There are many known types of rewinders, based on the principle of surface winding, for the production of rolls or logs of web material. Some examples of these automatic surface rewinders (in other words, those in which the logs are formed automatically in rapid succession and the log in formation is rotated by contact with an external system of belts or rollers) are described in U.S. Pat. No. 4,723,724, U.S. Pat. No. 4,856,725, U.S. Pat. No. 4,828,195, U.S. Pat. No. 4,962,897, U.S. Pat. No. 4,487,377, U.S. Pat. No. 4,931,130, U.S. Pat. No. 5,137,225, U.S. Pat. No. 5,248,106, U.S. Pat. No. 5,368,252, GB-A-2.105.688, WO-A-9421545.
Some of these rewinders, for example those described in EP-A-0 580 561 and EP-A-0 611 723 also produce logs without central winding cores.
These rewinders produce a high number of rolls per unit of time, and these are subsequently discharged to the exterior of the rewinder and are collected in a sorter or in an intermediate storage receiver. Before it is possible to proceed to the cutting of each log into smaller rolls and the subsequent packaging, it is necessary to glue the free tail edge of the web material wound on each log to prevent the unwinding of the end portion from causing problems in the subsequent phases, particularly in the packaging.
For this purpose, the logs discharged from the rewinder and collected in the accumulators or sorters following the machine are conveyed individually to a separate and subsequent section of the "converting" line in which one or more machines are provided for the gluing of the free tail edge of the material of each roll, these machines being commonly called tail sealers.
Examples of tail sealers are described in U.S. Pat. No. 3,044,532, U.S. Pat. No. 4,475,974, U.S. Pat. No. 4,963,223, U.S. Pat. No. 5,242,525, EP-B-0 481 929, WO-A-9515903, WO-A-9515902.
All the tail sealers have a station in which the free tail edge of the web material is unwound and positioned before the adhesive is applied.
The necessity of having a rewinder, an intermediate accumulator or sorter and a tail sealer (which in turn comprises a station for the unwinding and positioning of the free tail edge to be glued and a gluing station), causes the line to have large overall dimensions and makes it necessary to synchronize the different sections of the line with each other, resulting in high costs in respect of programming and control systems. These costs are accepted in plants with high output, of the order of more than 9-10 logs per minute, but cannot always be borne with lower outputs.
Disclosure of Invention
The present invention is based on the idea of combining the winding and gluing of the free tail edge of the log in a single section of the processing line, thus eliminating not only the intermediate accumulator or receiver, but also the station for the unwinding and positioning of the free tail edge of the log.
Essentially, according to the invention, the log is caused to be discharged as soon as it is formed from the winding cradle of the rewinder, with the tail edge unwound, directly onto a discharge surface along which the adhesive is applied to the roll to close the free tail edge during the rolling of the log on the discharge surface. The length of the free edge and the position of the adhesive on the roll are selected in such a way that as it is rewound the edge covers the line of adhesive and extends beyond it by a few millimeters, forming a tab that can be picked up. In this way the dimensions of the processing line are reduced drastically and also the programming and operation of the line are considerably simplified.
In practice, the method of winding according to the invention may comprise the phases of:
feeding the said web material to surface winding means; PA0 winding a predetermined quantity of the said web material onto a roll; PA0 dividing the web material; PA0 discharging the roll formed by the said surface winding means, with a free tail edge of the said web material unwound from it, onto a discharge surface along which the said adhesive is applied to the cylindrical surface of the roll; PA0 starting the winding of a new roll while the previously formed roll is discharged and glued.
The surface winding may be carried out by one of the conventional systems known at the present time. Preferably, the winding system which is used will comprise at least two winding rollers rotating in the same direction and forming between them a nip through which the web material to be wound passes. After the nip there is provided a winding area which is preferably formed by a third winding roller which is movable to permit and control the increase of the diameter of the log. If this winding system is adopted, at the end of the winding the web material is severed before the said winding cradle and the second winding roller is stopped to cause the completed roll to roll on it and to cause it to be discharged from the said winding cradle. By stopping the second winding roller, the roll can be discharged with a free edge of web material sufficiently long to allow convenient gluing, as will be shown more clearly by the following detailed description.
To improve the control of the phase of discharge of the log from the winding cradle, in this case it is advantageous to have the said first winding roller slowed down temporarily at the end of the winding, together with the rest of the machine, including the means of feeding the web material.
In practice, the adhesive is delivered from a delivery slit provided along the discharge surface and extending parallel to the axis of the roll.
The surface rewinding machine according to the invention comprises winding means forming a surface winding unit for the formation of the said rolls; before the said winding unit, means of dividing the web material which, at the end of the winding of a roll, sever the web material, thus generating a free tail edge of the web material wound onto the said roll and a free leading edge of web material for starting the winding of a subsequent roll; and a discharge surface after the said winding unit, onto which the formed rolls are discharged at the end of the winding. Delivery means are also disposed along the said discharge surface to deliver an adhesive to each of the said rolls when they roll on the said discharge surface, in order to glue the free tail edge of the web material wound on the roll, which is discharged by the winding unit onto the said discharge surface with the said free tail edge partially unwound.
In practice, the discharge surface has an adhesive delivery slit extending parallel to the axis of the roll. The log collects the adhesive from the slit as it rolls over it.
To obtain correct gluing of the free tail edge when the log rolls on the discharge surface, it is useful for the web material to be severed at the end of the winding in such a way that a sufficiently long free tail edge is left unwound from the log. This may be achieved, for example, by providing before the nip formed by the winding rollers a rolling surface forming with the surface of the said first winding roller a channel within which the winding of each roll starts. The web material is severed in the proximity of the entrance of the channel.
The severance of the web material may take place in various ways, depending among other considerations on whether the winding takes place with or without a central tubular core. Some examples of means of dividing the web material are described below.