01
Hydraulic principle introduction
This hydraulic system roughly includes nine parts. They are: 1, motor and high-pressure pump ; 2. High-pressure filter; 3. System relief valve; 4. Rodless cavity safety valve; 5. Main reversing valve and hydraulic lock + double hydraulic control one-way valve + Dual one-way throttle valve part; 6. Rod chamber safety valve ; 7. Rod chamber pressure regulating valve/ balance valve part; 8. Lower chamber hydraulic control one-way valve and control valve part; 9. Oil cylinder part.
02
Brief description of the functions of each part
1, motor and high-pressure pump: provide power and pressure to the working medium ( anti-wear hydraulic oil 46# HM-46 or VG-46), so that the cylinder can work normally under the set pressure;
2 , High-pressure filter: Coarse filter oil pump oil. Because of the high pressure, avoid problems such as excessive load on the oil pump, stalled motor or cracking of the oil pump casing due to failure to replace it in time after clogging. Generally, the filtration precision is below 20 microns (≤20 microns); the filter element can only roughly filter impurities and cannot play a fine filtration role;
3, system relief valve: mainly protects the safe (rated) working pressure of the oil pump in the oil station. It prevents the oil pump casing from cracking or the motor stalling and being damaged when the oil pump pressure is too high; it is a system protection valve or called a system safety valve;
4, rodless cavity safety valve/overflow valve: mainly limits the maximum lifting roller of the lower chamber Work stress. Prevent the lifting roller pressure from being too high, the inertia of the grinding roller caused by the excessive lifting speed of the grinding roller, and the force required to stop the grinding roller. There may be a sound of hitting the mechanical limit of the rack. It mainly plays the role of safety protection for the lifting roller, so it is called the lower chamber safety valve;
5. The main reversing valve is generally a three-position four-way valve (YV1 and YV2 and the electro-hydraulic reversing valve H-type valve.
The mid-position function has an M type , H-type, O-ring, Y-type, etc.). The picture shows the H type. The middle function is that the oil pump is in the unloading state, that is, the A and B chambers are unloaded. The hydraulic control one-way valve is closed, and the one-way valve of the throttling one-way valve is also closed. If you use a hydraulic lock (dual hydraulic control one-way valve, double one-way throttle valve ), you need to consider the neutral pressure relief function and the problem of hydraulic lock pressure relief closing (pressure maintenance required). Dual one-way throttle valves control the oil flow rate from the two chambers of the main valve to the upper and lower chambers of the cylinder.
① If there is no hydraulic lock: the main valve can be selected as Y-type or O-type directional valve. Considering that the inertia of a heavy roller will be large when it falls too fast, it is generally considered that the speed of loading the falling roller is slightly slower, and it is better to switch the oil inlet throttle valve of the rod cavity (YV1 side) to a smaller value. However, if it is too small, it will affect the vibration of the mill when the roller is dropped; the opening of the first cavity of the lifting roller is generally larger to ensure that the lifting speed is relatively faster. It is also considered that the weight of heavy-weight rollers is large, and the inertia required for stopping is also large. Therefore, the opening of the rod cavity should not be too large to avoid unsafe factors such as damage caused by hitting the mechanical limit of the frame. Generally, the opening is about 75-85%. Specifically, the opening of the double one-way throttle valve can be adjusted according to actual needs.
② If there is a hydraulic lock. It is necessary to pressure-relief and close the dual hydraulic control check valves after the main valve loses power. Generally, H-type valves can be selected. considers that when the opening of the throttle valve is too large, the pressure in the other chamber is too low, and the one-way valve in the other chamber cannot be opened. For example: when the roller is falling, the overall pressure rises slowly, and the hydraulic control check valve in the rodless chamber opens slowly. At this time, the opening speed of the large hydraulic control check valve in the lower chamber is also affected.
The roller has fallen on the material but the pressure in the lower chamber cannot be relieved, causing the roller to fall too slowly. At this time, the material layer is unstable and the vibration of the mill and pipe increases. In turn, there is vibration for a period of time when the roller is lifted. Once the pressure builds up and the material layer stabilizes, the vibration disappears. Therefore, it is necessary to adjust the opening of the double one-way throttle valve so that the hydraulic control one-way valve in the lower chamber opens faster.It is recommended that the opening should not be too large. Adjust according to actual needs.
