As we all know, cutting fluid is an important supporting material for metal cutting. The history of human use of cutting fluid can be traced back to ancient times. When grinding stone, bronze and iron, people know that watering can improve efficiency and quality. In ancient Rome, olive oil was used in the casting of piston pumps, and in the 16th century, tallow and water solvents were used to polish metal armor. From the 1775 British J. Wilkinson developed a successful trampoline for the processing of the cylinders of the Watt steam engine, the application of water and oil in metal cutting was accompanied. After a long development in 1860, various machine tools such as turning, milling, planing, grinding, gear machining and threading have appeared one after another, which also marks the beginning of larger-scale application of cutting fluid.
In the 1880s, American scientists first conducted the evaluation of cutting fluids. F·W·Taylor discovered and clarified the phenomenon and mechanism that the cutting speed can be increased by 30% to 40% by using a pump to supply sodium carbonate aqueous solution. The tool material used at that time was carbon tool steel, and the main function of the cutting fluid was cooling, so the term "coolant" was proposed. Since then, people have called cutting fluids a cooling lubricant.
With the continuous improvement of the understanding level of cutting fluid and the continuous enrichment of practical experience, it is found that injecting oil in the cutting area can obtain a good processing surface. At the earliest, people used animal and vegetable oils as cutting fluids, but animal and vegetable oils were prone to deterioration and had a short life cycle. At the beginning of the 20th century, people began to extract lubricating oil from crude oil and invented various excellent lubricating additives. After the First World War, research and use of composite oils synthesized from mineral oils and animal and vegetable oils began. In 1924, sulfur and chlorine-containing cutting oils were patented and used in heavy cutting, broaching, threading and gear machining.
The development of tool materials has promoted the development of cutting fluids. In 1898, high-speed steel was invented, and the cutting speed was increased by 2 to 4 times. In 1927, Germany first developed hard alloys, and the cutting speed was increased by 2 to 5 times than that of high-speed steel. As the cutting temperature continues to increase, the cooling performance of the oil-based cutting fluid can not fully meet the cutting requirements, and people have begun to re-emphasize the advantages of water-based cutting fluid. In 1915, an oil-in-water emulsion was produced, and in 1920 it became the preferred cutting fluid for heavy cutting. The first oil-free synthetic cutting fluid was developed in the United States in 1948 and increased in application in the 1970s due to oil price shocks.
In the past ten years, due to the continuous improvement of cutting technology, the emergence of advanced cutting machine tools, the development of cutting tools and workpiece materials, promoted the development of cutting fluid technology. With the in-depth development of advanced manufacturing technology and the strengthening of people's awareness of environmental protection, new requirements have been placed on cutting fluid technology, which will certainly promote the development of cutting fluid technology to a higher level.
The important role of cutting fluid
In the metal cutting process, the reasonable use of the cutting fluid can reduce the friction between the tool and the workpiece, reduce the cutting temperature, reduce the tool wear, thereby improving the cutting efficiency and processing quality, prolonging the tool life and reducing the processing cost. In the cutting process, the cutting fluid mainly serves to cool and lubricate.
(1) Cooling effect After the cutting fluid is poured in the cutting zone, the cutting heat is transferred by the cutting heat, convection and gasification, thereby cutting the cutting zone on the tool, the workpiece and the chip, thereby reducing the temperature of the cutting zone, achieving the cooling effect and improving the tool. Durability and machining accuracy of the workpiece.
(2) Lubrication The cutting fluid penetrates into the cutting zone, and the adsorption and chemical reaction occurs on the contact surface between the cutter and the chip and the workpiece, forming a lubricating oil film to lubricate, suppressing the generation of built-up edge, and effectively reducing Cutting force reduces the surface roughness of the workpiece. In addition, the cutting fluid has cleaning, chip removal and rust prevention.
Current status of cutting fluid
At present, there are many kinds of cutting fluids with different functions, but they can be divided into two categories, namely oil-based cutting fluid and water-based cutting fluid.
