finishing.com -- The Home Page of the Finishing Industry
A website for Serious Education, promoting Aloha,
& the most FUN smiley you can have in metal finishing.
    no popups, no spam
HomeFAQsSuggested
Books
Help
Wanteds
Advertise
on this site
FORUM
current topics
topic 30879

Plating Thickness variation in hard chrome plating

adv.     u.s chrome

A discussion started in 2004 but continuing through 2018

(2004)

Q. In hard chrome plating of piston rods (rod diameter 12.7 mm to 17.4 mm & length 150 mm to 500 mm), we are getting plating thickness variation up to 4 microns along the length and 2-3 microns on circumference. Could you please elaborate on the probable cause and the solution to the same.

Manoj Gupta
Automobile Shock Absorbers - Indore, M.P., India


(2004)

A. Hi Manjov. You didn't mention the thickness of the plating yet, so we don't know what the percentage variation is. And you didn't mention anything about the fixturing, so it's hard to say how to improve it. But, in general, chromium plating is more efficient at high current densities than at low current densities, so a high current density area will get much more plating than a low current density area. You need to be doing something fixture-wise to fix this (thieves, shields, anodes which conform better, rotation during plating, etc.) There is no solution adjustment that will cause the efficiency in the LCD area to even reach the efficiency of the HCD area, let alone exceed it. Good luck.

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


(2004)

Q. Specified plating thickness to be achieved is 5-12 microns. Job is being held longitudinally on a vertical fixture with Plastic robbers on top and bottom. 4 to 6 rods on one fixture. Current density is 2.5 to 3 Amps/ Sq.in.

Manoj Gupta
- Indore, M.P., India.


guffie book
Hard Chromium Plating

Robert K. Guffie

(2004)

A. Hopefully someone with substantial hands-on hard chrome plating experience will speak up if something sounds wrong, but this sounds to me like a reasonable variation in plating thickness for the conditions. Without rotating the parts, which would presumably be a very big problem, I doubt that you'll reduce that variation around the circumference. But slight changes in the shields, and making sure you have good agitation, may reduce the end to end variation.

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


(2004)

A. Manoj,

I think the thickness variation you describe for a hard chrome solution can't give you a better metal distribution then you have. If you like to have a better metal distribution change to electroless nickel.

Regards,

anders sundman
Anders Sundman
3rd Generation in Plating
Consultant - Arvika, Sweden



(2004)

A. Dear Mr Manoj,

If your spec says 5-12 microns, and you already have a tolerance of 7 microns and are achieving a variation of just four, everything seems to be working for you, the variation is within reasonable limits.

Khozem Vahaanwala
Khozem Vahaanwala
Saify Ind supporting advertiser
Bangalore, Karnataka, India

saify logo


(2004)

A. Dear Mr. KV,

I think you got it wrong tolerance and variation are two different things. The specs demand coating of 5-12 microns, which means that the coating can be minimum 5 microns and maximum 12 microns but does not say that it can vary from 5 to 12. I think you can get me. As far as the initial question is concerned, I think job rotation, fixture design and robbers can solve your problem. We plate rods 8 to 20 mm dia 7 to 14 microns, both parallel and true within 2 microns. Go ahead try a better job holding design.

ALL THE BEST

vikram dogra
Vikram Dogra
Irusha India - Chandigarh, India


(2004)

A. PLATING THICKNESS VARIATION DEPENDS ON
1. SURFACE PREPARATION
2. CONTROL OF BATH CONDITIONS
3. UNIFORMITY OF THE POWER SOURCE
4. ANODE PLACEMENT
5. SHIELDS, THIEVES
6. TANK DESIGN, etc.,
Practically variation is there .

ajay raina
Ajay Raina
Ludhiana, Punjab, India


(2004)

A. Manoj,

A. I'm agree with many here about your question about thieves and shields. To get a better metal distribution you must think about this. How long is your anode, because the anode must be a little shorter than the part. Are the anodes active. Is the anode arrangement so that it goes around the part. Sulphate ratio to the chrome, trivalent chrome metal contamination, temperature. Also a low current density will help you with a better metal distribution.

