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Status and development of cutting fluid technology

as we all know, cutting fluid is an important supporting material for metal cutting. The history of human using cutting fluid can be traced back to ancient times. When people grind stone, copper and iron, they know that watering can improve efficiency and quality. In ancient Rome, olive oil was used to turn the castings of piston pumps, and tallow and water solvent were used to polish metal armor in the 16th century. In 1775, j.wilkinson of England successfully developed a boring machine to heat and improve understanding, and then processed the cylinder of watt steam engine, accompanied by the application of water and oil in metal cutting. After a long development in 1860, various machine tools such as turning, milling, planing, grinding, gear processing and thread processing appeared one after another, which also marked the beginning of a large-scale application of cutting fluid

In the 1980s, American scientists first carried out the evaluation of cutting fluid. F · w · Taylor found and clarified the phenomenon and mechanism that using pump to supply sodium carbonate aqueous solution can increase the cutting speed by 30% - 40%. The cutting tool material used at that time was carbon tool steel, and the main function of cutting fluid was cooling, so the term "coolant" was proposed. Since then, cutting fluid has been called cooling lubricant

with the continuous improvement of people's understanding of cutting fluid and the continuous enrichment of practical experience, it is found that injecting oil into the cutting area can obtain a good machined surface. At first, people used animal and vegetable oil as cutting fluid, but animal and vegetable oil is easy to deteriorate and has a short service life. At the beginning of the 20th century, people began to extract lubricating oil from crude oil and invented various lubricating additives with excellent performance. After the first World War, they began to study and use the composite oil synthesized from mineral oil and animal and vegetable oil. In 1924, sulfur-containing and chlorine cutting oil was patented and applied to heavy cutting, broaching, thread and gear processing

The development of tool materials has promoted the development of cutting fluid. In 1898, high-speed steel was invented, and the cutting speed was 2 ~ 4 times higher than before. In 1927, Germany first developed cemented carbide, and the cutting speed was 2 ~ 5 times higher than that of high-speed steel. With the continuous improvement of cutting temperature, the cooling performance of oil-based cutting fluid can not fully meet the cutting requirements. At this time, people begin to pay attention to the advantages of water-based cutting fluid again. Water in oil emulsion was produced in 1915 and became the preferred cutting fluid for heavy cutting in 1920. In 1948, the first oil-free synthetic cutting fluid was developed in the United States, and its application was improved due to the impact of oil prices in the 1970s

in recent decades, the continuous improvement of cutting technology, the continuous emergence of advanced cutting machine tools, and the development of cutting tools and workpiece materials have 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 are put forward for cutting fluid technology, which will promote the development of cutting fluid technology to a higher field

the important role of cutting fluid

in metal cutting, the rational use of cutting fluid can reduce the friction between the tool and the workpiece, reduce the cutting temperature data: after the end of the experiment, reduce the tool wear, so as to improve the cutting efficiency and processing quality, prolong the tool service life, and reduce the processing cost. In cutting, cutting fluid mainly plays the role of cooling and lubrication

(1) cooling effect after the cutting fluid is poured in the cutting area, the cutting belt on the tool, workpiece and chip is removed through the conduction, convection and gasification of cutting heat, so as to reduce the temperature of the cutting area, achieve the cooling effect, and improve the durability of the tool and the machining accuracy of the workpiece

(2) lubrication cutting fluid penetrates into the cutting area, generates adsorption and chemical reaction on the contact surface between the tool and the chip and the workpiece, forms a lubricating oil film and plays a lubricating role, inhibits the generation of chip nodules, effectively reduces the cutting force and reduces the roughness of the workpiece surface. In addition, cutting fluid has the functions of cleaning, chip removal and rust prevention

current situation of cutting fluids

at present, there are many kinds of cutting fluids with different functions, but they can be summarized into two categories, namely, oil-based cutting fluids and water-based cutting fluids

(1) oil based cutting fluid oil based cutting fluid is cutting oil, which is mainly used for low-speed heavy cutting and machining of difficult to machine materials. At present, the following kinds of cutting oils are used:

① mineral oil: mineral oil commonly used as cutting fluid includes full loss system oil, light diesel oil and kerosene. They have good lubricity and certain rust resistance, but poor biodegradability

② animal and vegetable oils: animal and vegetable oils commonly used as cutting fluids include whale oil, castor oil, cottonseed oil, vegetable oil and soybean oil. They have excellent lubricity and biodegradability, but are easy to oxidize and deteriorate

③ ordinary composite cutting fluid: it is prepared by adding human oiliness agent into mineral oil. It has better performance than mineral oil alone

④ extreme pressure cutting oil: it is a composite oil prepared by adding sulfur-containing, phosphorus, chlorine, boron and other extreme pressure additives, oil-soluble rust inhibitor and oily agent into mineral oil

(2) water based cutting fluids water-based cutting fluids are divided into three categories, namely emulsion, synthetic cutting fluids and semi synthetic cutting fluids

① emulsion: it is composed of emulsified oil and water. Emulsified oil is mainly composed of mineral oil (50% - 80%), emulsifier, rust inhibitor and oily agent. Extreme pressure agent and preservative. The diluent is opaque and milky white. However, due to its poor working stability, short service cycle and opaque solution, it is difficult to observe the cutting condition at work, so the use amount decreases year by year

