Executive Summary
Many TLT readers identify microbial growth as the most persistent contamination challenge in metalworking fluid (MWF) management, consistently noting that that biocide additions are often a short-term fix, with system cleaning and fluid replacement the only reliable long-term resolution. Beyond contamination control, operator health and safety leads as the most influential selection factor beyond primary performance and cost, followed closely by fluid longevity and supplier technical support. Effective MWF management depends less on any single product choice and more on the quality of monitoring practices, supplier partnership and direct collaboration with the operators and engineers working with these systems daily.

Q.1. Describe the most persistent or challenging type of contamination (e.g., tramp oil, metallic fines, microbial growth, water quality issues) you encounter when managing MWFs, and briefly outline the methods you find most effective for controlling it on a practical basis.

Biocides that are needed for water-based systems.

Metallic fines are inevitable, as they are byproducts of the process itself. Filtration system keeps the fines content low. Skimming the coolant also removes a significant fines amount thanks to its affinity with the released oil.

Foam with distilled water.

Microbial growth and waste disposal.

Microbial growth in systems can be persistent and difficult to control. Factors such as tramp oil contamination can exacerbate the issue by providing a nutrient source, while contamination may remain entrenched in equipment even when lab data suggests acceptable fluid health. A common initial response is the addition of biocides, which carry potential health risks for employees. Without effective monitoring, systems may be repeatedly dosed while the underlying problem persists unresolved.

Microbial growth is in my opinion the most challenging contamination. The best response is to empty and clean the system; adding acticides is most of the time a short time solution.
 
In water-based MWFs, microbial contamination. Combat it with good fluid monitoring/maintenance (requires working directly with operators and engineers to implement), properly balanced formulations with antimicrobial components (biocides/fungicides/etc.) and biostable components (additives that don’t contribute as a food source to microbes).

Cross contamination with other in-house products. Cleaners and waste streams. Supplier support in identifying root cause and source of contaminant. Supplier knowledge of operations and processes are critical. In-house expertise in MWF maintenance and avoiding contamination is limited at best.

We have issues with older machines leaking hydraulic and spindle oil into sumps resulting in increased microbial growth and reduced sump life, and trouble getting machines cleaned out properly which results in swarf build up issues and microbial issues also.

Water quality issues. The good news is that when a customer’s water quality is poor, they usually know it. The multivalent cationics (read metals) are the real issue, as they are powerful emulsion breakers. The only long-term solution is to use non-ionic emulsifiers. Many MWF producers claim that elevating chlorides come from incoming water. This is false; although elevating chlorides are always a problem, their source is from the MWFs themselves.

In our experience the most persistent type of contamination when managing MWFs are water quality issues and metallic fines. The water hardness determines the foam behavior of many MWF emulsions. If the water is soft, below 140 ppm, increased foaming may occur. If the water is very hard, approximately 350 ppm, it may have negative effects such as formation of calcium soaps, weakened corrosion protection and reduced emulsion stability. Metallic fines is another problem that present the MWF in the machines. Without proper MWF filtration, these contaminants can cause several operational problems such as clogged or damaged spray nozzles, faster depletion of corrosion-inhibiting chemistry in the fluid, surface damage on precision components with tight tolerances, increased corrosion risk due to longer wetness time and galvanic interactions and as contamination builds and the MWF becomes less effective at protecting parts and maintaining process stability.

Microorganisms. Work with high pH level.

Which type of contamination generally requires the most effort or resources to manage in your MWF systems?
Tramp oil (hydraulic/way/spindle leakage)           8%
Metallic fines/swarf                 8%
Microbial growth (bacteria/fungi)         56%
Water quality issues (hardness, chlorides, etc.)         20%
External contaminants (cleaners, process fluids, debris) 8%
Based on an informal poll sent to 15,000 TLT readers.
Metallic fine.

The contamination could be different if the metalworking oil is a synthetic oil or a hydrocarbon type. In a synthetic oil the contamination could be less microbial, again a hydrocarbon metal working and the source of contamination is due to quality water in the blend. I believe that we are using synthetic metalworking and we must be sure that the water is clean without bacteria, and the operators must have clean hands.
 
Microbial growth changing the fluid is one way to control microbial growth, but that can be very costly. Adding a bactericide to the MWF will help and is economical.

Metallic fines, daily removal to minimize anaerobic bacteria proliferation and to reduce corrosion ferrous especially in cast iron grinding (brownish rust colored coolant).

All the types of contamination mentioned require attention or treatment through physical and chemical processes whereas when we talk about standards, we work upon specific one. The cases for biodegradable lubrication may be streamlined and therefore be bypassed. For practical methods changes can be vice-versa.

