Flash-free product

The disadvantages of the TM technique mostly relate to the costs. The mold structure for flash-free products is very complex and expensive to manufacture. Therefore, TM processes are mainly profitable for multi-cavity molds (usually over 20 cavities). 

FIGURE 1,252 Flash-free product (bellows) that was manufactured with a cold runner manifold... 

The process results in a seam and flash free container with a high quality molded neck. The preform is produced at a lower pressure than that used for injection molding, so the machine can be lighter and of lower cost constructed. The preform is formed under relatively low stress. Process is best suited to the production of smaller containers. 

Figure 7-55. Coextrusion blow molding can provide multiple layers, from two to at least six, flash-free with easy, high-speed production.

The main advantage of the TM process is the possibility of producing flash-free parts and to manufacture molded parts within narrow tolerances. Thus, the method can be used in particular for the production of small and complex parts. 

Note (a) If the deprotection proceeds too slowly (TLC control), the reaction mixture can be heated at +60°C. (b) Usually twice-repeated precipitation yields tritanol-free product. If necessary, 5 -deprotected oligonucleotides can be purified by flash chromatography (Kieselgel60,230-400 mesh, Merck, Art. 9385) using CHCl3 CH30H= 9 1, as a solvent system. 

Flash-free parts or parts with minimum flash are obtained Less wear on the mould Automatie production. 

Fire Hazards - Flash Point (deg. F) 182 CC (based on solution of 37 % fonnaldehyde and Methanol free), 122 CC (based on solution with 15 % Methanol) Flammable Limits in Air (%) 7.0 - 73 Fire Extinguishing Ageras Water, diy chemical, carbon dioxide, or alcohol foam Fire Extinguishing Agents Not To Be Used No data or recommendations found Special Hazards of Combustion Products Toxic vapors form Behavior in Fire Not pertinent Ignition Temperature (deg. F) 806 Electrical Hazard Not pertinent Burning Rate Not pertinent. 

When the kiln material is cooled it forms into crystallized clinkers. These are rather large irregular pieces of the solidified cement material. These clinkers are ground and a small amount of gypsum is added (usually about 1.5 to 3%). The gypsum prevents flash setting of the cement and also controls free CaO. This final cement product is sampled, analyzed and stored. The actual commercial cement is usually a hlend of several different cements. This blending ensures a consistent product. 

Methylene cyclopropene (5), the simplest triafulvene, is predicted to be of very low stability. From different MO calculations5 it has been estimated to possess only minor resonance stabilization ranging to 1 j3. Its high index of free valency4 at the exocyclic carbon atom causes an extreme tendency to polymerize, a process favored additionally by release of strain. Thus it is not surprising that only one attempt to prepare this elusive C4H4-hydrocarbon can be found in the literature. Photolysis and flash vacuum pyrolysis of cis-l-methylene-cyclopropene-2,3-dicarboxylic anhydride (58), however, did not yield methylene cyclopropene, but only vinyl acetylene as its (formal) product of isomerization in addition to small amounts of acetylene and methyl acetylene65 ... 

The solvent-free preparation of 1,2,3-trisubstituted imidazolidin-4-ones from aldehydes and N-substituted a-amino acid amides has been reported by Pospisil and Potacek (Scheme 6.202) [365], The general procedure simply involved heating equimolar mixtures of the aldehyde and amine building blocks under open-vessel micro-wave irradiation for 5 min at 200 °C. After cooling to room temperature, the imida-zolidin-4-one products were purified by flash chromatography. 

Perhaps the most striking new result is that, in all the various reactions investigated so far by flash photolysis, the end products of the photosubstitution are formed within a period of 10 s or less. Free radical anions are formed in some of the systems they have lifetimes of the order of 10 -10 s and they do not contribute significantly to substitution product formation. Evidendy in order to trace intermediates of the substitution reaction we have to resort to still faster methods (laser photolysis. Section 4). 

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