There are many factors that cause leakage in the hydraulic system of coal mine roadheaders, and although it is difficult to avoid it sufficiently, it can be well controlled. Whether it's oil temperature, cleaning, injection, filtration, or the standard, assembly, cleaning of components, or regular inspection and maintenance during commissioning, the TBM's hydraulic system is all affected. Therefore, it is necessary to comprehensively control the relevant factors and implement systematic and comprehensive leakage repair and treatment measures, only in this way can the probability of leakage be greatly reduced. The following is a countermeasure for the repair and treatment of the leakage of the hydraulic system of the coal mine roadheader.
1. Avoid oil pollution
Before assembling the hydraulic system, the hydraulic components need to be carefully cleaned, and the internal components need to be disassembled and overhauled in a dust-free environment. Install the primary filter at the position of the suction port of the hydraulic pump to ensure that the bottom of the oil tank is kept at a corresponding distance from the position of the suction port; The high-pressure fine filter is installed at the oil outlet to ensure that the filtration quality meets the operating requirements of the system and avoid the failure of the hydraulic system caused by dirt blockage; The filter screen is installed on the hydraulic tank partition to remove the impurities that have not been filtered out of the return oil filter. The metal protective ring is installed on the hydraulic cylinder to avoid dirt entering the cylinder, and can avoid the leakage problem caused by the erosion of the hydraulic cylinder by drowning; Before the safety hydraulic components, they need to be cleaned of impurities and iron filings; Tank filters are cleaned and inspected regularly, and filter elements are replaced if necessary. Before refilling the new oil, it is necessary to go through the corresponding period of placement and sedimentation, and the intermediate oil tank can be designed to filter and precipitate the new oil to ensure the cleanliness of the oil. Regularly inspect the hydraulic oil, and if there is oil-water separation, oil sedimentation, foam, and deterioration, the system needs to be cleaned quickly and the oil replaced.
2. Ensure the appropriate sealing surface roughness
The leakage problem will be formed when there is an axial scratch or too rough on the surface of the hydraulic system relative to the moving pair, and the oil film will be scraped off by the lip of the sealing ring in the case of small roughness (to reach the mirror surface), so that it is difficult to form an oil film, and the sealing edge will form a high temperature, which will increase wear, so the roughness of the sealing surface should not be too low or too high to ensure that the oil film of the sliding surface is not damaged during operation.
3. Scientific design and processing of sealing grooves
Good design and machining of hydraulic cylinder seal grooves is a prerequisite for avoiding premature damage to oil seals and reducing leakage. If the size of the groove in the piston rod and piston static sealing position is small, and the sealing ring in the groove lacks space to move, the bottom of the sealing ring will be damaged by the reaction force, resulting in oil leakage. It is necessary to design the roughness, size, shape, structure, shape and position tolerance of the sealing groove sealing surface according to the corresponding requirements and specifications. In order to avoid the leakage of oil from the position of the static seal, the tolerance and size of the sealing groove of the static seal should be scientifically designed to ensure that even if the static seal is extruded and deformed after installation, some depressions on the mating surface can be filled, and the internal stress of the seal can be increased.
4. Reduce vibration and shock
All tubes are fixed by damping brackets, so that the energy of vibration or impact is absorbed; With the help of damping reversing valves, the valve is slowly opened and closed, and the one-way throttle valve and other buffer facilities are designed at the end of the hydraulic cylinder; Reduction of impact volume by accumulator or low-impact valve; Pressure control valves are designed to protect all elements of the system; Reduce the number of joints applied as much as possible, and connect the fittings in a welded form as much as possible; Replace the spinal threaded joint with an elbow, tee joint, and threaded direct head; Whenever possible, replace a series of configurations with oil return blocks; Plug torque or bolt torque should be applied during the installation process to avoid damage to the seal and joint surface.
5. Reduce the wear of dynamic seals
Most of the hydraulic system dynamic seals are designed to be accurate, and if the dynamic seals are processed according to specifications, reasonable installation and proper application, they can ensure that there is no leakage for a long time. From a design perspective, the following measures can be implemented to extend the service life of the moving seals: eliminate the radial load on the drive shaft seals and piston rods; Protect the piston rod with rubber cover, protective cover and dust ring to avoid impurities (dust, etc.); Design and select suitable oil tanks and filtration facilities that are easy to clean to avoid the accumulation of dust in the oil; Minimize the running rate of the piston rod and shaft.
