PTFE gasket and flange sealing surface need to cooperate with each other to successfully seal
PTFE gasket and flange sealing surface need to cooperate with each other in order to be able to successfully seal, the most can not be ignored is to control the flaws with the mating flange surface, whether it is "big nick", "abrasion "Or" groove "and other surface defects are to be avoided, because PTFE gasket is difficult to seal or fill these defects. Flange surface finish can be "lines, roughness, waveform," and other concepts to describe.
Lines are the dominant direction of the rough surface of the flange, such as: multi-directional, record spiral, serrated and other surface finish lines should be consistent with the gasket centerline, such as circular flanges, surface lines should be Processed in a concentric or disc spiral form so that there is no line passing through the surface of the flange. If there is a straight polish line through the sealing surface, this will be a direct leak path.
Roughness is calculated from the center of the flange surface, the average projection and depression, with one thousandth inch (or meter) to represent. For serrated flange surfaces, the typical roughness is 125-500 microinches, while for non-serrated flange surfaces, the roughness is 125-250 microinches. Too rough flange, gaskets often can not be sealed, only try to use a softer gasket, and on the other hand, a high finish flange surface, such as the polished surface, it is difficult to seal, you must This is avoided because the sealing surface needs sufficient "bite marks" to provide sufficient friction to prevent the PTFE gasket from being blown or squeezed out, or excessive creep.
Waveform is the deviation from the overall flatness. Under normal conditions, there is no need to consider the problem of waveform. However, there are two cases that require special attention because excessive waveform is a very difficult problem to handle.
The first case is glass-lined equipment, in which the natural flow of molten glass creates a large degree of wave shape and the glass-lined flange is easily deformed at higher bolt torques. The solution is to use thicker, highly compressible gaskets.
The second case involves a warped flange. If this warpage is due to thermal deformation or internal stresses, the flange can be reworked if it is due to excessive bolt load or insufficient flange thickness The resulting warp, which we generally refer to as "bow deformation," is that the solution is to redesign the flange with greater rigidity, and sometimes reinforcements can be added to reinforce the structure without replacing the flange, and the other is to add more Of the bolts, you can also change the small but large bolt program more and smaller programs, thereby increasing the flexibility of the bolts, so that the joint better combination.