(1) Oil-based cutting fluid Oil-based cutting fluid, that is, cutting oil, is mainly used for low-speed heavy cutting machining and machining of difficult-to-machine materials. The cutting oils currently used are as follows:
1 Mineral oil: The mineral oil commonly used as cutting fluid has all-loss system oil, light diesel oil and kerosene. They have good lubricity and certain rust resistance, but have poor biodegradability.
2 animal and vegetable oils: animal and vegetable oils commonly used as cutting fluids are whale oil, castor oil, cottonseed oil, vegetable oil and soybean oil. They have excellent lubricity and biodegradability, but are easily oxidized and deteriorated.
3 ordinary compound cutting fluid: it is formulated with mineral oil in mineral oil. It performs better than mineral oil alone.
4-pole pressure cutting oil: It is a compound oil prepared by adding extreme pressure additives such as sulfur, phosphorus, chlorine and boron, oil-soluble rust inhibitors and oily agents to mineral oil.
(2) Water-based cutting fluids Water-based cutting fluids are classified into three categories, namely, emulsions, synthetic cutting fluids, and semi-synthetic cutting fluids.
1 Emulsion: It is composed of emulsified oil and water. The emulsified oil is mainly composed of mineral oil (content of 50% to 80%), emulsifier, rust inhibitor and oily agent. Extreme pressure agent and preservative composition. The dilution is opaque and milky white. However, due to its poor working stability, short cycle time, and opaque solution, it is difficult to observe the cutting conditions during operation, so the amount of use is decreasing year by year.
2 Synthetic cutting fluid: Its concentrated liquid does not contain mineral oil, and is made of water-soluble rust inhibitor, oily agent and extreme pressure agent. It is composed of a surfactant and an antifoaming agent. The diluent is transparent or translucent. The main advantages are: long service life; excellent cooling and cleaning performance, suitable for high-speed cutting; transparent solution, good visibility, especially suitable for use in modern processing equipment such as CNC machine tools and machining centers. However, the synthetic cutting fluid easily washes off the lubricating oil on the sliding parts of the machine tool, resulting in inflexible sliding and relatively poor lubrication performance.
3 semi-synthetic cutting fluid: also known as micro-emulsified cutting fluid. Its concentrate consists of a small amount of mineral oil (content 5% to 30%), oily agent, extreme pressure agent, rust inhibitor, surfactant and preservative. The diluent oil droplets are less than 1 μm in diameter and the diluent is transparent or translucent. It has the advantages of emulsion and synthetic cutting fluid, and makes up for the shortcomings of both, which is the development trend of cutting fluid.
Current status of cutting fluid additives
Cutting fluids are complex compounds that contain additives of several or even dozens of different ingredients. The composition of the additive not only directly affects the cutting performance (lubrication, cooling and cleaning performance) of the cutting fluid, but also affects the non-cutting performance of the cutting fluid (toxicity, corrosivity, contamination, periodicity of use and waste processability). The commonly used additives for cutting fluids are extreme pressure lubricants, rust inhibitors and preservatives. Therefore, these additives of the cutting fluid are not only excellent in performance but also non-toxic and harmless.
(1) Extreme Pressure Lubricants The pressure lubricants currently in use are mainly compounds containing sulfur, phosphorus and chlorine, such as sulfurized olefins, sulfurized animal and vegetable oils, thiourea, and phosphate esters. Chlorinated paraffin, etc., which chemically react with a metal surface at a high temperature to form a chemical reaction film, and perform extreme pressure lubrication during cutting. They have good lubrication properties but are environmentally polluting and harmful to the operator. With the increasing awareness of environmental protection, the use of such additives has now been restricted. At home and abroad, it is working on its alternatives. In recent years, the series of non-toxic and harmless borate additives have received extensive attention.
