Pulp molding apparatus and molds for use therein

Abstract

Press for making large molded pulp objects, which has a raisable and lowerable male mold half, perforated for suction dewatering after dipping into a pulp slurry. The molding surface of said male mold half is coated with an elastomer to preserve even surface contact with the molded pulp object during compression and during thermal expansion or contraction of said mold halves. Advantageous embodiments include vacuum distribution troughs beneath the elastomer layer in the male mold half, multiple wire mesh layers on top of the perforated elastomer layer, and slight lateral adjustability of the otherwise stationary female mold half.

Claims

1. A pair of metal mold halves suitable for pulp molding by compression and heating, comprising: a first metal mold half for application of a pulp slurry, said first metal mold half having a metal surface and comprising an elastomeric material spray coated or cast on the metal surface; and a second conforming metal mold half.

2. The pair of mold halves according to claim 1, wherein said first metal mold half is a perforated mold half suitable for suction dewatering of pulp.

3. The pair of mold halves according to claim 2, wherein one or several layers of wire mesh cover the elastomeric material providing a suction dewatering surface for pulp.

4. The pair of mold halves according to claim 1, wherein said first metal mold half is a male mold half and said second conforming metal mold half is a female mold half conforming to said male mold half.

5. The pair of mold halves according to claim 4, wherein said male mold half has a hollow interior vacuum cavity and multiple conduit pathways providing suction effect between said vacuum cavity and surface of said male mold half for suction dewatering of pulp.

6. The pair of mold halves according to claim 5, wherein said male mold half is provided under said elastomer material with troughs in said body of said male mold half communicating between dewatering holes in the elastomer layer and holes, leading to a vacuum cavity spaced in the bottoms of the troughs, for distributing vacuum effect under said elastomeric material.

7. The pair of mold halves according to claim 1 said elastomeric material has a thickness of between 10 and 50 mm.

8. The pair of mold halves according to claim 1, wherein said elastomeric material has a hardness of about 60-80 Shore A.

9. The pair of mold halves according to claim 1, wherein said elastomeric material has a different hardness on the sides of the mold half than on the bottom thereof.

10. The apparatus for use together with the pair of mold halves according to claim 1, comprising, a frame in which a first of said mold halves is mounted in means for translational movement towards a second mold half, means for compressing and holding said pair of mold halves fitted against each other and a bath of pulp slurry, wherein said means for translational movement are adapted for immersing a first mold half in said bath of pulp slurry and moving said first mold half into fitting compression against said second mold half.

11. The apparatus according to claim 10, wherein said second mold half is mounted for slight horizontal movement of at most 25 mm, to achieve correct alignment during fitting compression of said first mold half in said second mold half.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Embodiments herein will now be described in more detail with reference to the appended drawings, wherein:

(2) FIGS. 1(a)-1(f) shows an exemplary frame for use with a pair of mold halves according to embodiments herein, in various positions of the male mold half and in various sections to more clearly show how the components interact.

(3) FIG. 2 shows in perspective the pair of mold halves engaged in an exemplary embodiment of embodiments herein.

(4) FIG. 3(a) shows a cross sectional view through the male mold half shown in FIG. 2.

(5) FIG. 3(b) shows the same male mold half in perspective view.

(6) FIGS. 4(a)-(e) show the male mold half in various views without its covering wire mesh.

DETAILED DESCRIPTION

(7) The apparatus according to embodiments herein as shown in one embodiment comprises a frame 1, holding a stationary platform 2 on which is mounted a female mold half 3 and below it a movable platform 12 holding a male mold half 5. FIGS. 1(a), 1(b) and 1(f) show the apparatus in its mold-separated position and FIGS. 1(c), 1(d) and 1(e) shown the apparatus its mold-compressed position for forming the molded pulp shell. The same reference numerals for the same components are used throughout all of the drawings. The apparatus of this embodiment is shown in FIG. 1(a) in perspective view in the mold-separated position with the male mold half 5 submerged in a slurry bath 16. The liquid slurry itself is not shown in the figure. This same mold-separated position is shown in vertical section in FIG. 1(b).

