Current questions and answers:
Ruisite Product Page
Q. We've been working on SnSO4 bright acid tin plating onto copper. The condition we are using is 30 A for 30 min with current density of 11 A/sq ft. It is plated onto a long copper foil that is winded on a mandrel connected to the cathode. The anodes are several pieces of tin sheets in polypropylene bags. The anodes are connected and total anode area to cathode area is ~1:1. We have seen tin anodes darkening normally after each plating and the plated surface is shinny. Our question is that after each run, scrubbing the surface of anodes and washing anode bags takes 1-2 hours which is much longer than plating itself and that's limiting our ability for production. Would there be any potential problem in our setting?
Yangwei LiuA. It sounds to me like your anodes are going passive. I would try doubling your anode surface area and see if that eliminates the issue.
David De PenaQ. We are doing Bright tin plating in Acid Tin Bath. we are facing problem of gradual Current Drop in the set current.
Initially f we set the Current of 270-300 Amps. after some time it reduces gradually and comes to 130-160 amps. But Voltage is Same no change in the applied voltage.
We are loading 300 Dm2 material Area in the Barrels.
We check the Rectifier and also replace it but problem continues.
⇩ Related postings, oldest first ⇩
Q. We are doing electro-tin plating on copper wires. Lately we observed that the percentage of tin is depleting from the bath and the acid percentage was going up. With this we also observed that the tin anodes have black/grey film on them. could this be causing the high acid and low tin content, if so please advice why do the anodes have film on them and how to solve this problem.
Asit KumarA. Sounds like your anodes have gone passive and you are plating out of solution. Applied voltage is probably higher and possibly you see more gassing from the parts. Cause, normally less than a 1:1 anode : cathode ratio. Scrub clean, and add more anode area.
James WattsQ. Dear James, Thanks for getting back to my problem. I have checked the ratio and found that the anode area is twice the dipped wire in the tank. The problem is that when we start with new/clean anodes ,initially the voltage is about 2 volts and current about 90 amps but after sometime we observe the current going down and to maintain the current at 90 amps the voltage of the bath increases to about 4.15 volts. We are operating at about 250 amps/sf.ft current density. Also the acid content of the solution keeps rising.
ASIT KUMAR [returning]? What are your bath parameters? All components and temperature. How close do you keep them? What is your analysis schedule?
James WattsQ. Thanks for responding back.
The bath composition we are using is
Tin as metal 55 grms/litre
sulfuric acid 50 grms/litre,
the temp. of the main tank is room temp. about 32 deg c
there are 30 turns of wire in the tank
the wire dia is .350 mm
the dipped length of each turn is 3 ft 10 inches
the total area of wire dipped in the tank is . sq ft.
taking a current density of 250 amps/sqft we arrived at a current of
90 amps.
the speed of the wire is 75 mts/min
we add about 2 gm/litre gelatin to the tank .
What we observe is that the anodes are not consumed to a great extent. we analyse the solution on a daily basis and we notice that the tin content keeps going down and the sulfuric acid keeps increasing. the anodes also turn black.
To give you an idea of the solution the tin is in the range of 35 grms/ltr and the sulfuric acid has shot up to 102 grms/ltr. please suggest where is the problem. should we throw this solution and prepare a new solution ,if so please advise the tin and sulfuric acid concentration.
Q. We use acid bright tin plating bath. Conc-30 g/lit and sulfuric acid 120 ml/lit max. We normally use 4 anodes of size 300 x 100 x 12.5 mm. We usually get a bright good finish at 40 amp. But presently we plate at 30 to 35 amp and also we have been advised to reduce the anode surface to a min. 2 anodes. For the past 2 weeks we observe that the anode is not dissolving and the solution gets depleted of metal content which forces us to run plating by the addition of stannous sulfate. During the past years, since anode dissolution was more, the metal content normally shoots up and we used to dilute the bath.
Also when the anode dissolves, we have seen black coating on the anode surface which when cleaned, the bright crystalline surface will be exposed. Now we have no such film, but a dull grey coating with foaming from the anode surface even at a current of 20 amp. Since the plating is mainly from the bath, the finish is also not good. We use lesser brightening agent since it produces micro bubbles on the tiny object we plate. The bath consumes more additive. Since the anode is not dissolving, we have checked our electrical lines, activated the surface of anode and also tried with increasing and decreasing the cathode current density. What would be the factor affecting the dissolution of anode suddenly? Is it due to contamination of the bath or anode? Analytical reports of the solution shows the metal content and sulfuric acid content are within the specified range.
