US2951139A - Paper drier - Google Patents

Description

Aug. 30, 1960 R. s. WASHBURN PAPER DRIER Filed May 22, 1958 2 Sheets-Sheet l Robe/'7 S. Hsbburn Aug. 30, 1960 R. s. WASHBURN PAPER DRIER 2 Sheets-Sheet 2 Filed May 22, 1958 Eranzr Robe/'7 S. Wasbburn U ite rates atent PAPER DRIER Robert 3. Washhurn, Eeloit, Win, assignor to Beloit Iron Works, Beloit, Wis, a corporation of Wisconsin Filed May 22, 1958, Ser. No. 737,004

9 Claims. ((Il. 219-10.61)

The present invention relates to improvements in drying mechanisms, especially for paper machines, and more particularly with an improved drier drum of the type known as a Yankee Drier, and mechanism for removing the moisture from a continuously moving web.

Numerous devices have been heretofore provided for drying a continuously moving web of paper. These devices employed heat energy derived from various sources, and frequently employ steam. Electricity has been utilized for the drying of paper, such as by utilizing the resistivity of the contained water in the paper web or by using the paper as a dielectric between high frequency electrodes. feature of the present invention is to provide a mechanism which avoids disadvantages present, in mechanisms heretofore used, such as in the expense and complexity of the equipment required, the high rate of energy consumed, the effects of change in water content, and unequal drying effects.

The present invention contemplates the provision of a moving support for a web of paper such as a smooth oute surface on a rotating drum. Extending across the surface of the drum over a range of the annular periphery thereof are a plurality of parallel electrical conductors which exvtend equidistant from the drum surface and parallel to the drum axis. A high frequency voltage is impressed across the length of the conductors to generate a high frequency field which penetrates the outer surface of the drum inducing currents to generate heat energy. The conductors are closely spaced from the drum to provide a path of travel for the paper and yet insure flux penetration into the drum to generate heat energy for drying the paper web. The conductors are tubular in shape and are provided with headers at the ends which have chambers for accommodating the flow of coolant through the conductors to dissipate the heat energy generated due to the resistance of the conductors. In one form, plural sources of heat energy are provided with steam energized heating means heating said drum surface from within and electrical high frequency induction conductors being spaced opposite the outer surface of the drum to induce additional heat in the drum surface.

Accordingly, an object of the present invention is to provide an improved drying mechanism of the type described which will accomplish improved drying operation suitable for high speed drying of a continuous moving web of paper.

Another object of the invention is to provide an improved drying mechanism which will accomplish an improved more uniform and even removal of moisture from a traveling paper web.

Another object of the invention is to provide an improved web drier of increased capacity which is greater than in driers of the type heretofore used, such as those energized solely by a stream source.

A further object of the invention is to provide an improved drier suitable for use in a paper machine wherein electrical energy may successfully be employed for the generation of a drying heat energy which will obtain uniice form drying effects and will not be dependent upon moisture content of the paper.

Other objects and features will become more apparent with the teaching of the principles of the invention in con nection with the disclosure of the preferred embodiments thereof, in the specification, claims and drawings, in which:

Figure l is a perspective view of a drying mechanism embodying the principles of the present invention;

Figure 2 is a vertical sectional view taken along line II--Il of Figure 1, illustrating the effect of the high frequency field which is generated;

Figure 3 is a schematic showing of conductors and drum surface illustrating the penetration of the flux;

Figure 4 is a sectional view similar to Figure 3, and illustrating another form of construction of the electrical conductors and headers; and,

Figure 5 is an end elevational view of a drying mechanism illustrating certain elements in an alternative form.

As shown on the drawings:

Figure 1 illustrates a drying mechanism embodying the principles of the present invention as employed for removing moisture from a continuous web of material 10, indicated by the broken lines. The drier may be embodied in a drying station in a paper-making machine or the like. The web is carried over the surface of a cylindrical drum 14 having closed ends 16 and an annular shell 17 with an outer, fiat, smooth, planar surface 18 over which the web 10 is carried as the drum rotates. The drum is supported for rotation by a through shaft 20 which is suitably supported on bearings, not shown. The drum may be driven in rotation or may be carried in rotation by a web passing thereover which is suitably carried on other rolls that can be driven in rotation.

