GB2248638A

GB2248638A - Process and apparatus for needling a web in the making of a paper machine felt

Info

Publication number: GB2248638A
Application number: GB9116913A
Authority: GB
Inventors: Gunther Feyerl; Franz Konig
Original assignee: Textilmaschinenfabrik Dr Ernst Fehrer AG
Current assignee: Textilmaschinenfabrik Dr Ernst Fehrer AG
Priority date: 1990-08-17
Filing date: 1991-08-06
Publication date: 1992-04-15
Anticipated expiration: 2011-08-06
Also published as: JPH04352896A; GB2248638B; FR2665913A1; FR2665913B1; ITGE910106A1; GB9116913D0; IT1253240B; DE4126092A1; ITGE910106A0; ATA170490A; AT395025B

Description

a - 1 PROCESS AND APPARATUS FOR NEEDLING A WEB IN THE MAKING OF A PAPER

MACHINE FELT

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to a process of needling a web comprising synthetic fibers in the making of a paper machine and to an apparatus for carrying out the process.

Description of the Prior Art

Stresses are set up in a web as it is needled and may affect the shape of the web. Besides, the pinholes formed by the needles penetrating the web will disturb the uniformity of the surface of the web and this may be inconsistent with high requirements regarding the dimensional stability and surface finish of the web. Such high requirements must be met particularly by paper machine felts. To ensure a 1 relief from any stresses existing in the needled paper machine felts they must be treated in so-called tensioning calenders under the action of such temperatures and such tensions and for such a time that a substantial equalization of stresses, which is sufficient, e.g., for the required dimensional stability, has been achieved.

Paper machine felts usually consist of a woven backing and nonwoven webs, which have been needled to the woven backing. To ensure that a paper machine felt can be made which has the required dimensional stability it is necessary to provide a woven backing which is sufficiently free of stresses and accurately complies with the dimensional specifications. For this purpose the woven backing must be pretreated on a tensioning calender under controlled temperature and tension conditions. That pretreatment becomes more expensive as the weight of the woven fabric per unit of area increases and for this reason the tensioning calender which is associated with a needling apparatus is increasingly occupied for-the pretreatment of the woven backings and an additional tensioning calender is required for the aftertreatment of the needled paper machine felts.

Whereas it is known to subject felts or fiber mats to a heat treatment immediately before they are needled, such known heat treatments cannot Qffect a relief from stresses to the degree which is required for paper machine felts. For instance, continuous synthetic filaments are pulled over a knife edge before they are needled and are subsequently heated in order to increase the crimp which has been imparted to the fibers by the knife edge (DE-A-1 560 735). In another case (DE-A-3 135 247) continuous glass fiber strands of a mat are dried before and during the needling of the mat in that a sufficiently low humidity of the air and an elevated temperature are maintained. But such treatment will not have an influence on the needling process..

Summary of the Invention

For this reason it is an object of the invention to provide for the needling of webs in the making of paper machine felts a process which is of the kind 1 - 4 described first hereinbefore and in which the needling of the web gives rise to lower stresses so that an aftertreatment of the needled web may not be required or can be simplified.

It is another object of the invention to provide such a process which results in a needled web having a more uniform needled surface.

The objects set forth are accomplished in accordance with the invention in that the web is heated before it is needled and is needled when it is at an elevated temperature and is held under a tensile stress as it is heated and as it is subsequently needled.

The invention is based on the recognition that the resistance of the fibers to deformation, which resistance opposes the entraining of the fibers by the needles penetrating into the web, will not only affect the load on the needles but will also influence the stresses which are set up in the web as it is needled. The lower that resistance to deformation, the lower will be the stresses set up in 1 1 the web as it is needled and the lower will be the risk of a fiber breakage. Besides, the use of easily deformable fibers will have the result that the pinholes formed by the needles penetrating into the web will have a lower influence on the uniformity of the needled surface of the web. For this reason the needling conditions will be improved if fibers are used which present a lower resistance to deformation by the needling operation and if a tensile stress is additionally applied, which in combination with the action of the elevated temperature will tend to straighten the web. That additional straightening action on the woven backing to which a nonwoven web is to be needled in the making of a paper machine felt will eliminate the need for a more expensive preliminary treatment of the web outside the needling apparatus so that the tensioning calender otherwise required for that purpose can again be used for the aftertreatment of the needled paper machine felt, particularly because the inherent stresses set up in the web as it is needled are also reduced and are partly relieved as a result of the tensile stress applied during the needling operation.

1 Because the resistance of synthetic fibers to deformation can be reduced by a suitable temperature rise, the advantages afforded by a lower resistance of a web comprising synthetic fibers to deformation will be utilized if the web is needled when it is at an elevated temperature. Substantial advantages will be afforded even if the resistance of only part of the fibers of the web to deformation has been reduced by the temperature rise.

