How to implement Pulse Anodizing

Many people have talked about pulse anodizing for many years but it seems like a lot are still confuse and don´t see the benefits of using pulses for anodizing, both in hard anodizing and conventional anodizing.

The only whole book you'll find about pulse anodizing is my phd thesis, "Pulse Anodising of Extruded and Cast aluminium alloys" and then The Surface Treatment And Finishing of Aluminum And Its Alloys, by Wernick, Pinner & Sheasby does talk about pulse anodizing in several of its chapters.

There are several reasons for why so many anodizers have resistance against introducing pulse anodizing.

  • The investment in buying a new rectifier
  • Some have tried pulse anodizing already and it doesn´t seem to work
  • You already form oxide fast with DC
  • Education of employees

You will probably have to buy a new rectifier, a bigger one. This is true in most cases if you are already running full load on the rack, so the rectifier capacity is used fully. What we need is to be able to increase the current density (A/ft2).

So if it normally takes the company 40 minutes to run a 0.8 mil load sulfuric acid anodizing type II, class 1 coatings, by using pulse anodizing we should be able to decrease this process time with 50%, forming 0.8 mil in 20 minutes.

To do this we need to double the average current density. To do this we have to utilize the recovery period, and this is one of the reasons why some have tried pulse anodizing without much luck. If the pulse periods are to fast, as in milliseconds, the recovery period will not have time to take place.

Perhaps you are already forming 0.8 mil in 20 minutes using additives and/or a lower temperature.

In Metal Finishing Magazine, Jul/Aug 2009, I had an article about the return of investment (ROI) when changing from conventional DC anodizing to pulse anodizing.

Two different scenarios of investments for the imaginary company were set up. The company is running 24 loads per shift. The total area on each load is 215 ft2.

The first scenario is a small investment with a new rectifier and a bigger cooling system. The other scenario is a big investment with a new rectifier, cooling equipment, contact, racks and a new agitation system. The last investment scenario will probably only be interesting if the anodizing process is fully switched from conventional DC anodizing to slow square pulse anodizing.

Scenario 1 has an estimated cost of $40.000 for the rectifier and $40.000 for the new cooling system that can be used for the other anodizing tanks too, giving a total cost of $80.000.

Scenario 2 has the same cost for the rectifier and then up grading of the rest of the equipment mentioned above. The upgrade is estimated to $150.000 giving a total cost of $190.000.

The ROI in both scenarios is less than a year, which must be considered to be a valid investment.

A lot of the anodizing shops in the US are already using 24 – 30 V rectifiers so it could be sufficient to add a process controller to those rectifiers to be able to pulse anodize instead of buying a new rectifier. To do this an inspection will be need at the anodizing job shop to see which investments are needed to upgrade the existing DC rectifier to pulse rectifier.

The price of a rectifier is mostly depending on the voltage, and not so much of the current, so this scenario will have an even faster ROI. A process controller could be the HS 100 offered by American Plating Power. This process controller offers ramping, pulse as well as a surface mode. The operator only needs to enter the surface area on the parts that need to be anodized.

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