Water-based hydraulic fluids for hydraulic drives

Abstract

To provide the aqueous hydraulic fluid for the fluid pressure driving device, that can operate smoothly, can prevent environmental pollution caused by leakage of a hydraulic fluid, and can prevent fire outbreak.SOLUTION: The present invention relates to the aqueous hydraulic fluid for the fluid pressure driving device that operates by a liquid pressure, the aqueous hydraulic fluid contains water and sodium polyacrylate, an amount of sodium polyacrylate with respect to water in the aqueous hydraulic fluid is in a range of 0.3 to 1.5 mass%, and a hydrogen index is adjusted to be in the range of pH 9 to pH 11.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to water-based hydraulic fluids for hydraulic drives. [Background technology]

[0002] Hydraulic drive devices (e.g., hydraulic actuators including hydraulic cylinders, hydraulic motors, etc.) that are driven by the hydraulic pressure of pressurized hydraulic fluid are well known. Conventionally, hydraulic oils made from mineral oils or the like have been widely used as the hydraulic fluid for such hydraulic drive devices because they have appropriate viscosity and are highly effective in reducing sliding friction (see, for example, Patent Documents 1 to 6).

[0003] A hydraulic drive system, i.e., a hydraulic system, that uses hydraulic oil as the working fluid is usually provided with a hydraulic oil supply / discharge system for supplying and discharging the hydraulic oil discharged from a hydraulic pump to the hydraulic system. The hydraulic oil supply / discharge system is provided with a plurality of oil passages arranged between the hydraulic oil tank and the hydraulic system, and various hydraulic devices such as a hydraulic pump, oil passage switching valve, flow control valve, relief valve, and check valve that are interposed in these oil passages. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-110710 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-74518 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-68863 [Patent Document 4] Japanese Patent Application Publication No. 2018-84295 [Patent Document 5] Japanese Patent Application Laid-Open No. 2016-108919 [Patent Document 6] Japanese Patent Application Laid-Open No. 2017-002518 Summary of the Invention [Problem to be solved by the invention]

[0005] Hydraulic devices and hydraulic oil supply / discharge devices are structures in which many components are connected or linked, and therefore hydraulic oil may leak, for example, at the connection between one component and another. If such a hydraulic device is used to drive a water gate or the like installed in a river or irrigation canal, for example, if hydraulic oil leaks from the hydraulic device or hydraulic oil supply / discharge device, the hydraulic oil may get mixed into the water flowing in the river or irrigation canal, causing serious environmental pollution.

[0006] Furthermore, since hydraulic oil is flammable, there is a risk of fire spreading or an accident causing a fire in the hydraulic device and the hydraulic oil supply and discharge device.

[0007] The present invention has been made to solve these problems, and has an object to provide a water-based hydraulic fluid for a hydraulic drive system that can operate the hydraulic drive system smoothly, prevent environmental pollution due to leakage, and prevent the occurrence of fires. [Means for solving the problem]

[0008] The present invention, which has been made to solve the above problems, Pressurized Hydraulic power operated by the pressure of a liquid Cylinder or hydraulic motor A water-based hydraulic fluid for The aqueous hydraulic fluid contains water and sodium polyacrylate, and the amount of sodium polyacrylate relative to water in the aqueous hydraulic fluid of A range of 0.3 to 1.5 mass percent (preferably 0.4 to 1.35 mass percent) By doing so the law of nature, The viscosity at 25°C is 10 to 50 mPa·s. The hydrogen index is adjusted to within the range of pH 9 to pH 11.

[0009] In the aqueous working fluid according to the present invention, the hydrogen index is preferably adjusted to within the range of pH 9 to pH 11 by adding sodium hydroxide.

[0010] The aqueous working fluid according to the present invention contains propylene glycol, and the amount of propylene glycol added to water in the aqueous working fluid is preferably equal to or greater than the amount of propylene glycol added to water in an aqueous propylene glycol solution having a freezing point that is a preset lower limit temperature for system use within a temperature range that is lower than 0°C and higher than the freezing point of propylene glycol.

[0011] The aqueous working fluid according to the present invention preferably contains ethanol, and the amount of ethanol added to water in the aqueous working fluid is preferably the same as or greater than the amount of ethanol added to water in an aqueous ethanol solution whose freezing point is a preset lower limit temperature for system use within a temperature range that is lower than 0°C and higher than the freezing point of ethanol.

[0012] In the water-based hydraulic fluid according to the present invention, it is preferable that the hydraulic drive device is a hydraulic actuator that operates by the pressure of the liquid. [Effects of the Invention]

