Abstract: During the initial debugging and production operation of the JLM-46.4 vertical mill hydraulic system, faults such as inability to lift the grinding roller or load pressure, rupture and damage of the nitrogen airbag in the gas storage tank, and unstable hydraulic system vibration occurred. Based on the design principles of hydraulic and control systems, it is analyzed that these faults are mostly caused by secondary pollution caused by improper maintenance and repair, resulting in dirty hydraulic oil and blockage of hydraulic valves.
Keywords: raw material vertical mill; Hydraulic system; Fault diagnosis; solution
0. Introduction
A certain company is constructing a rotary kiln with a diameter of 5.2 m × 78 m, an online spray type decomposition furnace, and a dual series 4-2-2-2-2 five stage preheater clinker production line. The production line is equipped with two JLM3-46.4 raw material vertical mills, which are designed to grind materials with a particle size of less than 80 mm and control the fineness R80 sieve residue to be less than 12%. The actual production capacity reaches 320 t/h or more. During the initial debugging and production operation, various faults occurred in the hydraulic system, such as the inability to lift the grinding roller or load pressure, as well as the rupture and damage of the nitrogen airbag in the gas storage tank and unstable vibration of the hydraulic system. By combining the principles of hydraulic system and control system design, diagnosis, research and analysis were conducted, and measures were taken to solve the problem of equipment operation affected by hydraulic system failures.
1. Main technical data of vertical mill
The raw material vertical mill model JLMS46.4 has a grinding disc diameter of 4600 mm and a speed of 27.1 r/min. Gearbox model JLP250G, input power 2600 kW, speed ratio i=36.585:1. Main motor model YRKK800-6, rated power 2600 kW, speed 992 r/min; Stator voltage 10 kV, current 182 A; rotor voltage 2 450 V, current 651A. Hydraulic system main pump motor model: HM2-200L2-6/B35 power: 22 kW; oil pump model: PVH74QIC-RM-1S-10-C25-31, nominal flow rate 100 L/min, working pressure 14 MPa; Anti wear hydraulic oil ISO VG46.
2. Composition, principle, and control program of hydraulic system
(1) The hydraulic system of the vertical mill consists of an oil tank, plunger pump device, pipeline filter, functional valves (hydraulic control one-way valve, electromagnetic directional valve, plug-in one-way valve, double one-way throttle valve, throttle stop valve, overflow valve, plate ball valve, etc.), roller reversing valve group and pipeline, oil cylinder, control components (liquid level controller, differential pressure controller, pressure transmitter), accumulator, display instrument (pressure gauge, liquid level thermometer), and electric control cabinet.
(2) The hydraulic system of the vertical mill (as shown in Figure 1) provides appropriate loading force for the grinding roller, achieving automatic control of the grinding roller during operation, pressure replenishment, pressure reduction, roller lifting, roller dropping, automatic roller dropping, and cyclic filtration processes. During the normal operation of the system, the energy storage device is used to maintain operation, thereby reducing unnecessary energy loss.
Figure 1 Principle of Vertical Grinding Hydraulic System
(3) Hydraulic cylinder and pipeline system pressure holding test. The maximum working pressure set for the JLM-46.4 vertical mill hydraulic system is 14 MPa, and the pipeline pressure holding test follows the principle of gradually increasing from small to large.
Preparation before the experiment: Separate the grinding roller from the grinding disc with a rubber or wooden pad of at least 30mm, retract the mechanical limit to prevent accidental damage to the top wire. The rodless chamber of the hydraulic cylinder is directly connected to the oil tank. Adjust the overflow valves A and B, as well as the overflow valve C of the hydraulic pump itself, so that the overflow flow of the overflow valves A and C approaches the minimum value, and the overflow flow of the overflow valve B approaches the maximum value.
