Patent Application
20240327746
The present disclosure relates to an aqueous suspension and a cutting fluid including the same. More specifically, the present disclosure relates to a hexagonal boron nitride particle-based aqueous suspension including water, a hexagonal boron nitride (hBN) particle, and a dispersant, in which the hexagonal boron nitride (hBN) particle is uniformly dispersed and remains in a colloidal state for a predetermined period, thereby the aqueous suspension exhibits superior cutting performance to conventional O/W emulsion-type water-soluble cutting fluids and provides cooling and lubrication functions necessary for processing in various fields, and the present disclosure also relates to a cutting fluid that is used by further diluting the aqueous suspension with water.
Cutting fluids work on the processing surface between a tool and workpiece during a processing process, thereby providing cooling and lubrication functions. Thus, cutting fluids are used to improve the precision of surface processing of workpieces and extend tool life.
These cutting fluids are largely divided into oil-based/non-water-soluble cutting fluids and water-soluble cutting fluids, which are used by being diluted in water. Among these, the non-water-soluble cutting fluids have excellent lubricating performance and are used for precision processing. However, the non-water-soluble cutting fluids have a high risk of causing a fire due to the low oil boiling point, and also the cooling performance is low. Those characteristics make it difficult to apply the non-water-soluble cutting fluids to hard metals (Ti, Ni, and SUS). In comparison, the water-soluble cutting fluids have excellent cooling performance. However, the lubrication performance of the water-soluble cutting fluids is lower than that of the non-water-soluble cutting fluids, making it difficult to apply the water-soluble cutting fluids to precision processing of non-ferrous metals.
In addition, conventional oil-based non-water-soluble cutting fluids, as well as water-soluble cutting fluids, for use are mainly prepared by diluting with water fluids made from petroleum-based and ester-based vegetable oils. Accordingly, in the process of recycling cutting fluids, a problem of rotting due to microbial growth arises, and also, a significant foul odor is generated, which makes workers uncomfortable and working environments poor. In the case of the water-soluble cutting fluids, wastewater is difficult to treat due to the oil contained in the fluids. Meanwhile, the non-water-soluble cutting fluids are burned and destroyed, so the non-water-soluble cutting fluids have disadvantages such as generating significant carbon dioxide.
Meanwhile, Patent Document 1 (Korean Patent Registration No. 10-0665790) discloses a technology that uses vegetable oil as a base oil while emphasizing eco-friendliness, taking into account the impact on the environment. However, even with that technology, the problems arising from the use of oil-based water-soluble cutting fluids still persist. In addition, Patent Document 2 (Korean Patent Registration No. 10-2053046) and Patent Document 3 (Korean Patent Registration No. 10-2146032) disclose an eco-friendly water-soluble cutting fluid technology that uses alkaline electrolytic ionized water without using oil. However, the metal machinability of the technology is significantly lower than that of the conventional O/W emulsion-type water-soluble cutting fluids, so there are likely to be limitations in the application of the water-soluble cutting fluid disclosed by the technology.
Therefore, there is a need for a cutting fluid that exhibits both the lubrication performance of the non-water-soluble cutting fluids and the cooling performance of the water-soluble cutting fluids and at the same time is used through resource recycling. In recycling, the cutting fluid is carbon neutral due to not using oil, induces clean processing that minimizes the amount of cutting fluid used, and prevents or drastically reduces the generation of wastewater and waste oil.
Accordingly, to solve the problems, the present disclosure is designed. An objective of the present disclosure is to provide an aqueous suspension including water, a hexagonal boron nitride (hBN) particle, and a dispersant, in which the hexagonal boron nitride (hBN) particle is uniformly dispersed and remains in a colloidal state for a predetermined period, thereby the aqueous suspension exhibits cutting performance (precision of processing workpiece and tool wear) superior to that of conventional O/W emulsion type water-soluble cutting fluids, and to provide a cutting fluid including the same.
