CH711309A1 - A method of manufacturing a composite wooden pallet, a device for implementing the method and an injection mold for producing said pallet. - Google Patents

Abstract

The invention relates to a method for manufacturing a composite wood pallet in which a mixture of wood fibers and binder based on thermoplastic materials is prepared, and injected into a mold corresponding to the profile of said pallet said mixture in pasty form by a plurality of injection points disposed on the mold so that the path of the injected mass is the same regardless of the injection point and the sections of the pasty mass supply circuit are determined so that the flow rate is the same at each injection point. It also relates to a device with an injection circuit (10) having injection points (11) at the free ends of first branches of tubing (12), supplied at junction points (13) to bring the pasty mass of equally. The junction points (13) are the ends of second branches of tubing (15) supplying the junction points (13). The second branches of tubing (15) have a single mouth (16) corresponding to a third tubing (17) delivering the entire pasty mass for filling the mold of the pallet. The invention further relates to an injection mold for the manufacture of a composite wood pallet.

Description

Technical area

The present invention relates to a method of manufacturing a composite wood pallet, said composite wood consisting of a mixture of at least wood fibers from wood or the like and a binder of a thermoplastic material, said process comprising a phase of preparation of said mixture, this phase comprising the kneading of the components and the raising of the temperature of the mixture beyond the melting point of the thermoplastic material and an injection molding phase followed by a cooling phase of the pallet below the melting temperature of the thermoplastic material.

It also relates to a device for the manufacture of a composite wood pallet, said composite wood consisting of a mixture of at least wood fibers from wood or the like and a binder of a thermoplastic material, said device comprising means for preparing said mixture, including means for mixing the components and means for raising the temperature of the mixture beyond the melting point of the thermoplastic material and means for injecting the pasty mixture into a mold corresponding to the profile of said pallet and cooling means of the injected pallet below the melting temperature of the thermoplastic material.

Finally, it relates to a composite wood pallet, said composite wood being composed of at least wood fibers from wood or the like and a binder of a thermoplastic material.

Finally, it relates to an injection mold for the manufacture of said composite wooden pallet with the device above.

Prior art

Pallets, including pallets used for transporting food products, including fruits and vegetables, are usually pallets made of wooden planks, assembled by nailing. These pallets are sensitive to moisture, degrade under the shocks they experience when handling with the forks of palletizers or other forklifts. Exposed to permanent moisture in the holds of boats, these pallets are covered with mold that they transmit to the products transported. In addition wooden pallets indirectly cause a lot of injuries to users who prick wood splinters in the fingers and injure themselves with the rusty nails used to assemble the boards.

There are also on the market pallets entirely made of virgin synthetic material. Because of their price and low carrying capacity they are often reserved for more noble products, namely pharmaceuticals, cosmetics or textiles. One of the disadvantages of plastic pallets, usually hard plastics, is their relative fragility, especially in extreme cold, when the plastic is. weakened and becomes brittle at the slightest shock. In addition, the geometry of these pallets does not correspond to that of conventional pallets, of the European pallet type, for example, or to other types of pallets which are well known and intended for specific applications.

Indeed, it is very advantageous to recycle a partially damaged pallet, having suffered shocks to the point of being partially demolished. This is not the case with conventional wood planks that can only be repaired after damage, if the damage is not too great.

Presentation of the invention

The present invention proposes to solve the problems of pallets known and distributed on the market by producing a robust product, having the shape and dimensions of pallets considered standard, insensitive to humidity, economic and suitable for all applications and fully recyclable regardless of their condition.

For this purpose, the method according to the invention is characterized in that: the preparation phase of said mixture is carried out by producing a homogeneous mixture of at least the main components, namely ligneous fibers and binder in pasty form at a temperature at least equal to the melting temperature of the thermoplastic material, the injection phase of the pallet is carried out by injecting into a mold corresponding to the profile of said pallet said mixture in pasty form by a plurality of injection points disposed on the mold in predetermined locations, said predetermined locations are determined such that the path traveled by the pasty mass injected from its injection point to its end in the mold is substantially the same irrespective of the point of injection of said plurality of points injection, the sections of the feed circuit of the pasty mass are determined in such a way that the flow rate of said pasty mass is substantially the same at each point of injection.

