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An Overview of Options and their Application
The doctor blade appears to be a simple component of the flexographic printing
process but, as often is the case, appearances can be deceiving. The casual user might
wonder what is there to think about, a blade is only a piece of steel or plastic. To
better understand the need for all of the doctor blade options, consider the role of the
doctor blade.
Flexographic printing requires the Dr blade to provide a constant wipe throughout the pressrun, so
that the ink volume carried by the anilox roll to the plate is determined only by the
anilox volume. If the doctor blade is not working correctly, the ink volume carried to
the plate will include the anilox roll volume, plus some amount of surface ink Any sur-
face ink remaining on the anilox roll will be variable and lead to variation in the
printed product. To achieve constant wipe, different materials and edge profiles are
available so that you can better match a doctor blade to the application.
Years ago, there were only a few choices for doctor blade materials and profiles. Today,
the offering of materials, edge profiles, and added coatings has become so extensive that
the converter often needs help from a doctor blade supplier to determine the best blade
for the application. This article will take some of the mystery out of choosing a doctor
blade by providing an overview of the features of the various doctor blade materials and
configurations along with generalized application guidance.
Long before doctor blades were used in flexographic printing, blades made from
various types of steel had been used in other printing processes. Today, steel is still
the material of choice for high quality and repeatable doctoring results in any printing
process. There are bright and blue carbon steels, stainless steel, long life steel,
coated steel, and ceramics. But which steel is right for you?
First of all, bright and blue carbon steels are identical materials that share the same
metallurgical properties and features. The only difference between the two is the
cosmetic blue oxide process that is applied to the steel. It has been rumored that blue
steel was originally chosen for doctor blades, so that when a converter was making a
blade by hand shaping a bevel, he could easily see the bevel he was making as the blue
color was removed. Today, most converters are not making their own blades, so the
advantage of blue steel doesn’t apply anymore.
Carbon steel blades are economical choices when used with short-run process jobs on non-
porous substrates and inks that aren’t very abrasive. They can be used on all anilox
screens along with solvent, water, and some UV inks. If corrosion is an issue, a
stainless steel blade may be a better choice, but use caution when using stainless steel
blades with ceramic anilox rolls as some stainless steel materials have been associated
with plugged anilox cells through adhesive wear.
Long-life steel blades are excellent for use with abrasive inks, such as white inks or
other inks with high percentages of titanium dioxide, or solids and/or rough anilox
rolls. Long-life steels are typically made from tool steel alloys that offer good
resistance to adhesive wear. Adhesive wear is a welding like effect that quickly causes
blades to fail and is also a contributor to anilox roll scoring. Long-life blades are
more expensive than carbon or stainless steel blades, but the benefits they provide
easily justify their added costs when compared to press down time for blade changes
during a run and scored anilox roll repair costs.
Coatings can be applied to steel blades to further extend their life and the life of the
anilox roll. A coating will lower the coefficient of friction between the blade and
anilox roll, resulting in a clean wipe at lower pressures. However, the metal used in a
coated blade has to be the same high quality steel as an uncoated blade, or the blade
will not function properly. Another advantage with coated blades is that they typically
offer enhanced corrosion resistance. Try a coated blade in your application if you are
looking for a little more life, less corrosion, or a cleaner wipe than you are currently
getting from your uncoated blade.
Ceramic blade technology will yield the longest life and comes at the highest cost of all
blade materials. Ceramic blades are typically used with very abrasive inks or where you
are running four-color process work every day with standardized setups. Other
applications may include varnish or coating applications and corrugated applications,
where it could take hours to change a blade.
All of the metal blades discussed can be used for doctoring applications as well as
containment in dual blade flexographic chambers. Metal blades can vary in thickness from
0.004 in. to 0.020 in. and even thicker in some cases. Typical blade thicknesses are
either 0.006 in. or 0.008 in. with more demanding applications requiring the use of 0.010
in. or 0.012 in. thick blades. blades are typically used with very abrasive inks or where
you
are running four-color process work every day with standardized setups. Other
applications may include varnish or coating applications and corrugated applications,
where it could take hours to change a blade. All of the metal blades discussed can be
used for doctoring applications as well as containment in dual blade flexographic
chambers. Metal blades can vary in thickness from 0.004 in. to 0.020 in. and even thicker
in some cases. Typical blade thicknesses are either 0.006 in. or 0.008 in. with more
demanding applications requiring the use of 0.010 in. or 0.012 in. thick blades.
tips for better finishing with steel brushes
Steel wire brushes are a common and essential tool in any metal fabrication shop.
These brushes can be used for a variety of applications, including weld cleaning,
deburring, rust and oxide removal, surface preparation, and surface finishing.
