Melt cycle

Haymet and coworkers used an automated lag-time apparatus (ALTA) to obtain statistical data on the supercooling point (SCP, also known as freezing temperature) of water freezing to ice (Wilson et al., 2003) and water/tetrahydrofuran (THF) freezing to hydrate/ice (Wilson et al., 2005). The SCP is the temperature of spontaneous freezing of a solution (Zachariassen, 1982). A small sample (300 rL) was cooled linearly (at 4.5 K/min) until the sample froze. The frozen sample was melted, and then refrozen. This freezing-melting cycle was repeated over 300 times on the same sample. 

There are two levels of control in the LEAM process pertaining to coarse and fine adjustments of the operating conditions. The coarse adjustments are based on automatic set point conditions that are predetermined according to the phase of the melting cycle. The fuel and oxygen flow rates are predefined for low-fire and high-fire conditions. 

As a result of the increased efficiency of the EZ-Fire system, the melt cycle was reduced from over 8 to 5 A h for the EZ-Fire system (a 30% melt rate increase). The reduction in melt time enabled the customer to optimize the workload for the entire billet-casting operation. 

The high-purification in laboratory requires refluxing over sodium-potassium alloy followed by distillation under nitrogen 46). It is advisable to keep the distilled product in the molten liquid state, to prevent premature spontaneous polymerization due to crystallization-melting cycles. 

A melting cycle spans PA to several hours. For continuous molten metal production, foimdries install 2 to 4 rotary furnaces, which are operated consecutively. The thermal efficiency of the rotary furnace is very high, i.e. at 50 to 65 depending on the capacity. This high 5deld is achieved by using pure oxygen instead of air as the combustion medium. 

The lifespan of the refiactory is largely dependent on the oveiheating temperature and the charge composition. In the charging operation, mechanical shocks and cold start-ups need to be prevented. The furnace atmosphere, the holding time, rotational speed and the burner position also affect the refractory life. In normal conditions the refractory life is 100 to 300 melting cycles. 

The measurement of OIT based on TGA was used for monitoring the re-stabilization of post-use LDPE samples, subjected to multiple extrusion cycles. This method has abilities and hmitations as well which are discussed in literature (Kyriakou et al. 1999). The use of a re-stabilization system improved the oxidative stability of LDPE. A linear calibration curve correlating OIT values to the amount of re-stabilization system was obtained. Nevertheless, hmitations concerning quantitative determinations appeared to exist, as a change in the behavior of re-stabilization system during subsequent re-melting cycles was observed. 

The URTF employs the dry salt process and therefore optimises the energy required by the melting cycle. Oxy-fuel combustion can also be combined with oxygen lancing. 

Lundin and Yamamoto formed their alloys from metals of select purity . Major impurities in their samarium were < 0.038 wt% O, 0.02 wt% Ca, 0.005 wt% each Ce, Nd, Pr, B, Si and Zn and 0.003 wt% Zr. Their yttrium metal contained 0.037 wt% O, 0.01 wt% each Er and Tb and 0.005 wt% each Ce, Ho, Tb, Pr, B and Si. Alloys were prepared at 10 at% intervals and melted in sealed tantalum crucibles. Three or more melting cycles, well above the melting temperature, were performed before the thermal analysis of each alloy was carried out. 

If the same thermal stabilizers are used for both polymers, the amounts required to survive one melting cycle without excessive change of MW are quite different PP takes 3 to 10 times the stabilizer, as does HDPE. Polymers that are between PP and HDPE in the number of side groups (methyl or alkyl groups that behave like methyl) require amounts of thermal stabilizers between the extremes noted. 

Startup and shutdown Less than daily More than several times per day Same influence of OCV, high cathode potential, (local) potentitil cycle, but lower risk owing to lower cycle number than for automobile use Freeze-melt cycle is not now considered... 

Reprocessed— resin that has been through one or more melt cycles. This may be due to compounding, melt blending, recycling, regrinding, etc.—or a combination of the above. Note this term is widely used, and often loosely defined. Care should be taken to define and clarify the type of reprocessing that has occurred, and how many times the material has been reprocessed. 

Cube blending—another type of batch process, where a batch of pellets (aka cubes) of one resin are mixed with a batch of pellets of one or more other resins. The blending usually occurs at room temperature, in a large container, that is then shaken and/or tumbled. The advantage of this process is that is simple, inexpensive, and does not subject the resin to a melt cycle. The disadvantage is that it can be difficult to ensure a consistent mix throughout the entire batch (Figure 3.20). 

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