1Common failures of hydraulic pipeline parts of construction machinery

 Common failures of hydraulic pipeline parts in construction machinery mainly include failure of hydraulic hose assembly and failure of hydraulic steel pipe assembly! Pipe joint failure 3 "Hydraulic hose assembly is hydraulic hose (wire winding! Braided hose, cotton hose, etc.) and pipe joint (core! Outer jacket! Nut or flange core) are connected by special equipment to form a combined assembly, which can be directly connected Assembly and connection with other components in the hydraulic pipeline "Hydraulic steel pipe assemblies are generally welded from seamless steel pipes and pipe joints, and there are also ferrules! A ferrule assembly where the nut is directly mounted on a steel tube. "

1.1 Type of failure of hydraulic hose assembly! Causes and solutions

For the hydraulic hose assembly, the crimping part is the weakest part of the entire assembly, and most of the quality problems that occur are concentrated here. "Besides, due to the aging problem of rubber, the crimping part will leak when it exceeds a certain period." 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 the following 6 types: leaks in the crimping part! The hose bursts! The trachoma of the hose leaks oil! The hose assembly Oil leaks at the joints! The outer rubber of the hose is cracked! The cleanliness of the inner wall of the hose. "

1.1.1 Leakage at the crimping site

Due to the poor control of the size of the crimp, the aging of the rubber will cause the leakage of the crimp. "In actual operation, the choice of the size of the rubber tube and the core and the amount of crimp are important." The elastic deformation of the rubber makes its size control difficult. Currently domestic! There is no way for external technology to control its tolerance to a smaller range. "For example, the 19-pipe produced by Shenyang ISR Company has a nominal diameter of 19? 0.5mm, and the outer diameter of the two-layer steel wire braid reinforcement layer is 27.5? 0.8mm." According to the national 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 cores together, the cumulative tolerance will be 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 jacket after buckle, it is difficult to achieve the best compression ratio by controlling its buckling amount. It is easy to control in theory, but it is more difficult in the actual operation of mass production. The main reasons are:

Rubber tube reason

The dimensional accuracy of rubber hoses is not uniform. Even in the same batch of rubber hoses, different parts have different internal hole sizes. This is determined by the current production process of rubber hoses. "The current production process of rubber hoses has core braid and coreless braid. Both can only control the size within the tolerance range and can not maintain uniformity; the formula and production of the rubber can not maintain the consistency of its hardness and forming shrinkage ratio.

2) Core! Influence of jacket size

The outer diameter of the core and the inner diameter of the jacket are the key dimensions that affect the amount of buckle. At present, domestic production processes control the amount of buckle according to the shrinkage of the jacket. "The tolerance of the buckle amount introduced by the size tolerance of the core and the jacket is 0.3mm ".

The effect of shrinkage and deformation of the jacket!

Different jacket materials have different deformation and shrinkage after buckling due to the difference in mechanical properties. "If the jacket hardness is low, the internal stress of plastic deformation after buckling is small, and the locking force is small. If the jacket hardness is high, the steel wire may be The reinforced layer is buckled, and the inner hole is contracted after the buckle is polygonal (currently, multi-flap Huff buckle presses are used for buckle), which results in uneven locking force and is extremely detrimental to the seal. "If the core hardness is inconsistent, it will also cause buckle. After that, the amount of shrinkage and deformation is different, and the hardness is high, and the deformation is small, and it is easy to cause the wire to break; the hardness is low, the deformation is large, the core end is in the shape of a saddle, and the actual compression of the rubber is small, which is easy to cause leakage. Core! The eccentricity of the outer and inner dimensions of the jacket will also cause uneven deformation when buckled, which is also extremely detrimental to the sealing performance. "So, improve the production process of the hose! Measures such as effectively controlling the material of the core and jacket and the amount of buckle can effectively control the leakage of the buckle part. "

1.1.2 Hose burst

There are two kinds of phenomena of hose explosion. The first is the location of the mouth: first, the location of the mouth is within 25cm from the jacket at both ends of the hose, the second is the mouth of the jacket is 25cm away from the jacket; the second is the shape of the mouth: Regular; second, the fryer is more regular, linear. "According to the distance and shape of the hose fry, it can be judged that the failure of the hose assembly is the cause of the manufacture of the hose assembly! There are two types of causes for the hose itself.

If the hose bursts within 25cm from the jacket, this is the manufacturing reason of the hose assembly. "The amount of buckle is too large, which will cause the wire to be broken; 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 harsh, and the frequency of expansion and contraction is fast during work. At the same time, there are expansion and contraction stress and twisting stress at work, which will affect the service life of the hose.

