Tie-bar growth

One problem that most controls do not consider involves the effect of heat on tie-bars, which can directly influence mold performance, particularly at start-up. If the heat differs from top and bottom bars, it is necessary to insulate the mold from the platens. The insulator pad used also confines heat more to the mold, producing savings in heat and/or better heat control. The following paragraphs describe calculation of the elongation of these usually evenly heated bars, and of thermal mold growth (1). 

At maximum die height (178 in.) on a 500-ton injection-molding machine with a tie-bar diameter of 6 in. (or a cross-sectional area of 28.27 sq. in.), tie-bar elongation equals  

To calculate the effect of a small change in elongation on the force on a tie-bar, one solves for F  

At minimum die height, the change in force for the same elongation is  

Thermal Mold Growth. Uneven mold growth can occur with a temperature differential across the mold. Mold growth, G, is calculated by the following formula  

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Turning to more structural applications, Yan and Mindess [119-121] showed that steel fibres could considerably improve the bond between the matrix and conventional reinforcing bars under impact, primarily by inhibiting the growth of cracks emanating from the deformations (lugs) on the reinforcing bars. Also, Mindess etai [122] showed that steel fibres could considerably improve the impact performance of prestressed concrete railroad ties. 

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