New technological enhancements for Tissue Felts

Tissue felts cannot bear any irregularity, nor any defect. Even just one fiber sticking out from the felts surface is enough to impair the quality of paper produced. So, if for traditional paper types we can use “rather simple” felts, for tissue paper instead, exceptional products are required that only few producers in the world can manufacture.

At Binet Sul Liri S.p.A., research and development are a meticulous constant and the challenge represented by felts for tissue machines is a primary concern. Therefore we have developed a number of specific technical tools either for felt designing: FELT ENGINEERING. Than for technology evolution: SOFT-TOP and TWIN-TOP, and also for prototype trial testing – FELT TEST. Here are a few notes on these topics.

FELT ENGINEERING

It’s an exclusive software created, tested and now daily used by Binet sul Liri for designing of its felts. It is able to calculate all of the most important technical characteristics of the felt using equations deriving from physics of porous means, for example:

» distance between fibers in microns;
» open surface in cm2/m2;
» length, diameter, tortuosity of capillaries in mm and microns;
» percentage of contact surface;
» percentage of achievable dryness;
» effective pressure of the fibers on paper in Kg/cml;
» pressure drop at the suction box;
»  sum of loading loss in meters of water column in every section of the felt;
» felt thickness, new, compressed and critical thickness in mm;
» total deformation and deformation of every section of the felt in mm;
» total weight and weight of every section of the felt in gsm;
» total air permeability and permeability of every section of the felt in cfm;
» width of the nip in mm with and without the felt;
» water eliminated in l/s;
» drain speed in mm/s;
» active volume in cm3/m2;
» operating void volume in cm3/m2;
» optimal needling density in strokes/cm2;
» optimal needling depth in mm.

Advantages: evaluation, during design phase, of all technical characteristics of the felt to be produced and of all the possible implications deriving from every adjustment made. This way, often, a first felt supplied can perform better than standard ones.

The alternative: use of felts designed by similarity of position and production and eventually adjusted through following supplies. Commercial standard felts can give an acceptable efficiency and life-time when well designed and produced, FELT ENGINEERING guarantees optimization of machine clothing. Like all other components of the paper machine, felts can be designed and produced using engineered methods instead of being produced empirically as done till today. This is the only way to optimise product’s performance and moreover the efficiency of the press. In fact a conventional felt can result to be a good felt when it is well designed, but it’s unlikely to be the best felt achievable, as like a Binet felt!

SOFT-TOP and TWIN-TOP

One of the main problems in the tissue field is represented by the necessity to generate a very fine and dense paper side surface on the felt with the purpose to achieve: an excellent pick-up and holding of the sheet; filtration of the filling materials; high dryness; low re-wetting. To reach such goals, usually fine fibres and an intense needling are applied.

At Binet Sul Liri, research and development are a meticulous constant

The inconvenience of such procedures consist in the transportation of the fine fibres through the structure of the felt, producing a densification of also the internal layers, causing air and water permeability reduction. Consequently felts can become difficult to condition and to keep clean.

The system planned by Binet Sul Liri consists in the dissociation of the paper side functions with those of the rest of the felt: the paper side is built as a very light and perfectly consolidated baseless felt, meanwhile the complex of the base fabrics and of the internal batts trace the typology of a standard felt.

The two manufactured products are then assembled by means of particular procedures in order to maintain a very fine and dense surface along with a relatively open and permeable internal structure. To describe it synthetically and efficiently, we likely named this baseless structure “SOFT TOP®”.

Our tissue felts have gained so much from such application that in the majority of the cases they result to be of better-quality in comparison to the standard. Recently we have subsequently developed the concept by applying two light SOFT TOP structures instead of only one heavy structure, thus achieving other incredible advantages such as: highest speeds; reduced energy consumptions; production flexibility; extreme cleanliness of the felt and of the fabric in particular on Crescent Former machines; up to 50% more lifetime than the standard; extreme regularity of the profiles.

Such innovation, identified as “TWINTOP®”, seems to be the most interesting development of the tissue felt technology on the market at the moment. “SOFT-TOP®” and “TWIN-TOP®” are trade-marks by Binet Sul Liri and are exclusive applications of our firm.

FELT TEST

It is the squaring of the circle. It is a guiding system that allows you to test on a real sample designed on the basis of the customer’s requirements, the ability of the felt to:
» quick start-up;
» give the required amount of water to the vacuuming elements and to the NIP at the required speeds and with the available air flow;
» monitor evolution over time in terms of thickness, permeability and also water handling.

A full test of a sample measuring 8,0 m x 0,5 m, takes up to two weeks’ time and simulates a number of NIPs on the actual machine equal to 60-65 working days. Longer time may be necessary for special requirements. Measurements are taken once per hour on the first day to simulate the start-up, then once daily on the subsequent days corresponding to a once a week survey on the real machine.

The maximum speed of the pilot press is of 2200 m/min, the pressure of 100 kg/cml, therefore in line with the maximum commercial needs. There are two adductions of water, one to simulate the contribution given by the sheet, the other to simulate the one given by the washings. There are then two suction boxes with slots to simulate the conditioning and a suction box with holes measuring a meter lengthwise to simulate the suction press. After each element there is enough operational space for the insertion of measuring
instruments concerning the water content and felt permeability. There is also a hot air generator to simulate the effects of the vacuumed air temperature on the performance of the felt.

Conclusion

Thanks to these particular computer and technology tools, Binet Sul Liri is a candidate to be the most powerful supplier of tissue felts of the third millennium. Our developments and our conclusions are available to all manufacturers of paper machines and all paper producers in order to enhance and improve their productions and their technology.