JP7214185B2 - hydraulic cylinder system - Google Patents

Description

The present invention is a hydraulic cylinder comprising a hydraulic cylinder using pressurized water-based hydraulic fluid as a power transmission medium, and a hydraulic fluid supply/discharge device for supplying and discharging the water-based hydraulic fluid to and from the hydraulic cylinder. It is about the system.

Hydraulic cylinders, in which a piston slidably inserted in a cylinder reciprocates within the cylinder by the pressure of hydraulic fluid discharged from a pump, are generally used as actuators for various mechanical devices, civil engineering and construction vehicles, and the like. widely used as Conventionally, as hydraulic fluid for hydraulic cylinders, hydraulic fluid made from mineral oil or the like has been widely used because it has an appropriate viscosity and is highly effective in reducing sliding friction (for example, Patent Documents 1 to 4).

Hydraulic cylinders that use hydraulic oil as hydraulic fluid, that is, hydraulic cylinders, are usually provided with a hydraulic oil supply/discharge device for supplying/discharging hydraulic oil discharged from a hydraulic pump to/from the hydraulic cylinder. The hydraulic oil supply and discharge device includes a plurality of oil passages arranged between the hydraulic oil tank and the hydraulic cylinder, and a hydraulic pump, an oil passage switching valve, and a flow rate adjustment valve interposed in these oil passages. , relief valves, and check valves.

JP-A-10-110710 JP 2003-74518 A JP-A-2004-68863 JP 2018-84295 A

Hydraulic cylinders and hydraulic oil supply/discharge devices are structures in which a large number of members that constitute them are connected or connected, so hydraulic oil may leak at the connection between one member and another member, for example. When such a hydraulic cylinder is used to drive a water gate or the like installed in a river or irrigation channel, for example, if hydraulic oil leaks from the hydraulic cylinder or the hydraulic oil supply/discharge device, the hydraulic oil will be released. There is a problem that it mixes with water flowing in rivers and irrigation channels and causes serious environmental pollution.

In addition, since the hydraulic oil is combustible, there is a risk that fire may occur in the hydraulic cylinder and the hydraulic oil supply/discharge device due to the spread of fire, an accident, or the like.

SUMMARY OF THE INVENTION The present invention has been made in order to solve such problems, and it is possible to smoothly operate a hydraulic cylinder, to prevent environmental pollution caused by leakage of hydraulic fluid, and to prevent the occurrence of fire. It is an object of the present invention to provide a hydraulic cylinder system which can be prevented.

A hydraulic cylinder system according to the present invention, which has been made to solve the above problems,
a hydraulic cylinder using a pressurized water-based hydraulic fluid as a power transmission medium;
The hydraulic fluid supply/drainage device includes:
- A hydraulic fluid storage tank for storing a water-based hydraulic fluid;
A hydraulic fluid supply/discharge passage for supplying the aqueous hydraulic fluid stored in the hydraulic fluid storage tank to the hydraulic cylinder and for recirculating the aqueous hydraulic fluid discharged from the hydraulic cylinder to the hydraulic fluid storage tank;
A hydraulic fluid supply pump that is interposed in the hydraulic fluid supply passage forming a part of the hydraulic fluid supply/discharge passage and sucks, pressurizes, and discharges the water-based hydraulic fluid stored in the hydraulic fluid storage tank;
a passage switching valve interposed in the hydraulic fluid supply/discharge passage between the hydraulic cylinder and the hydraulic fluid supply pump for switching the flow direction of the water-based hydraulic fluid in the hydraulic fluid supply/discharge passage between the forward direction and the reverse direction; has
The water-based working fluid contains water and sodium polyacrylate, and the amount of sodium polyacrylate to water in the water-based working fluid is 0.3 to 1.5% by mass (preferably 0.4 to 1.35% by mass. ), and
The hydrogen index of the aqueous working fluid is adjusted within the range of pH9-pH11.
In the hydraulic cylinder system according to the present invention, the water-based working fluid contains propylene glycol, and the amount of propylene glycol added to the water in the water-based working fluid is in a temperature range lower than 0°C and higher than the freezing point of propylene glycol. is equal to or greater than the amount of propylene glycol added to water in the propylene glycol aqueous solution whose freezing point is the lower limit temperature for system use set in advance within.
Alternatively, in the hydraulic cylinder system according to the present invention, in the hydraulic cylinder system according to the present invention, the water-based working fluid contains ethanol, the amount of ethanol added to the water in the water-based working fluid is on the lower temperature side than 0 ° C., and It is equal to or greater than the amount of ethanol added to water in an aqueous ethanol solution whose freezing point is the lower limit temperature for system use set in advance within the temperature range on the higher temperature side than the freezing point of ethanol.

In the hydraulic cylinder system according to the present invention, it is preferable that the hydrogen index of the aqueous working fluid is adjusted within the range of pH9 to pH11 by adding sodium hydroxide.

