US2130665A - Method of and machine for drying or conditioning webs of paper and the like - Google Patents

Description

Sept. 2o, y1938.

2 sheets-sheet 1 D.' B. BRADNER ACEINE FOR DRYING OR CONDITIONI WEBS OF PAPER AND THE LIKE Flled Sept 18 1935 METHOD 0F AND M Sept. 20, 1938. D B BRADNER 2,130,665

METHOD OF AND MACHINE FOR DRYING OR CONDITIONING WEBS OF PAPER AND THE LIKE Filed Sept 18, 1935 2 Sheets-Sheet 2 73 E 77 70 nu I 77 #gl 9 3 26.70 39 2,5 9

@E KFM Patented Sept. 1938 UNITED STATES PATENT OFFICE METHOD OF AND MACHINE FOR DRYING OR CONDITIONING WEBS F PAPER AND THE LIKE Application September 18, 1935, Serial No. 41,171

14 Claims'.

'I'his invention relates to methods of and machines for drying or conditioning webs of paper and the like; and it comprises a supporting device such as a foraminous wire belt adapted to supporta moving web of paper, ablower, a duct connected to the discharge of the blower, said duct advantageously having converging walls, and adapted to discharge air into a diverging passageway formed by said supporting device and by an impervious member adjacent thereto; and it further comprises a method of conditioning webs, including supporting the web on one side on a foraminous carrier and blowing air at high velocity over the other side of the carrier and adjacent the supported side of the web, while maintaining the static pressure of the high velocity air adjacent the web substantially uniform and slightly subatmospheric; all as morefully hereinafter set forth and as claimed.

The invention is particularly adapted to the drying of paper after it has been coated, gummed or the like. It eliminates the necessity of cumbersome festoons with their attendant dimculties, and provides apparatus for drying or otherwise 25 conditioning webs rapidly, continuously and without injury. The webis held flat during the drying operation. According to the invention there is provided a machine having a pervious flow and reduced pressure whereby the web is lightly but rmly drawn against the support and air is passed rapidly across the entire width of 35 the web. The uncoated or dry side of the paper is in contact with the support. In the apparatus air isforced by a blower through a progressively constrlcted channel and delivered to the paper in a gradually diverging passageway.. the system 40 Vconstituting in essence, an embodiment of a Venturi tube. Air at relatively ylow velocity and relatively high static pressure thereby assumes a condition of relatively high velocity and low static pressure, and in the latter conditionr it impinges 'upon the web. It is arranged that the static pressure of this high velocityair shall beapproximately\uniformly less than atmospheric (or less than 'that on the opposite side of 'theweb)` across -the entire surface 'of"the,web, thusholding the ooweb flat against 1 the `supporting screen. Under" thesey conditions diffusion of water or other solvent from'the opposite, freshly coated side of the web is very fast and there results a very rapid rateof'dryingm` Y 56 vIn the accompanying drawings there is shown,

more or less diagrammatically, an example of a specific embodiment of the invention.. In the drawings, l

Fig. 1 is a perspective view, partly in section, of the drying machine, showing the air passage arrangement;

Fig. 2 is a plan view corresponding to Fig. 1 and showing the carrier for the web; and

' Fig. 3 isan end view of the apparatus of Fig. 1 illustrating the air passage system.

In the showings, in which like reference characters indicate like parts throughout, the machine is shown as having an endless foraminous carrier I0 adapted to support a web 9 and carried on two large drums Il (Fig. 2) only one of which is shown in Fig, 1. Driving means are shown for one drum,'comprising a pulley I2 and belt I3 driven by power means, not shown. Aswill be explained, the driving means are in some cases omitted. The carrier is advantageously of wide wire mesh, the wires being wavy, as shown, which eliminates the possibility of occurrence `of dead spots during drying. The apparatus is provided with supporting columns 50 carrying cross beams 5l on which are supported siderails i9. The carrier is movably supported on a plurality of spa-ced roilers I8 mounted in bearings 52 4on the side rails.

Below the carrier are positioned a plurality of air circulating units. Each unit comprises a double blower it driven by a belt I5v from a power shaft i6 driven by a motor Il as shown. The two outlet conduits 20 of the double blower are merged as Yat 2| into a passage of curving shape 22. The top of this passage merges into two plates or sheets 23 closely spaced from the carrier It. The inner portions of the sheets 23 are supported on longitudinally extending girders 26. The sheets 23 extend outwardly to the edges of the carrier and are slightly deiiected downward, thus providing two narrow passageways. between the plates and the lcarrier `whichy passageways progressively increase `slightly in cross vsectionalarea toward the edges of the carrier. The

amount and rate of this increase in` the cross sectional area of passageways 25 is important` for reasons hereinafter pointed out. A restricted throat portion 24 joins these passageways 25 with the duct 22 from the blower. This throat portion is the vmost constricted'passage in the system.

