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Hex chrome on internal diameters

I am having a problem plating HEX chrome on a internal diameter. I am plating a piece with a 6 inch ID measurement and using a 4 inch lead/tin alloy anode. I am chroming the piece at 9.5 volts. My problem is that no matter how long I allow the piece to run in the tank, the max thickness that I get is .004 per side. I am triing to get a thickness of around .008 per side. In the past this has never been a problem. The only difference between this piece and others that I plated is the wall thickness. A normal piece will have a wall thickness of over one inch. This piece has a thickness on less then a 1/4 an inch. Will the thickness of wall and the thickness of the chrome cause the piece to stop plating once the chrome has reached that .004 thickness? The piece is made of mild steel.

Jim Moore
Plating shop - Pennsylvania
2007

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Mega too high a voltage for a 1 inch anode to cathode spacing. 5V would come closer. I will offer a wild guess that your anode is passivating from the huge amount of oxygen that is being liberated.
Next, consider switching to a "mesh" lead/tin anode, possibly lead/tin/silver with a touch of bismuth (tire weights) to make it harder. This type of anode allows better fluid circulation and improves bubble elimination and eveness of plate. At 130F tank temp, you can get bright, hard chrome plating at a great rate per hour. I used 1/2 inch spacing and 4.5 volts. You can tweak this type of anode to get the plate to go where you want it and seriously decrease the dog bone effect at the ends. You can buy the mats, but we made our own. PS lead burning for assembly is a lot harder than it looks. Takes instruction, practice and the right torch/temperature/heat.

James Watts
- Navarre, Florida
2007

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Thank you for your response. I do believe the problem is the spacing. On the larger pieces we have about a 4 inch spaceing between the anode and cathode. At this spacing there has never been a problem with the chrome and we run them at the 9.5 volts. As far as the "dog bone" effect, we eliminated this by adding "THIEVES" to the top and bottom of the piece which we are triing to plate. The extra pices are made with the same material, they are at least a 1/4 the length, and have a 1/8 inch smaller I.D. measurment. I have experimented with different size "dummy thieves" and found that using this formula gives the best results.

I am going to try to do a similar piece with a 2 inch anode at lower volts!

Jim Moore
- Pennsylvania
2007

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2007

You are on to the right approach. 4 inches is almost like using tank anodes which 9.5 is still a bit high, but it appears to work for you. Is that voltage at the part or at the power supply? Has it been calibrated?
What are you using for an anode and what is the length of the part?
Tweaking the anode can save time and money and reduce the thief that is required.

James Watts
- Navarre, Florida

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2007

I am using a lead/tin anode. The items that I am able to plate with relitave ease are about 24 inches in length with a 10 to 12 inch internal diameter. The items that are giving me trouble are about 10 inches in length with a diameter of 5 to 6 inches. with the 4 to 6 inch ratio on the larger piece I was able to plate fairly well. When I started doing the smaller items I think the 1 inch ratio was to small like you said. When I used a smaller anode the piece was able to get all the thickness I was after. Although it did get a little "FUZZY" causing it to be stripped and started over. Now this was still at the 9.5 volts. I then replated it at 4 volts. At the lower volts I lost some speed but was able to get a desired result.

Just a side note question. What exactly do you mean by "tweaking" the anode? DO you mean masking parts of the anode off? I do alot of O.D. chroming, I am new to chroming I.D. tubing. Also the volts are measured at the power supply and have been calibrated. I am not sure how to measure it at the piece.

Jim Moore
- Pennsylvania

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Hi Jim,
With a mesh (which is a very coarse grid) you can cut small sections from different places to have less chrome plating. In some cases you might add an extra piece of lead rod to get an increased deposition in that area. Even tho it is a bit of trial and error to start, you can get very good at the anode design in a few tries if you pay attention to what you did and what the result was.
An anode will reduce in efficiency after a number of hours of use. You can rejuvenate it by scraping, but that is a messy job. We just scrapped the anode into the lead pot and made a new one (actually a set of them). If you run nothing but ID's, your trivalent builds up which will really slow down a plate rate. We used porous pots from Hard Chrome Consultants in Cleveland, OH. They worked really well and were about 1/4 of what the big companies wanted for their product.
Try 4.5 volts, 4.0 is a bit low, and then increase it by a tenth of a volt on possibly every second or third part until you get to 5 volts.
Measure your voltage with a voltmeter at or near the part/rack for a better or true voltage. Line loss can be significant after a few hours of plating.

James Watts
- Navarre, Florida
2007

Thank you for your help with this matter. I believe I am now headed in the right direction. Also I am very familar with HARD CHROME (from Ohio) I use them alot for supplies. I was looking into porus pots but not sure how effective they would be. I will have to give them a try.

Jim Moore
- Pennsylvania
2007