Hi, I am anodizing titanium parts for mounting mobile radios in a console. The components vary in size from small 4 x 4 inches to larger pieces 12” x 19”. The color I am hoping to achieve is grey. I have been successful with smaller pieces, but when I try larger ones I have encountered some problems. I am using a 10 amp variac with a 100 amp rectifier. I have a 20 amp ammeter in line with the anode. For a cathode I have a piece of copper (I have also tried one of stainless and one of aluminum) bent at a right angle immersed in my laundry tub which covers 2 of the 4 sides of the tub. I hang the parts from a titanium hook in the center of the tub. I work at room temperature with de-ionized or distilled water.
On small parts I set the voltage to 100 volts DC. I am using a solution of de-ionized water and ½% TSP (I tried higher TSP solutions, 2 to 3% and I immediately blow fuses when I turn it on) . When I turn on the power, I get an initial current surge up to 12 to 15 amps, it quickly subsides below 10 and gradually, after 90 seconds down to 1 amp or less. As the current draw drops the DC voltage increases to about 115 volts. Sometimes I try and keep the voltage around 100 volts by adjusting the variac as the current falls. This does not seem to vary the results.
My problem is with my larger panel fronts which are 19” wide and up to 12” high. When I try and anodize these, the current goes way up (almost 20 amps) and stays quite high for 10 minutes or more. While the current does drop off to 1 or 2 amps, it takes much longer to get there. Also, I must set the variac to about 60 to 70 volts DC output when I start and gradually turn the voltage up to 100 volts DC (or I blow fuses). My larger parts are close to the cathode (within an inch or two of the cathode when immersed in the tub.
My questions are:
Are my large parts too close to the cathode? Is distance a factor? If so, what is the minimum?
If the parts were further away front the cathode, could I (do I need to) use a higher TSP solution 3% perhaps to achieve the appropriate end result.
Does my cathode need to be on all 4 sides of the tub?
Do I need a VARIAC at all? If I am running at 100 volts anyway, Can I just use line voltage to my rectifier? Many times I run the variac wide open which is the same as not having it at all. My concern is that the VARIACS I have found all are rated about 10 to 12 amps. I draw close to 20 amps on larger parts and I am concerned that the VARIAC will fail in long term use. Lower voltages seem to be for different colors which I am not looking to do.
How long do I continue the process? 2 minutes seems OK for small parts. I monitor the current draw and on large parts, after 15 minutes, they are still drawing 1 to 2 amps. Small parts drop off quickly to less than ½ an amp after 90 seconds or so.
Does it make a difference in Cathode Material? Aluminum, Copper, Stainless? Should it cover all four vertical sides of the tub.
Any help or guidance would be appreciated.
On small parts I set the voltage to 100 volts DC. I am using a solution of de-ionized water and ½% TSP (I tried higher TSP solutions, 2 to 3% and I immediately blow fuses when I turn it on) . When I turn on the power, I get an initial current surge up to 12 to 15 amps, it quickly subsides below 10 and gradually, after 90 seconds down to 1 amp or less. As the current draw drops the DC voltage increases to about 115 volts. Sometimes I try and keep the voltage around 100 volts by adjusting the variac as the current falls. This does not seem to vary the results.
My problem is with my larger panel fronts which are 19” wide and up to 12” high. When I try and anodize these, the current goes way up (almost 20 amps) and stays quite high for 10 minutes or more. While the current does drop off to 1 or 2 amps, it takes much longer to get there. Also, I must set the variac to about 60 to 70 volts DC output when I start and gradually turn the voltage up to 100 volts DC (or I blow fuses). My larger parts are close to the cathode (within an inch or two of the cathode when immersed in the tub.
My questions are:
Are my large parts too close to the cathode? Is distance a factor? If so, what is the minimum?
If the parts were further away front the cathode, could I (do I need to) use a higher TSP solution 3% perhaps to achieve the appropriate end result.
Does my cathode need to be on all 4 sides of the tub?
Do I need a VARIAC at all? If I am running at 100 volts anyway, Can I just use line voltage to my rectifier? Many times I run the variac wide open which is the same as not having it at all. My concern is that the VARIACS I have found all are rated about 10 to 12 amps. I draw close to 20 amps on larger parts and I am concerned that the VARIAC will fail in long term use. Lower voltages seem to be for different colors which I am not looking to do.
How long do I continue the process? 2 minutes seems OK for small parts. I monitor the current draw and on large parts, after 15 minutes, they are still drawing 1 to 2 amps. Small parts drop off quickly to less than ½ an amp after 90 seconds or so.
Does it make a difference in Cathode Material? Aluminum, Copper, Stainless? Should it cover all four vertical sides of the tub.
Any help or guidance would be appreciated.
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