According to the hydraulic cylinder system of the present invention, water-based hydraulic fluid is used instead of hydraulic fluid as a power transmission medium. There is no oil contamination of the environment or oil contamination of the product as in the case of . For this reason, the hydraulic cylinder system can be effectively used for facilities where contamination by hydraulic fluid is a problem, such as water gate opening and closing devices, and facilities for manufacturing foods, cosmetics, medicines, and the like. Moreover, the water-based hydraulic fluid is non-flammable, and there is no possibility of fire occurring in the hydraulic cylinder system using the water-based hydraulic fluid, which is extremely advantageous in terms of fire prevention.

1 is a configuration diagram showing an example of a hydraulic cylinder system according to the present invention; FIG. It is a block diagram of a dynamic friction coefficient measuring device. It is a graph which shows the viscosity of sodium polyacrylate aqueous solution, and the relationship of a density|concentration. It is a graph which shows the viscosity of sodium polyacrylate aqueous solution, and the relationship of temperature. It is a graph which shows the dynamic friction coefficient of sodium polyacrylate aqueous solution, and the relationship of a density|concentration. 1 is a graph showing the relationship between freezing point and concentration for ethanol aqueous solution and propylene glycol aqueous solution.

Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings. In this embodiment, a hydraulic cylinder system using a hydraulic cylinder as a hydraulic actuator using pressurized aqueous hydraulic fluid as a power transmission medium will be described, but the present invention is applicable to other than the hydraulic cylinder ( For example, it can be similarly applied to a hydraulic drive system using a hydraulic motor, a hydraulic pump, etc.).

<Overview of hydraulic cylinder system>
FIG. 1 is a configuration diagram showing an example of a hydraulic cylinder system according to the present invention. The hydraulic cylinder system S includes a single-rod double-acting hydraulic cylinder device 1 using pressurized water-based hydraulic fluid as a power transmission medium, and an operation for supplying and discharging the water-based hydraulic fluid to and from the hydraulic cylinder device 1. A liquid supply/drainage device 2 is provided. The hydraulic cylinder device 1 includes a substantially cylindrical cylinder 3 , a substantially cylindrical piston 4 fitted or inserted into a cylindrical hollow portion of the cylinder 3 (hereinafter referred to as a “cylinder hollow portion”), and one of the pistons 4 . It has an elongated cylindrical (round bar) piston rod 5 attached to the end. The hydraulic cylinder device 1 is of a vertically placed type in which the central axes of the cylinder 3, the piston 4, and the piston rod 5 are arranged so as to extend in the vertical direction (vertical direction). The hydraulic cylinder device is not limited to a vertical type, and may be of a horizontal type or an inclined type.

The tip of the piston rod 5 (the end opposite to the piston 4) is connected to a load 6 (for example, a water gate door) that is moved by the hydraulic cylinder device 1 in the axial direction of the piston rod. Below, the position of the cap side in the hydraulic cylinder device 1 is called "upper (upper side)", and the position of the rod side is called "lower (lower side)".

The piston 4 can move (slid) in the vertical direction within the hollow portion of the cylinder. The hollow portion of the cylinder is vertically partitioned by the piston 4. A first liquid chamber 7 is formed above the piston 4 (on the cap side), and a second liquid chamber 8 is formed below the piston 4 (on the rod side). It is In the hydraulic cylinder device 1, when pressurized hydraulic fluid is supplied to the first fluid chamber 7, the pressure of the hydraulic fluid causes the piston 4 and the piston rod 5 to move downward, and the pressurized hydraulic fluid is supplied to the second fluid chamber 8, the pressure of the hydraulic fluid causes the piston 4 and the piston rod 5 to move upward, thereby moving the load 6 in the vertical direction.

When the hydraulic cylinder device 1 operates (when the piston slides), the hydraulic fluid supply/discharge device 2 supplies pressurized hydraulic fluid to any one of the fluid chambers (first fluid chamber 7 Alternatively, the working fluid is supplied to the second fluid chamber 8) and discharged 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. The first port P1 of the passage switching valve 11 is connected to the first fluid chamber 7 via the first hydraulic fluid passage 12, and the second port P2 is connected to the second fluid chamber 8 via the second hydraulic fluid passage 13. It is A hydraulic fluid supply passage 14 is connected to the third port P3 of the passage switching valve 11, and a hydraulic fluid return passage 15 is connected to the fourth port P4. The ends of the hydraulic fluid supply path 14 and the hydraulic fluid return path 15 (ends not connected to the passage switching valve 11) are introduced into a hydraulic fluid reservoir 16 that stores the hydraulic fluid.

