Grooved feed throat

The solids conveyance rate strongly depends on two frictional interactions  

By maximizing feed/barrel friction and minimizing feed/screw friction, solids conveyance is maximized. Typically, a threefold increase in extruder output is obtained using a grooved feed throat instead of a smooth one at the same screw speed. 

In addition to increased output, grooved feed throats have a couple of other benefits. A decrease in output variation (i.e., less surging) often results from creating high barrel friction. This is because of a decreased sensitivity to fluctuations in two common variables  

slippery materials such as very high molecular weight polyethylene are often easier to extrude with this system as the grooves catch the pellets allowing the screw flight to force them forward. 

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Figure 3 J Grooved feed throat used for high output systems...

With respect to screws for blown film extrusion, there are specific design objectives in addition to the general ones mentioned above. Because blown film extruders often utilize a grooved feed throat, the conveyance rate of pellets is generally very high. Therefore,... 

For blown film extrusion, particularly with polyethylene, the most common technique for preventing variations in feeding is to use a grooved feed throat. This component... 

Does it have a grooved feed throat on the barrel ... 

You should know specifics as to the barrel, if it is lined type of lining, has a grooved feed throat, type of barrel heating and cooling, voltage of heater bands, number of zones on the barrel, location of thermocouples, and does it contain a melt transducer to read the extrudate actual temperature. 

In some cases the feed throat has shallow grooves machined into the internal surface. The purpose of these grooves is to promote a higher feed rate down the barrel. Because of the high-energy input into the solids here, throat cooling is even more important... 

Extruders equipped with grooved barrel sections often have a specially designed feed throat section to accommodate this grooved section. A schematic feed throat section is shown in Fig. 3.12, where the effective length of the grooves may range from three to five diameters. 

Since the groove depth can be adjusted to zero depth, the feed throat can be easily cleaned out upon material change-over in other words, no material can get trapped in the grooves. 

Disk Feeder n A horizontal, flat or grooved, rotating disk at the bottom of a hopper feeding a continuous extruder that controls the feed rate by varying the speed of rotation of the disk, or by varying the clearance between the disk and the scraper that directs the feed from the disk into the feed throat of the extruder. 

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