Injection solidification

The soil-cement mixing wall (SMW) is an in situ technology for the fixation, stabilization, and solidification of soils contaminated with metals and semivolatile organic compounds. SMW can be used to treat soils contaminated with pesticides, polychlorinated biphenyls (PCBs), phenols, and poly aromatic hydrocarbons (PAHs) to depths of up to 100 ft. The technology uses hollow-stem augers to inject solidification/stabilization agents and blend them with the soil. 

Impco Trac Series of molds travel a closed path through stations or clamping, injection, solidification, and unloading. 

In most spinning processes, the fiber emerging from the spinneret is drawn down to a desired dimension before complete solidification. In some production lines, a laser beam is uti1i2ed to monitor the dimensions of emerging thread any alteration is recorded and if required, the dope deHvery rate, take-up rate, and internal-injection medium deHvery rate are adjusted automaticaUy. 

Dicyclopentadiene is also polymerized with tungsten-based catalysts. Because the polymerization reaction produces heavily cross-Unked resins, the polymers are manufactured in a reaction injection mol ding (RIM) process, in which all catalyst components and resin modifiers are slurried in two batches of the monomer. The first batch contains the catalyst (a mixture of WCl and WOCl, nonylphenol, acetylacetone, additives, and fillers the second batch contains the co-catalyst (a combination of an alkyl aluminum compound and a Lewis base such as ether), antioxidants, and elastomeric fillers (qv) for better moldabihty (50). Mixing two Uquids in a mold results in a rapid polymerization reaction. Its rate is controlled by the ratio between the co-catalyst and the Lewis base. Depending on the catalyst composition, solidification time of the reaction mixture can vary from two seconds to an hour. Similar catalyst systems are used for polymerization of norbomene and for norbomene copolymerization with ethyhdenenorbomene. 

Polymers are not as stiff as metals, so sections have to be thicker. The first rule of mould design is to aim for a uniform section throughout the component. During moulding, hot polymer is injected or pressed into the mould. Solidification proceeds from the outside in. 

An example of the effect on production rates is provided by injection moulding. The longer it takes after injection for solidification of the polymer to occur, the longer will be the overall cycle. (Provided the moulding is not distorted on ejection it will only be necessary to form a rigid skin to the moulding.)... 

Flare systems must be protected against any possibility of partial or complete blockage by ice, hydrates, solidification, etc. Seal Drums and Y-seals requiring winterizing should be provided with temperature-controlled steam injection to maintain the seal water temperature at 4 to 10 C. This limits the quantity of water vapor entering the flare stack. 

Fig. 4.46 One embodiment of SCORIM where the device (B) for producing shear during solidification, by the action of pistons (D) and (E), is placed between the injection moulding machine barrel (A) and the mould (C) (Courtesy of Brunei University)...

Shear controlled orientation in injection moulding (SCORIM) is based on the progressive application of macroscopic shears at the melt-solid interface during solidification in the moulding of a polymer matrix. 

However, in the non-isothermal case the pressure is also high at low injection rates. This is because slow injection gives time for significant solidification of the melt and this leads to high pressures. It is clear therefore that in the non-isothermal case there is an optimum injection rate to give minimum pressure. In Fig. 5.28 this is seen to be about 3.0 x 10 m /s for the situation considered here. This will of course change with melt temperature and mould temperature since these affect the freeze-off time, //, in the above equations. 

Between the injection nozzle on the end of the extruder and the gate that leads into the mold cavity the polymer flows through a channel known as a runner . It is vital that the polymer does not solidify in the runner before the mold is completely filled. We can prevent premature solidification in the runner in one of two ways we can use a large diameter unheated (cold) runner in which the polymer solidifies after the polymer in the mold cavity, or we can use a heated (hot) runner in which the polymer does not solidify. Moldings that are produced... 

The most suitable solvents for extracting SPA from fats are acetonitrile (113,125,126, 139,142) and water-alcohol mixtures. The fat is usually dissolved in hexane or petroleum ether, and SPA are extracted into acetonitrile (105,110-113,125,126,128). The disadvantages of acetonitrile extraction are that (a) BHT recovery is low and (b) moderately high levels of interfering compounds are coextracted. The advantage of aqueous methanolic extraction of SPA from nonpolar solvent is that the fat is mostly excluded (99,114). Hammond (99) described a methanolic extraction of a melted fat sample, heated to 40-50°C, followed by transfer of the mixture to a deep freeze for a few hours to aid the solidification of any excess fat from methanol. The methanol layer was then decanted and filtered prior to the addition of an internal standard and direct injection. 

Free injection of a reactant mixture to an open mold followed by polymerization and solidification (curing, crystallization, and so on) in thermostated sets is the most widely used method of manufacturing large-sized moldings, such as plates, slabs, and other items of a simple or complicated shape. 

In addition to high-speed photography, which was used to obtain the results discussed above, other methods have been used to visualize flow, for example, the tracer method.279"281 A typical experimental device consists of a capillary viscometer connected to a mold, which is a simple model of plunger-type injection molding unit.279 A special device was used to introduce tracers of different colors in regular succession. After sample solidification, it is possible to examine the position of the various colors on the surface (Fig. 4.47 a) or through the volume by cutting sections (Fig. 4.47 b). It can be seen that the tracers are positioned symmetrically near the surfaces and that they have a V-type shape, with the tip oriented toward the stream. 

The method of incomplete mold filling is effective for investigating injection molding of fiber glass-loaded polypropylene and polystyrene melts.283 After solidification, samples were prepared for microscopic investigation. The authors determined the distribution and orientation of the fibers in different sections of the article and thus were able to clarify the pattern of flow in different parts of the mold as a function of the process parameters. They concluded that the width of the (cavity)... 

In situ solidification/stabilization refers to the injection and mixing of binders into contaminated soils and sediments. Although the process can be effective, obstructions, deep contamination, shallow water tables,... 

Most real cases of polymer melting (and solidification) involve complex geometries and shapes, temperature-dependent properties, and a phase change. The rigorous treatment for such problems involve numerical solutions (12-15) using finite difference (FDM) or FEMs. Figure 5.9 presents calculated temperature profiles using the Crank-Nicolson FDM (16) for the solidification of a HDPE melt inside a flat-sheet injection-mold cavity. The HDPE melt that has filled the cavity is considered to be initially isothermal at 300°F, and the mold wall temperature is 100°F. 

Fig. 5.9 Dimensionless temperature in a thin injection mold during solidification of HDPE. [Reprinted by permission from C. Gutfinger, E. Broyer, and Z. Tadmor, Polym. Eng. Sci., 15, 515 (1975).]...

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