It is probably intuitive for most of us that if the thickness of an extruded tube is too thick, speeding up the puller (haul-off) will thin out the wall and visa versa. This is indeed what extrusion technicians do during the "sizing process" when they "dial in" wall thickness. Experienced technicians can often achieve "size" within a few iterations of the sizing process. Inexperienced technicians however often find themselves still out of size after many many iterations of the sizing process, leading to piles of scrap and non productive time. How can we take the skill out of the sizing process, and get the inexperienced extrusion technician "up to speed" (yes there is a pun there) right away?

The diagrams above shows two extruded tubes or sheaths. The first shows a tube with the required wall thickness, the second shows the wall thickness we are currently extruding, which in the case shown is too thick. The two simple calculations determine what the corrected puller speed should be to attain the required wall thickness. It normally takes two or three iterations of this calculation to attain the correct size.

These calculations really do work, and new extrusion technicians will surprise themselves at how quickly they can get "up to speed".

Note : The equations are actually an approximation of the true mathematical equation, and that is why more than one iteration is required to achieve size, particularly for gross changes. The simplified math's finds greater acceptance "out on the shop floor" and two or three iterations are not over burdensome anyway.