Pulsed curing systems

Pulsed curing systems are widely used in the manufacture of medical devices, electronics, semiconductors, and optical fibers. Pulsed xenon lamps can be made in a variety of shapes to fit specific requirements, such as 360° illumination. Examples of different designs are in Figures 3.5 and 3.6. 

The first coupling of a LINAC with infrared spectroscopy has been performed by Palmese et al. in order to study in situ kinetics of radiation-induced cationic polymerization of epoxy systems. The aim of the study is to understand the curing behavior of polymers under irradiation. A UV light source and an electron beam (10 MeV pulse width of the beam from 2.5 to 10 pm) are coupled to a portable near infrared (NIR) instrument. Briefly, a portable NIR spectrometer (Control Development Incorporated, South Bend, IN, USA) is used,... 

Apart for exothermic curing reactions, another thermal effect has to be considered, due to the interaction of ionizing radiation with matter. The temperature profile depends on the balance among (on one hand) the rate of heat production, due both to curing reactions and radiation absorption, and (on the other hand) the heat released, in unit of time, by the system toward the environment. Taking constant the geometry of the reacting system, the heat released toward the environment is constant, while the heat production increases with the pulse frequency. 

Microwave-assisted curing of epoxy resin systems was one of the first applications of MW in polymer chemistry and is the most widely studied area in polymer chemistry under both continuous and pulse microwave conditions. The structure, dielectric properties, toughness, mechanical strength, percentage of cure, and glass transition temperature of the epoxy formulations have been investigated [1]. 

Five basic lamp systems are available to produce UV radiation (1) medium-pressure mercury vapor lamps (2) electrode less lamps (3) pulsed xenon lamps (4) hybrid xenon/ mercury vapor lamps and (5) low-pressnre germicidal lamps. Medium-pressure mercury lamps that emit a wide range of wavelengths are by far the most important radiation sources for curing of coatings. 

Recently, we have developed a real time pulsed NMR(RTPNMR) system(2) controlled by a microcomputer as shown in Figure 3 to study dynamics of structure formation in polymer systems. It has been successfully applied to study crystallization process (3), gelation process(4) and so on. In this paper, application of RTPNMR for characterization of curing process of epoxy resins, polymerization crosslinking process of diacetylenes, and orientation process of liquid crystalline polymers(LCPs) under magnetic field are described. Papers related to the detailed analysis of these data will appear in the near future. EXPERIMENTAL... 

In the early works, it was found that the pulse method could lead to the fastest heating of epoxy resins [98] and improve their mechanical properties [99]. For example, it was shown that a computer controlled pulsed microwave processing of epoxy systems that consisted of diglycidyl ether of bisphenol A (DER 332) and 4,4 -diaminodiphenyl sulfone (DOS) in a cavity operated in TM012 mode could be successfully applied to eliminate the exothermic temperature peak and maintain the same cure temperature at the end of the reaction [100]. The epoxy systems under pulsed microwave irradiation were cured faster, and it was possible to cure them at higher temperatures when compared with a continuous microwave or conventional thermal processing. 

In short, Unanipathy aims at maintaining proper health by conserving symmetry in the different spheres of a man s life. Unani practitioners not only cure bodily diseases but also act as ethical instructors. When the equilibrium of the humors is disturbed and functions of the body arc abnormal, in accordance to its own temperament and environment, that state is called disease. Unani medicine believes in promotion of health, prevention of disease, and cure. The health of a human being is based on six essentials that have to be maintained in order to prevent diseases. The six essentials are (1) atmospheric air, (2) food and drink, (3) sleep and wakefiilness, (4) excretion and retention, (5) physical activity and rest, and (6) mental activity and mental relaxation. Another distinctive feature of the Unani system of medicine is its emphasis on diagnosing a disease through examination of Nabd (Arabic for pulse), haul (urine), and boraz (stool). 

Ice ingestion has caused disastrous failures on gas turbines. A few companies also make instrumentation that will detect incipient ice formation by measurement of physical parameters at the turbine air inlet. Sometimes, if the pulse-type filter is retrofitted, the anti-icing detection instrumentation may already be there. The pulse filter, however, provides a preventive cure that will work, r ardless of whether the icing-detection instrumentation is accurate, as the cleaning pulse is triggered by a signal that depends on differential pressure drop across the filter elements. If a pulse filter is used, idng-detection instrumentation, which is normally necessary in a system that directs hot compressor air (bleed air) into the inlet airstream, is not required. 

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