Wall thickness considerations

Another limitation on wall thickness consideration for thermoplastic is the effect that it has on molding blemishes called sink marks where the surface of the plastics part develops a dished-in area that looks like a finger depression. Thick sections, particularly thick sections of varying thickness, are most likely to cause sink marks on the part. It is true that the molding conditions determine the extent of the... 

But there are many practical applications where no known wall thickness change can be obtained from the radiographic film under consideration because at the exposure it was not... 

Table 2. Minimum wall thicknesses to be measured by different transducer frequencies. Guidance of the tube (geometrical considerations)...

Economic and process considerations usually dictate that agitated thin-film evaporators be operated in single-effect mode. Veiy high temperature differences can then be used many are heated with Dowtherm or other high-temperature media. This permits achieving reasonable capacities in spite of the relatively low heat-transfer coefficients and the small surface that can be provided in a single tube [to about 20 m" (200 ft")]. The structural need for wall thicknesses of 6 to 13 mm (V4 to V2. in) is a major reason for the relatively low heat-transfer coefficients when evaporating water-like materials. 

Frequently wall thicknesses are increased to meet the planned service life, resulting in a considerable increase in the materials used. This not only raises installation and transport costs but also the weight, which makes construction more difficult. 

Earliest type, usually cheaper per unit cost, but sometimes less efficient than others. Available in widest variety of materials to fit service. Very sound structurally. Usually packed by dumping wet or dry, with larger 4-6-inch sizes sometimes hand stacked. Wall thickness varies between manufacturers, also some dimensions available surface changes with wall thickness. Produce considerable side thrust on tower. Usually has more Internal liquid channeling, and directs more liquid to walls of tower. Low efficiency. 

In some cases Negative Forming would not be suitable because, for example, the shape formed in Fig. 4.51 would have a wall thickness in the comers which is considerably less than that close to the clamp. If this was not acceptable then... 

The material, inside diameter (ID) and wall thickness are the three primary considerations in the selection of lines for a particular fluid power system. The ID of the line is important because it determines how much fluid can pass through the line without loss of power due to excessive friction and heat. The velocity of a given flow is less through a large opening than through a small opening. If the ID of the line is too small for flow, excessive turbulence and friction will cause unnecessary power loss and overheat the hydraulic fluid. 

Molded-in insert If metal inserts are to be molded into a plastic product consideration should be given to wall thickness around the insert (Table 3-18) and their shape. The shape should present no sharp edges to the plastic, since the effect of the edges would be similar to that of a notch. A knurled insert... 

The operating pressures and shear rates in the extrusion process are considerably lower than they are in molding. As it exits the die, but not necessarily when it leaves the process, the material is in an essentially stress-free condition. Depending on the wall thickness of the material and the particular material, there is orientation of the plastic to a greater or lesser controllable degree. Thin walls produce higher orientation in materials such as PP, that is a highly crystalline polyolefin, and which orients much more than materials such as PVC. 

Design Considerations for Injection Molded Parts (Parting lines, draft angles, wall thickness, fillets and radii, bosses, ribs, opening formations, shrinkage, gating, vents, potential knit lines)... 

SPAN module. It was mentioned at the beginning that the special polyacrylonitrile fibers of SPAN have a wall thickness of 30 gm, which is considerably thicker than the 8 gm wall thickness of the SMC modules [19]. As a consequence, the presence of stronger capillary effects from the special porous fiber material of the SPAN module would be a reasonable conclusion. Furthermore, the texture of the special polyacrylonitrile fibers is expected to have better surface properties, supporting the permeation of molecules as compared with synthetically modified cellulose. In conclusion, both convection and diffusion effectively contribute to the filtration efficiency in a SPAN module, whereas for the SMC membrane, diffusion is the driving force for molecular exchange, the efficiency of which is also considerable and benefits from the large surface-to-volume ratio. 

The pipe wall thickness is selected to resist the internal pressure, with an allowance for corrosion. Processes pipes can normally be considered as thin cylinders only high-pressure pipes, such as high-pressure steam lines, are likely to be classified as thick cylinders and must be given special consideration (see Chapter 13). 

Mesostructured materials with adjustable porous networks have shown a considerable potential in heterogeneous catalysis, separation processes and novel applications in optics and electronics [1], The pore diameter (typically from 2 to 30 nm), the wall thickness and the network topology (2D hexagonal or 3D cubic symmetry) are the major parameters that will dictate the range of possible applications. Therefore, detailed information about the formation mechanism of these mesostructured phases is required to achieve a fine-tuning of the structural characteristics of the final porous samples. 

To help ensure resistance to impact and internal pressure increases, plastic tank wall thickness is greater than steel tank thickness. Plastic tanks are typically >4 mm in thickness, whereas steel tanks are somewhat less than 1 mm in thickness. Plastic tanks, however, are considerably lighter in weight. 

The most important factor determining the mechanical properties of a syntactic foam is the distribution of its microspheres with respect to size, shape, and strength, the best properties being attained if these distributions are homogeneous19). Micro-spheres with the same shape and size can be obtained by sieving or flotation. Their mechanical strengths still differ considerably, even after sorting, due to wall thickness... 

With these criteria in mind, various reactors have been designed to satisfy the needs of the hydroprocesses, including hydrodesulfurization (McEvoy, 1996). Thus, reactors may vary from as little as 4 ft. in diameter to as much as 20 ft. in diameter and have a wall thickness anywhere from 4.5 to 10 in. or so. These vessels may weigh from 150 tons to as much as 1000 tons. Obviously, before selecting a suitable reactor, shipping and handling requirements (in addition to the more conventional process economics) must be given serious consideration. 

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