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topic 12860

Plating time too long / Calculating best plating rate


A discussion started in 2002 but continuing through 2018

2002

Q. I am using ammonium chloride zinc plating (barrel plating). For getting 3-4 microns it takes 2-3 hrs. We are plating to the fasteners of different types. How shall I reduce the time of plating? What factors can affect the plating time.

Santosh Z [last name deleted for privacy by Editor]
- Dubai, UAE


2002

A. Hi Santosh. It sounds like you have about one fifth of the current you need. Please start by cutting the load in half without reducing the amperage and tell us what happens. Thanks!

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey


2002

A. Adjusting your current density, higher, will increase plating rate. Also optimize other parameters in the solution, zinc metal, pH, temperature. Another variable to look at will be barrel design, barrel speed and loading in barrel. You should have a barrel that has the largest open surface area so you can get the most transfer of solution into the barrel.

George Shahin
George Shahin
Atotech - Rock Hill, South Carolina


2002

A. Factors that can affect plating rate.

1. Current Density can be increase to increase the plating rate. However, there is a maximum point where too high current density will create another set of problems such as burning and poor quality work.
2. Increasing the metal concentration in the process solution will increase the plating rate.
3. Bath pH concentration will impact plating rate. At lower pH concentration, hydrogen will plate out like a metal; thus, competing and lower the plating rate of the desired metal.
4. The concentration of the organic package such as wetters or brighteners will affect plating rate depending on the situation. For example, too much organic additives may reduce the plating rate, or wetters may be required so the part to have a good cathode film which may increase the plating rate.
5. Unwanted organic or metallic contamination will negative impact on the plating rate.
6. Temperature: most chemical processes increasing temperature can increase the rate of reaction such as increasing the plating rate, but it may also have a negative impact on the plating rate as well depending on the situation.
7. Solution agitation will affect plating rate. Increase the solution agitation will increase plating rate.
8. In a barrel plating operation, slower barrels speeds will increase the plating rate by increasing your coefficient of electrical contact within the barrel.

Karl Weyermann
- Lebanon, Kentucky



Acid zinc plating problem

2002

Q. Hi Everybody,

1. I have a problem in ammonium chloride zinc plating bath of not getting desired current. I am passing 10-16 volts but getting 500 amps, where it should be 1000 amps. What could be the reason.

2. Also if I process 33.6 sq.m. surface area in one barrel by passing 500 amps current, the what time it should take to get the 3-5 microns coating. Our supplier has given following spec. -

0.5 to 1.0 amp current per one Sq.Decimeter
time - 1 hour
coating thickness - 13 micron.

3. Also please let me know, for high carbon containing compounds which process is suitable, alkaline zinc (non-cyanide) or acid zinc, keeping in the mind that no loss of production rate.

Regards,

Santosh Z [returning]
- Dubai


2002

A. Hi Santosh.

1). It "should be" 1000 Amps based on what? Wanting it to be 1000 Amps so you can plate twice as fast is one thing, and having a valid reason to expect 1000 Amps may be another thing :-(

2). The Metal Finishing Guidebook has an "Electrochemical Equivalents" shortcut table which factors metal densities and valences into Faraday's Law so that you can directly read that it takes 14.3 A-hr/ft2 to deposit a 0.001" thickness of zinc, assuming 100 percent efficiency. Converting square feet to square decimeters, it should take 1.544 A-hr/dm2 to deposit 0.001". Converting mils to microns, it should take 0.0608 A-hr/dm2 to deposit a micron at 100 percent efficiency. Your supplier's numbers say you'll need 0.038 to 0.077; so let's go with the 0.077 A-hr/dm2 to deposit a micron. So 3 to 5 microns will take you .23 to .39 A-hr/dm2 to get your thickness. I hope there is a typo in your question because 33.6 square meters is several times too large of a load and would take 773 to 1290 Amp-hours to deposit 3-5 mils. I'd like to see you plating for under 30 minutes, not 1-1/2 to 2-1/2 hours, for 3-5 microns coating. Again, please put half the weight into the barrel and tell us what happens.

