Primarily applied in compounding and extrusion processes, continuous on-line blending offers flexible, efficient, and highly accurate proportioning of all ingredients directly at the extruder inlet in both flood-fed and starve-fed applications.
Unlike batch blending, continuous blending necessarily involves proportioning all components in one way or another, whether introduced as a single, dedicated ingredient (resin, filler, etc.), as a composite masterbatch pellet (pre-proportioned minor components in a resin carrier), or the downstream introduction of another recipe component through the extruder barrel).
Illustrated here is a typical continuous on-line blending configuration.
In this approach several gravimetric feeders (usually loss-in-weight) are clustered above the extruder inlet to simultaneously introduce ingredients, each at a rate determined by its assigned proportion of total blend throughput. Although more sophisticated in concept (by dynamically proportioning on the basis of feed rate, not statically on the basis of discrete weighments), continuous blending offers more significant advantages and on-going savings potential in suited applications.
Advantages, Limitations and Considerations
- Offers the flexibility of ‘on-demand’ proportioning and the economy of ‘just-in-time’ blending
- Independent, ingredient-by-ingredient feed rate control
- Avoids ingredient layering of sequential batch blending approach
- Dynamic (flow rate) proportioning at extruder eliminates need for mixing prior to extrusion
- No opportunity for segregation between blending and extrusion
- Eliminates batch blending’s need for separate storage and transport systems for pre-blend
- Compared to batch blending, relatively higher initial equipment cost due to dedicated gravimetric feed rate control for each ingredient
- Timescale of extruder throughput demands excellent short-term feeding performance