Start the hydraulic pump and first test the pressure of the rod chamber system: open the shut-off valve M, close the shut-off valve N, power on the solenoid valve YA1, hydraulic oil enters the rod chamber of the hydraulic cylinder, and the gas in the rod chamber is discharged in a timely manner. Slowly adjust the relief valve B to make the pressure in the rod chamber of the hydraulic cylinder reach 15 MPa, power off YA1, and the rod chamber of the hydraulic cylinder is in a pressure holding state. After holding for 10 minutes and checking for no leaks, the test is completed. Re test the pressure of the rodless chamber system: Close the cut-off valve M again to energize the solenoid valve YA2, allowing hydraulic oil to enter the rodless chamber of the hydraulic cylinder. Timely discharge the rodless chamber gas, slowly adjust the relief valve B to make the pressure in the rodless chamber of the hydraulic cylinder reach 12 MPa, turn off YA2, and keep the rodless chamber of the hydraulic cylinder in a pressure holding state. After holding for 10 minutes, check that there is no leakage in the system and complete the pressure holding test.
If leakage is found during the pressure holding test of the pipeline system, the shut-off valves M and N should be opened in a timely manner to rapidly reduce the pressure in the pipeline and reduce the leakage of hydraulic oil. During the process, it should be ensured that the pressure in the rod chamber of the hydraulic cylinder is more than 2 MPa higher than that in the rodless chamber to avoid roller lifting.
(4) Overflow valve and accumulator pressure adjustment setting.
The maximum pressure set for the JLM-46.4 vertical mill hydraulic system is 14 MPa. Under normal use, according to design requirements, ensure that the maximum working pressure of the hydraulic pump and pipeline is within the effective protection range. The pressure adjustment of relief valves A, B, and C should be completed in descending order after the pipeline pressure test. During the repeated pipeline pressure test, the hydraulic cylinder has a rod chamber pressurization action. Based on the reading of the rod chamber pressure gauge, the pressure of relief valve C of the hydraulic pump is set to 15 MPa, the pressure of relief valve B is set to 14 MPa, and the pressure of relief valve A is adjusted to 9 MPa. At this time, the state of relief valves A, B, and C is the rated pressure state of the system operation. The pressure of the accumulator is measured and adjusted using a dedicated gauge, and the nitrogen airbag pressure is generally set to 60% to 70% of the loading pressure.
(5) The logic action control program of the hydraulic valve in the hydraulic station is shown in Table 1. Specifically, when the hydraulic force P is less than the set value of 0.5 MPa and lasts for 10 seconds, the flashing pressurization program is executed. The electromagnetic reversing valve YA4 is always powered on, YA1 is powered on for 2 seconds, and the time interval of 15 seconds is cycled. Each cycle cycle increases the pressure value by 0.06-0.10 MPa until the system loading pressure is greater than the set value pressure and ends;
② When the hydraulic force P is greater than the set value of 0.5 MPa and lasts for 10 seconds, the flashing pressure reduction program is executed. The electromagnetic directional valve YA4 is normally powered on, Y3 is powered on for 2 seconds, and the time interval of 15 seconds is cycled. Each cycle cycle reduces the pressure value by 0.10 MPa until the system loading pressure is less than the set value pressure and ends;
③ When the hydraulic force P is less than the set value of 1 MPa and lasts for 10 seconds, execute the rapid pressurization program until the system pressure is 1.3 MPa higher than the set value pressure, and end;
④ When the system pressure P is greater than or equal to Ps+1 (MPa) or the set pressure P is less than or equal to Ps-1 (MPa), and there is no change after a delay of 10 minutes, the sound and light alarm will be triggered, and the feeding will be stopped and the roller lifting action program will be executed.
3. Fault diagnosis analysis and solution measures for vertical mill hydraulic system
(1) The nitrogen airbag in the accumulator storage tank is damaged, producing a "bang bang" sound and causing impact vibration in the pipeline. Use a dedicated pressure gauge to check whether the pressure of the nitrogen airbag in the diagnostic gas storage tank has decreased or is severely zero. If the pressure has decreased or is zero, it indicates that the nitrogen airbag is leaking and damaged.