6. Rod chamber relief valve: Ensure that the maximum working grinding pressure loaded in the upper chamber is less than or equal to the maximum pressure set by the system. It is also generally used as a safety valve; it can be flexibly adjusted according to the actual required pressure. It is recommended to have a gradient of 1-2MPa between the rod chamber pressure setting value and the system pressure.
7, rod cavity pressure regulating valve or balance valve (YV3 and controlled hydraulic one-way valve, throttle stop valve with handle). When the pressure in the rod chamber is higher than the central control set pressure, the solenoid valve is energized, and the valve automatically opens to release the pressure to the preset value, for example, the pump stops when ≥+0.5MPa. When the pressure drops by -0.5MPa, the system oil pump automatically starts to replenish the pressure in the chamber that has lost pressure until ≥+0.5MPa. (Note: This pressure range is generally 1MPa under normal circumstances. If it is too large, it will cause large pressure fluctuations and unstable grinding pressure. If the negative value is too low, it will affect the particle size of the material, thereby affecting the output; if the positive value is too high, the material layer will Instability and increased material return affect the stability of the mill.) The negative value is too large and the particle size cannot meet the requirements.
8, lower chamber hydraulic control check valve and control valve (YV4 and 5, liquid filling valve or cartridge valve). When loading and grinding, the hydraulically controlled one-way valve in the lower chamber is in a spring-pressed closed state. The valve is open. At this time, the hydraulic oil in the lower chamber is in a pressureless and free state (it needs to be noted that the slope difference cannot be too large during the pipeline layout and construction of the oil station, otherwise it will cause all the hydraulic oil in the lower chamber pipeline to return to the tank and the roller lifting time will be too long. Condition). The energy of the oil in the lower chamber is released through pipes and oil tanks. Once the filling valve or cartridge valve is unstable and cannot be opened properly, the lower chamber pipeline will vibrate violently.
will also affect the stability of the mill, causing the lower chamber pipe to vibrate, which will then cause unstable pressure and intensify the vibration of the grinding roller. The manifestation is: The frequency and amplitude of the expansion and contraction of the oil cylinder will increase, so the oil that needs to be released back and forth will be replenished. The quantity increases. Excessive frequency and amplitude will cause a temporary negative pressure in the pipeline, and the spring of the mushroom valve that should be opened is compressed and closed. At this time, the vibration of the hydraulic system becomes more severe and the vibration of the mill also intensifies.
The problem disappeared until the oil pump started and the bacterial valve was opened by the pump pressure. Once the pilot valve of the filling valve is energized and the valve core moves, the spring pressure pushes the valve core of the filling valve or cartridge valve to move and close the valve. After the power is lost, the self-locking device of the pilot valve locks the position of the valve core. The position and state of the valve core do not change until the solenoid valve on the other side is powered and pushes the valve core to move. When used, the filling valve can be either normally open or normally closed.
9. Oil cylinder part: The executor of actions such as loading pressure on the grinding roller or lifting the roller.
03
Frequently Asked Questions
1. The upper chamber does not pressurize and the roller cannot fall.
Possible factors: ①. The system relief valve fails; ②. The upper chamber safety valve fails; ③. The main reversing valve is stuck. In the middle function. ④. The hydraulic control check valve controlled by YV3 solenoid valve is jammed and relieved. ⑤. The lower chamber does not release pressure.
method: Check the system relief valve, main reversing valve and the safety valve and hydraulic control check valve of the upper chamber one by one. Of course, you can lift the roller. If the pressure rises normally and the roller can be lifted, it means there may not be a problem with the main reversing valve, and there may not be a problem with the pump and main relief valve.
Focus on checking whether the safety valve core in the upper chamber is intact and whether the spring, limit, etc. are normal. If the lower chamber does not release pressure, you can observe that the pressure does not drop, which is easier to detect. Solved by cleaning the valves where YV4 and YV5 are located.
