Page 60 - Plastics News September 2024
P. 60
TECHNOLOGY NEWS
est gen- eration. In an extremely efficient way, ing of deposits and enables the change of poly-
this melt blender continuously exchanges cen- mer or color within a very short period of time.
tral and boundary flows, thus yielding high mix- However, only if the blender housing is exactly
ing performance at short in- stalled length. What tuned to the melt blender and its interfaces an
is more, the parabol- ic flow profile approaching opti- mum cleaning behavior can be achieved.
the extruder outlet is converted effectively into a It is a known fact that the devil is in the details,
plug flow. Correspondingly, the melt dis- charged which is why it is recommended to purchase
from the melt blender flows at perfectly constant melt blenders as system solutions including their
speed and tempera- ture. This is the basic pre- specially de- signed housings and suitable con-
requisite for opti- mum process control. Thanks nection adapters.
to the pro- cess window considerably enhanced,
set- ting process parameters is much easier and Mechanical strength is a critical as- pect of melt
faster. Even with high extruder out- put rates, blenders. Under extreme cir- cumstances, e. g.
layer thickness tolerances, sur- face qualities and start-up after a short- ened heating phase, in-
other quality character- istics can be adhered to correct lay-out or insufficient design of melt
within the ranges defined. Additionally, distribu- blenders may even lead to destruction of the
tion of addi- tives and color pigments within in mixer structure, as well as of downstream com-
the melt is far more homogeneous. This can, for ponents such as feed blocks, dies and cal- ibra-
example, improve the protective ef- fect of an tion units. This is why melt blenders must have a
UV stabilizer added as a master- batch, or may robust design and must be made of correspond-
allow for lower dosage. To provide for optimum ing high-quality ma- terials by suitable produc-
benefit of the melt blender, it should sit at the tion methods. While, in industrial practice, one
end of the pro- cess line, if possible, i.e., right in always starts from the worst-case scenario, it
front of the die or feed block. is recommended to use melt blenders made of
highly rigid materials and with very thick-walled
Good Cleaning Behavior and High Strength structures only, as can be seen in the Title figure.
When choosing a melt blender, it is cru- cial for Retrofitting Demands
the unit to have outstanding self-cleaning prop-
erties, in addition to good mixing performance. In particular, when retrofitting an extru- sion
This is to make sure the flow passes homoge- line with a melt blender, the space available is
neously through the entire blender, in or- der to often limited. Highly efficient mixers with short
prevent deposits that will increase pressure loss installed lengths and low pressure loss have the
and require additional cleaning. The monolithic edge over larger units here. In most cases, such
structure of the patented SMB plus melt blend- types of mixers can be integrated very easily
er raises the bar in this respect. Extrusion trials into the existing plant, without having to displace
have shown that a red colored polypro- pylene the extruder or cool- ing line. If using pressure
is 100 % removed by a subsequent colorless PP drop-opti- mized melt blenders, the extruder is
after a cleaning time of only 5-6 times the melt usually able to make up for the addition- al pres-
blender volume (Fig. 2). Following this in-line sure drop without problems. If re- quired, an ad-
cleaning, no traces of red color could be found, ditional melt pump is very helpful here, but, in
not even when disassembling the blender. This fact, is rarely necessary.
op- timum self-cleaning behavior prevents build- Source – Plastics Technology
60 62 PL September 2024
PLASTICS NEWSASTICS NEWS
September 2024