The'air passage arrangement described isin effect a venturi. Air is delivered by the blower into conduit 2| Aat a given gage pressure and a given velocity.` In going through the throat por,- tion 24 the velocity increases and the static head falls.I The air then enters passageways 25 which, as hreinbefore pointed out, gradually increase in cross sectional area. The' dimensions of the passageways and the rate of increase of their cross sectional area are such that the air here is in a condition of high velocity and approximately uniformly reducedpressure across the whole web area. With a suitable blower the pressure is slightly subatmospheric.` In practice thegage pressure is of the order of magnitude of an inch of water (.04 pound per square inch) below atmospheric. This is suiiicientto draw the web down flat upon the carrier, where it is rapidly dried by the high velocity hot air blast.

Return air ducts 30 are provided to deliver the air back to the heater 33 and thence to the blower intake. Not all of the air is ordinarily recirculated. Gaps 34 are provided on each side of the apparatus between the carrier i0 and side walls 43. These allow some leakage of air in and out of the system. If desired all the air may be exhausted to .the atmosphere but to economize heat it is advantageous to recirculate a considerable portion.

'Ihe sides of the machine are provided with impervious heat insulated walls 43.

Figs. 1 and 3 show an air control arrangement which I have found useful in connection with this machine. As shown, the restricted throat portion 24 is provided with an inner pair of curved deflecting plates 39, forming two. channels 40 dividing the air stream and directing it into passages 25. The two deflectors also form between them an air passage 4I delivering to the center axial region of the web. A longitudinally extending damper 42 is provided by which means Ait is possible to direct air to the center portion of the. web in the required proportion, to secure e .n drying.

'I'he character of the moving carrier is important. It is desirable that there should be relative movement between the carrier and the moving web. Sometimes it suilices to keep the ca1--er stationary and simply movethe web with respect to it. That is, the apparatus may be provided with a stationary foraminous top. Usually I find it better to drive the carrier in the same direction as the paper but at a slightly different speed, which may be either faster or slower than the paper. The object securedxin each case is to insure relative to the carrier so that all portions of the under surface of the'paper are exposed to the air current. Otherwise imperfect drying and other defects might result. The word carrier l as used in the specification and claims refers to this supporting member regardless of whether it is stationary or driven as described. The carrier is conveniently made of woven wire of very open mesh. I have found that a screen composed of wire strands 0.08 inch in diameter with meshes 1 x 2 inches is satisfactory. The carrier can be made of thin perforated metal or of cloth, if desired. It is desirable that the longitudinal Wires of the screen be curved or staggered, as indicated in Fig. 2, so as to prevent any portion of the paper from Ibeing continuously in contact lwith the carrier througout the entire drying operation.

Observations on the behavior of the machine in operation indicate that in the immediate vicinity of ,an individual carrier wire the pressure is appreciably greater than that between the wires. These local pressure variations do not interfere with'the proper functioning of the mamovement of the paperchine as it is found that the web is held at against the carrier and is restrained from tendencies to curl. In operation the drying of the web is exceptionally rapid.

'I'he following example illustrates, by way of example, a typical paper drying operation utilizing the present machine.

Paper stock 39 inches wide and of a grade commonly used for making coated paper, weighing 50 pounds per ream (500 sheets-25 x 38 inches) was coated with a typical clay-watercasein coating composition containing 25 pounds of water per ream of coated paper. The coated paper was continuously delivered to one end of the carrier, which was moved at a speed slightly less than that of the web. Hot air was delivered to the under side of the paper by the blowers at a velocity of feet per second. The static pressure below the web was 3A inch of water below atmospheric and the temperature of the hot air blast was 275 F. The paper was completely dried in 10 seconds.. After leaving the other end of the carrier it was wound on a reel (not shown). In case even more rapid drying is desired, the top face of the web may be subjected to a warm air current. But for manypaper coating operations, I iind that the operation described, abstracting water-from the lower surface alone, gives a superior product.. The drying is sufiiciently rapid for all ordinary purposes. The ap paratus is well suited for drying uncoated paper. The apparatus is well adapted for drying other webs than paper; cloth for example. It can also be used for other web conditioning operations.

What I claim isz- 1. Machine for conditioning webs, comprising a conduit having walls converging to a narrow throat, a foraminous carrier for a web, a partltion member adjacent said carrier and slightly inclined with respect thereto, a passageway communicating with the throat and dened on opposite sides by said carrier and said partition member, said passageway thus gradually increasing in cross sectional area in a direction away from the throat, and means for delivering air through said conduit and throat into said passageway.

