High pressure oil pipe quality problems and solutions

1 Common faults of hydraulic pipeline parts of construction machinery
The common failures of hydraulic pipeline parts in construction machinery mainly include hydraulic hose assembly failure and hydraulic steel pipe assembly failure! 3 kinds of pipe joint failure "Hydraulic hose assembly is a hydraulic hose (wire winding! Braided hose, cotton hose, etc.) and pipe joints (core! Jacket! Nut or flange core) are crimped and connected by special equipment to form an assembly, which can be directly connected. Assembly and connection with other components in the hydraulic pipeline "The hydraulic steel pipe assembly is generally made of seamless steel pipes and pipe joints welded, and there are also ferrules! The ferrule type assembly with the nut directly assembled on the steel pipe".
1.1 Types of hydraulic hose assembly failures! Cause and Solution
For the hydraulic hose assembly, the crimping part is the weakest part of the whole assembly, and the quality problems that occur are mostly concentrated here. "In addition, due to the aging problem of the rubber, when it exceeds a certain period, the crimping part will also leak." Therefore, the hydraulic hose assembly is a wearing part and should be replaced regularly to avoid accidents. "The types of failures that often occur in hydraulic hose assemblies are as follows: Leakage at the crimping part! Hose burst! Hose sand holes leak oil! Hose assembly Oil leakage at the joint! Cracks on the outer rubber of the hose! Cleanliness of the inner wall of the hose".
1.1.1 Leakage at the crimping part
Due to the poor control of the crimping size, the aging of the rubber will cause the leakage of the crimping part. In actual operation, the selection of the matching size of the Rubber Tube and the core and the selection of the crimping amount are very important. The expansion and deformation of the rubber itself makes it difficult to control its size. Currently domestic! There is no way to control its tolerance in a smaller range, such as the 19 pipe produced by Shenyang ISR Company, the nominal diameter of the inner hole is 19? 0.5mm, the outer diameter of the two-layer steel wire braided reinforcement layer is 27.5? 0.8mm" and According to the national standard or ministry standard, the outer diameter of the core selected is 19?0.1mm, the inner hole of the jacket is 28.5?0.1mm, and the outer diameter is 37?0.1mm." To assemble the die together, the cumulative tolerance is?1.4mm , and the optimal compression ratio of rubber is 0.42~0.5mm. If you consider the shrinkage and deformation of the core and the outer jacket after crimping, it is difficult to achieve the optimal compression ratio by controlling the crimping amount alone. In theory, it is easy to control, but it is more difficult in actual operation of mass production. The main reasons are:
The reason for the rubber tube
The dimensional accuracy of rubber hoses is not uniform. Even in the same batch of rubber hoses, different parts have different inner hole sizes. This is determined by the current production process of rubber hoses. "The current production process of rubber hoses includes core braiding and coreless braiding. All can only control the size within the tolerance range and cannot maintain uniform consistency; the inner rubber formulation and production cannot maintain the consistency of its hardness and forming shrinkage ratio.
2) Core! The effect of coat size
The outer diameter of the core and the inner diameter of the outer jacket are the key dimensions that affect the amount of crimping. At present, the domestic production process controls the amount of crimping according to the shrinkage of the outer jacket. "The error of crimping amount introduced by the dimensional tolerance of the core and the outer jacket is 0.3mm. ".
Core! The effect of shrinkage and deformation of the jacket!
Core! The material of the jacket is different, and the amount of deformation and shrinkage after crimping caused by the difference in its mechanical properties is also different. If the jacket hardness is low, the internal stress of plastic deformation after withholding is small, and the locking force is small; The reinforcement layer is buckled, and the inner hole shrinks to a polygonal shape after crimping (currently, the multi-lobed Huff crimping machine is used for crimping), which results in uneven locking force, which is extremely unfavorable for sealing. If the hardness of the core is inconsistent, it will also cause crimping. Afterwards, the amount of shrinkage and deformation is different, the hardness is high, and the deformation is small, which is easy to cause the steel wire to break; the hardness is low, the deformation is large, the end of the core and the hose are in a saddle shape, and the actual compression of the rubber is small, which is easy to cause leakage. Core! The eccentricity of the inner and outer diameters of the jacket will also cause uneven deformation during crimping, which is also extremely detrimental to the sealing performance." Therefore, improve the production process of the hose! Measures such as effective control of the material and the amount of crimping of the core and jacket can effectively control the leakage of the crimped part."
