Coolant longevity is generally controlled by two primary factors:
1) Choosing the right coolant for the type of metal you are machining; and
2) Following best practices in coolant maintenance.
Choosing the Right Coolant
Some machine shops buy a certain coolant because the manufacturer offers the absolute lowest price per gallon. Others buy a coolant because the brand is advertised as extending tool and/or sump life. And some coolant is chosen only after a salesman has looked at your operation, assessed your needs, and made an appropriate recommendation.
How do you buy coolant? A company that has a central coolant system made of untreated concrete buried eight feet underground will not be buying a coolant that is designed to last a year or more because this “high-end” coolant is not the right coolant for the application. Even a “super” coolant would have a difficult time in this environment.
Your coolant sales professional should be able to recommend the best coolant for your operation. Choices are made based on the type of metal you machine and your specific operations. In general, synthetic coolants have a longer sump life than soluble oils, but synthetics have more limiting tool life properties. Semi-synthetics have very good operator acceptance, but some of the newer semis are high priced.
Coolant Maintenance
How well coolant is maintained is a key to the success of your coolant longevity. Cleanliness does matter! Removing tramp oil, maintaining coolant concentration at the recommended level, and improving filtration will help an average coolant to perform better. And it will help superior coolants last even longer than you thought possible. Many coolants on the market today are capable of lasting a year or more in your individual sumps as well as central systems. A two-year life expectancy for central systems is not unusual.
“Is My Coolant Wearing Out?” Maintenance
Yes and No! How’s that for an answer that covers all the bases? The truth is your coolant does wear out. You simply may not notice it because you are regularly adding fresh coolant to the sump. Some large systems will lose 10 percent to 15 percent of their total volume in water evaporation just setting over a weekend.
As your coolant ages, the rust preventive part of the coolant plates-out on freshly machined parts, doing its job to eliminate rust. However, as it does its job, the level of rust preventive remaining in the coolant is reduced.
Similarly, the biocide, another component of your coolant, is used up as it kills bacteria. The same is true for fungicide which is used up preventing mold and fungus growth. We usually don’t notice these subtle changes in the coolant because every day or two we add some fresh coolant to the sump with the makeup water.
There have been many advances in coolant technology over the years that allow manufacturers of metalworking fluids to provide coolants that have greatly extended sump lives, improved tool life, and achieved greater operator acceptance. Concern arises when the coolant has been in a system for a long time and proper filtration is lacking. If you pay a premium price for a high-end coolant made to last a year or more but you don’t maintain it, you’ll likely be pouring your dollars down the drain. The manufacturer of your coolant has done everything it can to provide the best, longest lasting product. But to make it last, you have to maintain it.
As soon as you start using fresh coolant, several things begin to occur. Water hardness in the form of minerals slowly increases in the coolant system along with metal fines that are too small to be filtered out. The coolant begins to deteriorate due to chemical contamination from outside sources such as coatings on castings, cleaners used by operators, and just plain dirt. In time, even the best coolants need to be changed.
You can usually tell when the coolant is past its useful life because problems begin to occur. If you purchased a coolant and expected it to last a year and it’s only been 11 months, perhaps your level of contamination was greater than you predicted.
There was a time when I was asked by a customer, “Why is my coolant usage up 25 percent?”
My response: “How is your production?”
“Why, we’re up 30 percent,” he said, answering his own question.
Well that’s the way it works for coolant life. If, in the past, you maintained your coolant well and you continue the same good practices and now your coolant life is a little shorter than usual, perhaps your production has been up and you’ve put more stress on the coolant.
What is the Best Way to Clean a Coolant System?
I usually answer this question by asking, “How much time do you have?” Production downtime costs money and unless you’re not using the machine, time is always an important part of the equation. Here is our:
Clean-Out Procedure for Individual Coolant Sumps with Central Systems
1. Remove all old coolant from the sump.
2. Remove metal fines and sludge.
3. Fill sump with enough water to circulate through pump.
4. Add 1.0 percent to 1.5 percent machine cleaner to the water in the sump.
5. If possible, add one-quart biocide for each 100 gallons of water. (DO NOT USE BLEACH)
6. Circulate for 2-4 hours through all coolant lines and nozzles.
7. Rinse off machine surfaces and thoroughly clean.
8. Pump out cleaner/biocide mixture and dispose of properly.
9. Remove any residual dirt, oil, etc.
10. Add water to the sump until it is about half full.
11. Add water and coolant together until the sump is completely full.
12. Check coolant concentration with a refractometer and adjust if necessary.
You might find that this procedure will take more time than you have. A shorter, albeit less thorough, approach is possible. Consider these steps:
Clean-Out Procedure for Individual Coolant Sumps & Central Systems (in a Hurry)
Add 1.0 percent to 2.0 percent of a mild machine cleaner to the existing dirty coolant. A mild biocide at one-quart per 100 gallons is also a good idea at this point. Circulate through hoses and pumps for several hours if possible. This will loosen some of the more difficult deposits of metal fines and dirt. Remove the old coolant and rinse down the system. Remove that small portion of water used for rinsing. Follow steps 10, 11, and 12 from the previous listing. Your system will not be as clean, but the time you save will get you back in production sooner.
Summary
A good coolant that is designed to last a long time in your system will last a long time if you provide adequate filtration and take care to remove contaminates. When it is time to change your coolant it’s a good idea to clean out the system properly. Then, your fresh coolant charge will last even longer than before.
Of course, the information provided here is general in nature and is best used as a guideline or starting point. If you have specific questions regarding coolant longevity, ask a qualified metalworking fluids provider. Maybe you can even play a round of “Stump the Coolant Guy!”
