The invention relates to a device for strengthening a conveyable fiber lap made, for example, of cotton, synthetic fibers or the like. The device comprises at least one endlessly circulating conveying device having, for example, two rollers. The outer surfaces of the rollers can convey the fiber lap and are provided with elements that engage the fiber lap and have a strengthening effect on the fiber lap.
In practical operations, fiber laps are subjected to repeated needle treatments with needle boards for strengthening the laps. In the process, the lap is stressed in a lap movement direction since the needles plunging into the lap during the needle treatment delay the lap relative to a continuous lap movement. In many cases, this leads to an undesirable longitudinal stretching of the lap. U.S. Pat. No. 5,909,883 discloses a withdrawing roller drive control that reduces the withdrawing speed during the needle intervention to take into account the lap withdrawing resistance which increases as a result of the entering needles. However, the design and control expenditure required for the drive control is comparably high.
Austrian Patent No. 259 246 B1 discloses reducing the tensional stress of the fiber lap during the needle insertion by designing one of a pair of withdrawing rollers such that it has diametrically opposite arranged driver cams for the fiber lap. Depending on the lift frequency of the needle board, a frictional connection between the withdrawing rollers and the lap results only if the lap is released by the needle board. An intermittent lap conveying drive of this type represents an advantageous precondition for a low-draft needle-treatment of the fiber lap, but also requires an even lap thickness that cannot be ensured in practical operations. Unavoidable thick and thin areas in the lap cause irregularities in the lap advancement, thus resulting in an irregular needle-treatment. In addition, thick areas in the lap can result in surface damage to the lap caused by the driver cams for the withdrawing roller which impacts the lap, possibly leading to a mechanical overload for the withdrawing rollers, particularly in the bearing region.
The known intermittent needle insertion has the further disadvantage of preventing a high operating speed. A previous suggestion called for the needles to be arranged rigidly on the outside surface of a belt that endlessly circulates around two deflection rollers. In the process, the fiber material is drawn, meaning a relative movement takes place between the needles and the fiber material. While the needles are inserted into and pulled out of the fiber material, at the two deflection locations, additional relative movements occur between the needles and the fiber material because the needles are positioned at a slant relative to the fiber material. These movements lead to drafts in a longitudinal direction and, in particular, to an uneven structure of the fiber material.