This application depends for priority on German Application No.: 197 15 174.4, filed Apr. 11, 1997
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1. Field of the Invention
The invention is in the field of corrugated composite sheet manufacture.
2. Background Art
The invention concerns a device for manufacturing a composite sheet comprising at least one corrugated sheet and at least one flat sheet that is glued to the wave peaks of the corrugated sheet, said device comprising at least one fluted roller for shaping and/or maintaining the shape of the corrugated sheet, said roller being covered with the corrugated sheet around a portion of its circumference during operation, and a gluing unit for applying a liquid glue used to attach the corrugated sheet to the flat sheet, with said gluing unit having a gluing roller whose outer surface is continuously coated with a glue film and whose axis is essentially parallel to that of the fluted roller, said gluing roller being driven at approximately the same peripheral speed as that of the fluted roller, and with it being possible, using means for moving the rollers closer together, to move said gluing roller, with its outer surface against the portion of the circumference of the fluted roller that is covered with the corrugated sheet, into a close-up position that allows the glue to be transmitted to the wave peaks of the corrugated sheet, thus forming a gluing gap.
For example, this type of device is used for the manufacturing of corrugated cardboard, particularly one-sided corrugated cardboard. In this case, a cardboard or paper sheet is moved between a pair of fluted rollers and stamped into a corrugated sheet. After the corrugated sheet passes through the stamping gap formed between the two fluted rollers, it is pressed against the fluted roller that comes after the stamping gap in the direction of the corrugated sheet using appropriate means, e.g., by creating excess pressure in the space surrounding the fluted rollers and the gluing roller, and moved past the gluing roller, at which point glue is transmitted from the gluing roller to the wave peaks of the corrugated sheet.
In conventional devices, the width of the gluing gap between the gluing roller and the fluted roller opposite it is adjusted so that the wave peaks of the corrugated sheet are immersed in the glue film applied to the gluing roller without coming into contact with or being pressed flat against the surface of the gluing roller. Thus, there is always a gap between the wave peaks of the corrugated sheet and the outer surface of the gluing roller. Ordinarily, the thickness of the glue film is in the range of 0.15-0.40 mm. Accordingly, in the case of conventional devices for the manufacturing of corrugated cardboard, the gluing gap between the gluing roller and the fluted roller must be precisely adjusted. Specifically, on the one hand, the gluing gap must not be too wide in order to ensure that the wave peaks of the corrugated sheet are actually immersed in the glue film. On the other hand, in the case of conventional devices for manufacturing corrugated cardboard, an excessively narrow gluing gap should be avoided in order to prevent the wave peaks of the corrugated sheet from being pressed against the outer surface of the gluing roller.
One possibility for precise adjustment of the width of the gluing gap lies in having an operator hold a test band of a known preset thickness (such as 0.07 mm) between the fluted roller covered with the corrugated sheet and the gluing roller.
The gluing roller is then gradually moved closer to the fluted roller. This operation is carried out with both the fluted roller and the gluing roller rotating. The gluing gap is made smaller and smaller until the operator feels tugging on the test band. In this manner, the actual gap between the gluing roller and the wave peaks of the corrugated sheet lying on the fluted roller is adjusted to the thickness of the test band (for example, 0.07 mm). However, such adjustment of the gluing roller has the disadvantage that it is only possible to adjust the gap width of the gluing gap once before the corrugated cardboard manufacturing device is actually put into operation, and it is not possible to verify or readjust this width during operation. In addition, it is dangerous for the operator to hold the test band between the rotating gluing roller and the running corrugated sheet. As soon as the operator feels tugging on the test band, he/she must immediately let go of the test band to avoid getting his/her fingers caught in the gluing gap. In the case of so-called one-sided machines for the manufacturing of one-sided corrugated cardboard, in which the corrugated sheet is held against the fluted roller by excess pressure, this kind of adjustment of the gluing gap is not possible. As the gluing unit with the gluing roller is located inside a pressure chamber in such one-sided machines, with said chamber necessarily being under excess pressure during operation of the machine so as to hold the corrugated sheet against the fluted roller, the operator can only gain access the gluing gap when the pressure chamber is opened and therefore not under pressure. In this case, however, the corrugated sheet does not remain against the fluted roller, thus making it impossible to adjust the gluing gap using a test band.
In addition, the method is known of adjusting the width of the gluing gap by means of sensory positional measurement. In one method, a non-contact distance sensor is attached to the frame of the gluing unit immediately next to the gluing roller, with said sensor measuring the distance to a target point on a bearing support of the fluted roller. The measurement value given by the distance sensor thus indicates the width of the gap between the frame of the gluing unit and the bearing support of the fluted roller in the area of the distance sensor. Another method consists of attaching a distance sensor to the frame of the gluing unit in the same manner, but with a smooth band attached outside the fluted area of the fluted roller being taken as the target point for distance measurement.
In a third method, the position of an adjustable stop, against which the gluing unit is pressed for specified adjustment of the width of the gluing gap, is determined by means of an appropriate sensor, such as a rotation angle indicator or a position sensor. Any displacement of the stop and thus the width of the gluing gap manifests itself in a corresponding change in the measurement signal emitted by the sensor. Thus the position of the stop is an indicator of the width of the gluing gap.
What the above three measurement methods have in common is that direct measurement of the gluing gap, whose width is the actual parameter of interest, does not take place. Rather, in all cases, distance or positional measurement takes place outside of the gluing gap. It has been found that the distance or positional measurement values obtained by such methods to not provide sufficient data on the actual width of the gluing gap. On the one hand, the measurement conditions at the various measurement sites may differ from conditions in the area of the gluing gap. On the other hand, under the prevailing operating conditions in a corrugated cardboard manufacturing machine, the available distance or position sensors operate relatively inaccurately, with the result that it is necessary to check the measurement device at regular intervals, and in some cases, to recalibrate it.