(8) The male mold half 5 is submerged in a pulp slurry bath 16 (99.5% water and 0.5% pulp fibers at 25-30 degrees C.) and a suction system 17 is connected to the hollow interior cavity 15 of the male mold, as shown in FIG. 1(b), whereby a coating of pulp slurry is sucked onto the surface of the male mold half 5.

(9) Six synchronously motor driven nuts on six long screw rods 4 move the male mold half 5 from the slurry bath 16 into pressure engagement with the female mold half 3, which is heated, in the compression position of the molds shown in FIGS. 1(c), 1(d) and 1(e).

(10) FIG. 2 shows only the two mold halves in engagement with each other. In embodiments one or both of the mold halves or the bodies of the mold halves may be made of metal. The female mold half 3 of massive aluminum is shown in longitudinal section, while only half of the length of the male mold half 5 is shown. The elastomer 6 covering the entire surface of the male mold half 5 is shown in longitudinal section only to reveal the structure of the male mold half 5 which is covered with troughs 14 for optimal even distribution of the vacuum suction while it drains the pulp of water. The detailed enlargement E2 shows more clearly these vacuum distribution troughs 14 and the holes 8 in the bottoms thereof leading to the vacuum cavity 15 within the male mold half 5.

(11) FIG. 3(a) shows the male mold half 5 in cross section and the FIG. 3(b) shows it in perspective view. In FIGS. 3(a) and 3(b) the male mold half 5 is shown complete, i.e. covered with the elastomer layer 6 and the wire mesh 7. The surface of said first half mold (5) may in embodiments be covered by being spray coated or cast with an elastomeric material.

(12) Embodiments of the male mold half 5 is made of hollow aluminum and is coated with an elastomer 6 which is ca 30 mm thick. According to a preferred embodiment this elastomer is sprayed onto the aluminum male mold half 5. It is also possible to cast the elastomer onto the aluminum mold half. A typical elastomer should be hydrophobic but not be subject to hydrolysis. An advantageous hardness, particularly for a sprayed on elastomer is 70 A-Shore, to provide optimal elastic properties. 5 mm diameter through-holes spaced 15 mm from each other cover the elastomer layer and connect to through-holes 8 in the aluminum body 9 of the male mold half 5. Within the male mold half there is generated a vacuum of 0.8-0.9 bar. On top of the elastomer layer there is a wire mesh 7. In this case it is a 100 mesh (i.e. 100 threads per inch) and is approximately 1 mm thick. The wire mesh can also be laid in multiple layers which will further contribute to distributing the vacuum forces is more evenly.

(13) The female mold-half 3, as shown in FIG. 1(f), is made of aluminum and has in this example a weight of 700 kg. It is heated to ca. 200 degrees C., for example by means of heating rods inserted in holes 13, as shown in FIG. 2, in the material of the female mold-half 3. This is the most energy effective method of heating the female mold-half. Its inner surface 3a, as shown in FIG. 1(f), will create the outer surface of the product. The two mold halves 3 and 5 can be made of porous aluminum to increase strength over using sintered material and to increase heat conductivity.

(14) FIGS. 4(a)-(e) show the male mold half 5 in side elevation, top view, longitudinal section (with enlarged detail), end elevation and perspective (with enlarged detail) respectively. In these views the male mold half 5 is shown without its covering wire mesh but with its elastomer layer. As can be seen well in the enlargement E4e, the entire elastomer surface is covered with small dewatering through holes 10 all over the surface. As can be seen in the detail E4c each of these holes 10 leads to a through 14 in the aluminum body of the male mold half 5, and from there via the holes 8 to the inner vacuum cavity 15 in the male mold half 5. The holes 8 are of larger diameter than the more numerous holes 10 in the elastomer layer 6 thus improving the vacuum effect dewatering the pulp. The male mold half is in embodiments provided with troughs 14 in the body of the male mold half under the elastomer material 6. The troughs 14 are communicating between small dewatering holes 10 in the elastomer layer and holes 8, leading to a vacuum cavity 15 spaced in the bottoms of the troughs 14, for distributing vacuum effect under the elastomeric material 6.