A filter 17 (or a strainer) is attached to the tip of the hydraulic fluid supply path 14 to remove foreign matter, dust, etc. from the hydraulic fluid sucked into the hydraulic fluid supply path 14 . It is immersed in the work solution stored in the 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 rays to sterilize the hydraulic fluid. As the ultraviolet lamp 18, it is preferable to use one that emits ultraviolet rays of 250 to 260 nm (for example, mercury spectral lines around 253.7 nm (UV-C region)), which have a particularly high sterilizing effect. It should be noted that the ultraviolet lamp 18 can be omitted if necessary.

A hydraulic fluid supply pump 20 driven by a motor 19 (which may be an engine) is interposed in the hydraulic fluid supply path 14 . The hydraulic fluid supply pump 20 sucks the hydraulic fluid in the hydraulic fluid storage tank 16 , pressurizes it, and supplies it to the third port P<b>3 of the passage switching valve 11 . A first bypass passage 21 is provided to connect the hydraulic fluid supply passage 14 on the downstream side (passage switching valve side) of the hydraulic fluid supply pump 20 with respect to the direction of flow of the hydraulic fluid, and the hydraulic fluid return passage 15 . A relief valve 22 for adjusting the pressure of the hydraulic fluid discharged from the hydraulic fluid supply pump 20 is interposed in the passage 21 .

A hydraulic fluid heating device 23 for heating the hydraulic fluid in the hydraulic fluid return path is provided in the hydraulic fluid return path 15 on the side of the hydraulic fluid storage tank from the connection with the first bypass path 21 . As the working fluid heating device 23, a heat exchanger or an electric heater using high-temperature steam or a heat medium as a heat source can be used. A cooler 24 for cooling the working fluid is provided in the working fluid return path 15 on the side of the working fluid storage tank from the working fluid heating device 23 . As the cooler 24, a water-cooled multi-tubular heat exchanger or the like can be used. Note that the cooler 24 can be omitted as necessary.

The passage switching valve 11 switches a supply/discharge path of hydraulic fluid to/from the hydraulic cylinder device 1 . The passage switching valve 11 is a solenoid valve controlled by a control device (not shown). a first state in which hydraulic fluid is supplied to the first hydraulic chamber 7 via the second hydraulic fluid passage 13; It can be set to any of the third states (shown in FIG. 1).

In the first state, the hydraulic fluid in the second fluid chamber 8 is returned to the hydraulic fluid storage tank 16 via the second hydraulic fluid passage 13 and the hydraulic fluid return passage 15, and in the second state, the first fluid is The hydraulic fluid in the chamber 7 is returned to the hydraulic fluid storage tank 16 via the first hydraulic fluid passage 12 and the hydraulic fluid return passage 15 . In the third state, the ends of the first hydraulic fluid passage 12 and the second hydraulic fluid passage 13 on the side of the passage switching valve are closed. The passage switching valve 11 may be configured such that the hydraulic fluid supply passage 14 and the hydraulic fluid return passage 15 communicate with each other in the third state.

In the first hydraulic fluid passage 12, a first pilot is arranged in order from the passage switching valve side to the hydraulic cylinder device side, basically blocking the flow of hydraulic fluid from the hydraulic cylinder device side to the passage switching valve side. An operable check valve 25 and a first check-valve equipped flow rate control valve 26 comprising a flow rate control valve 26a and a check valve 26b connected in parallel are interposed in series. The first check valve equipped flow regulating valve 26 does not particularly restrict the flow of hydraulic fluid from the passage switching valve side to the hydraulic cylinder device side, but the flow of hydraulic fluid from the hydraulic cylinder device side to the passage switching valve side is restricted. Adjust the flow rate. When the hydraulic pressure (pilot pressure) higher than the set pressure is applied to the second hydraulic fluid passage 13, the first pilot operated check valve 25 switches the passage from the hydraulic cylinder device side in the first hydraulic fluid passage 12. Allow hydraulic fluid flow to the valve side.

In the second hydraulic fluid passage 13, a second pilot is arranged in order from the passage switching valve side toward the hydraulic cylinder device side, basically blocking the flow of hydraulic fluid from the hydraulic cylinder device side to the passage switching valve side. An operable check valve 27 and a second check valve equipped flow rate control valve 28 comprising a flow rate control valve 28a and a check valve 28b connected in parallel are interposed in series. The second check valve equipped flow rate adjustment valve 28 does not particularly restrict the flow of hydraulic fluid from the passage switching valve side to the hydraulic cylinder device side, but the flow of hydraulic fluid from the hydraulic cylinder device side to the passage switching valve side. Adjust the flow rate. When the hydraulic pressure (pilot pressure) higher than the set pressure is applied to the first hydraulic fluid passage 12 , the second pilot operated check valve 27 operates from the hydraulic cylinder device side of the second hydraulic fluid passage 13 to the passage switching valve. Allow hydraulic fluid flow to the side.

