Page 34 - Plastics News October 2019

FEATURES

conveying material and not be wasted. It allows material ‡ +HDYLHU PDWHULDOV PD\ UHTXLUH D KLJKHU DLU YHORFLW\
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Elbows, Air Velocity, System Type ‡ /LJKWHU PDWHULDOV PD\ UHTXLUH D ORZHU DLU YHORFLW\
to minimize material degradation when traveling
There are many different types of elbows available, through the pipe.
depending on the application. Aluminum tubing and
elbows are used for most general conveying applications. ‡ 3DUWLFOH VKDSH DQG ZHLJKW DIIHFW WKH ZD\ PDWHULDOV
Stainless-steel is used for most general, mild-abrasion travel and are picked up in the air stream. For
conveying applications. Specialty elbows can replace H[DPSOH ÁDNH UHJULQG JODVV VWUDQG PDWHULDO DQG
standard elbows to reduce wear and minimize material calcium-carbonate loaded pellets have different
degradation. They can also reduce system maintenance conveying properties and require different
and replacement costs caused by wear issues. Several considerations. These variables may require a
VXSSOLHUV RIIHU HOERZV VSHFLÀFDOO\ GHVLJQHG WR UHGXFH change in air velocity to accommodate the change
VWUHDPHUV RU ÀQHV &HUDPLF OLQHG RU ZUDSSHG HOERZV in material shape and bulk density.
porcelain-lined elbows, heat-treated or nickel-plated ‡ 0DWHULDO FKDUDFWHULVWLFV DQG ÁRZ SURSHUWLHV DUH
elbows can be used for abrasion resistance. Glass elbows learned through testing processes and experience
also can be used for abrasion resistance. They are good with these materials.
for use with engineered resins and especially with glass-
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standard industry value suitable for most resins. On
Tee elbows, blind tees, or similar designs can be used occasion, conveying systems are designed and adjusted
IRU VRIW KDUG RU JODVV ÀOOHG PDWHULDOV ,Q VRPH FDVHV to accommodate the special needs of heavier engineered
there can be extreme pressure drops with these types resins (i.e. calcium-loaded pellet). If an older system was
of elbows. This can reduce the original system conveying designed for a heavier resin and the design parameters
capacity. Carefully review the system design when using have now changed to a lighter resin, then the air
this type of specialty elbow. velocity of the system may be set too high. This can

Air velocity is a very important factor in any conveying create a material problem with dusting (hard materials),
system. Making sure that material is moving at the right DQJHO KDLU VRIW PDWHULDOV RU SLSH GDPDJH JODVV ÀOOHG
velocity in the tube or pipe will ensure that it will be materials).
delivered from the storage or pick-up point to the end To adjust the air velocity for a particular material, the
point or process machine. If material is moving too slowly vacuum pump can be re-sheaved by reviewing the blower
and/or the air velocity is low, the material may have a curve based on the blower manufacturer’s data and
hard time moving in the air stream at the pick-up wand recalibrating the motor/blower rpm ratio. This improves
or the material take-off box. Material may tend to plug WKH RYHUDOO HIÀFLHQF\ RI WKH HQWLUH V\VWHP DQG UHGXFHV
at the bottom of long vertical rises or after elbows. the maintenance on the system components.
Lowering the air velocities while material is moving may The quality of the process can be maximized if the proper
cause the material to fall out of the air stream. Care type of conveying is implemented. In most cases, open-
must be taken that adjustment is done properly with loop conveying is adequate, and no special requirements
considerations for the entire system: need to be considered.
‡ ,I WKH PDWHULDO LV PRYLQJ WRR IDVW DQG WKH DLU YHORFLW\ But when a material has been dried and needs conveying,
is high, this may damage material. some resins are very sensitive to moisture regain. In
‡ ,I WKH PDWHULDO LV VRIW DQG WKH YHORFLW\ LV WRR KLJK VXFK FDVHV WKH SURFHVV ZRXOG EHQHÀW IURP D FORVHG ORRS
angel hair may form. conveying or a purge conveying system. A closed-loop
system minimizes the amount of time the dried material
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is exposed to ambient (outside) air from the time it is
‡ ,I PDWHULDO LV JODVV ÀOOHG DQG YHORFLW\ LV WRR KLJK LW dried until the time it enters the process machine. The
can wear through pipes and elbows material is conveyed from the central drying station
to the process machine using a source of recycled or

Plastics News October 2019 34