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topic 41698

How to prevent rust after removing oil?

A discussion started in 2006 but continuing through 2019


Q. Dear All,

I am a quality manager working for a plant that is producing building hardware components. We are importing metal parts from abroad and painting (wet paint) them. As the process is the application of wet paint by spray guns we have no surface cleaning and phosphate line like in a powder coating establishment. The surface cleaning (removing oil from the surface) is done separately in an industrial washing machine. While the parts are waiting for painting they rust. To prevent rusting we have to paint them immediately which is not always possible or put the part in a solvent in order to avoid the effect of humid atmosphere. Is there a simpler method or protective product I can use after washing and not have to clean before painting?


security technology - Turkei


A. The simplest way in my opinion: heat the parts. They will keep rust free until they cool down giving you a little more time to process. Another alternative would be to apply a primer designed to be used over rust before the final paint.

Guillermo Marrufo
Monterrey, NL, Mexico


A. Dear Tolga,

This is not a big problem. Better you use non-caustic type hot degreasing agent and can use passivation just after degreasing to protect metal from further oxidation or corrosion.

Navin Maheshwari
- New Delhi, India


A. I have found the use of an amine is very good in this type of application. It gives temporary flash-rust protection and should not affect the subsequent paint process as it is volatile. This sort of additive could be put in your aqueous wash system.

John Neale
- Halesowen, West Midlands, UK


A. Dear Tolga
when you make chemical degreasing for the steel you mainly remove the oils layer from the steel surface and it is become active so when it is exposed to the atmospheric oxygen it will directly make corrosion to avoid this problem you should two methods first your chemical degreasing suppler must be add some materials e.g.sodium nitrite to work as anti-rust or you should make anti- rust layer in the steel surface after degreasing stage.

Ali Gomaa
- Cairo, Egypt

Holding work in process for cleaning check without corrosion

February 27, 2019

Q. To combat different incoming part conditions of product cleanliness our facility performs in-process clean checks.
The materials we plate on are primarily red metals and, when QA is behind, some loads have prolonged sit times in water rinses which is causing heavy oxidation.

In a sense we're creating a larger issue than what has been received.

Is there a "safe" solution such as sodium bicarb that we can utilize without causing additional issues? I had used this for Aluminium prior to Zincating.

Joe Weizel
- Tempe, Arizona United States

March 1, 2019

? Hello Joe, you say you plate on "red metals" could you be more specific? Are the parts standing in a city water rinse or a DI rinse? If we know the exact metal substrates you plate on, what your final plate is, we can better help you.

Mark Baker
Electronic Plating - Phoenix, Arizona USA

March 2019

A. Hi Mark. I'm guessing he means metals subject to red rust, i.e., steel & iron parts. I'm confident that using a mildly alkaline staging tank, viz., the overflow from the first rinse after the electrocleaning tank, the problem will be greatly reduced and possibly eliminated.


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Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

sidebar2 March 1, 2019

thumbs up sign  Hello Ted, thank you for the clarification. I never heard the term "red metals" as a substrate before. Thank you also for the great work you do!

Mark Baker
Electronic Plating - Phoenix, Arizona USA

March 2019

A. Hi Mark. Thanks for the compliment; I've not heard the term either, I'm just guessing :-)

Readers: please remember that running this site is my delightful job, and I'm earning a pleasant semi-retirement living by doing it, so I'm not owed anything ... but our frequent responders like Mark are helping people without any compensation, so please try to find time to express your thanks when they help you!
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Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

March 4, 2019

Q. Mark, what I meant by "Red Metals" is Copper and Cu alloys, including Brass, BeCu, C97, and Cu. We would be sitting in a semi-clean counterflow rinse of City water and final plating including underplates are Au/Ni/Cu.

Joe Weizel [returning]
- Temp, Arizona USA

March 13, 2019

A. Hello Joe, sorry it took so long to get back to you. There are 2 things you can try. Using a dilute acid dip tank such as citric or sulphuric. The other option would be a clean DI rinse holding tank
I worked for a shop in Tempe, so I am well aware of the city water quality and it's not the best. Just be sure if the acids you choose are compatible with the different substrates you work with. A lab set up with samples would be best as a pilot.

Mark Baker
Electronics plating - Winston Salem North Carolina

September 3, 2019

Q. The DM water pH is 6.0 now; I am using it for cleaning or oil degreasing purpose in heat treatment shop. I am adding alkaline LT-44 at the concentration of 4% and maintaining 10.5 pH, but after 4/5 hrs of cleaning the part is getting rust.
So please anybody give me a solution and I am applying rust prevention dw2 on it immediately, but no use, it will get rust.

kiran gowda
Shree shakthi heat treaters - Bangalore, Karnataka, INDIA

September 2019

A. Hi Kiran. I don't know what "LT-44" is; the only thing that came up quickly on a Google search is "LT-44 acid tile cleaner", which sounds completely inappropriate. Please find a metal finishing chemicals distributor in your area, and find an appropriate cleaning solution. Good luck!


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Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

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