US1854191A - Apparatus for drying sheet material - Google Patents

Description

April 19, 1932.

H. E. HOLCOMB 1,854,191

APPARATUS FOR DRYING SHEET MATERIAL Filed June 1, 1929 INVENTOR B M7MMWW ATTORNEYS Am Patented Apr. 19, 1932 UNITED STATES PATENT OFFICE- HARRY E. HOLCOMB, OF STRATFORD, CONNECTICUT, ASSIGNOR TO FIBERFRAKS INC, OF

NEW YORK, N. Y., A CORPORATION OF NEW YORK APPARATUS FOR DRYING SHEET MATERIAL Application filed June 1, 1923. Serial No. 367,797.

This invention relates to the drying of wet fibrous material in continuous or semi-com tinuous webs or sheets, and the main object is to effect the rapid and efiicient transfer of heat from a source of heat to the liquid which is to be removed from the web or sheet.

While the invention is particularly applicable for the drying of rag felt paper to be used in making roofing material it will be understood that it maybe applied to any wet fibrous material in web or sheet form containing organic or inorganic fibres, such as textiles, various kinds of paper, fibrous sheets containing impregnating compounds and 16 sheets containing finely divided substances,

such as fillers and the like.

In order to rapidly remove the liquid from a sheet, a relatively large amount of heat is required to change the li uid at its boiling 20 point into its vapor state so t at it may escape from the solid material form-ing the ody of the sheet. As is well known the latent heat of vaporization of water is comparatively high. In the making of rag felt paper for roofing material the paper as'it comes from thepaper making machine in web form is now ordinarily passed around a series of steam heated cylinders to dry the paper before impregnatin it with asphalt or the like. The c linder driers are large cumbersome mac ines and a large quantity of heat is wasted due to radiation from the large surface area exposed to room temperature. Furthermore the efiiciency of such cylinder driers is low 85 due to the low boiler efliciency where the Water is converted into steam for use inthe cylinders, and also due to the. loss in heat which occurs in condensation after the steam has passed through the cylinders, and is of too low a temperature, for the purpose of effectively drying the paper. v

In carrying out my invention I maintain a metallic mass at a temperature above its boiling point and above the boiling point of the liquid to be removed from the web or sheet. I am aware that it has been proposed to dry paper by passing it through a bath of hot mercury, but such attempts have not been entirely satisfactory due to the fact that por- 50 tions of the mercury are entrapped in the does not come in direct contact with the sheet,

interstices of the sheet and are carried from the bath so that there is a high mercury loss and also there is a considerable loss due to oxidation of the mercury. In my improved process a mass of the liquid metal is maintamed at the desired temperature, but the heat from this metal is transferred to the sheet by heat conducting members preferably in the form of rollers so that the liquid metal 0 but the heating effect is efficiently transferred 6 to the sheet.

y means of my invention a more compact drying unit is obtained; there is a large saving of heat, due to the fact that there is less heat radiation; and 'the heat from the original source is effectively transferred directly to the sheet. There is thus a high over-all efliciency, a more rapid drying of the sheet, and very much less space required in the plant.

The metal bath which Iemploy may be molten lead, various alloys of lead with tin, bismuth, or cadmium, or combinations of these, or I may employ mercury. I preferably use a lead alloy which when heated does not give off vapors dangerous to the workmen. As the heat is transferred from the bath to the sheet by heat transferring rollers, it is possible to protect the surface of the molten metal from oxidation by floatingron the surface charcoal or finely divided re actory material, such as brick dust or the like. This is not'picked up by the rollers and thus does not come in contact with the sheet, but serves as a blanket to prevent heat radiation and oxidation. Alloys of lead are preferably employed instead of mercury because of the lower cost of such alloys.

By the term liquid metal I wish to include not only a pure "metal, but any desired I metallic allO In' the accompan ing drawings I have illustrated one embo iment of my invention.

In these drawings:

I Fig. 1 is a top plan View, and

Fig. 2 is a longitudinal section on the line 22 of Fig. 1.