(2) Anti-rust additive The anti-rust additive acts to prevent rusting of the workpiece. It is water-soluble and oil-soluble, and is used for water-based cutting fluids and cutting oils, respectively. Commonly used oil-soluble anti-rust additives are barium petroleum sulfonate, sodium petroleum sulfonate and the like. For water-soluble rust-preventing additives, sodium nitrite is a long-term effective anti-rust additive, but people have gradually realized that it is carcinogenic to humans. Chromate and dichromate also have good anti-rust effects on steel, but they are toxic and pollute the environment, and their use is limited. Phosphate rust inhibitors can pollute the environment and their use should be limited. Therefore, the development of new non-toxic and harmless rust inhibitors is a development trend. At present, synergistic effects of various non-toxic additives, such as high-efficiency rust-preventing additives compounded by organic amines, borate, benzotriazole, etc., have achieved good results. Molybdate is also an anti-rust agent with excellent anti-rust properties and non-toxicity.
(3) Preservative cutting fluid itself has the conditions for the growth and reproduction of microorganisms and fungi, and it is easy to spoil and deteriorate. The role of preservatives (or fungicides) is to kill or inhibit the growth of bacteria and molds in order to extend the life of the cutting fluid. Commonly used preservatives are phenolic compounds, formaldehydes, chlorine-containing and benzene-containing compounds. Although it has a strong bactericidal effect, it will harm the operator and pollute the environment, irritating the eyes and nose, and causing the operator to suffer from skin diseases and respiratory diseases. In recent years, due to environmental regulations, many countries have restricted the use of fungicides containing phenols, benzenes and formaldehyde, and actively sought new non-toxic fungicides. For example, copper salts prepared from carboxylic acids such as oleic acid, stearic acid, and lauric acid have a corrosion resistance of more than one year. The citrate single copper developed in the United States also has a good antibacterial effect. In recent years, preservatives formulated with borate esters, surfactants and integrators have also strong antibacterial properties.
At present, domestic products with preservatives in cutting fluids are rare, and it is rare to add preservatives to the use of cutting fluids. This is mainly due to the increase in the cost of the cutting fluid and the inconvenience of the use of the preservative. The future task is to develop and promote a preservative that is convenient and non-toxic at a suitable price.
Selection of cutting fluid
At present, there are many kinds of cutting fluids, and the performance is good or bad. If improperly selected, it will cause adverse consequences. The selection of cutting fluid should follow the following principles:
(1) The cutting fluid should have no irritating odor, no harmful additives to the human body, and ensure the safety of the user.
(2) The cutting fluid should meet the requirements of equipment lubrication and protection management, that is, the cutting fluid should not corrode the metal parts of the machine tool, do not damage the machine seals and paint, and will not leave hard gelatinous deposits on the machine guide rails, ensuring the use of The equipment is safe and working properly.
(3) The cutting fluid should ensure the anti-rust effect between the workpiece processes and not rust the workpiece. Sulfur-containing cutting fluids should not be used when processing copper alloys. When processing aluminum alloy, a neutral cutting fluid should be used.
(4) The cutting fluid should have excellent lubricating properties and cleaning performance. The cutting fluid with a high PB value and a small surface tension was selected and tested by a cutting test.
(5) The cutting fluid should have a long service life. This is especially important for machining centers.
(6) The cutting fluid should be adapted to a variety of processing methods and a variety of workpiece materials.
(7) The cutting fluid should be low in pollution and have a waste liquid treatment method.
(8) The cutting fluid should be at an appropriate price and convenient to prepare.
In summary, when selecting the cutting fluid, the user can select two or three kinds of cutting fluids with better comprehensive performance according to the specific processing conditions of the factory. After the factory trial, the performance is determined to meet the processing technology of the factory. Requires a cutting fluid at an affordable price.
The development trend of cutting
(1) Development of green cutting fluid
1 Mineral oil is gradually replaced by biodegradable vegetable oils and synthetic esters.
2 Oil-based cutting fluid is gradually replaced by water-based cutting fluid.
3 Develop additives with excellent performance and no harm to the human body and no pollution to the environment.
(2) Green use of cutting fluid
1 Promote the centralized cooling and lubrication system, which combines the separate cooling and lubricating devices of the machining equipment into one cooling and lubrication system to maintain the maintenance level of the cutting fluid.
2 Study dry cutting and minimum lubrication cutting to reduce the amount of cutting fluid used.
3 Research and promote new processes and technologies for the treatment of cutting fluid waste liquid to ensure that the discharged waste liquid has no pollution to the environment.
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