[0013] According to the present invention, hydraulic Cylinder or hydraulic motor Since it uses water-based hydraulic fluid instead of hydraulic oil as the power source, Cylinder or hydraulic motor Even if a hydraulic fluid leak occurs in the hydraulic fluid supply / discharge device, oil contamination of the environment or the product will not occur as in the case of a hydraulic actuator. Cylinder or hydraulic motor The water-based hydraulic fluid can be effectively used in equipment where contamination by hydraulic fluid is a problem, such as waterway opening and closing devices and manufacturing equipment for food, cosmetics, medicines, etc. Furthermore, water-based hydraulic fluids are non-flammable, and hydraulic pressure systems using water-based hydraulic fluids are Cylinder or hydraulic motor This is extremely advantageous in terms of fire prevention, as there is no possibility of a fire breaking out. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram illustrating the configuration of a dynamic friction coefficient measuring device. [Figure 2]1 is a graph showing the relationship between viscosity and concentration of an aqueous sodium polyacrylate solution. [Figure 3] 1 is a graph showing the relationship between viscosity and temperature of an aqueous sodium polyacrylate solution. [Figure 4] 1 is a graph showing the relationship between the dynamic friction coefficient and the concentration of an aqueous sodium polyacrylate solution. [Figure 5] 1 is a graph showing the relationship between the freezing point and the concentration of an ethanol aqueous solution and a propylene glycol aqueous solution. [Figure 6] FIG. 1 is a configuration diagram illustrating an example of a hydraulic cylinder system. [Figure 7] FIG. 1 is a configuration diagram illustrating an example of a hydraulic motor system. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0016] <About water-based hydraulic fluids> 1. What is water-based hydraulic fluid? Hydraulic devices such as hydraulic cylinders and hydraulic motors generally use hydraulic fluid made from mineral oil as a power transmission medium, but because mineral oil is flammable, there is a risk of fire spreading or an accident causing a fire in the hydraulic device. Furthermore, when hydraulic devices are used in river sluices, etc., there is a risk of damage to the aquatic environment over a wide area of ​​water downstream due to a large-scale leakage of hydraulic oil during an earthquake or other disaster. Therefore, the present invention proposes a new water-based hydraulic fluid as an alternative to hydraulic oil, which does not pose a risk of fire and does not damage the aquatic environment even if it leaks into a river or the like.

[0017] 2. Matters considered in the development of water-based hydraulic fluids The present inventors have investigated the following points when developing a new water-based hydraulic fluid. (1) Viscosity (dynamic viscosity) is equivalent to that of hydraulic oil (2) The temperature change of viscosity is small (3) The coefficient of dynamic friction between the sliding parts is equivalent to that when hydraulic oil is used. (4) Non-toxic to living organisms (5) Low environmental pollution due to leakage or discharge (6) There is no risk of fire (7) In cold regions, do not freeze at low temperatures. (8) Almost no deterioration due to oxidation (9) Low corrosiveness to rubber packing (10) Low metal corrosiveness to aluminum and iron materials (11) No adverse effects caused by water vapor in the air (12) Good bubble separation in the liquid storage tank (13) There is almost no biological deterioration (decay)

[0018] 3. Examples of main components of water-based hydraulic fluids (1) Pure water (distilled water) (2) Thickeners and sliding friction reducers (e.g., sodium polyacrylate (PANa), polyacrylic acid) (3) Antifreeze (e.g., ethanol, propylene glycol) (4) pH adjusters (e.g., sodium hydroxide) (5) pH of aqueous hydraulic fluid: 9 to 11

[0019] 4. Viscosity measurement of sodium polyacrylate aqueous solution (1) Using an Ostwald viscometer, the relative viscosity of the sodium polyacrylate aqueous solution to pure water was measured, and the viscosity of the sodium polyacrylate aqueous solution was calculated from this relative viscosity and the viscosity of pure water (known).

[0020] (2) Measurement results Figure 2 is a graph showing the relationship between viscosity and concentration of a sodium polyacrylate aqueous solution. From this graph, it can be seen that viscosity and concentration are almost directly proportional to each other. Furthermore, it is thought that the proportionality coefficient (slope) changes depending on the temperature.

[0021] [Table 1]

[0022] (3) Temperature dependence of viscosity Figure 3 is a graph showing the relationship between viscosity and temperature of a sodium polyacrylate aqueous solution. From this graph, it can be seen that the viscosity of a sodium polyacrylate aqueous solution (1 wt%) decreases as the temperature increases over the temperature range of 0°C to 50°C, and conversely, the viscosity increases as the temperature decreases. On the other hand, it can be seen that hydraulic oil has a greater temperature dependency than a sodium polyacrylate aqueous solution, and its allowable temperature range is also narrower.

[0023] 5. Measurement of the dynamic friction coefficient of sodium polyacrylate aqueous solution (1) The dynamic friction coefficient between sliding parts was measured using an aqueous solution of sodium polyacrylate (PANa) using the dynamic friction coefficient measuring device shown in Figure 1. This dynamic friction coefficient measuring device is equipped with a table, a cart that moves freely on the table, a weight connected to the front of the cart via a string, a pulley that guides the string, a movable object connected to the rear of the cart via a nylon line, a channel along which the movable object slides, and a tension gauge that measures the tension of the nylon line.

[0024] (2) Channel specifications A "U"-shaped channel made of stainless steel with a smooth inner surface Width 50mm Height 25mm Length 1500mm

[0025] (3) Specifications of the movable object A "U"-shaped channel made of stainless steel with a smooth outer surface that is housed within the groove of the channel and can slide in the longitudinal direction of the channel. Width 40mm Height 30mm Length 100mm Weight 92g

[0026] (4) Measurement method of dynamic friction coefficient Both ends of the channel were closed, a water-based hydraulic fluid was poured into the groove of the channel, and a movable object was placed inside. The movable object was then pulled at a constant speed in the longitudinal direction of the channel by a cart, and the tension was measured with a tension gauge. The measured tension value was then divided by the mass (weight) of the movable object to calculate the coefficient of kinetic friction.

[0027] (5) Adjustment of the moving speed of the cart and movable objects The moving speed of the cart and the movable object was kept constant by increasing or decreasing the mass of the weight loaded on the cart. The moving speed of the cart and the movable object was set very low (less than 2 cm / sec) so that the flow resistance of the water-based hydraulic fluid against the movable object could be reduced to a virtually negligible level.