The above problems in measuring the gluing gap are further aggravated by the temperature conditions prevailing in the environment of this gap. In a corrugated cardboard manufacturing machine, the fluted roller and the press roller, which is used to press the glued corrugated sheet together with a flat sheet, are heated by steam. The heat is absorbed by the paper sheets, i.e., the corrugated sheet and the flat sheet. The flow of heat depends on various parameters, including the thickness of the paper, the amount of glue, the running speed of the sheets, etc. Accordingly, the rollers are subject to temperature influences which cannot be precisely predicted and are difficult or even impossible to keep constant. These temperature influences lead to thermally-induced changes in the size of the roller and thus the width of the gluing gap as well. The machine frame is also subject to temperature variations that may be manifested in the form of changes in the width of the gluing gap.
The measurement system must also be capable of detecting these temperature-induced fluctuations in the width of the gluing gap in order to readjust this gap correspondingly. In view of the fact that even measurement of the basic position of the gluing gap is difficult in conventional distance or positional measurement methods, it is very difficult to precisely determine thermally-induced variations in the width of the gluing gap. This applies in particular in view of the fact that the temperature conditions at the sites at which the sensors are attached may differ considerably from the actual temperature conditions prevailing in the environment of the gluing gap. All of this leads to inaccuracies in adjusting the gluing gap which may result in fluctuations in the amount of glue applied to the wave peaks of the corrugated sheet, corresponding fluctuations in the quality of gluing of the corrugated sheet to the flat sheet, and corresponding fluctuations in and impaired quality of the end product.
Accordingly, the purpose of the invention is to make adjustment of the gluing gap easier in a device of the type mentioned at the outset.
The invention achieves this purpose by providing that the means for moving the rollers closer together are designed so as to press the gluing roller against the corrugated sheet and the corrugated sheet against the fluted roller.
In the solution according to the invention, the gluing roller is pressed with its outer surface against the corrugated sheet lying on the fluted roller, i.e., against the wave peaks of the corrugated sheet. At first glance, one might think that this would impair glue transfer from the gluing roller to the corrugated sheet, as the gluing roller presses against the corrugated sheet exactly at the position where the transfer of glue is desired (i.e., at the tips of the wave peaks of the corrugated sheet), thus causing a certain degree of displacement of the glue toward the lateral flanks of the wave peaks. Surprisingly, it has been found that this kind of effect does not occur. On the contrary, there is even an improved transfer of glue and thus and improvement in gluing together of the corrugated sheet and the flat sheet compared to the conventional method. It is thought that this has to do with the moistening conditions prevailing between the surface of the corrugated sheet and the glue. Specifically, it is thought that the adhesion forces acting between the surface of the corrugated sheet and the glue cause the glue that has been displaced to the flanks of the wave peaks to spread to the tip of the wave peaks, thus resulting in uniform and complete moistening of the wave peaks over their tips. For this reason, in selecting and setting the parameters affecting the transfer of glue, such as the type of glue, the paper quality, the peripheral speed of the gluing roller and fluted roller, the thickness of the glue film, etc, one should also take into consideration the moistening conditions between the surface of the corrugated sheet and the glue, and if applicable, carry out tests to determine the values of the parameters affecting the transfer of glue which allow optimal moistening of the wave peaks to be achieved. In any event, unexpectedly uniform gluing patterns of the corrugated sheet can be achieved, i.e., extremely uniform quality of glue application to the wave peaks of the corrugated sheet both over the length of an individual wave and over several successive waves in the direction of movement of the corrugated sheet.
The problems with respect to measuring and adjustment of the gluing gap existing with conventional corrugated cardboard manufacturing machines are avoided in the case of the present invention. The invention moves away from the conventional view that a preset space must be left between the wave peaks of the corrugated sheet and the outer surface of the gluing roller. Accordingly, although this type of space was conventionally considered to be the decisive parameter determining the quality of glue application, this is not the case in the present invention. Positional measurement of the width of the gluing gap in order to determine the available space between the wave peaks of the corrugated sheet and the outer surface of the gluing roller, with the accompanying problems described above, is no longer necessary. Because the gluing roller is pressed against the corrugated sheet, the compressive force with which said roller is pressed against said sheet constitutes an additional parameter which can be easily measured and adjusted. On the one hand, it is not necessary to measure this compressive force in the immediate area of the gluing gap, as said force can also be reliably determined at other sites located in the transmission path by measuring a force which is available at the other site and that generates the compressive force. On the other hand, thermally-induced dimensional changes in the area of the gluing gap can immediately be sensorially determined by means of measuring the compressive force, thus making it possible to easily correct such thermal influences by manually or automatically readjusting the compressive force.
The means for moving the rollers closer together should include setting means for setting a predetermined compressive force between the gluing roller and the fluted roller, so that, for example, in the case of different types of glue or differing paper quality, individually defined force conditions can be set in the gluing gap. Preferably, the means for moving the rollers closer together are control means for regulated maintenance of a preset compressive force between the gluing roller and the fluted roller. In this case, a target compressive force that can be externally preset or stored in a control unit is compared with an actual measured compressive force, and in the event of discrepancy, corresponding readjustment of the compressive force may be carried out until these discrepancies are eliminated. It is possible to store numerous values for the target compressive force in advance in the control unit in table form, said values being selected as appropriate depending on parameters such as the paper quality, type of glue, or viscosity of the glue.