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Ask the Expert Question-and-Answer Archive
(Hard Chrome Plating)

by Larry Zitko, ChromeTech, Inc.
January, 2002

Rectifier for a New Chrome Plating Line

Q. We are building a plating line. We need our tanks / pails to be 6 Ft deep x 6 ft wide by 30 ft long. We have doubts in regards of how to select an adequate capacity for the rectifier. Also, Could you recomend a supplier for this rectifier ?

Thank you in advance for your response.

A. Rectifiers for hard chromium electroplating are typically sized to match the size of parts to be plated in the tank, rather than the tank volume. The process is twofold:

First, add up the surface area of all parts that would be plated simultaneously in the tank. Usually, you have to consider the quantity of parts of various sizes that are available for plating during the year, and make some compromises. For example, if you intend to plate 300 parts per month that each have 1,000 square inches of plated area, but only 3 parts per month with 5,000 square inches, you may not want to size the rectifier, tanktop copper, bussing and cooling system large enough to plate 3 of the large parts at once. Instead, you may size everything smaller, and limit yourself to plating only 1 large part at a time.

Next, you must consider the cathode "current density" range for the parts o be plated. Hard chromium is usually electrodeposited within the range of 1 - 5 amps/sq.in., with 2-3 amp/sq.in. being commonplace. Let's consider some examples.

Let's say you want to plate 3 parts at once, and each part has 1,000 sq.in. of plated area. 3 x 1,000 sq.in. = 3,000 sq.in. total. If you want to plate these parts at a current density of 2 amp/sq.in., then the rectifier will have to supply 3,000 sq.in. x 2 amp/sq.in. = 6,000 amperes to the plating process. If you want to plate the same 3 parts at a higher current density of 3 amp/sq.in., then you will need 3,000 x 3 = 9,000 amps. If you only have a 6,000 ampere rectifier and want to plate 4 of these parts at once, you can still plate them simultaneously, but the maximum current density will be 6,000 amp / 4,000 sq.in. = 1.5 amp/sq.in. The plating rate of deposition decreases with the lower current density, but you are still plating more parts at once.

Several manufacturers or suppliers of DC power supplies (rectifiers) advertise in metal finishing industry periodicals and guidebooks, and also on the world wide web. In fact, you can find many of them listed here at NMFRC. From the home page, in the "Public Area", choose "Vendors", then "Surface Finishing Equipment", then "Rectifiers". I would encourage you to communicate with them to make your selection. It is important that your power supply be suitable for the hard chromium electroplating process, including the need for low ripple and long plating cycles.

Building a new plating line takes careful planning. I hope you have someone to make sure that the heating, cooling, exhaust ventilation, air pollution control and other subsystems are designed properly. The environmental issues are equally important. Good luck with your project.

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