② synthetic cutting fluid: its concentrated fluid does not contain mineral oil and consists of water-soluble rust inhibitor, oily agent and extreme pressure agent. Surfactant and defoamer. The diluent is transparent or translucent. The main advantages are: long service life; Excellent cooling and cleaning performance, suitable for high-speed cutting; The solution is transparent and has good visibility. It is especially suitable for CNC machine tools, machining centers and other modern processing equipment. However, synthetic cutting fluid is easy to wash 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 Microemulsion Cutting fluid. Its concentrated liquid is composed of a small amount of mineral oil (content is 5% - 30%), oily agent, extreme pressure agent, rust inhibitor, surfactant and preservative. The diameter of the diluent oil drop is less than 1 m, 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. It is the development trend of cutting fluid. LEGO has equipped more than 1000 injection molding machines in factories in Denmark, Mexico and Hungary

current situation of cutting fluid additives

cutting fluid is a complex compound, which contains several or even dozens of additives with different components. The composition of additives not only directly affects the cutting performance (lubrication, cooling and cleaning performance) of cutting fluid, but also affects the non cutting performance (toxicity, corrosion, pollution, service cycle and waste liquid treatability) of cutting fluid. The commonly used additives of cutting fluid mainly include extreme pressure lubricant, rust inhibitor and preservative. Therefore, these additives of cutting fluid should not only have excellent performance, but also be non-toxic and harmless

(1) EP 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. they react with the metal surface at high temperature to form a chemical reaction film, which plays an extreme pressure lubrication role in cutting. Their lubrication performance is very good, but they pollute the environment and are harmful to operators. With the strengthening of people's awareness of environmental protection, the use of such additives has been restricted. Domestic and foreign countries are beginning to study its substitutes. In recent years, non-toxic and harmless borate (ester) additives have received extensive attention

(2) antirust additive antirust additive is used to prevent the workpiece from rusting. It has two types: water-soluble and oil-soluble, which are used for water-based cutting fluid and cutting oil respectively. Commonly used oil soluble antirust additives include barium petroleum sulfonate, sodium petroleum sulfonate, etc. For water-soluble antirust additives, sodium nitrite has long been considered an effective antirust additive, but people have gradually realized that it has the possibility of carcinogenesis to human body. Chromate and dichromate also have good rust prevention effect on steel, but their use is limited due to their toxicity and environmental pollution. Phosphate antirust agents will pollute the environment, and their use should also be limited. Therefore, the development of new non-toxic and harmless antirust agents is the development trend. At present, using the synergistic effect of a variety of non-toxic additives, such as the high-efficiency antirust additive compounded by organic amine, borate, phenylpropanetriazole, etc., has achieved good results. Molybdate is also an excellent and non-toxic rust inhibitor

(3) preservative cutting fluid itself has the conditions for the growth and reproduction of microorganisms and fungi, which is easy to decay, deteriorate and stink. The function of preservative (or bactericide) is to kill or inhibit the growth of bacteria and mold, so as to prolong the service life of cutting fluid. The commonly used preservatives are phenolic compounds, formaldehyde, chlorine containing and benzene containing compounds facing today's litigation civilization. Although it has strong bactericidal effect, it will harm the operator, pollute the environment, stimulate people's eyes and nose, and make the operator suffer from skin diseases and respiratory diseases. In recent years, due to the restrictions of environmental protection regulations, many countries restrict the use of fungicides containing phenols, benzene and formaldehyde, and actively seek new non-toxic fungicides. For example, the copper salt made of oleic acid, stearic acid, lauric acid and other carboxylic acids in Japan has corrosion resistance for more than one year. Copper citrate developed in the United States also has good antibacterial effect. In recent years, the preservative made of borate ester, surfactant and integrator also has strong antibacterial ability

at present, there are few products with preservatives in cutting fluid in China, and it is rare to add preservatives in the use of cutting fluid. This is mainly due to the large increase in the cost of cutting fluid and inconvenient use due to the addition of preservatives. The task in the future is to develop and promote preservatives that are affordable, convenient to use and non-toxic

selection of cutting fluid

at present, there are many kinds of cutting fluid with good and bad performance. If it is not selected properly, it will cause adverse consequences. The selection of cutting fluid should follow the following principles:

(1) cutting fluid should have no pungent smell and contain no additives harmful to human body, so as to ensure the safety of users

(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, damage the seals and paint of the machine tool, and leave hard colloidal deposits on the guide rail of the machine tool, so as to ensure the safety and normal operation of the equipment

(3) the cutting fluid should ensure the rust prevention effect between working procedures of the workpiece and prevent the workpiece from rusting. When processing copper alloy, sulfur-containing cutting fluid should not be selected. Cutting fluid with neutral pH value should be selected when machining aluminum alloy

(4) cutting fluid should have excellent lubrication and cleaning performance. The cutting fluid with high Pb value of maximum non seizing load and low surface tension is selected and evaluated by cutting test

(5) cutting fluid should have a long service life. This is particularly important for machining centers

(6) the cutting fluid should try to adapt to a variety of processing methods and workpiece materials

(7) cutting fluid should have low pollution and waste liquid treatment methods

(8) cutting

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