Melt cushion

It is important, to take a closer look at the position of the screw in the holding pressure phase. At the start of the holding pressure phase, the cavity has already been filled with most of the melt, that it is meant to receive. A small quantity is subsequently injected to compensate for shrinkage. But even at the end of the holding pressure phase, some residual material should still be in the injection chamber. This melt cushion enables pressure to be transmitted between the screw and the cavity or sprue. This melt cushion is absorbed in the next shot. 

The use of a short nosed torpedo design, for the back flow valve assy, instead of the long type is often preferred due to the high melt compressibility of this material. Such a design often reduces melt cushion and product weight variability. 

Steam-Chest Expansion. In steam-chest expansion the resin beads in which gas is already present are poured into molds into which steam is injected. The steam increases the temperature close to the melting point and expands within the stmcture to create beads with food cushioning and insulating properties. Expanded polystyrene is widely used in this process for thermal insulation of frozen food packaging. 

Polyethylene foam sheet is used mainly in package cushioning, and also in roof insulation and extruded profile is also used as construction sealants and pipe insulation. It is made mainly by tandem extrusion. The first extruder melts the polyethylene and blends in liquid volatile organic foaming agent. The second extruder cools it to the optimum foaming temperature, and pumps it through a die into room-temperature air, where it expands into foamed sheet. 

Lead-tin alloys are the most commonly used solder materials for microelectronic packaging. Pb and Pb-rich alloys have one of the most desirable characteristics of C4 solders in that they are soft and compliant. The compliant nature of these alloys act a cushion for absorbing thermal and mechanical stresses and transfer minimum stresses to the die during microprocessor assembly processes. On the other hand, the melting... 

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