Page 36 - Plastics News October 2019

FEATURES

pretreated air that has a lower dewpoint than the DQ\ SDUW RI D V\VWHP ,W VKRXOG DOZD\V EH XVHG ZKHQ ÀOOLQJ
surrounding ambient air. a drying hopper to prevent ambient air from leaking into
the drying hopper and dryer air loop. A vented sequence
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air is eliminated. Dried material quality is improved and valve can be used in any area that is not near a drying
part defects are reduced. Even minimal air from outside KRSSHU 7KH EHQHÀW RI D YHQWHG VHTXHQFLQJ YDOYH LV
can contaminate the material. Closed-loop systems are WKDW LW ZLOO SURYLGH D VKRUW EXUVW RI DWPRVSKHULF ÀOWHU
used for materials that are sensitive to moisture regain in FOHDQLQJ DLU DFURVV WKH ÀOWHU ZKHQ WKH YDOYH VKLIWV DIWHU
short periods of time and must be contained to prevent or WKH FRQYH\LQJ ÀOO VHTXHQFH 7KLV LV D FRVW HIIHFWLYH ZD\
minimize the possibility of moisture regain after drying. WR NHHS WKH ÀOWHU VFUHHQ FOHDQ DQG UHGXFH PDLQWHQDQFH
on general conveying systems. The effectiveness of this
If a purging system is desired, then care must be taken in process depends on pressure differential and material
sizing the conveying pump. The time it takes to convey TXDOLW\ :KHQ FRPSUHVVHG DLU EORZEDFN LV XVHG IRU ÀOWHU
a “shot” of material from the source to the destination cleaning, a non-vented sequence valve is typically a
must be considered. The size and capacity of the vacuum better option because it will keep the pressurized burst
pump must be large enough to allow for the “lost time” of compressed air inside the vacuum chamber to provide
when the vacuum pump is conveying only the one shot of D PRUH HIIHFWLYH ÀOWHU FOHDQLQJ EXUVW
material in the line and the remainder of the time when
it is not conveying any material (lost time/lost capacity). One of the easiest ways to enhance an existing central
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capacity when purging systems are utilized, depending WKDW SURWHFWV WKH SXPS EORZHU ,I D ÀOWHU LV WRR VPDOO DQG
on the distance of the source material from the process. not cleaned properly, it can result in excessive pressure
drop that reduces the overall conveying potential and
Know your Receivers & Filters increases the brake horsepower required to run the
system.
Selecting the correct type and size of vacuum receiver
for the process is important to keep the conveying 0DNH VXUH WKDW WKH ÀOWHUV DUH ODUJH HQRXJK IRU WKH EORZHU
system running properly. Verify that the receiver is XVHG RQ WKH V\VWHP DQG KDYH WKH FRUUHFW ÀOWHU PHGLD IRU
large enough to match the throughput of the process the type of material being conveyed. Check to see that all
machine. Replace undersized receivers with larger- dust-holding containers are serviced regularly to prevent
capacity vacuum receivers to reduce the total number RYHUÀOOLQJ 7KLV ZLOO DOVR SUHYHQW GXVWLQJ QHDU WKH SXPS
RI ÀOO F\FOHV SHU KRXU RQ WKH V\VWHP 7KLV ZLOO LPSURYH DUHD $OO ÀOWHU PHGLD VKRXOG EH JHQXLQH 2(0 TXDOLW\ DQG
WKH RYHUDOO HIÀFLHQF\ E\ HOLPLQDWLQJ VRPH V\VWHP GHOD\ JDVNHWV VKRXOG EH SURSHUO\ VHDWHG LQ WKH ÀOWHU KRXVLQJ
time. Most vacuum receivers range in size from 0.1 to WR SUHYHQW OHDNDJH SDVW WKH ÀOWHU WKURXJK WKH EORZHU
6 ft³ capacity and are available with options that will which can cause blower damage.
enhance the performance of the system. Adding the
correct option will allow the receiver to operate more 8VLQJ D ODUJH ÀOWHU ZLWK PHGLD WKDW KDV JRRG UHOHDVH
properties, and setting the filter-cleaning pulse
HIÀFLHQWO\ 6RPH RSWLRQV LQFOXGH ZHDU ZUDSV IRU DEUDVLYH parameters for the dust loading of the system will reduce
PDWHULDOV DLU RSHUDWHG GLVFKDUJH JDWHV EXWWHUÁ\ YDOYH system pressure drop, keep the general area cleaner,
discharge gates, vibrating pads, 70° cone options for and reduce the overall power consumption of the entire
KDUG WR ÁRZ PDWHULDOV VSHFLDO ÀOWHU RSWLRQV DQG D conveying system.
variety of level sensors.
Angel Hair, Streamers & Dust
7KHUH DUH SHOOHW UHFHLYHUV ÀOWHUHG UHFHLYHUV ÀOWHUOHVV
UHFHLYHUV F\FORQH UHFHLYHUV KRSSHU ÀOWHU FKDPEHU If your conveying system has angel hair or streamers, the
combination receivers. Each is designed to be used to simplest thing to do is to re-sheave the vacuum pump.
FRQYH\ GLIIHUHQW PDWHULDOV ZLWK GLIIHUHQW ÁRZ SURSHUWLHV This will recalibrate the air velocity to the material
8VLQJ WKH FRUUHFW W\SH RI UHFHLYHU FRQÀJXUDWLRQ ZLOO properties and reduce the softening and streaking of
improve your overall conveying system performance. the material against the walls in the piping. If there is
excessive heat buildup in the piping, then there are times
Using the correct vacuum-sequencing valve with the
receiver is important for efficient central system when re-sheaving is not the answer. In those cases, the
operation. A non-vented sequencing valve can be used in streamers can be collected using an angel-hair collection

Plastics News October 2019 36