Arched bottom
The various bases that are used as the closing element of mostly cylindrical (tubular) pressure vessels or other process-related containers can be summarized as the curved base . Due to the flattened "hemispherical shape" they take up less space than the hemispherical shape, which is ideal for pressurization, with an only slightly thicker wall. A floor is made up of the middle spherical calotte (r 1 ), the outer rims (r 2 ) and the subsequent short cylindrical part as a board is referred to (h). The terms dished bottom and basket arch bottom with the associated radius ratios are standardized (see below).
The calculation bases for calculating the wall thickness of curved floors when exposed to internal pressure are available in Europe in the relevant regulations for the manufacture of pressure vessels according to the Pressure Equipment Directive 97/23 / EC (AD 2000-Merkblatt B3 as well as in the harmonized standard EN 13445-3). For other countries and regions, different regulations such as ASME U (in the USA) or the ML license (in China) apply . The greatest stresses (tensions) due to the internal pressure are in the area of the brim. For this reason, notches and other deformations should be avoided in this area.
The connection of the curved bottom with the cylindrical part of the container (shot) is usually made by a circumferential butt weld seam .
Dished bottom
With dished bottom according to DIN 28011 r 1 = D a and r 2 = 0.1 * D a , with dished bottom according to ASME F&D r 1 = D a and r 2 = 0.06 * D a ( F&D is an abbreviation for flanged and dished . In English this form is often referred to as torispherical head )
The shape was devised by Georg Kloppsch (1874–1951). Due to this shape, which is modeled on the egg, the containers are relatively pressure-resistant in relation to the ideal shape of the hemisphere.
The dished bottom is a little flatter than the common wicker arch bottom .
Dished bottom made of stainless steel: AD2000 W2-HP7 / 3 + 8/1
Dished bottom made of carbon steel: AD2000 W1 HP7 / 2 + 8/1
Basket arch bottom
For the arched bottom according to DIN 28013 , r 1 = 0.8 * D a and r 2 = 0.154 * D a .
The arched bottom (English (deep dished) torispherical head or also according to DIN 28013 ellipsoidal head or basket arch ) is slightly more arched than the dished bottom most commonly used in Germany. The basket arch floor comes very close to the shape of the 2: 1 elliptically shaped arched floor that is common in America.
Manufacturing
The production of such a floor is easier than that of a hemisphere. The production can take place both in the cold pressing process and in the hot pressing process; as a rule, however, by pressing the base onto the first radius (r 1 ) and then flanging the edge and thus also the second radius (r 2 ). Dished bottoms are also welded together from individual segments.