Causes of non-uniformity in feeding

The compound fed into extruder may be a ribbon, pellets or premixed powdered rubber. The ribbon is usually cut from sheet taken up from the sheeting mill-roll. The width of the ribbon is uniform but the thickness may be irregular. This is one of the potential 

For a given extruder and die combination the output rate is determined by the screw rpm and the properties of the compounds affecting reverse flow. However, this is only when the channel is full. For the starved operation, the insufficient feeding rate may result in the non-steady operation. 

In summary, there are a number of causes for disturbing the steady operation, which may not be completely eliminated. The result is not only the non-steady output rate but also non-uniform shrinkage (die swell), non-uniform surface appearance and other irregularities. Therefore, various homogenising devices are used, some as a modification of screw, others as homogenisers at the screw head or as postextrusion devices. 

Reprinted with permission from K. Okubo, Journal of the Society of the Rubber Industry, 

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