Types of CNC Coolants: How to Choose One in Machining?

Machining coolants are in four major categories with their respective formulations. However, it would help to choose a coolant based on its efficiency and comprehensive performance, considering the material and machining process involved. Below are the common types of machine coolant.

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Synthetic Fluids

These coolants are the cleanest because they do not contain petroleum or mineral oil. Synthetic fluids comprise rust inhibitors and chemical lubricants that break down in water. These fluids are mixed with water to produce a metalworking fluid. Therefore, these CNC coolants possess high cooling capacity, corrosion prevention, easy maintenance, and lubricity.

Moreover, synthetic fluids are primarily employed in high-heat, high-velocity machining processes like surface grinding because of their excellent cooling capacity. Heavy-duty synthetic fluids are ideal for handling several machining operations.

Synthetics are categorized as simple and complex or emulsifiable synthetics depending on their composition. Simple synthetics or true solutions are commonly used for light-duty grinding. On the other hand, complex synthetic concentrates contain synthetic fluids suitable for moderate to heavy-duty machining procedures. More importantly, complex synthetic lubricants allow high speeds and feed in machining operations.

Pros

• Synthetic fluids exhibit high microbial control and excellent resistance to rancidity.
• These lubricants provide excellent resistance to corrosion and high cooling capability.
• They offer greater stability after mixing with water.
• Synthetics allow easy maintenance because they are clean and suitable for various machining operations.

Cons

• Machine fluids, such as lubricating oils, can contaminate synthetic fluids easily. Hence, you have to manage and maintain these fluids effectively.
• Synthetics generate fine mists or foam due to moderate to high agitation conditions, even though they are less vulnerable to issues related to oil-based fluids.

Semi-Synthetic Fluids

Semi-synthetics are a hybrid of synthetics (polymer) and soluble oils. These fluids contain about 2-30% of mineral or petroleum oil in a water-dilatable concentration. The remaining percentage of a semi-synthetic fluid consists of water and emulsifiers. Other elements in the concentrate include biocide additives, wetting agents, and corrosion inhibitors. They are commonly referred to as performed chemical emulsions because water is its primary ingredient and emulsifies with water during the concentrate&#;s production.

These semi-synthetic fluids are usually translucent. However, their properties can vary from slightly translucent to opaque. Additionally, many of these semi-synthetics have good heat sensitivity. Hence, semi-synthetic oil molecules surround the cutting tool, ensuring better lubricity.

Pros

• They are excellent lubricants for moderate to heavy-duty applications.
• Semi-synthetic fluids allow cutting at faster feed rates and higher speeds due to their remarkable wetting and cooling properties.
• These fluids possess low viscosity, allowing better settling and cleaning properties.

Cons

• Water hardness impairs the stability of semi-synthetic fluids causing hard water scum deposits.
• These fluids foam easily because their cleaning additives provide less lubrication than soluble oils.

Straight Oil

These oils are obtained from petroleum, mineral oil, animal, and other elements like compounds, vegetables, and fats. These straight oils sometimes contain other ingredients, such as phosphorus, sulfur, and chlorine additives. Straight oils are usually insoluble in water and provide the best lubrication, rust prevention, better sump life, and easy maintenance.

Since bacteria will only thrive in fluids with water content, straight oils do not sour. These oils lessen the force produced as the cutting tool cuts the material, making clean cuts to ensure a smooth surface finish on the workpiece.

Pros

• Straight oil offers good lubricity and reduces friction in machining operations.
• They ensure excellent finishes and minimize tool wear and tear.
• These oils are often affordable and have high compatibility with several materials like bronze, steel, and iron, commonly used in machinery and equipment.

Cons

• Straight oils have poor cooling performance.
• They usually require higher maintenance and oil changes due to their high degradation properties.
• These oils are not ideal for specific high-performance applications.
• Straight oils exhibit adverse environmental impact if not properly disposed of.

Soluble Oils

Soluble oils, also known as emulsions or water-soluble oils, are excellent coolant choices for general machining purposes and are commonly used amongst water-soluble cutting fluids. Water-soluble oils often create emulsions when mixed with water. The result of the mixture comprises the base mineral oil and the emulsion to create metalworking fluid. It performs well in diluted form and offers excellent lubricity and heat transfer performance.

Soluble oils are cheap and commonly used in the metalworking industry. They comprise 60-90% petroleum, emulsifiers, or mineral oil and adhere to the workpiece during machining. It is ideal for lubrication and offers excellent rust resistance when mixed with a specific amount of rust inhibitor.

