Sometimes pulse anodizing seems difficult to figure out, specially for the aluminum alloys which are difficult to anodize.
So a question about Hard Anodizing an aluminum alloy with 10% silicon aluminum Alloy to 75µm thick layer with a pulse rectifier, suggesting the current density per square feet will get the following answer.
To get 75 µm you can use different kinds of electrolytes; a suggestion would be an electrolyte with 15wt% sulfuric acid at 54 - 60F or one created from sulfuric acid and an organic acid at a lower or same temperature.
With the sulfuric acid electrolyte established you should then proceed to use 40 A/ft² for the high current density period and 10 A/ft² for the low current density period. Then depending on the geometry you should try different pulse periods. My suggestion is to start with 60 seconds in the high current density period and 20 seconds in the low period.
It is important to remember that a pretreatment with fluoride will improve your result.
Also remember that lower silicon content will give you a possibility to use a higher current density in the high current density period.
Use higher temperature than conventional hard anodizing when processing high silicon alloys, you could try using a high current density period of 20 - 100 A/ft², and pulse periods t1=t2=30 seconds.
You should always consider starting your test runs with voltage controlled anodizing, high current density period 20 - 40V and low 15 - 25 V.
If you find this article useful, Anne Deacon Juhl is available for consulting, please send an inquiry to blog@aluconsult.com
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More about recycled aluminum and anodizing
Last Sunday, November 15 the Aluminum Association had its 12th America Recycles Day, the only day dedicated to raising awareness of recycling of aluminum and its positive impact on the world. This day encourages communities to get involved and educated, with a variety of recycling activities being held across the U.S.
Quick facts about recycling aluminum from the Aluminum Associations website:
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Quick facts about recycling aluminum from the Aluminum Associations website:
- A recycled aluminum beverage can is able to be back on the shelf in as little as 60 days.
- Aluminum cans are the most widely recycled beverage container in the country.
- There is no limit to the amount of times aluminum can be recycled.
- Recycling aluminum uses 95% less energy than making new aluminum.
- Overall, recycling saves energy and reduces greenhouse gas emissions.
Very often we think aluminum cans when we think about recycled aluminum but so much more is made of aluminum and can be recycled.
Anomatic Corp. is worldwide leader of anodized aluminum packaging for the cosmetic, healt and beauty, spirits, pharmaceutical cataogries and more.
During my search for material for the post about "The good and the bad about recycled aluminum" I found Anomatic Corp. a very interesting company who already have done a lot to be more environmental friendly.
Anomatic Corp. uses anodizing because of its environmental friendly properties.
Taken with courtesy from Aluminum Anodizers Council website the following should be said:
The environmental friendliness of anodizing is among its best properties.
Anodizing uses simple water-based chemicals, such as sodium hydroxide, sulfuric acid, soap and nitric acid all in diluted solutions. They can be treated easily and release no harmful by-products. The liquid by-products are recycled and returned to the process. Solid by-products can be isolated and diverted for use in the manufacture of alum, baking powder, cosmetics, newsprint, fertilizer and water purification systems.
The U.S. Environmental Protection Agency, which heavily regulates the production and use of solvent-based paints and flouropolymer finishes containing volatile organic compounds (VOCs), regards anodizing as an environmentally friendly process.
The by-product anodizing creates is composed primarily of aluminum hydroxide, some aluminum sulfate and water. It is harmless because it contains no significant amounts of heavy metals. In some cases, municipal sewerage treatment plants benefit from these by-products by using them as filters in the secondary treatment of sewage.
In the next number of the magazine Light Metal Age, you will be able to read the answers to my questions I got from Anomatic in my interview with Steve Rusch, the Marketing Director.
If you find this article useful and you would like to know more please contact me blog@aluconsult.com__________________________________________________
Surface treatment for Aerospace applications in Paris
I returned back to Copenhagen Tuesday afternoon from a great conference in Paris held by the French Cluster, ASTech and A3ST (Association de Traitement Thermique et de Traitement de Surface).
Lots of talk about Chrome VI free processes on the market, advantages and disadvantages.
My presentation for the 150 attendees was about the ROI of pulse anodizing, and why there are no excuses for not changing your conventional DC anodizing to Square wave pulse anodizing.
Being able to pay the investment of a new rectifier back in less than a year by increasing the productivity in the anodizing line, should be of any managers interest.
Discussions about anodizing as a pretreatment before paint and comparison with other Chrome VI free pretreatments, more about this later.
Paris as wonderful as ever :o)
If you find this article useful and you would like to know more please contact me blog@aluconsult.com
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Lots of talk about Chrome VI free processes on the market, advantages and disadvantages.
