US2079667A - Pulp molding - Google Patents

Description

May 11, 1937. G. w. SWIFT. JR

PULP MOLDING Filed March 13, 1935 Patented May 11, 1937 UNITED STATES PATENT OFFlCE- PULP MOLDING George W. Swift, Jr., Bordentown, N. .L, assignor to George W. Swift Jr., Inc., Bordentown,

N. 1., a corporation of-New Jersey Application March 13, 19b5, Serial No. 10,789

'2 Claims. (01. 92-3 and process involving the use of but a single mold of a special character, through which water from the suspension is drawn or sucked by difference in fluid pressure on the opposite faces of the mold in such manner that a sheet of the pulp flbres is progressively built up and compacted by liquid pressure, on one face of the mold, without requiring any mating mold or mechanical pressure in the main product forming operation. The invention is particularly useful in connection with the molding of products such'as cups or other deep receptacles involving the use of a mold whichpresents a highly irregular surface to the pulp suspensiom Prior efforts to mold pulp articles of the above character have involved the use of molds which are expensive to construct, and. in operation it has been difficult to form the product sufliciently uniformly on different parts of the mold. Molds constructed of perforated metal sheets or metal screening for example are exceedingly expensive, and are not adapted to be formed into markedly irregular shapes, since. marked distortion of the sheets distorts the openings to varying degrees, and involves patchwork on the surface of the mold which renders it irregular and variable in its water receiving qualities. Molds of spaced metal laminations likewise are costly, and involve expensive ,machining operations particularly if markedly irregular shapes of product are desired, and it is diflicult to build-up the product regularly since the water passages of the mold are alined in direction and therefore afford variable facility of flow of the water when the surface of the mold is irregular. These metal molds furthermore necessitate theuse of relatively large water passages which produce a rough surface on the product.

The invention aims to obviate the above difficulties, especially in respect to the molding of deep or otherwise highly irregular products.

Further objects and advantages of the invention will be in part obvious and in part specifically referred to in the description hereinafter contained which, taken in conjunction with the accompanying drawing, discloses one form ofapparatus suitable for use in carrying out the invention; such disclosure however is to be regarded as merely illustrative of its principles. In the drawing- Fig. 1 is a vertical sectional view showing a molding apparatus constructed in accordance with the invention, in. operative position in a receptacle containing pulp suspended in water.

Fig. 2 is a vertical section of a mold of the type used in practicing the invention and showing a 5 molded product in its formed position.

Fig. 3 is a bottom plan view of the mold shown in Fig. 2.

In carrying out the present invention, one face I of a mold of porous, stone-like material is ex- 10 posed to a liquid suspension of the pulp which is under atmospheric pressure, while the opposite face 2 of the mold is subjected uniformly over its active area to the action of a vacuum, whereby the water of the suspension is gradual- 15 ly drawn or sucked through the innumerable pores of the mold, by the difference in fluid pressures existing on opposite sides of the mold. Reference herein to the employment of a vacuum is to be understood as using the word in a 20 relative sense to include fluid pressure differentials between the opposite faces of the mold, of a like order to the above described mode of operation. As shown in Fig. 1 for example, the mold may form one wall of a hollow box-like hous- 5 ing 3, having a vacuum chamber 4 therein which is exhausted through pipe 5, and the molding apparatus thus constituted may be immersed in a suitable receptacle 6 containing the pulp suspension 1. The latter will be quite dilute, contain- 30 ing for example, about 98% water and 2% pulp by weight.

The face I .of the mold is shaped to conform to the shape of product desired to be made, the illustrated mold being designed for the formation 35 of egg containing trays, and having a flange 8 extending outwardly around it, and held against a ledge 9 extending around the interior of housing 3, by a clamping plate In and bolts II. The face I of the mold is also provided with a series 40 of individual receptacle forming portions l2 which project relatively deeply into the pulmsuspension,

and between these portions l2 are interposed a I2 thereof are in what may be termed the foreground, while the recesses I 3 project deeply into the face i of the mold, andthere are also a series of grooves or valleys I which extend less deeply into the face of themold between the receptacledefining portions l2 thereof, and define the walls 55 and strength, the relative liquid pressure against the outer surface of the pulp sheet, making it relatively strong and tough, without unduly clogging the pores of the mold or blocking or concentrating the building up of the pulp layer in different local areas of the mold so as to form an objectionably irregular product. The rate at which the layer or sheet isbuilt up will depend upon the fluid pressure differential used, and the thickness of the sheet will be in proportion to the amount of water passed through the mold.

