US2061976A - Process and apparatus for the drying of travelling webs - Google Patents

Description

Nov. 24, 1936. o. MERCKENS 2,061,976

PROCESS AND APPARATUS FOR um DRYING 0F TRAVELLING WEBB Filed Jafi. 29, 1956 v I INVENTbF Patented Nov; 2 11%35 PATENT? @FMQE PROCESS AND APPARATUS FOR THE DRYING- 035 TRAVELLING WEBS Otto Merckens, Darren, Germany Application January 29, 1936, Serial No. 61,496

In Germany June 29, 1934 6 @lafims. (Cl. 3 1 -48) This invention relates to a new or improved process and apparatus for the drying of travelling webs and, in particular, webs of cellulose, woodpulp, pasteboard, paper pulp and the like.

It is a known fact that the quality of paper, card, pasteboard and the like is improved if the drying thereof is performed slowly, carefully and protectively. Thus, in old paper mills, the paper was air dried slowly in large well-ventilated roof 10 spaces and the strength and durability of the product is recognized. Even today, special papers and boards are occasionally produced in this manner on account of the advantages derived. For large-scale production, however, slow protective drying has been replaced by rapid drying as by means of steam-heated cylinders, in order to obtain theoutput required. However, producers and consumers alike are both aware that the character and properties of the products are affected by such rapid drying.

In the paper industry, manufacturers has gone to the trouble of producing the pulp as near as possible to the paper-making machine, in order that the pulp may sufier no artificial drying and retain the appropriate swelling properties in a moist state for its further manufacture into paper, board or the like. During the latter stages, however, the drying of the product is still performed by means which act detrimentally upon'the prodnot. Steam-heated driers have the further serious disadvantage that the web, after strong compression in the wet presses, is incapable of assuminga desirable volume during drying.- Thus it is not feasible to obtain as large avolume as possible for a given weight, as is desirable in the case of some products.

An advance in the right direction has been madeby proposals to stress slow evaporation and to restrict highly heated driers with their fibredestroying effect. ,Thus, the dry sections of the plant have 'been enclosed and placed under vacuum, or air has been blown into compartments between drying cylinders. Also, attempts have been made to blow cold or hot air down on to the paper or feltor over the same, inv order to remove vapours from the drying groups. In particular, it has been proposed to apply suction at one surface and air pressure at the opposite surface at points where the web is un-supported. This, however, eifects only a surface treatment for the current removes the web from'the blowing means and escapes laterally. Air could penetrate the web only if the sides of the latter were sealed by clamping means, but this would render the web liable envelope or muff, to prevent marking, or a proto be torn. To avoid this danger, it has been proposed to employ travelling metal screens for hold ing the web and taking the tensional forces. For slow drying, the length and'cost of these means would render them impractical, apart from other 5 defects. Consequently, accelerated drying at temperatures of 159 C. to 200 C. has to be adopted. and the metal screens quickly acquire the same temperature as the drying cylinders and have the same detrimental eifects.

- 1c The present invention is distinguished in that it provides :ior evaporation' from the web by a relatively low speed air-flow with an absence or minimum of contact of the fibres with highly heated surfaces. It is based upon the conception 15 of causing the air moving means (whether operating by suction or pressure) to travel for a time with the material undergoing treatment. The resultant eifects is improved in proportion as the material is caused to bear more firmly and closely 2 against the air current means during the common travel.

The improved method is applicable whether the web under treatment travels without a companion web, as inthe latterpart of an after-drying 25 section of a paper-making plant, or with a companion web for support, as in the drying section or wet section of such plant. When a companion web is present the all current is caused to pass through both it and the web under treatment, for 30 generally the companion web will be the more pervious of the two.

The wide adaptability of the improved method makes it possible to deal with-requirements regarding the volume of the finally dried material. 35 Thus, there may be an appropriate adjustment of the tension' of the companion web which generally would consist of one of the so-called felts.

-In carrying the invention into practice, advantageous use may .be made of perforated cylinders 40 or drums with interior suction or pressure and having means forcovering, in known manner, such parts of the perforated surface as are not covered by the web under treatment. The number and disposition of such air current means will 45 depend upon rate of production and other considerations. The perforated surface of a cylinder may have a pervious covering, such as an tective felt may run with such cylinder. Where marking is of on importance or is not liable to be produced, these coverings are dispensed with.

The air current means travelling with the web is' not only convenient and adaptable but also lengthens the period for the passage of air which 55 i y period can be predetermined. In any case, the air passage can be effected in a quiet or gentle manner. Even papers heretofore considered impervious, or exhibiting only slight perviousness, are capable of being dried in accordance with this improved process, at least during a certain stage of the drying.

Air perviousness, rate of shrinkage and speed of drying vary with different materials, or even with one and the same material as the drying proceeds. Also, conditions due to sizing must.

- perforated blowing cylinders, where'desired.

