Hopper structure

A hopper structure for treating plastic granular material configured to establish a degree of mass flow in the plastic granular material, comprising an inner sidewall section arranged as an upper tubular sidewall, a tapered lower section having a delivery mouth for said plastic granular material and an elongated insert body, said insert body comprising a fluid tight upper portion and a lower portion arranged at said tapered lower section of the hopper and having its conicity facing away from said upper portion, said upper portion having an exterior surface extending from the base of the lower portion up to at least one half of a height of the upper tubular sidewall at an angle λ≧0 with respect to a vertical line wherein

• an upper gap for the plastic granular material is delimited between said inner sidewall section and said upper portion of said insert body and a lower conical gap is delimited between said tapered lower section and said lower portion of said insert body;
• at least one inlet for hot and dry air to said lower conical gap, said hot and dried air flowing, in use, from said lower conical gap directly to said upper gap through all of said plastic granular material therein contained and towards the top of the hopper structure;
• said tapered lower section of said hopper comprises at least one sidewall with a first tapering angle with respect to said vertical line, and said lower portion of said insert body has a second tapering angle with respect to said vertical line, said second tapering angle being less than said first tapering angle;
• and
• said degree of mass flow increases as said second tapering angle increases.