A mold of the above character is not directional i to any substantial extent, in respect to its qualities of afiording passage for the water through its pores, and thus the fibrous sheet \maybe built up quite uniformly even though the mold is highly irregularin shape, since the suspension i always flows in a direction substantially perpendicular to the various individual surface areas on the mold upon which the pulp particles are built up. The pores furthermore are so fine that a comparatively smooth surfaced product may be obtained, and if desired the surface of the molded product which is exposed to the pulp suspension, may be further finished off by the appli cation of a couch thereto as described in my prior Patent No. 1,983,324, dated December 4,

'- 1934, the product being finally separated from the mold by a pressure pulsation in the chamber 4, as also described in said prior patent. The product usually will next be subjected to a' dry ing operation, to remove excess moisture therefrom.

The face 2 of the mold as well as its face I may be. conformed substantially to the shape of the product to be molded, thereby producing a mold which is substantially uniform in thickness in the directions of travel of the water through its pores, and promoting the uniformity of the prodnot. The rate of deposit of the fibres on local areas of the mold moreover may be controlled by altering the resistance of the pores to the passage of the water, at the desired points. Pores of larger or finer size may be employed at such points, or if the thickness of the mold be materially increased or decreased at such points, the rate of deposit of the fibres will be relatively greater or less. For example in the use of a mold of the construction previously described, the pulp layer may tend to build up somewhat more rapidly towards the bottoms of the relatively deep and narrow valleys II or towards the bottoms of the deep recesses l3 and this tendency may be counteracted by providing pores of finer porosity at such points, 01'- thickening up the mold at such points. I,

A mold of the above character may be producedtby simple and inexpensive molding operations, using as a base silica or similar granular material such as is employed in the manufacture of abrasives, mixed with a suitable binder such said chamber and as feldspar and clay to form a plastic mass which can be readily molded into the desired shape. The mold may then be heated to a high temperature sufficient to fuse the clay and thus produce an open, porous structure of a refractory stonelike nature, which will be strong and durable. At points where it is desired to reduce the rate of deposit of the fibres as above described, finer grains of the base material may be employed, as'

indicated at IS in the drawing.

A heat resistant mold as above described has the'advantage that if its pores through long continued use become clogged with fibres or other deposits, they may be eliminated without injury to the mold by heating it to a. temperature high enough to reduce the clogging matter to a form in which it may be blown out by air pressure.

The present specification contains certain subject matter which is also disclosed in my prior copending application Serial Number 701,967, filed December 12, 1933, and entitled Pulp molds and process of making same.

This invention has more particularly to do with the molding of articles of irregular shape, i. e., having raised portions and/or depressions, as contrasted to fiat sheets which may be easily formed by well-known processes.

While the invention has been described as its steps are carried out-by the aid of the specific apparatus above described, it should be understood that changes may be made therein without departing from the invention in its broader aspects, within the scope of the appended claims.

I claim:

1. An apparatus for forming wet ul of; irregular contour, having a rec pt cl e z r i taming a thin pulp suspension in water of the character described, a housing having a vacuum chamber, a mold of porous stone-like material forming part of the walls defining said chamber and having one of its faces exposed to said chamber, and its other face recessed to conform to the shape of the article to be formed, said mold having pores of finer size adjacent certain recessed portions thereof, the last mentioned face of the mold being immersed in said liquid suspension of the pulp, whereby pulp will be progressively drawn from the suspension and deposited in sheet form on the last mentioned face of the mold, by the vacuum action of the chamber, with relatively reduced deposit of pulp on said last above mentioned portions of the mold.