When is the last time that you changed the anode bags and possibly reactivated the anode?
James WattsA. Hi Chithra,
Several things to clarify:
1. Any abnormal high rectifier voltage base on same current setting compare to previous?
2. Any significant amount of gas evolve from anodes?
3. Any change of anode supplier recently?
4. Did anode basket enclose with anode bag or diaphragm which solution flow is blocked?
5. Have you tried to take a pc of anode and plate in Hull Cell
⇦ huh?
or beaker [beakers on
eBay
or
Amazon [affil links] (with plating solution take from same plating tank as well) to verify if dark film able to form and/or anode able to dissolve?
Regards,
David
Q. Hello,
We are currently working to resolve an issue we seem to be having with our tin line and I'm inquiring as to whether there is a way to clean tin bars which have been polarized. We are attempting to create a fresh plating bath however we've replaced all of the tin bars, which should still have much life to them but currently cannot be used since the are black and polarized. Since the replacement of the bars was an expensive one, we would prefer to be able to salvage what we currently have.
We have already tried getting the bath temp to where it should be (around 100 °F) and having it circulate. The idea was that this should work however it seems that this hasn't been as beneficial to the cleaning of the anodes as we had hoped.
I appreciate any advice or help!
Q. Thank you for your response!
In an effort to solve our polarization issue, we are also looking having testing done for contamination of iron. From a previous question, I'm wondering if we should also have the bath solution tested for lead?
We haven't been as attentive as we should be to the testing of the plating bath. We currently test stannous tin, free acid, and have an outside lab test those in addition to some additives (MSA and a Primary). The in house testing is done on a non-regulated basis from what I have found (definitely not daily) and the outside testing is done monthly unless there's been an issue. We also only perform hull cell testing when there's been an issue. From reading the information on those pages, I noticed the need to determine the amount of free alkali daily as well?
It's obvious I need to have a better testing plan implemented regardless.
Thanks!
If you are looking for more details, kindly visit Tin plating process.
Nicole Hannis [returning]Q. Our company encountered faster oxidation rate of Tin anode and Tin anode turn black color 2 days in the bath.
Wayne LimQ. Hi Ted. We are using bright acid Tin.
The black sludge from the anode balls makes the anode bag choke. It is blocking the current and giving high voltage, making defects in the products.
A. Hello, The first thing I would do is give the bath a complete analysis. Be sure it is also analyzed for Stannic Tin. Too high a concentration will definitely cause you problems. Secondly, verify you are using pure tin anodes, and check the anode bars and baskets to ensure the proper current is being distributed. A clamp ampmeter is the best to use. For a bright tin sulphate bath, these are the recommended steps I would take.
Mark BakerQ. My situation:I recently conducted some Hull cell test on an acid tin solution at 2 amps for 10 minutes and noticed the anode turned brown. Does anyone know why this is?
Mark AllabushBy R. Savija
All specifications for electroplating, whether military, federal, ISO, ASTM or SAE-AMS specifications, have an initial section that contains essential information to be supplied by the purchaser to the electroplater. More times than not, much of this information is omitted from part prints and purchasing documents which opens the door to potential miscommunication and finishing shortfalls. This blog details some of the more common omissions that are discovered by Advanced Plating Technologies’ engineering staff during quoting or contract review of specifying a plating process.
Often a minimum/maximum thickness tolerance without a defined checkpoint cannot be realistically obtained with a traditional electroplating process. For example, a plating specification that lists a minimum plating thickness of 0.” and a maximum plating thickness of 0.” for all surfaces of an electroplated part would not be achievable on most part geometries due to the inherent variations in electrolytic plating distribution.
Plating thickness varies due to the inconsistent distribution of plating current on an electroplated part. Ionic plating current, like electrical current, takes a preferential path of least resistance with the corners and ends of a part receiving a higher current density and therefore higher plating thickness. If the design of a component requires a very tight plating tolerance, it is important to designate a functional surface where a plating thickness check point can be established. If the plating is specified as 0.” minimum and 0.” maximum with a specific checkpoint, a plating protocol can generally be developed to consistently meet this requirement. Any specific part dimensional tolerances should be addressed in combination with a plating thickness checkpoint to allow for a combined plating thickness and part dimensional inspection protocol.
