Metallic objects are usually plated with a metal coating for improved appearance, corrosion resistance or durability. Thickness determination is important for efficiency and cost-effectiveness as well as to determine when the plating bath needs replenishment. Without specialised equipment, it is still possible to calculate plating thickness, using a balance, a ruled vernier or micrometer, a manufacturer's data sheet, and a simple formula. The method of using the manufacturer's data sheet ordinarily works, but for ultimate accuracy, the second, weight technique, is superior.
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Things you need
- Object before plating
- Plating bath or the object following plating
- Balance or scales
- Ruled vernier or micrometer
- Manufacturer's plating bath data sheet
Calculate the surface area of the object before plating using the ruled vernier or micrometer. For instance, the outer surface of a cube consists of six squares. The surface area of the cube is equal to the surface area of those squares, added. As another example, the formula for the surface area of a sphere is four times 'pi' (approximately 3.14) times the square of the radius. There are equations for cones, cylinders and other common geometrical shapes. Use these formulas to determine the surface areas of simple geometrical pieces. It may not be possible to determine the exact surface area in some instances, but an approximate surface area may do. If there are to be a number of identical pieces plated, one may be used to obtain an approximation, then parameters adjusted as a "fine tuning."
Examine the manufacturer's data sheet to determine what current density should be used. Then, using the surface area, calculate the total current you will use to plate the object. For example, the data sheet indicates a current density of 3 amperes per square foot surface area. For a cube with sides of 2 by 2 inches, the surface area of the object is 24 square inches total. There are 144 square inches in a square foot. That means our cube has a surface area of 1/6 square foot. At a desired current density of 3 amperes per square foot, the current used is 1/2 ampere. If the data sheet says the bath deposits 50 microinches in 10 minutes and you plate the piece a half-hour, you will have plated 150 microinches.
Determine plating thickness another way. Taking the unplated piece, weigh it, plate it and reweigh it to determine weight increase. The average thickness can be determined using a mathematical expression derived below:
V = W / D or Weight, divided by Density = Volume.
V = (S x T) or Volume equals the Surface area times the Thickness. Therefore,
W / D = (S x T)
T = (W x S) / D
Using the above equation, thickness equals the weight of the plated metal (just the coating) times the surface area of the piece, divided by the plating density. Plating density is generally included in the manufacturer's data sheet.
Tips and warnings
- To achieve the best quality plate, follow all manufacturer's data sheet specifications, including those about filtration, temperature and agitation.
- Read and apply all MSDS warnings before beginning this project. Safety equipment should include safety goggles and gloves.
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