The weekend was great; your favorite team won the big game. You even wake up Monday morning almost happy to get to work so you can talk about the game with your friends. You’re half way through your first cup of coffee and turn on the coolant sump. Then, before you know it, whoa—Does that coolant stink, or what?
Getting grossed-out by Monday morning coolant odor is not a good way to start a new week! The good news is the coolant you use for machining doesn’t have to smell bad.
Whether you’re using full synthetic coolant, semi-synthetic, or water-soluble oil, when the coolant is fresh in your machine it should not smell bad. Occasionally, machine operators may object to the “chemical” smell from some of the coolants on the market. To make the coolant have less of a chemical smell fragrances are often added. The bottom line is fresh clean coolant should not have a bad odor.
So where does the smell come from? The plain fact is coolants support bacteria. Any self-respecting bacterium that lives up to its name, gives off a nasty, foul odor. Often the bacteria found in coolant are the same bacteria that grow on our skin. To combat the problem, coolant manufacturers use bacteria-killing biocides. Often, the level of biocide added to the coolant concentrate during manufacturing is low. This is because (in most cases) coolant is well maintained and high levels of biocide aren’t needed. Biocides are also expensive ingredients. So coolant-makers ask themselves, “why raise the cost of the product if we believe it will be well maintained?”
Now that we understand where the odors come from, let’s look at some ideas for preventing them.
1) Remove tramp oil. Tramp oil prevents water-soluble coolants from breathing or obtaining oxygen. When this occurs, bacteria that live and breed in the absence of oxygen (anaerobic bacteria) start to grow and multiply. Agitating (or stirring) the coolant aerates it and causes the anaerobic bacteria to die. That is why “Monday morning odor” usually only lasts a short time. The bacteria die off and the coolant smells a little better. Improving your tramp oil removal methods will help minimize odor problems.
2) Clean coolant lasts longer. Remember, the problem isn’t confined to tramp oil. Coolant can be contaminated by metal fines, other chemicals, cleaners, and residue from parts coming in for machining. Whatever steps you take to minimize these contaminants will help the coolant last longer and save you money.
3) Check coolant concentration. The proper mixture of coolant and water is dependent on the type of metal you are machining and the operation. Machining an aluminum alloy will require a stronger coolant solution than grinding cast iron. Usually, coolant is run at a concentration somewhere between 5 percent and 10 percent. When your coolant concentration is too high, you risk skin irritations. When the coolant concentration is too low, rust may occur. (We covered more on this issue in a previous article, Why do Parts Rust When the Coolant is Good?)
Lower coolant concentrations also mean lower biocide levels. So if the coolant has been in your sump for any length of time the biocide may already be depleted.
Check your coolant concentration with the aide of a refractometer. This inexpensive device will help you avoid the problems mentioned above by determining exactly what your coolant concentration is. Please remember that the reading on the refractometer is not always in direct percent. A 5 percent coolant solution will give you a refractometer reading anywhere from 1.5 to 5.5, depending on the type of coolant. The exact reading for the coolant you are using can be obtained from the literature your supplier provided or by checking the online chart here.
4) Aerate the coolant either over the weekend or on a continual basis. If anaerobic bacteria live and breed in the absence of oxygen, adding oxygen will eliminate or minimize bacteria growth. And when bacteria are gone, so are the odors! Aerate the coolant by adding a simple airline that pushes bubbles of air through the coolant. An inexpensive yet effective method is to purchase a small fish-tank aerator. Such units are usually less than $10. Another method is to turn on the coolant and let it circulate even if the machine is not scheduled for production. This is especially important during the summer months when warmer temperatures improve bacteria breeding conditions.
5) Change coolant on a regular basis. This doesn’t mean you have to change your coolant every month. Just as you replace a tool when it wears out, you should replace your coolant when it wears out. Think of it this way. If the coolant in a particular machine has been problem-free for nine months and suddenly you have odors, rust, or other trouble, you’ve discovered the “coolant life” for that machine is something less than nine months. Keep a record of cleaning and recharging dates for each machine. Doing so can help you schedule coolant changes before problems begin.
6) Finally, ask yourself, “Am I using the proper coolant for the job?”
Machining cast iron with water-soluble oil may create more odor problems than just the “Monday morning” type. Cast iron chips form neat little piles that become a productive breeding ground for bacteria. Some ingredients in water-soluble oils are an excellent food source for bacteria. The tightly packed chips act as an incubator and bacteria multiply quickly. Semi-synthetic or synthetic coolants work much better for machining cast iron. Water-soluble coolants are more suited to machining aluminum and steel alloys.
Summing it Up
The advice offered here for eliminating Monday morning coolant odors is the really the same advice I’d give for properly maintaining coolants. The odor just makes the issue more apparent. Talk to your coolant supplier about any problem you suspect may be coolant-related. Whether you have odor, rust, or dermatitis troubles your coolant supplier should be able to help you. The more experienced they are, the easier it will be for them to find a solution. By working closely with your coolant supplier on odor issues, it will make eau de la difference!
This article originally appeared in Shop Talk magazine in April of 2005. Shop Talk is published
by Magellan Publishing.