1.1.2 Hose burst
There are two phenomena when the hose bursts. The first is the position of the frying port: one is that the frying port is located within 25cm of the two ends of the hose from the jacket, the other is that the frying port is 25cm away from the jacket; the second is the shape of the frying port: one is that there is no frying port Regular shape; Second, the frying mouth is more regular and linear. "According to the distance and shape of the frying mouth of the hose, it can be judged that the failure of the hose assembly is the reason for the manufacture of the hose assembly! There are two types of reasons for the hose itself.
If the hose bursts within 25cm from the jacket, this is due to the manufacture of the hose assembly. "The amount of crimping is too large, which will cause the steel wire to be buckled; the system pressure is too high, and the jacket is the weakest link of the assembly, which will also cause Explosion; the working conditions of the hose are relatively bad, the frequency of expansion and contraction is fast during operation, and there are both expansion and deformation stress and twisting stress during operation, which will affect the service life of the Rubber Hose.
Therefore, controlling the amount of withholding and system pressure, changing the working conditions, etc. can better weaken the damage caused by the manufacture of the hose assembly." During operation, the oil pipe not only has to bear bending stress, but also torsional stress, so its failure frequency is high. After technical improvement, the length of the hose is lengthened to 1252mm, which reduces the influence of bending and torsional stress and reduces the frequency of failures. , to a certain extent, the probability of failure is reduced. "But to completely solve the problem, it is necessary to improve the working conditions and change the spatial position of the connecting steel pipe to improve the working conditions of the hose." The reasons for itself are "one is the reason for the manufacture of the hose, and the other is the unreasonable design and installation position of the hose." If the burst opening is in a regular line, it is the quality of the hose, such as the joints or the mechanical strength of the steel wire when the steel wire is braided. Some are caused by improper selection of the hose. "For example, the burst opening is irregular, which may be caused by the small bending radius or bending and twisting fatigue of the hose assembly after installation, or the hose is caused by external mechanical damage." For example, type 30F. When the loader system is improved, a 25/2S-1500C=45F hose assembly is used to replace the original 25 pipes (25 two-layer steel wire braided rubber hose, working pressure is 14Mpa; 25/2S two-layer steel wire winding pipe, working pressure is 18Mpa), the 25/2S tube appeared to burst after working for a month, and the explosion occurred in two places: one was at 20~30cm away from the jacket, and the other was in the middle position. "In a straight line" because the working pressure of the 25 two-layer steel wire braided hose cannot reach the design pressure, the 25/2S two-layer steel wire wound pipe is selected, but the designer does not understand the actual performance and use requirements of the 25/2S two-layer steel wire wound pipe: work It cannot be less than the minimum bending radius of 360mm, and cannot be used under dynamic pressure. "Therefore, the design only considers whether its working pressure meets the requirements of use." Moreover, the 25/2S two-layer steel wire winding pipe is limited in its structure, and the two-layer steel wire is wound. , The binding force between the layers is small, and it can only be used when the static pressure and the hose are basically stationary. "So the failure of the hose assembly is unavoidable." Finally, a 25 second-layer steel wire braided hose was re-produced. The problem was finally solved by increasing the strength of the steel wire layer and increasing the working pressure to 21Mpa."
1.1.3 Hose sand hole oil leakage
The phenomenon of trachoma and oil leakage is generally manifested as leakage or linear injection after the outer rubber of the rubber tube is bubbling. "The oil leakage of the rubber tube trachoma is mostly caused by the quality of the rubber tube." If the inner rubber contains impurities, there will be local damage or defects when it is demolded. "But sometimes the outer rubber bubbling is not necessarily a trachoma, and only anatomical analysis can draw the correct conclusion." For example, when the inner rubber is ruptured due to fatigue, the hydraulic oil will seep out from the rupture, penetrate and diffuse along the reinforcing steel wire layer, and the outer rubber will leak out. The weak part of the glue forms oil bubbles, forming the same phenomenon as trachoma oil leakage." This needs to be solved by improving the quality of the rubber hose.