In addition, in the present disclosure, the aqueous suspension is further diluted with water and used as a cutting fluid in metal processing, and one or more of alkaline electrolyzed water, metal rust preventatives, anti-freezing agents, anti-foaming agents, and preservatives are further added to not only improve the precision of processing metal workpieces to be cut and extend tool life, but also to achieve anti-rust, anti-freeze, anti-foam, and sterilization effects in preparing a hexagonal boron nitride particle-based cutting fluid. Based on that, another objective of the present disclosure is to provide a cutting fluid that is environmentally friendly and especially suitable for processing with a trace amount of lubrication.
The problems to be solved by the present disclosure are not limited to the technical problems mentioned above. Other technical problems that are not mentioned will be clearly understood by those skilled in the art through the description below.
An aqueous suspension according to an embodiment of the present disclosure for achieving the objectives preferably includes water, a hexagonal boron nitride (hBN) particle, and a dispersant. The hexagonal boron nitride (hBN) particle is preferably a hydrophilic particle that is wettable with water.
In the embodiment, the hexagonal boron nitride (hBN) particle is preferably synthesized at a temperature of 1600° C. or lower.
In addition, in the embodiment, the hexagonal boron nitride (hBN) particle preferably has a particle size D50 of 30 to 250 nm and a particle size D90 of 1 um or less for a primary particle and a secondary particle through the application of ultrasound for 24 hours. Meanwhile, when looking at the particle size from the aspect ratio (3 to 10), the specific surface area is preferably in a range of 10 to 90 m2/g.
In addition, in the embodiment, the hexagonal boron nitride (hBN) particle is preferably mixed with water at a weight ratio of 10 or less, and the dispersant is preferably mixed with water at a weight ratio (solid weight of the dispersant) of 10 or less.
In addition, in the embodiment, the water preferably includes alkaline ionized water of pH 10 or higher.
In addition, in the embodiment, as the dispersant, one or more selected from the group consisting of anionic, cationic, zwitterionic, and nonionic dispersants is preferably used alone or in combination.
In addition, in the embodiment, one or more selected from the group consisting of rust preventatives, anti-foaming agents, anti-freezing agents, and preservatives is preferably further included.
In addition, in the embodiment, one or more selected from the group consisting of Al2O3, MoS2, SiO2, ZrO2, CuO, SiC, TiO2, and diamond powder having a particle size D50 of 1 um or less for the secondary particle is preferably further included. In addition, in the embodiment, one or more selected from the group consisting of CNTs and graphene is preferably further included.
A cutting fluid according to another embodiment of the present disclosure is prepared by diluting each of the aqueous suspensions described above with water.
The cutting fluid is used in an MQL spray method.
In addition, the cutting fluid preferably further includes one or more selected from the group consisting of alkaline ionized water, rust preventatives, anti-foaming agents, anti-freezing agents, and preservatives.
A hexagonal boron nitride (hBN) particle-based aqueous suspension and a cutting fluid including the same according to an embodiment of the present disclosure can exhibit both the lubrication performance of non-aqueous cutting fluids and the cooling performance of water-soluble cutting fluids.
In addition, the cutting fluid can be carbon neutral due to not using any oil, induce clean processing that minimizes the amount of cutting fluid used, prevent the generation of waste oil, and minimize the generation of odor, thereby making working environments pleasant. Thus, the cutting fluid can be eco-friendly, and eco-friendliness thereof can be obtained through resource recycling by collecting and recycling the hexagonal boron nitride (hBN) particle.
In addition, the aqueous suspension according to another embodiment of the present disclosure is not limitedly applied to a cutting fluid for metal processing, but can also be applied for processing workpieces made of other materials such as plastics.
In addition, the aqueous suspension according to yet another embodiment of the present disclosure can also be applied as a lubricant for mechanical devices that experience various types of friction and wear due to the excellent lubricating function, high thermal conductivity, and release properties inherent to hexagonal boron nitride (hBN) particles.
Hereinafter, specific examples in which the present disclosure can be implemented will be described in detail as examples. These examples are described in sufficient detail to enable those skilled in the art to practice the disclosure. It should be understood that the various examples of the disclosure are different from one another but are not necessarily mutually exclusive. For example, specific shapes, structures, and characteristics described herein may be implemented in other examples without departing from the spirit and scope of the disclosure with respect to one example. Accordingly, the detailed description below is not intended to be taken in a limited sense. The scope of the disclosure is limited solely by the appended claims, together with all equivalents to which those claims, when properly described, are equivalent.
