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IndustryInsight
6

Januar y 2019 Why Pneumatic Conveying

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Handling Requirements

Nick Hayes
NHayes@volkmannusa.com

PROTECT YOUR As additive manufacture (AM) matures as a production
A
process, it requires some serious considerations to enable
clean, safe, and efficient handling of these dense metal
powders through the complicated process of loading for
PROCESS & use, re-use and screening. These include:
1. Loading new, virgin material into the machine. Dense
metal powders complicate this powder transfer. Their
weight dictates using forklift trucks to elevate the pow-
PRODUCT der containers to connect to the inlet of the feed hop-
per and discharge under gravity. Another difficulty is
the need to maintain inert conditions to prevent oxida- Nick Hayes
tion of the metal powder.
2. Unloading excess material from the build box overspill.As production volumes
increase, the current method of “ploughing” the material to the collection hopper
Sanitary 3. Unloading unused material from the build area around the finished component
at the end of the build box will necessitate better collection and handling.
either from within the machine or from an unloading station. With unused ma-
Magnetic terial being as much as 85% of the powder volume within the build box, it is
imperative to find a viable means of removing and repurposing it for future use.
Currently this is done by simple suction of material and vacuum conveying from
within the build box or removing the build box to an unloading station to remove
Separators 4. Screening the excess and/or unused material. All excess metal powder going
the powder.
through the build process needs to be screened to remove agglomerates to be
suitable for re-use. This requires a means of powder transfer to the screening sta-
Choose from a tion and back to the build operation.
5. Blending of used and virgin materials. There are many ongoing studies on the ef-
wide selection fects of blending varying percentages of used materials with virgin materials but
suffice it to say that the need for blending will increase, and methods of transfer
of magnetic to and from the blending unit need to be addressed.
6. Returning the blended and screened material to the AM machine. This process
separators that has the same requirements of the initial loading of material into the hopper.
Pneumatic vacuum conveying is the ideal solution for these processes for
meet or exceed several reasons: The receivers are easily installed on the AM machine or in
common Food association with the screener system; they offer containment of the powders,
keeping the environment clean; and advanced certified systems can accom-
Industry processing modate material with Minimum Ignition Energy values as low as 1mJ with-
out risk of explosion.
equipment requirements for The conveying system design when conveying dense metal powders has sev-
eral key requirements: ease of cleaning, minimal powder retention and high-
sanitation and hygiene. quality filtration to the sub-micron range, as well as vacuum transfer type. Ideally
the vacuum conveying process should be done with a low-velocity, dense phase
transfer requiring a high level of vacuum. This method eliminates abrasion of
the conveying lines and potential contamination of the metal power that can be
caused by lean phase conveying. It requires levels of vacuum between 15 and 22
in. Hg, eliminating systems using side channel (regenerative) pumps or Roots-
type units from consideration.
Vacuum conveyors also offer the advantage of maintaining a smaller footprint
when production expands. One can establish a complete loop with one main con-
veying line supplying powder to several AM machines’ vacuum receivers, while
keeping the bulk material supply in a separate room. The need for fork trucks
within the build area is eliminated. The same is true of the powder recovered
from the operation being transferred to the screening unit. Vacuum conveying
keeps these processes simple as it does not require a metering valve. Rather it
can collect material from the build box, unloading stations or overspill area and
transfer it to screening and further convey it back to a bin for blending or re-use.
Finally, Increased production requires minimized unloading time to facilitate
the next build. The physical nature of metal powders complicates this timing due
to particle and screen aperture size. Screening is typically slower than the actual
unloading time, thereby requiring incorporation of a buffer hopper system to al-
low rapid unloading independent of screening.
Industrial Magnetics, Inc. Nick Hayes is president of Volkmann Inc., which engineers and manufactures high-
888.582.0821 • www.magnetics.com performance vacuum conveying systems, including the PowTReX line for additive manu-
facturing. For more information, call 609-265-0101 or visit www.volkmannusa.com.