Understanding Shot Volume Factors…

I received this interesting question from a blog reader the other day…


I recently came across this term: Shot Volume Factor and the units are in^3/in (cubic inches per inch). 

I speculate that it is some kind of volume conversion number that when used will allow a user to quickly convert shot size from machine to machine. 

What is this term and how is it calculated?

My Response

As the screw travels forward, it displaced a specific amount of volume as it travels forward. This factor is a machine-specific value which converts the linear displacement of the screw into the volume displaced within the barrel. 

The shot volume factor can be calculated by determining the

 surface area in front of the screw.

Just multiply pi times the radius squared: π*(r^2)

Imperial Example:
1.2 inch diameter screw

π*(r^2) = (3.14)*(0.6in)*(0.6in) = 1.1in^3/in

Metric Example:
30mm diameter screw

π*(r^2) = (3.14)*(15mm)*(15mm) = 707mm^3/mm

Additional Thoughts

Once determined, just multiply the distance the screw travels times the factor to determine the actual displacement of the screw.

Adversely, if you know the estimated shot volume, just divide the volume by the shot factor to estimate the linear displacement necessary to fill the mold.

Calculating this for each machine can be a great way to help your employees quickly identify the differences between each machine.


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