Most electroplating specifications require hydrogen embrittlement relief baking for high strength or hardened steels having a strength greater than 180ksi or Rockwell hardness of 40 HRC or more. In addition, pre-plate stress relief bakes are often required within plating specifications for hardened or cold-worked ferrous materials. Often the hardness of a steel component is not listed on the drawing or purchase order which requires follow up during quoting or contract review. In some cases the hardness of a steel material is not so obvious, such as with music wire used in springs and wire-forms. The purchaser rarely specifies the tensile strength of music wire on the drawing. A closer examination, however of the music wire specifications such as ASTM A228 indicate that all music wire has a tensile strength well above180 ksi which is the strength equivalent of 40 HRc.
It is not uncommon for a metal finishing facility to receive parts with a heavy oil or heavy heat treat scale. This type of a condition is generally not discussed during the quoting stage nor are there advisories on part prints, specifications or purchasing documents. Excessive oil and heat treatment scale require additional operations to prepare the parts for successful finishing. The additional processes are often “off-line” in that they are a separate process independent from the plating line. Such processes include aggressive chemical descales, vapor degreasing and sand/vapor blasting processes. These steps add additional time/cost that are generally not included in a standard quote. In such cases, further discussion is required to determine the most cost effective way to prepare future orders of parts for plating. Often proper cleaning of parts prior to heat treatment, alternative heat treatment methods such as vacuum heat treating or cleaning prior to heat treatment can ensure parts are received ready-to-plate thereby eliminating additional preparatory steps.
It is a common misconception that electroplating can actually cover-up up surface imperfections on the part and that electroplating can significantly improve surface roughness. In most plating applications, this is not the case and it is generally recommended that the pre-plate surface roughness be slightly better than the desired post-plate surface finish. For example, if a post-plate Ra of 16uin is required, it is generally recommended that a pre-plate Ra of 10-12uin be provided. This is especially true of electroless processes such as electroless nickel that have virtually no “leveling” properties.
It is not uncommon for improper allowance to be made for plating buildup on threads. Since plating builds on two sides of the part and both sides of the thread land, a total of four times the nominal plating thickness should be used as a guide for the increase (male) or decrease (female) in thread pitch. The formula below details the calculation for change in pitch diameter as a function of the plating thickness and included angle (Note: the included angle for most common thread forms is 60-degrees):
As an example, a 0.” plating thickness will cause the pitch diameter of a male thread to increase by a factor of four or 0.” for standard 60° UNC or UNF threads. This plating buildup is even further exacerbated on the lead threads of long fasteners or shafts where a localized plating thickness at the lead thread may be as high as four to five times the nominal thickness depending on where the plating thickness checkpoint is established. In such a case, the target plating thickness of 0.” may be as high as 0.” as measured at the lead thread resulting in as high as 0.” increase in thread pitch. In such applications, it is very important to discuss allowances for thread pitch build and define a plating thickness checkpoint to ensure that parts can be successfully plated and meet post-plate gauging requirements.
For parts that are rack plated, allowance must be made for contact locations of the rack tips. The rack tips are what physically contact the part to fixture it throughout the plating process. At the rack tip contact points there will nearly always be rack marks and lack of full plating coverage. This is due to the fact that current passes through the rack tips and into the part at the contact points. In addition, plating chemistry/solutions cannot fully wet the surface of the part beneath the rack contact points. Due to the fact that the plating coverage will be incomplete with visible marks at the contact points, it is important that the purchaser convey non-functional or non-critical locations on the drawing where racking is permissible. This is usually a location where the purchaser deems that rack marks are not detrimental to the function or appearance of the part.
The above points detail just a few commonly overlooked areas that are critical to a successful outcome in a metal finishing process. By carefully reviewing the ordering information listed within most plating specifications, the purchaser can be assured that details critical to a successful plating outcome are detailed at time of quote or purchase. Advanced Plating Technologies is happy to provide guidance along these lines by talking with any of our estimating or process engineers. Visit the contact us section of our website to submit a plating inquiry or general question regarding specifying a plating process. Our Technical Library contains common plating topics, specifications and white papers specific to the plating process.
For more information, please visit silver plating machine.