In the construction illustrated in the drawings the web of fibrous material which is to 100 be dried is delivered between feed rollers 10 and 11 and may be carried along by a belt, blanket, or other conveying sheet 12 which maybe of endless form and passed around rollers 13 back to the (paper. making machine which is not illustrate The apparatus illustrated includes a tank 14 of such character .as will adapt it to contain a bath of liquid metal 15. This bath may be'heated in any suitable manner, as for instance by electric coils, superheated steam pipes, or the like. I have illustrated somewhat diagrammatically such heating means in the form of a series of burners 16 placed beneath the tank 14. Supported at the upper portion of the tank are a series of metal rollers 17 closely adjacent to each other and so positioned that their lower sides are immersed in the liquid metal, while their upper sides are above the surface of such liquid metal. The sheet or web A of material to be dried passes from the feed rollers between a pair of guide rollers 18 and thence across the upper side of the tank resting directly upon the upper sides of the rollers 17. It may be delivered from the apparatus through suitable delivery rollers 19. Thus the rollers are heated to substantially the temperature of the liquid metal and conduct this heat directly to the surface of the sheet or web without the latter coming in contact with the liquid metal. The rollers, of course, should be of some metal which has a far higher melting point than that of the bath 15 and which will not form an alloy with the bath at the temperature at which the process is carried out. In the case of rag felt paper used for making roofing material I may employ a bath of about 60% tin and 40% lead heated to a temperature of about 300 C. I have shown only four rollers in the bath, but it will, of course, be understood that a larger number may be employed if desired. I

The web may bepassed across the top of the tank at such a rate that it will be in contact with the rollers for about thirty seconds and experience indicates that under such conditions the web leaves the rollers 19 steaming and that when the web cools it is substantially It will, of course, be understood that the apparatus illustrated may be employed only for the initial or preliminary dryin and that the final drying ma be effected by heated cylinders or any ot er suitable apparatus, such as now employed, but it may be of very much smaller size than the usual dryingapparatus.

It will be noted that as the web passes over the rollers it is bent first in one direction and then in the opposite direction. This bend-- ing facilitates the escape of the moisture from the sheet during the drying action.

If it is desired to impregnate the sheet after drying the drying apparatus illustrated may deliver the sheet directly to an impregnating apparatus so that the sheet is made,

.dried and impregnated as a single continuous operation, thereby materially saving in the cost and time of production of the final product.

The Web may contain a high percentage of organic fibres which would ordinarily be charred by subjecting the sheet to a temperature of 300 C. when dried. Danger of charring the fibres is obviated by the fact that the sheet is wet when it reaches the first roller and passes from the rollers at such speed that the final portion of the moisture is removed as steam after the sheet leaves the final roller. The removal of this steam and the final portion of the wawr may be etfected by subjecting the sheet to a vacuum if desired. It a vacuum is to be employed the upper part of the tank may be enclosed and the sheet subjected to the partial vacuum while it is passing over the rollers. Obvious this partial vacuum will not have any material effect upon the liquid metal or the direct transfer of heat from'the latter to the sheet.

The rollers 17 being of metal rapidly transfer the heat from the liquid metal to the sheet independent of any rotation of the rollers, but the rotation is desirable because it continuously carries the highly heated lower portions of the rollers upwardly into contact with the sheet and because the rotation of the rollers serves to advance the sheet across the top of the bath. The sheet itself forms a cover for the tank so that the liquid metal is subjected to air current and the oxidizing effect of the air to the minimum extent even if the surface of the metal is not covered with a layer of charcoal or other protecting medium.

It will be obvious that the rollers and their rotating parts may be driven in any suitable manner.

I have illustrated somewhat diagrammatically an electric motor 20 and speed reducing earing 21 connected by sprockets and chain to the first roller 17 and from the shaft of this roller power is transmitted to the other rollers and to the feed and delivery rollers 18 and 19.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. An apparatus for drying sheet material, including an open liquid metal bath, means for passing the sheet across the top of the bath and out of direct contact therewith, and means for supporting the sheet during its movement and transmitting heat from the bath to the sheet.

2. An apparatus for drying sheet material, including an open liquid metal bath, means for passing the sheet across the top of the bath and out of direct contact therewith, and a plurality of sheet supporting elements immersed in the bath and havin portions above the bath for engaging the s eet.

3. An apparatus for dryin sheet material, including an open liqui metal bath, means for passing the sheet across the top of the bath and out of direct contact therewith, and a series of rollers partially immersed in the bath the sheet.

4. An apparatus for drying sheet material, including a bath of liquid metal maintained at a temperature above the boiling point of the liquid in said material, and a series of rollers partially immersed in the bath for advancing the material, supporting it out of contact with the. bath, and transferring heat from the bath to the material.

5. An apparatus for drying fibrous sheets, including a bath of an alloy oflead and tin maintained at a temperature above the boiling point of the liquid in the sheet, and a plurality of heat conducting members partially immersed in the bath and engaging the sheet for holding the latter out of contact with the bath.

Signed at New York in the county of New York and State of New York this 31st day of May A. D. 1929.

HARRY E. HOLCOMB.

and serving to support,

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