An aqueous suspension according to an embodiment of the present disclosure includes water, a hexagonal boron nitride (hBN) particle, and a dispersant. In this suspension, it is important that the hexagonal boron nitride (hBN) particle remains dispersed at a uniform concentration for a long time (1 day or more).
Synthesis of Hexagonal Boron Nitride (hBN) Particle
Generally, a hexagonal boron nitride (hBN) particle has a hydrophobic surface, thereby the hexagonal boron nitride (hBN) particle does not disperse well in water and does not have poor aqueous dispersibility, such as floating on the water surface or sinking below the water surface. Therefore, a hexagonal boron nitride particle prepared using conventional preparation methods cannot be used as it is.
Accordingly, in the present disclosure, the hexagonal boron nitride (hBN) particle is preferably synthesized by heat treatment in the air without controlling the gas atmosphere in which the synthesis is performed by using solid boron precursors and nitrogen precursors. The hexagonal boron nitride (hBN) particle is not synthesized by heat treatment in an inert atmosphere such as nitrogen or argon, which is a conventional preparation method. Also, the use of the hexagonal boron nitride (hBN) particles hydrophilic with high dispersibility in water is preferable. At this time, hydrophilicity is caused by atomic defects on the particle surface, dangling bonds, decomposition of water molecules, and hydroxyl groups resulting from the same.
To explain in more detail, the boron precursors and nitrogen precursors are mixed at a molar ratio of boron:nitrogen of 1:1. Afterward, synthesis is performed for 3 hours at a temperature of 1600° C. or lower, for example, 1500° C., in the air without controlling the gas atmosphere. The obtained powder is prepared by washing and purifying the synthesized product.
The reason is that when hBN powder with a particle size D50 of 30 nm or less is used, the shape of the particle is close to a sphere, so the shear direction of the processing surface and the sp2 bonding surface are not parallel. Thus, it is difficult to expect excellent lubrication performance during metal processing. In addition, when hBN powder with a particle size D50 of 1000 nm or more is used, precipitation by gravity occurs, thereby the dispersibility of the hexagonal boron nitride (hBN) particle in aqueous suspensions and cutting fluids including the same for metal processing is poor. In addition, it is difficult to control the concentration of the hBN particle during the processing process, making it difficult to use the particle for cutting fluids.
The specific surface area of the hBN particle was measured using a general gas adsorption method, and the range was limited as above. The reason is that the specific surface area is related to the aspect ratio (degree of flatness, 3 to 10) that deviates from the true sphere, so it is desirable that the primary particle size and aspect ratio correlate with the specific surface area in the range.
When a hexagonal boron nitride (hBN) powder prepared through the process is added into water without a dispersant, even when a high-shear stirrer is used for a long period (more than 6 hours), sedimentation occurs within 24 hours. Thus, it is difficult to manage uniform hexagonal boron nitride (hBN) concentration. Accordingly, what is needed is to use an appropriate dispersant at a weight ratio of 10 or less (solid weight of the dispersant), and to prepare an aqueous suspension in which more than 90% of hexagonal boron nitride (hBN) particle does not precipitate and exist in a suspended colloidal state even when stored for more than 1 day.
The dispersant is preferably an anionic dispersant. The dispersant may be selected from the group consisting of anionic, cationic, zwitterionic, nonionic, low molecular weight, or high molecular weight dispersant, or may be used alone or in combination, but is not limited thereto.
The aqueous suspension according to an embodiment of the present disclosure includes an anionic dispersant. The hexagonal boron nitride (hBN) powder may be included at a weight ratio of 10 or less. The dispersant may be usually added at a weight ratio of 10 (solid weight of dispersant) or less (100 g/L or less relative to water volume). The content of the dispersant can be appropriately selected considering the dilution ratio in water and the content of the hBN particle.
Likewise, in the aqueous suspension according to an embodiment of the present disclosure, the hexagonal boron nitride (hBN) powder may be included at a weight ratio of 10 or less, preferably a weight ratio of 1 or less. It is preferable to use an appropriate dispersant at a weight ratio of usually 10 (solid weight of dispersant) or less (100 g/L or less relative to water volume). Here, the content of hexagonal boron nitride (hBN) powder may vary depending on the processing environment such as tool material, tool shape, workpiece material, processing method, supply method, and application field. The aqueous suspension may have a low concentration of a weight ratio of 0.1 or less.
