machinery | Multi-screw extruders Right: Tech-
novel claims its four-screw Quad Screw extruder
evolved from its twin screw designs for
more demand- ing applications
polymer degradation. Energy can be introduced into the material very effi ciently because of the high surface: volume ratio. With the introduction of the company’s new RE1XPV, which has a 100 L/D, a new approach is now possible in reactive extrusion, Bauer claims. The machine can be used for polycondensation reactions for production of specialty polyamides such as PA11 and PA12. Extricom units with an L:D ratio of 100 provide useful residence times of anywhere from two minutes for high volumes up to 15 minutes for low volumes. “In 15 minutes you can do a lot in a continuous reactor,” Bauer points out. Interest is also growing for the use of the RingEx-
truder to produce TPS and TPV thermoplastic elasto- mers. “Customers are interested in our ability to reduce VOCs, as well as the very good dispersion we can achieve,” he says. RingExtruders tend to be more expensive than
twin-screw units, carrying a typical premium of around 10-15%. However, Bauer claims that operating costs are lower, estimating possible savings of 20-30% in specifi c energy input. This obviously brings dividends for users of larger machines. He says maintenance costs should also be lower, due to lower wear on parts. Extricom’s RingExtruder RE is available in two
Right:
Extricom’s RingExtruder
arranges its 12 intermeshing plasticising
screws around a fi xed core
different series, which differ in OD/ID ratios of the screw. On the LT/XP series, the OD/ID ratio is 1.55; on the XV/XPV series it is 1.74.
The planetary roll Planetary roller extruders have been around for many years but indications are that their use is
becoming more widespread. After a single-screw feed section, planetary roller designs have one central rotating spindle with teeth on it in the form of a multiple 45° helix. These engage with opposing teeth on a number of smaller, parallel spindles arranged around its circumference. These planetary gears also engage with teeth on the inside of the barrel and there is space between the intermeshing spindles through which melt can pass, driven forward by the gearing. There can be as many as 24 planetary gears around a single central spindle.
One major producer of planetary roller extruders, Germany-based Entex, points out that passing pressur- ised water passing through heat transfer channels in the central spindle, together with the use of two heating or cooling zones per barrel module, enables very close temperature control. in addition, the contact surface area between the gears and the material being pro- cessed is very large - between fi ve and ten times greater than in alternative compounding systems. The planetary roller extruder was invented at Chemische Werke Hüls in 1953 for compounding PVC. While this is still its primary application area, other applica- tions have developed over the years including compounding of polyolefi ns, ABS, PET, elastomers
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