Performance Effect
What effect does run-out have on the performance of an anilox?
In the press: The flexographic printing press is made up of many parts and pieces that all have to work together to get a finished product. All of the parts and pieces have specific jobs and tolerances. If one of those parts is out of tolerance, then the press will not perform properly. The anilox roller is a very important part of the press. If you have run-out over the manufacturer’s tolerance, it can lead to the following issues:
- Excessive stress on the base or sleeve. If the part is not running properly, it can create stress and generate heat. In extreme cases, it can break off shafts, damage sleeves internally, and damage other moving parts
- Excessive stress on the doctor blades and chambers. Anilox run-out can impact the ability of the doctor blades to meter correctly. In some cases, the chamber pressure will have to be increased to prevent leaking, which can wear doctor blades and seals quicker and damage the anilox
- Damage to the plates or transfer roll. To compensate for run-out, you would have to over-impress. This could cause the plate or transfer roll to be damaged along with print issues. This also could generate heat and stress that could damage the plate mandrel or transfer roll
- Reduced printing speed in order to prevent bouncing, reduce heat generation and printing issue
Laser Engraving: TIR also plays an important role in laser engraving. If the part being engraved has TIR issues, it will show up dramatically in the quality of the anilox engraving.
To understand this, you will need first to understand how a roll or sleeve is engraved. The laser setup at Interflex Laser Engravers consists of two adjustable chucks and an engraving head that traverses across the roll surface as the roll rotates. Once the engraving head is set at a certain distance from the anilox, it is locked into that location or focus point. If the anilox roll has excessive runout or taper (TIR), the focal point will change as it traverses. This could give you shallower or deeper cells around the diameter (runout) and across the horizontal roll face if the taper is not controlled.
In the example of a 1,200 lpi 2.0 bcm engraving, the depth is less than 0.0005-in. If your runout is 0.001-in., then the distance from the engraving head to the surface will change as it rotates. This can give you areas of engraved cells that are deeper and/or shallower around the engraving. If your taper or profile is greater than 0.001-in., you will have the same issue across the engraving horizontally. All these issues lead to downtime and frustration.
Total Indicator Reading
In the topics earlier, we discussed “run-out.” The other part of TIR is what we would call taper or profile. That is the difference that you could measure with a dial indicator going horizontally across the anilox face.
This is an important measurement to help prevent issues. Keep in mind that this test should only be performed prior to engraving. Testing after the anilox has been engraved can cause damage to the engraved surface. At Interflex Laser Engravers, we have an internal tolerance of 0.0005-in. Imagine that piece of paper again, but this time you are getting rid of five of the pieces. That would be half the thickness of the paper. This is important for doctor blade wear, doctor blade metering, laser engraving (as described already), and consistent release of inks and coatings.
Prevent Issues
Mitigation measures include the following:
- Check with your anilox providers on the tolerance they use for each roller they send you
- Make sure that they are referencing the bearing surface and not the centers of the anilox roller when recording TIR
- On shafted rolls, make sure that you have good bearings on the roller before you install it in the press. Even if the engraved and bearing surfaces are concentric, a bad bearing will cause issue
- Protect the shafts on a roll anilox, so they don’t get damaged or bent
- On a sleeve anilox, make sure to keep the inside of the sleeve and the outside of your press mandrel sanitary and sterile—clean it! If you get contamination, such as ink, damage, or even heavy dust, on the mandrel or the inside of the sleeve, it can cause that area to run-out
- Protect sleeve aniloxes—they are prone to damage and if they get hit or bumped, they can become out of round. Once this happens, they will not run concentric in the press
Foundational Element
TIR was one of the first things I learned in my 30+ years of working in this industry. It is truly one of the foundational elements needed in manufacturing and engraving any type of roller or sleeve used in flexographic printing.
Back on the farm, we had a saying: “You can’t make chicken salad out of chicken crap.” Without good TIR, your anilox roller will not perform correctly.
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