According to a preferred embodiment, the injection is advantageously carried out at low pressure by flow of the pasty mass inside the mold.

Advantageously, the inside of the mold is depressed to improve the fluid flow of the pasty mass for filling the mold.

For this purpose, the device of the invention is characterized in that: the injection means of the pasty mixture in a mold corresponding to the profile of said pallet comprise an injection circuit comprising a plurality of injection points disposed on the mold in predetermined locations, said injection points are located on the mold at predetermined locations defined so that the path traveled by the pasty mass injected from its injection point to the furthest place in the mold is substantially the same regardless of the injection point, the feed circuit of the pasty mass at said injection points comprises a plurality of tubular sections, and said tubular sections of the feed circuit of the pasty mass are determined in such a way that the flow rate of said pasty mass is substantially the same at the inlet of each injection point.

According to a preferred embodiment, said injection circuit comprises at least two stages, the first of which consists of a single inlet manifold of pasty mass, the second stage comprises at least two separate tubes, arranged for being fed in such a way that each of said at least two tubes receive the same quantity of pasty mass, during the same time, each of said at least two tubings having an outlet constituting an injection point in said mold, the sections of said tubings of the second stage being such that the sum of the pasty masses they transfer is equal to the sum of pasty mass passing through the inlet manifold.

The injection mold for the manufacture of a composite wooden pallet according to the invention is characterized in that it comprises an injection circuit arranged to feed the mold with a pasty mass of composite wood through a plurality of injection points, each of said injection points being connected to an inlet manifold which feeds the pasty mass through an injection circuit having at least two stages, each of said stages being arranged to distribute in an identical manner the pasty mass at the injection points of said plurality of injection points.

Brief description of the drawings

The present invention and its advantages will be better understood on reading the detailed description of preferred embodiments of the device, with reference to the appended drawings given by way of non-limiting indication, in which: <tb> Fig. 1 <SEP> represents an elevational view of an embodiment of an injection circuit of a composite wood pallet according to the invention, <tb> figs. 2A and 2B <SEP> illustrate a distribution diagram of the injection openings of a mold arranged to manufacture a composite wooden pallet according to the invention, and <tb> fig. 3 <SEP> is a top view of a palette called "European pallet", made by injection molding composite wood according to the invention.

Best ways to achieve the invention

The composite wood is a priori heterogeneous material which remains in the homogeneous state only when it is not subjected to stresses, in particular pressure variations during its injection into the mold. If the melt composed of particles or fibers of wood and a binder of a thermoplastic material and, if necessary of some neutral components called loads, is subjected to stresses, heavy wood particles and fillers have tend to be braked during the injection while the fluid material, the thermoplastic binder tends to flow in an accelerated manner. This phenomenon tends to cause dissociation of the molten mass which results in a poor quality product with at the ends of the injection path areas essentially composed of binder, or at least having a high concentration of binder and poor central areas. by binding and high in fiber that will eventually tend to crumble.

FIG. 1 is a perspective view of the injection circuit 10 corresponding to an injection mold (not shown) for the manufacture of a pallet 20, said European pallet, as shown in plan in FIG. 3. Note that this injection circuit 10, which corresponds to a specific type of pallet, can be adapted when another type of pallet is produced. However, the essential characteristics are implemented in all cases, namely the presence of a plurality of injection points disposed on the mold in predetermined locations so as to ensure a regular and uniform filling of the mold. In the embodiment shown, the injection points 11 are sixteen in number and correspond respectively to the free ends of sixteen first branches of tubing 12, arranged in a cross. The first six branches of tubing 12 are fed at four junction points 13 which distribute the pasty mass to the first six branches of tubings 12. The four junction points 13 are constituted by the free ends 14 of four second branches of tubings 15, arranged in cross, feeding the four junction points 13. The four second branches of tubing 15 have a single common mouth 16, which corresponds to the end of a third tubing 17 which delivers all of the pasty mass required for filling the mold for the manufacture of the pallet 20.

