Control Pour pressure

The plastics polymerize after entering a mold. Mixing two or more components (additives, fillers, and reinforcements) in the proper chemical ratio is accomplished by a high-pressure impingement-type mixing head. This mix is directed into the mold cavity at low pressure, where it chemically reacts to form a plastic. The components are mixed together at a given ratio and then directed or basically poured into a mold under controlled temperature, pressure, and rate of flow. They polymerize and cure in... 

Some additives have the ability to lower the pour point without lowering the cloud point. A number of laboratory scale flow tests have been developed to provide a better prediction of cold temperature operability. They include the cold filter plugging point (CFPP), used primarily in Europe, and the low temperature flow test (LTFT), used primarily in the United States. Both tests measure flow through filter materials under controlled conditions of temperature, pressure, etc, and are better predictors of cold temperature performance than either cloud or pour point for addithed fuels. 

Henry and McUmber (1977) reported on the systems R-22 -water and R-22-oil. They constructed an apparatus in which R-22 could be poured into water or mineral oil at various ambient pressures controlled by the pressure of argon gas in the system. Separate units were used for the water and oil tests. They demonstrated that they could achieve thermal explosions at 1 bar, in agreement with earlier tests (see Section VII). However, no such events were observed at system pressures of 2.2 or 8 bar even though the hot liquid temperature was varied over a wide range. 

This process resembles the open molding process except it is closed like a two-part compression mold (Chapter 14). A measured amount of plastisol is poured or pumped into the closed mold cavity, similar to close molding except that a slight pressure of about 5 psi (34.5 kPa) is applied. The mold is heated to fuse the plastisol then cooled. Later the mold is opened and the product stripped out. This process can provide for accurate thickness control, filling very complex shaped parts, and so on. 

The most intriguing question is why the plant s safety equipment and controls, which should liave been designed to cope with a chemical tliat is known to be subject to violent reactions, did not work. Tlie MIC tank liad tliree safety devices. A pipe leading from tlie tank contained a valve tliat was set to rupture if the pressure in the tank e.xceeded 40 psi. Beyond the valve there were two other safety devices. One was a flare (tower) to bum escaping gas. The other was a vent gas scrubber, a tower packed with loose niaterial tlirough wliich a solution of caustic soda could be poured onto rising MIC to decompose it. On December 3, 1984, tlie operator of the factory s control room noticed tliat the pressure in tlie MIC tank (see Figure 1.3.2) luid risen from 2 to 30 psi, and in a... 

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