Comparing twin screw extrusion versus single screw extrusion is an important exercise for most decision-makers who want to invest in extrusion technology. In the checklist below, based on our long term experience in providing twin screw extruders for a wide range of applications, here is a checklist of the main processing advantages of the Clextral twin screw extrusion technology.
Co-rotating twin screw extruders versus single screw extruders show :
- Remarkable mixing capability, due to the interpenetration of the screws and the broad diversity of specialized screw designs (such as reverse screw elements, kneading blocks, gear mixing elements, etc.) which allow the extent of shearing/mixing to be precisely adjusted; hence leading to control the degree of mixing in regards to mixing intensity and mixing quality (dispersive versus distributive). Conversely, mixing capability of single screw extruders is very limited, and any flow restrictions to enhance mixing through special screw designs lead to depress the extruder throughput.
- High level of process flexibility, due to throughput and screw speed independency, and capability to handle multiple processing functions in series (such as melting, mixing, cooking, venting, cooling, etc.) in one single extruder. Conversely, with single screw extruders throughput and screw speed are dependent, and screw designs with multiple processing functions in series are restricted.
- Better control of process parameters, that are: narrower residence time distribution, lower dispersion of shear rates and strain, higher convective heat transfer, accurate control of temperature profile; hence leading to much better control of shear-time-temperature histories in the extruder, to much wider range of mechanical energy inputs, and so to more consistency in regards to material conversion and product quality.
- Higher process productivity, due to positive pumping action of the screws, ability to handle wider varieties of raw materials and mix formulations including complex recipes, screw speed-aided compensation of screw wear (with single screw extruders process performances invariably decrease when screw wear increases), lower downtime.
- Higher economical opportunities and business potential than single screw extruders, owing to higher process flexibility and productivity, to produce wider range of end products, to convert materials and handle product quality more consistently, to compensate the effect of screw wear through screw speed adjustment.