Balanced mold

Runner layouts should be designed to deliver the plastic melt at the same time and at the same temperature, pressure, and velocity to each cavity of a multicavity mold. Such a layout is known as a balanced runner (Fig. 7.15). A balanced runner will usually consume more material than an unbalanced type, but this disadvantage is outweighed by the improvement in the uniformity and quality of the moldings. Balance in a multi-cavity mold with dissimilar cavities (known as a family mold) can be achieved by careful variation of runner diameter in order to produce equal pressure drops in each flow path. Such balancing can only be achieved efficiently by the use of computer flow simu-... 

The slag is batch tapped into a receiving room where it is cooled and broken up for disposal. The metal buUion is tapped from the furnace periodically via a siphon into 2-t cast-iron molds. Typical buUion content from an electric furnace in wt % is Sb, 13—18 Sn, 1—2 As, 0.5—1 Cu, 0.3—0.4 and Ni, 0.05—0.1. The balance is lead. 

There are many ways to measure these properties and some of them are proprietary. However, most laboratory tests are standardized by American Standard Testing Methods (ASTM). Many of them are interactive to various degrees. The rate and state of vulcanization is especially important to consider for components of heavier and thicker tines. The heat used to vulcanize the tine in a mold under pressure requites time to penetrate from both sides of the giant tine to the innermost portions. Securing a balanced state of cure, ie, the maximizing of physical properties in all the components, results in the innermost components having a faster rate of cure. The peripheral compounds should have a cure system which holds its physical properties well when overcured. 

The effects of specific fillers in molded goods appHcations are known (52), and are of special importance for water- and acid-resistant compounds. It is good pohcy to contact the suppHers for specific recommendations to meet the balance of properties required. 

Reinforcement reduces shrinkage far more than fillers do. Fillers help balance shrinkage, however, because they replace shrinking polymer. The sharp shrinkage reduction in reinforced crystalline resins can often lead to warpage. The best mold-to-size composites are reinforced amorphous composites. 

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