The web 10 first passes over a nip roll 22 formin a nip 24 with the drum M to lay the material flat on the outer surface lb of the drum. The web passing over the drum surface is carried through a drying zone, which extends over most of its travel over the drum surface. Doctor blades 26 may be provided at a location after the web leaves the surface of the drum to prevent material from adhering thereto.

Extending over the surface of the drum are a plurality of electrical conductors The conductors extend 1 lel to the axis of the drum, as defined by its supporting shaft 20, and extend parallel to each other. The conductors are equally spaced from the surface of the drum along their length with all of the conductors being substantially equally spaced from the drum surface.

Means are provided for applying a high frequency voltage across the length of the conductors. This voltage is illustrated as applied by a high frequency, alternating cur rent converter 30 which has electrical leads 32 and 3% connecting to headers 36 and 38 which support the ends of the conductors.

The alternating voltage applied across the length of the conductors generates a high frequency flux, inducing currents in the surface of the drum with the flux lines acting in accordance with the illustration of Figure 2. The individual currents heat the drum surface 13. The high frequency voltage converter 30, as shown schematically in Figure l, generates a voltage having a high frequeno, as shown, such as in the neighborhood of 9600 cycles per second. Also a practical but somewhat less desirable than the preferred form shown would be the use of vacuum tube oscillators generating high frequencie 0 the surface 18 as illustrated at 42. The high frequency voltage along the conductors generates a high frequency current in the surface 18, which is limited to a shallow depth of the surface of the drum, and thereby achieves high surface temperatures in the surface. These high surface temperatures can be generated at substantially the same rate as the heat is removed by the evaporation of moisture from the paper web carried on the surface 18. In this manner, a uniform evaporation and drying effect can be achieved in a rapidly moving web. The conductors 23 are spaced closely to the surface of the shell of the drier to attain the maximum electrical efficiency.

In the event that the width of the drier is such that it will require intermediate supports, a non-conductive material, such as Transite will be used, inasmuch as conducting materials would be heated to destruction by the induced currents. The intermediate supports may be designed so as to become part of channels for air flow to remove the vaporized water from the drying web.

The resistance of the conductors will generate heat in the conductor material. This is accommodated by the heat being carried off by a coolant. For this purpose, the headers 36 and 38 are constructed so as to be hollow and provide chambers therein for accommodating the flow of coolant through the conductors which are hollow in construction. As illustrated in Figures 1, 2. and 3, the conductors 28 are tubular in shape with a hollow interior *44 for accommodating the flow of coolant.

As illustrated in Figure 3, the header 38 forms a chamber 46 therein for a coolant, such as water, which flows through. the interior '40 of the tube 28. Each of the headers are substantially identical in construction and therefore, the view of Figure 3 will suflice to indicate the internal construction of each.

For convenience of installation and upkeep, the head-.

ers are formed in two sections. Header 36 has a section 48 and a section 50, which sections are held together by a hinge 52. A strap 54 connects to each of the sections to insure a complete electrical current. Each of the header sections '48 and 50 contains its individual chamber, and header section 48 is supplied with a coolant, such as Water, through an inlet line 56, and the header section 50 is supplied with a coolant through an inlet line 58. The coolant flows into the chambers within the headers and through the conductors 28. At the other end of the conductors, the header 38 is formed of a first section 60, and a second section 62 with the sections being connected by a hinge 64. The chambers within the sections have coolant outlet lines with an outlet line 66 leading from the header section 62, and an outlet line 68 leading from the header section 60. The inlet lines 56 and 58 are provided at one end of the headers and the outlet lines 66 and 68 at the other end and obtain improved flow characteristics.

As illustrated in Figure 4, the arrangement may be provided which will reduce the electrical coupling outward from the edge of the web being dried, in order that the material of the drier shell will be heated to its maximum only in the area covered by the web, and the drying will be uniform. In this construction, a conductor 28a is supported by a header section 62a having a chamber 46a therein. The conductor 28a is bent upwardly at 70 to increase the distance from the lowermost surface 72 of the conductor 28a and the surface of the paper web a. The bend 7t) curves at the edge 7 4 of the web, thus insuring uniform heating across the surface 18a of the drum, and preventing intense heating at the Web edge 74.

