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# CALCULATIONS FOR DESIGN OF FEEDING SYSTEM

The feeder must satisfy both of the following two requirements:

## Heat transfer criteria

MC : MN : MF = 1 : 1.1 : 1.2

where MF, MC and MN are modulus of feeder, modulus of casting, and modulus of the neck of feeder atย the junction of casting respectively.ย

For calculation of modulus of an object, see Fig.1 and Fig. 2.

## Feed volume criterion

VF โฅ ฮฑ VC / (ฮต โ ฮฑ)ย

where ฮต is the efficiency of the feeder, ฮฑ is the solidification shrinkage, and VF and VC are volume ofย feeder and casting respectively.ย
For efficiency of differently shaped feeders, see Fig. 3.

The higher of the two values of feeder volume given by equations (1) and (2) satisfies both requirementsย and thus taken as the actual volume of the feeder.

## DETERMINATION OF FEEDER SHAPE

According to Chvorinov, solidification time increases as the volume to area ratio or the modulus, M,ย increase. Thus

where, t is solidification time, and C is constant.

According to eq.(3), a sphere, having the smallest modulus per unit volume, is the ideal shape for aย feeder. But a spherical feeder practically too difficult to mould and consequently cylindrical feeders areย mostly used.ย

For a relationship between casting shape (M) and its solidification time (t) for variousย metals and alloys, see Fig. 4.

## 3. FEEDING DISTANCE

In normal conditions, there is a limit to how far a feeder can feed along a flow path. Up to this distanceย from feeder, the casting will be sound. Beyond this distance the casting will exhibit porosity. For
feeding distance rule, see Fig. 5.

## 4. INCREASING FEEING EFFICIENCY

There are number of ways by which the efficiency of a feeder can be increased. Some of the mostย common ways are:

1. Use feeder head with a higher feeding efficiency
2. Feeder insulation
3. Use of exothermic materials