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topic 1611

Hard Anodizing using Pulse Rectifier



A discussion started in 1998 but continuing through 2020

1998

Q. We currently do Hardcoat anodizing on high copper alloys using an old proprietary system called IMPERV-x.

The system is really hard to maintain as the company that mfg'd it is long ago out of business & it is impossible to get replacement parts.

One of the main items we hardcoat with this system is a very small (1/8" dia x 3/4" long) military part which is 2024 alloy. We have been processing this item for 10+ years.

With our Imperv-x system getting older & older we are considering switching to a new Pulse Rectifier. Should we expect to be able to run the above mentioned parts no problem with pulse rectifiers?

Any advice appreciated.

David A. Kraft
- Long Island City, New York


1998

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.

Pete Faxon
- Oxnard, California



affil. link
probert book
Aluminum How-To

"The Chromating - Anodizing - Hardcoating Handbook"
by Robert Probert
$89


affil. link
"Surface Treatment & Finishing of Aluminium and Its Alloys"
by Wernick, Pinner & Sheasby
from Abe Books
or
info on Amazon

1998

Q. Dear Sirs,

I will be very thankful to him if anybody sort out my this problem.

I have job in aluminium alloy which is to be hard anodized. The coating thickness requirement is 100 microns, Hardness req'd is 1200 VPN. The area of the job is 1.2 Sq. Ft. and required time would be around 8 mins.

To do this with the normal rectifier it is practically impossible in 8 min. using conventional rectifier. But if we use Pulse Rectifier it is possible we feel. If so what should be the specification of the rectifier? At what frequency should we operate the pulse?

In pulse rectifier if we need to maintain average current of 100 amps then maintaining duty cycle 50% and ON current for 1 millisecond and zero current for 0.5 millisecond then the maximum peak current will be 200 amps and minimum will be of course zero. In that case what will be effect on the surface of aluminium? it's hardness? and also on the temperature rise?

Is it acceptable to use such a high current? What should be the frequency range of the pulse rectifier to achieve 100 amps current?

Please explain.

Rajendra Khatavkar
- Pune, INDIA


August 30, 2009

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.

H.B. Rudresh
metal finishers - Bangalore, India


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,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


February 8, 2010

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

Anne Deacon Juhl
Anne Deacon Juhl
- San Diego, California, USA



To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)



1999

Q. We are interested to set up a hardcoat anodising plant with pulse rectifier. Please help us to get the pulse rectifier which is the best source and which is the best brand available. Also, let us know the various industrial applications of hard coat anodising.

With best regards

Masood. A. Khan M.D
- Bangalore-India


affil. link
"Theory and Practice of Pulse Plating"
from Abe Books

or

1999

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.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)



2005

We have a customer inquiring about the benefits of pulse rectification for hard coat anodizing, does it reduce cycle times, increase current density, etc. He would like to real-life examples instead of theory.

Craig Henry
- East Troy, Wisconsin


June 24, 2009

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.

Scott Eastman
- Springfield, Massachusetts, USA



To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)



July 26, 2011

Q. WHY IS PULSE RECTIFIER NEEDED FOR HARD ANODISING? WHY IS CONVENTIONAL RECTIFIER NOT SUITABLE?

INDUKUMAR NAIR
buyer - ALUVE ,KERALA,INIDA


July 28, 2011

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,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


November 30, 2015

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 sulphuric acid solution without additives.
Many suppliers do not like additive as it is expensive and difficult to maintain. Hence Pulse rectifier is used.

Rudresh. H.B.
- Bangalore, India


May 29, 2016

thumbs up signAs 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.

drew nosti
Drew Nosti, CEF
Ladson, South Carolina



peo

October 29, 2020 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. At our shop we are having troubles with hardcoating 2000 series aluminum. We get either an uneven coating or our parts burn. I do know that 2000 series aluminum is difficult to hardcoat due to amount of copper in the aluminum causing hot spots in the metal which leads to burning, but I've been researching ways to hardcoat 2000, and the best answer I've been seeing is to pulse hardcoat.

Our rectifiers do have the pulse setting on it. But I cannot find the manual for the rectifiers. It is a Dynapower touch pad, and I cannot find anything online that shows me how to use this pulse setting. I was wondering if anyone has any knowledge on how to work this pulse setting? ... and just to be clear I need it to be a simple explanation so I can teach our line operators how to do so. thank you

Jared Goddard
- Green Bay Wisconsin


October 31, 2020

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.

robert probert



Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
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