Inner melt removal

If the channel depth of the outer screw is reduced to zero, all the polymer melt is pumped toward the die hy the inner screw. This inner melt removal (IMR) screw was Invented by Kovacs [20] of Midland-Ross Corporation. It Is essentially a very complicated version of a barrier screw and does not offer any obvious advantages over conventional barrier screws. 

Once the mould is removed from the oven the mould starts to cool at a rate determined by the type of cooling - blown air (slow) or water spray (fast). There may be a overshoot in the internal air temperature due to the thermal momentum of the melt. This overshoot will depend on the wall thickness of the plastic product. In Fig. 4.61 it may be seen that the inner air temperature continues to rise for several minutes after the mould has been taken out of the oven (at about 13.5 minutes). 

Surface samples were collected in snow pits under ultra-clean conditions described elsewhere [13] with the exception that samples for anion analysis were collected in polystyrene cups precleaned without the use of acids. Ice core samples were cleaned to remove surface contamination using the "dry-core" procedure involving rinsing and melting of exterior surfaces with ultra-pure water [13]. Shallow-depth firn cores are permeable and the dry-core rinsing is unsuitable. Therefore an inner core of 2.5 cm diameter was taken from intervals of the 7.6 cm diameter South Pole firn core using a specially-built precleaned stainless steel corer within a -15 °C cold room. Prior to this coring, exposed ends of core sections were shaved away with precleaned stainless steel chisels. 

A solution of 8.2 g. (0.040 mole) of purified aluminum isopropoxide and 2.75 g. (0.011 mole) of 4-keto-l,2,3,4-tetrahydrochrysene in 25 cc. of dry toluene is refluxed for four hours, in an oil bath. After the solution has cooled slightly, 25 cc. of dry isopropyl alcohol is added to facilitate removal of acetone, the water is removed from the reflux condenser, and a water condenser set for downward distillation is attached to the top by means of a short bent tube (a Hahn partial condenser with a 1-cm. layer of isobutyl alcohol in the inner condensing tube may be used). The mixture is heated at such a rate that slow distillation occurs (2 to 5 drops per minute, the volume of solution should be maintained by further addition of solvent as needed). When the test for acetone is completely negative, f the toluene solution is cooled and the aluminum salt is decomposed with cold 10% sulfuric acid (from 5 cc. of concentrated sulfuric acid and 80 cc. of water). The product is separated with the toluene, and the solution is washed with dilute aqueous ammonia and water, and then evaporated at room temperature under a stream of air (solutions of secondary alcohols which are susceptible to dehydration should be evaporated at room temperature a stream of air should not be used with carbinols boiling below 200°). There is obtained 2.10 g. (76%) of colorless 4-hydroxy-l, 2,3,4-tetrahydrochrysene melting at 156-158°. Two recrystallizations from a mixture of benzene and petroleum ether bring the melting point to 160-162°. 

The inner tube is removed, the cyclohexane is melted as before, and a second weighed pellet of the unknown is added and stirred into solution. Before this pellet is added, it is well to make a rough calculation, based on the results of the first run, to make sure that the temperatures in the second run will remain on scale and, if necessary, to modify the weight of the pellet accordingly. The second run is carried out as before, after cooling in an ice bath to about the temperature at which freezing was obtained in the first run. 

In the entrained-bed gasifier, very fine coal (< 1 nun), sometimes as a water slurry, enters the gasifier and is mixed with steam and oxygen. Combustion is immediate and a very high temperature is achieved (1,800°C). Most of the ash melts and forms a slag over the inner wall of the vessel. The slag runs down the walls into a collector. Some ash is entrained in the synthesis gas which typically exits the top of the reactor. Heat is recovered by a waste heat boiler and the ash is then removed by means of a cyclone. 

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