2. An apparatus for forming wet pulp articles of irregular contour, having a rece'ptaclecontaming a .thin pulp suspension in water of the order of 98% water and 2% pulp, a housing havinga vacuum chamber, a mold of porous stonelike material forming part of the walls defining having one of its faces exposed to said chamber and its other .face of irregular contour and conforming to the shape of the article to be formed, the last mentioned face of the mold being immersed in said liquid suspension of the pulp, whereby pulp will be progressively drawn from the suspension and progressively built up in a sheet of substantially uniform thickness on the last mentioned face of the mold with the outer surface of the sheet in contact with the supply of pulp-in-water suspension contained in said receptacle, in accordance with the amount of water drawn through the mold by the vacuum action of the chamber.

3. The method of forming wet pulp articles of irregular contour from a thin liquid suspension of the pulp of the order of 98% water and 2% pulp, which comprises immersing an irregular face of a porous body of stone-like material in a supply of said suspension, and simultaneously exposing another face of such body to the action of a vacuum whereby pulp will be progressively drawn from the suspension and progressively built up in a sheet of substantially uniform thickness on the first mentioned face of the mold, with the outer face of the sheet in contact with the supply of pulp-in-water suspension, in accordance with the amount of water drawn through the mold by thejaforesaid vacstone-like material formingv part of the walls defining said chamber and having one of its faces exposed to said chamber and its other face of irregular contour and conforming to the shape of the article to be formed, the last mentioned face of the mold being immersed in said liquid suspension of the pulp, whereby pulp will be progressively drawn from the suspension and progressively built up in a sheet of substantially uniform thickness on the last'mentioned face of the mold with the outer surface of the sheet in contact with the supply of pulpin-water suspension contained in said receptacle, in accordance with the amount of water drawn through the mold by the vacuum action of the chamber, the first mentioned face of said mold also conforming substantially to the shape of the article to be formed.

5. An'apparatus for forming wet pulp articles of irregular contour, having a receptacle containing a thin pulp suspension in water of the order of 98% water and 2% pulp, a housing having a vacuum chamber, a.mold of porous .stone-likejmateriall forming part of the walls defining said chamber and having one of its faces exposed to said chamber and its other face of irregular contour and conforming to the shape of the article to be formed, the last mentioned face of the mold being immersed in said liquid suspension of the pulp, whereby pulp will be progressively drawn from the suspension and progressively built up ina sheet of substantially uniform thickness on the last mentioned face of the mold with the outer surface of the sheet in contact with the supply of pulp-in-water suspension contained in said receptacle, in accordance with the amount of water drawn throu h the 'mold by the vacuum action of the chamber, certain portions of the mold being so constructed and arranged as to increase the resistance'to the passage of water therethrough, thereby to adjust the rate of deposit of pulp on said last above mentioned portions as compared to the remaining active area of the mold.

6; An apparatus for forming wet pulp articles of irregular contour, having a receptacle containing a thimpulp suspension in water of the order of 98% water and 2% pulp, a housing having a vacuum chamber, a mold of porous stone-like material forming part of the walls defining said chamber and having one of its faces exposed to said chamber'and its other a face of irregular contour and conforming to the shape of the article to be formed, the last mentioned face of the mold being immersed in said liquid suspension of the pulp, whereby pulp will be progressively drawn from the suspension and progressively built up in a sheet of substantially uniform thickness on the last mentioned face of the mold with the outer surface of the sheet in contact with the supply of pulp-in-water vsuspension contained in said receptacle, in accordance with the amount of water drawn through the mold by the vacuum action of the chamber, certain portions of the mold being relatively thick in the direction of travel of water therethrough,-thereby to adjust the rate of deposit of pulp on said last above mentioned portions as compared to the remaining active area of the mold. i

7. A suction box for-pulp molding machines of the immersion type, comprising a housing having a vacuum chamber, a mold composed of a unitary mass of material having a porous structure, said mold being detachably secured to said housing and being of substantial thickness and rigidity, said mold also forming part of the walls defining said chamber and having its inner face exposed to said chamber and its outer face of irregular contour and conforming to the shape of the article to be formed thereon, whereby the vacuum action of said chamber operating through said mold progressively builds up pulp mersion of said moldin a pulp inwater suspension.

' GEORGE w. swim, Ja.

' in a sheet of substantially uniform thickness on the last mentioned face of the mold, during im-

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