Method for Manufacturing Castings by Using a Lost-Foam Pattern Casting Method

Abstract

A method for producing a ductile cast iron product, wherein the cast iron product contains sulfur in an amount of 0.009 to 0.015 wt % and magnesium in an amount of 0.035 to 0.050 wt %, and wherein a dried sand is used for a mold. The method can be suitably employed for producing, at a low cost, a ductile cast iron product which is not chilled and has a ferritic structure, and thus is soft and exhibits great ductility even when it is a thin product. The present invention has been completed based on the finding that the combination of the increase in a certain degree of the content of sulfur, which has been considered to be a substance interfering with the formation of spherical graphite, with the lowering of the rate of cooling allows the production of a ductile cast iron product which is not chilled and has a ferritic structure, and thus is soft and exhibits great ductility even when it is a thin product.

1 . A method for manufacturing castings by using dry sand and a foamed pattern as a lost-form pattern, the method comprising: 
 a step for pouring molten metal into a mold, wherein the molten metal has a temperature from 1,250 to 1,330° C., and    a step for reducing pressure in a mold.    
   
   
       2 . The method of  claim 1 , wherein the step for reducing the pressure in the mold is accomplished by decreasing the pressure in a ventilator channel that is disposed at a lower part of the mold and that is provided with holes communicating with sand in the mold.  
   
   
       3 . The method of  claim 2 , wherein, after the step for decreasing the pressure in the mold, it further comprises: 
 a step for increasing the pressure in the mold, wherein the step is accomplished by increasing the pressure in the ventilator channel.    
   
   
       4 . The method of any of claims  1 - 3 , wherein the pressure of the vacuum in the step for reducing the pressure of the mold is from 0.03 Mpa to 0.05 Mpa.  
   
   
       5 . The method of either  claim 3  or  4 , 
 wherein the step for reducing the pressure in the mold is applied from when the molten metal begins to be poured into the mold to when the molten metal has been poured, and    wherein the step for increasing the pressure in the mold is applied from when the molten metal has been poured to when the temperature of the castings descends to the temperature of ferrite-pearlite transformation.    
   
   
       6 . The method of any of claims  1 - 5 , wherein no binder is mixed with the sand used for molding.  
   
   
       7 . The method of any of claims  1 - 6 , wherein the material of the foamed pattern is a PMMA (poly methyl methacrylate), and wherein the material has its volume increased 40-50 times by being foamed.  
   
   
       8 . The method of any of claims  1 - 7 , wherein the entire surface or a part of the surface of the foamed pattern is coated with a mold wash having a bending strength of more than 15 Kgf/cm 2 .  
   
   
       9 . The method of any of claims  1 - 8 , wherein no feeder is disposed in the mold.  
   
   
       10 . The method of any of claims  1 - 9 , 
 wherein the foamed pattern that includes a runner, a gate, and a casting, is integrally made, or    wherein the foamed pattern that includes a runner, a gate, and a castings, is separately formed, and then is assembled by adhering them.