[0028] (6) Measurement results Figure 4 is a graph showing the relationship between the dynamic friction coefficient and concentration of a sodium polyacrylate aqueous solution. Table 2 below shows the measurement data. From this graph, it can be seen that at concentrations of PANa between 0.75 wt% and 1.0 wt%, the dynamic friction coefficient reaches a minimum of 0.011, which is comparable to the dynamic friction coefficient of hydraulic oil. As the concentration increases or decreases from there, the dynamic friction coefficient increases, but remains at most around 0.022, which is a sufficient practical level.

[0029] [Table 2]

[0030] 6. Appropriate sodium polyacrylate concentration The relationship between sodium polyacrylate concentration and viscosity and its temperature dependence is shown in Figures 2 and 3. The relationship between sodium polyacrylate concentration and sliding friction coefficient is shown in Figure 4. Therefore, if a) the appropriate viscosity is set to 10 to 50 mPa·s, referring to the graph in Figure 2, the corresponding sodium polyacrylate concentration is 0.3 to 1.5 wt%. Also, if b) the appropriate sliding friction coefficient is set to 0.02 or less, referring to the graph in Figure 4, the corresponding sodium polyacrylate concentration is 0.2 to 1.5 wt%. As a result, the concentration that satisfies both conditions a) and b) is 0.3 to 1.5 wt%. Furthermore, when the appropriate sliding friction coefficient is more preferably set to 0.015 or less (c), the corresponding sodium polyacrylate concentration is 0.4 to 1.35 wt% as shown in the graph of Figure 4. As a result, the concentration that satisfies both conditions a) and c) is 0.4 to 1.35 wt%.

[0031] 7.Prevents freezing in low temperatures (1) It is preferable to add ethanol or propylene glycol as an antifreeze to the aqueous sodium polyacrylate solution. However, if a large amount of propylene glycol is added, the viscosity may increase sharply at low temperatures. However, it has been found that if ethanol is added, the viscosity does not increase significantly even at low temperatures.

[0032] (2) Amount of antifreeze added Figure 5 is a graph showing the relationship between freezing point and concentration for an ethanol aqueous solution and a propylene glycol aqueous solution. This graph reveals that the freezing point of both solutions is 0°C at a concentration of 0 wt% (i.e., water), and that the freezing point decreases as the concentration increases. Therefore, even in aqueous working fluids containing sodium polyacrylate, the amount of antifreeze added to water is preferably the same as or greater than the amount of antifreeze added to water in an antifreeze aqueous solution whose freezing point is a preset lower limit temperature for system use within the temperature range of 0°C to the antifreeze freezing point.

[0033] 8. Comparison of water-based hydraulic fluid and hydraulic oil (1) Compressibility The hydraulic fluid in a hydraulic cylinder or hydraulic motor must be incompressible, and both water-based hydraulic fluid and hydraulic oil are incompressible.

[0034] (2) Viscosity (kinematic viscosity) A high viscosity (kinetic viscosity) of the hydraulic fluid is preferable from the viewpoint of preventing leakage from the sliding parts of the hydraulic cylinder or hydraulic motor, but a low viscosity is preferable from the viewpoint of reducing pressure loss in the hydraulic fluid passage. To achieve both, the viscosity of the hydraulic fluid at room temperature is generally set to about 10 to 50 mPa·s.

[0035] In the case of aqueous hydraulic fluids, if the sodium polyacrylate concentration is set to 0.3 to 1.5 wt%, the viscosity at room temperature (25°C) can be set to 10 to 50 mPa s. By increasing or decreasing the amount of sodium polyacrylate, the viscosity of the hydraulic fluid can be adjusted within the range of 10 to 50 mPa s.

[0036] In the case of hydraulic oil, the viscosity is adjusted by changing the type or blend of mineral oil used.

[0037] It is preferable that the viscosity of a hydraulic fluid change with temperature as little as possible. The viscosity of a water-based hydraulic fluid is generated by interactions between sodium polyacrylate and water, such as hydrogen bonds, ionic bonds, and hydrophobic bonds, but the temperature dependence of these bonding forces is relatively small. Therefore, the temperature change of the viscosity of a water-based hydraulic fluid is much smaller than that of hydraulic oil.

[0038] (3) Coefficient of sliding friction To reduce wear on the sliding parts of hydraulic cylinders or hydraulic motors, or on the gear meshing parts of gear pumps in hydraulic fluid supply and discharge systems, the smaller the coefficient of sliding friction at the sliding parts, the better. In this respect, water-based hydraulic fluids are equivalent to hydraulic oils.

[0039] (4) Deterioration due to oxidation It is essential that hydraulic fluids are resistant to deterioration due to oxidation reactions (especially at high temperatures). Water-based hydraulic fluids are basically made up of water and sodium polyacrylate, but sodium polyacrylate does not react with oxygen below its combustion temperature (several hundred degrees Celsius), so water-based hydraulic fluids do not deteriorate due to oxidation. On the other hand, hydraulic fluids made from mineral oils inevitably deteriorate due to oxidation, and the rate of deterioration increases the higher the temperature.

[0040] (5) Compatibility with packing Generally, the packing material for hydraulic cylinders or hydraulic motors is nitrile rubber, but sodium polyacrylate does not deteriorate nitrile rubber, so nitrile rubber packing can be used.

