Without a doubt, the most common problem operators have with water soluble coolant for surface grinding is one of concentration. Not that the injection mold making toolmakers have ADHD, but rather, it is a case of too little or too much concentrate in the coolant mixture.
The proper mixing of water soluble coolants is generally overlooked, with the subsequent poor performance of the cutting or grinding. Rust, bad odors, possible pitting of the metal and poor finishes are all indicators of the wrong level of concentrate.
Every manufacturer has specific mixing ratios listed for every type of coolant and every type of machining application. It is critical to follow these recommendations, as they were developed after extensive testing prior to marketing.
Typically precision surface grinding coolant mixing is done manually with little regard for the accuracy of the mixture. Because the results are not so readily apparent, this problems tends to persist and go undetected.
It is not enough to just guess and add coolant randomly. Take the time to figure this out and you will get better results.
Precision surface grinding needs the right coolant mixture
Most CNC machining or surface grinding operations require a “topping off” of the coolant due to evaporation or the fluid being carried off by chips or parts. Air hoses are notorious for slowly decreasing the fluid level during the blowing off cleaning operation.
This “topping off”, or “makeup”coolant should be less concentrated than the initial fluid. This helps maintain the proper concentration level with respect to the loss of water from evaporation and being carried off.
Symptoms of the wrong coolant concentration
- Poor milling or grinding finishes
- Shortened tool life of end mills, drills and carbide inserts
- Glazing or loading of grinding wheels
- Corrosion to the machine tool
- Foul odors from coolant
- Wasted money due to over concentrated mixtures
- Shortened sump pump life
Ooh ooh that smell! What is that nasty odor and where is it coming from? How can I get rid of this?
As an apprentice, my first job was to clean out a rancid sump pump from a very old milling machine. I nearly vomited at the horrendous odor, but this was my initiation I suppose. When I was finished, I made sure to ask and insist that somebody find out how to prevent this from happening again!
The reason some CNC machine coolants have that nasty sulfur odor is due to anaerobic bacteria action. That rotten egg smell can fill an entire room rather quickly and, in some cases, cause workers to become nauseous.
This bacteria must be eliminated before that odor will disappear. It does little or no good to try and mask it with a pleasant smelling additive, though some companies try this. The bacteria is alive, growing and eliminating nasty things into the coolant, thus the noxious odor.
How to get rid of CNC machine coolant odors
- Good housekeeping is essential
- Maintain correct coolant concentration levels
- Avoid or prevent contamination
- Keep the filters clean and do not allow coolant to accumulate in any areas
- Periodically clean the sump pump and entire machine
How to mix water soluble coolants
Many, if not most, small tool-and-die, mold making or other precision machine shops mix their coolant manually. This can work if the proper amounts are mixed and correct mixing procedures are followed. Like any industrial supplies, check with the manufacturer to learn exactly how to mix the concentrate.
Check the concentration level with a refractometer to be sure. This is easily done and the refractometer is not expensive.
On the other hand, leaving the coolant to an apprentice or unskilled worker is inviting problems. Unless the person mixing is trained properly, it is almost certain to be done wrong. Generally, the oil should be added last, after the water is added. Also, it is important to use chemically pure water, otherwise the PH level could be off or contaminates could enter the coolant.