Definitions of Various Draw Ratios

Another important parameter is the wall draw ratio (WDR). This is the gap between the tip and die divided by the wall thickness of the tubing. 

It should be noted that sometimes the area draw ratio is represented by the letters DDR as an acronym for drawdown ratio. Obviously, this can cause confusion with the diameter draw ratio. Often the area draw ratio is called simply the draw ratio. It is important therefore to check what exactly is meant when the term draw ratio is used. The ADR can be calculated from the WDR and the DDR as follows  

the wall and diameter draw ratios determine the area draw ratio in the extrusion process. A high ADR increases orientation and the chance of pinholes and breakaways. A low ADR reduces orientation and increases the chance of melt fracture. 

A fourth measure of drawdown is the draw ratio balance or DRB. This is the diameter ratio of the die and tip divided by the diameter ratio of the tubing. 

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