The present invention relates to a device for stabilizing a continuous paper web in a paper-making machine in the vicinity of a roll, to which the paper web is carried on a belt, comprising a box that is located upstream of the roll and extends along the side of the belt opposite the paper web, whose inside opens toward the belt and in which an underpressure is generated for sucking the paper web against the belt.
The present invention further relates to a method for stabilizing a paper web in a paper-making machine in the vicinity of a roll, to which the paper web is carried on a belt, wherein an underpressure is generated along the belt for sucking the paper web against the belt.
A device and a method of this kind for stabilizing a paper web are generally known (DE-A-44 02 105, DE-A-35 04 820).
In the case of high web running speeds, in particular when making paper grades of low basis weights, there is a risk of blisters forming as the paper web is transferred from a belt to a roll. This is so because the air necessarily entrained by the rapidly running paper web will be squeezed off in the nip between the belt, for example a felt, and the roll so that it has to escape laterally. If no additional counter-measures are taken this then results in a blister forming between the paper web and the belt before the point of entry into the nip (point of contact between the belt and the roll). The air enclosed in the blister must escape via the lateral edges of the paper web. The formation of such blisters is of course undesirable as it may lead to operational trouble and impair the paper quality.
The before mentioned DE-A-35 04 820 proposes for this purpose to generate an underpressure in the area preceding the transfer of the paper web to the roll, so as to suck the paper web against the belt in order to counteract the formation of blisters.
Further, it has been known from the before-mentioned DE-A-44 02 105 to expose a press felt, before its entry into the nip, to an underpressure over a first area of its path and to the action of steam over a following area, in order to de-water the press felt and, thus, to increase the dry content. In addition, the underpressure so produced counteracts the formation of blisters.
However, the known devices and methods are relatively complex and not easy to use in certain areas of a paper-making machine, i.e. such as press sections on the one hand and drying sections on the other hand.