Title: Method of making a blown bottle having a ribbed interior surface

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Abstract: Plastic containers having internal reinforcing ribs are formed by a molding operation including pre-blow and final-blow steps. The pre-blow step includes inflating a blowable plastic parison into contact with the cavity walls of a first blow mold to form a blown pre-form, the cavity walls of the first blow mold including a plurality of concave grooves to form a pattern of convex or proturburent ribs on the outer periphery of the pre-form. The final-blow step includes positioning the blown, ribbed pre-form within a second or final blow mold having a cavity defined by substantially smooth wall surfaces conforming to the exterior configuration of the desired container. Next, the pre-form is blown to stretch and expand against the cavity walls of the second mold, during which step the convex ribs on the exterior of the pre-form are flattened, forming concave portions intermediate convex reinforcing ribs on the internal wall surface of the container.


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