A feeder design is required to satisfy following criterions for a given hot spot:
Time required for Solidification process: An ideal feeder should solidify later as compared to the nearest hot spot. This criterion can be explained in terms of following mathematical representation:
Where, is the Mf represents the modulus of the feeder,
Mh stands for modulus of the casting region around the hot spot and
Kf is the feeder design factor.
The value of feeder design factor is required to be higher incase an intermediate section of casting is required between the feeder and the hot spot. It is observed that the modulus of the casting region increases when the feeder is connected. This is affected due to reduction in the area of heat transfer in reference to the feeder neck. Hence, the feeder size is increased.
Feed path : A clear path of feeder is defined in between the feeder and the casting region. Necessarily, for the flow of liquid from feeder to the hot spot, adequate thermal gradients must exist. To attain the above condition, the feeder is required to be designed in a way:.
Feeder volume : The feeder is required to balance the process of solidification shrinkage in the region of hot spot. The feeding efficiency of the feeder is dependent on the feeder dimensions, its shape, and the type of feeder (either open or blind). When the single feeder is associated with various other castings, the feed metal volume condition is probable to fail for larger castings having thin sections.
Thus, the design of the feeder pursues these steps:
- To calculate the modulus of casting region along the hot spot
- To find out the modulus of the feeder on the basis of solidification time conditions
- For choosing the dimensions of the feeder including its shape, value of aspect ratio, on the basis of feeder modulus
- Depending upon the feed path conditions, a feeder neck is designed accordingly
- To reevaluate the modulus of the casting region for a hot spot due to feeder neck and hence, redesigning the feeder
- To test the feed metal volume conditions and hence to increase the dimensions of a feeder system, if required
The design of a feeder system can be evaluated by casting assessments to identify the location and division of shrinkage porosity.Feeder Analysis
Solidification of castings is a non-linear trend, resulting in confront of designing and analysis. It requires an alteration of stage with deliverance of latent heat from a moving liquid to solid periphery. This heat is transmitted from the molten metal to reach the solidified segments of the casting, and finally via mold. This transferring process of heat involves universal modes of heat transfer as: conduction, convection and radiation are involved. The geometry of the castings and molds of cavity affects the analysis of the feeder and make it more difficult.