Free extrusion process is particularly
useful in extruding simple solid round or profiles that are flat strip.
However there is some sort of doubt if it can be used equally for extruding
complex profiles. Here, the tooling costs are more or less cheap. If
parameters like a proper die design, accurate control of air pressure, water
temperature, belt-puller speed etc are properly adhered to then it is quite
possible for free extrusion to provide perfect means for having profiles
with high degree of tight diameter tolerances.
A typical Free extrusion process works like this, the extrusion takes shape
by its entry into a water quench tank. There is a guide plate that controls
water flow and rollers are used to keep the product submerged. This method
is most suitable for small diameter tubing and rod, and other cross-sections
with lesser complications. In case of tubing, to prevent any chance of
collapsing adequate arrangement is to be made so that inside of it must be
vented to the atmosphere or provided with some sort of low positive
pressure.
The die orifice that is used in the process of free extrusion is typically
oversized, this allows a higher drawdown. Low internal air pressure is
introduced in the tube via the inside die ring, this helps to have a more
precise control of the dimensions.
Features of Free extrusion
Free extrusion into water is one of the most efficient ways to manufacture
tubings with small diameter. Some of the features include:
- High production rate that can go up to 137m/min(450fpm).
- Close tolerances around 0.04mm(+0.0015inch).
- Diameters of 3.2mm is also obtainable in tubing.
- Restrained internal stress levels.
Types of Free Extrusion
Free extrusion of tubing generally takes two forms. They are:
- Free Horizontal Extrusion
In this type of Free extrusion, the tube is extruded directly into the
water bath horizontally. This process is shown below:
- Free Vertical Extrusion
In this type of Free extrusion the tube is extruded directly into the
water by using a vertical method. The image is shown below:
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