Need to remove bright chromate and then nickel plate some steel parts

[WayneCothran]

Hello All,

I have a need to remove what I believe is bright chromate plating from steel, sand blast to rough up the surface, and then nickel plate the part. I know this flys in the face of what everyone is doing here, but this is a somewhat specialized application. I've read elsewhere in this forum the magic bullet for zinc removal is 2:1 Muratic acid and wait till the fizz dissipates. Is that accurate? Secondly, I've read that sandblasting is NOT the thing to do prior to EN plating - but I have no choice. So, what should I be looking for in terms of disaster avoidance there? And, lastly can this be done? Keep in mind I'm not looking for a show quality finish. This is to be used for an 'anti-stick' surface and just needs corrosion resistance from occasional handling and natuarlly occuring moisture. This will never be exposed to the elements - will always be indoors.

Any suggestions and information will be greatly appreciated.

Wayne

[zincplater]

From my experience, the 2:1 solution is the way to go. Works faster/better when the solution is warm. Wait until the fizz dissipates (should be an hour or less) and you're good to go.

I can't help you with the nickel questions, though (see my screen name).

[WayneCothran]

Thanks, zincplater, for your response. I've seen in several places on here where 2:1 is mentioned. I'm a little confused about the ratio being referred to. Are you talking about an off-the-shelf mixture of Muratic from a hardware store that's then dilluted further? The source of confusion stems from research that tells me Muratic is hydrochloric acid (HCL) and it's available in many concentrations up to about 38% after which it won't remain in solution without pressurization (I think). The 38% is a lab grade (I think) and a little difficult/expensive to obtain. I think I did read where others heat it to 120F before and during use. Is off gassing a problem after heating it? What precautions do you take other than ventilation? One more question if you don't mind, what do you use to neutralize the acid left on the part? This part is a weldment and I'm concerned about leaving acid between the components that make up the part. Thanks again!

[WayneCothran]

I knew I had another question, zincplater. Perhaps I should've waited, but in your experience what happens to the surface of the steel after stripping? Is it dark and dull? Or, bright and shiny? Or, some other combination?

[zincplater]

Warm (80 or 90 degrees) is about as much as I heat it. Most of the time, my solution is about 60 degrees and works fine. I used 2 parts tap water to 1 part off-the-shelf muriatic acid.

A fan in a nearby window helps. I certainly wouldn't do it in a small space.

After the bubbling stops, I rinse the part in fresh water, followed by distilled water. Sounds like you'll need to immerse your part, then hit it with compressed air, then repeat.

The "stripped" parts usually resemble new, unpolished stainless. A little time with fine wire wheel brings a good shine.

[XK120DHC]

Thanks, zincplater, for your response. I've seen in several places on here where 2:1 is mentioned. I'm a little confused about the ratio being referred to. Are you talking about an off-the-shelf mixture of Muratic from a hardware store that's then dilluted further? The source of confusion stems from research that tells me Muratic is hydrochloric acid (HCL) and it's available in many concentrations up to about 38% after which it won't remain in solution without pressurization (I think). The 38% is a lab grade (I think) and a little difficult/expensive to obtain. I think I did read where others heat it to 120F before and during use. Is off gassing a problem after heating it? What precautions do you take other than ventilation? One more question if you don't mind, what do you use to neutralize the acid left on the part? This part is a weldment and I'm concerned about leaving acid between the components that make up the part. Thanks again!

Wayne;
The home improvement gallon jugs of Muriatic Acid (aka "Swimming Pool Cleaner") are generaly 30% HCI, 70% water. It is rare that the hobby plater has/needs 100% HCI, so a mix of 2:1 would be using the "Swimming Pool Cleaner". I've never heard that any acid/water mix needed pressurization to stay mixed.. most of us just give the container of "mix" a bit of a shake before using it as a stripper, activator, etc. (plating tanks often require agitation, helps with keeping things mixed). If you get into additional types of plating, you will find you will use several ratios of Muriatic/water mixtures. same with "Battery Acid" (also around 30% acid, but many folks test" theirs, via Specific Gravity, to determin the exact percentage.. generally the average is 25%).
Heating ANY acid will produce gassing, same with our plating baths. There are recommended "average" temps to use then there are "never reach this temperature if you are smart". In any case, proper ventilation is mandatory with ALL home plating.
Other precautions are: Have Caswell's Plating Manual handy at ALL times (RTFM), have ALL the MSDS Sheets (two sets-- one in the shop, one in the house. BOTH where you can "lay hands" on them in minutes) for EACH chemical you are using.. even household ammonia (if a fire should happen, the Fire Dept WILL need to know, for their own safety and the safety of your neighbors, what chemicals might be burning), have a couple of big boxes (or a dozen one pound boxes) of Baking Soda to neutralize certain acid spills, refer to MSDS Sheets for other neutralizing agents for other chemicals you have/use and keep some on-hand. Lottsa paper towels as well as "Oil-Sorb" (kitty litter without the perfume) to use to make a perimeter dam to prevent any spill from getting into the storm drains or the ground. LABEL all your jugs, bottles, solutions, etc. Some chems require glass bottles, keep these bottles in plastic buckets, just in case the glass breaks.. ALWAYS check to be sure the type of plastic bottle/jug you are using is compatible with the chemical you are putting into it. (HDPE can be used for certain mixtures of Nitric Acid, but an HDPE Milk Jug is WAY too thin to contain that acid.. Common sense is required, as well) ALL containers MUST have gas/leakproof, screw-on lids. I use "peel & stick" labels, but I use clear "Packing Tape" over them to protect the label from smearing, falling off, etc. Lastly, Get and USE a Respirator with "Acid Gas" cartridges. and "paint style" respirator is fine as long as it doesn't require proprietary (odd ball) filter cartridges.. good old standard, screw-in round carts are what you want. You will have to order the Acid/Gas carts. Also get the "Dust Filters" that snap on the outside of the cartridges.. You'd be surprised how much dust is in the air, these days.. Besides, when the dust filter clogs up. it's cheaper to replace them than the screw-in carts.
Some of these things may seem silly, they aren't.. especially when a label has fallen off of a "jug of something" that was under the bench, in the back corner and is covered with an inch of dust.
Hope this is of some help..

[WayneCothran]

Thanks, XK120DHC, and zincplater for the info. XK120DHC and I must be on the same wavelength. That's exactly how my containers are labeled, secured, and within their own secondary containment. MSDS are handy, but not copies in multiple locations - that's a great idea and I'll rectify that. I know that anything can/will happen, but my shop is an all steel structure that's rather large and the plating chems are isolated from combustibles excepting their containers with ABC extinguishers nearby.

I finally found where I saw low temp and pressure are required for HCl concentrations greater than 40%. This was ripped from wikipedia and hasn't been verified: "Hydrochloric acid is produced in solutions up to 38% HCl (concentrated grade). Higher concentrations up to just over 40% are chemically possible, but the evaporation rate is then so high that storage and handling need extra precautions, such as pressure and low temperature. Bulk industrial-grade is therefore 30% to 34%, optimized for effective transport and limited product loss by HCl vapors. Solutions for household purposes in the US, mostly cleaning, are typically 10% to 12%, with strong recommendations to dilute before use."

The above was my source of confusion regarding HCl concentration.

Thanks again guys for the info. You've been a great help.
Wayne

[zincplater]

You're welcome.

[XK120DHC]

Glad to be able to help... Enough people sure helped me.. As you learn, your "payback" will be to help the next new guy..

[CarWiz]

I'll just add this: Don't store your HCL jug near any metal that you care about. The plastic jugs will weep clorine gas after a while and cause rusting of bare steel and iron.