A first on-off valve 30 is provided in the first hydraulic fluid passage 12 on the side of the hydraulic cylinder device from the first check valve flow rate adjustment valve 26 , while the hydraulic cylinder device side is provided from the second check valve flow rate adjustment valve 28 to the hydraulic cylinder device side. A second on-off valve 31 is provided in the second hydraulic fluid passage 13 on the side. At a position on the passage switching valve side from the first and second on-off valves 30 and 31 and on the hydraulic cylinder device side from the first and second check valve flow control valves 26 and 28, the first hydraulic fluid is A second bypass passage 32 is provided to connect the passage 12 and the second hydraulic fluid passage 13 , and a third on-off valve 33 is interposed in the second bypass passage 32 . These first to third opening/closing valves 30, 31, 33 are manually opened and closed (for example, the first and second opening/closing valves) when flushing the first and second hydraulic fluid passages 12, 13, for example. The valves 30 and 31 are closed and the third on-off valve 33 is opened.).

Note that the first check valve equipped flow rate adjustment valve 26 may be interposed in the second hydraulic fluid passage 13 instead of the first hydraulic fluid passage 12 . In this case, the first flow regulating valve with check valve 26 is interposed between the second pilot-operated check valve 27 and the second flow regulating valve with check valve 28, and the check valve 26b is a passageway. It is arranged to block the flow of hydraulic fluid from the switching valve side to the hydraulic cylinder device side.

<About water-based hydraulic fluid>
1. What is water-based hydraulic fluid? Hydraulic systems such as hydraulic cylinders and hydraulic motors generally use hydraulic fluid made of mineral oil as a power transmission medium. may cause a fire. In addition, when the hydraulic system is used for a water gate of a river, etc., there is a risk that a large amount of hydraulic oil will leak in the event of an earthquake or the like, damaging the water environment over a wide area of water on the downstream side. Accordingly, the present invention proposes a novel water-based hydraulic fluid that does not cause a fire and does not damage the water environment even if it leaks into a river or the like, as a hydraulic fluid that can replace hydraulic fluid.

2. Matters Considered in Development of Water-Based Hydraulic Fluid The inventors of the present invention considered the following matters when developing a novel water-based hydraulic fluid.
(1) Viscosity (kinematic viscosity) is equivalent to that of hydraulic oil (2) Viscosity temperature change is small (3) Dynamic friction coefficient between sliding parts is equivalent to that of hydraulic oil (4) No toxicity to living organisms (5) Low environmental pollution by leakage or discharge (6) No possibility of fire (7) No freezing at low temperatures in cold regions (8) Virtually no deterioration due to oxidation (9) Low corrosiveness to rubber packing (10) Low metal corrosiveness to aluminum-based materials and iron-based materials (11) No adverse effects due to mixing of water vapor in the air (12) Liquid storage tank (13) Almost no biological deterioration (corruption)

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

4. Measurement of viscosity of sodium polyacrylate aqueous solution (1) Using an Ostwald viscometer, measure the relative viscosity of sodium polyacrylate aqueous solution to pure water. The viscosity of the sodium acid aqueous solution was calculated.

(2) Measurement Results FIG. 3 is a graph showing the relationship between the viscosity and concentration of the sodium polyacrylate aqueous solution. From this graph, it can be seen that the viscosity and concentration are in a substantially direct proportional relationship. In addition, it is considered that the proportional coefficient (gradient) changes according to the temperature.

(3) Temperature Dependence of Viscosity FIG. 4 is a graph showing the relationship between the viscosity and temperature of the sodium polyacrylate aqueous solution. From this graph, it can be seen that the viscosity of the 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, hydraulic oil has greater temperature dependence and narrower allowable temperature range than the sodium polyacrylate aqueous solution.

5. Measurement of Dynamic Friction Coefficient of Sodium Polyacrylate Aqueous Solution (1) A dynamic friction coefficient measuring apparatus shown in FIG. 2 was used to measure the dynamic friction coefficient between sliding portions when using a sodium polyacrylate (PANa) aqueous solution. This kinetic friction coefficient measuring device consists of a table, a carriage that runs freely on the table, a weight connected to the front part of the carriage via a thread, a pulley that guides the thread, and a nylon line attached to the rear part of the carriage. It is equipped with a movable object connected via a channel, a channel in which the movable object slides, and a tension gauge that measures the tension of the nylon line.

(2) Channel specifications Stainless steel U-shaped channel with smooth inner surface Width 50mm Height 25mm Length 1500mm

(3) Specifications of movable object Stainless steel U-shaped channel with a smooth outer peripheral surface that is housed in the groove of the channel and is slidable in the longitudinal direction of the channel Width 40 mm Height 30 mm Length 100 mm mass 92g

(4) Method of measuring dynamic friction coefficient Close both ends of the channel, pour water-based hydraulic fluid into the groove of the channel, insert a movable object, pull the movable object in the longitudinal direction of the channel with a cart at a constant speed, and measure the friction with a tension gauge. The tension was measured and the dynamic friction coefficient was calculated by dividing the measured tension by the mass (weight) of the movable object.

