Hull Cell: What is it, How & Why to use it, and Much More

A. Jiggle cell is a 1000 ml cell that like Hull Cell ⇦ ? enables to examine in lab conditions of plating solutions. It is a bent panel that gives more info on solution then Hull Cell, mainly on low current densities and roughness.

The only manufacturer I know is Mcgean-Rohco.

A. I have used jiggle cells, but I have not found them to be of much more value than the Hull Cell. The cell is a tall, tipsy, contraption which moves the panel up and down. You bend the cathode into an -L- or a -b-. Then after you plate it, open up the closed area to view the extreme low current density areas. You can see as much by looking at the back of a plated Hull Cell panel. Shelf roughness is something you supposedly can check, but anode bags only work when you don't disturb them. Nobody lifts anode bags out a solution, and then expects smooth plating.

A. We used the Jiggle Cell and it is the best way to test some plating solutions, mainly Copper Acid and Fe/ZnFe... it show us the low current density areas, as the Tom says.

A. Hi Peter. Public forums don't work well if people can't read the entries; please do your best to post in English on this one.

You'll see small variations in different reference works, but per C. Boulanger in "Investigation of optimal conditions for zinc electrowinning from aqueous sulfuric acid electrolytes", here are the dimensions of the 267 ml cell:

Your other questions are answered elsewhere in this thread.

Luck & Regards,


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

A. Hi Tommy.

The 1000 ml Hull Cell uses a larger 5" x 3-1/4" test panel. In addition it squared off to a rectangular shape with that extra triangular space behind the test panel used, apparently, for extra volume. But sorry I don't know the dimensions.

(from alertsales.com/wp-content/uploads/2020/08/Hull_Cell_Plating_Tests.pdf

Luck & Regards,


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

A. Hi Paul. I have no hands-on experience with hull cell testing 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 Mel Platt above, but also
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 not necessarily porcelain -- some 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 Limec. In the opinion of industry icons a lot smarter than me, everyone doing any plating needs a Hull Cell. Here are fout reasons that I can think of offhand.

Firstly, although 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, some defects in the plating solution, like contaminants or lack of addition agents, can be identified by the fact that they cause poor plating at certain current densities more than others.
Fourthly, 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.

Please post your questions about nickel sulfamate plating under one of our threads about that topic. Sorry for the inconvenience but when threads veer from their main topic, readers can't find stuff.

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)

Ed. note: The result of this calculation is displayed on a Hull Cell Ruler.

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: That sprinkerlink.com domain no longer exists, but the article is available at link.springer.com/article/10.1007/BF01030192 for a $39.95 fee to the middlemen sitting between the uncompensated researchers and the starving students  🙂  

... but ResearchGate.net is currently offering it for free at https://www.researchgate.net/publication/227203087_Primary_current_distribution_in_the_Hull_cell_and_related_trapezoidal_geometries/link/550bdba00cf265693cefb333/download

A. Hi Peter. That's a very normal range for most production plating. Converting to English units because the Hull Cell rulers I see are in English units, it's 18.6 to 46.5 ASF ... and just about dead centered on the Hull Cell panel if you plate at 2 Amps.

Plating time really can't be estimated because zinc might be plated to 5 µ and nickel plated to 20 µ for example.

Luck & Regards,


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

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.

Hull Cells

on eBay or

Amazon

(affil links)

A. I am not really sure what you are asking, but I suspect you have been asked to use a Hull cell to determine the plating characteristics of an alloy system. A Hull Cell can be mathematically modeled as the local current density on the working electrode is related to the geometry of it (the working electrode) relative to the auxiliary electrode. However, when plating an alloy, its composition will be dependent on the applied current density. Therefore, by using a Hull cell, you can controllably alter the alloy composition across the working electrode surface. The composition can therefore be modeled once you know your operating parameters and the properties of the alloy.

A. Hi Veerendra

A Hull cell is not used to measure plating speed.
Its principle use is to determine the optimum range of current density or to diagnose problems with organic additives, etc.

Use your hull cell to find the best operating current density; then plate a sample panel of known surface area at this CD and measure the thickness.

Don't be tempted to run the process at the absolute maximum current density, however tempting to reduce the process time, as it will be more sensitive to small variations in the process.

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. 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. 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. 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 ⇦ on eBay or Amazon [affil links] for agitation.

But alloy plating is very difficult, and your chances of electrodepositing NdFeB sound lower than of winning the Powerball lottery. 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".

But 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, and 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,

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,

A. Hi Thomas. The Hull Cell is deliberately designed to exceed reasonable values at both the high current density and low current density ends of the panel, so I don't know that it's appropriate for what you are trying to do. But if you want to plate at 1.5 A/dm2 (13.4 ASF), what you actually want to do is find 13.4 near the middle of a Hull Cell ruler, which you will on the 1 Amp scale. So plate at 1 Amp.
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

Ed. note: ... or just print one out at the proper scale (see 'Hull Cell Ruler' on this page.