What Is Forming Fabric?
The forming fabric of paper machine clothing (PMC) is playing a crucial role to dewater the pulp and form the paper sheet, support the sheet as it formed and carry to the next pressing section during the paper production. It’s composed of one or two endless fabric loops.
A properly designed constructed and maintained forming fabric will help the former produce a sheet that meets end-products specification at an acceptable production rate. In addition to excellent fiber support, efficient dewatering property, make the smooth surface of the sheet, the forming fabric also has good running stability and abrasion-resistant capacity.
Forming fabrics for the paper machine are made by weaving together yarns oriented in the machine direction (MD) and cross-machine direction (CD). There are many different weave patterns but they can be grouped into four general categories or styles based on the number of CD yarn layers.
The four fabric styles are：
- Single-layer, one set of CD yarns woven together with one set of MD yarns.
Double layer – two sets of CD yarns stacked on top of each other, woven together with one set of MD yarns.
- Double-layers, two sets of CD yarns stacked on top of each other woven together with one set of MD yarns, to enhance the abrasion resistance property and fiber support.
- Two and a half layers – The double-layer forming fabric has a flaw of the poor balance of the dehydration efficiency and fiber support, so two-layer and half come out. Additional CD yarns typically smaller in diameter added to the top layer of a double layer fabric to provide better fiber support, also expands the space and enhances the dehydration ability and service life.
- Although the two and a half layer forming fabrics have good advantages, it is not unassailable, it does not maximize the characteristics of the upper and bottom layer due to structural limitations, so the triple-layer emerge on demand. Triple-layer – two single-layer fabrics bound together by a set of smaller CD strands, to get much better-supporting points. The surface layer is flat heald which has the better property for sheet forming, the bottom layer in four, five or six healds to get good wear resistance.
The Triple-layer forming fabric has congenital insufficiency. First, the upper layer and the bottom layer are easily dislocated due to the force or damage of the connecting line or even “divided” and scrapped. Second, the bonding line has a negative effect on both forming and dehydration. In order to overcome these shortcomings, we have the self-supported binder (SSB) forming fabrics. The SSB structure utilizes the upper weft yarn to combine the bottom layer directly, without the additional binding yarns, which comprehensively maintains the advantages while overcoming the deficiencies of the three-layer fabrics.
Forming Fabrics Monofilament Yarn Material
- To avoid the blemish on the paper sheet, the most important requirement of monofilament is uniformity diameter over the entire length of the yarn.
- High tenacity polyester (PET) monofilament yarns are used in the warp (MD) to provide the required high tension of the forming fabrics, and the diameter of MD yarn usually between 0.12 to 0.30 mm.
- The monofilament yarn in the weft (CD) of the paper side is usually 100% polyester in high density to get better fiber support, while the mechanical (bottom) layer is composed of 50% polyester and 50% nylon in thicker diameter to ensure better wear resistance property. Nylon monofilament provides good abrasion resistance, but it’s not stable in hydrolyzed as PET under humidity conditions, so it will not exceed 50% typically. The diameter of the weft (CD) yarn is usually between 0.11 and 0.45 mm.
Main Property of Forming Fabrics
A properly designed constructed and maintained forming fabric will help the former produce a sheet that meets end-products specifications at an acceptable production rate. The variables design and construction of paper machine forming fabrics influence overall sheet quality. The main property of Forming fabrics is as follows:
- Dehydrate property, expressed parameter by air permeability and Drainage Index (DI). The pulp concentration is roughly 0.4%~1%, that is, more than 99% of the pulp is water, and about 96% of the water is dewatered in the forming section. The forming fabric has to dehydrate a huge volume of water in a short span of time.
- Fiber support capacity: expressed by the Coefficient of Fiber Support(FSI). Good forming fabrics not only need to drain the water rapidly but also have to support the fibers on the surface to form a sheet. Good fiber support of the forming fabric improves the sheet characteristics such as flatness, smoothness, printability and strength properties, also avoids fiber embedding or clogging of the forming fabric, reduce the loss of fine fibers and fillers.
- Mechanical property: The mechanical property of a forming fabric includes:
- The transmission ability to transfer the sheet to the press section on the paper machine, and the ability to guide and drive the forming fabric itself.
- Stability in lateral to ensure good sheet flatness of the side part, and stability in longitudinal to enhance efficiency and running property.
- Good stiffness which will increase the transfer capacity of the paper machine and efficiency.
- Excellent wear resistance make the forming fabric to be long service life.
Features of Bonfilt’s Paper Machine Clothing
The running property of the forming fabric and the quality of the formed sheet depend on the retention rate and forming of the fiber. Bonfilt’s paper machine clothing has the features of below:
- Good and properly designed woven structure, excellent drainage efficiency and fiber support, easy clean and maintain.
- Made out by the top quality of raw material, which has even yarn diameter, good strength and wear resistance property and longer service lifetime.
- Woven by Texo looms to achieve a highly precise and smooth surface.
- Max. width 13.5M.
- Bonfilt have a complete portfolio of the paper machine clothing, the single to triple layer of forming fabrics.
- Endless seam by automatic seaming machine, no-marking and has nearly the same property as the fabric surface.
- Heat setting by Juergens oil roller heat setting machine to anti-deforming and better dimensional stability, low elongation, smooth running performance.
- The formed sheet has a non-marking surface, high acceptable rate.