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6. Scientific design of the installation plate
In the case where the mounting surface is bolted to the floor or valve block of the hydraulic system of the roadheader, in order to avoid the seal being damaged by the extrusion groove or to obtain the desired initial sealing effect, it is necessary to ensure that the mounting surface is straight, and the sealing surface is finished, to ensure that the surface roughness value is lower than RM 0.8 μm, and that the plane error is smaller than 0.01/100 mm, to prohibit radial scratches from existing on the surface, to ensure that the screw connection preload is large enough to avoid surface separation.
7. Assemble the sealing ring reasonably
In order to attach the sealing ring, it is necessary to apply a guide tool and prohibit the use of metal screwdrivers, etc., to prevent oil leakage due to scratches of the sealing ring. For directional sealing rings, it is necessary to ensure that the pressure oil cavity corresponds to the lip during the assembly process, and pay attention to the protection of the lip to prevent being scratched by burrs or sharp edges of the parts. For sealing surfaces with selective contact, such as the shaft end of the driving gear of the hydraulic pump, a double-lip sealing ring is required. Before the installation of the combination seal, it is necessary to boil the seal in hydraulic oil to the corresponding temperature, and apply professional closing and guide sleeve tools during the installation process, and carefully install it in accordance with the relevant instructions.
As far as possible, choose seals and hydraulic parts produced by regular enterprises to ensure that the performance, model, and specifications of the components meet the standards. The assembly process prevents human factors from damaging the seals and avoids scratches such as sharp edges or burrs of parts. In addition, it is important to use diesel fuel to clean the seals, as the application of gasoline will speed up the aging of the seals. The maintenance process of leakage control and leakage prevention should be strengthened, such as electrostatic spraying, brush plating, etc., to thicken the inner wall of the cylinder, the piston surface, and the valve stem locally or integrally, and then process to the required size. The installation of threaded pipe joints requires the PTFE raw material tape to be wound on the thread, and the pressure test and flaw detection check need to be carried out before installing the welded parts or castings, and the pressure of the withstand pressure test is 150%~200% of the operating pressure. In the case of oil seals installed in the seat holes, special tools are required to guide them to avoid deflection of the position.
8. Control the oil temperature to prevent the seal from deteriorating
Too high oil temperature is a key factor in premature deterioration of seals. At oil temperatures above 60 °C, the viscosity of the oil decreases significantly and the seals deteriorate, causing leakage problems in the hydraulic system. According to the analysis, a 10 °C increase in oil temperature will reduce the service life of the seal by half, so it is necessary to control the oil temperature below 65 °C. Therefore, it is necessary to separate the return pipe and outlet pipe in the oil tank with a partition to reduce the distance between the motor or cylinder and the oil tank, and reduce the application of right-angle elbows in the pipeline as much as possible. In addition, it is necessary to pay attention to the compatibility of sealing materials and fluids, and select the materials and types of seals and hydraulic fluids according to relevant manuals or instructions.
Maintenance personnel need to regularly inspect hydraulic system components to investigate a series of component performance degradation issues in real time to prevent oil temperature increases in the system due to oil channeling through small holes. In addition, it is also necessary to regularly check the hydraulic heat dissipation facilities such as the internal spray and the external spray circuit of the water filter, and clean up the scale in the components in time to solve the problem of reducing the amount of water sprayed, or replace the new accessories. In order to improve the cooling effect, the water cooling system can be designed in the main return pipe and oil tank with high heat generation.
9. Repair or replace leaking sealing elements
For obvious external leaks such as joint leakage and tubing rupture, the damaged parts can be directly replaced, and the relief valve can be adjusted. For the leakage in the hydraulic components, it is necessary to determine the fault first, such as the lack of operating pressure of the hydraulic system, if the hydraulic motor runs smoothly, and there is no significant fault problem at the unloading port, then the operating valve parts that can be replaced with other normal oil circuits and faulty oil circuits, the lower pressure is the internal leakage of the relief valve, and the new parts can be replaced or the valve core can be cleaned when solving this problem. After the end of the service, the tank level is checked and if there is a shortage of fluid, the appropriate level is replenished.
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