Heads and closures

The ends of a cylindrical vessel are closed by heads of various shapes. The principal types used are  

Hemispherical, ellipsoidal and torispherical heads are collectively referred to as domed heads. They are formed by pressing or spinning large diameters are fabricated from formed sections. Torispherical heads are often referred to as dished ends. 

The preferred proportions of domed heads are given in the standards and codes. 

Standard torispherical heads (dished ends) are the most commonly used end closure for vessels up to operating pressures of 15 bar. They can be used for higher pressures, but above 10 bar their cost should be compared with that of an equivalent ellipsoidal head. Above 15 bar an ellipsoidal head will usually prove to be the most economical closure to use. 

A hemispherical head is the strongest shape capable of resisting about twice the pressure of a torispherical head of the same thickness. The cost of forming a hemispherical head will, however, be higher than that for a shallow torispherical head. Hemispherical heads are used for high pressures. 

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The objective in packaging cool sterilized products is to maintain the product under aseptic conditions, to sterilize the container and its Hd, and to place the product into the container and seal it without contamination. Contamination of the head space between the product and closure is avoided by the use of superheated steam, maintaining a high internal pressure, spraying the container surface with a bactericide such as chlorine, irradiation with a bactericidal lamp, or filling the space with an inert sterile gas such as nitrogen. 

Unstayed flat heads and covers can be designed by very specific rules and formulas given in this subsection. The stresses caused by pressure on these members are bending stresses, and the formulas include an allowance for additional edge moments induced when the head, cover, or blind flange is attached By bolts. Rules are provided for quick-opening closures because of the risk of incomplete attachment or opening while the vessel is pressurized. Rules for braced and stayed surfaces are also provided. 

There are a variety of igniter designs which are currently employed in solid-propellant rockets. These types include rocket-exhaust (pyrogen), pyrotechnic, and hypergolic igniters, each of which can be located in the head-end closure of the motor or in the exhaust nozzle at the aft-end of the motor. The heat-transfer information appropriate to each of these possible combinations is discussed in the following sections. 

There are two junctions in a torispherical end closure that between the cylindrical section and the head, and that at the junction of the crown and the knuckle radii. The bending and shear stresses caused by the differential dilation that will occur at these points must be taken into account in the design of the heads. One approach taken is to use the basic equation for a hemisphere and to introduce a stress concentration, or shape, factor to allow for the increased stress due to the discontinuity. The stress concentration factor is a function of the knuckle and crown radii. 

The filling mandrels are comprised of a set of filling tips that are held within a protective air shower this is a small area within the filling machine that is typically fed with sterile filtered air. When the molds are beneath the air shower, the filling tips are lowered into the neck of the partially formed container and the containers are filled. The mandrels then return to the protective air shower, and the containers are sealed by a second mold set (head mold), which forms the neck and closure of the BFS containers. 

The closures of BFS containers are formed within the automated process by the head mold set which closes around the top of the severed section of parison following filling. The integrity of the container and closure is generally tested by a manual or automated method of leak detection performed outside of the filling environment following removal of excess plastic (deflashing) from the filled product units. 

Closures between heads and cylinders, often taking the form of clamps, split rings, or bolts, are also an important consideration in the proper design of the pressure vessel, for it is these components that must hold the vessel head to the cylinder. It is important to recognize the force that is exerted on the closure. For example, in a 1000 psi vessel, a circular head with a diameter of 12 in. will have over 110,0001b of force pushing on it. This force must be evenly divided between bolts or spread out over the clamp or split ring closure. 

Since pails are small enough to be handled manually, steel handles are often attached for this purpose. It is also common to reduce the diameter of the bottom or top chime to facilitate stacking. These containers are widely used in the pharmaceutical industry for the in-house handling of tablets. Tight-headed pails with one closure only are often fitted with specially shaped tops which have a raised portion instead of a recess above the double seam. This is known as an interrupted chime, and its purpose is to allow the pails to be stored in the open without the risk of water accumulating in the head and penetrating the closure by capillary action. 

Container/closure seal integrity has been reviewed by the Parenteral Drug Association (1983) and the Parenteral Society (1992). Variation in the overall height of the combined vial and closure will result in different closure-seal forces being applied at the crimping head. Quality control tests are proposed such as the dye intrusion challenge, liquid loss or bacterial... 

The product of an electrocyclic reaction results from the formation of a new a bond. For this bond to form, the p orbitals at the ends of the conjugated system must rotate so they overlap head-to-head (and rehybridize to sp ). Rotation can occur in two ways. If both orbitals rotate in the same direction (both clockwise or both counterclockwise), ring closure is conrotatory. 

In addition to the hemispherical and ellipsoidal heads, the torispherical head has been used extensively for closures on a large variety of cylindrical vessels. It is shaped, not as an ellipsoid, but by the use of two radii. The crown radius is the radius of dish for the spherical crown which constitutes the major portion of the head, and the knuckle radius, sometimes referred to as the comer radius, is the radius joining the spherical crown to the cylindrical shell. Heads of this type require less forming than ellipsoidal dished heads, so forming costs are lower. 

Pilocarpine is marketed as tablets (Salogen), an ophthalmic solution, and gel. It penetrates the eye well and is the miotic of choice for open-angle glaucoma and to terminate acute angle closure attacks. It also is used for the treatment of xerostomia (dryness of the mouth) caused by radiatioh therapy of the head and neck, Sjogren s syndrome, or as a side effect of some psychotropic drugs. 

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