Reliability analysis of push-in ferrule-type pipe joint seal

Cause of leakage
1. The steel pipe is not inserted in the end
2. The nut is not tightened
3. The outer surface of the steel pipe is scratched or the steel pipe is not round.
4. The steel pipe is too hard

Reliability analysis of the sealing of card sleeve type pipe joint

Leakage of pipe joints in the hydraulic system cannot be ignored. Leakage can cause reduced efficiency, increased oil temperature, unstable actuators, and environmental pollution. Directly affecting the normal use of hydraulic equipment, how to improve the sealing reliability of the joint body is exactly the subject that design and manufacturing enterprises and users have been facing.

The card sleeve joint has a simple structure, light weight, small size, easy to use, no welding, and has good pressure resistance, vibration resistance, heat resistance and reliable sealing. Therefore, it can be used in high-temperature, high-pressure and vibrating pipelines, and is an ideal connector in hydraulic systems.

National standard for single-edge ferrules, manufacturing precision according to GB3764-83, surface hardness 550~800HV, core 220~300HV, hardened layer depth 0.03~0.05mm. After years of comparative tests and market research, it is found that the single-blade ferrules designed and manufactured according to the national standard have the following problems: 1. The sealing reliability of large-diameter ferrules is poor, especially for high-pressure pipelines with a diameter of more than 28mm. 2. The edge of the ferrule is easy to bite the wall of the tube. 3. During the assembly process, it is easy for the arched part to yield, which is poor in heat resistance and vibration absorption. 4. Repeated assembly performance is poor.

Through the analysis of the double-edged ferrule, the comprehensive inspection and test of the German-made double-edged ferrule are found, regardless of the large and small diameter, the high and medium pressure seal reliability is higher than the domestic single-edged ferrule. Comparison of intrinsic quality of domestic single-edged ferrules and double-edged ferrules: The hardened layer of domestic single-edged ferrules is 25~30um deep, and the hardness of hardened layer is 700HV, which is relatively brittle. The core hardness is 170HV, and the elastic limit is low.

The hardened layer of the double-edged ferrule is 30um deep, the hardness of the hardened layer is 750HV, and the core is 220HV.

The double-edge progressive ferrule, the depth of the hardened layer changes with the diameter, and the hardness also changes with the diameter, the core hardness is 250~260HV.

Taiwan-made steel single-blade ferrule, hardened layer 35~45um, hardness 700HV, good toughness, core hardness 180HV.

Double-edge progressive ferrules, an additional prefabricated deformation groove, make the double-edge cutting tighter and more labor-saving, and when the double-edge cutting into a certain depth, the thrust ring restricts the cutting edge from excessively cutting into the outer wall of the steel pipe At the same time as the depth, it also ensures that the elastic zone has a high yield resistance, and the size of the outer diameter and inner hole is different from that of a single edge. The sealing principle of the ferrule type pipe joint: the right end of the ferrule is pressed against the nut, and the left end is squeezed into the gap between the taper hole and the pipe in the joint body, so that the outer cone surface of the ferrule forms a conical contact seal, the ferrule The inner edge of the steel pipe is embedded in the outer wall of the steel pipe. A closed ring groove is pressed out of the outer wall of the steel pipe and cut into the seal. The friction force prevents the nut from loosening. The elastically deformed part can absorb the vibration in the hydraulic pipeline. In addition, the tail of the ferrule also tightly embraces the steel pipe to form a collision seal.