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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