Finishing Talk Forums - The Online Surface Finishing Community - Heaters plating up

Re: Heaters plating up

2008-05-08T18:39:03Z

In my experience the output terminals of the rectifier should be floating and not grounded. Grounding of the output terminals usually causes stray currents and likely is the root cause of the heatrers plating up.

Re: Heaters plating up

2008-03-26T17:35:39Z

Bipolarity is also a potential factor. Is only one end being plated? That is the simplest way to check for bipolarity. I still think he needs to check the potential above ground first. How much current is there? If this is such a problem, how come we're the only ones talking about it?

Re: Heaters plating up

2008-03-26T00:16:39Z

I was wrong to deviate off topic. Ripple is a topic for another discussion, I suppose. My initial reply was to add a small wire from the anode bussing to the heater outer tube. The idea here was to make the heater anodic so that you would force the copper buildup to stop and even slowly dissolve back into solution. The reason for the buildup in the first place could stem from several reasons. In my experience, bipolarity and stray current are the 2 most common. We haven't really discussed bipolarity here, but it is when a strong magnetic or electric field creates induces another magnetic or electric field nearby. Think of a bar magnet and several nearby iron nails. Each nail in turn becomes slightly magnetic as it enters the field of the main magnet. One end of the nail becomes slightly "North" and the other end is slightly "South". You could daisy-chain the nails together if the magnet is strong enough to affect them all. Electricity is very similar to magnetism. If you have a piece of conductive material (your heater) floating around near a strong electric field and it does not already have an electrical current passing through it (aka it is not generating its own electrical field), it is possible for the conductive material to assume a slight current flow. This is why live entry and live exit are so commonly used. As a part is being removed from a plating bath and it looses contact with the cathode system, it briefly has no strong polarity to it and can be subject to bipolarity. If the bipolarity is strong enough, it can cause part of the piece to become passive, and subsequent operations can fail. Duplex nickel (or 3x or 4x, too) is particularly sensitive to this in my experience. By simply adding a small wire from the anode system to the heater, you introduce a small positive charge to the heater, which will prevent the bipolarity from forming.

Re: Heaters plating up

2008-03-25T20:05:53Z

Guys, RIPPLE is NOT superimposed AC, as your replies indicate. Ripple is defined as "...the extent to which the DC (from a rectifier) deviates from the ideal..." (ref. ELECTROPLATING by Frederick A. Lowenheim pp. 160). By nature of the alternating current being rectified (converted to DC) and by the nature of the filtration of the rectified current, the "Ripple" can be as much as 50%, or very close to 0. Dr. Lowenheim goes on to relate that ripple is normally of little importance in electroplating operations. In chrome plating, ripple is a problem. It is not a problem in copper plating. Superimposed AC could cause problems in bright acid copper plating. It should also be noted that ripple is not gonna cause heaters to plate out nor will superimposed AC! Stray DC current probably would. Take a milliammeter, and measure the current potential between the heater and the ground. That won't tell you WHERE the current is coming from, but it will tell you how big the leak is. When you know how big the leak is, then you'll know if it is a situation where all you have to do is a little housekeeping, or if you have your heater leaning on the cathode bus. Finally, why is a little plating on your heater such a problem? If you don't have a problem using the wrong type of heater in your acid copper, so what if it plates out a little? If the plating gets too thick on the heater sheath, chip it off and put it back in the anode baskets where it belongs, and with the money you save, tell your cheapskate boss to buy a teflon coated heater!

Re: Heaters plating up

2008-03-19T23:23:48Z

External rectifier sounds like a good idea. I had to calibrate one rectifier today and I only seen 25 mV AC ripple with a shunt across the load (sorry about earlier typo). Damn control cards, rectifiers and gate cards are via 1980 and are from Controled Power. Difficult to get "perfect" as far as amp output and feedback to the PLC. But I gotta use what I have. Fault current is if a heater shorts to ground (Titainium sheath). This would put 277VAC current into the anode and short out who knows what.

Re: Heaters plating up

2008-03-19T13:58:15Z

Back to the heaters plating up....... here is what we do in our tanks. We actually use a separate axillary rectifier such as a laboratory or hull cell rectifier. You would not want to use a large capacity rectifier because all you need to impose is a very small "trickle" of direct current. An anodic charge should be imposed on the outside shell of the titanium (or stainless) heater above the solution level. We run a small wire from the cathodic side of the axillary rectifier to a small piece of carbon and place this carbon cathode within about 6" of the heater. Then we adjust the output of the axillary rectifier to about 1/2 volt dc. This small secondary electrical input should have no side effects. It is important that the wire connections to the heater and carbon cathode be above the solution level. At the voltage I recommend, you will see only see about 1 ampere. The amperage is limited by the size of the cathode. The shell of the heater is connected to the factory ground and in no case should this ground be disconnected. This ground is to direct a possible shortage to ground ( 0 potential difference).

Re: Heaters plating up

2008-03-19T00:06:30Z

Ripple is measured by the percentage of VAC to VDC. If you measure 2VDC and measure 0.2VAC, you would have 10% ripple (0.2/2 = 0.1 or 10%). I'm assuming you meant "less than 100mV AC" and not "100mV DC", right? In that case, 100mV divided by the DC voltage you measured at the same time would give you your ripple. BTW, ripple should always be measured with material in the bath. Measuring ripple in an idle tank can give bogus readings. What kind of faulty current are you talking about that would cause scrap?