It is within the scope of the invention to employ pulsating air pressure and thereby to achieve a certain breathing effect.

The air current means travelling with the web may incorporate regulator means for adjusting the temperature and positive or negative pressure, of the air, and also the quantity of air. Thus, a suitable heating element may be applied to the means for providing the air current and also an air forcing means may be applied either directly to the air current means or disposed remotely therefrom and connected therewith by suitable conduits.

Further features and practical expedients will appear from the following description which has reference to the accompanying drawing wherein is illustrated diagramatically, and by way of example only, one example of paper making plant adapted for carrying out the improved-method.

In the drawing:

Figure 1A is a diagrammatic view in side elevation of the face portion of=a paper making machine embodying the principles of my invention; and

Figure 1B is a similar view showing the remainder of the paper making apparatus.

The paper-making machine illustrated consists of section I in which the paper-mass is applied to the companion web, section II which constitutes the wet section, section III which is the dry section and section IV which is the afterdrying or conditioning section. Section I is not of present interest, but the individual further sections II, III and IV are of interest. Thewet section II consists of three wet presses a, a 11,

between the press-rolls of each of which a felt,

b, b b", is conducted by means of a number of guide-rolls c. These felts successively receive the web 01 of material. The drying of the felts 2), b Z1 may be performed in'any desired manner. In the presentexample through-blowing perforated drums e, 2 e ,.havebeen assumed.

The felts b and 11 also each pass in known manner through pairs of washing rolls which are correspondingly indicated by f. The felt b furthermore, also travels past a suction-device 9 before it reaches the drier e The first warm-air blower or drier h is now interposed between the wet-presses a and a for example. all papers which are already somewhat air-pervious at the degree'of humidity obtaining at this cated, as in the other cases, by radial lines.

Closed steam- It maybe employed at this point with point. The drier 72. effects primarily a. careful warming up and warming through of the paper web which should facilitate the removal of the water at the press a and initiate .the drying operation proper in a harmless manner. Normally, and also as illustrated, the web 0! of material at this point is pressed firmly against the shell of the blowing drum h, by a felt i which is conducted over guide rolls 0 with the interposition of a drier 7' which may also be a blow-through drier. The paper web and the felt are then blown through with a strength depending upon the conditions obtaining at the time.

For the blowing means, the shell of the cylinder h is provided with perforations which are indi- Located in the interior of the cylinder is an air distributing member k, for example constructed like a segment as seen in cross-section, through which the drying air is supplied .to the interior of the cylinder and which in turn by a plate k permanently covers the part of the perforated shell not enveloped by the web d of material. As illustrated, an air-pervious protective felt 21 or in other cases an envelope or muff, may run around the cylinder in order to avoid any marking of the web of material by the perforated shell. Furthermore, perforations k may be provided in the cover-member it from which escapes only as much air as may be necessary in any given case to dry successive portions of the drum and drum covering orenvelope as they pass by the openings k. This arrangement is duplicated in the drum Z in the drying section III. Naturally arrangements may be provided in the drum for preventing useless lateral escape of air even in cases where the webs to be treated may have different widths as compared with the length of the drum.

The web d, of material then passes next into the dry section III. This consists of a set of upper drying cylinders 1, 1 Z Z and also a corresponding set of lower cylinders m, 111. m, m and a glazing, smoothing or calendering cylinder n. The web runs around the cylinders Z and 2 without a felt or companion, whereas a felt o accompanies it around the cylinders l and Z It runs similarly around each of the cylinders of the lower series, i. e. with a felt 0 around m and m and with a felt 0 around 1n and 111. finally a felt 0 runs around the smoothing or calendering cylinder 12. All of the felts are likewise conducted around a number of guide rolls 0 and are themselves dried in a'manner similar to or the same as that which has already been described for the wet section II, e. g. by means of through-blow cylin-' ders p. In the example illustrated, the only difference is that the felts running around the cylinders m m", m are conditioned anew from cylinder to cylinder by the interposition of individual through-blow drums which serve as guide-rolls or are additional thereto.

If now, it is desired to employ the improved method of the invention in conjunction with the above described preparatory drying in the Wet section or, even without this, in the dry section, then the drying cylinders Z, m may take the form of blow-through drums of the same kind as the drum h in the Wet section II. In this case, the difierent construction of the interior of the drum, as illustrated, is not important, but it is important that the parts of the shells of the drums remaining uncovered, by the material to be dried should be prevented by some means from permitting the useless escape of drying air. Naturally, there is freedom of choice in regard to the number and aooaevo state-which includes moving the newly formed disposition of the drying cylinders to be constructed as blow-through drums so that very difierent manufacturingconditions can be suited. In the present instance, only 1 1 Z are-constructed as blow-through drums and the remaining cylinders I, 721., m l, m, m and, obviously, it

are constructed in known manner and as hitherto as steam-heated individual units. This may prove appropriate, for example, if it is desired to produce papers smooth or glazed on one side. Furthermore, as to the covering of the shell of the drum, its drying andso forth, use may be made, as to details, of the same features as are illustrated for the drum 7:. in the wet section.