3). For high carbon, you need acid zinc. Because of hydrogen overpotential you can't plate them in an alkaline bath.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



To minimize your searching efforts and to offer multiple viewpoints, we've combined some threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.



Low current density

2002

Q. Hi Everybody,

We are plating screws in acid zinc plating process. The screws have threads & so in barrel plating, the current passes varies with different areas.

Always we are getting poor coating at low current density area, somewhat grey/black coating. How shall I improve to get good coating in low current density area. As there is poor coating rate at low current density area we requires more time to achieve the required coating. Please help.

Regards,

Santosh Z [returning]
- Dubai


2002

A. You are probably over filling your barrel. Adding an extra 10% to the load and having 90% failure rate is not cost effective. Second, check your barrel. Have the holes been peened shut slightly? Can you open the hole up a few thousandths to get better solution flow into the barrel?

James Watts
- Navarre, Florida


2002

A. Sounds like the barrels are too full or the barrel holes are plugged . Solution transfer is most important. You should use the largest hole you can without losing parts. Check to see if the holes are plugged or closed and if so clean them or drill them out!

drew nosti
Drew Nosti, CEF
anodizeusa1
supporting advertiser
Ladson, South Carolina


2002

A. As is already suggested you may be filling the barrel little too much. Also check the Metal : Chloride ratio. To get best results at LCD it should be 1 : 5 / 1 : 5.5.

R.K. Khare
- Mumbai, India


2002

A. I am in agreement with both arguments about oversized load and ratio of chloride/metal. Instead of clogged barrel holes you may be using a cylinder with too small holes resulting in a lower than anticipated current density. Also, by having a brightener imbalance you may not be getting the best lcd coverage. Further, check you pH. Operating at the lower end of the range will generally improve lcd distribution at a marginal increase in brightener consumption. The ratio of metal/chloride will vary from process to process. Check your vendor recommendations. Also check bath temperature. Too low temperature will result in dull, gray lcd. BTW, check with your vendor for a troubleshooting guide.

Gene Packman
process supplier - Great Neck, New York



To minimize your searching efforts and to offer multiple viewpoints, we've combined some threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.



2002

Q. Hi Everybody,

We are using ammonia-ammonium chloride acid zinc plating chemicals in barrel plating. The suppliers specification is at 0.5 to 1.0 amp/sq.dm. current we should get 13 microns coating thickness. But we can achieve only 3-4 microns in hour. Our barrel load is 60 kgs of screws i.e. about 13 sq.m. area. As per standard specification for load the screws should be loaded about 30 kgs. We are processing double surface area due to high production requirement. The anode surface area we are providing for three barrels i.e. 39 sq.m. cathode, is just 4 sq.m.

I would like to know if there is any relation of anode surface area with coating formation rate. Please tell me if I increase anode surface area then shall I get faster coating formation.

Regards,

Santosh Z [returning]
Dubai


simultaneous 2002

thumbsdown We're always happy to try to help you or anyone, Santosh, but Arrrggghhhh! :-)

You've asked this same question three times previously, and it's been answered three times already by 7 plating experts, and you have rejected the answers because you insist on overfilling the barrels.

No matter how badly you may WANT to, it simply won't work. Your situation is not unique, everyone everywhere the world over would like to put twice as much work in their barrels for more production :-)

Please operate more shifts, or install a 2nd plating line, or farm out part of the volume, and stop foolishly overfilling the darned barrels. Start trying to plate right instead of insisting on knowingly plating wrong; it is just SO ridiculous.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey


2002

A. I am normally kinder than this response. BUT! this is a typical stupid management decision. The specifications are there for a reason! In short, you can not drive enough current thru the holes or mesh to plate. In addition, the barrel cannot function properly because it is too full so does not flush enough new solution into the tank to have enough metal ions to be able to plate. I am sorry to be nasty, but I have lived thru just this stupidity by managers that know absolutely zero about plating.

