Reduce paint thickness in Cathodic Electrodeposition (CED) system?

A. Hi Supinder,
Ohm's Law (V=IR) is always true, but it's often easier to visualize when rearranged as "I = V/R", i.e. the current that will flow through the system is equal to the voltage you put on the system divided by the resistance of the system. If you want to double the current flow you need to double the voltage, or cut the resistance in half.

But I don't really understand the question ... more words please. Luck & Regards,


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

Q. I agree about this V=IR , but voltage I applied and current amp output delivered I want how to measure resistance in our CED bath for understanding.

A. If you are unable to control the thickness, the problem may lie elsewhere. You need to check if the voltage displayed is the same as the voltage applied on the component.

A. Dear friend,

In my opinion may the conductivity of ED bath is too low. Because I have the opposite problems from you. Since I want to raise the thickness (now is about 20 micron) but the only difference parameter was conductivity of ED Bath whereas too high in mine.

The data parameter from my process are :

1.NV 14.67%
2.Coating voltage is 140 V (range 80 to 160 V)
3.pH is 6.25 (range from 5.9 to 6.3)
4.Conductivity is about 1545 micro Siemens/cm. (standard is 1100 to 1400).
5.Ratio F1 to F2 is 1:10

I also used the latest technology of ED Paint, which is Acrylic CED-Lead Free

A. Dear Mr.Manish,

I understand your problem.

You want to control the outer DFT without disturbing any line condition.
In this case you can cover the anode cells simply with the PVC pipe of good quality (Quality in the sense of Good Chemical Resistance).
After doing this definitely you will get reduction of 6 to 8 µ DFT.
Your throw power will not affect after doing this (Kindly check up with the paint supplier).

regards,

A. Dear Manish,

One other way of reducing the DFT of your EDP is in choosing mineral fillers with a very fine particle size, good dispersion properties and good flow properties. It often happens that due to cost reasons, producers change the mineral filler included in the original formulation to a cheaper grade locally available. In this case, many properties of the EDP - including the DFT - are getting worse.
Especially the dispersion behavior of the fillers affect the DFT very much. If the filler is not dispersed properly, you will find agglomerates that are actually much larger than the original particle size of the filler. Also the flow properties are affected negatively by a bad dispersion.
There are only very few mineral fillers that are working properly in EDP systems, one I know is called Sillitin.

Best Regards
Christian

A. Dear Manish,
I feel sorry to say that the CED you are using have very low rupture limit. Generally rupture limit of CED is more the equal to 350 volt. Nobody can help you; just change the paint supplier.

A. Dear Manish

Please check the Solvent level of the bath and co relate with the production trend You may be feeding the bath in the higher rate , that means your bath will be fresh and that's why you are getting high DFT.

This is the same problem I observed in my line . I reduced Solvent level.Drained permeate at regular frequency to Keep the DFT and Finish in good condition.

Thanks

Srinivasan

A. Dear
Please check the applied voltage which is shown by the rectifier & increase the bath conductivity ,reducing the bath temp.

thanks,

A. You did not write about the number of anode cells and type of anode cells. However, reduce the number of anodes, or cover the membrane from bottom side.

A. How to reduce Dry Film Thickness?: there are several way to reduce DFT --
1. Decrease applied voltage.
2. Increase of MeQ (milliequivalents) value by adding pH adjuster.
3. Purge of permeate to reduce solvent content.
4. For CED line that have high turn over set MeQ value in maximum specification.
5. Increase conductivity of anolyte tank, it will up MeQ value.

Regards

A. Dear Manish,

You please reduce your anode no. or Reduce solvent level is only way to reduce DFT. You should must ask your supplier for that. If you will use Sixth generation CED Paint Your problem will resolve.

A. Dear Manish,
Please check calibration of displays & DFT meter etc, then change any variable one by one and note the impact/ results. The change should be economical, not increase the wastage of energy or material. Following steps may help you to overcome this problem:

1: Conductivity of Anolyte seems to be very high as 2500 micro Siemens; decrease gradually as 2400-2300-2200.......
2: Reduce the solvent percentage;
3: Although it may not possible to reduce the dip time in your system but my suggestion is to reduce the dip time any way; will save the cost & energy and also help to reduce the ED thickness.
4: The concentration of electrodes are higher than dipped body area. Reduce the electrode quantity and increase the distance in between the electrodes.
Hope you will post the result of successful measure you have taken so far.
Regards,

A. Dear Manish,
At such parameters still you are getting high DFT, so please check Anode:Cathode it around 1:4 if it's less than this then increase it with isolating/disconnecting some anode.