My presentation for the 150 attendees was about the ROI of pulse anodizing, and why there are no excuses for not changing your conventional DC anodizing to Square wave pulse anodizing.
Being able to pay the investment of a new rectifier back in less than a year by increasing the productivity in the anodizing line, should be of any managers interest.
Discussions about anodizing as a pretreatment before paint and comparison with other Chrome VI free pretreatments, more about this later.
Paris as wonderful as ever :o)
If you find this article useful and you would like to know more please contact me blog@aluconsult.com
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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.
If you find this article useful and you would like to know more please contact me blog@aluconsult.com __________________________________________________
Acid Etch, the hot topic
At the 18th annual International Anodizing conference & Exposition held by Aluminum Anodizers Council in Fort Worth last week, the hot topic was definately Acid Etch.
There were several presentations and during the Q&A session the topic came up one more time. So what is Acid Ecth and what makes it different from caustic (alkaline) etch, what is its benefits and what do we need to keep in mind when acid etching our aluminum parts.
First some comments on why we want to etch the aluminum surface before the anodizing step. After removing grease, oil, dirt and other contaminants on the surface, we are now having a clean surface to use for the formation of oxide in the anodizing tank.
Yet most of the times we need to do more about this surface to get the wanted visual appearance on the surface after anodizing.
So during the etching step the surface imperfections such as extrusion lines and scratches are smoothed out, producing a more uniform appearance changing from the brigth aluminum surface to a more matt, satin finish depending on the etching time and a couple of other parameters.
Caustic soda which is what the alkaline etch mainly consists of is very aggresive to the aluminum surface. The chemical reaction has to be inhibited to work properly but there are still a high dissolution of aluminum during the process. The amount of aluminum dissolved for a conventional, well-operated caustic etch is around 10g/ft2.
Due to the high viscosity of the caustic etch the following rinse step needs plenty of water and min. of two rinse tanks.
Introducing an acid etch step into the anodizing process will give some immediately benefits.
Some of these are less sludge and easier rinsing operation due to the fact that the acidic solution, almost neutral in some formulations, doesn´t dissolve as much aluminum as the caustic. There are an energy saving because of a lower process temperature and less fume from the process tank (10% of the fume from alkaline etching).
The reason for the significant waste treatment reduction is the fact that the acid etch results in less than 1g/ft2 dissolved aluminum to get a matte finish. The fluoride ions react and attack everything in the microstructure leading to an attractive matte finish, which differs from the one found with alkaline etching.
So the most significant difference from the caustic etch is the difference in look, because the acid etch reduces more of the extrusions effect.
One thing is important to keep in mind and that is the fact that fluoride attack the titanium racks.
The two presentations about the subject from anodizers with experience in using acid etch both mentioned that you will still need both types of etching solution in your production line. The main reasons for this are:
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There were several presentations and during the Q&A session the topic came up one more time. So what is Acid Ecth and what makes it different from caustic (alkaline) etch, what is its benefits and what do we need to keep in mind when acid etching our aluminum parts.
First some comments on why we want to etch the aluminum surface before the anodizing step. After removing grease, oil, dirt and other contaminants on the surface, we are now having a clean surface to use for the formation of oxide in the anodizing tank.
Yet most of the times we need to do more about this surface to get the wanted visual appearance on the surface after anodizing.
So during the etching step the surface imperfections such as extrusion lines and scratches are smoothed out, producing a more uniform appearance changing from the brigth aluminum surface to a more matt, satin finish depending on the etching time and a couple of other parameters.
Caustic soda which is what the alkaline etch mainly consists of is very aggresive to the aluminum surface. The chemical reaction has to be inhibited to work properly but there are still a high dissolution of aluminum during the process. The amount of aluminum dissolved for a conventional, well-operated caustic etch is around 10g/ft2.
Due to the high viscosity of the caustic etch the following rinse step needs plenty of water and min. of two rinse tanks.
Introducing an acid etch step into the anodizing process will give some immediately benefits.
Some of these are less sludge and easier rinsing operation due to the fact that the acidic solution, almost neutral in some formulations, doesn´t dissolve as much aluminum as the caustic. There are an energy saving because of a lower process temperature and less fume from the process tank (10% of the fume from alkaline etching).
The reason for the significant waste treatment reduction is the fact that the acid etch results in less than 1g/ft2 dissolved aluminum to get a matte finish. The fluoride ions react and attack everything in the microstructure leading to an attractive matte finish, which differs from the one found with alkaline etching.
So the most significant difference from the caustic etch is the difference in look, because the acid etch reduces more of the extrusions effect.
One thing is important to keep in mind and that is the fact that fluoride attack the titanium racks.