Regards,

anders sundman
Anders Sundman, 4th Generation Surface Engineering
    Sundman & Nylander AB
Arvika, Sweden




sidebar February 14, 2008

Q. I noticed that one of the factors listed in the chrome plating process includes "shields and thieves". Can anyone elaborate on what these items are, and if so - what exactly they do?

Eric Burns
- Buffalo, NY USA


February 14, 2008

A. Shields are widely used in plating in general, but not so much in hard chrome plating. They are pieces of plastic placed in an appropriate place somewhere between the anode and the cathode to block a short electrical path (solution path). The current cannot flow through them, so the 'shortest path' for the electricity, which might have built up too much plating on a protruding corner of the part, doesn't exist anymore and the electricity must take a different path that hopefully leads to better plating distribution.

Thieves are pieces of scrap connected to the cathode, maybe a length of wire, that is placed near the high current density corners and edges to steal the current and prevent the part from burning or plating too thick in that area.

So shields and thieves approach the problem differently, but are intended to do pretty much the same thing.

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



February 10, 2011

Q. My name is WALMIK PAWAR I am in NASIK. We mfg. piston ring from dia. 48 to 160 mm. I have big problem in chrome plating. The problem is chrome thickness variation within length and circumference.

WALMIK PAWAR
PLATING SHOP EMPLOYEE - NASHIK, MAHARASHTRA, INDIA


Need 50 micron chrome plating thickness but can only get 25

August 6, 2014

Q. What are the probable reasons for not getting chrome plating thickness as required? Required is 50 micron but able to reach up to 25 micron only.

sandip mahajan
- ahemadabad, Gujarat, India


July 2014

A. Hi Cousin. Your question is too brief. Are you saying that you can't get 50 microns even if you plate for two days? Or are you saying that you don't achieve it in the arbitrary time period that you wish?

Let's start with a Faraday's Law calculation to determine what efficiency you are achieving -- What is the total surface area of the plated parts, the plating time, and the amperage reading of the ammeter on the rectifier?

Regards,

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



January 15, 2018

Q. I have a shaft of dia. 170 mm and I have to chrome plate it to have a final dimensions of dia. 169f7, i.e. (168.957 / 168.917). What is the machine tolerance that has to be maintained to chrome plate it by 25 µm ± 5 µm?

Vikram Kulkarni
- Dammam / Saudi Arabia


January 2018

A. Hi. If the minimum allowable final size is 168.917 and it has the minimum of 20 µm of chrome, the diameter will increase by only .04 mm, so before plating it must be 168.877 mm or more before plating. If the maximum allowable final size after plating is 168.957 and it has the maximum of 30 µm on it, the diameter will increase by .06 mm, so it must be no larger than 168.897 before plating.

Regards,

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



May 8, 2018

Q. Hard Chrome Plating:

I am trying to plate a 1" x 4" panel uniformly on one side using a rack that has a plate that measures 4.75" x 1.75". The 1x4 is mounted onto the plate and held with two 10-32 bolts on edges. I plated at 2 ASI for a surface area of 16.63 in^2 for 45 minutes. I got less plating in the center and more plating on the edges. Shall I use robbers or shields to limit the build up on the edges? The rack is already behaving as a robber.

Orlando Castro
- Los Angeles, California, USA


May 2018

A. Hi Orlando. A sketch or photo of the arrangement would probably be worth a thousand words. Although I've seen shields successfully employed in plating, I have personally never seen them used in chrome plating and am not optimistic about it. I think the most straightforward solution would be a properly shaped conforming anode rather than a shield or a robber.

Regards,

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



This public forum has 60,000 threads. If you have a question in mind which seems off topic to this thread, you might prefer to Search the Site

ADD a Comment to THIS thread START a NEW threadView CURRENT TOPICS

Disclaimer: It's not possible to 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 may be deliberately harmful.

  If you need a product/service, please check these Directories:

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental ComplianceTesting Svcs. & Devices


©1995-2018 finishing.com, Inc., Pine Beach, NJ   -   About finishing.com   -  Privacy Policy
How Google uses data when you visit this site.