[0041] (6) Metal corrosiveness Hydraulic cylinders or hydraulic motors and hydraulic fluid supply / discharge devices are generally made of aluminum alloys or iron alloys, but metal materials for hydraulic devices other than aluminum alloys are acidic (hydrogen ions H + ) corrosion does not occur, and alkali (hydroxide ion OH - ) corrosion does not occur. Aluminum alloys are prone to corrosion due to alkalis (hydroxide ions OH) when the pH exceeds 11. - ) may cause corrosion. When the pH of the water-based hydraulic fluid is in the range of 9 to 11, corrosion hardly occurs even if aluminum alloy parts are used in the hydraulic cylinder, hydraulic motor, or hydraulic fluid supply / discharge device. Therefore, it is preferable to adjust the pH of the water-based hydraulic fluid to 9 to 11. Furthermore, hydraulic oil has relatively low metal corrosiveness as long as it does not contain sulfur.

[0042] (7) Effects of water vapor contamination Hydraulic systems are generally closed systems, designed to prevent the intrusion of foreign matter such as dirt and dust from the outside. However, since they are not completely sealed, they cannot prevent the intrusion of water vapor from the atmosphere. For this reason, water vapor from the atmosphere can get into the hydraulic oil in hydraulic systems, causing the oil to deteriorate and become cloudy. Since water-based hydraulic fluids are mostly water, the intrusion of water vapor from the atmosphere does not cause any particular problems.

[0043] (8) Possibility of fire Water-based hydraulic fluids are mostly water and therefore non-flammable, meaning there is no risk of fire occurring in hydraulic cylinder systems or hydraulic motor systems that use water-based hydraulic fluids, which is extremely advantageous in terms of fire prevention.On the other hand, hydraulic fluids made from mineral oils are flammable, so there is a possibility of fire occurring in hydraulic cylinder systems or hydraulic motor systems due to the spread of fire or accidents.

[0044] (9)Toxicity / environmental pollution Sodium polyacrylate or polyacrylic acid is used as a thickener in the manufacturing of food and cosmetics, and has extremely low toxicity to living organisms. Therefore, the toxicity of water-based hydraulic fluids to living organisms is extremely low, and even if they are discharged into rivers, etc., they will not adversely affect the aquatic ecosystem.

[0045] Sodium polyacrylate or polyacrylic acid has extremely low toxicity to living organisms, and in a natural environment where nutrients such as nitrogen compounds and phosphorus compounds are abundant, it is biodegraded by microorganisms, ultimately becoming carbon dioxide and water. Water-based hydraulic fluids are aqueous solutions, and if they leak into rivers, etc., they immediately mix with the water and do not settle to the bottom or float on the surface. Therefore, even if water-based hydraulic fluid leaks into rivers, lakes, etc. from a hydraulic cylinder system or hydraulic motor system, it will be decomposed by the self-purifying mechanism of nature, and its environmental pollution potential is very low.

[0046] Hydraulic oil is toxic to living organisms, and if it leaks into rivers, lakes, marshes, etc., it floats on the water surface and severely deteriorates the aquatic environment.

[0047] (10) Bubble behavior Generally, the working fluid in hydraulic cylinder systems or hydraulic motor systems is in constant contact with air in the working fluid tank, so air dissolves almost to the saturation solubility. The air saturation solubility changes roughly in proportion to the pressure of the working fluid. Therefore, in places in the working fluid circulation circuit where the working fluid is in a reduced pressure state (below atmospheric pressure) (for example, at the pump suction port), some of the air dissolved in the working fluid becomes unable to dissolve, resulting in the formation of tiny bubbles. These bubbles will dissolve into the working fluid when the pressure of the working fluid rises again, but it takes a certain amount of time for the bubbles to completely dissolve into the working fluid. For this reason, residual air bubbles can cause pump cavitation and erosion of parts.

[0048] At atmospheric pressure, the air saturation solubility of mineral oil hydraulic fluid at room temperature is about 9% by volume, while that of water-based hydraulic fluid is about 2% by volume. As the air saturation solubility of water-based hydraulic fluid is smaller than that of hydraulic fluid, fewer bubbles are generated, reducing the occurrence of pump cavitation and erosion of parts.

[0049] When bubbles are present in a hydraulic fluid, the bubbles are compressible, which can cause malfunctions in the operation of hydraulic cylinders or hydraulic motors driven by pressurized hydraulic fluid. Furthermore, when bubbles are adiabatically compressed due to pressurization of the hydraulic fluid, the bubbles become very hot if heat dissipation to the outside of the bubbles is poor (for example, approximately 800°C at 10 MPa). Therefore, when hydraulic oil is used as the hydraulic fluid, the temperature of the hydraulic oil adjacent to the bubbles becomes high due to poor heat dissipation to the outside of the bubbles, which can lead to thermal degradation or oxidation.

[0050] Water-based working fluids generate fewer bubbles than hydraulic oils, reducing malfunctions in hydraulic equipment caused by bubbles. Furthermore, water-based working fluids have high thermal conductivity (about five times that of hydraulic oils) and a large heat capacity, so the heat generated in the bubbles by adiabatic compression is quickly dissipated outside the bubbles, preventing the bubbles from reaching very high temperatures. Therefore, the water-based working fluid adjacent to the bubbles does not become very hot. Furthermore, water-based working fluids do not oxidize or thermally deteriorate, even if their temperature rises to their boiling point.

