Flash formation

Explain how each of the following machine control parameters can affect flash formation in injection molding ... 

Another difference between the processes is the flash formation and its removal. As it is reinforced with fibers, it becomes difficult to remove the flash formed. As compression molding uses semipositive molds, there would be some material loss in the form of flash. 

The reliable encapsulation of inserts - without damage and at the same time inexpensively and without flash formation - is possible through the use of flexible sealing elements A 4200 (MurSeal ), Figure 2.124 shows the use of such seals in an example of a wrist strap for car doors. 

According to the current state of technology, it is only possible to encapsulate metal inserts with thermoplastic materials under series conditions without flash formation or damage in the injection molding process. Often interchangeable inserts made from copper, aluminum, or another metal are used in the mold. Here, the inserts cannot be individually adapted to the depositors, which will make regular replacement necessary. Another possibility is to compress the inserts in the injection mold. This can temporarily avoid flash formation. In this context, it must be noted, however, that damage to the injection mold and the insert surfaces will occur. 

Parting plane Edge rounding Flash formation... 

When processing polyphenylene sulfide, it is necessary to vent injection molds appropriately, because the sulfurous degradation products cause mold corrosion. Because of the low melt viscosity the vent holes have to be narrow (flash formation). That is why poorly stabilized compounds require frequent and quite involved mold purging [573]. 

Mounting one mold on the arm is fairly straightforward. Multiple molds require careful design for mounting on a single spider. Improper mounting can result in an abnormally high rate of wear and tear on the mold and excessive flash formation on the part. 

Viscosity of moulding compoimd too low (high internal mould pressures and low flow resistance favour flash formation). 

The flash point of furfural is 143°F by Tag Closed Cup. Because of its chemical reactivity, furfural should be kept away from strong acids, alkaHes or strong oxidi2ing chemicals. When furfural is stored for long periods in contact with air, there is a gradual darkening of color, increase in acidity, and formation of a soluble polymer. 

The pressure used in producing gas wells often ranges from 690— 10,300 kPa (100—1500 psi). The temperature of the inlet gas is reduced by heat-exchange cooling with the gas after the expansion. As a result of the cooling, a liquid phase of natural gas liquids that contains some of the LPG components is formed. The liquid is passed to a set of simple distillation columns in which the most volatile components are removed overhead and the residue is natural gasoline. The gas phase from the condensate flash tank is compressed and recycled to the gas producing formation. 

The solvent is 28 CC-olefins recycled from the fractionation section. Effluent from the reactors includes product a-olefins, unreacted ethylene, aluminum alkyls of the same carbon number distribution as the product olefins, and polymer. The effluent is flashed to remove ethylene, filtered to remove polyethylene, and treated to reduce the aluminum alkyls in the stream. In the original plant operation, these aluminum alkyls were not removed, resulting in the formation of paraffins (- 1.4%) when the reactor effluent was treated with caustic to kill the catalyst. In the new plant, however, it is likely that these aluminum alkyls are transalkylated with ethylene by adding a catalyst such as 60 ppm of a nickel compound, eg, nickel octanoate (6). The new plant contains a caustic wash section and the product olefins still contain some paraffins ( 0.5%). After treatment with caustic, cmde olefins are sent to a water wash to remove sodium and aluminum salts. 

Acid Heat of formation, kl / mol Flash point, °C Heat of combustion, kl / mof... 

Dichloroethylene is usually shipped ia 208-L (55 gal) and 112-L (30 gal) steel dmms. Because of the corrosive products of decomposition, inhibitors are required for storage. The stabilized grades of the isomers can be used or stored ia contact with most common constmction materials, such as steel or black iron. Contact with copper or its alloys and with hot alkaline solutions should be avoided to preclude possible formation of explosive monochloroacetylene. The isomers do have explosive limits ia air (Table 1). However, the Hquid, even hot, bums with a very cool flame which self-extiaguishes unless the temperature is well above the flash poiat. A red label is required for shipping 1,2-dichloroethylene. 

Stabilized tetrachloroethylene, as provided commercially, can be used in the presence of air, water, and light, in contact with common materials of constmction, at temperatures up to about 140°C. It resists hydrolysis at temperatures up to 150°C (2). However, the unstabilized compound, in the presence of water for prolonged periods, slowly hydrolyzes to yield trichloroacetic acid [76-03-9] and hydrochloric acid. In the absence of catalysts, air, or moisture, tetrachloroethylene is stable to about 500°C. Although it does not have a flash point or form flammable mixtures in air or oxygen, thermal decomposition results in the formation of hydrogen chloride and phosgene [75-44-5] (3). 

Seawater Distillation. The principal thermal processes used to recover drinking water from seawater include multistage flash distillation, multi-effect distillation, and vapor compression distillation. In these processes, seawater is heated, and the relatively pure distillate is collected. Scale deposits, usually calcium carbonate, magnesium hydroxide, or calcium sulfate, lessen efficiency of these units. Dispersants such as poly(maleic acid) (39,40) inhibit scale formation, or at least modify it to form an easily removed powder, thus maintaining cleaner, more efficient heat-transfer surfaces. 

Flash vacuum pyrolysis of 2-methoxycarbonylpyrrole (11) gives the ketene (12), characterized by IR absorption at 2110 cm. On warming to -100 to -90 °C the dimer (13) is formed (82CC360). Flash vacuum pyrolysis of indole-2-carboxylic acid (14) results in loss of water and the formation of a ketene (15) showing absorption at 2106 cm (82CC360). 

The intermediacy of N-arylbenzotriazoles in the formation of carbazoles from o-anilinobenzenediazonium salts has already been mentioned in Section 3.03.2.3. The parallel conversion of 1,4- and 1,5-diphenyl-l,2,3-triazoles to 3-phenylindole with minor amounts of the 2-isomer has been effected by flash vacuum pyrolysis (Scheme 106a) (75JCS Pl)l). Similar treatment of 1,3,5- or 3,4,5-triphenyl-1,2,4-triazole provides 1,3-diphenylisoindole (Scheme 106b) <75JCS(P1)12>. 

The isomerization of oxaziridines (1) to acid amides with migration of a substituent from C to N is a general reaction and is always observed when no other reactions predominate under the relatively harsh conditions (heating to above 150 °C or photolysis). Even then one can make acid amide formation the main reaction by working at 300 °C (57JA5739) and by dilution techniques. For example, caprolactam (63) is formed in 88% yield by flash pyrolysis of oxaziridine (52) at about 300 °C, whereas decomposition of (52) at lower temperatures gives almost no (63) (77JPR274). 

The formation of transient benzazetidinones (251) in the photolysis and thermolysis of benzotriazin-4-ones (250) is well established (76AHC215) and the highly hindered adamantyl derivative has actually been isolated from flash pyrolysis of 4-adamantylbenzotriazinone (73JCS(Pl)868). A second route to such hindered benzazetidinones involves cyclization of the iminoketene valence tautomer (252 R = Bu ), the latter being generated by deprotonation of the anthranilium salts (253) (71JA1543). 

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