Up until approximately the middle of the 19th century, due to the lack of equipment, it was impossible to imagine reducing spools of material into thin strips with continuous longitudinal cutting, something which is so common nowadays.
The cut was made with difficulty by hand using simple lever or mechanical cutters with guillotine shears, which required considerable physical effort to operate.
In 1851, the professional blacksmith Peter Gandenberger founded a small engineering company in Darmstadt and later developed simple cutters. He used the first circular metal sheet discs, the so called sheet steel saucer shaped knives, which at that time did not undergo any form of tempera treatment. He fitted these geometric tools of equal size on the upper and lower knife holder shafts, using distancing sleeves to obtain different cutting widths.

These knives were fitted permanently on the respective shafts using lateral screws. Thanks to their circular shape, that is, to "their endless cutter" they allowed you, for the first time, to make a continuous longitudinal cut of a ribbon unwound by a spool, which after this operation was again wrapped around thinner spools. These cutting tools, over the decades, have evolved into the present day high productivity ones. As well as the "shear cutting" described above, new methods have been discovered such as the score cutting system and the split cutting system, briefly described below.

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Present

When working on the paper, the cutting tool can be distinguished according to its geometric shape.
The circular knives allow for a longitudinal cutting procedure and in a certain sense, have a dragging action on the material to be cut. Working with circular knives, three principal cutting systems stand out:

At present, the paper ribbons are almost always subdivided longitudinally with a shear cut and score cut. At present, they are the most commonly used cutting systems, although the split cut still carries a certain importance with the exception of the longitudinal cutting of paper.

Due to the considerable increase in working speeds achieved over the last few years for rewinder machines in working paper, there is a clear tendency towards the adoption of the shear cutting system in its different versions. Leaving aside the following descriptions of the main differences in the three cutting methods, this article is limited to highlighting the tools for shear cutting.

The characteristic differences between the three cutting systems are:

1) Shear cutting
Leaving aside the numerous forms of usage, opposing circular knives which overlap are used, as they have the most varied cutter patterns. See diagram

2) Score cutting
In this case, an upper wedge-shaped pressure knife in a special support is pressed against the paper ribbon being carried by a roller which is as hard as glass. The paper is then cut under pressure.
The knife holders can be easily dismantled from the bar and this allows for the fast substitution of the blade. Adjusting other cutting widths, you will need to use suitable templates.
The pressure used by the knife cutter is 4-6 atm and the maximum pressure is 8 atm.
The "alfa" angle, as well as the cutting pressure must be suited to the various thicknesses and quality of the material to be cut and are essential for a perfect cut. See diagram

The working pressure used by this knife cutter is 4-6 atm and the maximum pressure is 8 atm. The angle and cutting pressure must be suited to the thickness and kind of material to be cut in order to obtain the best cutting and wear conditions.

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3) Strip cutting
A thin circular knife is used, rotating at high speed and with a very sharp cutter which penetrates the paper ribbon conducted along two idle rolls or on grooved sleeves.
Compared to the tightly locked, self-hardened sheet steel saucer shaped knives which we mentioned in the first paragraph and which were used in the second half of the 19th century, at present the knife holders which actually support the cutting tool are fitted with different locking systems aimed at adjusting the cutting width faster.
The simplest system is made up of the screw locking. At a later date, wedge type locking was adopted. This was then substituted by locking with eccentric locking rings on the smooth shaft due to the increased cutting speed of cutters. On large machines with high speed and diameters of the shafts, compressed air locking established itself.
Depending on the cutters' characteristic data, such as the speed of cutting, width of the work, minimum cutting widths, the tools for the shearing procedure are fitted to the upper and lower conducted knife cutter shafts, or the lower knives are fitted to the respective shaft. With upper tools, however, knife holders for shear cutting with pneumatic adjustment are preferred. In the case of very high cutting speed and large working widths, more and more the lower knife holder shaft, abundantly sized for the requests here, is abandoned, inserting lower knives with individual commands with knife holders for the pneumatic shear cut.
Depending on the sector it is being used in, the operational shapes of the cutting tools (circular knives) can be distinguished. Among the upper tools are saucer shaped knives, hollowed upper knives and increasingly more so nowadays, a vast number of flat circular knives with corresponding cutter angles. The lower knives, on the other hand, always have a cylindrical shape.
As far as the material used for circular knives is concerned, we can say that mainly chromium-carbon alloy steel is used.
As well as the choice in material and a perfect heat treatment during manufacturing of the circular knives, the cutter surfaces are also very important for their quality and duration. Still today, tools with maximum precision smooth surfaces are used.

For further information on the longitudinal cutting technique of paper, film and sheets using DELSAR knives, click HERE.

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