Crosscutter for web materials

Details Crosscutter for web materials Crosscutter for web materials

1999-10-22

2001-10-30

Rada, Rinaldi I. (Department: 3724)

Cutting

Tool or tool with support

Rotatable type

C083S698410, C083S331000

Reexamination Certificate

active

06308605

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a crosscutter for web materials, particularly paper.
DE-U-89 00 516 discloses a crosscutter for corrugated paper or board, which has a cutter block in the form of a composite carbon fibre material tube, to which is fitted by means of screws a cutter beam or support. Bearing and driving take place by means of metallic bearing stubs, which are incorporated into the tube.
DE-A-195 45 003 discloses a cutter shaft, which has an outer shell of a hollow metal section, particularly aluminium and which passes round an inner shell of a composite fibre material, where the cutter beam is constructed in the outer shell. For bearing and mounting purposes shaft journals are fixed in torsionally and fluxurally stiff manner.
In order to be able to cut different formats or sizes with crosscutters and without changing the cutter shaft, it is e.g. known from DE-C-36 08 111 to nonuniformly drive the cutter shafts using unbalance gears or preferably controllable electric motors with high accelerating and decelerating moments. The speed of the cutter shafts is decelerated during a revolution for cutting a format longer than the synchronous format determined by the circumference of the cutter shafts and at the time of cutting is reaccelerated to the web speed. It is also possible by periodic acceleration to a circumferential speed above the web speed to cut formats shorter than the synchronous format. The angle values of the requisite cut lengths and the possible accelerating and decelerating values determine the synchronous cut length, i.e. the cutter shaft diameter.
OBJECT OF THE INVENTION
An object of the invention is to provide a crosscutter for web materials, which has a considerable variation scope with respect to the synchronous cut length and satisfies all the requirements with respect to the construction, particularly the cutter shaft fitting, the possibility of applying enormous torques and having an adequate torsional and flexural stiffness or rigidity for the cutter shaft.
SUMMARY OF THE INVENTION
As a result of a very favourable shaft cross-section, the light metal cutter block compensates the lower modulus of elasticity compared with steel with respect to the torsional and flexural rigidities. Compared with a lightweight construction using composite carbon fibre materials (CFKs), it simultaneously permits a direct fitting of the cutter to the cutter block, which would not be possible with CFKs. In the case of a conventional steel cutter shaft construction, due to the high mass moment of inertia it is not possible to apply the accelerations and decelerations occurring due to the required divergences from the synchronous cut length. This more particularly applies for the presently preferred large crosscutters with a web speed of up to 400 m/min.
Large synchronous cut lengths do not cause a problem for the cutter shaft according to the invention. However, it can also be used for smaller synchronous cut lengths than the conventional lengths, e.g. of 500 mm. With the conventionally required web widths of approximately 2,000 mm, a cutter shaft with a single cutter on the circumference would only have a travel circle diameter of approximately 160 mm, which would not be possible in the earlier arrangements and materials due to the necessary flexural rigidity. Thus, in the case of the cutter shaft according to the invention it is possible to choose a form with two cutters on the circumference, which bring the cutter shaft to twice the diameter, which does not permit adequate acceleration values in conventional steel cutter shafts due to the then high mass moment of inertia.
This is possible, particularly because the cutter beam or support can be directly incorporated into the light metal cutter shaft, so that the external diameter important for the torsional and flexural rigidity need only be slightly smaller than the cutter travel circle. In the case of CFK cutter shafts, which would intrinsically appear suitable for such extreme conditions, for stability reasons steel cutter beds would be required and which as a result of the large cutter travel circle give rise to an excessive mass moment of inertia and whose fixing to the cutter block is problematical and weakens the latter.
The peak values of the driving torque and the corresponding braking moment are at approximately 5,000 Nm. Cutting force-caused bending moments must also be absorbed. These forces require a firm, secure seating of the shaft bearings and the synchronous gears transferring the drive. This is unachievable with a shaft end construction made from the cutter block material, i.e. light metal, particularly aluminium alloy. Thus, in the invention the shaft ends are made from a high strength material, particularly steel. The difficultly solvable problem of the fixing between the light metal cutter block and the steel shaft ends requires special measures, which in the case of the invention are formed by the flange, which extends over the entire circumference of the cutter block and ensures a positive and/or nonpositive connection. Particular preference is given to a both positive and nonpositive connection, in which in particular both connection types are such that they can alone transfer the driving torque. Although it is preferable to provide the construction of the shaft end with flange at both ends of the cutter shaft, in a one-sided arrangement of the drive only the drive-side shaft end need be connected in this way, because there, in addition to the bending moments, the driving moment must also be transferred.
The connection between the flange and the substantially cylindrical cutter block can take place nonpositively by frictional grip. For this purpose it is possible to insert in the circular cylindrical recesses, which can continue in bores or holes extending longitudinally over the cutter block, bushes with a particularly well-fitting, low-backlash screw thread and can optionally also be bonded therein. Into said bushes can be screwed fixing screws, which press the flange onto the end face of the cutter block. For an optimum force closure and to secure against the loosening of the bushes, the end face of the cutter block can be positioned somewhat lower than the latter, so that the flange only engages on the end face of the cutter block and not on those of the bushes. Through the choice of a fine thread between the bushes and the cutter block there is a self-locking action thereof under force. The transfer of the considerable screw forces consequently takes place in very large-area manner on the less strong material of the cutter block. This would scarcely be possible with a direct screwing in of the fixing screws.
The cutter block preferably has several recesses for reamed bolts, which are also distributed over the circumference and which are fitted therein and into the flange and optionally secured by locking screws. They form a positive connection.
The construction of the shaft ends with shaped-on flange consequently permits a very large-area transfer of the forces. Very high contact pressures must act with a nonpositive transfer. They can be applied to a very large surface area, so that despite the high screw forces there is no need to fear overstressing of the light metal material. These frictional forces act due to the fact that substantially the entire circumference (except for the cutter beam recesses) is available for frictional force transfer, whereas the end face portions made from another material, such as the area of the bushes, are set back with respect to the aluminium end face and cannot disturb the frictional force transfer.
Particularly as a result of the combination of the frictional grip and reamed bolts, i.e. through a simultaneous positive and nonpositive connection, an operationally reliable force transfer is possible in this particularly critical case of a connection between two parts of a cutter shaft. The nonpositive transfer ensures that it is completely backlash-free, because it could otherwise work loose. The self-closure by the reamed bolts

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