When the hexagonal boron nitride (hBN) particle has a content at a weight ratio of above 10, it is undesirable because the particles cannot maintain dispersibility for a long time, and precipitation is accelerated. When the dispersant is added at a weight ratio (100 g/L relative to water volume) of above 10 (solid weight of dispersant), a problem of the detergent working as a foreign substance on the workpiece after processing arises.
Water used in the aqueous suspension according to an embodiment of the present disclosure may be appropriately selected from one or more of distilled water, deionized water, tap water, groundwater, and industrial water. Additionally, the water may be alkaline ionized water of pH 10 or higher and may include electrolytic ionized water having a hydroxyl group, which is produced by electrolysis of water.
Specifically, it is preferable to prepare an aqueous suspension by mixing water, a hexagonal boron nitride (hBN) particle powder, and a dispersant in appropriate amounts as described above, and then dispersing the mixture through homogenization in a high-pressure homogenizer.
In addition, the aqueous suspension according to an embodiment of the present disclosure may further include one or more selected from the group consisting of rust preventatives, anti-foaming agents, anti-freezing agents, and preservatives. The mixing ratio and input amount of each of the components can be appropriately determined depending on the processing environment, application field, and amount of water dilution for the preparation of the cutting fluids.
First, the rust preventatives are added to suppress corrosion such as the prevention of rust on the metal workpieces to be cut. The type of the rust preventatives for use is not particularly limited, and one type or a combination of two or more types thereof can be used. For example, amine-based, organic-based, inorganic-based, and non-ferrous metal-based rust preventatives can be mixed with distilled water, deionized water, and water to prepare and use a rust preventive liquid. In the case of the amine-based type, the rust preventatives included in the rust preventive liquid are preferably at least one selected from the group consisting of diethylamine, triethylamine, cyclohexyl amine, ethanolamine, monoethanolamine, triethanolamine, propanolamine, monopropanolamine, and isopropanolamine. In the case of the organic-based type, the rust preventatives included in the rust preventive liquid are preferably carboxylic acid, and the carboxylic acid is preferably at least one selected from the group consisting of sebacic acid, undecanedioic acid, and dodecanedioic acid. In the case of the non-ferrous metal-based type, the rust preventatives included in the rust preventive liquid may be benzotriazole, tolytriazole, and mercaptobenzotriazole.
To suppress a foam made during the preparation process of the aqueous suspension and during the cutting process with cutting fluids containing the same, the anti-foaming agents may be further added. The anti-foaming agents may be used alone or in combination with two or more types of silicone-based anti-foaming agents such as polydimethylsiloxane, modified polydimethylsiloxane, organic silicone derivatives, silicone ethoxylate, and silica.
As the aqueous suspension and the cutting fluids including the same are used multiple times in the cutting process, microorganisms proliferate and cause bad odor. To prevent this, especially in summer, preservatives can be further added. The addable preservatives may include sodium benzoate, benzisothiazolinone (BIT) compound, triazine compound, benzotriazole compound, and tolyltriazole compound.
The anti-freezing agents may be further added so that the aqueous suspension and the cutting fluids including the same can be used even at temperatures below 0° C. in winter. The anti-freezing agents may include one or more ingredients selected from propylene glycol or ethylene glycol.
In addition, the aqueous suspension according to an embodiment of the present disclosure may further include one or more selected from the group consisting of Al2O3, MoS2, SiO2, ZrO2, CuO, SiC, TiO2, and diamond powder. The components preferably have a secondary particle size D50 of 1 μm or less. In addition, the aqueous suspension may further include one or more selected from the group consisting of CNTs and graphene. The role of these additional components is to supplement the lubrication mechanism resulting from the unique properties of the hBN particle.
Cutting fluids according to an embodiment of the present disclosure is prepared by diluting the aqueous suspension described above with an appropriate ratio of water to suit the use environment or processing purpose. Usually, aqueous suspensions are diluted 10 to 20 times with water. However, the dilution degree may be less or more depending on the processing environment, such as tool material, tool type, workpiece material, processing method, supply method, and application field.
