Anodising rectifier and power requirements

A. Hi Syed. If you're planning on running 24/7 you can divide your 5000 square feet by your 8 hours to determine your hourly production. But if you're planning a single shift, remember that it will take 1-1-1/2 hours before the 1st part is finished each day, so you'll have to divide the 5000 by 6-1/2 -- it's a pretty big difference.

The next question is what thickness do you need because the required time to process a piece will be roughly proportional to the thickness. If you're doing architectural work, or parts to be dyed black you may need 0.0005" to 0.0008" thickness, say an hour of anodizing time depending on the alloy, but other work of 0.0002-0.0003" thick and other alloys might take only half an hour of anodizing time or even less.

With these numbers, and planning on anodizing at 12 ASF you should be able to do the arithmetic. It's probably better to size the new rectifier for 18 ASF though, and a 24-volt rectifier is probably a good idea.

----

Hi Faisal. Your questions are very similar to Syed's, so the answers are as well. Rectifier voltage and anodizing time vary with the alloy, but probably 20-25 minutes for 5 µm / 0.0002".

It is always a good idea to retain an experienced consultant because readers are probably happy to answer your questions but if you haven't done this before you're likely to not ask some important ones :-)

Luck & Regards,

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A. Hi Sanjay. Things need to be in proportion: a sports car would not have 1 steering wheel, 1 seat, 1 hubcap, and 1 radio speaker; rather, it might have perhaps 1 steering wheel, 2 seats, 4 hubcaps and 6 radio speakers. So too when one designs an anodizing line, it is usually not a matter of having one of everything, but of deciding how many of this item and how many of that are needed to keep things in proper productive balance.

If you have the same number of anodizing cells as cleaner, etch, desmut and rinse cells, all of the latter are condemned to being empty virtually all of the time--probably not a very cost effective approach!

30 minutes sounds on the light side for architectural anodizing anyway; I would probably design such a line so that it has at least 2 anodizing cells. Depending on the size and the number of steps, you might also want two hoists as well, since an operator may not be able to complete all of the steps in fifteen minutes.

I can't really say for sure without more information, but on first impression I agree with you: 24 loads per 24 hours may be too few to be economically feasible, and even 48 sounds like a rather leisurely production pace if you have the hoists and the people. Good luck.

A. Assuming that you have one anodize tank and are happy with the product, the only way you can get a significant increase is to have about 3 hoists, 6 or more complete sets of fixtures and enough people to rack, unrack, run and pack. Theoretically, you might have a load every 35 minutes from one tank if everything was very well organized, and no breaks, no eating or adequate fill in help.
If you want to find out what is wrong, go work, not watch, on the line for a full shift for a complete week with no meetings or phone calls. I predict that you will find it very enlightening.
Be ready to open your pocket book for more equipment and improvements and you will see improvement.

Ted's line design comments are very valid.

A. What I would recommend is that you stay on the production line as long you can be. Doing so you will notice an instant production raise.The anodizing tank is the bottleneck of a line but if you are employing at least two hoists I think you can get at least 38-40 loads/day.

A. Hello Sanjay,

I am sure you won't remember my face. But I did visit your plant at Thane as well as your office on different occasions between 1992 and '93. In all the occasions, I was asked these type of questions casually, especially at Thane. And I do remember saying the similar words as Ted Mooney and others in the thread have mentioned here.

If you really want to increase the productivity, you got to increase the no. of tanks and hoist and also the manpower. However, I always felt that with existing facility, you could increase the productivity at least 40 to 50% max by proper planning and motivation of the plant personnel.

PS: Standard Disclaimers apply.

Best wishes,

Aluminum How-To
"Chromating - Anodizing - Hardcoating"
by Robert Probert

Also available in Spanish

You'll love this book. Finishing.com has sold almost a thousand copies without a single return request :-)

A. The 24 volts would be plenty; 15 volts would probably be adequate for some alloys. But I figure 7 square meters is 75+ square feet. That means your maximum possible current density would be 13.3 ASF. That might be okay as an operating plan, but marginal for a purchasing plan. A new anodizing rectifier for the future should probably be sized for about 18 ASF.

I wish the rest of the world would enter the 21st century and start using our complex & impenetrable foot-pound-second system instead of the simple metric system :-)

A. Ian,

Your rectifier should be plenty if you are doing type II anodizing ... you will not have enough volts to do type III. I don't have my conversion chart here at home (I don't think we Americans will ever totally convert to the metric system), but you want to anodize around 12-15 amps per square foot of surface area (for type II), so.. 1000 amps will be plenty. I'm not sure if you were asking what the work to cathode ratio should be.. but you want to keep it around 3-1 (work to cathode).

