US2046750A - Pressure inversion process of making hard board products - Google Patents

Description

- UNITED STATES PATENT OFFICE I 1' awe-r50 PRESSURE INVERSION PROCESS OF MAK- ING HARD BOARD PRODUCTS William H. Mason and Charles H. Westphalen,

Laurel, Mlss., assignors to Masonite Corporation, Laurel, Miss, a corporation of Delaware No Drawing. Application April 12, 1934,

' Serial him-720,247

17 Claims. (Cl. 92-61) The present invention relates, to a process of press such as is preferably used, provision may making hard fiber products, andis an improvebe made for equalizing the pressure on theindiment on the, patent to Mason No.-1',663,505, vidual boards. granted March 20th, 1928. The invention has for The pressure initially applied is extra high and 5 an object to enable the production of an improved is adapted to press out substantially the maximum hard board or other fiber product practically free quantity of expressible liquid water, and to secure from surface defects, by providing an improved extra high surface qualities in such skin-like mode of hot pressing, herein called a pressure portion -of the board as is being consolidated inversion process. In accordance with the imat the smooth surface farthest from the wire proved pressure inversion process, extra high mesh, through which mesh the expressed wal0 pressure is initially applied for a short interval ter escapes. The escaping water carries with it to a fiber body, or wet lap containing considersolubles; and the resulting reduction of solubles able water, as for example, more than 25% ,of remaining in the board is-of advantage because, water, usually more'than 50% of water. 'I'herewith too great soluble content, there is increased after the pressure is reduced and the hot prestendency to production of surface defects. Some 1.) sure operation is carried on under such reduced saving in expense and reduction in drying time pressure, except that for the higher density are obtained by the efllcient expression of liquid boards the pressure may be raised again when water. Y the moisture content has been sufliciently re- Aftera short interval at the extra-high initial duced. pressure the water outflow is over, and the pres- 20 A further object is to save drying time and the sure, preferably without ever being completely expense ofheat-drying out of water, which by released, is reduced to a lower pressure adapted the present process is pressed out more effectively in combination with the effect produced by the by the high initial pressure. Other objects will ig er in ia Pressure to Yield a board of the appear in the following description of illustrative sired density. About one minute at the extra 25 procedure, it being understood that the invention high pressure and one-half minute time for iis not limited to the particular procedures defooting the redu n have v n good r tsscribed herein, but is as broad as the claims. In making a board of l1.05 specific gravity,

The fiber to be used is made from growths, for example, the extra high initial pressure may such as trees, grasses, canes, corn-stalks, and the be about 400-500 pounds per square inch, and 30 like containing ligno-cellulose fiber; The ra reduced after about one minute to about 100-125 materials may be shredded or ground or fibrated P d per Sq e inch and drying completed in in other ways, so long as plenty of the non-celluabout 10 minutes or less for a board thick. lose content is retained in the fiber with the Lower or higher pressures will reduce or raise cellulose to secure elfective coalescing or bonding the density. It was noted, for example, that with 35 with high wet strength of the hot pressed board. an initial p ssu of 200 p u s p r squa i Explosion by high pressure steam of wood chips, ed y a reduced Pressure of 60 pounds p followed by partial refining, as by beating, is the square inch, a board of .9 specific gravity was preferred mode of fiber preparation. Made of p du e and d y Completed in about 20 n- 40 such ligno-cellulose fiber, the product, as a utes for a board thick. These figures are 40 board, has high wet strength and appears to b illustrative onlyyand there may be considerable bonded by the natural non-cellulose material in variation on either side. the fiber. A small percentage,as 2%, of petro- Use of the ordinary temperatures heretofore latum or other waterproofness-enhancing agent available for manufacture of hard board from is preferably incorporated. Extraneous binders wet lap as, for example, temperatures in the gen- 45 and fillers are permissible, but not essential. eral neighborhood of 350-400 F. requires times The wet lap, usually containing about 60% of about as stated above, but a material saving in water is introduced in a heated platen press with time can be obtained by heating the platens and wire mesh between a face thereof, preferably the boards to an apparently critical high tem-" the lower face, and a press platen. perature over about 430 F. and preferably about 50 To secure best and most uniform results the 450-550 F., which hasbeen found to bring out press should have provision for rapid control of a new plasticity not available at temperatures heating steam to the platens, controls for rapidly I below about 400 F. and. thus to make the best moving the platens toward and away from one and hardest board.

another, and in the case of a multiple platen This pressure reduction, following the initial 55 application of extra high pressure, is observed, when using a 21 platen hydraulic press, making 20 boards at a time, to be accompanied by a temporary expansion of the boards, which expansion may be up to about 10 or 15% of the finished thickness of board, and is particularly noticeable if the pressure is reduced rather rapidly, as may be done if desired. By this expansion the remaining water content in'the board is apparently redistributed throughout the mass and largely withdrawn from the preferably smooth finish surface furthest away from the wire mesh, thereby minimizing likelihood of producing defects at such surface.

The drying is continued at the lower pressure, preferably without change, the pressure being followed up as shrinkage takes place, and maintained until the product is dry. The shrinkage and its follow-up is readily seen in a multipleplaten press to considerably exceed the expansion incident to the pressure reduction.

After the moisture has been reduced, for example reduced down to around 5% or less, the pressure can be increased if desired, particularly with the higher gravity board, up to the initial extra high pressure or higher as desired, as for example 1000 pounds per square inch, to get the benefit of high pressures in the final stages of the operation but the lower pressure may be carried through until the board is finished. So long as scorching is avoided, the final pressure and temperature application may be kept up, and applied to the board for a time after it is dry. The steam valves to the platens can be closed and the boards removed as soon as dry and the platens allowed to cool somewhat before the next pressure application, though the heating steam may be applied uninterruptedly if desired.