In addition, depending on conditions such as usage environment or region, the cutting fluids may further include one or more selected from the group consisting of alkaline electrolyzed water, rust preventatives, anti-foaming agents, anti-freezing agents, and preservatives. Specifically, the cutting fluids may be prepared by adjusting the mixing ratio for the cutting fluids to contain a 34 or more weight ratio of water or alkaline electrolyzed water, a 10 or less weight ratio of aqueous suspension, a 20 or less weight ratio of rust preventive, a 25 or less weight ratio of anti-freezing agent, a 1 or less weight ratio of anti-foaming agent, and a 10 or less weight ratio of preservative.
To confirm the cutting performance of the cutting fluids according to an embodiment of the present disclosure, examples and comparative examples were prepared and tested as follows.
First, for use in examples and comparative examples, the boron precursors and nitrogen precursors are mixed at a molar ratio of boron:nitrogen of 1:1. Afterward, synthesis is performed for 3 hours at a temperature of 1500° C., in the air without controlling the gas atmosphere. The obtained powder is prepared by washing and purifying the synthesized product.
10 L of water, 200 g of hexagonal boron nitride (hBN) powder prepared above, and 100 g of dispersant Aerosol OT-100 were mixed for test preparation. Afterward, the mixture was processed in a high-pressure homogenizer five times at a low-pressure cycle of about 7,000 psi at a speed of 0.1 L/min, and twice at a high-pressure cycle of about 15,000 psi. The aqueous suspension prepared through dispersion processing was divided into 15 g portions, and each was diluted in 3 L of tap water to prepare cutting fluids. The fluids were put into an MQL feeder and sprayed on the processed area.
10 L of water, 200 g of hexagonal boron nitride (hBN) powder prepared above, and 100 g of dispersant Aerosol OT-100 were mixed for test preparation. Afterward, the mixture was processed in a high-pressure homogenizer five times at a low-pressure cycle of about 7,000 psi at a speed of 0.1 L/min, and twice at a high-pressure cycle of about 15,000 psi. The aqueous suspension prepared through dispersion processing was divided into 45 g portions, and each was diluted in 3 L of tap water to prepare cutting fluids. This was put into an MQL feeder and sprayed on the processed area.
10 L of water, 200 g of hexagonal boron nitride (hBN) powder prepared above, and 100 g of dispersant Aerosol OT-100 were mixed for test preparation. Afterward, the mixture was processed in a high-pressure homogenizer five times at a low-pressure cycle of about 7,000 psi at a speed of 0.1 L/min, and twice at a high-pressure cycle of about 15,000 psi. The aqueous suspension prepared through dispersion processing was divided into 15 g portions, and each was diluted in 300 g of alkaline electrolyzed water (pH 11) and 3 L of tap water to prepare cutting fluids. The reason for adding alkaline electrolyzed water separately here is to increase the pH and provide water-based sterilization and cleaning effects. The fluids were put into an MQL feeder and sprayed on the processed area. (Comparative Example 1) Alkaline electrolyzed water
Cutting fluids were prepared by preparing 3 L of pH 11 alkaline electrolyzed water without any additives.
10 L of distilled water and 200 g of hexagonal boron nitride (hBN) prepared above were introduced for test preparation. Afterward, the same as in the embodiments, the introduced mixture was processed in a high-pressure homogenizer five times at a low-pressure cycle of about 7,000 psi at a speed of 0.1 L/min, and twice at a high-pressure cycle of about 15,000 psi. The aqueous suspension prepared through dispersion processing was prepared. However, after 24 hours, more than 50% of the hexagonal boron nitride (hBN) particle precipitated, making it impossible to produce the desired cutting fluids.
(Comparative Example 3) Atomization spray of O/W emulsion-type water-soluble cutting fluids using MQL supply method
Cutting fluids were prepared by diluting 300 g of commercially available O/W emulsion-type water-soluble cutting fluid OLEX CUT 7500FE with 3 L of tap water. The prepared cutting fluids were put into an MQL feeder and sprayed on the machining area.