As illustrated in Figure 5, in one form a plural heating source is provided for drying a paper web 76. The web passes over an outer surface 78 of a drum 80. The drum 80 is sealed and is in the form of a pressure vessel having closed end walls such as 82 joined at their annular outer edge to an outer shell 84 of the drum which has the planar, smooth, outersurface 78. Steam is admitted to the interior of the drum through a steam line 86 from 'porting hub 93.

a steam source 88. The steam is drained from the drum through a line W to a drain container 92. The steam within the drum heats the shell 84 to vaporize the water in the web 76 which is carried over the surface of the rotating drum.

The web is supplied to the drum over a nip roll 94 forming a nip 96 with the drum $0. The Web moves over the drum surface under a plurality of conductors 97 which extend parallel to each other and parallel to the axis of rotation of the drum, as defined by its sup- The conductors 97 have substantially the same construction as the conductors 23 in the embodiment of Figures 1 to 3, or Figure 4.

A high frequency electrical voltage is impressed across the length of the conductors 97 to induce heat generating currents in the outer surface of the shell 84 to augment the heat of the steam within the drier drum. The heat generated by the electricity flowing through the conductors increases the capacity of the drum above that permitted by the limitations of the steam source and the pressure limitations on the drier drum. Thus, the auxiliary heat source for the steam heated drier increases its capacity and performance.

In operation of the mechanism illustrated in Figure 1, a web '19 of paper or the like passes over the nip roll '22 and up over the outer surface 13 of the shell of the i zdrum 14. The web passes through the drying zone defined by the electrical conductors 28, which induce currents in the outer surface 18 of the drum shell to generate heat at the rate at which the heat is removed by moisture evaporating from the web. High frequency electrical energy is applied to the conductors by leads 32 and 34 connected to the headers 36 and 38. The headers are hollow to form chambers therein to accommodate a flow of coolant through the hollow conductors and carry away heat generated due to the resistance of the conductors.

Thus, it will be seen that I have provided an improved drying mechanism for removing moisture from a continuous web of material which meets the objectives and advantages hereinbefore set forth. An improved and more uniform drying is performed with the controlled heat generation, and increased capacity is achieved with the other attendant advantages referred to and apparent from the foregoing disclosure. 7

I have, in the drawings and specification, presented a detailed disclosure of the preferred embodiments of my invention, and it is to be understood that I do not intend to limit the invention to the specific form disclosed, but intend to cover all modifications, changes and alternative constructions and methods falling within the scope of the principles taught by my invention.

I claim as my invention:

1. A mechanism for reducing the moisture content of a web material such as paper comprising a drying surface on which a web of moisture containing material is supported and subjected to elevated temperatures for evap oration of the moisture, means for moving the surface to carry the material past a drying zone, a plurality of elongated parallel closely spaced electrical conductors extending parallel to said surface at said drying zone whereby heat energy will be generated in said surface with a flow of high frequency current through the conductors, a first connector of a first polarity, and a second connector of an opposite polarity, said conductors connected to the said connectors to cause a flow of current therethrough with adjacent conductors being of the same polarity.

2. A mechanism for reducing the moisture content of a web material such as paper comprising a drying surface on which a web of moisture containing material is supported and subjected to elevated temperatures for evaporation of the moisture, means for moving the surface to carry the material past a drying zone, a plurality of elongated parallel spaced electrical conductors extending parallel to said surface at said drying zone whereby heat energy will be generated in said surface with a flow of high frequency current through the conductors, means for impressing a high frequency voltage across the length of said conductors, and coolant carrying means positioned for conducting a flow of coolant in heat transfer relationship with said conductors to remove heat generated due to electrical resistance of the conductors.

3. A mechanism for reducing the moisture content of a web material, such as paper comprising a drying surface on which a web of moisture containing material is supported and subjected to elevated temperatures for evaporation of the moisture, a cylindrically shaped drier drum having an annular smooth drying surface on which a web of moisture containing material is supported and is subjected to elevated temperatures for evaporation of the moisture, a plurality of elongated hollow tubular electrical conductors extending across the surface of the drum at a uniform distance from the surface along an axis parallel to the drum, and means for impressing a high frequency voltage across said conductors to generate induction heat in said drying surface and evaporate moisture from the web.

