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Promotion and application of jacketed pipe joint on domestic truck cranes

promotion and application of jacketed pipe joint on domestic truck cranes

China Construction machinery information

qyl6k ~ qy50k truck cranes produced by Xuzhou Heavy Machinery Factory have been put on the market in large quantities since their inception in 1998. K series truck cranes are popular with users because of their advanced technology, beautiful appearance, high reliability, no oil leakage and other advantages. One of the reasons is the use of the world's most advanced pipe connector - Ferrule pipe joint

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ferrule type pipe joints are widely used in the pipeline system of oil, gas and corrosive media. The working pressure is as high as 40MPa, which can be called the most advanced pipe joint in the pipe joint family. It adopts a unique ferrule connection principle, with reasonable structure and convenient use. It does not need flaring, welding or any special assembly tools

ferrule type pipe joint was first invented by German ermeto company in 1930. It is mainly composed of three parts: 1) joint body with 24 degree conical hole, 2) ferrule with sharp inner edge, 3) nut for pressing. When the nut is tightened, the ferrule is pushed into the conical hole of the joint body under the pressure of the nut and deforms accordingly. At this time, the ferrule is in close contact with the conical surface of the joint body to form a spherical seal. At the same time, the inner edge of the ferrule is automatically clamped into the outer wall of the steel pipe. The middle part of the ferrule is slightly arched and has a certain elasticity, which is conducive to sealing and preventing the nut from loosening. The tail of the ferrule also shrinks radially to hold the pipe, So as to play the role of reliable connection and sealing

the ferrule type pipe joint has experienced many improvements and developments since its birth. In the 1980s, the main structural feature is the use of progressive multi edge ferrules, including two progressive working blades, a stop edge and a horn shaped ring tail, which greatly improves the alternating bending strength and pull-out strength of the joint. The stop edge indicates the assembly location, thereby improving the reliability of the assembly. In the 1990s, the ferrule type pipe joint changed the traditional rigid seal of the ferrule into a more reliable elastic seal. At the same time, the locating ring was used to accurately position the ferrule in the locating ring. The joint did not need to be pre installed, which not only improved the reliability of assembly, but also reduced the difficulty of assembly and improved the efficiency of assembly

at present, the application history of ferrule pipe joints in China is still very short. Our factory has successfully applied imported ferrule pipe joints to cx01032 and ltm1050 all over the ground as early as the 1980s. Finally, due to the high cost, it is impossible to form batches. However, it is quite difficult to promote domestic ferrule pipe joints. Only a few domestic crane manufacturers have partially used domestic ferrule pipe joints on truck cranes, such as chassis hydraulic system. No one can always use ferrule couplings on the hydraulic system. In order to improve the manufacturing level of the crane, reduce the welding workload and system pollution, and improve the cleanliness of the hydraulic system, we are determined to apply the domestic ferrule pipe joint to the truck crane of our factory as soon as possible

through the investigation of the main manufacturers and user visits of domestic ferrule pipe joints, we found that the domestic ferrule pipe joints have the following defects:

1. China's current standard for ferrule pipe joints was implemented in 83 years, and there has been no research and improvement in the past 20 years. It has developed to the fifth and sixth generations abroad, but we are still in the first generation, and even can't catch up with the level of the earliest generation abroad

2. In terms of national standards, there are also many shortcomings, such as incomplete connector series, low pressure level, and unable to cope with all kinds of complex applications with high pressure

3. There is no national standard reducer joint. Although there is a ministerial standard reducer joint, it is difficult to bear high pressure due to materials, heat treatment and other reasons. For the same reason, the B-type buckle type rubber hose joint used together with the ferrule type pipe joint cannot be used in construction machinery

4. According to the national standard, 35 steel or Y20 steel is generally used as the joint body and nut of the ferrule type pipe joint; The ferrule is made of 10 steel, and its surface heat treatment hardness is hv550 ~ 800, and the core hardness range is hv220 ~ 300; No. 10 cold drawn (or cold rolled) seamless steel pipe is used. The requirements for the manufacturing accuracy of the ferrule and the heat treatment hardness of the cutting edge are high, and the requirements for the hardness and roundness of the small and medium-sized plates of the surface water new material of the steel pipe are also high. In addition, the domestic manufacturers lack experience in producing ferrule pipe joints, and the proportion of unqualified products is high. If the hardness of the ferrule cutting edge fails to meet the requirements, or the surface hardness of the steel pipe is too high, and the roundness is unqualified, As a result, the ferrule joint often leaks oil and unplugs in the hydraulic system