(5) Adjustment of moving speed of cart and movable object The moving speed of the cart and movable object was made constant by increasing or decreasing the mass of the weight loaded on the cart. The moving speed of the carriage and the movable object was very small (less than 2 cm/sec) so that the flow resistance of the aqueous hydraulic fluid to the movable object could be reduced to a substantially negligible level.

(6) Measurement Results FIG. 5 is a graph showing the relationship between the dynamic friction coefficient and the concentration of the sodium polyacrylate aqueous solution. Table 2 below shows the measured data. From this graph, the dynamic friction coefficient becomes the minimum value of 0.011 when the PANa concentration is 0.75 wt % to 1.0 wt %, which is a level comparable to the dynamic friction coefficient of hydraulic oil. As the concentration increases or decreases from there, the dynamic friction coefficient increases, but it is at most within about 0.022, which is a sufficiently practical level.

6. Appropriate Sodium Polyacrylate Concentration The relationship between sodium polyacrylate concentration and viscosity and its temperature dependence are shown in FIGS. Also, the relationship between sodium polyacrylate concentration and sliding friction coefficient is shown in FIG. Therefore, a) when the appropriate viscosity is set to 10 to 50 mPa·s, the corresponding sodium polyacrylate concentration is 0.3 to 1.5 wt %, referring to the graph of FIG. Also, b) when the sliding friction coefficient is set to 0.02 or less, the corresponding sodium polyacrylate concentration is 0.2 to 1.5 wt %, referring to the graph of FIG. As a result, the concentration that satisfies both conditions a) and b) is 0.3 to 1.5 wt %.
Further, c) when the appropriate coefficient of sliding friction is more preferably set to 0.015 or less, referring to the graph of FIG. 5, the corresponding sodium polyacrylate concentration is 0.4 to 1.35 wt %. As a result, the concentration that satisfies both conditions a) and c) is 0.4 to 1.35 wt %.

7. Antifreezing at Low Temperatures (1) It is preferable to add ethanol or propylene glycol as an antifreezing agent to the sodium polyacrylate aqueous solution. However, if the amount of propylene glycol added is large, the viscosity may increase rapidly at low temperatures. It has been found that the addition of ethanol does not significantly increase the viscosity even at low temperatures.

(2) Addition amount of antifreeze agent Fig. 6 is a graph showing the relationship between the freezing point and the concentration of an aqueous ethanol solution and an aqueous propylene glycol solution. From this graph it can be seen that both aqueous solutions have a freezing point of 0° C. at a concentration of 0 wt % (ie water), from which the freezing point decreases as the concentration increases. Therefore, even in a water-based working fluid containing sodium polyacrylate, the amount of antifreezing agent added to water is set in advance within the temperature range of 0 ° C. to the freezing point of the antifreezing agent. The amount of antifreeze added to water in the aqueous solution is preferably the same or greater.

8. Comparison of Water-based Hydraulic Fluid and Hydraulic Oil (1) Compressibility Hydraulic fluid for hydraulic cylinders must be incompressible, and both water-based hydraulic fluid and hydraulic oil are incompressible.

(2) Viscosity (kinematic viscosity)
The viscosity (kinematic viscosity) of the hydraulic fluid is preferably high from the viewpoint of preventing fluid leakage at the sliding portion of the piston and cylinder in the hydraulic cylinder, but low from the viewpoint of reducing pressure loss in the hydraulic fluid passage. preferable. In order to achieve both, the viscosity of the hydraulic fluid at room temperature is generally set to about 10 to 50 mPa·s.

In the case of a water-based working fluid, if the concentration of sodium polyacrylate is 0.3-1.5 wt %, the viscosity at room temperature (25° C.) can be 10-50 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.

In the case of hydraulic oil, the viscosity is adjusted by changing the type or composition of the mineral oil used.

It is preferable that the hydraulic fluid has a small change in viscosity with temperature. The viscosity of the aqueous working fluid is caused by interactions such as hydrogen bonding, ionic bonding, and hydrophobic bonding between sodium polyacrylate and water, but the temperature dependence of such bonding strength is relatively small. Therefore, the temperature change of the viscosity of the water-based hydraulic fluid is much smaller than that of the hydraulic fluid.

(3) Sliding Friction Coefficient In order to reduce wear at the sliding portion between the piston and cylinder of the hydraulic cylinder, or at the gear meshing portion of the gear pump in the hydraulic fluid supply/discharge system, the sliding friction coefficient at the sliding portion should be small. Smaller is better. In this regard, water-based hydraulic fluids are equivalent to hydraulic fluids.

(4) Deterioration due to oxidation It is essential that the working fluid is resistant to deterioration due to oxidation reactions (especially at high temperatures). Water-based hydraulic fluids are basically composed of water and sodium polyacrylate, but sodium polyacrylate does not combine with oxygen below its combustion temperature (several hundred degrees Celsius), so deterioration due to oxidation occurs in water-based hydraulic fluids. Absent. On the other hand, hydraulic oil made of mineral oil inevitably deteriorates due to oxidation, and the deterioration rate increases as the temperature rises.