From the dry section III, the web passes into the after-drying arrangement IV; This consists, in the present instance, primarily of two blowthrough drums q and g otherwise corresponding to the drums h, Z 1 or 1 around which the web of material then runs without a companion felt, as in the case of the drum Z action and thus the'output capacity is particularly large because the paper, already preliminarily dried to a considerable extent, has meanwhile become highly air pervious. Following this, after a guide roll o has been passed, there may also be provided a set of cooling drums, consisting in the present instance of two blowthrough drums and 1 which are conveniently of the same construction as the drum it already men-'- tioned. The moving paper web is cooled by these with a current of cold saturated air or supersaturated air by the blow-through method and is finally conditioned to its proper humidity depending upon the requirements of the particular case.

The internal arrangement of the drums, as already mentioned, may be devised in various ways as shown for the sake of comparison, in the drums h, 2 and Z Heating units may also lie-accommodated in any particular distributing member is, as indicated. for example by the small circles in the drum Z.

The drying method set forth should be carried into effect most simplywlth blow-through cylinders of the kind mentioned= However, in place thereci, use may also be made, for example, of a caterpillar-band running above and below the material to be dried and having suction and/or pressure areas and also of other appropriate arrangements. What is primarily important for the selection of the means for carrying out the method is that the air current means should travel fora time together with .the material to be dried and that the latter should bear closely on the former. In'addition, if the supply of drying air to theweb' is effected with sumcient air-tightness, the method can'also be performed with the aid of suction drums, acting on the opposite side, of an otherwise like kind of construction, or of other suction devices which accompany the web for a time with the same efiect.

1. The method of progressively drying and developing the texture of paper or similar cellulosic pulp-derived products from the moist state,

which includes confining successive portions 2. The method of progressively drying and.

developing the texture of paper or similar cellulosic pulp-derived products from the moist The drying wet material along in the form of a web, repeat= edly passing drying air through successive portions of said web as it moves along, alternating each of said drying air treatments with the direct application of heat to the web, and finally passing cooling and moisture laden air through said web.

3. In a machine for progressively drying and developing the texture of a web of paper from the moist state, in combination, means for continuously moving said web through the machine, a hollow rotatable drum, the cylindrical wall of which is perforated, means for guiding said web about a portion of the peripheral extent of said drum, a segmental casing disposed within said drum and having, openings communicating with the interior thereof, a closure device for blanking that part of the perforated cylindrical wall of the drum which is not covered bythe web, means for pressing said web firmly and closely against said portion of the wall of said and a heating device disposed within said air casing, whereby warm drying air is positively and uniformly forced through the successive portions of said webas they move through the machine.

developing the texture of a web of paperv from the moist state, in combination, means for continuously moving said web through the machine, a hollow rotatable drum, the cylindrical wall of whibh is perforated, means for guiding said web about a portion of the peripheral extent of said drum, an annular protective envelope of relatively soft pervious material surrounding said drum and interposed between said web and the perforated wall of said drum to prevent marking of the web, means for supplying air under pressure to theinterior of said drum, whereby it is caused to pass through said pervious envelope and said web, a closure for blanking oif that part of the perforated cylindrical wall of the drum which is not covered by said web, said closure being provided with an opening for the passage of a current of cleaning d ng air through said envelope.

5. In a machine for progressively g and developing the texture of a web of paper from the moist state, in combination, means for com tinuously moving said web through the machine, a hollow rotatable drum, the cylindrical wall of which is perforated, means for guiding said web about a portion of. the peripheral extent of said drum, an annular protective envelope'of relatively soft pervious material surrounding said drum and interposed between said web and the perforated wall of said drum to prevent marking of the web, a segmental casing disposed within said drum andhaving openings communicating with the interior thereof, said casing also hav ing a wall serving as a closure device for blanking that part of the perforated cylindrical wall of the drum which is not covered by the web, means for' introducing air under pressure into said passing, means for pressing said webfirmly and closely against said portion ofthe wall of I said drum, whereby drying air is positively and uniformly forced through the successive portions of said web as they move through the machine, said caslngwallor closure beingprovided with minor perforations for passingblasts of cleaning" and drying air through said drum'ancl envelope. 6. In amachine for progressively drying; and

developing the texture of a web of paper from the moist state, in combination, means for continuously moving said web through the machine, a hollow rotatable drum, the cylindricalwall of which is perforated; means for guiding web about a portion of the peripheral extent of said drum, means for supplying warm drying air under pressure to the interior of said drum, another similarly perforated'drum about which said web is subsequently guided, means for supplying cool saturated air under pressure to the interior of said last named drum, whereby currents of warm and cool moist air are respectively passed through 5 successive portions of said web.

o'r'ro MERCICENS.

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