2. The lower chamber is not pressurized and the roller cannot be lifted.
Possible factors: ①. The system relief valve fails; ②. The lower chamber safety valve fails; ③. The main reversing valve is stuck. In the middle function.④. The pilot valve of the hydraulic control check valve in the lower chamber is stuck (the valve where YV4 and YV5 are located), causing the hydraulic control check valve to not close or not close tightly. ⑤. The upper chamber does not release pressure.
Method: Check the system relief valve, main reversing valve, safety valve in the lower chamber, and pilot valve of the hydraulic control check valve one by one. Of course, the loading action can be performed. If the pressure rises normally, the roller can fall on the material layer, and the pressure rises normally, it means that there may not be a problem with the main reversing valve, and there may not be a problem with the pump and main relief valve.
Focus on checking whether the safety valve core in the lower chamber is intact and whether the spring, limit, etc. are normal. If the pressure in the upper chamber does not decrease, it can generally be observed and the upper chamber balance valve is directly cleaned.
3. The upper chamber does not release pressure. After the roller falls under its own weight, the lifting roller does not press up.
Possible factors: ①. The system relief valve fails; ②. The main reversing valve is stuck. In the middle function. ③. YV3 and the hydraulic control check valve in the upper chamber are stuck; ④. The hydraulic control check valve and pilot valves YV4 and YV5 in the lower chamber are stuck. ⑤. Both the upper and lower chambers have poor pressure relief.
Method: Check the system relief valve, the safety valve in the upper and lower chambers of the main reversing valve one by one. Pay attention to disassembly and cleaning. If the valve core is severely ground, it needs to be replaced with new spare parts.
In addition, you need to pay attention to whether the valve combination pad is installed and intact. After disassembly and cleaning, follow the above two methods to test one by one. Disassemble the pilot valves in the upper and lower chambers one by one, clean and check the condition of the valve core.
4, the upper chamber does not release pressure, and the pressure in the lower chamber rises normally. The pressure in both chambers increases, the roller lifting speed is extremely slow, the mill vibrates violently, and even stops.
This situation will show that the pressure in both chambers is high. Even as flush. The roller rises extremely slowly. The mill vibrated violently. Even jump-stop.
Possible situations:
①. The main reversing valve is not reversing well, and high-pressure oil enters both chambers, but the speed is extremely slow.
②, YV3 solenoid valve is stuck, and the pilot oil cannot open the hydraulic control check valve controlled by it;
③, the hydraulic control check valve is stuck and cannot be opened normally;
④, the throttle stop valve with handle is closed, and there is a rod cavity The oil returned to the tank cannot be decompressed and returned to the tank, causing the upper chamber to be pressurized. To lift the roller, the pressure in the lower cavity must be increased to lift it. The speed is extremely slow and the mill vibrates violently at this time, which often easily causes the vibration to exceed the standard and the protection to trip and stop.
⑤. There is a possibility of internal leakage/internal leakage in the oil cylinder.
⑥. For systems with a quick roller lift valve group, the quick roller lift valve group may have internal leakage or the cartridge valve may not be closed tightly.
Method: Focus on checking the grinding condition of the valve core of the YV3 solenoid valve; whether the hydraulic control check valve it controls is intact. Check whether there are scratches on the damping and whether the return position is correct, etc. Whether the spring is effective; whether the opening of the throttle stop valve with handle reaches about 85%. Check whether there is internal leakage in the oil cylinder; check whether the cartridge valve group is not tightly closed.
04
pressure adjustment (site debugging method)
1, system pressure. Close the high-pressure ball valve (usually installed) in the upper and lower chamber pipes of the oil cylinder, and tighten the safety valves in the upper and lower chambers. Loosen the valve stem of the system relief valve until it is loose.
Check and confirm that the ball valves of each oil return pipeline on the valve table are open. Start the oil pump. If the main reversing valve has a neutral oil discharge load function, it needs to be reversed. For example, the solenoid valve that performs a command to lift the roller can be energized.
Gradually tighten the stem of the system relief valve to increase the pressure to the value specified in the system drawing. Be careful not to tighten too quickly to avoid overloading and overpressuring the motor and pump. Stop the pump once and restart it. If the pressure does not change, it is considered that the adjustment is complete.Just tighten the locking nut of the valve stem.