[0051] In addition, in general, in hydraulic cylinder systems or hydraulic motor systems, a bubble floatation separation device is attached to the hydraulic fluid storage tank, and the higher the density of the hydraulic fluid, the greater the buoyancy of the bubbles, and the better the bubble separation efficiency.

[0052] The density of hydraulic fluid made from mineral oil is 0.85 g / cm 3 The density of water-based hydraulic fluid is about 1g / cm 3 Therefore, when a water-based hydraulic fluid is used, the buoyancy of the air bubbles in the air bubble flotation device is greater than when hydraulic oil is used, making it easier and faster to remove the air bubbles.

[0053] (11) Biological deterioration (decay) Sodium polyacrylate or polyacrylic acid, the main raw material of water-based hydraulic fluids, is an organic compound containing carbon, hydrogen, or oxygen, and can basically serve as a nutrient source for microorganisms. Therefore, if there is a sufficient supply of nitrogen compounds, phosphorus compounds, etc., necessary for the growth of microorganisms, water-based hydraulic fluids may be biodegraded (putrefied) by microorganisms.

[0054] However, since there is no possibility of nitrogen compounds, phosphorus compounds, etc., which are essential for the growth of microorganisms, entering a hydraulic cylinder system or hydraulic motor system, which is a nearly closed system, there is no possibility of normal microorganisms growing in the water-based hydraulic fluid, and biological deterioration (putrefaction) of the water-based hydraulic fluid does not occur. Furthermore, if water-based hydraulic fluid is discharged into rivers, lakes, etc., the water-based hydraulic fluid will be biodegraded because there are large amounts of nitrogen compounds, phosphorus compounds, etc. present in the outside world.

[0055] (12) Antifreeze When a hydraulic cylinder system or hydraulic motor system is installed in a cold region, it is essential that the hydraulic fluid does not freeze in winter. In this case, it is preferable to add ethanol or propylene glycol as an antifreeze to the water-based hydraulic fluid to prevent freezing. The amount of ethanol or propylene glycol added is adjusted depending on the operating temperature.

[0056] [Table 3]

[0057] <Legal regulations regarding water-based hydraulic fluids> 1. Characteristics of raw materials for water-based hydraulic fluids (1) Sodium polyacrylate or polyacrylic acid Although they are synthetic chemicals, they are extremely low in toxicity or harmfulness to living organisms, and sodium polyacrylate or polyacrylic acid, which are of food additive quality, are used as thickeners in the food industry. The use of sodium polyacrylate or polyacrylic acid is not legally restricted from the viewpoint of protecting living organisms.

[0058] (2) Ethanol Ethanol is used as a medicine and beverage, and has extremely low toxicity or harmfulness to living organisms.

[0059] (3) Propylene glycol Propylene glycol is used as a quality improver in pharmaceuticals, cosmetics, and foods such as noodles and cooked rice, and has extremely low toxicity or harm to living organisms. Propylene glycol is flammable and is classified as a Class 4 hazardous material under the Fire Service Act, but the propylene glycol concentration in processed water is far below the flammable limit. Therefore, processed water is not subject to regulations under the Fire Service Act due to the presence of propylene glycol.

[0060] (4) Sodium hydroxide Sodium hydroxide dissolves in water as sodium ions (Na + ) and hydroxide ions (OH - ), and although a high hydroxide ion concentration in water makes it more alkaline, both ions are naturally present in living organisms and are not toxic or harmful to living organisms. Therefore, aside from being subject to regulations based on alkalinity or pH, the use of sodium hydroxide itself is not legally restricted from the perspective of protecting living organisms.

[0061] 2. Regulations for water-based hydraulic fluids Water-based hydraulic fluids are discharged or discarded into bodies of water after their useful life has expired, but if they are discharged into public waters (rivers, lakes, and oceans), they may be regulated by the Water Pollution Control Act or its supplementary ordinances, and if they are discharged into public sewerage systems, they may be regulated by the Sewerage Act or its supplementary ordinances.The Water Pollution Control Act or Sewerage Act or their supplementary ordinances regulate that if effluent or wastewater discharged from a business or other facility contains specified hazardous substances (28 types) related to health, the concentration of hazardous substances in the effluent or wastewater must be below the emission standards, regardless of the amount of discharge.

[0062] On the other hand, for the quality of effluent or wastewater related to living environment items that are not directly toxic or harmful to living organisms, the Water Pollution Control Law and the Sewerage Law require that the average daily discharge of effluent or wastewater is 50 m 3 There are no restrictions on discharges from establishments that discharge less than 10m3. 3 In the above cases, some prefectures regulate emissions.

[0063] Water-based hydraulic fluids do not contain any harmful substances related to health as defined in the Water Pollution Control Act or the Sewerage Act. In addition, in hydraulic cylinder systems or hydraulic motor systems that use water-based hydraulic fluids, the water-based hydraulic fluid is circulated, and after the end of its useful life, only approximately 500 to 1,000 liters of water-based hydraulic fluid is discharged into public water bodies or public sewerage systems. Therefore, even in prefectures where the strictest additional standards are applied, an average of 10 m per day is discharged from hydraulic motor systems that use water-based hydraulic fluids. 3 There is no possibility that the above wastewater or wastewater will be discharged into public water bodies or public sewerage systems. Therefore, in hydraulic cylinder systems or hydraulic motor systems that use water-based hydraulic fluid, when the water-based hydraulic fluid is discharged into public water bodies or public sewerage systems, it is not subject to regulations under the Water Pollution Control Act, the Sewerage Act, or their additional ordinances.