2. Machine for conditioning webs comprising a foraminous carrier for a web, a conduit having walls converging to form a narrow throat, an extension of said walls disposed slightly inclined with respect to the web carrier and dening an air passage formed on the one side by the carrier member and on the other by the extension of the walls of the throat portion, said air passage gradually increasing in cross sectional area to provide approximately uniformly lowerpressure on the one side of the carrier than on the other, and a. blower adapted to discharge into said conduit.

3. Machine for conditioning webs comprising a blower, a foraminous carrier for a web and means for delivering air over a substantial area of that surface of the web supported by said carrier at high velocity and at a pressure substantially uniformly less than that on the opposite side of the web, said means comprising a conduit of progressively decreasing cross sectional area leading from'the blower, a partition member adjacent the carrier and forming in conjunction therewith an air passage into which air may-be delivered through said conduit, said air passage increasing gradually in cross sectional area in the direction of the passage of air therethrough.

4. Machine for conditioning webs comprising a foraminous carrier for` a web, a blower, an air duct leading from said blower to said carrier and returning to said blower, said carrier forming a part of one wall of said duct, said air duct gradu-h for heating air, a conduit gradually converging to a constricted throat, means for forcing heated air through said conduit and throat, a partitionmember connecting with a wall of the throat, and forming in conjunction with the carrier a gradually enlarging passageway adjacent the carrier to carry air at high velocity and subatmospheric pressure along the side of the web in contact with the carrier, return ducts connecting said passageway with said air forcing means and bleed means putting the system in communication with the atmosphere.` A

6. Machine for conditioning a web comprising a foraminous supporting device adapted to support a moving web, a blower, conduit means leading from the blower to a zone adjacent the central portion of the web so as to discharge air to the supported side of the web in a narrow path between the two edges thereof substantially centrally of the web as the web travels over the supporting device, partition members closely adjacent the supporting device and forming in conjunction therewith gradually enlarging passageways adjacent the supporting device through which the air flows at high velocity and at substantially uniformly lower pressure than that exi'ting on the unsupported side of the web and means near the edges of the web for removing air from the vicinity of the web.

7. Machine for conditioning a web comprising a foraminous supporting device adapted to support a moving web, a blower, a conduit connected to the blower and tapering to form a narrow throat portion substantially centrally of the web, sheet members spaced from the supporting device, the distance between the sheet members and the supporting device gradually increasing towards the edges of said device, and means in thethroat portion to deect air along the supported side of the web to each edge thereof through passageways bounded by the supporting device and by said sheetV members.

8. The apparatus of claim 3 wherein the fof raminous carrier for theI web is an endless wire screen belt and means are'provided for moving the carrier and for moving the web at dierent relative speeds.

9. Method of conditioning webs which comprises supporting the web on oneside of a foraminous carrier and passing air at high velocity over the other side of the carrier while maintaining lthe static pressure of the high velocity air adjacent thexcarrier substantially uniform and slightly subatmospheric.

10. Method of conditioning webs which comprises passing air at high velocity over one side of the web, supporting this side of the web on a foraminous carrier and holding the web against the carrier by maintaining the static pressure of the high velocity air adjacent thereto substantially uniformly just below the pressure on the opposite side of the web.

11. Method of conditioning webs, which comlprises imparting velocity to a stream of air;

passing the stream through a contracting passageway to increase its velocity and decrease its static pressure; then causing it to iiow, at high velocity and low static pressure, in contact with and substantially parallel to the surface of the web, maintaining its static pressure substantially uniform', by causing it to pass through a gradually enlarging passage, while it is in contact with the web, and supporting the web on the side exposed to the stream of air.

12. Machine for conditioning webs, comprising a conduit having lwalls converging to a narrow throat, a foraminous carrier for a web, partition members adjacent said carrier and slightly inclined with respect thereto, two passageways having a common inlet `communicating with the throat, said passageways being defined on opposite sides by said carrier and said partition members, and thus increasing gradually in cross sectional area in a direction away from the throat, and means for delivering air through said conduit and throat into both of said passageways.

13. A machine for conditioning web material comprising a blower, a foraminous supporting device adapted to support a moving web, a constricted throat near the central portion of said supporting device, a conduit leading from the discharge side of the blower to said throat, sheet members near said supporting device and slightly inclined thereto, said sheet members and supporting device defining passageways which lead from `said throat to the edges of said supporting device and gradually increase in cross sectional area away from said throat, and means for conducting air to the central portion of said supporting device between said passageways.

14The machine of claim 13 in which means are provided for regulating the amount of air conducted to the central portion of the supporting device.

DONALD B. BRADNER.

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