I was thinking about this after I posted. I've made an error in my formula, someplace. Don't go by postings until I've had a little time to verify a few things.
Ok..checked things out and it turns out that I double counted the sq/ft in calculation. The sq/ft is already accounted for when the power supply amperage set as M_D correctly points out.
I edited my previous post so that no one mistakenly follows the bad advice.
The REAL formula is:
720 minutes divided by Current Density times Desired Thickness in Mils.
So, to achieve a coating thickness of 1 mil (25.4 microns) at 4.5 amp current density:
720/4.5 x 1 = 160 min
for 1/2 mil thickness (which is perfectly acceptable):
720/4.5 x 0.5 = 80 min
Now to jtagger19's specific questions:
Quote:
I have an area of .13 sq/ft and I'm ussing LCD at 4.5 A/sq.ft.
I have no problem anodizing for 60 mins
but now I have to shorten that time
I've been reading on this 720 rule
correct me if I'm wrong
.138 sq/ft x 4.5a = .625 AMPS on my rectifier
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This is correct.
Quote:
720/4.5x.13 = 20.8 minutes on the tank
correct me if I'm wrong but does this mean that I can use 20 mins and get the same result as I had before at 60 minutes
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You made a similar mistake to me by inserting the sq/ft of the workpiece into the equation. The size of the work piece is already taken into account when you set your rectifier to .625 amps.
The actual formula for you would be:
720/4.5 x 0.5 = 80 minutes (The 0.5 is the desired thickness of the coating in mils)
You can reduce the time required by raising the current density, or by reducing the thickness of the coating you desire. Good dyeing can be achieved at about 1/3 mils or above, so I wouldn't go below 0.33.
0.4 mils is a good number if time is a concern. It will give you a 10 micron thickness with good dyeing qualities if anodizing time is a major consideration.
You could even bump your current density up to 6 amps and go with a thickness of 0.4 mils. That would drop your time to 48 minutes.
720/6.0 x 0.4 = 48 min