A. I somewhat stand corrected..thanks, Ted..I mis-calculated the meter-to foot number...however I believe his 1000 amps will BARELY be enough to anodize at 13 asf. Ya'll remember..back in grade school..when they said "10 years from now, EVERY country will be using the metric system"...sheeesh..its been almost 20 yrs.. and we STILL aren't there.

A. I've designed many anodizing lines and I'm sure I designed for more than that, but I don't actually run the lines, Marc, so I yield to your actual experience; I thought 13.3 ASF was low but Robert Probert's book says 12 ASF.

A. You're correct, Ted, he would be pushing the limits -- but I guess I tend to look at things from a different point of view sometimes. I got the impression he had a job he needed to get done, and assuming it wasn't going to be an ongoing production job where the purchase of another rectifier could be an option, that he could "get by" using his current set-up. Sometimes ya just gotta wing it a little bit in our business as long as quality isn't affected. And while running at 13 asf may take a wee bit longer to get his desired thickness, I still believe he could achieve a quality product in the end. (Go St. Louis Blues!)

A. Hi,
To calculate the energy that you use we need voltage, current and time of processing. We have the time. You give the current density at 13 ASF. Taking a batch load of 110 sq ft (the mid-value), the current is
110 * 13 = 1430 amps.
I guess that the voltage is greater than 16 and less than 20, so let's take 18 volts.
Power used is
18 * 1430 = 25740 watts = 25.740 kw
Time is 0.5 hours so energy in kwh is
25.740 * 0.5 = 12.87 kwh
If the efficiency of your power supply is 80% then load on supply is 12.87 * 100 / 80 = 16.0875 kwh. There is a big difference between the the calculated kwh and actual.
There are 3 possible explanations:
1) I have made a mistake in the calculations
2) The figures I have used are incorrect, especially the assumed efficiency
3) The kwh (27-28) that you quote includes the cooling demand.

Regards
Harry

A. Hi James. Setting up a hard anodizing plant is a large undertaking which, in my opinion, ought to involve retaining an anodizing consultant. You might look at our Directory of Consultants.

But to your specific questions, there appears to be a typo in your question since you say your available tank is 200 mm wide and you need a minimum of 800 mm wide. If it's actually 2000 mm wide, it could hold two loads at a time, which might be useful -- but hopefully you realize that an anodizing line requires a lot more tanks than one :-)

You need to start with the area of the load, and an estimate of the required Amperage and voltage -- perhaps 30 ASF at 75 volts. From this you calculate the rectifier size and the transformer size.

This would give you the maximum instantaneous cooling load, but recognizing the anodizing solution in the tanks and the cooling water reservoirs, etc., the system will have some thermal inertia/momentum, so you probably don't have to size the cooling system for quite the maximum instantaneous load, maybe 75%-80% of it.

I think titanium is a better bet than lead, and that an external heat exchanger is a better idea than cooling coils in the tank. Don't forget a really powerful air agitation system (or eductor system) for hard anodizing. Good luck.

Regards,

A. Hi Alberto. Anodizing tends to require more volts and fewer amps than most electroplating. (Most plating operates at about 4.5 to 9 volts, whereas anodizing will take 12 to 18 volts; many metals are electroplated at about 30 to 40 ASF, whereas anodizing will be about 12 to 18 ASF.

But the biggest difference is that you have to start anodizing at low voltage and slowly ramp up. That's because (per Ohm's Law), current is inversely proportional to resistance, and there is very little resistance in raw aluminum, but a lot of resistance in anodized aluminum. If you don't start at low voltage you'll burn the parts; if you stay at low voltage, you won't build anodizing thickness.

But damaging the rectifier? I don't think so as long as you turn it down at the start.

Regards,

Aluminum How-To
"Chromating - Anodizing - Hardcoating"
by Robert Probert

Also available in Spanish

You'll love this book. Finishing.com has sold almost a thousand copies without a single return request :-)

A. Hi Nitin. You can review our Introduction to Anodizing for a quick intro to the subject, then you might be interested in Robert Probert's "Aluminum How To" or a similar book. But if you have no experience in anodizing, I would suggest that you not proceed without retaining an anodizing consultant. Good luck.

Regards,

A. Hi David. We appended your inquiry to an existing thread on the subject. You'll need at least 12 volts absolute minimum even for selected alloys, preferably 18 volts, whereas your unit generates only 7.5 volts. Sorry, it's not enough.You'll need an amperage capacity of, say, 18 amps per square foot of surface area you will be processing.

Regards,

• Topic 0967 "Increasing Type III (Hardcoat) Anodizing Capacity"