(15) The male mold-half 5 after being dipped in the slurry bath 16, as shown in FIG. 1(a), dewaters the slurry through vacuum to approximately 20% dryness (80% water) and the male mold-half 5 is then pressed into the female mold-half 3 down to a gap of ca. 1 mm between the two mold halves. It can vary for this particular product between ca. 0.8 and ca. 1.2 mm without detrimental effects. Due to absorbing heat from the female mold-half 3 (pre-heated to ca. 200 C.), the aluminum male mold-half 5 (initially ca. 25 C.) expands over its length approximately 7-8 mm with corresponding expansions in its width (2.5 mm) and height (1.5 mm). This is compensated for by the elastomer layer 6. The temperature of the hot female mold-half 3 will in turn drop ca. 13 degrees C. during the compression process. The temperatures in both the female and male mold-halves will vary up and down during the compression process thus repeatedly changing slightly the dimensions on the molds. In conventional pulp molding processes, these dimensional variations would cause stresses and unevenness in the finished product, possibly even ruptures. In this particular exemplary product, without an elastomer layer, the temperature of the female mold-half must be rather precise, i.e. in this example between ca. 195 and 204 C. This precision is difficult to achieve and maintain in an industrial process of this type. These problems have been experienced even in the manufacture of relatively small pulp molded products, and require precise adjustment of the temperature to avoid them. Most pulp molded products, such as egg cartons, are several millimeters thick and are thus more porous and it makes no difference whether such products have a rough surface. A product with a rough surface cannot be used in many applications. For a large product, the problems of dimensional heat expansion/contraction will be greatly increased. These problems have hitherto made it impossible to manufacture large pulp molded products with reasonable reject rates and with a smooth surface.

(16) Embodiments herein was developed in order to produce shells for caskets with very few rejects and no necessity of precisely monitoring and continually adjusting the temperatures of the two mold-halves. Since the elastomer is used to absorb much of the dimensional variation of the male and female mold-halves, they can be made much lighter and thinner than otherwise since they will not require a large mass to prevent temperature variations. For instance in this example the female mold-half weighs ca. 750 kg. If it had to maintain a more constant temperature it might have to have a mass of several tons, requiring more energy to heat such a large mass and maintain the heat.

(17) A casket has in general curved sides, something which is expensive to produce in plywood or with wood planks. According to embodiments herein it is possible to produce shells of ca. 1-2 mm in thickness, which provides the maximum stiffness. Thicknesses greater or less than this thickness (1-2 mm) provide less stiffness. It is also possible to fit multiple finished shells inside one another to provide multi-ply strength.

(18) These problems are solved by covering or coating the surface of the male mold-half with an elastomeric material, onto which the wire mesh or meshes is/are then applied. This elastomeric material continually compensates for the varying dimensions of the two mold-halves during the compression/heating process.

(19) By virtue of embodiments herein there is a larger operating window for the process. The design according to embodiments herein is much more forgiving. For example, the compression and drying of the wet pulp will cool off the mold-halves, with accompanying dimensional changes.

(20) According to one embodiment of embodiments herein the elastomer is sprayed onto the surface of the male mold half, but a more complicated casting process is also possible whereby the elastomer is cast onto the male mold half 5.

(21) It is also advantageous to mount the stationary mold half (in this case the female mold half 3) to be slightly horizontally moveable (+25 mm) to make sure that any heating expansion will not prevent a correct horizontal alignment between the male 5 and female 3 mold halves during the pressing operation. In embodiments of an apparatus for use together with a pair of mold halves as described herein a second mold half is mounted for slight horizontal movement of at most 25 mm, to achieve correct alignment during fitting compression of a first mold half 5 in the second mold half 3.

(22) It is also advantageous to equip the pulp molding apparatus 1 with mechanical jacks, combined with a more incremental final stage for the compression step. This final stage can also be accomplished with the aid of hydraulic pistons.