Patent Application
20180187379
Generally, embodiments herein relate to molding of large pulp objects, the molds used therein and the apparatus for producing large objects of molded pulp using such molds.
More specifically, different embodiments of the application relate inter alia to different mold linings and in one non-limiting embodiment to the pulp molding of large objects such as coffins.
Pulp molding is known in the art for producing small packages such as egg cartons, disposable food dishes, box inserts and other protective packaging materials etc.
U.S. Pat. No. 6,245,199 describes a method of pulp molding trays where the starting material is a suspension containing cellulose fibers. The male mold half is dipped in a bath of the suspension, and the mold halves are then pressed together under heat and pressure.
SE 529 897 C2 describes the pulp molding of a tray where a dewatering receptacle is used to shape a tray of pulp which is then transferred to a compression tool where the tray is subjected to pressure and heat. It involves a transfer step and is not readily usable for large containers.
However, none of the related art discloses or hints at how to achieve the solutions provided by embodiments herein.
Embodiments herein intends to solve a complex of difficult-to-reconcile interrelated problems still present in the designs of the prior art:
Hitherto it has been very difficult to use existing pulp molding methods to produce very large objects. This is due partially to the problem of thermal expansion and contraction of the two metal mold halves used in the compression of the pulp in the press. If the dimensions of the mold halves change, due to unavoidably becoming cooler and hotter during the compression process, the strength of the container will be compromised and the surface will not be smooth and even. This is not a problem if the surface quality and the strength of the finished object is of no great importance, such as for packaging materials or disposable dishes, but where the strength and surface finish of the finished molded product is of great importance then this is a problem.
One such very large product, where strength and finish are of the utmost importance, are caskets, although the present solution is not limited thereto.
It would also be a great advantage if the production steps could be severely reduced in number and complexity.
In general it is difficult to achieve uniformity of strength and surface in pulp molded products, particularly in such products which are thin.
This entire complex of problems listed above finds its solution in embodiments herein as defined in the appended main patent claim.
Various embodiments of the disclosure comprises a pair of mold halves 3, 5 suitable for pulp molding by compression and heating, comprising a first half 5 for application of a pulp slurry and a second conforming mold half 3, wherein the surface of said first half mold 5 is covered with an elastomeric material.
Further embodiments of the disclosure comprises:
A pair of mold halves wherein said first mold half 5 is a perforated 8 mold half suitable for suction dewatering of pulp.
A pair of mold halves wherein one or several layers of wire mesh 7 cover the elastomeric material 6 providing a suction dewatering surface for pulp.
A pair of mold halves wherein said elastomeric material 6 is adapted to absorb thermal contraction and expansion of said mold halves 3, 5 during compression of a molded pulp container.
A pair of mold halves wherein bodies of said mold halves 3, 5 are made of metal.
A pair of mold halves according to one of the preceding claims characterized in that said first half 5 is a male mold half and said second mold half 3 is a female mold half conforming to said male form half.
A pair of mold halves wherein said male mold half 5 has a hollow interior vacuum cavity 15 and multiple conduit pathways 8, 10 providing suction effect between said vacuum cavity 15 and the surface of said male mold half for suction dewatering of pulp.
A pair of mold halves wherein said male mold half is provided under said elastomer material 6 with troughs 14 in said body of said male mold half distributing vacuum effect under said elastomeric material 6.
A pair of mold halves wherein said elastomeric material 6 has a thickness of between 10 and 50 mm.
A pair of mold halves wherein said elastomeric material 6 has a hardness of ca. 60-80 Shore A.
A pair of mold halves wherein said elastomeric material 6 has a different hardness on the sides of the mold half than on the bottom thereof.
A pair of mold halves wherein the mold halves 3,5 are metal mold halves and/or the bodies of the mold halves 3,5 are made of metal.
A pair of mold halves wherein the surface of said first half mold 5 is covered by being spray coated or cast with an elastomeric material.
A pair of mold halves wherein said mold halves being metal mold halves 3, 5 suitable for pulp molding by compression and heating, comprising a first half (5) for application of a pulp slurry and a second conforming mold half 3, wherein the metal surface of said first half mold 5 is spray coated or cast with an elastomeric material.
A pair of mold halves wherein said male mold half is provided under said elastomer material 6 with troughs 14 in said body of said male mold half 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 said elastomeric material 6.
Embodiments of the disclosure further comprises an apparatus for use together with a pair of mold halves as defined in embodiments of the disclosure, comprising, a frame 1 in which a first of said mold halves 5 is mounted in means for translational movement towards a second mold half 3, means for compressing and holding said pair 3,5 of mold halves fitted against each other and a bath 10 of pulp slurry, characterized in that said means 4 for translational movement are adapted for immersing a first mold half in said bath 16 of pulp slurry and moving said first mold half into fitting compression against said second mold half.
Further embodiments of the disclosure comprises:
An apparatus wherein said second mold half is mounted for slight horizontal movement, to achieve correct alignment during fitting compression of said first mold half 5 in said second mold half 3.
An apparatus 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 5 in said second mold half 3.
Embodiments herein will now be described in more detail with reference to the appended drawings, wherein:
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.
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, whereby a coating of pulp slurry is sucked onto the surface of the male mold half 5.
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
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 more evenly.
The female mold-half 3 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 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 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.
The male mold-half 5 after being dipped in the slurry bath 16 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.
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.
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.
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.
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.
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.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1550864-1 | Jun 2015 | SE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SE2016/050626 | 6/23/2016 | WO | 00 |
