Differences between elliptical end caps with different straight edges
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Differences between elliptical end caps with different straight edges: First, according to the regulations, the straight edge height of elliptical end caps below DN2000 is generally 25 mm, while it is 40 mm for those above DN2000. However, there are also end caps below DN2000 with a straight edge height of 40 mm. The question is: why not use straight edges of 40 mm in all cases? Second, for end caps below DN2000, what are the differences in terms of manufacturing when the straight edge height is 25 mm versus 40 mm? Third, in terms of usage, what are the differences between end caps with a straight edge height of 25 mm and 40 mm for those below DN2000? Thank you!
The cutting dimensions are different, that’s all. There’s no difference; for those with a diameter of 2000 or less, the straight edge height is set at 40 because the old standards specified this value. I think these drawings are based on the previous designs, following those old standards. Now, JB/T4746－2002 has standardized this requirement; to facilitate manufacturing and reduce the need for molds, it specifies that for diameters of 2000 or less, the height of the straight edges should be 25 mm, with the 40 mm specification being eliminated. For diameters greater than 2000, the height of the straight edges is set at 40 mm.
For oval end caps, different heights of the straight edges result in different stress levels, in addition to differences in the cutting dimensions； Meanwhile, when welding the head to the A-flange, in order for the weld to meet the requirements of GB150, the height of the straight edge of the head is often set at 40 mm
The new standard JB/T4746－2002 specifies that for heads with a diameter of DN2000 or less, the straight edge length is now 25 instead of 40; only heads with a diameter larger than DN2000 still use a straight edge length of 40.
The purpose of straight edges is to prevent the stress in the weld area from overlapping with the secondary stresses at the boundaries. 25 and 40 are the standard values; larger values can also be used depending on the order
With such a short straight edge height, wouldn’t it cause problems when preparing welding grooves for thicker equipment?
Agree with what was said on the second floor. According to JB/T4746－2002, the fold thickness is uniformly set at 25 for diameters of DN2000 and below, and at 40 for diameters above DN2000. The problem you're facing is one that arises from the transition between the old and the new. There is not much difference in the height of the two types of folds in terms of usage. It is to reduce the number of molds and facilitate production.
The original standards for end caps determined the height of the straight edges based on the specifications and thickness of the end caps, with these heights being set at values such as 25 mm, 40 mm, and 50 mm. This made it difficult to choose suitable options for end cap design, and an increase in the height of the straight edges tended to cause longitudinal wrinkles. So the 50mm setting was removed. The height of the straight edges also affects the total height and volume of the head. The height of the straight edges in terms of its rationality. It shall be determined by the drawing. The height of the straight edges in the standard is also recommended, serving as a reference for designers when making choices.