Method for making a mold for casting metallic melts

Abstract

The invention relates to a method for producing a mould for casting metallic melts, in particular for casting titanium, titanium alloys or intermetallic titanium aluminides. Said method consists of the following steps: a contact layer is produced by applying a first slicker containing a first metal oxide powder as an essentially solid component to a moulded core, a first sanding layer is produced on the contact layer formed from the first slicker by sanding with a second metal oxide powder and the layer sequence formed from the contact layer and the first sanding layer is radiated with infrared light for a predetermined period of time. According to the invention, for speeding up the drying process, a first dry mass of the first slicker contains a hydraulic binder.

1 . Method for making a mold for casting metallic melts, in particular for casting titanium, titanium alloys or intermetallic titanium aluminides, with the following steps:
 making a contact layer by applying a first slicker onto a mold core, which first slicker contains a first metal oxide powder as an essential solid component,   making a first sanding layer on the contact layer formed from the first slicker by sanding with a second metal oxide powder,   irradiating the layer sequence formed from the contact layer and the first sanding layer with infrared light for a specified period of time,   characterized in that   a first dry mass of the first slicker contains a hydraulic binder.   
     
     
         2 . Method as defined in  claim 1 , wherein the first dry mass contains 1 to 30 wt. %, preferably 8 to 17 wt. % of the hydraulic binder. 
     
     
         3 . Method as defined in  claim 1 , wherein the hydraulic binder is a calcium aluminate cement. 
     
     
         4 . Method as defined in  claim 1 , wherein a grain band of the first metal oxide powder has a range from 0 to 50 μm and advantageously a medium grain size (d 50 ) in the range from 8 to 20 μm. 
     
     
         5 . Method as defined in  claim 1 , wherein the second metal oxide powder has a medium grain size in the range from 130 to 200 μm. 
     
     
         6 . Method as defined in  claim 1 , wherein the first and/or second metal oxide powder is formed from at least one metal oxide which is selected from the following group: Y 2 O 3 , CeO, MgO, Al 2 O 3 . 
     
     
         7 . Method as defined in  claim 1 , wherein the first dry mass contains less than 90 wt. % of the first metal oxide powder. 
     
     
         8 . Method as defined in  claim 1 , wherein a coating layer surrounding a layer sequence of contact and first sanding layer is made. 
     
     
         9 . Method as defined in  claim 1 , wherein the coating layer contains MgO as the essential component. 
     
     
         10 . Method as defined in  claim 1 , wherein a second dry mass for making the coating layer contains a hydraulic binder, preferably a calcium aluminate cement. 
     
     
         11 . Method as defined in  claim 1 , wherein a second dry mass contains at least 40 wt. % MgO as well as at least 20 wt. % of the hydraulic binder. 
     
     
         12 . Method as defined in  claim 1 , wherein the second dry mass contains at least 1 wt. % of one or more of the following oxides: Fe 2 O 3 , SiO 2 , CaO, Al 2 O 3 . 
     
     
         13 . Method as defined in  claim 1 , wherein before making the coating layer, an intermediate layer sequence formed from an intermediate layer and a second sanding layer is applied onto the layer sequence formed from a first contact and first sanding layer. 
     
     
         14 . Method as defined in  claim 1 , wherein the contact and/or the intermediate layer are applied using the injection method. 
     
     
         15 . Method as defined in  claim 1 , wherein a second slicker contains a first MgO powder as the essential solid component. 
     
     
         16 . Method as defined in  claim 1 , wherein the second slicker contains a hydraulic binder, preferable a calcium aluminate cement. 
     
     
         17 . 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. 
     
     
         18 . Method as defined in  claim 1 , wherein the second sanding layer is made by applying a second MgO powder onto the intermediate layer. 
     
     
         19 . Method as defined in  claim 1 , wherein the first and/or third dry mass and/or the sanding layer/layers contains/contain at least 1 wt. % of one of the following oxides: CeO 2 , La 2 O 3 , Gd 2 O 3 , Nd 2 O 3 , TiO 2 . 
     
     
         20 . Method as defined in  claim 1 , wherein a moisture content of the layer and/or the intermediate layer sequence is reduced to a specified value after they are made. 
     
     
         21 . Method as defined in  claim 1 , wherein the specified value is in the range from 10 to 60% residual moisture, preferably less than 20% residual moisture. 
     
     
         22 . Method as defined in  claim 1 , wherein a drying time per layer or intermediate layer sequence is less than 25 minutes, preferably 5 to 15 minutes. 
     
     
         23 . 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. 
     
     
         24 . Method as defined in  claim 1 , wherein the fraction of the hydraulic binder in the second and/or third dry mass is greater than in the first dry mass by at least 2 wt. %, preferable by at least 5 wt. %. 
     
     
         25 . 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. 
     
     
         26 . Method as defined in  claim 1 , wherein, after making the coating layer, the mold core is removed by melting or burning out the material forming the mold core. 
     
     
         27 . Method as defined in  claim 1 , wherein melting the material forming the mold core and/or an additional drying of the layer and/or intermediate layer sequence is performed using microwaves. 
     
     
         28 . Method as defined in  claim 1 , wherein a green body formed after the removal of the mold core is sintered at a sintering temperature of more than 800° C. and less than 1200° C.