Method and installation for densifying porous substrates by chemical vapour infiltration

Abstract

An installation for densification of porous substrates by CVI comprises an oven, a zone for loading substrates in the oven, means for heating substrates loaded in the loading zone, at least one inlet for admitting reactive gas in the oven, and at least one gas heating zone situated in the oven between the reactive gas inlet and the loading zone. At least one gas preheating device is located outside the oven and is connected to the gas inlet so as to preheat the reactive gas before it enters the oven.

1 . An installation for densifying porous substrates by chemical vapour infiltration, the installation comprising: 
 an oven,    a zone for loading substrates into the oven,    means for heating substrates in the loading zone,    at least one inlet for admitting reactive gas into the oven,    at least one gas heating zone situated in the oven between the reactive gas inlet and the loading zone, and    at least one gas preheating device situated outside the oven and connected to at least one reactive gas inlet to the oven, so as to preheat the reactive gas before it enters the oven.    
     
     
         2 . An installation according to  claim 1 , wherein the preheating device comprises an electrical heater tube inserted in a duct for feeding reactive gas to the reactive gas inlet of the oven.  
     
     
         3 . An installation according to  claim 1 , wherein the preheating device comprises a gas boiler having at least one duct passing therethrough to convey a flow of reactive gas to be preheated.  
     
     
         4 . An installation according to  claim 3 , wherein the boiler is connected to an outlet for removing effluent gas from the oven so as to use at least a fraction of the effluent gas as fuel gas for the boiler.  
     
     
         5 . An installation according to  claim 1 , wherein the preheating device comprises an electrically heated oven having at least one tube passing therethrough to carry a flow of reactive gas to be preheated.  
     
     
         6 . An installation according to  claim 1 , further including an expander located between the preheating device and the inlet for reactive gas into the oven.  
     
     
         7 . An installation according to  claim 1 , wherein the preheating device includes temperature regulator means.  
     
     
         8 . An installation according to  claim 1 , for densifying annular substrates placed in a plurality of stacks, the installation including a plurality of heater zones each situated between a respective inlet for reactive gas into the oven and a respective location for an annular stack in the loading zone.  
     
     
         9 . An installation according to  claim 8 , having a plurality of individual feed pipes for preheated reactive gas connected to the reactive gas inlets into the oven.  
     
     
         10 . An installation acorn to  claim 9 , wherein the individual feed pipes are connected to a preheating device via a common pipe.  
     
     
         11 . An installation according to  claim 9 , wherein the individual feed pipes are connected to respective devices for preheating reactive gas.