James Watts
- Navarre, Florida


2002

Hi Jim,

I wouldn't blame management stupidity with just the available information. Loading of barrels and barrel cathode current density are highly variable.

I want to know about how full (by volume) the barrels are filled, What size and how many holes in the barrel, chemistry of the bath, how many amperes, pH, temperature, distribution of plating on the screws.

And I would ask: Size of the anodes, composition (slab, slugs, type of basket), distance from barrels, how many across from each basket, are two barrels sharing anode baskets?

pooky tom pullizi signature
Tom Pullizzi
Falls Township, Pennsylvania


2002

Sorry Tom, the man said his spec was for 30 KG and he was putting in 60 kg. The spec came from somewhere, probably the Mfgr.'s recommendation for that product. Sounds to me like the barrel is so overloaded that it just is not going to work if that is the case! Ted's response covers it well. The man is looking for fu fu dust to make his improperly operated line work. I have yet to find a reliable vendor for it.

James Watts
- Navarre, Florida


2002

thumbs up sign Hi Jim,

Armed with the knowledge that this letter has been around the track 4 times already, I am no longer interested in it either.


Tom Pullizzi
Falls Township, Pennsylvania


December 20, 2017

Hello Santosh!
The plating thicknesses is mainly the function of
1. Plating time
2. Current and voltage fed
3. The appropriate surface area of the material to be plated
4. Plating Bath pH, etc.

If you constrain all other factors you have to alter the
1. voltage and current fed
2. Total Mass of material to be loaded into a barrel

As you said you are loading almost about twice of the barrel capacity then to get the desired plating thickness you have to change the other process parameters to compensate the increased surface area.
1.plating time
2.voltage and current fed
because the surface area directly gets doubled if you load twice the capacity.

Hope it may help...

Best regards,

Bhavik Vadhiya
- Rajkot, Gujarat, India


December 2017

thumbs up sign Hi Bhavik. Thanks for replying to this letter. Although it's an older one, this site is intended for long term reference, and your reply will help future readers if not Santosh.

wikipedia
Will-o'-the-wisp

Although it's true that you need twice the current if you put twice the load in the barrel, that does not mean that you can make a grossly overloaded plating barrel work. Let's not offer people who overload their barrels a will-o'-the-wisp :-)

Regards,

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



November 21, 2018

Q. Hi, this is Ankush here.

My question is for silver plating.

How is plating time calculated per micron?
I tried to refer to the the book link but somehow didn't get inputs on page no 812.

Could you help me with that?

Also how ideal bath volume can be considered?

Ankush s.
- Pune, India


November 2018

A. Hi Ankush. Page 812 of the digital version of the Metal Finishing Guidebook is the correct link, and tells us that it takes 6.2 amp-hours to deposit a silver coating of 0.001" on a square foot of surface (at 100% efficiency, and silver plating is close to 100% efficient). Aside from converting units, the only missing factor is how fast you can plate (what current density you can use) and this number is empirical rather than theory-based. 5-10 amps per square foot might be a good estimate for rack plating.

You apparently have looked at our Intro to Faraday's Law but perhaps you haven't really had a chance to work hard to fully understand it yet :-)

Please do not cast your questions in the abstract because we can't possibly explain the process and philosophy of designing a silver plating installation in the general case in a brief forum response; and the answers will depend on plating volume, and whether you will be rack, barrel, or reel-to-reel plating, etc. Instead, please introduce your situation and tell us what kind of parts you want to silver plate, how many, how thick, and why -- all the data you have -- then we can almost surely help with how long the plating time will be, how big the plating tank should be, and what you first steps should be. Good luck.

Regards,

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


December 1, 2018

A. Hi Ankush
Tables and calculations will allow you to estimate the weight of material deposited and therefore the average thickness.
However in a practical plating application the metal will rarely deposit equally all over the part. This can be quite useful in, for example, achieving a thick deposit where it is needed while saving metal in less critical areas.
It is usual to estimate the thickness then plate some parts and measure the actual thickness at the critical point and use this to adjust the time accurately.

geoff smith
Geoff Smith
Hampshire, England



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