Nominal design rules

The elimination of sharp inside radii is important to the design of ribs as well. For free-standing ribs, that raises a paradox in that it becomes difficult to provide generous radii at the base of the rib and still maintain the nominal wall rule of not increasing the wall thickness by more than 25%. The effect of changing the inside radii from 0.25W to 0.5W is demonstrated in Fig. 8.14. The 25% increase in wall thickness is represented by the circle which is 1.25W. In Fig. 8.14a, the radii at the base of the rib are 0.25W, and they are 0.5W in Fig. 8.146. Note how much thicker the rib is in Fig. 8.14a (Ti) than it is in Fig. 8.146 ( 2). There is a danger that the tip of the rib will become too thin when draft is taken into consideration 0.040 in should be regarded as a... 

Ribs (B) and metal inserts (E, H) are not recommended for preforms, but they can be used with the other versions. The minimum inside radius (IR) is 0.125 in for preform-molded parts and 0.062 in for SMC-and BMC-molded parts. Long-fiber compression-molded parts can be trimmed in the mold. For Class A finishes in SMC parts, the inside radius at the base of a rib should be 0.020 in otherwise it should not be less than 0.060 in. The thickness at the base of the rib (B) can be equal to the nominal wall thickness (W), however, it must not exceed 0.75W under Class A surfaces. The height of the rib (C) should be 2 to 3 times the nominal wall thickness (W) and the draft should not be less than 1° per side except for ribs imder Class A surfaces (which can handle the cost premium) where it can go down to 0.5° per side. These same rib design rules apply to boss wall thicknesses for these parts. In-mold coating can be used for high-class finishes. 

The splice plates should he made half as thick as the skins, for maximum theoretical efficiency, to make each end of the bonded overlap equally efficient. However, early tests of such joints showed a propensity for fatigue failures in the spKce plate, where the skins butted together, rather than in the skins, which had a nominally equal stress. Consequently, the splice plates were made one gauge thicker. The overlaps in this table can be approximated by a simple design rule, that the overlap be 30 times the thickness of the central adherend (skin). If there is a substantial stiffness imbalance between the adherends, the load transfer through the bond will be intensified at one end, with respect to the other, resulting in decreased shear strengths. 

Components without Specific Ratings Components such as pipe and butt-welding fittings are generally furnished in nominal thicknesses. Fittings are rated for the same allowable pressures as pipe of the same nominal thickness and, along with pipe, are rated by the rules for pressure design and other provisions of the code. 

The studies indicated that a flow reduction to 60% of the nominal flow for the Mark II SA in the core periphery could be detected with CCPM at 80 mm position, whereas a flow reduction to 45% is required to cross the clad hot spot temperature. The design provisions such as radial entry of sodium flow into the SA and high purity of sodium maintained, rules out blockage of flow through SA of the order mentioned above. 

It should be noted that die smallest size packings in the Bolles-Fair correlation are nominally 12 mm (O.S in.) in diameter. If the general rule of 8 1 ctdunui packing diameter is to be maintained, then a minimum column size of 100 mm (4 in.) is indicated. This is a crucial point in the design of pilot facilities and the development of scaleup parameters. It is not yet possible to go to the tmy pacUngs for laboratory tests (using, say, column diameters of 25-50 mm) and s obtain reliable scaleup data. 

If the requirement of the application is such that dimension B must be maintained, the design can be improved as shown in Fig. 8.336. Here, the large center block of material has been cored out to alleviate the sink condition by creating a wall variation that does not exceed 25% of the nominal wall (D < 1.25A). This rule has been used both to create the... 

The diameter D) of a round gas channel should not exceed 1 in (Z) < 1 in). Gas channels in wall sections are determined experimentally and are very much a function of the wall thickness. The height H) of the gas channel should not exceed 3 to 4 times the nominal wall T) of the part (if s 3 to AT). The width (W) should not exceed 2.5 to 3 times the nominal wall (T) (W < 2.5 to 3T). The basic rules regarding uniform wall and inside radii outlined in Sec. 8.2 apply to gas-assisted injection molded parts, except for the gas channels. However, careftil consideration must be given to gate location, gas nozzle location, and channel path location to assure proper application of the principle. The prospective molder should be consulted during the design phase to get it right. 

With wall thicknesses in the range of 0.040 to 0.060 in, it is clearly impossible to adhere to all the ftindamental rules of proper injection-molded part design (rib thicknesses will be greater than 70% of the nominal wall). This means that surface finish problems will result and texture is required to mask these flaws. In any case, wall thickness variations should not exceed 25%, inside radii should not be permitted to go below 0.020 in, and design details that restrict flow should be avoided. Furthermore, the thinner parts are less rigid at the time of ejection from the mold. Thus, much larger ejector pins must be used than would be used for normal injection molding and there would be more of them. 

As the result of an extensive study for the PVRC, it was determined that within the restrictive limits and rules that follow, a nozzle can be designed that does not have 100% replacement of an area but has the nominal stress essentially maintained. 

A tall vessel constructed with a cylindrical shell and flat closure ends is to be installed near Etenver, Colorado. The inside diameter of the cylindrical shell is 8 ft, the nominal wall thickness is 1.0 in., and the straight length from head weld seam to head weld seam is 125 ft. The flat heads are 6.0-in. nominal thickness. What is the total lateral wind force used for design of the vessel following the rules of the ANSI A58.1 Code ... 

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