How frequently does your facility typically take significant action specifically to address or remove MWF contamination (beyond routine top-offs and standard machine filtration)?
Continuously (e.g., tramp oil separators always operating) 16%
Daily                           8%
Weekly                                   28%
Monthly                                  0%
Only when specific problems (odor, performance dip) arise 32%
Rarely or never                           16%
Based on an informal poll sent to 15,000 TLT readers.
Microbial growth.

Microbial contamination and water quality are the biggest challenges. Microbial contamination is primarily due to strict regulations governing raw materials (which increases the risk of resistance developing). In terms of water quality, the main concerns are the tendency to form foam (especially in new machine tools with high pressures and flow rates), the risk of corrosion (due to the introduction of salts such as chloride and sulfate) and emulsion stability (due to high salt content). Monitoring dip slides and pH levels for microbiological analysis and conductivity measurements related to water quality are the most effective methods. When it comes to water-related issues, determining water hardness and chloride/sulfate levels can also be helpful; however, this is only practical in a laboratory setting. 

Micro growth and tramp oil contaminations. Using skimmers to eliminate tramp oils and weekly check of bacteria and fungi and control the microbial growth.

Q.2. When evaluating or selecting new MWFs, what are the most important factors your organization considers beyond primary performance (lubricity/cooling) and initial purchase cost (e.g., operator health and safety profile, environmental impact/disposability, fluid longevity/stability, ease of maintenance)?

Environmental, health and safety (EHS), performance, operations flexibility considerations.

The fluid properties have to be detectable by the regular lab tests.

Operator health and safety, and ease of maintenance.

When selecting a new MWF, which factor besides primary performance and initial cost typically carries the most weight in the final decision at your organization?
Operator health and safety profile          28%
Environmental impact/disposal considerations 12%
Expected fluid longevity/sump life          24%
Ease of maintenance/monitoring simplicity 8%
Compatibility with diverse materials/operations 8%
Supplier technical support and service          20%
Based on an informal poll sent to 15,000 TLT readers.

Hazards, longevity, service, supplier’s willingness to take samples and help manage the system.

Additional requirements include conducting supplier health assessments to evaluate their ability to provide technical support, maintain multiple blending locations and support a global footprint. Each manufacturing facility must also assess the product safety profile and environmental impact specific to its location. Compatibility with diverse materials and processes is a must.

Health and safety profile.
 
We don’t purchase MWFs. We produce them, so I will talk to what we hear most from our customers. The number one priority to any customer is making the part. If the fluid can’t make the part (doesn’t have the right balance of lubricity, extreme pressure performance and cooling properties), then it doesn’t matter how sustainable or safe the product is. Beyond making the part, the total cost to produce the part is a big consideration. Looking into the total cost per part takes into account the performance, cost of the fluid, in-use concentrations, die-life/downtime, scrap, etc. The second factor is typically the health and safety of their workforce. While these things are the most important factors, environmental impact and waste management are also essential in product selection.

Fluid longevity and low to zero maintenance. There is little interest in dedicating maintenance personnel to MWF systems.

Biostability (for increased sump life) and operator safety. Ease of treatability is another for wastewater treatment.

One the most important factors is work with the product stewardship, stability and ease to maintenance.

pH stability, multimetal compatibility.
 
Lubricity/cooling.

First the MWFs must have the minimum environmental impact, and an excellent fluency in order to provide good cooling to the workpiece and the lathe tool, and the operators must use gloves to protect their hands.

Environmental impact.

What is generally the single biggest negative consequence your operation experiences as a direct result of MWF contamination?
Reduced fluid life/increased disposal frequency and cost          16%
Increased maintenance labor/costs (cleaning, additive adjustments) 16%
Poor part quality/surface finish issues/staining                  20%
Noticeable reduction in tool life                          12%
Operator health/safety concerns (odor, dermatitis)           0%
Unscheduled machine downtime                         24%
Minimal negative consequences observed                           12%
Based on an informal poll sent to 15,000 TLT readers.

Operator health.

Ease of disposal and maintenance and material compatibility.

Any local distributor available.

The cases for biodegradable lubrication will be of much more ease and impacted.

Biostability.

It varies greatly depending on the sectors to which parts are supplied. In fields such as medical technology, cleanability and residue formation are critical factors in meeting the specific requirements of those industries. In other sectors, certifications are required (e.g., aviation). Compatibility with materials, particularly aluminum and its alloys, is also an important criterion. However, due to reporting requirements to government agencies (particularly in Europe), health and environmental protection have also become increasingly important.

Lubricity and longevity are the most important factors to select new products.
Editor’s Note: Sounding Board is based on an informal poll sent to 15,000 TLT readers. Views expressed are those of the respondents and do not reflect the opinions of the Society of Tribologists and Lubrication Engineers. STLE does not vouch for the technical accuracy of opinions expressed in Sounding Board, nor does inclusion of a comment represent an endorsement of the technology by STLE.