(5) Compatibility with packing In general, nitrile rubber is used for packing of hydraulic cylinders, but sodium polyacrylate does not degrade nitrile rubber, so nitrile rubber packing can be used.

(6) Metal corrosiveness Hydraulic cylinders and hydraulic fluid supply and discharge devices are generally made of aluminum alloys or iron ^alloys . ) and alkali (hydroxide ion OH ⁻ ) do not cause corrosion. Aluminum alloys may be corroded by alkali (hydroxide ion OH ⁻ ) at pH 11 or higher. When the pH of the aqueous hydraulic fluid is in the range of 9 to 11, corrosion hardly occurs even if parts made of aluminum alloy are used in hydraulic cylinders or hydraulic fluid supply/discharge devices. Therefore, it is preferable to adjust the pH of the aqueous working fluid to 9-11. It should be noted that the hydraulic oil has a relatively low metal corrosiveness unless it contains sulfur.

(7) Effect of water vapor contamination Hydraulic equipment is generally a closed system, and is structured to prevent foreign matter such as dirt and dust from entering from the outside. Intrusion of water vapor cannot be prevented. For this reason, in the hydraulic system, water vapor mixes into the working oil from the air, causing deterioration and clouding of the working oil. Since most of the water-based working fluid is water, intrusion of water vapor from the atmosphere does not cause any problems.

(8) Possibility of Fire Since water-based hydraulic fluid is mostly water, it is nonflammable, and there is no possibility of fire occurring in hydraulic cylinder systems that use water-based hydraulic fluid, which is extremely advantageous in terms of fire prevention. On the other hand, since hydraulic oil made of mineral oil is flammable, fire may occur in the hydraulic cylinder system due to spread of fire, accident, or the like.

(9) Toxicity/Environmental Contamination Sodium polyacrylate or polyacrylic acid is used as a thickening agent in the fields of food and cosmetic production, and has extremely low toxicity to living organisms. Therefore, the toxicity of the water-based hydraulic fluid to living organisms is extremely low, and even if it flows into a river or the like, it will not adversely affect the aquatic ecosystem.

Sodium polyacrylate or polyacrylic acid has extremely low toxicity to living organisms, and in a natural environment where there are sufficient nutrients such as nitrogen compounds and phosphorus compounds, it is biodegraded by microorganisms, and finally carbon dioxide and water It becomes The water-based hydraulic fluid is an aqueous solution, and when it leaks into a river or the like, it immediately mixes with the water of the river or the like, and neither settles on the bottom of the water nor floats on the surface of the water. Therefore, even if the water-based hydraulic fluid leaks from the hydraulic cylinder system into a river, lake, or the like, it will be decomposed by the self-cleaning action of the natural world, and the environmental pollution is very low.

Hydraulic oil is toxic to living organisms, and when it leaks into rivers, lakes, etc., it floats on the water surface and greatly deteriorates the water environment.

(10) Behavior of Air Bubbles Generally, the hydraulic fluid of the hydraulic cylinder system is in constant contact with air in the hydraulic fluid storage tank, so the air dissolves almost to the saturation solubility. The air saturation solubility varies roughly proportionally to the pressure of the working fluid. For this reason, in places where the working fluid is in a decompressed state (below atmospheric pressure) in the working fluid circulation circuit (for example, at the suction port of the pump), part of the air dissolved in the working fluid cannot be dissolved. Air bubbles are generated. These bubbles will dissolve in the hydraulic fluid when the pressure of the hydraulic fluid rises again, but it takes a certain amount of time for the bubbles to completely dissolve in the hydraulic fluid. Therefore, residual air bubbles may cause cavitation of the pump and erosion of parts.

Under atmospheric pressure, the air saturation solubility of mineral oil at room temperature is about 9% on a volume basis, but in the case of a water-based working fluid, it is about 2% on a volume basis. As described above, since the water-based hydraulic fluid has a lower air saturation solubility than the hydraulic fluid, the amount of air bubbles generated is reduced, and the cavitation of the pump and the erosion of the parts are reduced.

If air bubbles are present in the hydraulic fluid, they can compromise the operation of the hydraulic cylinder driven by the pressurized hydraulic fluid because the air bubbles are compressible. Further, when bubbles are adiabatically compressed by pressurization of the working fluid, the temperature of the bubbles becomes high (for example, about 800° C. at 10 MPa) if heat dissipation to the outside of the bubbles is poor. For this reason, when hydraulic oil is used as the hydraulic fluid, heat dissipation to the outside of the bubbles is poor, so the hydraulic oil adjacent to the bubbles may reach a high temperature and be thermally deteriorated or oxidized.