Analysis reasons: Poor quality of nitrogen bag, damaged inlet and outlet valves of gas storage tank, impurities in hydraulic oil causing nitrogen bag damage, pressure fluctuations resulting in vibration impact and "bang bang" noise.
Solution: Replace the high-quality nitrogen airbag made by a professional manufacturer or replace the damaged inlet and outlet valves of the gas storage tank, improve the structure of the bacterial valve to increase the strength of the valve stem, clean the impurities in the hydraulic pipeline, and use an oil filter with a filtration accuracy of no more than 5 μ m to filter. Add hydraulic oil to achieve NAS7 level.
(2) The flange of the hydraulic pipeline is leaking oil. Reason: The main reasons are aging and damage to the sealing components, improper installation causing burrs, uneven flanges, misaligned flanges, loose bolts, and stress on the pipeline, resulting in flange oil leakage due to flange misalignment.
Solution: Regularly (check once every 12 months) replace aging seals; When installing the seal, it should be straightened and completely placed into the groove to prevent damage to the seal due to compression and force, which may cause it to fail; Adjust the two flanges of the pipeline to be concentric and parallel, evenly tighten the connecting bolts, and securely fix the pipeline to prevent swinging and oil leakage.
(3) When the oil pump and filter are working normally, the grinding roller and lifting roller are normal, but when lowering the roller, the grinding roller does not lower or there is a malfunction where the lifting roller does not move. The lifting of the grinding roller is normal, and the main reason why the grinding roller does not lower when lowering is that the hydraulic oil has not entered the rod chamber of the oil cylinder, resulting in the inability to apply pressure and lower the grinding roller. The main reason why the lifting rollers do not move is that hydraulic oil has not entered the rodless and rodless chambers of the oil cylinder, resulting in the inability to load and lift the rollers.
Solution: After analysis and inspection, it was found that the three position four-way solenoid valve is damaged or stuck due to dirty oil. The valve core can only work on one side and cannot work on the other side, or both sides cannot work properly in reverse direction. Replace the worn three position four-way solenoid valve with a new one; Dirty oil caused jamming. Disassemble and clean the three position four-way solenoid valve, and filter the hydraulic oil. The oil cylinder works normally, and the lifting and grinding rollers are also functioning properly.
(4) Two of the four grinding rollers can be lifted to the designated position, while the other two grinding rollers have a slower lifting speed and cannot be lifted into place within the set time (120 seconds). According to the fact that there are already two grinding rollers that can be raised, there is no problem with the hydraulic system and no other mechanical issues have been checked. The main reason is that there is still compression space for the oil inside the other two grinding roller cylinders, and there is excess gas inside the cylinders due to slow roller lifting.
Solution: After safely depressurizing the rodless chamber of the oil cylinder, use a wrench to loosen the exhaust plug of the oil cylinder, promptly depressurize and discharge the gas inside the oil cylinder, turn on the oil pump again, and lift the four grinding rollers into place at the same time.
(5) The grinding roller cannot lift up. The central control operation started the roller lifting command until the program ended, but the on-site grinding roller did not lift up. Based on years of processing experience and the schematic diagram of the hydraulic control system, the comprehensive diagnosis is that the oil did not enter the rodless chamber of the cylinder or leaked in the pipeline and hydraulic components. The specific main reasons are: ① blockage of the system filter; ② The oil pump is damaged and there is no oil entering the rodless chamber cylinder; ③ Leakage of rodless cavity pipeline; ④ The shut-off valve M on the rodless chamber pipeline is not closed; ⑤ The solenoid valve Y4 is still energized or the valve core is not in place after power failure; ⑥ The hydraulic control one-way valve is stuck.
The corresponding solution is: ① Clean the clogged filter; ② Replace the damaged oil pump; ③ Handling flange seals for rodless cavity pipelines; ④ Close the shut-off valve M connected to the rodless chamber pipeline tightly without leakage; ⑤ Handle the power outage of solenoid valve Y4 or clean the valve core of solenoid valve Y4; ⑥ Clean the hydraulic check valve controlled by solenoid valve Y4 and filter the hydraulic oil. After implementing the above measures, the hydraulic system works normally and the grinding roller lifting roller is normal.
