Melt Filter

Why is melt filtration necessary and how is it accomplished What would an operator observe if a melt filter were to rupture ... 

Add with stirring 22.5 g S0C12 in 100 ml ether in 20 ml portions to a solution of 15 g 3,5-dimethoxybenzyl alcohol, 1 ml pyridine and 200 ml ether. Let stand and wash with 2X100 ml cold water separate and dry, evaporate in vacuum the ether to get 16 g 3,5-dimethoxybenzyl chloride (I). Recrystallize from petroleum ether. 16 g (I), 300 ml ethanol, 30 g NaCN, 75 ml water reflux three hours and pour onto 400 g ice. After ice melts, filter and recrystallize precipitate from petroleum ether to get about 14 g 3,5-dimethoxybenzyl CN (II). 5 g 50% NaH in mineral oil wash three times with pentane or hexane fill flask with N2 or argon and add dimethoxyethane or dimethylformamide (freshly distilled from K if possible). Stir and add 9 ml methyl iodide. Carefully add 8 g (II) and stir twelve hours. Add ice water and neutralize with NaHC03 to pH 7-8. Extract with ether and dry, evaporate in vacuum the ether (can distill 170/0.1) to get about 9 g alpha, alpha-dimethyl-3,5-... 

A melt filter should be introduced in the downstream process to eliminate solid contaminants such as residual glass, metal, sand, paper or wood, as well as decomposed or cross-linked polymers. 

Perhaps it was only natural that people steeped in Greek philosophy would think of trying to make gold when they encountered the rich Egyptian tradition of practical chemistry. Hadn t Aristotle said that transformations were possible Isn t that what happened when, for example, cinnabar (mercury ore) was heated Heating the red material, cinnabar, caused a pool of liquid metal to form. Didn t other chemical transformations take place when substances were heated, dissolved, melted, filtered, and crystallized ... 

However, a melt filter shows that there are limits even in this area. If several layers of screens are used, the wires in the screen mesh greatly reduce the theoretically available screen surface. The polymer flow depends on the random location of the individual screen layers with respect to one another, i.e., the details are not known (Fig. 11.11). 

Process engineers generally find simplified diagrams and formulas sufficient to estimate the pressure in these components. There is standardized pressure for melt filters, determined experimentally, which is dependent only on the screen mesh count and the flow exponent of the polymer. Should the screen mesh count be changed while all other parameters remain constant, the pressure loss of the screen will alter in proportion to this standardized pressure (Fig. 11.12). 

Figure 11.12 Estimated pressure drop at a melt filter...

A PEL/polycarbonate blend with higher impact resistance Ultem 1000 resins melt filtered to 40 microns... 

The head/die system (Fig. 2.11) receives the melt stream as it exits the barrel. Components in this system include the head assembly, adapter, breaker plate, melt filter, and die. 

The most common form of melt filtering is the use of screen packs. The screen pack is held in the breaker plate by melt pressure as the polymer exits the barrel. The breaker plate often contains a pocket to hold screens that are nominally the same diameter as the screw. 

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