US2323918A - Drying fiberboard and the like - Google Patents

Description

July 13, 1943. J. F. KIERNAN 2,323,918

DRYING FIBER BOARD AND THE LIKE Filed Maren 26, 1941 ATTORNEYS Patented July 13, 1943 UNITED STATES PATENT OFFICE DRYING FIBERBOARD AND THE LIKE Joseph F. Kiernan, Brooklyn, N. Y. rilpplicatio'n March 26, 1941, Serial No. 385,220

(Cl. :i4-23) 2 Claims.

This invention relates to fiber board and the like, and particularly to the drying of such board after fabrication.

The object of the invention is to provide a process for quickly and effectively drying the board without causing warpage due to inequalities in the drying eect.

Further objects of the invention particularly in accomplishing the drying without expensive mechanism or procedures will appear from the following specification taken in connection with the accompanying drawing in which Fig. 1 is a vertical sectional view of apparatus showing a typical stage of the drying mechanism;

Fig. 1a is a sectional view on enlarged scale showing a detail of the roll and head parts in the apparatus of Fig. 1; y

Fig. 2 is a similar view showing a modification; and

Fig. 2a is a sectional view on enlarged scale illustrating the cooperation between the roll and the surrounding shell structure.

Fiber board of bagasse, wood pulp and the like after fabrication into` sheet form on screens or the like contains a large amount of moisture and must be dried before it is ready for shipment or use.` The drying of'this material is difficult 4and great care is required to subject pieces to even, uniform drying so as to avoid inequalities and irregularities which would cause an uneven shrinking effect and result in a warping of the material.

' In prior operations the sheets of fiber board or the like are carried horizontally through long air drying chambers, for instance, on driven rollers, such as shown at 8 in Fig. l carrying the sheets of ber board F and subjected to currents of hot air to carry oil the moisture. The sheets are often one half an inch or more in thickness, and the tendency is for the outer earlier dried portions of the sheets to insulate the inner undrled portions which are thus rendered very diiiicult to reach and long drying chambers and long times of exposure 'are required to reduce the moisture to desired degree while maintaining even drying conditions throughout each sheet.

In the process of this invention the sheets while being conveyed through the drying chamber are subjected to pressing contact above and below by members compressing the material to bring the successive fiber layers into more intimate contact with each other so that heat is conducted inward from each surface to the in. terior or core portions of the sheet. Then upon relief of the pressure the inner heated moisture is free to expand outward through the still heated outer fibers of each surface of the sheet. This expansion as the stock leaves the roll also opens the fiber structure and gives access to relatively dry heated air from within the heated chamber permitting this air to penetrate into the pore spaces o1 the material. While in this position this heated air evaporates a percentage of the moisture of each fiber until it is compressively heated and exhaled at the following roll, this exhalation of evaporated moisture being augmented by the continuedtendency of the inner heated moisture to expand outward through the still heated outer fibers of each surface of the sheet. In this way by making successive internal heat applications with intermediate expansion and drying of the material, the heat is conveyed rapidly into the material and the moisture expanded out. In most casesit will be desirable to heat the rolls themselves so as to conduct additional heat directly from the roll surfaces int'o the material.

In the apparatus illustrated diagrammatically in Fig.A 1, sets of rolls 9 -and l0 are substituted at intervals for the conveyor rolls 8, these rolls preferably being driven at peripheral speeds corresponding to the peripheral speeds of the conveyor rolls 8. The rolls preferably are heated for instance by steam or internal gas jets I2 as indicated or electrically where conditions warrant. The surfaces of these rolls 9 and IU may be cylindrical as shown or undulated, corrugated or grooved to grip and irregularlypress into the surface of the ber board material "s it passes. Between the heating stations' hoods I4 may be provided kept under lower pressure to draw away the air and moisture from the surface of the sheets.

The inward iiow of the air and moisture intov the hood is illustrated in Fig. l showing the d irection of the currents l5 drawing the gases over the surface of the fibers at the expansion stage following the roll compression and providing for a ow of the moisture laden air from directly under the roll to the vent pipe.

As illustrated in Fig. 2 the heated rolls I9, 20 may be supplied with hot dry air under pressure and provided with jet openings 2| permitting the escape of this drying air through the periphery of the roll cylinders into the material, the periphery of the roll not in contact with the material being housed in a shell 22 slidingly, closing the ports 2| and directing the escaping leakage ai.

'- from opposite directions on to the upper and carrying the heated currents along the surface of the board in each direction between the rolls. This will give a smooth engagement of the material with the shell in case there is any contact and preclude the possibility of the material being snagged or roughened by the sheet metal edge of the jacket and will spread the heated air currents over a large area of the material under treatment and for a longerperiod of time.

In al1 of these treatments of the material the bers are pressedA together and simultaneously heated so as to carry the heat down into the material from the pressing, heating surface. Then the release of the pressure opens the fibers and permits the volatilized vapors topescape and rendersthevsurface accessible to the surrounding hot air of the drying chamber. The successive beatings concentrate the heat application along a narrow area giving a temporary high concentrated heating under pressure instead of the distributed relatively lower temperature air treatment of the prior art, and this temperature concentration of the heat combined with the pressing of the bers together is quickly effective to transmit the heat into the interior of the ber board and overcomes the insulating eiect of the drying of the outer fibers.

The result is that with' a uniform distribution of the heat and pressure across and along each sheet the heat is applied much more effectively and efiiciently throughout all of the fibers. Time is saved and the length of lthe dryingl chamber reduced, and there is a corresponding increase heat and pressure along al1 portions of a'trans' verse area extending crosswise of the board, simultaneously supplying currents of drying air to the surface of said sheet at said area,` thus progressively bringing the successive fiber layers into more intimate contact with each other and conducting heat inward from each surface, and releasing the pressure on said surfaces to allow said surfaces to expand after the application of said compression, and thereafter circulating said air over the surfaces of the board as it expands to remove moisture therefrom.

2. 'In an apparatus for drying fiber board the combination of a series of sets of cooperating pressing rolls relatively superposed and contacting opposite faces of the board and compressing and feeding the board, certainof said rolls being hollow and peripherally perforated, and means for supplying air under pressure within said hollow rolls so as to force said air through said perforations and into the board throughout its surface under compression, said means comprising a member closing off the ow through such of said perforations as are not adjacent to said surface so that the air supply from saidrolls is confined to the perforations adjacent the surface of said board.

JOSEPH F. KIERNAN.

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