Pros

• These oils facilitate better cooling and lubrication because of the water and oil blend.
• Soluble oils are multipurpose and are ideal for light and medium-duty operations, including various ferrous and nonferrous applications.
• You may accompany operations such as tapping and broaching handled with straight oils using heavy-duty soluble oils.

Cons

• The coolant tank encourages microbial growth of bacteria and fungi when improperly maintained.
• Oil in the mixture results in rust control problems, evaporation losses, and tramp oil contamination.

Oil Coolers - An Overview 

Vehicle engine and machinery lubricants (or in this context, simply &#;oil&#;) are engineered to perform within particular temperature ranges based on their intended application.  There is an inherent relationship between oil&#;s temperature and its consistency, which is described as the oil&#;s Viscosity &#; a technical measure of a fluid&#;s ability to flow.  Higher viscosity equates to a thicker consistency that does not flow well (imagine honey), and lower viscosity results in a thinner consistency that flows freely (imagine water).  

With lubricating oils, cold temperatures and high viscosity often mean more friction and less coverage over moving parts, whereas high temperatures result in low viscosity and good coverage (up to a point).  Extremes in either direction are bad &#; very cold oil may not flow at all, and very hot oil may break down and &#;boil off&#;, both cases offering greatly reduced protection to moving parts.  As such, selecting the right oil for the job is essential.  

In your average commuter automobile, oil typically sees operating temperatures between 230°F and 260°F.  At this temperature range, properly selected oil will offer the right viscosity, flowability, coating protection, and heat absorption to keep the engine running as expected.  As operating temperatures climb beyond this range, normal oils start to experience negative effects, such as:

• Accelerated degradation 
• Oxidation 
• Chemical breakdown, decomposition and separation 
• Reduced life
• Reduced viscosity leading to excess friction 
• Vaporization (&#;boil off&#;) 
• All of the above leading to heat- and friction-induced damage to mechanical parts, up to and including complete engine failure  

By now, the point is clear: high oil temperature is detrimental.  How can modern engines and powertrains combat high oil temperatures ensuring proper performance and long operational life?  By installing an oil cooler!  

Oil Coolers are mechanical heat exchangers that expel waste heat from lubricating fluids, typically into the atmosphere similar to a standard vehicle&#;s radiator, but in some cases directly into an engine&#;s onboard cooling fluid loop.  Read on to learn all about Oil Coolers, their applications, and key selection considerations.  

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Oil Cooler Applications

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When most people think of lubricant in the context of vehicles, engine oil usually comes first to mind.  While engine oil is indeed the most frequently handled lubricant in oil cooler applications, there are other fluids that can benefit as well - power steering fluid, transmission fluid, differential fluid, and any number of engineering machinery lubricants.  Because there are practically endless applications for oil coolers, let&#;s focus on the most common application conditions, such as:

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• High Temperature Climates &#; geographical areas with high ambient temperatures offer less forgiveness to engine lubricants, as mechanical systems can&#;t dissipate their heat to the atmosphere as well as when outdoor temperatures are low. 

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• High-Load, Low Airflow Conditions &#; especially with enclosed power transmission and stationary systems, heat produced from high-load equipment that does not receive ample air flow needs additional means of dumping waste heat.  

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• High RPM Systems &#; friction is especially problematic at high engine RPMs, making such applications perfect for oil coolers to help protect sensitive parts by keeping oil temperatures low.  

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• Emergency and Mission-Critical Equipment &#; when it comes to emergency response generators and engines, failure is not an option.  This counts for first responder vehicles and backup infrastructure generators as well (such as those used for hospital ICU wards).   

• Frequent Start/Stop System &#; certain vehicles and mechanical conveyance systems start and stop very frequently, and are under high load (generating high heat) during their short bursts of activity.  In these systems, onboard cooling is usually not enough, as more heat has to be dumped in less time.  

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• Rinse Cooling &#; certain industrial applications use lubricating oils to rinse over mechanical tooling, such as with CNC machining systems.  Here, lubricants rinse away debris and particulates while also removing work-induced heat.  Dealing with the rinse particulates can be challenging, but assuring a cool, consistent tool temperature is worth the effort.

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Ideal applications for oil coolers typically target one of two primary functions:

1. To bring a lubricant&#;s temperature down within its recommended operating range in order to avoid heat-induced failure (solving for system reliability), or
2. To extend a lubricant&#;s operating life (solving for system efficiency)

Regarding this second function, we&#;re referring to the chemistry theorem known as the Arrhenius Law which states that for every 10°C decrease in a lubricant&#;s base temperature, oil life is doubled.  This law gives us pretty good motivation to employ oil coolers anywhere possible, if for no better reason than reducing the waste, downtime, and cost involved in replacing lubricants.        

