Flange sealing surface and gasket matching solution
2019.04.22
In order for the gasket to be able to seal successfully, the degree of defects on the surface of the flange mating with the gasket must be well controlled. Surface defects such as large nicks, grooves, or scratches must be avoided, because the gasket is difficult to To seal or fill in these deficiencies. The finish of the flange surface can be described by concepts such as "roughness, texture, waviness".
1. Roughness
Roughness is the average value of protrusions and depressions calculated from the center of the flange surface, expressed in ten thousandths of an inch (or meter). Typical roughnesses are 125-500 micro inches for serrated flange surfaces and 125-250 micro inches for non-serrated flange surfaces. If the flange is too rough, the gasket is often unable to be sealed, and only softer gaskets can be used as far as possible. Avoid, as the sealing surface needs sufficient "bite" to provide sufficient friction to prevent the gasket from being blown out or squeezed out, or excessive creep.
2. Texture
The grain is the dominant direction of the roughness of the flange surface, for example: multi-directional, record spiral, serrated, etc. The grain of the surface finish should be as consistent as possible with the centerline of the gasket, such as a circular flange, the surface grain should be Machined as concentric circles or record spirals, this avoids having a line through the flange surface, which would be a direct leak path if there was a straight lapping line through the sealing surface.
3. Waveformity
The waviness is the deviation relative to the entire flatness. Under normal conditions, the waviness does not need to be considered, but there are two situations that require special attention, because excessive waviness is also a very difficult problem to deal with.
The first case is glass-lined equipment, in which the natural flow of molten glass will form a large wave degree, and under high bolt torque, the glass-lined flange is also easily deformed. The solution is to use thicker, highly compressible gaskets.
The second case involves warped flanges. If the warping is due to thermal deformation or internal stress, then reprocessing the flange is fine. If it is due to excessive bolt loading or insufficient flange thickness The resulting warpage is generally referred to as "bow deformation". The solution is to redesign the flange with greater stiffness. Sometimes stiffeners can be added to strengthen the structure without replacing the flange. Another solution is to add more It is also possible to change the few and big bolts to many and small ones, thereby increasing the elasticity of the bolts and making the joints better combined.
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