Home > MacroLetter > 10.1 - Spring 2006 > Exfeed Exchangeable Extruders

Universal Extruders with Exfeed Exchangeable Sleeve in the Extruder Feed Throat

Today, mostly in film extrusion, single screw extruders are classified as smooth bore or grooved feed extruders. Generally speaking, they serve the same purpose, but both have their own unique advantages.  They convey bulk material into the screw channel, compress the resin from bulk solid density to its liquid density by friction and heating called melt. Then the melt is mixed by one or various mixers to produce a homogeneous mass with a desired pressure.

In smooth bore extruders, the axial flow to move the solids forward is very low at the feed throat due to the low frictional forces at the smooth barrel wall. With little pressure created at the feeding section, the solids must be then compressed and melted at the compression section to produce pressure to overcome the back pressure created in the screen changer, adapter and die.

In grooved feed extruders, the feed throat is equipped with axial grooves in rectangular, trapezoidal or hemispherical shapes. The grooves are normally reduced in size in the axial direction. The grooves will dramatically enhance the frictional effect between the solids bed and the barrel wall to promote axial flow. To avoid early melting and negatively affecting the effectiveness of solids conveying in the feeding section due to high frictional effect, intensive cooling must be applied to the feed throat to remove the frictional heat.  Due to the high friction created in the feeding section, the screws are normally designed with constant feeding depth and have a depression in the middle section to bring the pressure down to a desired
level to overcome the downstream pressure. Due to the ability to feed efficiently, groove feed extruders typically produce 40% - 50% more output than smooth bore extruder for the same diameter.

In today's market, most smooth bore and grooved feed extruders are designed quite differently, due to the cooling and the grooves of the feed section.  If one has a smooth bore extruder and wants to convert it to a grooved feed extruder, the task is quite complex or almost impossible. Macro Engineering has introduced a new feed section for its MacroPlast extruders that allows their conversion from a smooth bore to a grooved feed or vice versa.  The new feed section, named Exfeed for “exchangeable extruder feed” section will come standard with every MacroPlast extruder (Figure 5).  Customers will have the option of buying a MacroPlast extruder with an Exfeed section retrofitted as smooth bore or grooved feed.  Should their product range change in the future, the extruder can be converted from one type to the other in three to five hours.