Key Considerations in Selecting an Oil Cooler 

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Lubricant coolers are typically offered in four styles, utilizing either air-to-fluid or fluid-to-fluid heat transfer.  

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Stacked Plate Oil Coolers

Using high volume, large surface area plates stacked together in a common frame, stacked plate oil coolers tend to offer the highest performance lubricant cooling, though at the highest cost.  Stacked plate coolers are very efficient thanks to their high heat transfer potential, and can also outlast the below two finned options thanks to their more resilient construction.  This style is common for OEM coolant-to-oil designs that sit inline with an engine&#;s oil pump and filter, but can also be provided as air-to-oil transfer in special housings.
 

Bar and Plate (aka Plate and Fin) Oil Coolers 

With a very similar design to a standard vehicle coolant radiator, the bar and plate cooler design consists of many fluid-carrying plate channels through which hot oil flows.  Air passes directly over these channels, immediately dispelling heat as air flows through the cooler&#;s fins.  This design offers a very good balance between performance and cost, on account of offering higher surface area in a smaller footprint.  Most often, this style is mounted inline with a system&#;s coolant radiator, with a powered fan equipped to force air through both heat exchangers.  

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Tube and Fin Oil Coolers

This cooler style consists of a continuous, serpentine tube that has thin metallic fins attached in high density, with narrow open channels between fins where air flows across.  Lubricant flows through the tube, and heat is transferred from the fluid across the fins, where airflow then dispels this heat to the atmosphere.  Because of their design, tube and fin coolers are only slightly effective, as well as prone to performance decline as the many light gauge fins distort or become damaged.  

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Shell and Tube Oil Coolers 

Mainly found in special machinery and large vehicle applications, shell and tube oil coolers provide efficient coolant-to-oil heat transfer in a housing mounted away from the engine block.  Anywhere that oil can be pumped away from the powertrain being cooled via tubing or hose, this design can be leveraged with great success &#; better accessibility, wider mounting options, and higher potential for radiant heat loss through the shell.

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There are a ton of details to review when selecting a new Oil Cooler, but thanks to our deep experience and technical expertise, we can often match an application to an existing core design and customize it from there into a perfect match.  The below features are found on all Cincinnati Radiator Oil Coolers as standard options, which will exceed the requirements of most vehicular and machinery applications.  

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• Technical Design:  an Oil Cooler can only be as good as the sizing profile it&#;s designed to provide, so all inquiries should start with a detailed review of the application, minimum and maximum temperature expectations, oil specifications, and any special operating nuances (like particulate debris).  

• Construction:  bar and plate construction is the most preferred style, selected for its very simple assembly and easy repair should there ever be a problem.

• Materials:  all-aluminum materials offer the best combination of low weight, high thermal transfer, and economical cost.

• Cleaning:  both pre-and post-brazing, Oil Coolers should receive a thorough cleaning pass inside and outside of the unit to ensure proper fabrication and in-situ performance.

• Assembly:  Oil Coolers are engineered for a specific heat transfer target based on airflow, surface area, and temperature delta, which means that each Oil Cooler should be assembled to very exact dimensions and tolerances in order to achieve the expected design point.

• Brazing:  brazing connections using high-alloy aluminum with additional sheet cladding achieve deeper penetration, which helps combat leaks even under aggressive conditions over many years. 

• QC:  to assure that the assembly process was a complete success, every unit should be fully checked prior to shipment for dimensional accuracy, brazing penetration, joint integrity, and zero leakage.  

• Packaging: the fins on an Oil Cooler are made of very thin aluminum sheet, often down to 0.2mm thick, and must be fully protected for shipment by carefully packaging the assembly.  

• Warranty:  Cincinnati Radiator offers a year or 3,000 hours Warranty on all of our aluminum-core heat exchangers, including Oil Coolers.

• Maintainability:  our Oil Coolers are built with a long life in mind, intended to be fully cleaned, serviced, repaired, and remanufactured over time.  

• Customer Support: after the purchase, buyers should expect full and readily available support should they have any questions around installation, operation, and troubleshooting concerns, at any time during the long life of their new Oil Cooler.  

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Mission-critical vehicles and equipment in over a dozen infrastructure sectors rely on heat transfer components manufactured by Cincinnati Radiator.  CR works directly with Original Equipment Manufacturers and Aftermarket service channels to supply premium-grade, long life radiators, coolers, and full cooling packages into extreme applications all over the world.  With our expanding inventory and fabrication space at our Fairfield, Ohio facility, we pride ourselves on having a personal touch, ultra-fast lead times, and one-off custom design capabilities.  For your next vehicle or heavy equipment heat transfer project, call us at (513) 874-, us at , or visit our website at https://cincyradiator.com/.    

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