Mixable room temperature castable polyurethane system

Abstract

The present invention relates to a polyurethane compound which has particular utility as a potting compound for fan exit guide vane assemblies of commercial gas turbine engines. The polyurethane compound comprises a formulation of polyurethane prepolymers mixed with an aromatic amine curing agent (hardener) in a volumetric mix ratio in the range of from about 0.9:1 to about 1:1. The polyurethane prepolymer consists of a blend of different polyethers based on diphenylmethane diisocyanate (MDI). The amine curing agent is a blend of oligomeric diamines with an aromatic diamine with a catalytic component. Both of the blends, in an uncured state, are liquid at room temperature.

What is claimed is:  
     
         1 . A polyurethane compound comprising a first component and a second component, said first component consisting of a blend of different polyether based MDI prepolymers, each of said polyether prepolymers having a different diphenylmethane diisocyanate content and said second component comprising an amine curing agent consisting of a blend of diamines.  
     
     
         2 . The polyurethane compound according to  claim 1 , wherein said first and second components are present in a volumetric mix ratio of the first component to the second component in the range of from about 0.9:1 to about 1:1.  
     
     
         3 . The polyurethane compound according to  claim 1 , wherein said first and second components are present in a volumetric mix ratio of the first component to the second component in the range of from about 0.95:1 to about 1:1.  
     
     
         4 . The polyurethane compound according to  claim 1 , wherein each of said first and second components when in an uncured state is liquid at room temperature.  
     
     
         5 . The polyurethane compound according to  claim 1 , wherein said first component has a NCO content in the range of from about 11.5% to about 14.5%.  
     
     
         6 . The polyurethane compound according to  claim 5 , wherein said NCO content is in the range of from about 12% to about 14%.  
     
     
         7 . The polyurethane compound according to  claim 5 , wherein said NCO content is about 13%.  
     
     
         8 . The polyurethane compound according to  claim 1 , wherein said first component comprises a blend of a first diphenylmethane diisocyanate component having a density of about 1.2 g/cm , an equivalent weight of about 286 g/mol and a NCO content in the range of from about 13.5% to about 16.5% and a second diphenylmethane diisocyanate component having a density of about 1.06 g/cm , an equivalent weight of about 375 g/mol, and a NCO component in the range of from about 9.7% to about 12.7%.  
     
     
         9 . The polyurethane compound according to  claim 1 , wherein said first component has a first diphenylmethane diisocyanate component with a NCO content in the range of from about 14% to about 16% and a second diphenylmethane diisocyanate component with a NCO content in the range of from about 10.2% to about 12.2%.  
     
     
         10 . The polyurethane compound according to  claim 1 , wherein said first component has a first diphenylmethane diisocyanate component with a NCO content of about 15% and a second diphenylmethane diisocyanate component with a NCO content of about 11.2%.  
     
     
         11 . The polyurethane compound according to  claim 1 , wherein said second component comprises a blend of two oligomer diamines having different equivalent weights and an amine having chlorine groups attached thereto.  
     
     
         12 . The polyurethane compound according to  claim 11 , wherein said second component has an amine to NCO stiochiometric ratio between about 0.85:1 and about 1.05:1.  
     
     
         13 . The polyurethane compound according to  claim 12 , wherein said amine to NCO stiochiometric ratio is between about 0.9:1 and about 1:1.  
     
     
         14 . The polyurethane compound according to  claim 12 , wherein said amine to NCO stiochiometric ratio is about 0.95:1.  
     
     
         15 . The polyurethane compound according to  claim 11 , wherein said second component comprises a blend of a first oligomeric diamine having an equivalent weight of about 235 g/mol and a density of about 1.04 g/cm 3 , a second oligomeric diamine having an equivalent weight of about 415 g/mol and a density of about 1.04 g/cm 3 , and a diamine having an equivalent weight of about 190 g/mol and a density of 0.95 g/cm 3 .  
     
     
         16 . A polyurethane compound for potting vanes for use in a turbine engine, said polyurethane compound comprising: 
 a first component comprising a blend of different polyethers based on diphenylmethane diisocyanate; and    a second component comprising a blend of oligomeric aromatic diamines and an aromatic diamine with a catalytic component.    
     
     
         17 . The polyurethane compound according to  claim 16 , further comprising each of said first and second components being liquid at room temperature when in an uncured state.  
     
     
         18 . The polyurethane compound according to  claim 16 , further comprising a volumetric mix ratio of the first component to said second component in the range of from about 0.9:1 to about 1:1.  
     
     
         19 . The polyurethane compound according to  claim 16 , wherein said first component comprises a blend of a first polyether based diphenylmethane diisocyanate prepolymer having a first NCO content and a second polyether based diphenylmethane diisocyanate prepolymer having a second NCO content, which second NCO content is different from aid first NCO content.  
     
     
         20 . The polyurethane compound according to  claim 19 , wherein said blend has a NCO content of about 13%.  
     
     
         21 . The polyurethane compound according to  claim 16 , wherein said second component comprises a blend of two oligomer diamines having different equivalent weights and a diamine having chlorine groups attached to it.  
     
     
         22 . A method for making a polyurethane compound comprising: 
 providing a formulation of polyurethane prepolymers in liquid form at room temperature;    providing an aromatic amine curing agent in liquid form at room temperature; and    mixing said polyurethane prepolymer formulation with said aromatic amine curing agent in a volumetric ratio of 0.9:1 to about 1:1.    
     
     
         23 . The method according to  claim 22 , wherein said step of providing a formulation of polyurethane prepolymers comprises providing a blend of different polyether based MDI prepolymers.  
     
     
         24 . The method according to  claim 23 , wherein said step of providing a blend of different polyether based MDI prepolymers comprises blending a first polyether based MDI prepolymer having a NCO content in the range of from about 13.5% to about 16.5% with a second polyether based MDI prepolymer having a NCO content in the range of from about 9.7% to about 12.7%.  
     
     
         25 . The method according to  claim 22 , wherein said step of providing an aromatic amine curing agent comprises providing a blend of oligomeric diamines and an aromatic diamine with a catalytic component.  
     
     
         26 . The method according to  claim 25 , wherein said blend providing step comprises blending two oligomeric diamines having different equivalent weights with said aromatic diamine.