Flash dryers are sold in different sizes. The most common size
sold is a heater face of 16 x 16. If the image to be cured
is 14 x 14, there is plenty of heat to cover the image. The
flash dryer must have temperature control so the temperature can be turned
down, and the face of the heater positioned about 1-1/2 to 2 above the
Often screen printers will ask for a larger flash like 18 x 18. In most
cases that is because they do not have temperature control and must position
the heater about 6 above the garment to prevent scorching. However,
the center of the image will get cured before the outer edges. The objective
is to cure all the ink evenly rather than the center more than the outside
Flash dryers are sometimes sold ever larger than 18 x 18, such as 18 x
24 for printing oversized images. Larger heaters cost more to
operate. A 16 x 16 has 256 square inches to heat up. An
18 x 18 is 324 square inches, or 27% larger and more expensive
to operate. The 18 x 24 is 432 square inches, or 69% more
expensive to operate than a 16 x 16.
Flash dryers are available in different voltages. What you want is heat, and heat
is measured by watts. Watts are volts time amps. If you get a flash
dryer at 220 volts, you typically will get more heat. Sometimes that
extra heat really pays off for you.
When buying a flash dryer, safety is a concern with a surface that can be 600 degrees. So
casters are a must to allow the dryer to move when bumped, and a base heavier
than the top to prevent tipping over. The base should be under the platen
rather than be spider legs sticking out that you can trip over when walking
by with a pile of shirts in your arms.
Another major issue when selecting a flash dryer is whether the unit will have an automatic
feature or not. This feature typically is a foot pedal you step on after
printing a color when rotating the platen to the flash position. The
foot pedal provides a signal for the heater to rotate about 90 degrees to position
the heater over the platen. The automatic units come with a dwell timing
device that you set for the number of seconds you want the heat to be
over the garment. After that number of seconds have elapsed the heater
rotates back to the starting position. The starting position is away
from the platen so that inks do not get over cured. However, hot inks
continue to cure. An ink that is tacky or like putty immediately after
the flash cure will continue to cook and might feel drier and a little harder
by the time the ink cools to room temperature.
A flash cure is ideal when the ink is left tacky or malleable like putty, but not hard
and dry. That is normally 6-8 seconds of heat, but in special circumstances
can be longer. However, the time will never be as long as 30 seconds. If
a shop does not have a flash with the automatic feature, there will be at least
30 seconds of heat before the next garment can be printed and rotated.
Frequently a second, third or more colors will be printed and flash cured. The first
color flash cured is being cured each time the garment is flash cured, and
the accumulation of heat can frequently result in the first color being fully
cured. After all colors have been printed, the entire image gets cured,
but inks printed on top of a cured ink will not bond to that first ink. That
is why there are so many shirts with cracked and fading images.
When flash curing transfers, the flash time is shorter, because paper does not have the
insulating value of fabrics. Ink on paper will cure much faster. By
contrast, ink on a thick garment like a sweat shirt, or a garment that is damp
will require longer than normal to bring the ink to a temperature level where
the ink gels turning tacky or soft like putty.
For video information on this subject, see:
Screen Printing Flash Dryers