In recent blogs, we’ve described metalworking fluid (MWF) as being like a lever. It costs little by itself but can move your total costs up or down significantly. A fluid that fails will not only waste your fluid investment, but result in decreased efficiencies, scrapping, reworking, poor quality parts, and costs related to poor operator acceptance and/or health problems.
Let’s take the opportunity to examine some reasons fluids fail and how to address them.
Tramp oil contamination
Numerous problems can result when foreign substances contaminate your MWF. Tramp oils can increase (or create) smoking and misting, compromise filter effectiveness, increase foaming and dermatitis, or decrease the fluid’s ability to cool and prevent corrosion.
Tramp oils are often from the machine itself, such as hydraulic fluid or way lubes. Some have remained on the workpiece from earlier in the manufacturing process. Apart from vigilance to keep them out of the MWF, the best way to deal with tramp oils is to select a fluid that naturally rejects them. This will usually mean either a synthetic or an advanced-formula semi-synthetic.
This phenomenon can interfere with work as foam obscures the workpiece and the fluid fails to cool or lubricate effectively at the point of contact. It can also lead to shorter pump life due to cavitation. Lastly, it causes increased fluid loss. This all raises maintenance, rework and fluid expenses.
Again, dealing with this issue can come down to selecting the right MWF. Synthetics tend to have low foaming characteristics, as do the newest semi-synthetics. If you’re using an older generation MWF fluid, you’ll need to monitor a number of factors, including water hardness, fluid depletion, temperature, pressure and flow rate. Be sure to trial any fluid before implementing it shopwide, and test samples frequently.
Concentration and mix
Maintaining the mix in a water-based MWF can be a challenge of its own. Too much water can lead to problems ranging from biological contamination to increased corrosion to lack of lubricity. Having too little water can lead to ineffective cooling and affect the performance of some additives.
No MWF mix is truly fill and forget, and as work goes on each day evaporation, oil being carried away with the finished piece, and additives being consumed as they do their jobs will reduce the amount of fluid in your reservoirs by as much as 10% and subtly change the mix itself. To avoid failure with all but the most advanced fluids, you’ll need to monitor the performance and makeup of your fluid and regularly add a “makeup mix” to keep it in top condition.
Bacteria and fungi growth can do far more than produce unpleasant odors. For example, fungi can irritate operators’ skin. Bacteria can indirectly cause corrosion by consuming the anti-corrosion additives in fluid, decreasing pH, or cause fluid breakdown by consuming the emulsifying agents. They find plenty to eat in the machining environment, since most additives contain nitrogen or sulfates, metal swarf often contains sulfur compounds, and water supplies derived from reservoirs or artesian wells often contain magnesium or calcium sulfate. This not only provides them a meal, but results in Monday morning rotten egg odor.
Preventing this problem requires careful attention to the dissolved oxygen content of your mix and maintaining proper levels of biocide. Additionally, ensure your machines stay as clean as possible and fluid circulates freely. Using a state-of-the-art biostable semi-synthetic can also ensure your fluid contains few dinner guests and is therefore longer-lasting.
Nearly every metal humans work with is trying to return to its natural state or some other useless form, and there are plenty of forces (from bacteria to stray electrical current) trying to help it along.
To prevent corrosion, make sure your mixture is as rich as the manufacturer recommends; more water usually means more corrosion and an overly diluted mix also has a lower concentration of anti-corrosion additives. Ensure the water has chloride levels lower than 100 ppm and sulfate levels lower than 200, as high concentrations of these compounds can promote corrosion either directly or by changes in conductivity. The use of high quality, low conductivity water treated through reverse osmosis or ion exchange is recommended to extend the life of metalworking fluids, reduce corrosion and deposits. Lastly, choose a fluid with anti-corrosion properties tailored to the metals in use in your machinery and workpieces, and evaluate its performance in a trial before using it shopwide.
While all of these problems can be conquered with diligence and close monitoring, the best solution is to use fluids that incorporate the latest chemical engineering and are specifically formulated for your needs.