SubscribeThe rise in popularity of Flexible dies over the past 15 years has been meteoric, with the vast majority of Label converters now preferring this affordable and highly efficient method of cutting to that of the more expensive solid engraved dies or the slower running flat bed cutters. However with familiarity comes complacency.
In its formative years the Flexible die was simply chemically etched and at most, hand engraved to a finished edge, tolerances were flattering and as a product it became the third option for die cutting, ideal for computer or plane labels on short to medium runs where the press was almost set to a fixed repeat. Now the Flexible die is a high precision tool which is etched, CNC engraved, back ground to guarantee an extremely tight height tolerance and can be laser hardened for extra long runs.
Multi level dies and even cut through dies are regularly supplied and most impressive is the sheer range of filmic materials the Flexible die can convert, but, and it is a big but, the Flexible die is only as good as the Magnetic cylinder it sits on. All the efforts die manufactures go to ensuring the tightest of tolerances are maintained during die manufacture is wasted if mounted on a cylinder with an incorrect Air Gap.
Flexible Dies and Magnetic Cylinders
So what is the Air Gap and what makes it so important?. Put simply the Air Gap is the difference in diameter between the bearer and the Magnetic surface, (see fig 1) the trade standard for this Air Gap is 0.96mm on diameter or 0.48mm on radius.
Figure 1
Problems begin with ware on the bearer of the Magnetic cylinder, this reduces the diameter of the bearer and the Air Gap, this reduction in the Air Gap causes the Flexible die to cut deeper into the backing liner which increases die fatigue and reduces overall die life. Unfortunately with today’s short run domination of the label market place, die life is not as noticeable an indicator of tooling health as it used to be, as a high percentage of Flexible dies supplied rarely run until completely fatigued. So the problem of reduced Air Gap or even worse an uneven Air Gap, where one bearer has worn faster than the other, can stay undetected for sometime.
The cause of this bearer ware is an age old story of good housekeeping or the lack of, cylinders running without lubrication, excessive and or uneven pressure application, worn or damaged bridge bearings are just a few of the possible causes of bearer damage. The problem is that this one Magnetic cylinder has a multitask roll and is not a one job cylinder, as such it needs to be cared for and cosseted in its use. The storage and use of the Magnetic cylinder is crucial not only to its life but the successful running and longevity of numerous Flexible dies.
At Kocher + Beck UK Ltd we have recognised for sometime the issue of Magnetic cylinder care and offer our customers a training session for press operators on the correct procedures for using Magnetic cylinders and Flexible dies, in addition we offer a periodic health check on Magnetic cylinders to ensure the all important Air Gap is maintained within acceptable tolerances, each cylinder is tested for Air Gap both gear and non gear side, a visual check for surface damage is made and a full report is produced colour coding each cylinder depending on its status for use.
Figure 2
One of the biggest causes of bearer damage as already highlighted is excessive or uneven pressure application and in truth with modern pressure gauges (see Fig 2) uneven pressure should be seen as a clear indication of some underlying problem with the cylinder or anvil. Increasing or applying excessive pressure to a cylinder normally occurs when an operator is trying to obtain a deeper or even cut into the liner, the reasons for this can be use of a worn cutter, use on different material to that which the Flexible die was made or an already worn Magnetic cylinder or Anvil. In any case applying more pressure has little or no effect as once contact of the bearer to anvil is made, any more pressure is only attempting to squeeze the metal of the Magnetic cylinder bearer.
To successfully control cut depth be it to much or to little has been available for some years in the form of adjustable anvils such as the GapMaster system from K+B, with this type of system the press operator takes control of the Air Gap by way of an adjuster knob at the front of the die station, therefore pressure can be set to the minimum required to eliminate bounce and all further adjustments are made via the Air Gap. (see fig 3)
Figure 3
In addition on the GapMaster adjustment is available left to right to eliminate uneven cutting across the Magnetic cylinder.
This highly accurate adjustment system eliminates the need for pressure loading, thus increasing Magnetic cylinder life and Flexible