- We claim:

1. Process of making hard products, such as board and the like, of a body of ligno-cellulose fiber containing a sufiiciently high proportion of non-cellulose to produce, thorough bonding and containing 25% .or over of water, which comprises pressing same in a hot press with wire mesh between the fiber body and a press platen with initial application of relatively high pressure, and then reducing the pressure, and continuing the drying of the product in place between the heated platens under pressure considerably lower than that initially applied, but not, however, below about 60 lbs. per square inch.

2. Process as in claim 1, in which the initial pressure is several times the lower pressure used later.

3. Process as in claim 1, in which the body of fiber contains 50% or over of water.

4. Process as in claim 1, but in which the pressure is again raised-prior to completing the board and after the moisture has been reduced to about 5% or under.

.5. Process as in claim 1, in which the initial pressure is approximately 400-500 pounds per square inch, applied for approximately 1 minute, followed by pressure of about 100-125 pounds per square inch applied for approximately 10 minutes, and the hardboard produced is of specific gravity approximately 1-1.05.

6. Process as in claim 1, in which'the initial pressure is approximately 200 pounds per square inch, applied for approximately 1 minute, followed by pressure of about 60 pounds per square inch applied for approximately 20 minutes, and the hardboard produced isof specific gravity approximately .9.

7. Process of making hard products such as board and the like, of a body of llgno-cellulose fiber containing a suiflciently high proportion of non-cellulose to produce thorough bonding and containing 25% or over of water, which comprises pressing same in a hot press with moisture escape conduits between the fiber body and a press platen with initial application of relatively high pressure, and then, without the pressure having ever been completely released, completing the drying of the product in place between the heated press platens, and under much lower pressure.

8. Process of making a hard board or like product which comprises nearly drying under moderate pressure of approximately 60425 pounds per square inch after initially applying pressure several times as high to a body of lignocellulose containing 25% or over of water and containing plenty of the noncellulose thereof to insure thorough coalescing and bonding, and after the board is nearly dried, completing the drying under a reapplication of elevated pressure.

9'. Process as in claim 8, in which temperature of 430 F. or over is applied to the board during the application of pressure.

10. Process as in claim 8, in which temperature of 430-550 F. is applied to the board during the application of pressure.

11. Process of making hard products, such as board and the like, of a body of ligno-cellulose fiber containing a suficiently high proportion of non-cellulose to produce thorough bonding and containing 25% or over of water, which comprises pressing same in a hot press at a temperature of over 430 F. and preferably about 450550 F. with wire mesh between the fiber'body and a press platen with initial application of relatively high pressure, and then, without the pressure having ever been completely released, completing the drying under much lower pressure whereby to make a product of high dry and wet strength and substantially free from surface defects in a single press-drying operation.

12. Process of making hard products, such as board and the like, of a body of ligno-cellulose fiber containing a sufi'iciently high proportion of non-cellulose to produce thorough bonding and containing 25% or over of water, which comprises pressing same in a hot press at a temperature of over 430 F. and preferably about 450- 550 F. with wire mesh between the fiber body and a press platen making initial application of relatively high pressure, and then materially reducing the pressure without, however, completely releasing the pressure and completing the drying of the product between the heated press platens at the reduced pressure, whereby to make a hard product of high dry and wet strength substantially free from surface defects in a single pressdrying operation.

13. The process of making hard products, such as board and the like, of a body of ligno-cellulose fiber containing a suillciently high proportion of non-cellulose to produce thorough bonding and containing 25% or over of water, which comprises pressing same in a hot press with wire mesh between the fiber body and a press platen with initial application of relatively high pressure whereby to drive water out especially from that part of the body of fiber adjacent said wire mesh; redistributing the remaining water content throughout the entire fiber body by lowering the pressure without completely releasing same, and

non-cellulose to produce thorough bonding and 1 containing 25% or over of water, which comprises pressing same in a hot press at a temperature of over 430 F. and'preferably about 450F550" I". with wire mesh between the fiber body and a press platen with initial application of relatively high pressure whereby to drive water out especially from that part of the body of fiber ad- Jacent said wire wesh; redistributing the remaining water content throughout the entire fiber body by lowering the pressure without complete- 1y releasing same, and completing the dryingwhile maintaining a pressure on said body of the lowered order of pressure, whereby to make a hard, dense board of high dry and wet strength and-substantially free from surface defects in a single press-drying operation.

15. Process of making products, such as board and the like, of a body of ligno-cellulose fiber containing a sufilciently high proportion of noncellulose to produce thorough bonding and con taining 25% or over of water, which comprises subjecting said fiber body to a single-step press drying operation in a hot press with wiremesh between the fiber body and a press platen com- 5 prising making initial application of relatively high pressure, and then without the pressure having ever been released, completing the drying under much lower pressure, and following up such pressure application as shrinkage occurs and until the board is dry, whereby to make a hard product of high dry and wet strength, substantially free from surface defects. l o

16. Process as in claim wherein the temperature applied in the hot-pressing is over 430' E45 and preferably about 450-550 F.

1'1. Process of making hard products such as board and the like, of a body of ligno-cellulose fiber containing a sufliciently high proportion of non-cellulose to produce thorough bonding and containing or over-o! water, which comprises pressing same in a hot press at a temperature of about 350-430 F. with moisture escape conduits between the fiber body and a press platen with initial application or relatively high pressure, and 25 then, without the pressure having ever been completely released, completing the drying of the product in place between the heated press platens, and under much lower pressure. I

WILLIAM H. MASON. CHARLES H.