1.1.4 Oil leakage at the joint of the hose assembly
The leakage at the joint is mainly caused by the inconsistency of the dimensional accuracy of the transition joint between the hose assembly joint and other parts of the hydraulic system. "For example, the connection between the ferrule type rubber hose assembly and the 24b inner taper pipe joint is often due to poor assembly of the ferrule or internal The quality problem of the taper pipe joint causes leakage at the fitting. For example, when the C-type rubber hose assembly is mated with the flared pipe joint, the assembly joint is a 60b cone, and the flared pipe joint is a 60b outer cone, and the angle tolerance of both is the same ? 30c, assuming that the dimensions of the two are just at the upper and lower limits, it is actually a wire-sealed fit. If the tightening force during assembly is not enough or the vibration during operation is too large, it is easy to cause leakage.
Therefore, rationally design the connection assembly size! It is very necessary to improve the assembly accuracy."
1.1.5 Cracks on the outer rubber of the hose
The inner rubber of the hose is an oil-resistant sealing layer, the middle is a steel wire reinforcement layer, and the outer rubber layer is just a protective layer. It seems that its role is insignificant, but it protects! Aesthetic effect "There are many outdoor operations of construction machinery, and the outer rubber of the hose should have the ability to resist ultraviolet rays. Otherwise, the outer rubber of the rubber hose will age and crack under the sun and rain, which will affect the appearance and make the user mistakenly believe that the rubber hose is damaged." For special purposes The rubber hose should use different rubber formulations to meet the needs." For example, Longyan Construction Machinery Co., Ltd. sent a batch of loader to the Qinghai-Tibet Plateau, and specially added a layer of tin foil to protect the outer surface of the rubber hose to resist the ultraviolet rays of the plateau, which is a good solution. solve this problem".
1.1.6 Cleanliness of the inner wall of the hose
After the hose is cut off, a large amount of rubber powder will accumulate at the fracture, and the inner wall of the core-braided hose will have residual silicone oil and talc powder for demoulding, and it is difficult to remove the silicone oil and rubber powder mixed together. If burrs, iron filings or other dirt enter the hydraulic system, it will contaminate the hydraulic oil and cause serious failure of other parts of the system. "Adopt the newly developed sponge! The method of compressed air can solve the above problems well, and at the same time, it is necessary to prevent other secondary pollution in the production process, such as the cleaning of the workshop environment and the cleaning of the test liquid.
1.2 Common fault types of hydraulic steel pipe assembly! Cause and Solution
Due to the small degree of bending of the steel pipe during installation, the positional accuracy of the steel pipe assembly is required to be high. Therefore, the common failure of the steel pipe assembly is that the spatial position accuracy does not match, and it cannot be installed and connected. "The harsh working conditions of construction machinery, such as vibration, welding, etc. The welding seam and the rubber hose assembly! The connection seals such as pipe joints are easy to loosen and cause leakage"
1.2.1 Spatial position accuracy does not match
Such problems can generally be found during assembly and connection, and can be corrected in time without much impact on the quality of the entire construction machinery. "Surveying and mapping design of steel pipe assembly! Bending of steel pipes! Fixtures and fixtures during welding are required. Put forward higher requirements to ensure the spatial position accuracy of the product. "If there is an error in the size, the forced borrowing during installation will cause internal stress to the steel pipe assembly. When the machine is working, its vibration will cause leakage at the weld or joint seal. ".
1.2.2 Leakage of steel pipe assembly
The leakage problem of the steel pipe assembly mostly occurs at the weld and joints. "General steel pipe or joint blisters! Leakage caused by cracks can be found during product testing, and some will also occur after a period of use." Steel pipe assembly Leakage occurs at the weld.
