Preform Design Process

To get even wall thickness throughout the container, just like for extrusion blow molded containers, the preform must be programmed to put additional polymer where the most stretch will occur. Since the core and the cavity of the injection mold are fairly permanent, one cannot make changes on the fly as one can in extrusion biow molding. Therefore, the designing must be done upfront. 

The most efficient method is to have the supplier use finite element analysis (FEA) to do a simulation. One can use trial and error approaches, but since the process involves cutting metal on a mold, it is faster and less expensive to use a computer simulation. The FEA program chosen must be capable of nonlinear calculations in order to properly model the nonlinear material properties. 

Contour plots of the wall thickness distribution for the injection blow molding simulations. 

The author (Culter) then made bottles from the preform design and checked the resulting wall thickness distribution, which is shown in Fig. 12.12. The two plots are for a bottle corner (upper) and for the middle of the concave side panel (lower). Reasonably close agreement was found between the model and actual practice. 

Comparison of simulation results with measured data at the comers. 

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The advance in computer aided engineering (CAE) using hnite element analysis (FEA) methods makes virtual design and development of containers possible. Stress level under top load, internal pressure, or vacuum can be evaluated. Additionally, the blowing process can be simulated, and material distribution and wall thickness throughout the container can be estimated [21,22]. The blow simulation is also used to evaluate and optimize the preform design. 

Preforming - The process of producing a preform which consists of filling a mold with the polymer powder, compaction of the resin by pressing it down in a press and finally removal of the preform from the mold. The mold is usually operated at the room temperature and is designed to allow easy escape of the air during the resin compaction. Also see Preform. 

Carbon—carbon composites for rocket nozzles or exit cones are usually made by weaving a 3D preform composed of radial, axial, and circumferential carbon or graphite fibers to near net shape, followed by densification to high densities. Because of the high relative volume cost of the process, looms have been designed for semiautomatic fabrication of parts, taking advantage of selective reinforcement placement for optimum thermal performance. 

Textile technology is used to mechanically or aerodynamicaHy arrange textile fibers into preferentially oriented webs. Fabrics produced by these systems are referred to as dry-laid nonwovens. Dry-laid nonwovens are manufactured with machinery associated with staple fiber processing, such as cards and gametts, which are designed to manipulate preformed fibers in the dry state. Also included in this category are nonwovens made from filaments in the form of tow, and fabrics composed of staple fibers and stitching filaments or yams, ie, stitchbonded nonwovens. 

In the reinforced RIM (RRIM) process a dry reinforcement preform is placed in a closed mold. Next a reactive plastic system is mixed under high pressure in a specially designed mixing head. Upon mixing, the reacting liquid flows at low pressure through a runner system to fill the mold cavity, impregnating the reinforcement in the process. Once the mold cavity is filled, the plastic quickly completes its reaction. The complete cycle time required to produce a molded thick product can be as little as one minute. 

The combination of the two approaches that have obvious advantages therefore presents an attractive reaction design with added value in the inventions and optimizations of existing processes. We hereby give an overview of current achievements in this field. However, there is a rather limited number of published data on strictly defined multicomponent reactions in which aU the reactants are added at once to the reaction mixture, due to the technical characteristics of the systems (e.g. number of inlets) or the possible complications due to side reactions such reactions are conducted in a multistep mode or employ preformed intermediates. These reactions are also taken into account on the condition that the process is conducted continuously without purification of the intermediates and that the final product contains scaffolds originating from three or more starting molecules. 

Liquid-phase infiltration of preforms has emerged as an extremely useful method for the processing of composite materials. This process involves the use of low-viscosity liquids such as sols, metal- or polymer-melts. Using this infiltration process, it is possible to design new materials with unique microstructures (e.g. graded, multiphase, microporous) and unique thermomechanical properties (graded functions, designed residual strains and thermal shock). 

The largest volume of fluoroelastomers (about 60% of total) is processed by compression molding. A blank (preform) is placed into a preheated mold, compressed, and cured at the appropriate temperature (see above) for a time established empirically. A good estimate for the curing time in the mold is the value of Co from the measurements by oscillating disk rheometer. In the mold design, it is necessary... 

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