Multilayered press felt

Abstract: A press felt is disclosed having a plurality of horizontal layers of parallel unwoven yarns, bound vertically together by a thread. The disclosed structure exhibits high compac­ tion resistance and water retention characteristics. One of the layers may be made of resilient yarns to act as a shock absorber.

Description: This invention refers to a press felt in the press section of a papermachine according to the preamble of claim 1. Such press felt was in prior use by Thomas Josef Heinbach Gmbtt and Co D-5160 Düren. A major portion of the art of paper making consists of sequential stages in which water is removed from a paoer web. These various stages are differentiated by different methods to remove the water from the web. One such method is to provide a press felt for contacting the web while the felt and the web are passed through a high pressure region formed by a press nip. During this process water pressed out of the web is forced into or absorbed by the press felt. It has long been recognized that an ideal press felt must be permeable to water, must resist compaction. and must maintain its dimensional stability. Numerous woven and non-woven fabrics have been suggested as press felts however improved result is continuously sought. GB 1 224 629 snows and describes an endless screen which is obviously to be used in tne forming section of the paper machine. This known screen is composed of three or four layers of filaments which are bonded together at the cross-over points with an adhesive providing adhesive filled gussets between the filaments at the cross-over points. Such screen is not suitable for use in the press section of the paper machine because the gussets reduce the ability to absorb water from the paper web in the press section. They also reduce the flexibility and provide considerable problems in manufacture. It is the object of the present invention to provide a press felt which has the ability to retain relatively large quantities of water, which resists compacting and has a long useful life. This object is met by the features of the characterizing part of claim 1. The proposed press felt has a number of desirable physical characteristics. Each layer provides a suoport platform which supports the other layers while the felt is passed through a press nip. As a result the felt is able to withstand numerous, repetitive compression cycles before the caliper deteriorates to a point where it can no longer handle water. In other words, the feit exhibits relatively large compaction resistance. and at the same time the physical construction of the felt insures its dimensional stability. Furthermore, it is well known that "knuckles" formed when one yarn cnanges levels or is partially wraoped around another yarn in woven fabrics are weakness points which wear away relatively raoidly. Since the proposed felt structure lacks "knuckles" its useiul life is much longer. In addition the proposed felt structure can be manufactured on well-known looms. From GB 2 101 643 there is known a belting fabric for use in reinforced conveyor belts comprising a number of warp and weft cord layers which are bound by binder cords, the object being to provide a reinforced conveyor belt which has a higher degree of transverse and longitudinal rigidity or resistance to flexing. These features. however, are not desirable with press felts for paper machines. Therefore. this prior art gives no suggestion to bind the layers of a press felt by binder threads in order to obtain the advantages set out above. It is important that the spacings between the strands of yarns in the proposed press felt remain fixed. If they were allowed, or caused to shift, the water-storing capabilities of the felt would be adversely affected. This could happen if the binder threads extend in the machine direction, for, in such case, they would be subjected to tension on the running paper machine. This would tend to change their orientations as they bind the layers, thereby making the fabric structure as a whole less stable. Therefore the binder threads extend in the cross macnine direction only where they are not subjected to large levels of tension. This allows allows the binder threads to be made thinner than the yarns of the layers esp. the yarns of the top layer so that impressions in the paper web are minimized. Owing to the fact that not only the yarns of the first, third and fifth layer are in a vertically stacked relationship but also the yarns of the second and fourth layer, the binder threds pass perpendicularly also through these layers so that the stability in machine direction is increased as the tendency of the second and fourth layer to shift with respect to the first, third and fifth layer is minimized. Therefore each layer forms an effective and stable platform for the adjacent layers, whereby a high degree of incompressibility is obtained. Preferably one of the layers, in particular a middle layer, is made of an elastomeric yarn to add resilience to the structure thereby increasing its sensitivity to compaction. A preferred embodiment of the invention and a modification thereof are shown in the accompanying drawings. Figure 1 is a perspective, partially sectional view of a press felt constructed in accordance with the invention; Figure 2 is a top view of Figure 1; Figure 3 is a sectional view taken along line 3-3 in Figure 2, and Figure 4 shows an alternate embodiment of the invention. Reference is now made to Figures 1-3 in which an endless press felt 10 is shown comprising five layers in generally parallel planes with each layer comprising a plurality of parallel yarns. The layers are identified in the Figures respectively by numerals 12, 14, 16, 18 and 20. The yarns of the first, third and fifth layer (i.e. layers 12. 16 and 20) are oriented in machine direction MD while the yarns of the second and fourth layer (i.e. layers 14 and 18) are oriented in the cross-machine direction CD. The layers are not interwoven. One or more relatively thin threads 22 are used to bind the layers vertically together. For example two threads 22' and 22'' may be used to bind the yarns of the center or middle layer 16 to the top and bottom layers 12 and 20 respectively as shown in Figure 3. This type of construction insures that the individual yarns of the layers do not shift laterally. Preferably the threads 22' and 22'' alternate from one row to another as shown in Figure 2, each row extending in a cross-machine direction. Alternatively, a single thread 22 may be used to bind the layers vertically as shown in Figure 4. Thread 22 is passed perpendicularly through each layer. Threads 22 are disposed in the cross-machine direction. The yarns forming the individual layers are spaced to form an open fabric. The interstices formed between these yarns enable the felt to absorb and carry relatively large amounts of water from a paper web. Preferably the yarns are plied monofilament or plied multifilament nylon yarns and the thread is a multifilament nylon thread. In order to increase the resilience and compaction resistance of the felt, the yarns of a middle layer f.i. of the third layer 16 should be made of a softer, more resilient material such as polyurethane monofilament. This layer acts as a shock absorber to dampen the effects of sudden compressive forces on the felt.

Claims: A press felt for use in the press section of a papermachine comprising: a) five layers (12,14,16,18,20) of unwoven parallel coplanar yarns, the yarns of the first, third and fifth layer extending in machine direction (MD) and being in vertically stacked relationship, and the yarns of the second and fourth layer extending in cross-machine direction (CD) the yarns of one layer not binding the yarns of adjacent layers, and b) separate binder threads (22,22',22'') which extend in cross machine direction (CD) and are passed perpendicularly between the layers, said binder threads weave over only one yarn of said first layer (12) at a time and only one of said binder threads (22,22',22'') being between each adjacent pairs of said second layer (14), the yarns of each layer being plied monofilament or plied multifilament yarns and the binder threads (22,22',22'') being multifilament threads which are thinner than the yarns of the first layer (12), characterized in that the yarns of the second and fourth layer (14,18) are in a vertically stacked relationship. The press felt according to claim 1, characterized in that the yarns of the layers are engaged by alternate binder threads (22',22''). The press felt according to claims 1 and 2, characterized in that the yarns of the first, second and third layer are bound by a first set of binder threads (22') and the yarns of the third, fourth and fifth layer are bound by a second set of binder threads (22'') whereby the threads of the first and the second set alternate.. The press felt according to any of claims 1 to 4, characterized in that one (16) of said layers is made of a resilient yarn to form a shock-absorbing layer. The press felt according to claim 4, characterized in that said shock-absorbing layer (16) is a middle layer. The press felt according to claim 4, characterized in that said resilient yarn of said shock-absorbing layer (16) is polyurethane monofilament.

Inventors: CROOK ROBERT L, CROOK, ROBERT L.
Applicants: ALBANY INT CORP, ALBANY INTERNATIONAL CORP.
Application year: 1985
Main classification: D21F1
IPC codes: D03D11, D21F1, D21F7