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Filling the flexibility gap

Die cutting system claimed to offer wider capabilities

An adjustable anvil enables Kocher + Beck’s GapMaster die cutting system to process the wide range of substrates used for pressure sensitive labels.

According to K + B, conventional die cutting units, which use threaded spindles to increase or reduce the cutting pressure, offer limited opportunities for varying the cutting depth. This method can change the air gap – the distance between the cutting edge and the surface of the anvil roller. The increased cutting pressure results in distortion of the bearer rings and the surface of the anvil roller. Each time the pressure is increased, the mechanical load on each element of the die cutting unit also increases. However, changing the cutting depth using this technique is only possible within a very limited range – 15 micron at most.

Many modern synthetic facestocks tend to be 85 micron and often even thinner than 70 micron. This low density changes the die cutting ability. The process, which includes penetration of the cutting edge into the face material to the point where bursting takes place, now has to work within exceptionally reduced tolerances. To ensure bursting of the facestock and avoid cutting into the release liner requires exact adjustment of both the cutting pressure and depth.

Kocher + Beck’s solution, the latest version of the GapMaster system, is said to offer effective changes in the journals, bearer rings and the adjustment system. The core of the system is a special anvil roller. Because the body of the die cutting cylinder and the operation of the bearer rings of the anvil roller use different journal technologies, the air gap can be adjusted without changing the cutting pressure. With the integrated KMS 3 pressure measurement system, cutting pressure can be adjusted before the production run. It operates at comparatively low values of 400-700 lb/in and remains unchanged throughout the run.

The opportunity to change the position of the anvil roller without changing that of the bearer rings is said to be the most significant difference compared to conventional die cutting systems. The anvil roller adjustment facility allows the air gap to be manually adjusted in steps of 0.8 micron – in parallel on both sides or on the drive side alone. This allows the possibility of evening out thickness tolerances in the release liner, or to compensate for bearer wear by changing the air gap on one side only – during the production run.

This patented technology offers the opportunity for processing pressure sensitive constructions of different thicknesses with the same cutting tool. This is true for the combination of flexible dies and magnetic cylinders, as well as solid die cutting cylinders. Closing the air gap compensates for any reduction in the cutting edge height due to wear. With conventional systems, the solution is to raise the cutting pressure.

According to K + B, when conventional systems reach the limit for increasing the mechanical loads, its system can increase the cutting depth even more – without compromising accuracy. The adjustable air gap makes it easier for the user, not only to adjust the die cutting more accurately, but also to keep it constant during the whole run.

The GapMaster is also said to offer advantages with narrow web presses. With an adverse ratio between web width and printing length, deflection of the magnetic cylinder often results in cutting problems. A wider web width and smaller diameter of the magnetic cylinder result in higher deflection of the cylinder. With the K+B system, it is said to be possible to fall outside this ratio as adjustment of the required cutting depth is achieved with lower pressure on the bearer rings. Thus it is possible to use magnetic cylinders with a diameter of 12in in machines with a working width of 16in for good cutting results, depending on the geometry of the blanks and the type of press.

In everyday production, the system is said to require the lowest possible cutting pressures. This reduces wear on all components and increases the life of magnetic cylinders, bearings, anvil rollers, journals and bearer rings by as much as 20 times, according to Kocher + Beck.