Types of ellipsoidal heads-HHA, EHA, EHB, THA, THB, SDH
The customer order description is EHA DN400x8 ellipsoidal heads GB/T25198-2010 Grade:Q345R.It is clear that the standard for the ellipsoidal head is GB/T25198-2010,and the customer needs the EHA type ellipsoidal heads.
So below i will introduce the types of ellipsoidal head in the GB/T25198-2010 standard.It is mainly divided into following types:
1. Hemispherical head (HHA);
2. Elliptical head,elliptical head including ① (EHA) based on internal reference,② (EHB) based on outside the standard;
3. Ellipsoid shaped head,including ①(THA) based on internal standards,② (THB) based on outside the standard;
4. Spherical crown head (SDH).
According to the description of customer provide with the corresponding drawing,it is not difficult to see that the size of DN400x8corresponds to D1 and h,then H can be calculated according to the formula,H = D1/4 + h. In the figure,σ is not a fixed value,in the standard of GB/T25198-2010,there is a special description of the σ value.The value of σ is related to the tolerance of the outer circumference and inner diameter of the ellipse head.
For example,the nominal diameter DN is between 300-600,when 2≤σ≤4,the outer circumference tolerance is -4~+4,the inner diameter tolerance is -1.5~+1.5;when 4≤σ≤6,the corresponding tolerance are -6 ~+6 and -2~+2;when 6≤σ≤16,the corresponding tolerance are -9~+9 and -3~+3;when 16≤σ≤22,the corresponding tolerance are -12~+12 and -4~+4.
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