Softener, intermittent

In commercial practice, packaging is produced from continuous web on intermittent-motion thermoforming/die-cut machines. The web edge is clamped and conveyed into a heating box. If a plastic with a narrow softening temperature is used, heating is carefully controUed from top and bottom. 

A glass object can be used for indefinite periods below its annealing temperature but only for very short intermittent periods at the high end of its softening range. Fused silica is obviously very useful for high-temperature apparatus and Vycor, which contains a few percent of other oxides, is almost as good. At elevated temperatures fused quartz will devitrify, i.e., ciystallize and become opaque. 

Water softening is carried out on an industrial scale by means of automatic apparatussThere are two kinds, namely, intermittent and continuous. In the former the water is mixed with the necessary chemicals, the precipitated hardness is allowed to settle, and the clear softened water drawn off. In the continuous form the precipitate is removed partly by gravity but chiefly by means of a filter. The essential parts of a water softener are (i) a reagent tank, (ii) a reaction tank, (iii) a precipitation tank connected generally with a filter, and (iv) a soft-water collecting tank. 

Polyphenylene oxide (PPO) ru A thermoplastic, linear, non-crystalline polyether obtained by the oxidative polycondensation on 2,6-dimethylphenol in the presence of a copper-amine complex catalyst. The resin has a wide useful temperature range, from below —170 to +190°C, with intermittent use to 205° C possible. It has excellent electrical properties, unusual resistance to acids and bases, and is pro-cessable on conventional extrusion and injection-molding equipment. Because of its high coat PPO is also marketed in the form of polystyrene blends (see Noryf ) that are lower-softening (Tg of PS is about 100°C vs 208°C for PPO), and have working properties intermediate between those of the two resins. 

Conventionally, this type of coating is applied by plasma at a temperature of about 2()0°C, which has limited its application of surfaces such as metals and ceramics. The CVD technology, however, enhanced by a plasma source operated only intermittently (PECVD), can function at around 50-8()°C. Combined with plasma washing in a specific atmospheric gas, it has been possible to coat thermoplastic materials with much lower softening points. 

Heavy Open-Gear Compounds. These are very heavy bodied tarhke snbstances designed to stick tenaciously to the metal surfaces. Some are so thick they must be heated or diluted with a solvent to soften them for application. These products are used in cases where the Inbricant application is intermittent. 

Thermo-responsive polymers have also been used in endotracheal tubes (ETT). A commercialized example is the RUSCH endotracheal tube from Teleflex, which allows the tube to soften at body temperatnre for greater patient comfort, while the smooth tnbe tip is molded and gently cupped to minimize trauma during intubation. It is made from a thermosensitive PVC via formnlation. Since the thermosensitive PVC is expected to readily conform to a patient s anatomy for improved performance and patient comfort, the formulated thermosensitive PVC could also be used in an intermittent catheter, thoracic drainage catheters, etc. 

The TDS content of BFW should be minimized by upstream treating. In former days, hot lime water softening was employed. In most modern process units, ion exchange resin is used to demineralize BFW. "Blowdown" is the water that is drained out of the boiler to control the accumulations of TDS or silicates in the boiler. My old design value for this flow was 10 percent of the makeup BFW flow. Two types of blowdown from a boiler are used continuous blowdown from the steam drum, and intermittent blowdown from the mud drum both will reduce silica. Note that with the continuous blowdown, heat recovery equipment may be economically justified. 

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