Cutting fluids were prepared by diluting 5 L of commercially available O/W emulsion-type water-soluble cutting fluid OLEX CUT 7500FE 10 times more with tap water. The prepared cutting fluids were put into a Flooding low-pressure pump supplier and sprayed on the machining area.
The particle size distribution and dispersibility of hexagonal boron nitride (hBN), the manufacturing method of which was described above, in each Example and Comparative Example are shown in Table 1 below.
In each example, the hBN particle remained in their colloidal state even after 1 day. Meanwhile, in the case of Comparative Example 2 where no dispersant was used under the same conditions, more than 50% of the hexagonal boron nitride (hBN) particle precipitated after 24 hours, making it impossible to use as a cutting fluid, so the following cutting performance tests were not conducted.
Cutting performance tests were conducted as follows using the remaining cutting fluids except Comparative Example 2. The milling machine tool used for the cutting performance test was the Doosan NX6500II machining center. The metal workpieces to be cut were SUS304 100×100×70 (mm3), and the tool was a YG1 10-pie 4-flute end mill. The tool wear of 5 the end mill was measured with Keyence VHX5000, and the surface roughness of the surface of the workpieces to be cut was measured with Mitutoyo SJ201. An MQL supplier for cutting fluid atomization used WINMIST equipment to spray cutting fluids onto the machining area at a speed of 400 cc/hr. A Flooding supplier used a general low-pressure pump to spray cutting fluids onto the machining area. The milling-cutting process conditions were set as shown in Table 2 below.
The workpieces were side milled, and three wear points on the end mill's flank surface were measured in 1 pass (10 m) units and the maximum values thereof were recorded. The criteria for ending cutting processing was when the wear length of the end mill's flank surface was 0.2 mm or more or when a processing distance reached 80 m (8 passes).
For a detailed explanation regarding the supply method of cutting fluids during cutting processing, in the minimal quantity lubrication (MQL) supply method used in Comparative Examples 1, 3, and Examples, each prepared cutting fluid was put into the same MQL equipment, atomized into an aerosol, and sprayed on the cutting area. In addition, in the Flooding spraying method used in Comparative Example 4, cutting fluid was sprayed into the cutting area in liquid form using a flooding supply method through a low-pressure pump.
As a result of the cutting performance tests above, as in Comparative Example 1, when only alkaline electrolyzed water was used as a cutting fluid, cutting of the metal workpieces to be cut was difficult, and tool wear was severe, so the initial cutting process was stopped. It was determined that cutting was not performed smoothly with only the cooling function without the lubrication function.
In the case of Comparative Example 3 using a commercially available O/W emulsion-type water-soluble cutting fluid, during the processing process, smoke and a smell of burning oil were generated. Therefore, it was confirmed that oil-based cutting fluids were difficult to apply to the MQL spray method.
As can be seen in
In addition, it was confirmed through additional tests that improvements in the surface roughness of the metal workpieces to be cut and tool wear were obtained. In addition, anti-rust, anti-freezing, anti-foam, and sterilization effects were also achieved by adding one or more from alkaline electrolyzed water, metal rust preventatives, anti-freezing agents, anti-foaming agents, and preservatives. This shows that the suspension is environmentally friendly since the suspension does not contain oil components for metal processing and can especially be applied for processing with a trace amount of lubrication.
The aqueous suspension according to one embodiment of the present disclosure is not limited to application as a cutting fluid for metal processing as above, but can also be applied 10 for processing workpieces made from other materials such as plastics. In addition, the aqueous suspension can also be applied as a lubricant for mechanical devices that experience various types of friction and wear due to the excellent lubricating function, high thermal conductivity, and release properties inherent to hBNs.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2022-0150719 | Nov 2022 | KR | national |
| 10-2023-0008141 | Nov 2022 | KR | national |
This application is a continuation of International Application No. PCT/KR2023/017258 filed on Nov. 1, 2023, which claims priority to Korean Application No. 10-2022-0150719 filed on Nov. 11, 2022 and Korean Application No. 10-2023-0008141 filed on Nov. 11, 2022, the entire contents of which are herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/KR2023/017258 | Nov 2023 | WO |
| Child | 18739887 | US |