The two presentations about the subject from anodizers with experience in using acid etch both mentioned that you will still need both types of etching solution in your production line. The main reasons for this are:
- Gives a different matte finish than caustic etch
- Needs to have the caustic etch for stripping aluminum racks
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Questions about Type III, hard anodizing
One of the questions which I hear from time to time is how sealing influence the properties of the coating. The following questions are some of most common ones regarding sealing of hard anodized coatings.
So yes, there are a huge difference in abrasion resistance of hard anodized forged material EN AW 6082 T6 and cast alloy G-AlSi7Mg.
- How does hot sealing influencing the abrasion resistant on Type III, hard anodized coatings?
- Can the parts be hard anodized and dyed black without influence the abrasion resistance?
When you order hard anodizing, you have to decide if you need the highest abrasion resistance of the surface for your application or not. If you do then don´t specify sealing.
As told in an earlier post the aluminum oxide is converted into aluminum hydroxide which are softer and more voluminous during the hot sealing process.
So the question on dyed hard anodized parts has the same answer because you need to seal you parts after the dying.
Yes, You will decrease the abrasion resistance if you dyed the hard coating but you will increase the corrosion resistance and capture your color.
- How does EN AW 6082 behave during hard anodizing?
Alloy 6082 is doing great when hard anodized. The reason for this is the alloying elements. This alloy has the following composition, which gives absolutely no problems when hard anodizing your part.
- Is there a difference in abrasion resistance hard anodized between forged material EN AW 6082 T6 and the cast alloy G-AlSi7Mg, and can you hard anodize this alloy at all?
AlSi7Mg has 6 – 8 % silicon which makes it very difficult to do both Type II and Type III anodizing. The oxide layer formed during the anodizing process consist of a lot of small silicon particles which decreases the corrosion resistance and wear resistance.
So yes, there are a huge difference in abrasion resistance of hard anodized forged material EN AW 6082 T6 and cast alloy G-AlSi7Mg.
I will make a future post of what are the best alloys for hard anodizing.
If you find this article useful and you would like to know more please contact me blog@aluconsult.com
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Anodizing: A mature or an evolving process?
"Anodizing is a mature and well known technology", when people say this to me it seems like nothing needs to change, everything has been invented and every good idea has already been tried before.
Maybe anodizing is an "old" and well known technology but when I am in contact with the industry I meet people saying, "Wow, there is actually an explanation for what´s happening daily in the production"
How do we, as an industry, create new resources with a modern look at anodizing, covering traditional, and new technologies. Resources that can replace all of the old books out there and give new inspiration to people so new inventions will happen.
And how about all the knowledge in the old books, and in all the people who works and have worked with anodizing everyday?
How can we gather all the knowledge, educate and use it wisely to improve the whole anodizing industry?
To increase the use of anodized aluminum we have to change our minds and believe that 1+1 = so much more than 2. We must work together, be open minded, and share ideas, information and knowledge.
A way to do this is by joining the Aluminum Anodizers Council with a mission to not only gain new knowledge but also to contribute.
Paul Fisher from ISFA said a couple of months ago, “There can never be enough education in the metal finishing industry.”, and, "We must all begin to take an active role in the transfer of this knowledge, by any means possible.
In January we all heard the words "Yes, we can" and we can make changes, also in the finishing industry. We just need to keep the internal flame burning, remember our passion and our integrity, believe in what we are doing and remember that most people are afraid of changes, even the ones which are doing them good.
If you find this article useful and you would like to know more please contact me blog@aluconsult.com
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Maybe anodizing is an "old" and well known technology but when I am in contact with the industry I meet people saying, "Wow, there is actually an explanation for what´s happening daily in the production"
How do we, as an industry, create new resources with a modern look at anodizing, covering traditional, and new technologies. Resources that can replace all of the old books out there and give new inspiration to people so new inventions will happen.
And how about all the knowledge in the old books, and in all the people who works and have worked with anodizing everyday?
How can we gather all the knowledge, educate and use it wisely to improve the whole anodizing industry?
To increase the use of anodized aluminum we have to change our minds and believe that 1+1 = so much more than 2. We must work together, be open minded, and share ideas, information and knowledge.
A way to do this is by joining the Aluminum Anodizers Council with a mission to not only gain new knowledge but also to contribute.
Paul Fisher from ISFA said a couple of months ago, “There can never be enough education in the metal finishing industry.”, and, "We must all begin to take an active role in the transfer of this knowledge, by any means possible.
In January we all heard the words "Yes, we can" and we can make changes, also in the finishing industry. We just need to keep the internal flame burning, remember our passion and our integrity, believe in what we are doing and remember that most people are afraid of changes, even the ones which are doing them good.
If you find this article useful and you would like to know more please contact me blog@aluconsult.com
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