The shape of the first heat describes the pouring probably the most concise and it is the significant advantage over all manufacturing alternatives. The first heat is also based on the idea of the hot shake out process with targeted subsequent cooling. Is the augmentation of the requested dimensions and a reduction in costs from the first heat due to economic regeneration and reduction in the use of raw materials an utopia or the consistently linking of individual processes?
The increasing complexity of parts leads to a higher use of core packages in greensand systems and applications in which the core packages are sized in a way that the emerging forces can be absorbed without a supporting mold. Both variations are suboptimal and have different disadvantages.
The core package being set up in the greensand mold can be placed only with slackness (or with varying input tension) due to manufacturing tolerances and consequently there is only a transfer of pouring forces into the carrier mold, when the slackness is eliminated by deformation of the core (or by getting higher input tension to the necessary level due to deformation). With different tolerances the inevitable results are avoidable variations of dimensions and weights. The combination of sand systems is another challenge.
Core packages ready for casting, additionally take over the task of complete force absorption by substitution of low priced green sand mold. The disadvantage of this method lies primarily in the cost of the additional chemical binder and volume-related higher costs in the later processes of regeneration.
In applications where the total production is not in core packages, the use of green sand plant and its infrastructure make sense and can be significantly improved through an additional process. A void between the green sand mold and the weight-reduced core package is filled with dry and binder-free sand. Controlled by slight vibration the filling achieves a homogeneous density distribution and it will make an ideal stabilizing of the core package. The forces that occur during the filling of the mold will be lead off without deformation of the outer core parts directly by the already applied sand filling in the direction of the green sand mold. Since the behavior of the uplift is limited by this kind of power absorption, the ventilation can be led through the binder-free sand. The result is a complete separation of liquid iron and the green sand mold, if the sprue with descent is integrated in the core package. Figure 1 shows a comparison of the current practice and the additional process described above.
After sufficient cooling the binder-free sand will be returned to the filler sand circulation by a simple turn of the flasks. The mutual contamination of the other two sand systems is achieved by removal of the upper box and the turn-over of the casting and the core sand.
The process alternative to core packages ready for casting in Figure 2 consists again of a filling with binder-free sand, a transport frame and a weight for the casting procedure. The transfer of the casting energy towards the frame and the weight on top of it, is carried out by the homogeneous sand filling and therefore the core package can be performed weight-optimized.
Also in this version, the binder-free sand is separated early from the casted core package.
In both process versions a weight minimization of core packages is made possible by implementing a filler sand circulation, and in subsequent thermal isolation of the casted core packages, a temperature equalization takes place between the casting and the core sand, which is plotted in the diagram 1 above the core sand-iron ratio.
Even when the sand of the core package is heated inhomogeneously under conditions of application and in dependence on the position to the casting and its formation, it is possible already for small core sand/iron ratios to rise the core sand to a temperature level, which meets the requirements of the complete regeneration.
Reduced application of binders by weight-reduced core packages, volume and temperature-induced reduction of regeneration costs, resource savings and environmental reliefs are essentially defining characteristics of the introduced process versions, some of them consist of patents, or corresponding patent applications.
Dipl.-Ing. Frank Iburg
Dipl.-Ing Gelson Montero