Explain why outside-diameter dimensional control is easier than inside-diameter dimensional control for extruded pipe
What will be an ideal response?
The outside diameter is usually set by forcing the still-soft extrudate outward against forming rings in the cooling tank. To obtain dimensional control for the inside diameter, a mandrel needs to be extended into the cooling bath for sufficient length that the extrudate will cool while in contact with the mandrel. While this is conceptually simple, actual practice is quite difficult. Some factors that must be allowed for are the thermal contraction of the pipe, difficulty in start-up, and adherence of the material to the cold mandrel.
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