Difference between hydraulic expansion and bladder expansion for heat exchangers

The expansion principle of tube expansion varies, which leads to significant differences in the expansion methods and the resulting expansion outcomes

This post was last edited by gn_1984 on 2017-7-17 at 15:58. I. Hydraulic tube expansion process (flexible expansion) The hydraulic tube expansion process, also known as soft expansion, allows for the expansion of a large number of pipe fittings at once. Hydraulic expansion is a new type of expansion joining technique; it involves applying high hydraulic pressure to the inner surface of the tube, causing the tube to plastically deform and thus expand into the inner surface of the plate hole. The expansion head used in hydraulic expansion joining is a mandrel with a diameter slightly smaller than that of the pipe’s inner diameter. Multiple seals are present on the outer circular surfaces at both ends of the mandrel, and an oil inlet hole is located in the middle of the mandrel. High pressure is applied to the section of pipe between the two seals, causing the pipe to deform plastically and thus enabling expansion joining. The structure of the hydraulic tube expander is shown in Figure 3. II. Technical features of the liquid-bag type hydraulic tube expansion technique: 1. Over-expansion is unlikely to occur; 2. The quality of the expansion process is uniform and reliable; 3. It is possible to perform expansion on heat exchangers with any tube sheet thickness; 4. The residual stress in the tubes after expansion is low; 5. The expansion medium does not contaminate the joints; 6. It requires less labor effort and results in higher production efficiency; 7. Lower precision requirements are needed for the dimensions of the heat exchange tubes; 8. Mechanical damage to the heat exchange tubes is minimal, and no axial elongation occurs. The biggest difference between this technology and the \"O\"-ring expansion joining technique is that the liquid-bag hydraulic expansion joining method does not require high precision in terms of the dimensions of the heat exchange tubes; moreover, the expansion process does not cause any contamination to the inner surface of these tubes. It represents a new type of expansion joining technique that suits China’s national conditions. Working principle of the liquid bag type hydraulic tube expansion machine: The liquid bag type hydraulic tube expansion technique makes use of the principle of pressure increase to generate an ultra-high pressure sufficient to cause plastic deformation in the heat exchange tubes. This pressure is applied to the inner wall of the heat exchange tubes through an elastic liquid bag, resulting in plastic deformation of those tubes; this deformation allows them to fit tightly around the tube sheet holes and thus be expanded and fixed in place within them. Using a liquid bag to seal the expansion medium prevents the expansion medium from contaminating the joint during the expansion process, which helps to avoid welding defects. Due to the large variations in the inner diameter of domestically produced heat exchange tubes, the outer diameter of the expansion joints can be adjusted on-site by grinding, based on the diameter of the tubes. The expansion joining process is extremely simple: after the tube and the tube sheet are assembled, the expansion head is inserted into the tube hole, and the expansion button is pressed; the expansion jointing machine then automatically carries out the processes of applying pressure, maintaining that pressure, and releasing it, all in accordance with the set expansion pressure. Since this expansion joining process does not contaminate the joint, it is generally possible to weld directly after expansion without cleaning the pipe ends. In summary: the liquid-bag type expansion tube tool is a type of hydraulic expansion tube tool and belongs to the category of flexible expansion tube machines.

Hydraulic expansion joining is a type of flexible expansion joining; it uses water or other liquids as a driving force, and the high pressure causes the liquid bag to expand, thereby increasing the fit between the heat exchange tube and the tube sheet. Mechanical expansion involves using a mechanical expander roller to compress the heat exchange tube, thereby bringing it into close contact with the tube sheet. Many people say that hydraulic expansion yields better results after expansion compared to mechanical expansion, but this is not the case. In my opinion, mechanical expansion is more stable and more efficient than hydraulic expansion. Hydraulic expansion is more suitable for applications where the expansion length is relatively long; for expansion lengths of less than 100, mechanical expansion is the better choice. Hydraulic expansion joining technology in China is not yet that stable