Since the water-based hydraulic fluid generates less air bubbles than the hydraulic fluid, malfunction of the hydraulic system due to air bubbles is reduced. In addition, the water-based hydraulic fluid has a high thermal conductivity (approximately five times that of hydraulic fluid) and a large heat capacity, so the heat generated in the air bubbles due to adiabatic compression is quickly dissipated outside the air bubbles, and the air bubbles do not reach a very high temperature. not. Therefore, the water-based working fluid adjacent to the bubbles does not reach a high temperature. The water-based driving liquid is not oxidized or thermally deteriorated even if its temperature rises to its boiling point.

In general, in a hydraulic cylinder system, a hydraulic fluid storage tank is provided with an air bubble separation device.

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

(11) Biological deterioration (corruption)
Sodium polyacrylate or polyacrylic acid, which is the main raw material of the aqueous working fluid, is an organic compound containing carbon, hydrogen or oxygen, and can basically serve as a nutrient source for microorganisms. Therefore, when the nitrogen compounds, phosphorus compounds, etc. required for the growth of microorganisms are sufficiently supplied, the aqueous working fluid may be biodegraded (putrefied) by the microorganisms.

However, nitrogen compounds, phosphorus compounds, etc., which are essential for the growth of microorganisms, cannot enter the hydraulic cylinder system, which is a nearly closed system. There is no biological degradation (putrefaction) of water-based hydraulic fluids. When the water-based working fluid is discharged into a river, lake, or the like, the water-based working fluid is biodegraded because nitrogen compounds, phosphorus compounds, and the like are present in large amounts in the outside world.

(12) Antifreeze When the hydraulic cylinder system is installed in cold regions, 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 antifreezing agent to the aqueous working fluid to prevent freezing. The amount of ethanol or propylene glycol to be added is adjusted according to the operating temperature.

<Legal regulations on water-based hydraulic fluids>
1. Characteristics of raw materials for water-based hydraulic fluids (1) Sodium polyacrylate or polyacrylic acid These are synthetic agents, but they have extremely low toxicity or harm to living organisms, and are of food additive-level quality. is used as a thickening agent in the food sector. The use of sodium polyacrylate or polyacrylic acid is not legally regulated from the viewpoint of protection of living organisms.

(2) Ethanol Ethanol is used as pharmaceuticals and beverages, and has extremely low toxicity or harm to living organisms.

(3) Propylene Glycol Propylene glycol is used as a quality-improving agent in pharmaceuticals, cosmetics, and foods such as noodles and rice, and has extremely low toxicity or harm to living organisms. Since propylene glycol is flammable, it is classified as Class 4 hazardous material under the Fire Defense Law, but the concentration of propylene glycol in the processed water is much lower than the flammability limit concentration. Therefore, processed water is not subject to regulation by the Fire Service Law due to the inclusion of propylene glycol.

(4) Sodium Hydroxide Sodium hydroxide is ionized into sodium ions (Na ⁺ ) and hydroxide ions (OH ⁻ ) in water. Both ions are ions that originally exist in living organisms, and are not toxic or harmful to living organisms as substances. Therefore, aside from being subject to regulations based on alkalinity or pH, the use of sodium hydroxide itself is not legally regulated from the standpoint of protecting living organisms.

2. Regulations on Water-Based Hydraulic Fluids Water-based hydraulic fluids are discharged or discarded into water areas after the service life has passed. It may be regulated by additional ordinances, and if it is discharged into the public sewage system, it may be regulated by the Sewerage Act or its additional ordinances. Under the Water Pollution Control Law, the Sewerage Law, or additional ordinances, if effluent or sewage discharged from business establishments, etc., contains prescribed hazardous substances (28 types) related to health items, regardless of the amount of discharge, , the concentration of harmful substances in effluent or sewage is regulated to be below the discharge standards.

On the other hand, regarding the water quality of effluent or sewage related to living environment items that are not directly toxic or harmful to living organisms, the Water Pollution Control Law or the Sewerage Law stipulates the average daily discharge of effluent or sewage. There are no regulations on emissions from business establishments with a ^volume of less than 50m3. Some prefectures have additional ordinances that regulate the discharge of effluent or sewage if the average daily discharge amount is ^10m3 or more.

The water-based hydraulic fluid does not contain any harmful substances related to health items stipulated in the Water Pollution Control Law or the Sewerage Law. In addition, in a hydraulic cylinder system using a water-based hydraulic fluid, the water-based hydraulic fluid is circulated and used, and after the service life has elapsed, only about 500 to 1000 liters of the water-based hydraulic fluid is discharged into public water areas or public sewers. be. Therefore, even in prefectures where the strictest additional standards are applied, it is possible that an average of ¹⁰ m3 or more of effluent or sewage per day is discharged into public water areas or public sewage systems from hydraulic cylinder systems that use water-based hydraulic fluids. There is no gender. Therefore, in a liquid cylinder system using a water-based hydraulic fluid, when the water-based hydraulic fluid is discharged into a public water area or a public sewage system, there is no regulation by the Water Pollution Control Law, the Sewerage Law, or their additional ordinances.