One reason wire brushes are so widely used is that, unlike solid abrasive wheels,
steel filaments will not remove base material or change part dimensions. Wire brushes
clean surfaces in the same manner as sandblasting, except that rather than particles of
sand colliding with the work surface, wire tips make contact with the workpiece. The
combination of good-quality, hardened steel wire tips with the energy of high surface
speeds enables the brushes to separate surface contaminants from base material.
Steel brush
also is versatile, with many different configurations available to meet the requirements
of each application. For example, brushes with long filaments are conformable and able to
follow contoured surfaces, and short trim brushes are fast-acting and suited for severe
applications. Another variable is the fill density: Low-density brushes offer good
flexibility for surface cleaning operations on irregular surfaces, and high-density
brushes produce a fast brushing action and long brush life.
In addition, steel brushes are nonloading. In other words, they do not become clogged
with particles and debris when used to remove paint and similar coatings.
Perhaps because wire brushes are such a familiar item, they are easy to overlook and
often receive insufficient attention. However, five tips can help you improve the
performance and life span of your wire brushes.
1. Use the Highest Safe Speed
Power wire brushes, like cutting tools, operate most effectively when the speed and
pressure of the operation properly match the demands of the application. In most
operations, using the highest speed with the lightest possible pressure will ensure the
fastest brushing action and longest brush life.
Increasing brush speed to the highest safe speed increases the face stiffness and
brushing action. A fine-wire brush rotating at a high speed often produces the same
results as a coarse-wire brush rotating at a slow speed, but it generally lasts longer.
Therefore, you will achieve the lowest production costs by using the finest wire that
will do the job.
If the brush speed is insufficient, frustrated operators typically apply more
pressure (see Figure 1). However, excessive pressure causes overbending of the filaments
and heat buildup, resulting in filament breakage, rapid dulling, and reduced brush life.
Instead of applying greater pressure, try using a brush with more aggressive action,
such as one with a larger filament diameter and/or a shorter filament trim length, or one
with a knot type instead of crimped wire. Or you can try increasing brush surface speed
by increasing rotations per minute (RPM) or brush diameter.
You'll need to determine the correct operating speed for each application. For
safety, it is imperative never to exceed the maximum safe free speed (MSFS) or RPM rating
that the manufacturer publishes for each type of brush.
Safety Considerations for Robotic Cleaning Machines
This year, facilities are using automatic
floor scrubbers 24% more than they were last year1 to meet a higher demand for cleaning.
As facilities continue to invest in robotic cleaning machine, and more new technology arrives on
the market, safety is top of mind. It will continue to be important to maintain the
strictest safety measures in the way buildings are cleaned as well as how autonomous
cleaning machines are programmed, operated and maintained. This toolkit will address
safety issues introduced by the adoption of robotic cleaning machines and some of the
standard operating procedures, protocol and features that can help improve safety.
A closer look at OSHA’s guidelines for
robotics safety
The Occupational Safety and Health
Association (OSHA) has been training inspectors to look for robotic safety issues in all
sectors of industry for the past three decades2.
More recently, OSHA published Guidelines for Robotics Safety, a
technical manual intended for operators to learn more about potential hazards as they
work together with robotic machinery. According to this guide, OSHA categorizes the six
most common causes of robotic safety hazards:
Human errors
Control errors
Unathorized access
Mechanical hazards
Environmental hazards
Electric, hydraulic, and pneumatic power sources
With these categories in mind, we’ve prepared the following
recommendations to help equipment purchasers and facility maintenance workers find
autonomous cleaning machines that have the necessary safeguards in place to ensure a safe
working environment between humans and robots.
Conduct a risk assessment.
A risk assessment is the cornerstone of any new work plan that
involves robotic machinery, including autonomous cleaning equipment. Work with your
cleaning equipment distributor or directly with your technology manufacturer to perform a
full risk assessment prior to investing in a robotic cleaning machine. Licensed
distributors of advanced robotics technology should have a proven risk assessment plan
they can guide you through, considering your specific needs, facility type and workforce
to completely assess all risk.
Your risk assessment will aim to pinpoint foreseeable hazards and
relevant hazardous conditions that may arise when you introduce a robotic cleaning
machine into your facility.
Based on OSHA’s six causes of safety issues, your risk assessment
should focus on:
Startup and programming procedures
Environmental conditions
Location of the robot
Requirements for corrective tasks
Human error
Possibility of robot malfunctions
The risk assessment process will help determine the appropriate type
of functional safety controls needed to reduce risk to an acceptable level. All findings
brought about by your risk assessment should be written in a Standard Operating Procedure
(SOP) that will be incorporated into your facility plan and training programs and should
be accessible to anyone who may interact with the machine.
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- Created: 23-11-21
- Last Login: 23-11-21