[0064] Next, a specific example of a hydraulic drive system using a water-based hydraulic fluid according to the present invention will be described. In the following embodiments, a hydraulic cylinder system using a hydraulic cylinder and a hydraulic motor system using a hydraulic motor will be described as hydraulic actuators that use pressurized water-based hydraulic fluid as a power transmission medium, but the present invention can also be applied to hydraulic drive systems that use something other than a hydraulic motor (for example, a hydraulic pump, etc.).

[0065] <Hydraulic Cylinder System Overview> FIG. 6 is a configuration diagram showing an example of a hydraulic cylinder system. The hydraulic cylinder system S includes a single-rod, double-acting hydraulic cylinder device 1 that uses pressurized water-based hydraulic fluid according to the present invention as a power transmission medium, and a hydraulic fluid supply / discharge device 2 that supplies and discharges the water-based hydraulic fluid to the hydraulic cylinder device 1. The hydraulic cylinder device 1 includes a substantially cylindrical cylinder 3, a substantially cylindrical piston 4 that is fitted or inserted into a cylindrical hollow portion of the cylinder 3 (hereinafter referred to as the "cylinder hollow portion"), and a slender cylindrical (round rod-shaped) piston rod 5 attached to one end of the piston 4. The hydraulic cylinder device 1 is a vertically-mounted type in which the central axes of the cylinder 3, piston 4, and piston rod 5 extend vertically (up and down). The hydraulic cylinder device is not limited to being a vertically-mounted type, and may be a horizontally-mounted or inclined type.

[0066] The tip end of the piston rod 5 (the end opposite the piston 4) is connected to a load 6 (for example, a gate body of a water gate) that is moved in the direction of the central axis of the piston rod by the hydraulic cylinder device 1. Hereinafter, the position on the cap side of the hydraulic cylinder device 1 will be referred to as "upper (upper side)" and the position on the rod side will be referred to as "lower (lower side)."

[0067] The piston 4 can move (slide) up and down within the hollow cylinder portion. The hollow cylinder portion is divided into upper and lower portions by the piston 4, with a first fluid chamber 7 formed above the piston 4 (cap side) and a second fluid chamber 8 formed below the piston 4 (rod side). In the hydraulic cylinder device 1, when pressurized hydraulic fluid is supplied to the first fluid chamber 7, the piston 4 and piston rod 5 are moved downward by the pressure of the hydraulic fluid, and when pressurized hydraulic fluid is supplied to the second fluid chamber 8, the piston 4 and piston rod 5 are moved upward by the pressure of the hydraulic fluid, thereby moving the load 6 up and down.

[0068] The hydraulic fluid supply / discharge device 2 supplies pressurized hydraulic fluid to any one of the fluid chambers (the first fluid chamber 7 or the second fluid chamber 8) of the hydraulic cylinder device 1 when the hydraulic cylinder device 1 is operating (when the piston is sliding), and discharges hydraulic fluid from the other fluid chamber (the second fluid chamber 8 or the first fluid chamber 7). The hydraulic fluid supply / discharge device 2 is provided with an electromagnetic passage switching valve 11, which is a 4-port 3-position directional control valve. A first port P1 of the passage switching valve 11 is connected to the first fluid chamber 7 via a first hydraulic fluid passage 12, and a second port P2 is connected to the second fluid chamber 8 via a second hydraulic fluid passage 13. A hydraulic fluid supply passage 14 is connected to a third port P3 of the passage switching valve 11, and a hydraulic fluid return passage 15 is connected to a fourth port P4. Ends of the hydraulic fluid supply passage 14 and the hydraulic fluid return passage 15 (ends not connected to the passage switching valve 11) are introduced into a hydraulic fluid tank 16 that stores hydraulic fluid.

[0069] A filter 17 (or strainer) is attached to the tip of the hydraulic fluid supply path 14 to remove foreign matter, dust, etc. from the hydraulic fluid drawn into the hydraulic fluid supply path 14, and this filter 17 is immersed in the hydraulic fluid stored in the hydraulic fluid storage tank 16. The hydraulic fluid storage tank 16 is provided with an ultraviolet lamp 18 that irradiates the upper surface of the stored hydraulic fluid with ultraviolet light to sterilize the hydraulic fluid. It is preferable to use an ultraviolet lamp 18 that emits ultraviolet light of 250 to 260 nm (for example, mercury spectral lines around 253.7 nm (UV-C region)), which has a particularly high sterilizing effect. Note that the ultraviolet lamp 18 can be omitted if necessary.

[0070] A hydraulic fluid supply pump 20 driven by a motor 19 (or an engine) is provided in the hydraulic fluid supply path 14. The hydraulic fluid supply pump 20 draws hydraulic fluid from the hydraulic fluid storage tank 16, pressurizes the hydraulic fluid, and supplies it to the third port P3 of the passage switching valve 11. A first bypass path 21 is provided to connect the hydraulic fluid supply path 14 downstream (on the passage switching valve side) of the hydraulic fluid supply pump 20 with the hydraulic fluid return path 15 in terms of the flow direction of the hydraulic fluid, and a relief valve 22 is provided in this first bypass path 21 to adjust the pressure of the hydraulic fluid discharged from the hydraulic fluid supply pump 20.