5. The assembly process of setting the safety distance head for the ferrule type pipe joint is complex, which requires a certain level of technology and experience in assembly, especially the pre assembly of the ferrule type pipe joint is more important. The pre assembly quality directly affects the sealing and anti pullout ability of the ferrule. In order to improve the quality of pre assembly, foreign countries have used a large number of special equipment - pre assembly machine. At present, there is no professional prefabrication machine manufacturer in China. The prefabrication of ferrule pipe joints mostly depends on manual prefabrication, which is not only inefficient, but also has a considerable relationship with the technical level and working attitude of workers, and the assembly quality is very unstable

6. The domestic combined ferrule joint cannot reach the corresponding pressure level

due to the above reasons, domestic ferrule couplings have not been widely used in cranes with high safety requirements. After analysis and research, we have taken the following measures:

first, select domestic manufacturers. The manufacturer with good product quality shall be appointed, and the manufacturing size of ferrule shall strictly follow the national standard:

secondly, the steel pipe used for ferrule joint shall be strictly selected. Generally, No. 20 seamless steel pipe is used in the hydraulic system of truck crane, with high surface hardness and large roundness tolerance, which is difficult to meet the requirements of ferrule joint. For this reason, we put forward the following requirements for the production of steel pipes: No. 10 seamless steel pipes, no oxidation annealing, hardness not greater than hrb75, curvature not greater than 1.5mm/m, outer diameter deviation ± 0.1, wall thickness deviation ± 0.1, surface phosphating and coating antirust oil (this can eliminate the pickling process)

third, assemble in strict accordance with the regulations. First, cut the pipes according to the required length. It is best to have a special sawing machine. If the conditions are not met, the grinding wheel cutting machine can also be used. However, the number of pipes cut at one time cannot be too large, generally 3 ~ 5. Then, it must be trimmed with a file to ensure the roughness of the outer wall of the pipe and the perpendicularity of the central line of the pipe and the fracture surface. Generally, it is basically vertical with the naked eye. After that, deburring, iron filings and dirt shall be removed, and pre assembly can be carried out after the above work

the ferrule can generally be pre installed manually, and the pre installation machine should be considered when the batch is large. The manual pre assembly can be carried out on the Bench Vise. First, put the nut and ferrule on the pipe in turn. Note that the direction of the ferrule edge should be close to the pipe end, and insert the pipe into the taper hole in the connector body in place. At this time, rotate the nut by hand, and rotate the pipe at the same time. When the pipe cannot rotate, it indicates that the ferrule has begun to clamp into the pipe. Rotate the nut by a wrench for one and a half turns, and then disassemble it for inspection. The ferrule should be cut into the outer wall of the steel pipe, and the contact is even, The notch position shall be free of deflection, and the ferrule shall not have axial displacement, but it can rotate around the steel pipe. After passing the inspection, you can enter the formal assembly. At first, you still rotate the nut by hand until it can't rotate, and then change the wrench. If there is no torque wrench, the ordinary wrench can also be used. In order to make the ferrule joint reach the appropriate sealing torque, our experience is: when tightening the nut with a wrench, we begin to feel very relaxed, and after a few rounds, we feel the resistance increases rapidly. At this time, we only need to rotate 1/2 turn with force (1/4 turn for EO joint) to complete the installation. Using this assembly method, we tested on the test bench, that is, one end of the pipe was blocked, and the other end was connected to the press with a ferrule joint. Pressurize to 31.5mp, without leakage and unplugging. Then we carried out the loading test and achieved success once again

finally, the combination method can be adopted. At this stage, the reliability of domestic ferrule joints is still difficult to compare with imported joints, especially in the larger specifications. Therefore, our factory adopts the method of combining imported and domestic ferrule joints, that is, domestic ferrule joints are used when the outer diameter of steel pipe is less than 15, and imported joints are used for the key basic technologies of biological preparation of basic chemical raw materials when the diameter is greater than 15. This not only improves the reliability of products, but also reduces the cost compared with all imported ferrule joints, and has received good results