Hard chrome plating problems

A. What is the density of the current, expressed in amperes per square decimeter (a/dm2), is observed on these details?
If we take your measurements h = 5000 mm and d = 550 mm, then the total area S will be 863.5 dm2. Given the current strength of 17000 A, it turns out that only 19.6 a/dm2 to the surface of the part, instead of the necessary 35 a/dm2. This leads to the fact that the coating develops only in areas with increased current density - at the ends and the beginning of the part.
Another potential problem affecting the process is the insufficient area of the anodes compared to the area of the part (it should be 2: 1 or at least 1.1: 1). Based on the photograph of your bath, they are difficult to see, but we can assume that they are not enough. The small area of the anodes, if so, can provoke the appearance of trivalent chromium in the electrolyte, which will reduce the roof capacity of the electrolyte, and as a result the coating will besiege even worse.
If the opportunity to conduct precipitation on the Hull cell?

A. I suggest lower your temp to 56-58 °C.
Since your rod is hollow, it itself is getting heated up in the process of being plated and causing the temperature to rise around the area to be plated.

Wish you good luck

A. About hard chroming: Make sure that the stainless steel is given a good reverse etch in a separate chrome tank reserved for this purpose, otherwise you risk contamination with nickel and trivalent chromium. Also be watchful of operating temps.; allow job to warm up in solution. About the hardened steel: this has given me grief in the past, also particularly tuftrided crank journals, steels with moly in and nodular steel and iron cranks. I have found the newer high speed deposit chromium solution a bit more temperamental regarding adhesion. I converted back to the old formula and the thou per hour trade off is, I think, worth it for less stuff ups. Just check that the rubber in contact is not chattering, or it might be screeming the plating off, like needle rollers do.
Best wishes, mark

A. Problem one really needs a hands on inspection of process at site. But you can check out post plate rinsing for a start, The rest needs a look in person. Problem two appears to be the result of poor pre treatment practice and perhaps bad solution maintenance. At this distance this is the best one can suggest.

Regards,

A. PROBLEM:-
1. BUBBLING:- IMPROPER CLEANING, INTERRUPTED CURRENT.
2. CLOUDINESS:- HIGH TEMP, LOW CURRENT, BATH OUT OF CONTROL.
3. PITTING:- GAS TRAPPED.

FIRST COMPONENT SHOULD BE POLISHED, THEN CLEANED PROPERLY, AFTER THAT PLATING.

1. SOAK CLEANING
2. WATER RINSE
3. ANODIC CLEANING
4. WATER RINSE
5. ALKALI NEUTRALIZED
6. ETCHING,CHROMIC ACID
7. PLATING HARD CHROME
8. DRAG OUT
9. DRAG OUT
10. DRAG OUT
11. CHROME NEUTR.
12. HOT WATER.
13. DRY.

A. Hey there,
you did not write anything about your latest analysis results. Also, are you using a catalyzed bath, then you should also consider doing an analysis.

Good Luck,

Dominik

A. Hello Anders,

Do an analysis on the chromic acid for contaminants like iron, aluminium, copper, trivalent chrome. Control the anodes so they are active. I think the ratio between chromic acid and sulphate is wrong.

Read my article about chrome plating in the library here on finishing.com

Regards,

A. Hi, I'm a hard chrome plater and had very similar problems when I started. The pitting could be many things, from the parts being porous, poor cleaning & etching, and even the wax used for masking.

Sometimes if your wax is dirty or contaminated, you can see rust (like pitting) through the glycerine after you have done the first part of the masking.

Also leaving work in the hot wax too long can cause pitting problems if your wax is dirty (some people de-mask in the wax tank, therefore contaminating it with chemicals and water, etc.). A new wax put an end to my pitting problems --simple but not something people think of!

As for your grey discolouration, have you had an analysis of your solution? Are the anodes clean? Is the vat stirred after being topped up (cold water sits on top and causes burning to the part)? Sounds silly, but a guy from another plating firm visited my factory and asked why I stirred the vats - then he said his parts looked grey and horrible!

The newer the solution, the brighter the finish and also the chrome is harder; but it does dull down with age -- maybe its time to renew yours ?

A. Could be:

-shadowing from an edge
-etching too long, not long enough
-etching current too high
-plating current too high, calculate using L*D*3.1416 for 1thou an hour plating current.
-temperature too cold


Could be a number of things, guide me through your plating process and I may be able to help you.

A. Hi John,

While pending defect part photo for ref, you may verify below possible causes:

1. Too high metallic impurities content in plating solution.
2. Too low cathode efficiency at LCD area.
3. Poor bath solution wetability.
4. Operating parameters out of control (Cr, specific gravity, pH, complexer, temperature, etc).
5. Insufficient barrel movement if doing barrel plating.
6. Inadequate post rinsing and drying.

Regards,
David

A. Main cause cold be improper working of Anodes, secondly lower current density, thirdly are you using heat transfer equipment to cool the temperature of the tank during plating operation? If not, rise in temperature could also be a cause of non plating. This can happen also due to excess etching at the particular area due to more active anodes.

A. I am working as Production engineer in Hard chrome shop.
Our job sizes
Dia 80 x lenth 1000mm, Dia 90 x length 1000 mm.
I have faced this problem 2-3 times.
You have to increase your bath temperature between 55-60 °C. Etching temp 50-55 °C.
Also need to increase chrome concentration between 250 to 300 gm/lit.
Sulphate ranges from 3.2-3.5

A. Hello Ron
You did not mention if you use a conventional Chromic-Sulfuric bath? What is the bath temperature? Do you use a stick anodes or conforming anode? What the distance from the anode to the part?
If you got a dull grey Cr plating in the middle, there is a chance that current is a little too low. Based on your data, the current density is ~300 ASF. It should be a good set point, but probably there is some current robber (fixture?). Try to run same test again with a little higher current ~350ASF --> 115 amp and verify the bath temp.
Good luck