Foamed polyester extrusion equipment which can be used in plants for producing sheets, boards or tubes of foamed polyester

Abstract

Foamed polyester extrusion equipment has two co-rotating screws defining with an internal walls of an insulated frame, first degassing zone between a feeding zone at a feeding inlet for polyester and a first tight zone, a second degassing zone downstream of the first degassing zone, foaming agent inlet zone downstream of the second degassing zone and a pumping end zone for melted material downstream of the foaming agent zone. The first degassing zone carries out forced atmospheric degassing at lower temperature and has a first vent stack adjacent the first tight zone. The second degassing zone carries out vacuum degassing at a temperature equal to or greater than the melting point of the treated polyester material. The first degassing zone has, upstream of the first vent stack, a nozzle for inlet of preheated nitrogen gas to entrain vapours.

What is claimed is: 
     
         1 . Foamed polyester extrusion equipment comprising a thermo regulated frame provided with a feeding inlet of pure and/or recycled polyester material, inside of said frame two co-rotating screws are arranged, said co-rotating screws defining with the internal walls of said frame a first degassing zone interposed between a feeding zone placed at said feeding inlet and a first tight zone, a second degassing zone placed downstream from said first degassing zone and separated from the latter through said first tight zone, a foaming agent inlet zone placed downstream from said second degassing zone and separated from the latter through a second tight zone and a pumping end zone of the melted material placed downstream from said foaming agent inlet zone, wherein:
 said first degassing zone is adapted to carry out a forced atmospheric degassing at a temperature lower than the melting point of a treated polyester material and comprises a first vent stack placed at a first segment of said first degassing zone adjacent to said first tight zone,   said second degassing zone is adapted to carry out a vacuum degassing at a temperature equal to or greater than the melting point of said treated polyester material and   said first degassing zone comprises, upstream from said first vent stack, a nozzle for the inlet of preheated nitrogen gas into said first degassing zone adapted to entrain vapours present in said first zone towards the atmosphere carrying out said forced atmospheric degassing.   
     
     
         2 . Foamed polyester extrusion equipment according to  claim 1 , wherein said first degassing zone comprises an extractor hood, adapted to activate the draught of said first vent stack carrying out said forced atmospheric degassing, on top of said first vent stack. 
     
     
         3 . Foamed polyester extrusion equipment according to  claim 2  wherein said extractor hood is arranged on top of said first vent stack. 
     
     
         4 . Foamed polyester extrusion equipment according to  claim 3 , wherein said extractor hood is arranged away from a mouth of said first vent stack and it can be brought close to said first vent stack in order to activate the draught of the vent stack. 
     
     
         5 . Foamed polyester extrusion equipment according to  claim 1 , wherein said second degassing zone comprises a first segment in which a second vent stack is provided, followed by a second segment in which a third vent stack is provided, said first and second vent stack being connected to at least one vacuum member, wherein said first and second segment are linked to form a single degassing zone. 
     
     
         6 . Foamed polyester extrusion equipment according to  claim 1 , wherein downstream from said second tight zone said foaming agent inlet zone comprises a second nozzle for the inlet of at least one foaming agent in said treated polyester material.