Machine processing plants usually have many different processing operations, and each operation has its own specific coolant requirements. In order to meet these requirements, hundreds of products with different functions are derived from the coolant formula.
In the past, machining plants often prepared different coolants on site to meet the requirements of engineers for using roller coolants for each machine tool. However, different coolants in the workshop caused cross-contamination and incompatibility of waste liquid. In addition, various coolants have also caused an increase in inventory.
Nowadays, mechanical processing plants tend to use one or a limited amount of coolant in all processes of the workshop.
This practice urges coolant suppliers to develop more comprehensive products, which can help solve the problems of cooling, lubrication, anti-corrosion and microbial control while manufacturing excellent products. However, for so many processes and a large number of coolant varieties on the market, mechanical processing plants have encountered complex challenges in selecting the best and most economical coolant for their operations.
In addition, there is always a phenomenon that different people have different views on the best coolant for each specific process. A basic understanding of how the components of the three main types of coolant (pure oil, soluble oil and synthetic agent) affect the performance can simplify the selection of coolant.
Function of soluble oil components
Component function
Mineral oil lubrication and rust prevention
Grease improves lubricity.
Extreme pressure additives (sulfur, phosphorus, chlorine) improve tool life
Emulsifier can be mixed with water.
PH initiator improves rust resistance and biological stability.
Insecticides control bacteria and mold.
Defoamer control foam
Antioxidants prevent oxidation and make it shiny.
Consumer's preference for pigments and fragrances
Characteristics of base coolant (in descending order, excluding the influence of additives)
Lubrication cooling
Pure oil composition
Soluble oil semisynthesis
Semi-synthetic soluble oil
Synthetic pure oil
Pure oil
Pure oil insoluble in water comes from petroleum (mineral oil), animal or vegetable oil and can be used "directly" without being diluted with water.
These oils have the characteristics of good lubricity and rust resistance, long fuel tank life and easy maintenance. In addition, they will not deteriorate, because organisms usually can only survive in aqueous liquids.
Pure oil can be a mixture of one or more different base oils, and can contain boundary and/or extreme pressure additives, such as sulfur, phosphorus or chlorine compounds. Pure oil can reduce the force generated when the tool cuts metal, so the tool cuts cleanly and forms a smooth surface on the workpiece.
Additives can improve the lubricity of pure oil and strengthen the buffer between cutting metal and tools. Under extreme processing conditions, additives may exceed 20% of the product composition.
Although they are more expensive than similar products without any additives, pure oil with additives plays a vital role in processes with important surface roughness and tool life, such as extrusion grinding, strict process and tapping and deep hole drilling.
In addition, pure oil can also prevent micro-bonding in heavy-load machining, and additives can improve the anti-bonding performance of metals.
However, pure oil is not flame retardant, which will produce smoke, thus forming a processing environment that is unfriendly to operators. Pure oil may also leave an unpleasant oil film on almost every surface of the factory.
emulsified oil
Soluble oil is suitable for light to heavy processing operations, including non-ferrous and ferrous metal processing.
Wetting agents and extreme pressure additives can expand the application range of soluble oil to include heavier processing processes that usually use pure oil.
Soluble oil is usually divided into semi-synthetic oil or truly soluble oil, which mainly depends on the oil content in concentrated oil.
Soluble oil concentrate contains 40% or more oil, which is mixed with water to form metal cutting fluid. These cutting fluids provide cooling due to the mixing of oil and water-water has a high heat capacity and can dissipate heat well-and the wetting ability is realized by mixing oil and water, and they usually leave a protective coating on the moving parts of machine tools.
Although soluble oils bring high-quality lubricating fluids that can prolong the life of tools, they do not always have the same lubricating properties as pure oils. They also need more maintenance than pure oil. The use of water makes the historically soluble oil easy to produce microorganisms and more prone to corruption. Therefore, processing plants must abide by strict preventive and maintenance measures to prolong the life of their oil tanks.
Operators need to pay close attention to the type of water injected and the type of water soluble in oil.
