In order for a plastic film to be stretched at equal rates in the longitudinal and the transverse direction a highly specific geometrical flow pattern must be established in the stretching zone. This flow pattern involves diverging radial flow lines; the velocity at any point is directly proportional to the distance from the convergences point of the flow lines. These geometrical facts lead to certain design requirements for a machine to be used in the production of plastic film with uniform two-way orientation. In order for new concepts to be expressed in terms of practical working designs for machinery, mechanical development is required. The reduction to practice of the foregoing concept is shown by the accompanying illustrations.

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