Hardcoating using Pulse Rectifier

• Topic 0208 "Interference coloring of aluminum by pulse anodizing"

A. The 2000's, especially 2024 and especially heat treated 2000's require higher free acid to prevent the problems you are having, run the free acid on up to 220 g/L.

A. David,

A. We have been pulse hard anodizing for 15 years. So long as we set the automatic ramp slow enough and control the maximum voltage we don't have problems with 2024. We use a conventional solution with 1% oxalic acid added.

A. Dear Sir,

There are many issues which need to sort out.

1. You cannot get hard anodising of 100 microns in 8 minutes. On an average you may require minimum 70 minutes to get to your 100 microns even if you use proper Pulse.

2. Your pulse on and off time is high frequency. Generally your need on time and off time in the range of 0.5 sec to 10 sec.

3. You need to work with low temperature of around 0 °C. in hard anodising. Or else you may have to use proprietary additives to work with temp range of 8 to 12 °C

4. You need to have proper experience and information about anodising, hard anodising and use of Pulse rectification.

5. The conc. of electrolyte, temperature of operation also plays important role in thickness and hardness of coating.

6. Further please consult with somebody who has worked in hard anodising before proceeding.

A. Hi Rajendra. I am not especially versed in pulse anodizing but I must agree with Rudresh that your desired process time is impossible -- out of the realm of possibility by approximately a full order of magnitude.

Luck & Regards,

A. Dear Sir,

The most important reason for using using pulse anodizing is the recovery period.

If an anodizing voltage E1 is quickly reduced to a lower value E2, the current falls to a very low value and may take a considerable period of time, amounting to minutes, to attain the steady state condition characteristic of the second voltage: but if the voltage reduction is carried out slowly the recovery is much quicker.

Sunny regards
Anne

A. "Best" is only opinion, Masood, and sorry but we cannot print brand & sourcing recommendations or slams on this semi-anonymous site (why?), but there are a number of manufacturers of pulse-plating rectifiers. Good luck.

A. Pulse rectification has many benefits. Run times can shorten with increased amperage. For example, I have processed blasted 6061 parts at 25 amps/ft2 for 1.5 hours at an end voltage of 76v to acquire .002 of hardcoat. I took the identical load and processed pulse at 40 amps/ft2 with a 10 sec on/2 sec off wavelength for the pulse in 55 min with an ending voltage of 71.1v to acquire .00198 of hardcoat. Overall this is a 50% savings of energy and a 35% savings on production time. Depending on required amps/ft2 needed for processing pulse wavelengths may have to be adjusted to give the rectifier ample time to achieve amps needed. The more amps needed the longer the wavelengths. For a 2250 amp run I process at 10 sec on/2 sec off.

A. Hi, Indukumar.

A conventional rectifier is suitable for hard anodizing in the general case. In fact, I would bet that there are many more conventional rectifiers in service for hard anodizing than pulse rectifiers :-)

But if you want to work at the state-of-the-art, some people feel that pulse anodizing offers advantages, especially on 2xxx aluminum. Dr. Anne Deacon Juhl did her PhD thesis in pulse anodizing, so you may wish to google her; I believe you can buy copies of that thesis. Good luck!

Regards,

A. Mr.Indukumar

Anodising is an exothermic reaction. Lots of heat is generated. Hard anodizing needs more thickness beyond 40 microns. Generally it is done at 0 °C. Pulse rectifiers does on and off of current during the process. During Off time, heat is not generated and hence helps in build up.
Alloys like 2024 are very difficult to do hard anodizing in conventional sulfuric acid solution without additives.
Many suppliers do not like additive as it is expensive and difficult to maintain. Hence Pulse rectifier is used.

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As of today I am keeping an open mind on the use of pulse on Anodizing. So far I have never seen any objective evidence that pulse gives faster or harder or better Taber results. I see lots of opinion but NO case studies of pulse vs. standard rectification. If the only thing you get is to be able to use higher AMPS without burning then pulse is just a means to an end not a result. Still open to feed back with OBJECTIVE EVIDENCE.