How to connect the cylinder head and cylinder barrel in hydraulic cylinder machining? The connection method for machining the cylinder head and cylinder barrel needs to balance sealing performance and pressure resistance. Its design requires the synergistic effect of structural optimization, material selection, and processing technology to ensure long-term stable operation under high-pressure conditions. Common connection methods include flange connections, threaded connections, tie rod connections, semi-ring connections, and welded connections. Each method achieves the dual goals of sealing and pressure resistance through a specific mechanism.
Flanged connections use bolts to fasten the flanges of the cylinder head and cylinder barrel. The preload of the bolts causes elastic deformation of the contact surfaces, filling microscopic gaps and forming an initial seal. To improve the sealing effect, O-rings or metal gaskets are usually placed between the contact surfaces. Their elasticity can compensate for displacement caused by machining errors and vibration. At the same time, the flange must have sufficient thickness to distribute the bolt tension and avoid localized stress concentration that could lead to cylinder barrel deformation. This connection method is simple in structure, highly reliable, and widely used in medium- and high-pressure hydraulic cylinders.
Threaded connections achieve a seal by screwing the cylinder head and cylinder barrel together. Their sealing performance depends on the machining precision of the threads and the fit clearance. To prevent leakage, the thread root is often designed with rounded corners or a trapezoidal cross-section to distribute hydraulic pressure and reduce stress concentration. Additionally, sealant can be applied to the thread surface or a sealing ring can be installed to fill the gap and enhance the sealing effect. The advantages of threaded connections are compact structure and easy assembly/disassembly; however, strict control of thread coaxiality and surface roughness is necessary, otherwise, eccentricity can easily lead to seal failure.
Tie-rod connections apply preload through a tie rod that runs through the cylinder barrel and cylinder head, ensuring a tight fit between the end cap and cylinder barrel. Tie rods are typically made of high-strength alloy steel, heat-treated to provide sufficient tensile strength and fatigue life. To ensure a seal, the contact surfaces between the end cap and cylinder barrel need precision machining, with a surface roughness of Ra0.4 or less to reduce leakage channels. Furthermore, the tie rod layout must be symmetrical and uniform to avoid cylinder barrel deformation due to uneven stress. This connection method is suitable for large hydraulic cylinders, and its advantages include easy assembly/disassembly and reusability.
Semi-ring connections achieve fixation by embedding a semi-ring into a groove between the cylinder barrel and cylinder head. Their sealing performance depends on the precision of the fit between the semi-ring and the groove, as well as the preload. The semi-ring is typically made of spring steel or stainless steel, and its elastic deformation tightly adheres to the groove wall, preventing it from being pushed out by hydraulic pressure. To enhance the sealing effect, a wear-resistant coating can be applied to the contact surface between the semi-ring and the groove, or a sealing ring can be installed to reduce wear and leakage. The advantages of semi-ring connections are compact structure and high strength, but they require high machining precision and strict control of the groove's dimensions and shape errors.
Welded connections achieve a permanent connection by directly melting the contact surfaces of the cylinder barrel and cylinder head. Their sealing performance is determined by the quality of the weld. Before welding, the contact surfaces must be cleaned and pre-treated to remove impurities such as oil and oxide layers, ensuring good fusion between the weld metal and the base material. During welding, welding parameters, such as current, voltage, and welding speed, must be controlled to avoid defects such as porosity and cracks. The advantages of welded connections are simple structure and reliable sealing, but they are not detachable and are suitable for applications with extremely high sealing requirements and no maintenance.
Regardless of the connection method used, strict processing techniques and testing methods are required to ensure sealing and pressure resistance. For example, the contact surfaces of the cylinder barrel and cylinder head need to be ultra-precision machined to reduce surface roughness; connecting parts need to undergo non-destructive testing to eliminate internal defects; and pressure testing is required after assembly to verify sealing performance. In addition, the choice of materials is also crucial. Cylinder barrels and cylinder heads are usually made of high-strength alloy steel or stainless steel to withstand high pressure and corrosive media.
