Closure thread design

Probably the largest compound vessels built were two triple-wall vessels, each having a bore diameter of 782 mm and a length of 3048 mm designed for a pressure of 207 MPa (30,000 psi). These vessels were used by Union Carbide Co. for isostatic compaction unfortunately the first failed at the root of the internal thread of the outer component which was required to withstand the end load (40). A disadvantage of compound shrinkage is that, unless the vessel is sealed under open-end conditions, the end load on the closures has to be resisted by one of the components, which means that the axial stress in that component is high. 

One aspect of pressure vessel design which has received considerable attention in recent years is the design of threaded closures where, due to the high stress concentration at the root of the first active thread, a fatigue crack may quickly initiate and propagate in the radial—circumferential plane. Stress intensity factors for this type of crack are difficult to compute (112,113), and more geometries need to be examined before the factors can be used with confidence. 

The development of finite element methods, since the late 1960s, has made possible the exploration of a wide range of variables relevant to the design of screwed plug closures. Work (126,128—132) on the stress at the toot of the first loaded thread, where most failures occur, and the load distribution along the thread length has led to the conclusions that the load carried by the first three threads decreases considerably as the number of active threads increases to 20, and the load carried by the second thread, is approximately 75% of the load on the first thread, f, and that on the third thread, fj, about 60% of f, that on the first thread, regardless of the number of threads. 

Bottle caps made from different plastics are extensively used. Some closures are of the simple cork snap type design, but most are of the screw type. Strong, accurate threads can be molded, which represent undercuts. Simple designs should be used when permitted, such as wide-pitch threads. The thread should be designed to start about 1 /32 in. (0.08 cm) from the end of the face perpendicular to the axis of the thread. It is usually practical to mold up to 32 threads per in. more than this number can give certain molders trouble. 

Small bottles, 187 mL, are closed with crown caps or roll-on aluminum caps. For special customers such as airlines, these closures are used also on 750-mL bottles. The roll-on or ROPP closure is the more popular of the two. These are aluminum cups, 30 mm in diameter and 22 mm high, with an inner elastomer plastic seal. After the caps are placed on the bottle, rotating dies roll the aluminum over the threads of the bottle. Bottles for these caps have a specially designed thread finish. 

The overall effectiveness of most containers relates to the design of the bottle neck and closure and the material from which the closure and container are made. Where a flexible material is used, a buttress thread (BS 5789, 1979) is recommended. However, if the material is substantially harder, e.g. HDPE, PP, or PVC, a conventional type 60° thread (BS 1918, R3/2 and R4 finishes for glass) can be employed. 

Much information is available on the deformation and fatigue behavior of simple thick-walled cylinders [10-17], but it must be remembered that most process reactors will not be a simple hollow cylinder. Components such as connectors, threads and sleeves, windows, and removable closures make a complete analytical solution for a high-pressure system design problem quite involved. Useful design criteria for thick-walled vessels can be derived, however, under the assumption that the material of which the vessel is made is isotropic and that the cylinder is long (more than five diameters) and initially free from stress. The radial and tangential stresses in the walls are then only functions of the radius coordinate (r) and the internal pressure. Given the outer-to-inner wall radius ratio as o/i = w, and the yield point (To) of the material, the yield pressure (py) is... 

While the PDIs of the REMP macrocycles are higher than those typically reported for the ring-closure approach, the molecular weights obtained are by far the highest reported to date for a cyclic polymer synthesis. The catalyst design optimization has yielded improved polymerization catalysts, and promises to broaden the versatility of this route. For example, by using a dendronized monomer, Grubbs and coworkers have demonstrated the synthesis of dendronized cycHc polymers and confirmed their cyclic structure with AFM [59], and have also synthesized cycHc polymers with threaded rotaxanes [60]. 

From a design standpoint, the total hydrostatic end force, H, is taken by the threads in a threaded closure, or by the studs in other designs. Various types of gaskets can be used with either design but all are the self-sealing type such as Bridgman, delta or double cone. 

Crum ASD. The distribution of load over threads of a threaded closure, including temperature effects and local imperfections. High Pressure Technology, Material Design Stress Analysis and Applications, ASME PVP-Vol. 148 1988. 

Chaaban A, Muzzo U. On the design of threaded-end closures for high pressure vessels. High Pressure -Codes, Analysis and Applications, PVP-Vol. 263, ASME 1993. 

Apparel accessories are inspected in the same manner as other textile and apparel products. Accessories are checked during preproduction, production, and postproduction with a final inspection. Various fashion accessories include closures, interlinings, sewing threads, elastic waistband, and other design elements. These accessories should be able to withstand the care and maintenance procedures devised for the clothing (Nayak and Padhye, 2014). The selection criteria for various accessories are described in Chapter 6. A brief inspection procedure for the accessories is described in the following section. 

Stress relaxation behavior of the polymers has been overlooked by many design engineers and researchers, partly because the creep data are much easier to obtain and is readily available. However, many practical applications dictate the use of stress relaxation data. For example, extremely low stress relaxation is desired in the case of a threaded bottle closure, which may be under constant strain for a long period. If the plastic material used in the closures shows an excessive decrease in stress under this constant deformation, the closures will eventually fail. Similar problems can be encountered with metal inserts in molded plastics and belleville or multiple cantilever springs use in cameras, appliances, and business machines. 

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