[0071] A working fluid heating device 23 for heating the working fluid in the working fluid return path 15 is provided in the working fluid storage tank side of the connection with the first bypass passage 21. The working fluid heating device 23 may be a heat exchanger or an electric heater that uses high-temperature steam or a heat medium as a heat source. In addition, a cooler 24 for cooling the working fluid is provided in the working fluid return path 15 in the working fluid storage tank side of the working fluid heating device 23. A water-cooled multi-tube heat exchanger or the like may be used as the cooler 24. The cooler 24 may be omitted as necessary.

[0072] The passage switching valve 11 switches the supply / discharge path of the hydraulic fluid to the hydraulic cylinder device 1. The passage switching valve 11 is a solenoid valve controlled by a control device (not shown), and can be set to any one of a first state in which the hydraulic fluid pressurized by the hydraulic fluid supply pump 20 and supplied to the third port P3 is supplied to the first fluid chamber 7 via the first hydraulic fluid passage 12, a second state in which the hydraulic fluid is supplied to the second fluid chamber 8 via the second hydraulic fluid passage 13, and a third state (the state shown in FIG. 1 ) in which the hydraulic fluid is not supplied to the hydraulic cylinder device 1.

[0073] In the first state, the working fluid in the second fluid chamber 8 returns to the working fluid tank 16 via the second working fluid passage 13 and the working fluid return path 15, and in the second state, the working fluid in the first fluid chamber 7 returns to the working fluid tank 16 via the first working fluid passage 12 and the working fluid return path 15. In addition, in the third state, the ends of the first working fluid passage 12 and the second working fluid passage 13 on the passage switching valve side are closed. The passage switching valve 11 may be configured so that the working fluid supply path 14 and the working fluid return path 15 are in communication with each other in the third state.

[0074] In the first hydraulic fluid passage 12, there are disposed in series, in this order from the passage switching valve side to the hydraulic cylinder device side, a first pilot-operated check valve 25 which basically blocks the flow of hydraulic fluid from the hydraulic cylinder device side to the passage switching valve side, and a first check valve-equipped flow control valve 26 which is composed of a flow control valve 26a and a check valve 26b connected in parallel to each other. The first check valve-equipped flow control valve 26 does not particularly restrict the flow of hydraulic fluid from the passage switching valve side to the hydraulic cylinder device side, but adjusts the flow rate of hydraulic fluid from the hydraulic cylinder device side to the passage switching valve side. When hydraulic pressure (pilot pressure) equal to or higher than the set pressure is applied to the second hydraulic fluid passage 13, the first pilot-operated check valve 25 allows the flow of hydraulic fluid in the first hydraulic fluid passage 12 from the hydraulic cylinder device side to the passage switching valve side.

[0075] In the second hydraulic fluid passage 13, there are disposed in series, in this order from the passage switching valve side to the hydraulic cylinder device side, a second pilot-operated check valve 27 which basically blocks the flow of hydraulic fluid from the hydraulic cylinder device side to the passage switching valve side, and a second check valve-equipped flow control valve 28 which is composed of a flow control valve 28a and a check valve 28b connected in parallel to each other. The second check valve-equipped flow control valve 28 does not particularly restrict the flow of hydraulic fluid from the passage switching valve side to the hydraulic cylinder device side, but adjusts the flow rate of hydraulic fluid from the hydraulic cylinder device side to the passage switching valve side. When hydraulic pressure (pilot pressure) equal to or higher than the set pressure is applied to the first hydraulic fluid passage 12, the second pilot-operated check valve 27 allows the flow of hydraulic fluid in the second hydraulic fluid passage 13 from the hydraulic cylinder device side to the passage switching valve side.

[0076] A first on-off valve 30 is provided in the first working fluid passage 12 on the hydraulic cylinder device side of the first check valve-equipped flow control valve 26, while a second on-off valve 31 is provided in the second working fluid passage 13 on the hydraulic cylinder device side of the second check valve-equipped flow control valve 28. A second bypass passage 32 connecting the first working fluid passage 12 and the second working fluid passage 13 is provided at a position closer to the passage switching valve than the first and second on-off valves 30, 31 and closer to the hydraulic cylinder device than the first and second check valve-equipped flow control valves 26, 28, and a third on-off valve 33 is interposed in this second bypass passage 32. These first to third on-off valves 30, 31, 33 are manually opened and closed, for example, when flushing the first and second working fluid passages 12, 13 (for example, the first and second on-off valves 30, 31 are closed and the third on-off valve 33 is opened).

[0077] The first flow control valve with check valve 26 may be disposed in the second working fluid passage 13 instead of the first working fluid passage 12. In this case, the first flow control valve with check valve 26 is disposed between the second pilot-operated check valve 27 and the second flow control valve with check valve 28, and the check valve 26b is disposed so as to block the flow of working fluid from the passage switching valve side to the hydraulic cylinder device side.

[0078] <Hydraulic Motor System Overview> FIG. 7 is a configuration diagram showing an example of a hydraulic motor system that drives a door body of a sliding door opening and closing device that opens and closes an opening (such as a crossing passage) of a river bank or the like.

[0079] The hydraulic motor system MS that drives the door body 51 of the sliding door opening and closing device is provided with a hydraulic motor 52. The hydraulic motor 52 moves the door body 51 in the horizontal direction via a reducer 53, a sprocket 54 (e.g., a chain sprocket), and a rack 55 that meshes with the sprocket 54.