The main reason for the leakage at the welding part of the steel pipe assembly is caused by the welding quality problem. "The material of seamless steel pipe is generally 20# steel, and the material of pipe joints is mostly 35# or 45# steel, and the two materials with inconsistent carbon content are welded. Together, the welding stress is large, the two materials are difficult to fuse, and it is easy to produce pores! Trachoma or de-soldering phenomenon "The main welding method currently used is manual arc welding! Carbon dioxide gas shielded welding and brazing, therefore, the most important thing to improve the leakage problem is to derust the welded part before welding! Degreasing, opening welding grooves and other processing links, and preheating can also be carried out if conditions permit."
The leakage of the steel pipe assembly occurs at the joint, and the sealing of the steel pipe assembly and other parts is often done with a ferrule type! Flare! There are several reasons for leakage at the pipe joint, such as the looseness of the threaded connection, the failure of the seal, the mechanical damage of the sealing joint, or the matching accuracy of the assembly and other parts. "For example, the groove of the /O0 ring is too deep, the aging of the sealing ring, the loosening of the fitting caused by mechanical vibration, and the bumping of the flared conical sealing surface will cause sealing failure." Therefore, the steel pipe assembly must be protected. Match the sealing surface well to avoid mechanical damage to the sealing surface during production, transportation and assembly.
1.2.3 Cleanliness of steel pipe assembly
Just like the hose assembly, the hydraulic system also has high requirements on the cleanliness of the steel pipe assembly. "The cleanliness of the steel pipe assembly is more difficult to meet the requirements than the hose assembly". The main factor that affects the cleanliness of the steel pipe assembly is the burr! Iron filings and rust "The most difficult thing to deal with is the rust problem" For the surface of the steel pipe, it can generally be treated by galvanizing or phosphating on the surface, or spraying paint according to the requirements, which can meet the requirements" but the inner wall of the steel pipe is rougher than the outside. , it is also easier to rust, even if it is coated with anti-rust oil, the oil will evaporate over a long time and it will also rust. The method that can be taken is: for steel pipes with an inner diameter of 19mm, use sandblasting to remove rust; 19mm steel pipe, first pickle with dilute acid, then clean the steel pipe, apply anti-rust oil after drying, and seal the port to maintain the cleanliness.
1.3 Common faults of pipe joints
The common faults of pipe joints, in addition to the problems mentioned in the above-mentioned rubber hose assembly and steel pipe assembly, there are also two faults in pipe joint cracking and leakage caused by matching accuracy.
1.3.1 Cracking of pipe joints
The cracking of pipe joints is the most common problem. "Sand inclusion! Impurities and other material defects, as well as the strength of the blank! The microstructure and so on will cause material cracking." The pores of the casting blank itself! The trachoma is serious, which will directly affect the performance of the pipe joint. "When the material is not selected properly, it is easy to cause the pipe joint to crack." For example, cold-drawn blanks are used for thin-walled parts. The metallographic structure is elongated along the axis, and the radial bearing strength is weak. It is easy to cause cracking when assembling and tightening. For example, the Z14 ferrule type welding end straight pipe joint produced by a certain factory is made of cold-drawn hexagonal steel. Longitudinal axial cracks "The number of cracks is not large, one or two occur occasionally, less than 1%, but rework, cutting, and reassembly are time-consuming and laborious" and the material was tested for flaws and no cracks were found in the material. After the stock of more than 1,200 joints All of them were extruded with a specially designed inner cone indenter (without damaging the mating surface), and it was found that 8 cracks were found. The reason for the cracks was found that the radial strength of the joints was not enough, and then the forging blanks were used to improve their metallographic properties. The organization, the problem was solved, and the cracking phenomenon never happened again.
1.3.2 Leakage caused by matching accuracy
The dimensional accuracy of the pipe joint can easily lead to oil leakage at the connection and fitting. Even if the dimensional accuracy of the pipe joint meets the requirements and the matching accuracy with the steel pipe assembly, rubber hose assembly or other components is ignored, problems will occur. !Produce and strictly control its dimensional accuracy to reduce and prevent leakage.