Re: Heaters plating up

2008-03-18T22:34:45Z

Alright, you guys haven't gave up on me yet. Great. Here is the heaters that are in the tank. [url=http://www.process-technology.com/processtechnol/mots.htm]P, F, S, and T Series, Metal Heaters[/url] Bath is sulfuric acid, copper sulfate. Rectifiers are 4VDC 500 amp maximum. We usually use less than 180 amps DC. I have checked ripple before with our oscilloscope, and usually do not see over 100mV DC. I swung this idea by my boss, which is the cheapest person there is, and he said we may try it. I say we replace them all with PTFE encapsulated heaters instead, but business is really slow right now, so I doubt we will spend the money. We were concerned when we have acutal fault current, and how it may mess up our plating process causing scrap.

Re: Heaters plating up

2008-03-18T17:42:11Z

[quote=skelton;1408]Also, if you have the ability to check "ripple", you may have some stray current that may be causing some of this to happen. [/quote] Not to nit-pick but ripple and stray current are 2 very different monsters. I agree that ripple should be below 5%, or 10% worst case. Stray current is any other current than the one introduced by the rectifier(s). Sometimes you can get current coming through your steam lines, water pipes, etc. Stray current is very often a nightmare of a nightmare to find. Ripple should be much easier to check with a good quality RMS digital multimeter. Not to go too far off-topic, but my sister company Fluke makes some great multimeters. :-) :D

Re: Heaters plating up

2008-03-18T16:57:39Z

This is an old one, but a good one..... It appears that you are on tract to get your heaters grounded. I highly suggest Dustin's recommendation to implement anodic current to the heater tube itself, but you need to ensure that it is in fact connected and drawing anodic(+) current to stop plating. If you cannot weld a connector to titanium tube, you could try a conductive adhesive and hope that the chemistry does not remove adhesive. Or, you could use a stainless hose clamp to make connection to your anodic connector and then securely connect to the anode bar. The correct material for acid copper is Quartz and PTFE (Teflon). This may be your quickest solution, however, most expensive route to resolving the problem. If you are copper plating in an alkaline-cyanide or non-cyanide plating bath, stainless steel is recommended. Could you please indulge us on your copper process, this may help us some. Also, if you have the ability to check "ripple", you may have some stray current that may be causing some of this to happen. Ripple voltage is the magnitude of fluctuation in DC output voltage at a specific output current. This assumes the AC input voltage and frequency are kept constant. Most common levels do not exceed 5% of AC input voltage and can be the culprit in some cases. Let us know how you make out with this, it seems you have been struggling with this for sometime now. Good luck.

Re: Heaters plating up

2008-03-18T10:34:53Z

Okay, now I'm getting a better picture. In my mind I thought you were using Ti steam coils. Now I see that you are using electric heaters. By all means, ground the electrical part of the heaters. I'm no electrician, but I believe that a single phase wiring job should include a hot lead, neutral lead, and ground. Three phase should include 3 hot leads, 1 neutral, and 1 ground, but I could be wrong, and 3 phase power sometimes makes me scratch my head. When you run your small wire from an anode to the heater, but sure that the wire is somehow touching the outside metal cylinder. Having the wire only run to the internal elements may not get you to where you want to be. As far as the Ti dissolving into the tank, I've never really seen that happen. I'm assuming that you are using the correct material for the bath. I'm assuming that you have an acid copper bath, right?

Re: Heaters plating up

2008-03-17T22:47:23Z

Process Tech says to ground the heater to earth also. I would think removing the ground wire would cause a potential electrocution hazard, so I can't do that. They are 480VAC 5000 watt heaters, 2 in each tank, side by side. Single and three phase. What would a ground fault do, mess up the plating current? Hopefully pop the fuses. We do not have ground fault protection on the heaters. Our tanks are plastic and not grounded.

Re: Heaters plating up

2008-03-17T22:37:28Z

The small wire should be fine. In fact, it should limit the current going out through the heater to the tank. As more current goes through the heater, it should start to anodize and form an oxide layer that will further inhibit current flow. You should also have enough anode area that the current coming off of the heater shouldn't be a problem. At least, it has never been a problem for me. Do not ground the wire. Simply run a small wire directly from the heater to the nearest anode connection. Remove the grounding wire from the heater as this is not needed and may cause problems.

Re: Heaters plating up

2008-03-17T21:36:48Z

Run a wire to the heater? You mean a wire to from the heater ground to the anode? Close to the heater itself? We have 4VDC 500 amp rectifiers. Will this throw off the current to the work in the tank? Won't it burn up the small wire with all the current going through it to ground instead of the plating bath/work? Thanks for the tip! I received the same tip from Process Technology. I will try it.

Re: Heaters plating up

2008-03-17T01:05:44Z

Run a small gauge wire (12-16) from an anode to the heater. This will "anodize" the heater and prevent buildup from forming. Plus, it will slowly redissolve the copper back into the solution. Be sure to keep the wire out of the solution, or it may dissolve.