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Anhui Towin Machinery Co., Ltd 

Add:B-122,No38,Yinhu North Road,

ETDZ,Wuhu,Anhui,PRC

Tel: 0086-553-8295880   

Fax: 0086-553-8295880

E-mail: paper@ahtowin.com,

tinpmc@ahtowin.com



PMC Summary

PMC

Paper Machine Clothing (PMC) products are solution-based, custom-designed fabrics and belts critical for the formation, dewatering and transport of the paper sheet through a paper machine. PMC represents only a small proportion (approximately 2 percent) of the total cost of manufacturing, but has a significant impact on the quality of the paper, the efficiency of a machine, its production rates and overall cost of operation. PMC products includes forming fabrics, press fabrics, dryer fabrics, shoe press belt and other transport belt for paper machine.


Forming fabrics

Formerly, the fourdrinier wire was a bronze wire mesh. Plastic forming fabric substitutes became available in the 1960s, and although more expensive, have largely displaced bronze wires on modern PMs. Nevertheless, the word "wire" remains in use as a general term for both types.

Forming fabrics have since evolved from single layer design to:

-1.5 layer.

-Double layer and Two and half layer.

-SSB Triple layer. 

The term SSB is the industry classification for "Sheet Support Binder" fabrics and is described as "a multi-layer forming fabric, in which the binding yarns become a part of the structure linking top to bottom and helping to support the sheet". 

In each case, the desired properties are built into the individual layers. They thus aim to reconcile the conflicting demands of: drainage; retention; paper quality (eg: lack of visible wire marking); web support and release; drive energy; fabric stability; ease of cleaning and long life. The most influential fabric properties on paper structure and PM performance are: air permeability; fabric density; modulus; fiber support index; drainage index; caliper; and void volume. The longer life of fabrics means less downtime for wire changing and thus extra production.


Press Fabrics

Within the press section of the paper machine, press felts are used both for the transport and for the dewatering of the paper web. Press felts (press fabrics) play an important role in the dewatering process.

The sheet is carried into the press section on soft resilient “felts” or, more correctly, press fabrics. Traditionally, press felts were made of 100% wool because wool has the ability to be compressed in the press nip and spring back without being compacted. Press felts were so named because they were manufactured with the filling or “felting” process, in which a loosely woven cloth is densified into a hard fabric as can be seen in felted hats or pool table covers. The fabrics are now referred to as press fabrics because they are produced through needle punching rather than felting.

Formerly, they were literally ordinary natural fiber (eg: wool) felts descended from those used by the handmade papermaker. An early stage of improvement simply consisted of a soft batt layer (next to the paper) needle punched to the woven synthetic fiber base (batt on base).

The high solids presses put heavy demands on felts to provide high water handling capacity, and maintain felt life, resistance to compaction and wad burns, while not marking the paper. Multibase (laminated) structures were therefore developed, with the desired properties built into 2-4 individual separate layers laminated together (batt on mesh), with a finer MD batt to improve water removal. Monofilament yarns are normally used, but some felts utilize braided yarns (multifilaments), so as to reduce marking by the crossover knuckles.

Traditionally, felts have been of the continuous loop felt type (endless), but pinned seamed felts (seamless) are gaining popularity because they reduce felt change time. They are run on most types of press and with most major grades of paper.

When the sheet is carried through the presses by the fabric, water is squeezed out and into the fabric, further reducing the sheet’s water content. The paper surface finish is further influenced by the press fabric design. As the sheet leaves the press section, it is typically 40% fiber and 60% water, depending on the sheet grade and the paper machine.


Dryer Fabrics

The original dryer felts were tightly woven structures that did little more than hold the paper web near to the dryer cylinder. In the 1960s, open mesh fabric structures (dryer fabrics, dryer screens) were introduced, so that drying was assisted by pocket ventilation air able to pass through the fabric into the pocket. In addition, special patterns (eg: skip dent) caused the fabric to create a pumping action that further assists in evacuating the air, with this effect sometimes being variable in the CD.

Current weave designs include:

- Double layer design is common. It has large voids for contaminants, but hard knuckles (that may pick the web) and limited surface contact for heat transfer.

- 1.5 layer warp float weave (on web side) is also common. It provides better heat transfer, but contaminants in the small voids are hard to remove.

- Double cloth extended warp float weave is special for single tier dryers. This weave design provide good contact with the paper web and improve aerodynamic properties of the fabric surface and cleanliness. This weave design with flat fluoropolymer yarns (ie: 'nonstick' to contaminants ) next to the web, and a back side of standard monofilaments. The voids are easily cleaned, and air permeability well retained.

Most dryer fabrics are made from polyester. For high temperature conditions, heat- and hydrolysis-resistant materials are used. Fabrics are sometimes coated to repel dirt or reduce static electricity, but the coating may have a limited life.

Fabrics for high speed single tier dryers require special geometries:

- Uncontrolled air flows can cause runnability problems, such as wrinkles (ie: creases), web flutter, and edge breaks in conventional dryer sections.  They are particularly disruptive at high speeds.  Dryer fabric air permeability has a strong influence on air flow patterns - as do high fabric roughness (on the paper side), and also fabric structure.

- The speed difference between paper web and fabric is reduced by using a large diameter vacuum roll. It is reduced further by thin highly asymmetric fabrics. Such fabrics bring the interior 'layer' of the fabric, which travels at a constant speed, closer to the surface of the paper web.

Where impingement drying is used, former Beloit's pilot work has employed fabrics made of polyphenylene sulfide (PPS) and polyetheretherketone (PEEK) to resist the high temperatures (eg: 370°C). PEEK also has good abrasion resistance and mechanical properties.

Spiral dryer fabrics constructions are a departure from woven dryer fabrics. Spiral fabrics are an endless construction formed by joining helical formed loops of monofilament yarn. The joining yarn passes through the “eye” formed when the right-hand helical formed yarns merge into each other. The spirals are oriented in a cross-machine direction. Spiral fabrics are available in a broad permeability range. Permeability reductions are achieved by inserting cross-directional yarns into the open area of the spiral. There is no weak link since spiral fabrics do not have traditional seams like woven fabrics. In addition, spiral constructions offer higher levels of wear and damage resistance and are very suitable for challenging positions. In the past, spiral designs were used extensively on brown paper applications. However, through processing and material improvements, spiral fabrics today have no application limitations. They run on some of the fastest publication grade machines.


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