Extrusion methods

Abstract

.Iadd.An improved extrusion method is provided to produce plastic tubes having at least one end thereof an increased wall thickness. The method includes the steps of continuously advancing plastic material through an extruder to form a cylinder, cooling the extruded cylinder as it passes from the extruder, periodically increasing the speed at which the plastic material is fed to the extruder relative to the speed at which the cylinder is drawn from the extruder to produce a section having an increased wall thickness and dividing the cylinder thus formed. .Iaddend.

What is claimed is: 
     
       1. A process for the production of plastic tubes which have at least at one end thereof an increased wall thickness for a predetermined length, said process comprising continuously advancing plastic material through an extruder to produce a continuous extruded cylinder, cooling the extruded cylinder as it is discharged from the extruder whereby the plastic material is hardened thereat, engaging the thus cooled cylinder to draw the same through the extruder and past the region where the cylinder is cooled, periodically increasing the ratio of the speed at which the material is fed to the extruder relative to the speed at which the cylinder is drawn from the extruder .Iadd.by periodically decreasing the speed at which the cylinder is drawn from the extruder .Iaddend.to upset the tube where it is discharged from the extruder to form periodic increases in thickness in the cylinder .Iadd.at selected areas .Iaddend.and dividing the cylinder thus formed with the periodic increases in thickness to produce tubes which have increased wall thickness at least at one end thereof. 
     
     
       2. A process as claimed in claim 1 wherein said ratio is periodically increased to values greater than 1 by reducing the speed at which the cylinder is drawn from the extruder. 
     
     
       3. A process as claimed in claim 1 wherein said .[.ratio of speeds.]. .Iadd.speed at which said cylinder is drawn .Iaddend.is periodically reduced for a time period in which the predetermined length of increased wall thickness is produced. 
     
     
       4. A process as claimed in claim 1 comprising widening the tubes at the ends of increased thickness to form sockets adapted for connection with pipes. 
     
     
       5. A process for the production of plastic tube members having at least at one end thereof for a predetermined length, an increased wall thickness, said process comprising continuously extruding from an extruder aperture a plastic tube, solidifying the plastic tube by cooling, conveying the cooled plastic tube by a conveying device acting on the solidified tube, guiding the tube as it emerges from the extruder aperture through a calibrating collar and cooling the tube thereat, increasing at intervals, which correspond to the desired length of increased wall thickness.Iadd., .Iaddend.the ratio of the speed with which the tube is extruded from the extruder aperture.[.,.]. relative to the speed with which the conveying device conveys away the solidified tube to a value which is greater than 1, whereby the non-solidified zone of the tube is upset to a greater wall thickness during said intervals in the calibrating collar, and dividing the tube into tube members at said zones of increased thickness whereby said members will have at least at one end thereof an increased wall thickness. 
     
     
       6. A process as claimed in claim 5 wherein said ratio of speeds is increased by reducing the speed at which the tube is conveyed by the conveying device. 
     
     
       7. A process as claimed in claim 5 comprising widening the tube members at the ends of increased thickness to form sockets adapted for connection with pipes. 
     
     
       8. A process for the production of plastic tubes which have at least at one end thereof an increased wall thickness for a predetermined length, said process comprising continuously advancing plastic material through an extruder to produce a continuously extruded cylinder, partially cooling the cylinder in a first cooling stage located immediately beyond the extruder, completely cooling the cylinder in a second stage at a distance from the first stage whereby the cylinder is completely solidified, engaging the thus cooled cylinder to draw the same from the extruder through the cooling stages, applying pressure to the interior of the cylinder to cause the cylinder to peripherally engage a surrounding collar at the first cooling stage whereby said cylinder assumes a substantially constant outer diameter at said first stage and is at least partially solidified thereat, periodically increasing the ratio of the speed at which the material is fed to the extruder relative to the speed at which the cylinder is drawn from the extruder to form periodic increases in thickness of the cylinder at the collar whereat the outer diameter remains constant while the inner diameter of the cylinder is reduced, and dividing the cylinder thus formed with the periodic increases in thickness to produce tubes which have increased wall thickness at least at one end thereof. 
     
     
       9. A process as claimed in claim 8 wherein said ratio of speeds is periodically increased by decreasing the speed at which the cylinder is drawn from the extruder. 
     
     
       10. A process as claimed in claim 8 wherein said .[.ratio of speeds.]. .Iadd.speed at which said cylinder is drawn .Iaddend.is periodically reduced for a time period in which the predetermined length of increased wall thickness is produced. 
     
     
       11. A process as claimed in claim 8 comprising widening the tubes at the ends of increased thickness to form sockets adapted for connection with pipes.