No registration, no passwords; no pop-up ads -- just aloha, fun, & authoritative answers.
As an eBay Partner & Amazon Affiliate we receive compensation for qualifying purchases.
Home /
Search 🔍
the Site
pub  Where the world gathers for
plating, anodizing, & finishing Q&As since 1989


Current density in copper strike

Q. We have an aluminum prep line leading up to a sulfamate nickel plate. Just before nickel plate we utilize a copper strike bath. I noticed that it is common protocol to begin the copper strike at a relatively high current density for a short time then switch to a lower current density for a longer time. What is the reason for the switch from higher to lower current density ? Thanks ... Greg Fuqua

Greg Fuqua
- Jacksonville, Florida

A. Sounds like the reverse procedure to me, but you would have to tell us the current density at the start and when you drop the current. You may be too high or too low at some point.

Is this copper strike over some zincate coating? -tom

tom pullizzi animated    tomPullizziSignature
Tom Pullizzi
Falls Township, Pennsylvania

A. This is a common practice to strike at a higher current density for a short time when plating complex shapes. The copper covers the low current density areas faster before the zincate dissolves and blistering occurs. Once there is total coverage you can turn the amperage down to normal ranges.

jim conner
Jim Conner
Anoplex Software
supporting advertiser
Mabank, Texas USA
Anoplex logo

What does Surface Current Density mean?

Q. I see many electroplating books talk about Surface Current Density, like "the copper plating current density is 0.2-0.3A /dm2"

Can anyone explain it ? Does it mean if I have copper area dm2 I need 0.2 A DC ? Or it depends on area of solution?

qwee qweee
- amman, Jordan
July 2, 2020

A. Hello Qwee.
You are correct. It refers to the relationship between the surface area of the parts, pieces, or items which you are trying to electroplate and the electroplating current which you should use.

If the item which you are trying to plate is a thin rectangular plate 1 dm x 1 dm, its surface area is 1 dm^2 on each side, so its total surface area for both sides is 2 dm^2. If the book suggests plating it at 0.2-0.3 A/dm^2, then you need to use a current of 0.4 to 0.6 Amps.

However, that seems to be a very low current density. Typical current densities for most copper electroplating would probably be about 10X higher.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey
July 2020

Q. Thank you for reply.
For rectifiers it gives unit of current like 50A or 100A ?
What does that mean ... does is mean 50 A-hour ?

For chrome plating and for current surface many books take about 20 to 30 A/dm2
And rectifier that give 50 A it's good for it?

qwee qweee [returning]
- amman, Jordan
July 4, 2020

A. Hi again. If the rectifier capacity is 50 A, that means it can supply up to 50 A. If you are trying to do chrome plating at 20 A/dm2, you will be able to electroplate parts with a surface area of up to 2.5 dm^2, that is 50 / 20.

If you want to plate a part with a surface area of 1 dm^2 at 30 A/dm^2 you would set the rectifier to 30 Amps. If you keep the rectifier on for 10 minutes at 30 Amps, you will apply 30 x 10 = 300 A-minutes or 5 A-hours.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey
July 2020

Q. Hello my friend,
Here you told If you are trying to do chrome plating at 20 A/dm2, you will be able to electroplate parts with a surface area of up to 2.5 dm^2, that is 50 / 20.)
This for 1 min right?
And for car wheel, I mean a normal car wheel, I suppose it has 15 dm2 and from books it told for chrome plate you need like 25 A/dm2, then what amperage must rectifier have?

qwee qweee [returning]
- amman, Jordan
July 4, 2020

A. Hi Qwee. I think you need to slow down and think this through because, despite several examples, you are now asking me to do the arithmetic of multiplying 25 by 15  :-)

I am very sure that you can multiply 25 x 15, so I'm afraid you don't fully understand the concept of what A/dm2 means yet :-)

One minute of chrome plating time might be enough; but I think 2 minutes would be closer to typical.

Unfortunately I have no idea what you know and don't know about nickel-chrome plating of wheels, so I don't know if you are almost ready to go or whether have no idea at all yet what you are doing. Please tell us!

I'm happy to stick with the question of "what does A/dm^2 mean" for as long as you like ... but if you have no plating experience it will be impossible for me to teach you 10% of what you need to know to chrome plate aluminum wheels -- not that I've personally done it anyway :-)   I'm happy to answer specific questions, but thousands of people visit this site each day, and each 20 minutes spent providing personal tutoring is time in which I could have posted 5 or 6 of the questions they've submitted instead of blowing them off :-)  Apologies.

Have you read our "Introduction to Chrome Plating"?

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey
July 2020

July 6, 2020

Q. Yes MY friend Ted I'm new on these electroplating subject.
I'm still confused about these units A/dm2.
I am trying to enter this field, but it is difficult.
I think I need to do experiments about these electroplating.

Yes, I read "Introduction to Chrome Plating" and many posts here.
Can you talk more about these unit A/dm2 ?

- Amman

A. Hi again. "A" stands for Amperes, the amount of electricity or current flowing. It is a measurement similar to how much water is flowing in a river, or how much traffic is flowing on a highway. More water is flowing in a mighty river than in a small stream; more traffic can flow on a 6-lane highway than on a village road. More Amperes can flow through heavy copper bus bars than through the skinny wires of a pair of earbuds. Amperes is actually a count of how many electrons are flowing from the anode to the cathode through the rectifier and copper wiring/bussing in any given time period. And however many Amperes flow through the rectifier and copper from the anodes to the cathodes, an equal amount must flow through the solution in the opposite direction.

"dm" is an abbreviation of decimeter, a unit of length; "dm2" is an abbreviation for square decimeters, a unit of area. The screen size of a small smart phone is about half of a square decimeter, and the screen size of a very large smartphone is about a square decimeter.

Chrome plating is done at somewhere around 20 A/dm2. If the surface areas of your wheel is 15 dm2 you would need 300 A.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey
July 2020

(No "dead threads" here! If this page isn't currently on the Hotline your Q, A, or Comment will restore it)

Q, A, or Comment on THIS thread -or- Start a NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

Chemicals &
Consult'g, Train'g
& Software

About/Contact  -  Privacy Policy  -  ©1995-2024, Pine Beach, New Jersey, USA  -  about "affil links"