Therefore, controlling the amount of buckle and system pressure, changing the working conditions, etc., can better weaken the damage caused by the manufacturing of the hose assembly. "For example, a 19-L1152BZ oil pipe used in the bucket lifter cylinder of a machinery plant 50, bucket During work, the oil pipe must not only withstand bending stress but also with torsional stress. Therefore, its failure frequency is high. After technical improvements, the length of the hose was extended to 1252mm, reducing the impact of bending and torsional stress and reducing the frequency of failure. To a certain extent, the probability of failure is reduced. "But to completely solve the problem, we must improve the working conditions and change the spatial position of the connecting steel pipe, so as to improve the working conditions of the hose." If the hose bursts 25cm away from the jacket, this is a hose. The reason itself is "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 cracks are regularly lined, it is the reason for the quality of the hose. Some are caused by improper selection of the hose. "If the crack is irregular, it may be that the bending radius of the hose assembly is too small after installation. Caused by bending and torsion fatigue, or caused by mechanical damage to the hose. For example, when the 30F loader system is improved, a 25 / 2S-1500C = 45F hose assembly is used to replace the original 25 hose (25 two-layer steel wire). Braided hose, working pressure is 14Mpa; 25 / 2S two-layer steel wire wound pipe, working pressure is 18Mpa), 25 / 2S pipe has one after another one month of work. The explosion of the hose occurs in two places: one is in the At a distance of 20 ~ 30cm from the jacket, the first one is "the shape of the fryer is linear along the winding direction of the steel wire" in the middle position. Because the working pressure of the 25 two-layer steel wire braided hose can not reach the design pressure, the 25 / 2S two-layer steel wire wound pipe is selected. The designer does not understand the actual performance and use requirements of the 25 / 2S two-layer steel wire wound pipe: it must not be less than the minimum bending radius of 360mm when working, and it cannot be used under dynamic pressure "so the design only considers whether its working pressure meets the use requirements" Moreover, due to the structural limitations of the 25 / 2S two-layer wire-wound pipe, the two-layer wire is wound, and the binding force between the layers is small. It can only be used in the case of static pressure and the hose is basically stationary. "So the hose assembly Failure occurs it is difficult to avoid the "last re-production of a 25-story steel wire braided hose, increasing the strength of the steel wire layer will increase the working pressure to 21Mpa, finally solved the problem."

1.1.3 Oil leakage from trachoma

Tracheoma oil leakage is generally manifested as leakage or linear spray after bubbling the outer rubber tube. "Hole trachoma oil leakage is mostly caused by the quality of the hose." If the inner rubber contains impurities, local defects or defects will occur when the mold is released. "But sometimes the outer rubber bubbling is not necessarily trachoma. Only correct anatomical analysis can lead to correct conclusions." For example, the inner rubber ruptures due to fatigue, and the hydraulic oil will seep from the rupture, penetrate and diffuse along the reinforcing steel wire layer, and the outside Oil bubbles form weak spots in the glue, forming the same phenomenon as oil leakage from trachoma "This needs to be solved by improving the quality of the hose.

1.1.4 Oil leakage at the hose assembly joint

The leakage at the joint is mainly caused by the mismatch in the dimensional accuracy of the hose assembly joint and the transition joint of the other parts of the hydraulic system. "For example, the sleeve type hose assembly and the 24b inner cone joint are often connected due to the poor assembly of the sleeve or the internal Leakage at the fitting caused by the quality of the taper joint. For example, when the C-type hose assembly is connected with the flared pipe joint, the assembly joint is a 60b taper, and the flare pipe joint is a 60b outer taper. The angular tolerances of both are ? 30c, assuming that the two dimensions are exactly at the upper and lower limits respectively, then the actual line seal fit, such as insufficient tightening force during assembly or excessive vibration during work are likely to cause leakage.

So, reasonably design the connection assembly size! It is necessary to improve assembly accuracy. "

1.1.5 Cracked rubber outside the hose

The inner rubber of the rubber hose is an oil-resistant sealing layer, and the middle is a steel wire reinforcement layer. The outer rubber layer is only a protective layer. It seems that its role is insignificant, but it serves as protection! Aesthetic effect "There are many outdoor operations of construction machinery. The outer rubber of the hose should have the ability to resist ultraviolet rays. Otherwise, the sun and the rain will cause the outer rubber of the hose to age and crack, which will affect the appearance and make users mistakenly think that the hose is damaged." For special purposes The rubber hose should use different rubber formulas to meet the needs. For example, Longyan Engineering Machinery Co., Ltd., a wholesaler to the Qinghai-Tibet Plateau, specially adds a layer of tin foil to protect the outer surface of the hose to protect it from ultraviolet light on the plateau. Got this problem. "

1.6 1.1.6 Cleanliness of the inner wall of the hose

After the hose is cut, a large amount of rubber powder will accumulate at the fracture. Silicone oil and talcum powder for mold release will remain on the inner wall of the core-woven hose. It is difficult to remove the silicone oil and rubber powder when mixed together. Deburring iron filings or other dirt will contaminate the hydraulic oil if it enters the hydraulic system, causing serious failure of other system components. "Use a newly developed sponge! The method of compressed air can well solve the above problems, 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 fluid.