Cardboard sheet punching machines for the manufacture of boxes are part of the corrugated cardboard transformation industry, so that at the end of the line blocks of differing number of sheets, one on top of the other, are obtained.
It is usual in the manufacturing process of punched boxes that several boxes are obtained from a sheet, to benefit to the maximum from the surface area in every strike, where the sectors of the sheet from which the different boxes will be obtained are joined by small points, forming blocks when the sheets are stacked.
Therefore, it is necessary to separate the different blocks of a stack of sheets, after first breaking the joint lines between the sectors of each sheet, and therefore separating the blocks that form those sectors.
Block separators are known that logically give rise to greater productivity than when the separation of the sectors of each sheet is manually carried out, different types of separators being known.
Specifically in the Spanish invention patent number 522521, of the company Bobst, a system based on a hydraulic anchoring of one of the two blocks which forms the stack of sheets is described, in order that a tensile horizontal movement applied to this block brings about its separation with respect to the other, by tearing along the punched lines that join both blocks.
The system described in that invention patent presents a series of disadvantages, since on one hand great anchoring and separation pressure is required, due to the fact that all the sectors of the block have to be separated at the same time by traction, with respect to the other sectors that belong to the same sheet, which implies having to work at high pressures that cause damage in the cardboard.
Furthermore, the hydraulic activation for putting the system into operation requires undesirable maintenance by the clients.
Also the problem that is implied by the fact that the joining points have to be small to reduce the separation effort, causing problems in the corresponding stacker, should be added.
Another disadvantage that the above-mentioned separator presents, in that invention patent, consists of the fact that it is only capable of handling small stacks of sheets, with the consequent decrease in speed of the punching machine, to which it is necessary to add the inability of separating different types of shapes of sectors formed in the sheets.
For its part, in the French patent number 2514296, of Raymond Lucas, a machine is described equally intended to separate by tearing along corresponding pre-cut lines, the parts or sectors established in a series of stacked sheets, separation being carried out by displacement of one of the parts or blocks.
In the European patent 0292067, of the Pallmac company, the separation of the punched blocks of sheets is carried out by pressing downwards of one of the parts or blocks, that is, there is a pivot point, the input means of the sheets remaining fixed, the outgoing means pivoting and the pivoting being carried out in a downwards sense.
The disadvantages that this system presents consist in that the minimum length of the outgoing means must be the half of the width of the punching machine, in addition to which the corresponding anchoring plates, used to keep the incoming block fixed, are adjustable in the direction of advance, having a damping system to reduce differences in height in the blocks. Anchoring is carried out by using a number of columns that project at the bottom from between the conveyor belts the adjustment of the means of anchoring being carried out, so that it is only possible to tackle complex shapes by raising the upper part of the machine.
The fact that in this invention patent anchoring takes place from below, and with columns between the conveyor belts, does not allow the blocks to remain uniformly held over the entire surface, because of which damage occurs in them.
Finally, in relation to this invention patent, to state that during the separation of the blocks, the downwards pivoting from the outgoing medium until the work-line “breaks”, with which the line of separated blocks must be taken outside the separator before the next separation, giving rise to significant loss of time.
Also German patents 1142293 and 235997 can be mentioned, relating also to separators for the purpose referred to previously.
Finally, the company Thermoguard Equipment Inc. uses systems based on related patents in which separation is carried out by means of two pairs of cylinders, one, of short stroke, placed at floor level, and another, of longer stroke, placed on the upper part of the machine, so that the blocks remain at mid-way between said two pairs of cylinders, those being separated about a pivot point that is far from the separation point.
The disadvantages that this system presents can be summarised as follows:                The location of the pivot point causes the effort necessary for separation to be very high.        The use of a hydraulic machine, with the disadvantages referred to.        The anchoring plates are not adjustable in the direction of forward movement, because of which it is not possible to separate complicated shapes.        It is necessary to withdraw the separated block to proceed with the next separation, with the corresponding loss of time.        