[0080] The hydraulic motor system MS includes a hydraulic fluid supply / discharge device 56 that supplies / discharges the water-based hydraulic fluid according to the present invention to the hydraulic motor 52, a control panel 57 (operation panel) for controlling or operating the hydraulic motor system MS, and a pair of limit switches 58 for stopping the movement of the door body 51 at a predetermined position. Three-phase AC power is supplied to the control panel 57 from a power source 59. The hydraulic fluid supply / discharge device 56 and the control panel 57 are placed on a stand (not shown) that can be climbed and lowered by an operator, allowing the operator to easily operate them.

[0081] The hydraulic fluid supply / discharge device 56, which supplies / discharges water-based hydraulic fluid to / from the hydraulic motor 52, includes a pump 61 driven by a motor 60 supplied with power from a control panel 57, a first passage 63 and a second passage 64, which are each connected to the hydraulic motor 52 and supply / discharge the water-based hydraulic fluid stored in a hydraulic fluid storage tank 62 to / from the hydraulic motor 52, and a passage switching valve 65 that switches the direction of the water-based hydraulic fluid flowing through the first passage 63 and the second passage 64 between a forward direction and a reverse direction. The pump 61 is disposed in the first passage 63.

[0082] By operating the control panel 57, the passage switching valve 65 can be set to any one of a first state in which the water-based working fluid discharged from the pump 61 is supplied to the hydraulic motor 52 via the first passage 63, a second state in which the water-based working fluid is supplied to the hydraulic motor 52 via the second passage 64, or a third state in which the water-based working fluid is returned to the working fluid storage tank 62 without being supplied to the hydraulic motor 52. The hydraulic motor 52 rotates forward when the water-based working fluid is supplied in the forward direction via the first passage 63, thereby moving the door body 51 in the closing direction, and rotates reversely when the water-based working fluid is supplied in the reverse direction via the second passage 64, thereby moving the door body 51 in the opening direction.

[0083] Between the passage switching valve 65 and the hydraulic motor 52, a first stop valve 66 is provided in the first passage 63, and a second stop valve 67 is provided in the second passage 64. The first stop valve 66 has a first external connection port 66a connected to the first passage 63 on the hydraulic motor side, and a second external connection port 66b connected to the first passage 63 on the passage switching valve side. The second stop valve 67 has a first external connection port 67a connected to the second passage 64 on the hydraulic motor side, and a second external connection port 67b connected to the second passage 64 on the passage switching valve side. A connector equipped with a check valve is attached to the tip of each of the external connection ports 66a, 66b, 67a, 67b for connection to external pipes, pressure gauges, etc.

[0084] The hydraulic motor system S or the door body 51 of the sliding door opening and closing device can be operated, for example, in the following procedure.

[0085] When the gate body 51 is to be moved in the closing direction, the operator operates the control panel 57 to drive the pump 61 with the motor 60 and set the passage switching valve 65 to the first or second state. As a result, the water-based hydraulic fluid discharged from the pump 61 is supplied to the hydraulic motor 62 via the first passage 63 or the second passage 64. The rotor of the hydraulic motor 62 rotates, and this rotation is reduced at a predetermined reduction ratio by the reducer 53 and transmitted to the sprocket 54. As a result, the sprocket 54 rotates, and in response to this, the rack 55 meshing with the sprocket 54 and therefore the gate body 51 move horizontally, closing or opening the opening in the embankment. [Explanation of symbols]

[0086] S Hydraulic cylinder system, P1 1st port, P2 2nd port, P3 third port, P4 fourth port, 1 hydraulic cylinder device, 2 hydraulic fluid supply / discharge device, 3 cylinder, 4 piston, 5 piston rod, 6 load, 7 first liquid chamber, 8 second liquid chamber, 11 passageway switching valve, 12 first hydraulic fluid passage, 13 second hydraulic fluid passage, 14 hydraulic fluid supply passage, 15 working fluid return path, 16 working fluid storage tank, 17 filter, 18 ultraviolet lamp, 19 electric motor, 20 hydraulic fluid supply pump, 21 first bypass passage, 22 relief valve, 23 hydraulic fluid heating device, 24 cooler, 25 First pilot operated check valve, 26 First flow control valve with check valve, 26a flow control valve, 26b check valve, 27 second pilot operated check valve, 28 second check valve with flow control valve, 28a flow control valve, 28b check valve, 30 first on-off valve, 31 second on-off valve, 32 second bypass passage, 33 Third shut-off valve, MS hydraulic motor system, 51 door body, 52 hydraulic motor, 53 reducer, 54 sprocket, 55 rack, 56 hydraulic fluid supply / discharge device, 57 control panel, 58 limit switch, 59 power supply, 60 motor, 61 pump, 62 hydraulic fluid storage tank, 63 first passage, 64 second passage, 65 passage switching valve, 66 first stop valve; 66a first external connection port; 66b second external connection port; 67 second stop valve; 67a First external connection port, 67b Second external connection port.

Claims

[Claim 1] A water-based hydraulic fluid for a hydraulic cylinder or hydraulic motor that operates by the pressure of a pressurized liquid, the aqueous hydraulic fluid contains water and sodium polyacrylate, and the amount of sodium polyacrylate relative to the water in the aqueous hydraulic fluid is set to a range of 0.3 to 1.5 mass percent, thereby achieving a viscosity of 10 to 50 mPa s at 25°C; An aqueous hydraulic fluid having a hydrogen index adjusted to a range of pH 9 to pH 11.

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