What is the Draw down ratio (DDR) and draw ratio balance (DRB) calculations?

Draw down ratio (DDR) and draw ratio balance (DRB) calculation need to be made to insure that correct product sizes are produced. These calculations are available in standard extrusion texts.
Without performing calculations for tip and dies sizes, based on the final product dimensions and the consideration for the polymer being processed, and the quenching method being used, the
achievement of the correct final product dimensions will be difficult.

The draw down ratio (DDR) is simply the ratio of two areas. The first area is the annular exit area of the die assembly, produced by the tip outer diameter and the die inner diameter. The
second area is the cross-sectional area of the final annular extruded product. This calculation dies not take into account the die (extrudate) swell as the melt emerges from the head assembly
exit annulus. The draw down ratio can be a low as 1:1 in the case of certain profile extrusion processes, to as high as 100:1, as in the case of small diameter fluoropolymer tube extrusion.
More often, ratios of 1.5:1 to 5:1 are found.




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