Melt-reservoir systems

Melt-Reservoir Systems (Tank-Type Applications)... 

In spite of a number of variations in equipment, two basic types of systems are used to heat and apply hot-melt adhesives melt-reservoir and pressure-feed systems. 

These systems heat only a small amount of adhesive at a time, thereby eliminating some of the problems inherent in a reservoir system. Several versions of the first-in first-out equipment are in use. In one type, granules or pellets of adhesive are loaded into a hopper. The adhesive melts on a heated grid, then flows to a gear pump and is immediately transferred under pressure, through an electrically heated hose, to a heated gun. This equipment can feed hot melts at the rate of 9.1 kg or more per hour, even though less than 500 grams of adhesive is maintained in the molten state. 

The major types of continuous application equipment have been wheel coaters and glue line nozzles. Simplest is a grooved wheel which turns in a melted reservoir of glue. These have been highly refined to where the amount of adhesive is controlled by a doctor blade for quantitative application. A further refinement is the development of the print cylinder, where an internally mounted doctor blade allows a precise pattern to be printed on either flexible or rigid substrates. Patterns can vary from one inch to a width of 72 inches, and system can operate at speeds greater than 1,000 feet per minute. 

In most cases, the activator impurity must be incorporated during crystal growth. An appropriate amount of impurity element is dissolved in the molten Ge and, as crystal growth proceeds, enters the crystal at a concentration that depends on the magnitude of the distribution coefficient. For volatile impurities, eg, Zn, Cd, and Hg, special precautions must be taken to maintain a constant impurity concentration in the melt. Growth occurs either in a sealed tube to prevent escape of the impurity vapor or in a flow system in which loss caused by vaporization from the melt is replenished from an upstream reservoir. 

In many ways, chloroaluminate molten salts are ideal solvents for the electrodeposition of transition metal-aluminum alloys because they constitute a reservoir of reducible aluminum-containing species, they are excellent solvents for many transition metal ions, and they exhibit good intrinsic ionic conductivity. In fact, the first organic salt-based chloroaluminate melt, a mixture of aluminum chloride and 1-ethylpyridinium bromide (EtPyBr), was formulated as a solvent for electroplating aluminum [55, 56] and subsequently used as a bath to electroform aluminum waveguides [57], Since these early articles, numerous reports have been published that describe the electrodeposition of aluminum from this and related chloroaluminate systems for examples, see Liao et al. [58] and articles cited therein. 

Table 4.2 gives current estimates for the relative abundances of the isotopes in the solar system. The isotopic compositions of most elements, especially those that exist as solids, come from measurements of terrestrial materials. Because the Earth has experienced extensive melting and differentiation, it can be considered a homogeneous isotopic reservoir. However, each of the elements can experience both equilibrium and kinetically based isotopic fractionations during igneous, evaporative, and aqueous processes. The range of compositions introduced by such processes is small for most elements and so does not obscure the overall picture. 

Frezzotti ML, Peccerillo A, Bonelli R (2003) Magma ascent rates and depths of crustal magma reservoirs beneath the Aeolian volcanic arc (Italy) inferences from fluid and melt inclusions in xenoliths. In De Vivo B, Bodnar RJ (eds) Melt Inclusions in Volcanic Systems Methods, Applications and Problems. Elsevier, Amsterdam, pp 185-205... 

For successful use of such adhesives, not only must the formulation be suitable but the system for application also must be efficient. The molten adhesive must be maintained in a fluid condition and at the correct temperature for application over-heating could cause degradation, and if it is too cold the viscosity of an adhesive might be too high. The hot fluid is pumped to the substrate through a suitable nozzle but if the distance between the reservoir and the nozzle is appreciable there may be cooling and a need for heated hoses. Sometimes, molten adhesive is transferred to a coater of the heated-roller type, where again the control of temperature is important. There is a wide variety of equipment for application and every manufacturer of hot-melt adhesives will advise on systems that are suitable for use with them. 

Most non-chondrule solids in the inner Solar System experienced thermal processing (see Chapter 8) that could have modified their initial oxygen isotopic composition (Yurimoto Kuramoto 2004). The complicated structure of meteoritic oxygen isotopes is difficult to reproduce simply by physical mixing of different reservoirs. Apart from thermal processing (e.g. melting, vaporization, condensation), a large mass-independent chemical process is required. The exact mechanism for this likely photochemical process is yet unknown, but the available constraints leave only a few pathways open. 

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