If mixed with hard water, soluble oil will deposit on workpieces and machine tools: groundwater may be hard, or it may contain chloride ions or sulfates that accelerate corrosion.
Mechanical processing plants should use first-class coolant with sufficient corrosion resistance, or they may need to add oil tank preservative to the coolant. On the other hand, foaming problems may occur when processing with soft water and soluble oil-based coolant, so it is necessary to use defoamer and other fuel tank additives.
Semi-synthetic coolant
Semi-synthetic coolant is prepared by adding up to 40% petroleum to water-dilutable concentrate. Emulsifiers, wetting agents, preservatives, extreme pressure components and pesticides can also be added.
These coolants are usually translucent, but they may also be transparent or completely opaque.
Semi-synthetic coolant can be widely used in cutting tools, providing good lubricity for medium and heavy load machining. Through them, operators can cut and feed at a higher speed, because they usually have better cooling and wetting properties than soluble oils.
Semi-synthetic coolant is prepared with less oil, and sometimes it has better sedimentation and cleaning performance. Because their oil content is less than pure oil or soluble oil, they also produce less smoke.
The disadvantage of semi-synthetic coolant is similar to that of soluble oil-water hardness affecting its stability. The mixed use of hard water and water components may lead to the formation of hard water deposits in the oil tank, while mixing with soft water will produce foam.
Synthetic coolant
Synthetic coolant does not contain petroleum-based oil. Usually, they contain water-insoluble lubricating oil and rust inhibitor. The supplier provides the composition in the form of concentrate, similar to soluble oil, which is mixed with water to form a cooling liquid.
Since only additives and water are added to the concentrate, the composition also has a high cooling function. At the same time, they are most suitable for high-heat and high-speed metal cutting, such as surface grinding. Additives have a far-reaching influence on lubricity. When added to some components, they can produce better lubrication effect than pure oil without additives.
Heavy composite materials have been fully developed in the past few years and can now cope with most loading processes.
Composite coolant can be divided into several grades according to its composition:
Simple cutting fluid is used in light load grinding operation. When they are mixed in the oil tank, they will form a transparent liquid, so the operator can see the cut metal.
Composite cutting fluid contains synthetic lubricating oil, which can be used for high-speed medium/heavy load cutting. They also form a transparent solution in the oil tank.
Emulsified cutting fluid contains chemicals that form specific lubricating oil characteristics, and its appearance is similar to soluble oil.
The composition has the ability to prevent acid deterioration, and generally has good microbial inhibition. Most composite materials are used for corrosion protection, and they have outstanding cooling ability.
Traditionally, composite materials have many disadvantages. Components are usually more expensive than similar oils. In addition, some composite operations are very clean.
That is to say, its characteristics like cleaning agent will make some compounds lead to the failure of machine tool seal and the operator's skin and mucosa are dry. Many synthetic coolants leave a sticky residue.
Some people think that synthetic agents are not easily atomized by oil, but this is not necessarily true. Depending on their composition and operation, they may not produce oil mist, which often appears in soluble oil, but they may still be atomized by oil, causing inflammation of nasal, laryngeal and intraocular mucosa. Because they do not contain oil, the composition may be more harmful to human skin.
Suggestions on Correct Selection of Coolant
The best coolant can protect the machine tool, prolong the tool life and provide an environment recognized by the operator and the environmental health and safety department.
According to the suggestions of machine tool manufacturers and coolant suppliers, select the best coolant to optimize all parameters.
Factory operators and engineers usually rely on the proprietary knowledge of coolant suppliers to discuss and recommend the best coolant for processing materials. Most factories want to reduce the types of coolant used as much as possible, so as to reduce the cost of coolant maintenance and treatment, and can buy a large number of coolant to further save money.
Some machine tool manufacturers require their products to use special coolant. A large number of machine tool manufacturers provide recommended coolant tables, and stipulate that the warranty of users who do not use the recommended coolant is invalid. When considering buying machine tools, the processing factory should find the machine tool manufacturer and explain the coolant currently used in the workshop. Then, the manufacturer and the coolant supplier can jointly determine the effectiveness of the existing coolant in various new machine tools.