Nowadays 3 main methods are used for a cylindrical iron casting : casting in sand-clay molds, centrifugal casting and shell mold casting. However, these methods, though having many advantages, are fuul of disadvantages, and the main one is the presence of two crystallization fronts, which leads to the inevitable formation of shrinkage defects in castings. Using molding compounds does not exclude gas porosity and slag penetration into the body of the casting.
The need to produce thin-walled molded parts with high mechanical properties and without the common casting defects (shrinkage porosity, chemical heterogeneity, oxide and slag inclusions, etc.) resulted in the development of various methods of casting by freezing. A characteristic feature of these casting methods is that the volume of the solidified metal is less than the volume of the metal poured into the mold and forming the casting process takes place under the action of unidirectional heat removal in the free supply liquid metal solidification front during the solidification time. In this case, the gas bubbles,non-metallic and slag inclusions are pushed by the crystallization front and do not get into the body of the casting.
Particular interest is a new method of continuous cyclic casting using directionally solidification without a rod.
Dwg 1. Schematic diagram of the continuous cyclic casting hollow shells without a rod: 1 – metal line; 2 – joining sleeve; 3 – stationary part of the mold; 4 – the movable part of the mold (clamps); 5 – casting
Molten metal is fed into a water-cooled steel mold comprised of stationary and movable portions to fill it to a height equal to the resulting casting. Then the feeding of the metal stops and they wait to make the necessary thickness of the workpiece freezing. The solidified crust is removed upwardly from the stationary mold and the melt. Simultaneously with the beginning of the extraction blank melt located in the axial part falls on the vacated areas of the working sleeve mold and freezing begins on the next casting. At the same time a new batch of melt is given into the mold, the movable part of the mold returns to the original position and is re-filled up to the desired level.
Schematic diagram of the continuous cyclic casting hollow shells without a rod.
Thus, after a specified period of time the mold is removed from the casting, equal to its height, and a new portion of the metal is poured. Formation of cast billets occurs during aging crust solidified in the mold, and the casting process is carried out in a continuous-loop mode. High-temperature heat treatment process is carried out in individual cells annealing. Temperature is maintained in the annealing mode of each of the cells due to the accumulated heat of the castings (the temperature is 1050 ... 1100 ° C), which eliminates the need for additional energy consumption for heating.
In 2006, "TECHNOLIT" for the first time in the foundry practice built and put into operation the foundry "freeze casting." In the shop there are concrete floors and daily wet cleaning. All the thermal energy from the cooling of melting furnaces and casting machines is used for the heating of industrial buildings. Technological waste from all stages of the machining is used as a feedstock material.