S hydraulic cylinder system P1 first port P2 second port
P3 3rd port P4 4th port 1 Hydraulic cylinder device
2 hydraulic fluid supply and discharge device, 3 cylinder, 4 piston, 5 piston rod,
6 load 7 first liquid chamber 8 second liquid chamber 11 passage switching valve
12 first hydraulic fluid passage; 13 second hydraulic fluid passage; 14 hydraulic fluid supply passage;
15 Hydraulic fluid return path 16 Hydraulic fluid reservoir 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 flow control valve with first check valve;
26a flow control valve; 26b check valve; 27 second pilot operated check valve;
28 flow control valve with second check valve, 28a flow control valve, 28b check valve,
30 first on-off valve, 31 second on-off valve, 32 second bypass passage,
33 Third on-off valve.

Claims (4)

A hydraulic cylinder system comprising a hydraulic cylinder using pressurized water-based hydraulic fluid as a power transmission medium, and a hydraulic fluid supply/discharge device for supplying and discharging the water-based hydraulic fluid to and from the hydraulic cylinder,
The hydraulic fluid supply/drainage device includes:
- A hydraulic fluid storage tank for storing a water-based hydraulic fluid;
A hydraulic fluid supply/discharge passage for supplying the aqueous hydraulic fluid stored in the hydraulic fluid storage tank to the hydraulic cylinder and for recirculating the aqueous hydraulic fluid discharged from the hydraulic cylinder to the hydraulic fluid storage tank;
A hydraulic fluid supply pump that is interposed in the hydraulic fluid supply passage forming a part of the hydraulic fluid supply/discharge passage and sucks, pressurizes, and discharges the water-based hydraulic fluid stored in the hydraulic fluid storage tank;
a passage switching valve interposed in the hydraulic fluid supply/discharge passage between the hydraulic cylinder and the hydraulic fluid supply pump for switching the flow direction of the water-based hydraulic fluid in the hydraulic fluid supply/discharge passage between the forward direction and the reverse direction; has
The water-based working fluid contains water and sodium polyacrylate, and the amount of sodium polyacrylate to water in the water-based working fluid is in the range of 0.3 to 1.5% by mass,
The hydrogen index of the aqueous working fluid is adjusted within the range of pH9 to pH11 ,
The water-based hydraulic fluid contains propylene glycol, and the amount of propylene glycol added to the water in the water-based hydraulic fluid is the lower limit of system use set in advance within a temperature range lower than 0°C and higher than the freezing point of propylene glycol. A hydraulic cylinder system characterized in that the amount of propylene glycol to be added is equal to or greater than the amount of propylene glycol added to water in an aqueous propylene glycol solution having a temperature as a freezing point . A hydraulic cylinder system comprising a hydraulic cylinder using pressurized water-based hydraulic fluid as a power transmission medium, and a hydraulic fluid supply/discharge device for supplying and discharging the water-based hydraulic fluid to and from the hydraulic cylinder,
The hydraulic fluid supply/drainage device includes:
- A hydraulic fluid storage tank for storing a water-based hydraulic fluid;
A hydraulic fluid supply/discharge passage for supplying the aqueous hydraulic fluid stored in the hydraulic fluid storage tank to the hydraulic cylinder and for recirculating the aqueous hydraulic fluid discharged from the hydraulic cylinder to the hydraulic fluid storage tank;
A hydraulic fluid supply pump that is interposed in the hydraulic fluid supply passage forming a part of the hydraulic fluid supply/discharge passage and sucks, pressurizes, and discharges the water-based hydraulic fluid stored in the hydraulic fluid storage tank;
a passage switching valve interposed in the hydraulic fluid supply/discharge passage between the hydraulic cylinder and the hydraulic fluid supply pump for switching the flow direction of the water-based hydraulic fluid in the hydraulic fluid supply/discharge passage between the forward direction and the reverse direction; has
The water-based working fluid contains water and sodium polyacrylate, and the amount of sodium polyacrylate to water in the water-based working fluid is in the range of 0.3 to 1.5% by mass,
The hydrogen index of the aqueous working fluid is adjusted within the range of pH9 to pH11 ,
The water-based working fluid contains ethanol, and the amount of ethanol added to water in the water-based working fluid is lower than 0°C and higher than the freezing point of ethanol. A hydraulic cylinder system characterized in that the amount of ethanol added to water in the aqueous ethanol solution is equal to or greater than that .
3. The hydraulic cylinder system according to claim 1, wherein the amount of sodium polyacrylate to water in the water-based hydraulic fluid is in the range of 0.4 to 1.35% by mass. The hydraulic cylinder system according to any one of claims 1 to 3, wherein the hydrogen index of the water-based hydraulic fluid is adjusted within the range of pH 9 to pH 11 by adding sodium hydroxide. .

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