4. A mechanism for reducing the moisture content of a web material such as paper comprising a drying surface on which a web of moisture containing material is supported and subjected to elevated temperatures for evaporation of the moisture, means for moving the surface to carry the material past a drying zone, a plurality of spaced hollow tubes extending at a uniform distance from the drying surface and along the surface at the drying zone, means for impressing a high frequency voltage across the length of said tubes, and means connected to the ends of said tubes for causing a flow of coolant through said tubes whereby induced drying heat is generated in said surface and resistance heat in said tubes is carried away by the coolant.

5. A mechanism for reducing the moisture content of a web material comprising in combination a rotatably mounted drying drum having a relatively smooth annular outer drying surface for carrying an endless web of material, a plurality of hollow tubular elongated conductors formed of electrically conducting material extending parallel to each other across the surface of the drum and being equally spaced from the drum to define a paper drying zone on the drum surface opposite the conductors, a first header at one end of said conductors having a hollow flow conducting chamber therein communicating with the interior of the tubular conductors, means for delivering a flow of coolant into said first header chamber, a second header positioned at the other end of said conductors having a coolant chamber therein communicating with the tubular conductors to receive the flow of coolant, means conducting coolant away from said second header chamber, and electrical means for impressing a high frequency voltage to each of said headers whereby an inductance field will be created surrounding each of the conductors to induce heat in the surface of the drum as it rotates beneath the conductors to evaporate the moisture of the web material carried thereon.

6. A mechanism for reducing the moisture content of a web of material comprising in combination a web support member having a planar surface for supporting a web of paper in a drying plane, means for moving said web support member along a paper treatment path, a first heating means positioned adjacent said path and located to heat the web supporting surface to evaporate moisture from the web, and a second heating means positioned adjacent said supporting surface on the same side of said web as paper comprising electrical conductors adjacent said planar surface, means attached to the electrical conductors for impressing a high frequency voltage on said conductors for increasing the temperature of the surface for further evaporating moisture from the paper.

7. A mechanism for removing moisture from a web of paper passing through a paper machine or the like comprising a relatively smooth planar surface for affording support to a web of material to remove moisture from the material, means adjacent the web support member opposite the surface carrying the web for heating said member and evaporating the moisture by hea transmitted to the web from said supporting surface, electrical conducting means on the opposite side of said web support member adjacent the web of paper carried thereon, and means connected to said conducting means for impressing a high frequency voltage across said conducting means causing a high frequency electrical induction field and inducing heat in said support surface to increase the evaporation of moisture from the web.

8. A mechanism for drying a web of paper or the like comprising in combination a rotary drum having an annular outer web supporting surface, steam heating means located internally of the drum to heat said surface, means for directing a flow of heated steam to said steam heating means, a plurality of electrical conductors extending parallel to the axis of the drum adjacent the surface thereof and substantially evenly spaced therefrom, and means for impressing a high frequency voltage across the length of said conductors to generate a high frequency inductive field and generate heat in the surface of said drum for enhancing the evaporation of said moisture from said web.

9. In a mechanism for drying a continuous web of material comprising in combination a substantially smooth, fiat, planar metal drying surface, means defining a drying zone, means for moving said surface to carry a web of paper through said drying zone, and means for heating the outer surface only of said metal surface in said drying zone whereby the heat will be transferred outwardly to the web carried thereon at a rate equal to the rate at which the heat is carried away by the evaporation of moisture from the web, said heating means including a plurality of closely spaced parallel conductors, a first common connector connected at one end of each of the conductors at one side of said surface, and a second common connector connected at the other end of each of the conductors at the other side of said surface to transmit a uniform How of current through each of said conductors.

References Cited in the file of this patent UNITED STATES PATENTS 2,000,684 Allen et al. May 7, 1935 2,319,174 Wilson May 11, 1943 2,454,370 Beaubien Nov. 23, 1948 2,459,622 Cohoe et al. J an. 18, 1949 2,532,460 Phillips Dec. 5, 1950 2,674,809 Meinhofer Apr. 13, 1954

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