Screen Mounting
KOENEN has designed a mounting system,
which guarantees optimal uniformity
and solvent resistance to the
mounted screen. The optimum screen
mounting parameters have been
determined for each type of fabric,
whether stainless steel or polyester
fabric . Only selected fabrics
with perfectly round wires are
used. This is the reason for
the longer service life of our
screens. "Oval/non-circular" wires
may tilt during printing. Another
reason for our optimum service
life is the long dwell time of
the fabric in our mounting system
allowing a uniform state of wire
tension to stabilize reducing
crimping. We mount our screens
at angles of 22,5°,
30°, 45° oder 90°. The special bonding process used is solvent and heat
resistant. The glue can be removed from
the bonding surfaces without
mechanical abrasion. This allows
screen printing frames being
mounted as often as required
without loosing their plane parallelism.
The mechanical properties of stainless steel fabrics and their effects on the tensioning rocess
Stainless steel fabrics can tolerate higher tension due to the higher yield point. A higher screen tension allows a smaller off-contact distance. The smaller the off-contact distance the higher the registration accuracy.The diagram shows the strain curve characteristics of our stainless steel fabrics. Until the yield point is reached, the strain increase is linear with the increasing force. In this range the strain is elastic (recoverable), i. e. the fabric returns to its original position when the load is removed. If this yield point is exceeded the fabric will be plastically deformed (irreversibly).
With our fully automatic, computer-controlled tensioning process we ensure that the fabric is always only tensioned within the elastic range. Through optimum utilization of the strain curve characteristics we can achieve a reproducible screen tension of ± 1 N/cm and subsequently maximum screen life during the printing process.
Conclusion
The yield point must never be exceeded during the printing process. An elastic strain reserve for the printing process must be taken into account when mounting the fabric onto the screen printing frame.The recommended screen tension for our stainless steel fabrics varies with the print requirements. The diagram shows that depending on the selected tension range a working reserve 0.1 % to 0.5 % remains for the printing process.
Frame selection
Our stainless steel wire fabrics are tensioned significantly higher than synthetic fabrics. The screen printing frame must absorb and hold the fabric tension. It must therefore be dimensionally stable to achieve reproducible print results. Metal frames must be used for KOENEN stainless steel wire fabrics. We recommend cast aluminum or stainless steel profile frames if the fabric is mounted to the frame.Calculation principle for frames for thick film technology
Screen manufacture
After thorough degreasing, the stainless steel wire surface provides excellent adhesion for all types of films and emulsions. KOENEN stainless steel wire fabrics can be exposed to high intensity light sources with minimal light undercutting.Printing (off-contact distance and squeegee pressure)
The required off-contact distance depends on a number of factors such as fabric tension, paste viscosity, and squeegee speed as well as the print image itself. Therefore no generally valid recommendations can be given except: Always begin with the smallest possible off-contact distance. If the paste fails to release neatly from the screen, increase the off-contact distance by small increments.Printing accuracy
If the registration accuracy does not meet requirements despite a minimum off-contact distance, the print result can be significantly improved by increasing the frame size while maintaining the original print image size.Further details you will receive upon request.
