Cooling lubricants, also known as cutting fluids, are liquids that are used to cool and lubricate the cutting edge of machine tools during the machining process. These fluids serve several important functions, including reducing friction, dissipating heat, and flushing away chips and debris.

There are several types of cooling lubricants available, each with their own set of properties and advantages. The most common types include oil-based, water-based, and synthetic fluids.

Lubricants types

Oil-based cooling lubricants are made from mineral oil and are typically used in heavy-duty machining operations, such as drilling and turning. They offer good lubrication and cooling properties, but can be messy and difficult to clean up. An oil-based coolant lubricant typically contains a mixture of lubricating oil (95-98%), rust inhibitors (1-2%), and corrosion inhibitors (1-2%). Some oil-based coolants may also contain additional components such as extreme pressure additives and anti-wear additives (0,5-1%) which improve the lubricating properties of the oil and help to protect against wear and tear. However, it should be noted that oil-based coolants are not widely used in most cooling systems because they are not as effective as water-based coolants in dissipating heat

Water-based cooling lubricants, also known as emulsions, are made from a mixture of water and oil. They are popular in light-duty machining operations and are less messy than oil-based fluids. They are also easier to clean up and have less impact on the environment. A water-based coolant lubricant typically contains a mixture of water (60-80%), antifreeze such as ethylene glycol or propylene glycol (15-25%), lubricating oil (1-2%), rust inhibitors such as nitrite, molybdate, and silicate (1-2%), 1-2% of corrosion inhibitors (silicates, borates, phosphates, and nitrogen-based inhibitors), pH adjusters (typically between 7 and 9), biocides and additional components such as dyes and fragrances. 

Synthetic fluids are becoming more popular. These fluids are made from synthetic oils and offer excellent lubrication and cooling properties, as well as being biodegradable and non-toxic, making them more environmentally friendly. A synthetic coolant lubricant typically contains a mixture of: Synthetic lubricating oil (80-90%) to provide the lubrication and cooling properties of the coolant lubricant, the type of synthetic oil used can vary depending on the specific product, but examples include polyalphaolefin (PAO) and polyalkylene glycol (PAG); Rust inhibitors (to prevent rust and corrosion from forming on the metal surfaces of the cooling system) such as nitrite, molybdate, and silicate (1-2%); Corrosion inhibitors (1-2%) to help to protect against corrosion caused by dissolved oxygen and other dissolved gases (silicates, borates, phosphates, and nitrogen-based inhibitors); Extreme pressure additives such as sulfur-phosphorus and chlorine-phosphorus compounds (0,5-1%); Anti-wear additives, to protect against wear and tear caused by friction, especially in high-stress or high-temperature conditions, examples include zinc dialkyldithiophosphates and boron derivatives (0,1-0,5%); pH stabilizers; Biocides.

On the basis of the materials and applications, specific formulations are prepared which are suitable, for example, for cutting and grinding, for turning, milling and drilling operations, for heavy-duty and high-temperature uses, for lasting protection from oxidation, for minimizing environmental impact (through biodegradable oils), for gears, turbines and other mechanical or pneumatic parts. Coolants can be divided into two macro-families, whole or miscible. The whole ones are usually based on mineral oils and are used concentrated, while the miscible ones are diluted in water from 3 to 8% (manually or automatically by the plant).

Maintenance

Regular maintenance of the cooling lubricant system typically involves the following steps:

• Check the coolant level in the system and add as needed, the fluid concentration is read by refractometer.
• Check the condition of the coolant. If the fluid is dirty or contains debris, it should be drained and replaced. Over time, sludge and microlife may develop.
• Start the engine and run it for a few minutes to circulate the coolant lubricant throughout the system.
• Check for leaks or other problems and fix them if necessary.
• Continuously check the chemical-physical parameters, such as pH and temperature.

It is important to always check the manual before using a coolant lubricant, as different types of vehicles, engines and systems may have different requirements.