2, upper chamber pressure. After debugging the system pressure, the main valve is reversed to allow the loading action valve to be energized and the upper chamber pressure is observed. Gradually loosen the stem of the upper chamber safety valve. It is appropriate until the pressure is 1-2MPa lower than the system pressure.
After stopping the pump, reopen the reversing valve and give the drop roller pressure command (the central control can cooperate with the coordination of people on the control cabinet next to the machine), and observe whether the pressure is consistent with the set value. If they are consistent, it is considered that the rod cavity pressure has been adjusted well. Otherwise, adjust it again.
3, lower chamber pressure. After adjusting the loading pressure of the upper chamber, lift the roller to change the direction of the main valve, and then loosen the valve stem of the lower chamber safety valve. Generally, the pressure of the lower chamber lifting roller should not be set too high.
is generally set to 5-7MPa (Note: The reliability of safety valves is extremely high. No matter domestic or foreign brands, there are not many good ones at present, so generally the safety valves of both chambers are closed, and only the system relief valve operation).
The above three steps can generally adjust the system, loading and roller lifting pressure. After debugging, open the outlet of the oil station and the high-pressure ball valves in the upper and lower chambers of the oil cylinder, and prepare for the central control operation test.
In the above method, the pressure of the upper and lower chambers is "major and small". You can also use " minor and major". For example: When adjusting the loading pressure of the upper chamber, first loosen the valve stem, then switch the main valve to the loading mode, then start the pump, and gradually tighten the valve stem to the required value. Both methods are possible. Relatively speaking, the method from small to large is relatively safer.
05
Hydraulic system maintenance and suggestions
Most (≥85%) hydraulic system failures are caused by dirty oil. Oil dirt is divided into dirt caused by particulate impurities and viscosity reduction caused by moisture.
1, particulate impurities. In addition to the early installation failure, the later impact mainly comes from the abrasion and wear of metal and seals between the hydraulic cylinder's piston rod and guide sleeve, the hydraulic piston and the hydraulic cylinder, and enters the hydraulic oil. External phenomenon: The color of the hydraulic oil gradually changes. Generally: light yellow, yellow, light black, black.
Methods: ① To avoid the influence of large particles in the early stage of installation, set up an inlet and outlet oil filter. ②. Periodically replace the filter element. ③. Regularly use high-precision oil filter machine to filter and clean the bottom of the fuel tank, purge the cylinder and clean the pipes to perform regular hydraulic oil maintenance. Otherwise, it is necessary to use high-precision (above 5 microns) to replace the new oil filter into the oil tank.
2, moisture. With changes in climate and air humidity. The temperature of hydraulic oil is generally between 35-45 degrees. The air in the unfilled space of the fuel tank forms a heat exchange place due to the hot oil surface. Moisture from the air enters the fuel tank. As the oil pump suction filter and pump agitation, moisture is fully mixed into the hydraulic oil.
As time increases and moisture increases, the viscosity of the hydraulic oil gradually decreases, and the pressure maintaining of the hydraulic valve and the lubrication effect of the hydraulic oil decrease. This will cause increased wear on pump valves and cylinders, shortening their lifespan. Increases the frequency of replacement and increases costs. When the oil station is stationary, stratification will be found.
The specific details are as follows: when the oil cylinder was disassembled and inspected, it was found that there was floating rust at the bottom of the cylinder barrel and corrosion at the bottom of the oil tank at the oil station.
Method: Regularly use a high vacuum oil filter to remove water and impurities. Hydraulics are maintained and maintained.
3. Current industry status.
Most users are aware of the impact of particulate matter. Because the valve core of the high-pressure filter is clogged and the alarm is visible, and the color change of the hydraulic oil in the tank is visible. Hydraulic oil is generally replaced or filtered on time; however, very few users know or pay attention to the problem of moisture affecting viscosity.Especially in the south, where there is abundant rainfall and hot and humid weather, the water inflow rate is much faster than in the north. Therefore, it is recommended that the South should be dewatered and maintained once every three months. Water should be removed once every four months in summer and autumn in the north, and once every 5-6 months in other seasons. Tracking method: Take samples and go to the quality inspection center to test particulate matter and viscosity for cleanliness testing to better understand the quality of the oil.
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