The role coolants play in CNC machining cannot be overemphasized. They maintain optimal machine performance by preventing overheating, ensuring proper lubrication, and promoting chip removal. However, coolants are prone to contamination over time. Tramp oil, bacteria and metal particles compromise their integrity and how well they function. If left unchecked, these contaminants cause tool wear and pose risk to the operators.
Regular testing of CNC coolants is essential to identify potential issues before they become major problems. This article will explain why testing for contamination in CNC coolants is important and the best ways to go about it.
Why Is Testing for Contamination Important in CNC?
CNC machining relies heavily on coolants for lubrication and proper heat dissipation. However, these coolants become contaminated over time, which compromises their function. There are many reasons why testing for contaminated coolants is important in CNC. They include
- Contaminated coolants accelerate tool wear and reduce cutting accuracy. The cutting tools dull faster and will need to be replaced.
- Coolant contamination leads to surface finish issues and dimensional inaccuracies.
- The acidic contaminants in the coolant system will corrode the machine components. Particulates clog the system and damage pumps and nozzles.
- Contaminated coolants can cause skin irritation and respiratory issues.
- Furthermore, contamination increases operating costs due to increased energy requirements and downtime.
How Can You Identify Signs of CNC Coolant Contamination?
The presence of contaminants in the CNC coolant system usually produces visible changes that are easily recognizable. When carrying out milling and turning operations, you should always look for these signs and address them early.
Visual Changes
Most of the time, you will notice visible signs of coolant contamination before anything else. They indicate various types of issues. Contaminated coolants have different colors, from milky and cloudy to green or yellow tint. You may also see a shiny, oily film on the coolant surface. Additionally, foam and sediments can form in the coolant tank.
Foul Odors
Contaminated coolants usually give off foul odors that indicate microbial growth. A rotten egg-like smell signals the presence of anaerobic bacteria living in low-oxygen conditions. Furthermore, a sour and musty odor shows fungal and aerobic bacteria growth within the system. You can also get a sharp chemical odor, indicating coolant degradation or an imbalance in the chemical composition. These odors are unpleasant and negatively impact the working environment.
Skin or Respiratory Irritation
Regular exposure to contaminated coolants leads to skin and respiratory issues. Tramp oils and metal particles lead to skin irritation when someone is in direct contact. Additionally, contamination with microorganisms causes itching and redness. Furthermore, fumes from contaminated coolants can trigger an allergic reaction. The individual may experience coughing and shortness of breath.
Poor Machining Performance
Contaminated coolant directly affects machining performance. Poor coolant quality reduces the lubricating and heat dissipation properties. This causes overheating of the cutting tool as it shapes the workpiece. Inconsistent coolant flow leads to chatter and visible tool marks. The surface of the machined parts will be rough and unappealing. All these reduce machining performance and increase scrap rate.
Frequent Coolant Filter Clogging
Another sign of coolant contamination is the frequent changing of clogged filters. Coolant filters help to remove contaminants like dirt, sludge, and metal particles. Additionally, biofilms and microbial colonies are usually found on these filters. The increased need to replace coolant filters shows a heightened level of contamination. The contaminants accumulate at a fast rate and can disrupt workflow.
Increased Coolant Consumption
You will also experience increased coolant consumption in cases of heavy contamination. The presence of unwanted bodies makes the coolant degrade faster. For this reason, it requires more frequent replacements or top-ups. Some contaminants destabilize coolant chemistry, leading to faster evaporation and loss of performance. Furthermore, the contaminated coolant may be diluted. You will need more volume for the same function.
Best Methods to Test CNC Coolants for Contamination
CNC coolants can become contaminated with tramp oils, microbial growth, and particulate matter. Knowing the signs may not be sufficient for accurate detection. As a CNC machinist, you should be familiar with the following methods to test coolants for contamination.
pH Testing
You should always check for the acidity and alkalinity level of the CNC coolant before concluding if it is contaminated or not. Most CNC coolants are alkaline, with pH ranging between 8.5 and 9.5. Any deviation from this will affect performance. To check the pH of the fluid, dip the strip or meter probe into the sample and wait for a few seconds to get the reading. Low pH level indicates acidity due to bacterial growth and coolant degradation. On the other hand, high readings result from chemical reactions with contaminants.
Coolant Concentration Testing
The concentration of coolant directly impacts its cooling and lubrication abilities. Both under and over-dilution can cause performance issues. You should use a refractometer to perform coolant concentration testing. To go about this, calibrate the refractometer with distilled water. After that, place a drop of the coolant on the device lens. Look through the refractometer and record the reading. Compare the measured concentration to the manufacturer’s specifications.
Microbial Testing
You can also test the CNC coolant for the presence of microbial growth. Bacteria, fungi, and mold are the leading cause of coolant degradation. It is important to detect and address them early to prevent system breakdown. There are different ways to perform microbial testing. The general one involves submerging a dip slide into the coolant tank and incubating for 24-48 hours. You then compare the slide’s growth to the reference chart included in the test kit. If the contamination is severe, consider sending samples to a standard lab for detailed analysis.
Tramp Oil Testing
Tramp oil is a common contaminant found in CNC coolants. It originates from hydraulic fluids, lubricants and machine leaks. The presence of tramp oils reduces system efficiency and promotes microbial growth. You can perform tramp oil testing by visual observation. Check the coolant surface and look out for a shiny oil film floating. You can also use a skimmer to separate the tramp oil to assess the level of contamination. It is important to identify and fix leaks to prevent further contamination.
Filtration and Sedimentation Analysis
You can also analyze particulates such as metal chips and solid dirt. They accumulate in CNC coolants over time and reduce how well they function. For the sedimentation test, a sample will be collected in a transparent container. Allow it to settle for a pre-determined time and inspect the bottom for sediment. Furthermore, you can also carry out filtration analysis. Pass a sample through a filter paper. Examine the residue left on the paper. High sediment levels and excessive particles indicate contamination.
Conclusion
You should routinely test CNC coolants as part of the machine maintenance. This action is not just a preventive measure. It is critical in maintaining operational efficiency and ensuring workplace safety. The presence of contaminants such as microbial growth and tramp oil compromise coolant performance and lead to frequent downtime. You can detect and correct issues on time by incorporating effective testing measures to check for pH, concentration, and microbial growth.
