The Flow Characteristics of a Die

How the Aluminium flows within a die is of great importance. The flow will not be straight

through any die because of the effects of drag / friction within the die and this will have the

effect of distorting the flow. How much distortion to the flow has a direct relationship to

the quality and shape of the extruded profile.

As this is a difficult concept to understand it will be made easier to visualise with the

sketches and diagrams in the explanation. Some basic facts have been listed on which all

Technicians will agree.

These details are true for both Solid and Hollow profiles. It is also true that the effects will

be more pronounced as the alloy is changed from a softer alloy to a harder alloy.

As already mentioned the effects of a recess or for that matter the insides of a " port " will

have the initial effects on the flow of the aluminium. It will generally start to bend the flow

from the area of least resistance to that of greatest resistance. The amount of bending to the

flow is in direct proportion to the amount of resistance encountered. The combinations are

almost infinite, but, factors like the depth and opening dimensions for a recess or port are

all important and the conclusions are self evident for these matters. The friction generated

on the inside surfaces is also a contributing factor, but, not critical as the Aluminium does

not move to any great degree once it has come into contact with the extremities of a recess

or port opening. However, the velocity and pressure are usually sufficient to keep the

Aluminium moving over the surface of the central web and mandrel areas and the

reduction in drag / friction in these areas will pay dividends. The reduction of drag in these

areas will help prevent the nitride layer from being pulled away and slightly reduce heat

and pressure.