What is a Hull Cell Test, Why is it done, Where to Get a Hull Cell

A. Hi May.
It's possible that all you are looking for is a standard 267 milliliter cell ⇦this on eBay or Amazon [affil links] . You may also need a small rectifier (power supply), and/or a heater to maintain correct plating temperature. But there are also modifications like hanging cells, jiggle cells, double-size cells, etc. If you tell us what kind of plating you are doing, readers may be able to help you further regarding those specialty Hull Cells.
Luck & Regards,


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

A. Hi Limec. In my opinion, and the opinion of some industry icons a lot smarter than me, everyone doing any plating needs a Hull Cell for three reasons that I can think of offhand.

Firstly, and this one may apply less strongly to nickel electroforming than other plating, a Hull Cell lets you see what will happen at very high and very low current density in case a part you are making will require plating in that range.
Secondly, it helps you spot trends before you make defects -- if the good plating range is declining from one Hull Cell test to the next, you have advance notice that the problem may soon extend into the current density range you are using.
Thirdly, and this applies to everyone doing any kind of plating, you should never make additions to your tanks based on theoretical calculations. Rather, you should do the theoretical calculation, make adds to the Hull Cell ... and only after you have verified the results of the add do you go on to scale it up to bath size.

Hull Cells are available from many suppliers ⇦this on eBay or Amazon [affil links] , but as previously noted, we're drowning under spam (over a thousand e-mails a day interfering with our effort to post technical Q&As), and we can't exacerbate that problem by rewarding it.

Regards,

A. Hi Hector,

This is the formula to calculate current density for a Hull Cell panel.

c=i(5.1-5.25logx)
c= current density
i= current applied
x= distance to be measured on the panel (panel side close to anode is HCD area and side away from anode is LCD area)

A. It might help if you would tell us about the plating bath you want to evaluate ...

A. Dear Mr. Holmes:
You need to be more specific in your question.
Hull Cell can be applied to many electroplating processes, with different purposes.

A. Applied current and testing time all depend on what you are testing in the Hull Cell. There are set conditions for different plating systems, details of which can be found in any reputable book that discusses the Hull Cell. Try The Canning Handbook [on eBay, Amazon, AbeBooks affil links]. No one can answer your query unless you say what you are doing.

A. Hello,
Hull-cell current to be employed depends on the type of plating you are investigating and the average current density and maximum operating current density you are likely to encounter in the production tank.The purpose of the Hull cell experiment is to know the plating quality at different current densities in single test. Generally, for vat plating it is customary to use 5 amps and 10 minutes to get the test result. 5 amps will give a range of 0-200 amps/sq. ft current density.This range, I think, will be sufficient for most of the decorative or commercially useful applications.
Good Luck!

A. The Hull Cell was invented by RO Hull and a paper was published in 1939 by him about it. I suggest you track down this paper as it may well describe the mathematics behind the system. There is also a book called The Hull Cell by Walter Nohse [on eBay in English, Amazon in English, & AbeBooks in original German affil links] ; this was published in 1966 by Robert Draper, Teddington. Again this may well contain the math you require.

The actual math is quite easy to work out once you have understood the principles of the cell, but it is made even easier by computational modeling; so if you cannot track down the above texts, you may want to attempt solving it yourself.

A. Try this site: www.springerlink.com/content/x118154920626732/ ⇩
for "Primary current distribution in the Hull cell and related trapezoidal geometries". Quite possibly deeper than you need.
Jim

Ed. note Oct 2020: The sprinkerlink.com domain no longer exists, but the article is available at springer.com as link.springer.com/article/10.1007/BF01030192. It's $39.95 in this age where we've chosen to make billionaires out of middlemen :-)   ... but maybe someone will sell you that whole Issue 22 of the Journal of Applied Electrochemistry 1992 for 50¢ or so :-)

A. Hi, David. Figuring the average current density should be no trick. You just divide the total amperage by the surface area of the component, and it doesn't matter what the anode to cathode spacing is. The current density will vary across the component -- highest at edges and corners, lowest in the middle of expanses. Anode to cathode distance matters for this, but probably not at much as the geometry of the part. Software is available for modeling current density across a part but it's not a trivial calculation and more likely involves finite element analysis.

Regards,

A. When using Hull Cell the volume utilised is quite small and depletion of metal and or brighteners occur at a surprisingly high rate.
It's a good idea to use a perforated cell in a larger volume of electrolyte so that the electrolyte remains relatively constant.

A. The Hull Cell is an excellent tool for determining how an electrolyte acts under different current densities. The current density at any particular point on the Hull Cell plate will be dependent on the current applied to the cell, and there are standard Hull Cell tests that will tell you these values. When transferring this information to a real plating cell, the difference is that the anode-cathode distance should be the same for as much of the plating part as possible, otherwise you will get differential plating rates. Once you know the optimum current density for plating from your Hull Cell test and have calculated the surface area of your plating part in your larger tank, you can work out the total current you need to apply to your part. In practise, the greater the anode-cathode distance, the better the thickness distribution will be.