A. Dear Manish
You should check these points to reduce the DFT of your component.
1)What is the Anode : cathode ratio
2) You should cover the bottom portion of anode with pvc .
3) You should increase the P/b Ratio of your system.
4) you should check the Actual current and voltage and ramp up time for your system.

Regards
Ravi

A. Dear,

Please note how much time taken to reach maximum DFT, then after cut down the half of the deposition time without changing any bath parameter. you will get lower DFT if not cut it another half. Generally, DFT depends upon deposition time, voltage, micelle size and surface charge ratio.

A. Dear all,
To reduce dry film thickness we must concentrate on voltage (280-320), process time (120-130 secs), pH (5.8 to 6.0), conductivity(1200-1600), Meq-24to28, NVM-18 to 22, anolyte conductivity- 500 to 700, voltage rampup time has been separated to 3 stages (10,5,5), hold on (30,25,55), solvent%- 1 to 2

A. Dear Manish,
Increase the P/B ratio and change the permeate water (25% permeate in two days time and do this step in four times).

A. Dear Mr. Manish,

Please check the Bacteria contamination or growth in CED bath, bacteria growth can lead to higher deposition.

A. Mr.Manish,

I understand your parameters and I suggest you reduce the pH to 5.70 from 5.90~6.10 for reducing thickness ... because pH range is 5.10 to 6.10. So you can maintain pH within 5.50~5.70. It helps to reduce the thickness of the component. I tried many times and got results: low pH can build low DFT.

A. Please check the solvent level (flow controller) of the tank and circulation rate for smooth CED coating and bubble free.

A. Check suction of circulating pumps after shutting the pumps.
See if there is any leakage.

A. It leads to peeling off.

A. The voltage can be controlled automatically so that the DFT remains the same even when the surface area changes.

A. To reduce the thickness of the coated film you have to add hydrogen peroxide to the bath in the range of 1-10%; it acts as a hydrogen scavenger. Hydrogen gas evolves making defect in the deposited film like pits and makes the surface non uniformly covered -- the problem is in the hydrogen gas evolved, you can use other scavengers like nitroethane.
I think this is the method to get uniform and reduced thickness.

Thanks

A. Welded area usually having spatters and gloss bleed. It will not allow CED coating/paint to stick to the surface over a period of time rust formation will happen.
It is very important to clean the weld spatters & gloss bleed before any paint coating.

For reducing ED coating (CED DFT) you may reduce the bath temperature to less than 25 (22 - 25) & voltage (140-180)

A. Hi Suman. "Handbook of Electropainting Technology" has at least 6 sub-chapters devoted to pH; I don't have a copy of "Electrocoating -- A Guidebook", but good books on the subject are best when you are interested in the abstract science of a subject. Vendors might be able to meet with you as well to discuss such general topics as well.

This forum handles highly specific shop problems well, as you can see, but there probably isn't much that people can do for you in a forum of this type to help with abstract theoretical discussion.

If you are having a specific problem, please carefully detail it (i.e., use more words in your question than you want in the answer), and I'm pretty sure the readers can help. Good luck!

Regards,

A. Hi Rohit. The two that I just mentioned to Suman are the only books I know of; I've only read the one. Good luck.

Regards,

A. Hi cousin Rohit. This page is about how to reduce the thickness of CED coatings. There have been some explicit & repeated suggestions, so please try your best to cast your question in terms of the suggestions that have been offered and commenting on the proposed solutions. Thanks!

Regards,

A. Hello jason , Hello amit,

I think you both have same problem with excess throwing; I think three ways we can decrease the DFT:
1) Decrease paint solids
2) By Decrease in pH (5.5- 5.6)
3) Addition of solvent which reduces the viscosity of tank

So by this way we can control on DFT

A. Hi Sunil. I don't think your concern was actually about UV resistance, so we moved your posting off of the thread where you posted it, and onto this page which is about controlling thickness, and which already offers many suggestions. It sounds like 20 to 25 micron thickness is generally readily achievable.

But if the spec says 25 to 30 microns why are you anxious to change it? What is the substrate material and its surface roughness? A thickness which is sufficient for a polished substrate may not be satisfactorily pore-free on some rough surfaces. What follows the CED? -- Powder Coating? What precedes it -- a reliable zinc phosphate? Thanks!

Luck & Regards,

A. Dear sir,.
Please check the solvent content in bath, if it high ,
By reducing the solvent content in the bath DFT also will reduce

Thanks Sudhakar! Five previous writers offered the same relationship: "lower solvent = lower DFT". It's a bit counter-intuitive because higher solvent does means lower viscosity as one responder noted ... but competing forces overwhelm that effect as confirmed by graphs in the previously mentioned W. Machu Handbook of Electropainting Technology.

Luck & Regards,