The process can be carried out with conventional needling means if they are preceded by means for heating the web and are associated with means for tensioning the web as it travels through the needling means so that the fibers will sufficiently be heated and held under a sufficient tensile stress. The synthetic fibers contained in a web must be heated to a temperature which is not in excess of their softening point so that the fibers can be more easily be deformed and can be re-oriented. In the present process the method by which the fibers are heated is not highly significant although it is recommended to move the web past well-known infrared radiators or in contact with heating rollers.

t In the selection of the design of the means for tensioning the web the magnitude of the tensile stresses to be applied will have to be taken into account. If only relatively low tensile forces are required it will be sufficient to use one tensioning car, provided that the frame of the needling means is properly supported. If a higher tensile stress in the woven fabric is required to ensure an adequate straightening action the web must be tensioned between two tensioning cars provided at opposite ends of the needling means. It must be born in mind that tensile forces between 5 and 10 kg/cm width are specified for relatively heavy woven backings for paper machine felts.

The heating means may be provided at a plurality of locations and may be associated with the needling means in various ways. But in view of the space which is available the heating means may desirably be mounted on the tensioning car.

Brief Description of the Drawing

Figure 1 is a schematic side elevation showing an apparatus for carrying out the process according to the invention, partly broken away.

Figure 2 is a view which is similar to Figure 2 and illustrates a modified apparatus according to the invention for exerting stronger tensile forces.

Detailed Description of the Preferred Embodiment

The invention will now be explained more in detail with reference to the drawing.

The embodiment shown in Figure 1 comprises a conventional apparatus for a needling of paper machine felts. Two needling means 1 are provided for needling the web 2 from the outside and from the inside, respectively. The web 2 comprises a woven backing and nonwoven webs applied to the backing. Each needling means 1 comprises needle board means 3', which define a needling region and are operable to reciprocate in the direction of the penetrating movement of the needles, a web support 4 and a stripper 5, which is disposed between the needle board means 3 and the web support 4 and together with the web support 4 serves to guide the web 2 to be needled. The returning course of the web 2 can be needled from both sides and the stripper of one needling means may be used as the web support of the other needling means. The web 2 has been joined to form an endless tube and extends in loops between a common frame 6 for the needling means and the tensioning car 7 of tensioning means. The frame 6 carrying the needling means 1 is provided with additional supports 8 for taking up the tensile forces exerted by the tensioning car 7. Before entering the needling region the web 2 must be heated to decrease the resistance of the synthetic fibers of the web 2 to the deformation by the needles of the needle board means 3 as the needlespenetrate into the web 2 and tend to entrain the fibers. For that purpose the tensioning car 7 is provided with heating means 9, which consist of an infrared radiator that is directed to the web 2. The actions of the temperature and tension tend to straighten the web 2 so as to equalise the stresses over the width of the - 10 web and to eliminate any undulations of the woven backing. Besides, lower stresses will be set up in the web 2 as it is needled because the heated fibers can be more easily pulled into the nonwoven web. For this reason there is no need for a more expensive pretreatment of the web by tensioning calenders,, which have otherwise been provided for that purpose outside the needling apparatus. Moreover, the inherent stresses set up in the web as it is needled are lower so that the.aftertreatment of the needled web is facilitated. In addition, the fact that the fibers have a low brittleness will reduce the risk of fiber breakage and the pinholes formed in the web by the penetrating needles will adversely affect the surface finish of the needled web to a lower degree.

The embodiment shown in Figure 2 differs from the one shown in Figure 1 only by comprising different means for tensioning the web 2. To apply higher tensile stresses up to 16 kg/cm, web width the web 2 is tensioned by two tensioning cars 7, which are provided at opposite ends of the frame 6 which carries the needling means 1. Because the loads on the frame 6 are now balanced and the main tensioning v - 11 forces are taken up by the tensioning cars there is no need for the additional support 8 provided for the frame in the embodiment shown in Figure 1. Heavier webs can be straightened by an exertion of stronger tensioning forces. The advantages afforded by the heating of the synthetic fibers as regards the straightening of the web and during the needling thereof are utilized also in this embodiment.

1

Claims

CLAIMS is 1. In a process of needling a web, which comprises synthetic

fibers, in the making of a paper machine felt, the improvement residing in that said web is heated before it is needled and is needled while it is at an elevated temperature and is held under a tensile stress as it is heated and as it is subsequently needled.
2. In an apparatus for needling a web, which comprises synthetic fibers, in the making of a paper machine felt, which apparatus comprises needling means for needling said web as said web moves in a predetermined direction of travel through a predetermined needling region, the improvement residing in that heating means are provided for heating said web before it enters said needling region and tensioning means are provided for tensioning I! said web adjacent to said heating means and in said needling region.
3. The improvement set forth in claim 2, wherein said tensioning means comprise at least one tensioning car.
4. The improvement set forth in.claim 3, wherein said tensioning car carries said heating means.