A. Hello Jack. We appended your inquiry to a long and interesting thread on the subject. So please read it and think about what you would like to research in particular, then ask a specific question and we'll try to help. Good luck!

Regards,

A. Try Larry King Corp. I did business with them for years. They sell the cells, the flat panel cathodes, and anodes.

You can make your own 500 ml Hull cell. I did. Check out the dimensions and get the plexiglass pieces cut. Plexiglass is easy to join with solvent cement.

A. Hi Julia. Sorry, no, a Hull Cell is terrible as a general plating tank :-(

Regards,

A. Hi again, Julia. I guess you're not asking about a hull cell as a testing device but as a small general purpose electroplating tank for your magnet.

It's not ideal for that for a few reasons, including the fact that a hull cell is designed to plate only one side of an item rather than both sides. I think you'd be much better off using a glass beaker [beakers on eBay or Amazon [affil links] so you can put an anode on each side of the part and so you can easily use a hotplate/magnetic stirrer ⇦this on eBay or Amazon [affil links] for agitation. Good luck!

Regards,

A. I would use a plastic polyethylene shoebox as a plating tank.

I'm not clear on what is being plated here. I was plating Cu and I used 3/8" copper tubing as anodes. I flattened little sections at one end, drilled holes, and joined them to the mickey mouse "busbar" with brass screws. Worked fine.

Ni would be tougher. Anodes there are generally Ni "crowns" and you would have to have some kind of conductive anode basket to contain them.

A. Hi Ricardo, there are many styles of Hull Cells including perforated hanging hull cells (for use within a plating tank), double size (534 ml) cells, 1000 ml cells, and "jiggle cells". There is also a different kind of test cell called a Haring (search the site) or Haring-Blum cell which is used to measure throwing power; which can be used for thickness distribution measurements as well.

But it seems to me that a Hull Cell is the ideal tool for thickness distribution determinations. There are youtube videos specifically about this; here is one courtesy of EPI / Electrochemical Products Inc. [a finishing.com supporting advertiser]...

Regards,

Hi Thomas.

adv.
Download the EPI Finishing Utility app and you'll have your ruler, plus other stuff :-)

Regards,

A. Go to google.com - images - and search for hull cell ruler pdf and you will get a lot of choices. Even in the restrictive climate in the EU that shouldn't be a problem.

A. Hi Thomas. I don't have the reference which offers that equation, but it seems to be more of a "curve-fitting" formula than a derivation based on first principles.
Current density is most often expressed in A/dm², and it must be in this case because were it measured in A/m² or A/cm² the current density would be 100X lower or 100X higher, and that sounds unreasonable.

Since a Hull Cell panel is 10 cm long, and log10 = 1, x must be measured in centimeters. At a current of 1 amp then,
CD at 1 cm from HCD end is 5.10 A/dm²
CD at 5 cm from HCD end is 1.43 A/dm²
CD at 8 cm from HCD end is 0.36 A/dm²
CD at 9 cm from HCD end is 0.09 A/dm².

My limited understanding is that the formula is considered valid and usable only between 1 and 8 cm from the HCD end, so the fact that log0 is undefined and approaches negative infinity doesn't matter.

Luck and Regards,

Hello,

Thank you Ted for your comments! I will try to construct my own Hull cell ruler with this formula.

Best Reagards

A. Hi Paul. I have no hands-on experience with hull cell testing, let alone for chrome plating, but you must run it at operating temperature, not room temperature. My understanding is that a perforated hull cell is suggested for chrome plating because of the otherwise fast temperature rise.

It seems that one approach is to hang a porcelain perforated cell in your chrome tank, whereas another approach suggested & offered by www.yamamoto-ms.co.jp/en is to place the 267 ml perforated hull cell into a 1000 ml enclosure tank -- I'm not sure of their material of construction but I don't think it's porcelain -- lots of plastics are sufficiently resistant to chrome.

Although there are guidelines for how long to run hull cells, in your case of decorative chrome where plating times are typically in the 30 sec to 2 min. range, I would think you would want to run it for the same amount of time as your plating time the first time around to get a feel for coverage; 5 A sounds right..

Luck & Regards,

A. Hi Jorge. To the best of my knowledge the Haring Blum Cell has no special dimensions, just the ability of the anode on one side of the cathode to be 5X as far from the cathode as the anode on the other side. The article "Throwing Power Measurement: The Assaf Cell" ⇨
gives some good history and formulas.

But yes, you can calculate throwing power from thickness measurements on a Hull Cell panel. EPI offers a youtube video on how to do it.

Luck & Regards,