(6) The loading pressure of the grinding roller cannot be increased, it cannot be pressurized, and the grinding roller cannot be lowered. The main reason is that: ① the oil circuit shut-off valve N is not closed; ② There is a leakage in the rod cavity pipeline; ③ Electromagnetic valve Y3 is still working with electricity or the valve core is not in place after power failure; ④ The hydraulic check valve 21 controlled by solenoid valve Y3 is stuck; ⑤ The overflow valve is blocked and leaking.
Solution: ① Close the corresponding oil circuit shut-off valve N; ② Handle the leakage of the rod chamber pipeline; ③ Power off or clean the valve core of solenoid valve Y3; ④ Clean the hydraulic control one-way valve controlled by solenoid valve Y3; ⑤ Clean and block overflow valve A. After implementing the above measures, the hydraulic system works normally, and the grinding roller pressure roller works normally.
(7) The hydraulic oil pump and oil cylinder hydraulic system are working normally. After pressurization, the piston of a certain grinding roller's oil cylinder rises and falls slightly, and the piston rod extends and retracts little or hardly moves. Main reasons: ① Inspection revealed that the joint bearing of the connecting rod with the oil cylinder piston rod was broken and damaged; ② The hanging ear rod has a production aging defect crack at the threaded position.
Solution: ① Disassemble the fractured rod joint bearing and replace it with a new one, and then load the grinding roller to work normally; ② Replace the new lifting lug rod assembly.
(8) During the normal production and operation of the grinder, the hydraulic system of the oil cylinder works normally, and the oil cylinder sways up and down as a whole during flashing loading.
The main reason is that the joint bearing of the oil cylinder base lifting ear is broken and damaged, and the oil cylinder is not firmly fixed and moves up and down. The solution is to dismantle the fractured joint bearing and replace it with a new joint bearing GEG200ES/2RS. After loading, the oil cylinder does not move up and down, and it is firmly fixed and works normally.
(9) The hydraulic plunger pump produces noise.
The main reason is: ① Air is mixed into the oil (forming bubbles); ② Loose fastening bolts of axial piston pumps or motors cause external vibration; ③ The oil level in the fuel tank is too low; ④ Low oil temperature and high viscosity resistance.
The corresponding solution is: ① Check the leakage point of the system pipeline and exhaust it for treatment; ② Tighten and loosen the foundation bolts; ③ Add oil level to the marked position on the scale; ④ Check that the temperature control system, heating system, and cooling system are in good working condition to ensure automatic oil temperature control. Oil tank temperature control: ≤ 25 ℃ heater starts, ≥ 25 ℃ oil pump starts automatically, ≥ 38 ℃ heater stops, oil supply port temperature control during operation: ≤ 25 ℃ sound and light alarm (manually turn off cooling water), ≥ 43 ℃ sound and light alarm (manually turn on cooling water).
4. Conclusion
Various faults occur in the hydraulic system of the raw material vertical mill, such as the inability to lift the grinding roller or load pressure, as well as the rupture and damage of the nitrogen airbag in the gas storage tank, and unstable vibration of the hydraulic system. Based on the design principles of hydraulic system and control system, after diagnosis, research and analysis, it is believed that most of these faults are caused by secondary pollution caused by improper maintenance and repair, resulting in dirty hydraulic oil and hydraulic valve blockage, which needs to be gradually investigated on site. Suggest taking dust prevention measures, strengthening maintenance and upkeep management on site; Check the oil filter to control oil contamination. The filter element should be cleaned or replaced after continuous use for more than three months, and the air filter should be cleaned regularly; Regularly clean to ensure that the hydraulic oil filter meets the cleanliness level NAS1638-7. The above measures have achieved good results and can be used as a reference.
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