure heavy metal parts, the lighter parts get over baked. The lighter parts usually account for the bulk of the production. Improvements in the air flow of the oven can even out the bake, such as concentrating the air on the heavy metal parts. First, the amount of savings for such a change should be calculated. The following method can be used to determine the amount of extra bake off and film shrinkage that might be occurring. The method described below should be done several times to establish an average.
Determining Bake Off and Film Shrinkage
- Determine the current bake profile of the different parts;
- Determine which part has highest bake or the one you want to target; Note: The part that is used should be small, no larger than 4 x 6 inches. A smaller part reduces the chance for error. The weight of ecoat applied to a panel is small. The greater the ratio of panel weight to ecoat weight the greater the chance for error.
- Remove six pieces of the chosen part after phosphate and before ecoat;
- Bake the six parts for 30 min at 200F;
- &Weigh each part and record the weight; Note: The scale should be capable of measuring 0.1mg.
- Place each part back on the line and ecoat;
- Remove the parts after ecoat and before the oven;
- Bake the parts for 2 hours at 200F;
- Weigh each part and record the weight;
- Place three of the parts back on the line and bake in the production oven;
- Bake the other three parts at the new bake curve;
- Weigh each panel and record the weight;
- Determine the % bake off for each panel using the following formula.
Wt. of Dried Film - Wt. of Cured Film x 100
Wt. of Dried Film |
Wt. of dried Film =
Wt. of dried coated panel - Wt. of uncoated panel
Wt. of Cured Film =
Wt of Baked coated panel - Wt. of uncoated panel |
- Measure the film builds on all the panels. Note: when measuring electrocoat films use a gage that measures at least to two decimal places. In addition, the gage needs to be properly calibrated with the correct shims.
- Determine the film shrinkage using the following formula.
Film build of target bake–Film build of production bake
Film build of production bake |
- Compare the % bake off and film shrinkage for the two bakes;
- Determine savings using the following method.
| Difference in Film Shrinkage x usage for part being studied x cost of electrocoat |
Example:
Film Shrinkage improvement was 5% for a part that accounted for 50,000 gallons of electrocoat use a year at a cost of $12 a gallon.
| 0.05 x 50,000 x $12 = $30,000 a year in savings |
Applied coating costs are affected by many variables. These variables are controllable and/or changeable. The key factor is to identify the variables and determine the impact of changing and/or controlling them. The procedures and formulas here should enable an average electrocoater to do this. Repeat the procedures several times or until there are consistent results. The procedures should be repeated for different parts. Try parts that vary in size and rack density. Watch for differences in the process when running the tests, try and equate differences to the results. Good decisions are based on good data.
The cost of electrocoat is usually a high percentage of the total operating costs of an electrocoater. Changes to the applied cost of electrocoat can have an impact on operating costs and profits. You are in the business to make money and profits are important.