Ceramic Anilox rolls don’t wear out, they carry more
ink than a comparable cell count chrome anilox roll and, most
importantly, permit the use of doctor blades. Gradually, the
superior print quality of the ceramic anilox roll is lost as its
cell volume is reduced by the buildup of a microscopic film. The
lower effective cell volume results in reduced color density and
loss of print quality. Other visible effects of the film are light
streaks, wavy lines, low color spots and even the streaks that were
previously attributed to gear chattering.
Ultrasonic cleaning is now recognized as being the most successful
method of removing ink, coatings and adhesives from engraved
rollers. However, it is extremely important to select an ultrasonic
cleaning system which is specifically designed for ceramic rollers
and a system which will clean without damaging the fine screen cell
walls.
Ceramic anilox rolls cannot be properly cleaned with conventional
mechanical methods. The ceramic cell cavities are far smaller than
even the finest brush bristles. Although blast systems can clean
coarse anilox rolls, only ultrasonic cleaners can thoroughly and
safely clean the fine count anilox rolls being used today.
As ultrasonic cleaning of ceramic laser engraved anilox and gravure
rollers gains increasing acceptance as the preferred method of
frequent, reliable cleaning, so too have the fears been voiced by
printers who have experienced cell damage. To cut through the
confusion an assure the print industry that ultrasonic cleaning can
be undertaken with complete confidence, Rajendra Pal, managing
director of TRANSONIC™, explains how the most common problems
experienced to date may be successfully overcome.
Firstly, it must be admitted that conventional ultrasonic tanks -
even those that claim to feature a frequency modulation system - can
prove unsuitable for the safe cleaning of complex ceramic anilox
rollers. The danger lies in damage that may be caused by the
creation of hot spots and dead spots within the cleaning liquid -
known and nodes and anti-nodes. These occur when sound waves
generated at the transducers, travel to the top of the liquid and,
on returning, collide with the next wave. This creates a hot spot of
intense cavitation, below and above which there is formed an area of
less cavitations - a dead spot. These hot spots are potentially
harmful to ceramic anilox roller cells.
In the early days it was common practice to mechanically move
sensitive components up and down the tank - or by rotating a roller
in the tank - and thus attempting to avoid damage. As the frequency
of operation dictates where the hot spot would be, some ultrasonic
cleaning equipment producers tried to design ways of varying the
frequency.
The most usual way was to use the incoming mains cycle to influence
the inductance of the frequency control coil - a system in
widespread use today. However, this approach is not entirely
acceptable in that frequency may be affected by main fluctuation and
power surges, leading to lack of stability.
To eradicate this entire problem of hot spots, TRANSONIC™ bases
all its Transonic ultrasonic cleaning systems on the incorporation
of an RKT SW generator of a patented design, unique to the company.
It provides a pre-determined frequency sweep circuit, operated by
its own, independent, low voltage supply, which maintains uniform
distribution divorced from line fluctuations. This results in the
hot spot being moved up and down 100 times a second, thus preventing
damage occurring due to a power concentration in one point of the
roller.
It is also essential to ensure that the transducers do not run hot
internally as this could lead to uneven distribution and components
failure. Again, Transonic™ has solved this potential hazard by
commissioning high quality bronze conductors, purpose-built to a
registered design, and employs special assembly methods, which
prevent internal heating problems.
All Transonic™, Transonic cleaning systems provide frequency of
operation of 30 kHz +/- 2, with secondary bar frequencies 10 -100Hz.
If simple precautions are taken to study the technical
characteristics of an ultrasonic cleaning system and to insist on
the provision of pre-determined frequency sweep circuit, then no
more effective or safer means of ceramic anilox roller maintenance
can be found. Cell damage - which quite rightly, greatly concerns
both printers and roller manufacturers - can be considered a risk of
the past and this cost efficient, sure and successful method may be
chosen with complete confidence
Multi
Stage Aqueous Ultrasonic Cleaners
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