Soft temperature control

These are also referred to as hard temperature control, if heat is drawn from the mould, and soft temperature control, if heat is to be supplied. Separate temperature control for the two halves of the mould is also important from this point of view. The parts of the mould on which the component is shrunk, such as cores, for example, will accept more heat, and thus will be more strongly heated, if they are not temperature controlled in a suitable fashion. Parts of the mould from which the component shrinks away accept less heat and will therefore remain colder without temperature control. In extreme cases, it can even happen that one half of the mould, with the core parts, has to be cooled, while the other half has to be heated, so as to obtain the same mould temperature in both halves of the mould. 

Fluids are usually used for mould temperature control, because both heat extraction and heat supply can be controlled equally well. Electrical heating for soft temperature control is certainly very rapid, but still not fast enough on its own it would cause excessively high temperature variations. In all cases, electrical heating is used in conjimction with fluid temperature control, the latter being there to provide - if required - for sufficiently rapid heat extraction (so as to keep the temperature variations low). This combined temperature control system does indeed obtain the best results, but of course costs are significantly higher, and only rarely economically acceptable. So in what follows only pure fluid temperature control will be considered. 

For higher hard control requirements and for all cases involving soft temperature control, fluid temperature control units (forming units, heating units and cooling units) are used, which pump up a temperature control medium (water and oil) through the temperature control system of the mould. The cycle temperature of the temperature control medium is adjustable, and is adjusted for a pre-set value. 

Describe the reaction engineering of a kitchen toaster. The reactions are thermal drying (which alone makes stale bread) and thermal decomposition and oxidation of starch, which requires temperatures of -300°C. [Recall that the bread appears white until it is nearly done, and then it browns quickly and blackens if left in too long. Recall also that good toast has a brown layer < 1 mm thick while the interior is still white and soft. The control of temperature profiles and heat transfer aspects are essential in producing good toast.]... 

Soft segments One of the two phases which make up polyurethane. The soft segment is composed of long-chain polyether or polyester polyols. The soft segment controls many of the polyurethane properties such as tensile and tear strength, hydrolysis and chemical resistance, glass transition temperature, and flexibility. 

That soft digestion enhanced by US was first demonstrated by Kannan and Pathan [15], who soft-digested aqueous benzoic add In the experimental device shown in Fig. 3.3. The cylindrical geometry for the sample was intended to ensure uniformity in the solid surface and improved accessibility by the liquid phase. The solid was immersed in a water bath with temperature control at 31 °C. The ultrasonic source was a probe that was inserted vertically into the water bath. The device was rated at 500 W and 20 kHz frequency. Trial experiments of USASD without temperature control of the water bath... 

The nonvolatile residuum is used to produce road asphalt (sometimes referred to as bitumen) as well as a variety of asphalt grades for roofing and waterproofing. It is produced to certain standards of hardness or softness in controlled vacuum distillation processes. Asphalt is a residuum and cannot be distilled even under the highest vacuum because the temperatures required to volatilize the residuum promote the formation of coke. Asphalts have complex chemical and physical compositions that usually vary with the source of the crude oil. 

Typical soft bake temperatures are 90-120°C for 60 seconds on a hot plate, followed by a cooling step on a chill plate to achieve uniform wafer temperature control. The boiling points of most resist solvents are on the order of... 

The graph indicates the need to remove moisture from the insulation before the heater is heated up to operating temperature. This is done at 100 °C for around 15 minutes, and should be programmed into the temperature control system. Every time the temperature of the HR system falls below 50 °C, this operation needs to be repeated (the soft start phase - see Section 5.5). 

Weigh accurately a suitable quantity of the well-mixed sample in a tared silica or platinum basin. Heat first by means of a soft flame, such as that of an Argand burner, to volatilise as much as possible of the organic matter, then transfer the basin to a temperature-controlled muffle furnace, at a temperature preferably not exceeding 420°. 

The power consumed by the mill is, however, once again, converted to frictional heat in the nip. The temperature control system for this mill must first heat and stabilise the roll temperature at the correct preset figure (say 150°C for soft and 170°C for hard mixes), and secondly remove the excess friction heat. 

Extrusion Resins. Extmsion of VDC—VC copolymers is the main fabrication technique for filaments, films, rods, and tubing or pipe, and involves the same concerns for thermal degradation, streamlined flow, and noncatalytic materials of constmction as described for injection-molding resins (84,122). The plastic leaves the extmsion die in a completely amorphous condition and is maintained in this state by quenching in a water bath to about 10°C, thereby inhibiting recrystallization. In this state, the plastic is soft, weak, and pHable. If it is allowed to remain at room temperature, it hardens gradually and recrystallizes partially at a slow rate with a random crystal arrangement. Heat treatment can be used to recrystallize at controlled rates. 

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