Selecting a Conveyor Dryer
The considerations for flash dryers apply to conveyor dryers. There
are other considerations as well.
If three phase service is available to the building, and the conveyor is designed as
three phase, you cut your power bill by 41% from the power factor.
If the conveyor has temperature control, ask if the temperature control switch is
solid state or if the current is going through the switch. Switches designed
for the power to go through the switch are typically rated for only 15 amps,
and the heater may be drawing that many amps. Operating at the maximum
rating will most likely burn out the switch. If the conveyor is located
in a rural or remote area where the local utility does not control voltage
fluctuations, then the switch will have a shorter life. Turning the switch
on from the high heat end of the spectrum allows the current to rush in the
circuit shocking the switch. A smarter practice is to turn the switch
on from the low heat end to let the current to flow before turning the heat
up. Of course, a solid state arrangement with relays avoids these risks
to the conveyor failing. Controls for heat and belt speed should be located
away from heat for a long life.
Conveyor hoods should be fully insulated so you, your associates and customers do not
get burned touching the hood. If water based inks are being run through
the conveyor, the inks must be dried first, and remaining pigment cured second. If
inks are dried and cured under one hood, there must be a lot of air removed
to remove the moisture, and that will make the conveyor inefficient. The
conveyor should be designed with separate sections for drying and curing.
The conveyor must have doors, or you are wasting heat going out the doors. Such dryers
without doors are not effective curing inks near the doors. You want
the inks subjected to heat for as long as possible for the heat to penetrate
through the ink film.
A DC motor will be quiet, but an AC motor will have an irritating whine.
Four point tracking allows adjusting the belt tracking from both ends of the dryer. Without
four point tracking, getting a belt to track straight can be very frustrating.
The belt must be fiberglass, Teflon coated, with the edges sewn and sealed. Nylon
belts, by contrast, stretch with heat, start to wander, and then end up frayed
along the edges. Nylon belts will get holes and have to be replaced. A
fiberglass belt that tracks straight will last forever.
Your business will expand. Will your conveyor expand with you, or will you have
to sell the dryer to buy a larger dryer?
The conveyor should be placed within 20’ of a wall or ceiling where the fumes will
be vented. If that is a side wall, the bend in the vent pipe or tube
should be gradual and not 90 degrees. Like a garden hose, water will
flow better through a gradual bend than 90 degrees. If the distance
is greater than 20’, then a booster fan will be needed to assist the
natural convection of the conveyor to push the lint out of the shop. Too
much of a push will make the conveyor inefficient. The fan could also
be an induction fan at the wall or end of the vent tube.
When you buy something new the last thought on your mind is probably maintenance, but
ask anyway. For example, if the hood has to be removed, what is involved? Some
companies pop rivet the hoods on making them very difficult to remove for maintenance.
For additional reading on this subject:
To see a video on the subject:
“Screen Printing Conveyor Dryers”