Multilayer pipe and method for manufacturing one

Abstract

A multilayer pipe which comprises at least an inner layer and an outer layer. The inner layer is made of extrudable plastic, such as polyethylene PE, cross-linked polyethylene PEX or polypropylene PP. The outer layer forms a fire-protecting layer and the matrix plastic of the outer layer is also made of extrudable plastic. A foaming agent, which does not react during the manufacture of the pipe, is mixed with the matrix. Further, the outer layer contains at least one additive in such a manner that the outer layer has a pipe-reinforcing component and a fire-retardant component. Most preferably, at least the outer layer is extruded by an extruder having a screw length ratio of less than 10 to its biggest diameter.

1 - 8 . (canceled)  
   
   
       9 . A method for manufacturing a multilayer pipe having at least an inner layer and an outer layer, the method comprising: 
 coating the inner layer formed using extrudable plastic with the outer layer, wherein the outer layer of the pipe contains a halogen-free fire-protecting agent and at least the outer layer is extruded by an extruder having a screw length ratio of less than 10 to its biggest diameter.    
   
   
       10 . A method as claimed in  claim 9 , wherein the outer layer contains reinforcing fibers which are oriented in a conical extruder to an angle differing from the axial direction during the manufacture of the pipe.  
   
   
       11 . A method as claimed in  claim 9 , wherein the outer layer contains a foaming agent and the properties and extrusion temperature of the foaming agent are selected in such a manner that the foaming agent does not react during the manufacture of the pipe.  
   
   
       12 . A method as claimed in  claim 9 , wherein the outer layer contains a foaming agent and the properties and extrusion temperatures of the foaming agent are selected in such a manner that the foaming agent reacts when the pipe is exposed to fire to convert the outer layer to a foamed layer.  
   
   
       13 . A method as claimed in  claim 12 , wherein the foaming agent comprises azodicarbonamide.  
   
   
       14 . A method as claimed in  claim 9 , further comprising: 
 prior to the coating, covering the inner layer with an intermediate layer having a heat-conductivity that is higher than that of the inner layer.    
   
   
       15 . A method as claimed in  claim 9 , wherein the outer layer contains short-cut fibers and/or ceramic whiskers fibers.  
   
   
       16 . A method as claimed in  claim 9 , wherein the inner layer is formed using a cross-linked polyethylene PEX.