Extrusion 4-2017

Portfolio of Pelletizers has Systems for

every Type of Operation

By Frank Asmuss,

global product manager,

BKG

pelletizing systems,

Nordson Corporation

There exists a vast potential for

pelletizing systems, driven by

strong global growth in con-

sumption of plastic products and

a gathering trend toward meet-

ing this demand through loca-

lized polymer production. In

countries where plastics con-

sumption is growing most

rapidly, more and more raw

materials for plastic products

will come from domestic resin

manufacturers, compounders,

and recyclers.

s the leading supplier of underwater pelletizing systems,

Nordson Corporation is prepared to meet the full range of

requirements that the huge and diversified global market can

be expected to present. These may range from basic systems

calling for minimal investment, to sophisticated and automated

production lines, to fully engineered turnkey operations for

high-volume producers serving multinational markets. Nord-

son’s BKG

range of underwater pelletizing systems has a

tiered structure, with different types of equipment available for

different levels of cost and sophistication.

In addition to a comprehensive portfolio of underwater pelletiz-

ing systems, Nordson offers related melt processing compo-

nents as part of its Nordson Polymer Processing Systems (PPS)

family of brands. These include Xaloy

screws and barrels for

extrusion and injection molding lines, BKG

melt filtration sys-

tems, melt pumps and polymer valves. Working with plastic

producers and extrusion machinery OEMs, Nordson is prepared

to recommend and design fully integrated underwater pelletiz-

ing production operations.

Underwater pelletizing: how it works

In underwater pelletizing, molten thermoplastic is extruded or

pumped through a die body containing holes arranged in a cir-

cular pattern. The downstream die face is completely encapsu-

lated in water, and as the molten material exits the die holes, it

is immediately cut by a rotating cutter and quenched by the

flowing water. The molten material solidifies, taking the shape

of a sphere to minimize surface tension, thus creating a round

pellet. These round pellets are then transported by water flow

away from the cutting chamber and into a secondary step

Polymer Processing

Extrusion 4/2017

Polygon Filter & Water Tank

(Images: Nordson)

where water and pellets are separated, most commonly by

means of a centrifugal dryer. After exiting the dryer, the round

pellets generally have very little surface moisture and are ready

to be packaged in a container or transported to another pro-

cess, if applicable.

A consistent melt pressure is critical to maintaining a uniform

pellet shape as well as avoiding freeze-off of the polymer in the

die holes. In order to ensure the necessary constant melt pres-

sure, Nordson can supply a BKG

melt pump that rotates at a

constant speed, metering a constant volume of polymer. This is

an example of how customers benefit from the depth of pro-

duct offerings within the Nordson PPS portfolio.

One advantage of underwater pelletizing over the alternative

method of strand pelletizing is that it can be used with materi-

als over a wide range of viscosities, whereas very low-viscosity

materials cannot form a strand, and highly filled materials cre-

ate fragile strands. In fact, underwater pelletizing can be used

not only for all thermoplastic polymers but also materials which

behave like thermoplastics. Some examples include: polyole-

fins, styrenics, PET, polyamides, PMMA, polycarbonate, TPEs

and TPU’s, hot-melt adhesives, natural resins (e.g. chewing

gum), PVC, and synthetic resins (e.g. epoxy resin).

The spherical pellets formed in underwater pelletizing flow bet-

ter than the cylindrical pellets created in strand pelletizing, re-

melt with less energy, and package more densely. All three dif-

ferences result in energy savings in comparison with strand pel-

letizing. In addition, underwater pelletizing systems are more

compact, and because they are totally enclosed systems, no

dust or vapor emissions take place.