Roller coverings in the graphic industry should not be a daily topic of
conversation because the fulfillment of the customer requirements is
the responsibility of the Supplier. Compromises in print quality,
increased waste and machine down times are unacceptable in todays
competitive world and can not be afforded by printers.
Thus the innovative concepts and continuous developments of roller
coverings - compounds for the various printing fields such as and
Newspaper Web Offset Illustration Web Offset for both the Inking Units
and Dampening Units that have been developed throughout the years
through active partnerships with worldwide leading machine
Roller coverings for the graphic industry should not be a printers
daily concern, as the fulfillment of all product requirements is the
responsibility of the roller manufacturer.
In today's competitive field, no cost conscious printer can afford to
make compromises in print quality, allow excessive paper waste or
avoidable machine downtimes.
The innovative concepts and developments of our product
line have continuously evolved through many decades of active
partnerships with the worlds leading printing machine manufacturers.
Al Dobowi research team has developed new compounds designed especially
for the extreme demands of newspaper web presses. These compounds
resist the shrinking caused by soy-based inks, which means they can run
longer at the same settings. The frequent resetting of rollers in
newspaper pressrooms is a thing of the past.
As more and more newspapers venture into color printing, they require
more precision from their presses than they have in the past. Al Dobowi
rollers deliver the precision needed for color printing because they
are engineered to the optimum specifications of the press manufacturers. CONCENTRICITY What does this mean?
According to the dictionary, concentric means having the same center.
A very simple definition.
What this should mean to a printer is also very simple: If the rollers
you are using are not concentric, they are defective.
For a roller to be concentric, all parts of that roller must be made
and kept true to the center hole. The original center hole of the
journal is machined into the core when it is manufactured. The rubber
covering is applied and is built to that same center hole, ensuring the
concentricity of the journal to the core to the rubber.
The importance of concentricity in
If you have a roller recovered just once, there is a 20% chance that it
is no longer concentric. The odds multiply each time you have that
roller recovered. During the recover process, your core is handled and
turned on a lathe several times. Each time this is done, there is one
more opportunity for the center hole to be wallowed out. Each time
a bearing puller is used there is a chance of nicking or damaging the
uniformity of the center hole.
Defective (non-concentric) rollers are the underlying cause of many
of the problems that create so much frustration for a printer. If you
have ever spent the afternoon chasing dry-ups you will know exactly
what we are talking about. The lack of concentricity in a printing
roller causes uneven pressure, which in turn causes vibration, which
creates heat. These heated spots then dry up the fluids near them;
thus disrupting your ink and water balance. Premature wear and end- pitting on a roller may also be attributed to the fact that the roller
lacked concentricity. Also, you cannot hope to set this defective
roller correctly if with each quarter turn of the roller, the stripe
size varies anywhere from 1/16th of an inch to 1/8th of an inch.
When you consider that it only requires approximately .006 inch
movement to create a correct stripe, if you set a roller on the low
side and it was out of concentricity by as little as .003 inch you
would be squeezing the high side .009 inch. If you set the roller on
the high side and it is out enough, this will result in winking. Being
out by .003 inch is common on used roller cores; we have seen them out
as much as .008 inch.
Of course, if your running your press at only 5,000 impressions per
hour, you really don't have anything to worry about. However, if you
are a high-speed printer, concentricity is essential to you.