Brazing: Removing Oil and Grease
Brazing: Cleaning Off Oil and Grease
I had two separate calls today. Both of them involved brazing problems in which cleanliness was an issue. In both cases they were using a solvent as a degreaser.
The tool industry is full of people who work with machinery as though they were born with a wrench in there hand so I’m going to try and construct an analogy explaining grease removal in terms of tools.
Suppose you’re working on a machine and you ask me to hand you a wrench. If you have a set of 7 or 9 or 11 wrenches than the chances of me handing you the correct wrench just on the information given is maybe 1 in 7, 1 in 9 or 1 in 11.
There are different kinds of oils and greases. There are lots of ways to classify them but they are generally put into something like five or seven different classes.
So the oil and grease you want to clean off is like the nut you want to turn. Selecting a solvent to do the cleaning is like selecting the right wrench.
Using a strong caustic solution, such as Easy Off oven cleaner, is like using a crescent wrench or a pair of vise grips to turn the nut. It is not the ideal tool but it is sure to get the job done no matter what size nut you have.
Solvents do not remove oil and grease. Solvents just dilute it. If you put a shot of whiskey in a glass, you can add as much water as you want to and dilute the whiskey but there will still be whiskey. Only the concentration will change.
If you put a little oil in the bottom of the bowl and add water to it, then the oil will float on top of the water. Bowls typically get wider as they get taller, so the more water you added the farther out the oil will spread and the thinner the layer will be.
Caustic solutions saponify oils and greases. Saponify means they actually break down the oils and greases into soap or soap like components. Two things are important here. The oils and greases are actually destroyed. The oils and greases are broken down into components that are easy to rinse off with plain water.
Now that we have covered all that, I do have to admit that every day throughout industry people successfully clean with solvents. The above is important because a cleaning problem from a process using solvents may be solved by switching to a caustic-based solution. I mentioned easy off oven cleaner because it is easy to use, readily available, everybody is aware that it could be dangerous and has special rinsing agents that make it easy to remove. We did a test on different cleaners for saw blades and the most economical and most effective was a gallon jug of barbecue grill cleaner from a local janitorial supply. You can also use straight lye but straight lye is typically straight sodium hydroxide were straight caustic soda. A commercially prepared cleaner will typically have additives to make it more effective and other additives to make it easier to remove by rinsing.
Tags: brazed tools
2 Responses to “Brazing: Removing Oil and Grease”
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We will run into an issue after soaking our new saw plates in a mix of sodium hydroxide and water to breakdown the oil the new plates are coated with, then rinsing them with clean water the plates will start to form surface rust when drying. The rust will form in the pockets also, does the industry have a solution to stop the plates from rusting? Normally we are prepping the plates for tipping right after the rinse, but there are times when they will sit and while air drying the rust forms. Basically we are toying with the idea of adding a rust inhibitor to the clean water rinse and wondering if it is possible that the added inhibitor would affect the flux and braze with the plates are tipped.
Flash Rust
Flash Rust is rust that happens really fast. Sometimes you can even watch it happen. One cause of flash rust on saw blades occurs in window plants. The application is cutting vinyl in a window plant. PVC is vinyl is Polyvinyl chloride. The out-gassing of chlorine forms salts and can cause flash rust.
Flash rust is caused by chlorides and other soluble salts (such as sulfates and nitrates,) located on the surface of steel. Phosphorus especially as iron phosphate can be a real problem. If these contaminants are present and water is added a bloom of flash rust quickly appears.
Soluble salts initiate and accelerate corrosion of steel, and become deeply embedded within the corrosion product. The salts stimulate corrosion through an osmotic action by pulling moisture from the air and through any protective coatings. It is in this form that they achieve their highest level of chemical stability.
All liquid coatings are permeable, thereby allowing the salt on a substrate to “pull” moisture through the coating, causing active corrosion of the substrate long before the protective coating fails. This is commonly seen on structures or objects with blistered paint, which when removed, rust is seen on the surface. In nearly all cases, the coating was applied over salts.
Also, when the moisture is combined with chlorides, a mild hydrochloric acid is often formed, causing degradation of the substrate.
Salts left on a surface prior to the application of protective coatings can be the cause of several occurrences.
Prevention of Flash Rust
To prevent flash rust, the soluble salt contaminants must be removed from the steel.
It is nearly impossible to totally remove all contaminants from surfaces; there are usually some very low levels of salt contaminants remaining after decontamination. There are chemical soluble salt removers that may be added to aid in the removal of soluble salts. They are typically a liquid, organic, non-hazardous and biodegradable and are designed to solubilize both chlorides and sulfates. The soluble salt remover must come in contact with salt ions in order to solubilize them, therefore, any barrier, such as rust, must be removed.
To protect against flash rusting, a small amount of fluid concentrate (0.5% to 1.0%) should be added to the rinse water. This is done to prevent any flash rust.
This gentleman is an expert on flash rust and his company makes chemicals to prevent it.
James Ueberfluss
Applications Research Chemist
WPC Technologies, Inc.
Milwaukee, WI 53204
Tell: 414-225-2400
E-mail: jueberfluss@wpctech.com