Method for making a mold for casting highly reactive molten masses

Abstract

The invention relates to a method for producing a casting mould for casting highly reactive melts, in particular for casting titanium, titanium alloys or intermetallic titanium aluminides. Said method consists of the following steps: a contact layer ( 1 ) is produced by applying a first slicker containing a first Y 2 O 3 -powder as an essentially solid component, to a mould core, the contact layer ( 1 ) formed from the first slicker is sanded with a second Y 2 O 3 -powder containing Y 2 O 3 as the essential component. With respect to a particular efficient process, a first dry mass for producing the first slicker contains at least 75 wt. % Y 2 O 3 and as additional solid components, at least 1.0-25 wt. % of a hydraulic binder.

1 . Method for making a mold for casting highly reactive molten masses, in particular for casting titanium, titanium alloys or intermetallic titanium aluminides, with the following steps:
 making a contact layer ( 1 ) by applying a first slicker onto a mold core, which first slicker contains a first Y 2 O 3  powder as an essential solid component,   making a first sanding layer ( 2 ) on the contact layer ( 1 ) by sanding the contact layer ( 1 ) with a second Y 2 O 3  powder containing Y 2 O 3  as the essential component,   characterized in that   a first dry mass for making the first slicker contains at least 75 wt. % of Y 2 O 3  and as a further solid component at least 1.0 to 25 wt. % of a hydraulic binder.   
     
     
         2 . Method as defined in  claim 1 , wherein the first dry mass contains less than 90 wt. % of Y 2 O 3 . 
     
     
         3 . Method as defined in  claim 1 , wherein the first slicker is applied onto the mold core using the injection method. 
     
     
         4 . Method as defined in  claim 1 , wherein a grain band of the first Y 2 O 3  powder is in the range from 0 to 50 μm and advantageously has a medium grain size (d 50 ) in the range from 8 to 20 μm. 
     
     
         5 . Method as defined in  claim 1 , wherein the second Y 2 O 3  powder has a medium grain size (d 50 ) in the range from 130 to 200 μm. 
     
     
         6 . Method as defined in  claim 1 , wherein the hydraulic binder is a calcium aluminate cement. 
     
     
         7 . Method as defined in  claim 1 , wherein a coating layer surrounding a layer sequence (A) of contact ( 1 ) and first sanding layer ( 2 ) is made. 
     
     
         8 . Method as defined in  claim 1 , wherein the coating layer ( 5 ) contains MgO as the essential component. 
     
     
         9 . Method as defined in  claim 1 , wherein a second dry mass for making the coating layer ( 5 ) contains a hydraulic binder, preferably calcium aluminate cement. 
     
     
         10 . Method as defined in  claim 1 , wherein the second dry mass contains at least 40 wt. %, preferably at least 60 wt. % of MgO as well as at least 20 wt. % of the hydraulic binder. 
     
     
         11 . Method as defined in  claim 1 , wherein the second dry mass contains one or more of the following oxides: Fe 2 O 3 , SiO 2 , CaO, Al 2 O 3 . 
     
     
         12 . Method as defined in  claim 1 , wherein before making the coating layer ( 5 ), an intermediate layer sequence (B) formed from an intermediate ( 3 ) and a second sanding layer ( 4 ) is applied onto the layer sequence (A) formed from the contact ( 1 ) and first sanding layer ( 2 ). 
     
     
         13 . Method as defined in  claim 1 , wherein the intermediate layer ( 3 ) is made by a second slicker applied using the injection method. 
     
     
         14 . Method as defined in  claim 1 , wherein the second slicker contains a first MgO powder as the essential solid component. 
     
     
         15 . Method as defined in  claim 1 , wherein the second slicker contains a hydraulic binder, preferably calcium aluminate cement. 
     
     
         16 . Method as defined in  claim 1 , wherein a third dry mass for making the second slicker contains at least 50 wt. % of MgO and at least 20 wt. % of the hydraulic binder. 
     
     
         17 . Method as defined in  claim 1 , wherein the second sanding layer ( 4 ) is made by applying a second MgO powder onto the intermediate layer ( 3 ). 
     
     
         18 . Method as defined in  claim 1 , wherein the first and/or third dry mass/masses and/or the sanding layer/layers contains/contain at least one of the following oxides: CeO 2 , La 2 O 3 , Gd 2 O 3 , Nd 2 O 3 , TiO 2 . 
     
     
         19 . Method as defined in  claim 1 , wherein a moisture content of the contact layer ( 1 ) and/or the intermediate layer ( 3 ) is reduced using infrared radiation to a specified value after their application. 
     
     
         20 . Method as defined in  claim 1 , wherein the specified value is in the range of 10 to 60% of residual moisture, preferably less than 20% residual moisture. 
     
     
         21 . Method as defined in  claim 1 , wherein the fraction of the hydraulic binder in the first dry mass is less than in the second or third dry mass. 
     
     
         22 . Method as defined in  claim 1 , wherein the fraction of the hydraulic binder in the second and/or third dry mass is by at least 2 wt. %, preferably by at least 5 wt. % greater than in the first dry mass. 
     
     
         23 . Method as defined in  claim 1 , wherein the first and/or second slicker has/have a viscosity of not more than 1000 mPas, preferably between 450 and 750 mPas. 
     
     
         24 . Method as defined in  claim 1 , wherein after making the coating layer ( 5 ), the mold core is removed by melting and burning out the material forming the mold core 
     
     
         25 . Method as defined in  claim 1 , wherein a green body formed after removing the mold core is sintered at a sintering temperature of more than 800° C. and less than 1200° C.