Cost Calculations for Potting Compounds
I. Potting Compound
Potting compounds are normally sold by weight since it is an easy method of measurement. However, resins are used to fill a void or volume so therefore the user should be concerned as to the cost per unit volume. Some potting compounds are higher density than others so comparing the cost per pound, $/lb, does not give the true cost.
As an example, if potting compound A has a mixed cost of $3.00/lb. and a mixed density of 8.3 lb./gal (SpG of 1.0) and a second potting compound has a mixed cost of $2.75/lb. and a mixed density of 12.4 lb./gal (SpG of 1.5) then if you selected the lower cost per pound material ($2.75/lb) it would actually cost you more in the potting compound than if you used the higher cost lower density potting compound. Here is how to make the calculation:
Potting compound A: 3.00 $/lb. x 8.3 lb./gallon = 24.90 $/gallon or 24.90 $/gallon/231 cubic inch/gallon = 0.108 $/cubic inch.
Potting compound B: 2.75 $/lb. x 12.4 lb./gallon = 34.10 $/gallon or 34.10/231 ( cubic inches per gallon) = 0.148 $/cubic inch.
If you used one cubic inch of potting material you would save $0.04 per unit. When comparing different potting compounds calculate the cost per unit of volume to determine the difference before deciding on the potting compound to be used.
The easiest way to determine how much potting material is to be used is to weigh the part empty, add water to the unit equal the amount of potting compound that will be used. The most accurate weight measurement will be by the gram. There are 454 grams in a pound so you can convert that to pounds by divide the grams by 454. Then use this equation to determine cubic inches of material: lbs of water/8.3 x 231. If you are working in the metric system the number of grams of water equals the same number of cubic centimeters.
If you can not use this method to determine the amount of potting material then estimate it by measuring the dimensions of the shell or mold and calculating the cubic inches or cubic centimeters and then divide by 2. A quick estimate of the potting compound needed would be one-half of the volume.C. Design for Low Cost
Design of the unit will greatly affect the amount of material used in the unit, which is a large part of the cost. The potting compound can be the largest cost of the unit if designed incorrectly. Reduce the amount of potting compound used by allowing enough space for air to escape but the minimum amount of material or a divided case as shown in this picture.
If this is not possible you may be able to tilt the case when dispensing the potting compound as shown in the picture. This requires that the case remain in this position until it has hardened so special holders need to be made.
II. Dispensing system
Maintenance of the equipment is a must and costs must be included for new part that wear.
Wipe-up towels, ratio check cups, cleaning solvent are require so some cost should be added for them.
Plan to have a factor for waste of the resin system of 2-5%.
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Last Modified: July 20, 2012