Since the flow of pasty mass must flow fluidly without restraint to avoid stresses tending to degrade the homogeneity of composite wood, it is essential that the flow is substantially the same at sixteen points. injection 11, on the one hand and at the four junction points 13. The sum of pasty material delivered to the sixteen injection points 11 is substantially equal to the sum of pasty material delivered to the four junction points 13 and corresponds to the totality of material pasty delivered at the common mouth 17.

The arrangement of the first pipes 12 and the second pipes 15 relative to the third pipe 17 is illustrated in more detail by the plan view of FIG. 2A. It will be noted that the tubes have different sections to fulfill the fluid flow conditions imposed on the pasty mass. Fig. 2B, which is a sectional view of the circuit 10, illustrates the differences in section between the pipes of the circuit 10. On the basis that in order to achieve a fluid flow it is essential to avoid the small injection mouths through which the pasty mass is put under a high pressure, it has been planned to make mouths relatively large section. By way of non-limiting example, the mouths of the sixteen injection points 11 have been made with a diameter of 8 mm, which corresponds to a cross-sectional area for said first pipes of approximately 50.26 mm <2>. Each of the four junction points 13 feeds four injection points 11. The flow rate at these junction points 13 must be sufficient to meet the demand, which means that the surface area of the section of the second manifolds 15 must be four. once that of the first pipes 12, ie 201.06 mm 2 corresponding to a tubing diameter of about 16 mm. The surface of the section of the third pipe 17 must be sufficient to feed the four second pipes 15, namely 804.24 mm <2>, corresponding to a pipe diameter of 32 mm.

It is understood that for smaller objects, both the number of injection points and the tubing sections can be reduced. For the manufacture of larger objects according to this technology, the number of injection points, their arrangement and the section of the supply pipes of the pasty composite wood mass will have to be adapted.

By way of example, a pallet of the European pallet type 20 is represented in FIG. 3. It comprises a platform 31 made of planks fixed on crosspieces 32 raised by studs and fixed at their base on supports parallel to the crosspieces 32. The complete pallet is manufactured by injection molding composite wood, so that it does not include more individual boards joined by nails. Since the pallet is molded from composite wood produced from recycled materials, the cost of a pallet is very low and pallets are fully recyclable regardless of their condition, even if they are damaged.

The present invention is not limited to the embodiments described, but may have obvious variations for those skilled in the art, but contained in the scope defined by the claims.

Claims (6)

1. A method of manufacturing a composite wood pallet, said composite wood consisting of a mixture composed of at least wood fibers from wood or the like and a binder of a thermoplastic material, said process comprising a preparation phase of said mixture, this phase comprising mixing the components and raising the temperature of the mixture beyond the melting temperature of the thermoplastic material and an injection molding phase followed by a cooling phase of the pallet below the melting temperature of the thermoplastic material, characterized in that: The preparation phase of said mixture is carried out by producing a homogeneous mixture of at least the main components, namely ligneous fibers and binder in pasty form at a temperature at least equal to the melting temperature of the thermoplastic material, The injection phase of the pallet is carried out by injecting into a mold corresponding to the profile of said pallet said mixture in pasty form by a plurality of injection points placed on the mold in predetermined locations, Said predetermined locations are determined in such a way that the path traveled by the pasty mass injected from its injection point to its end in the mold is substantially the same regardless of the injection point of said plurality of injection points, The sections of the feed circuit of the pasty mass are determined in such a way that the flow rate of said pasty mass is substantially the same at each injection point. 2. A method of manufacturing a composite wood pallet, according to claim 1, characterized in that: the injection is carried out at low pressure by flow of the pasty mass inside the mold. 3. A method of manufacturing a composite wood pallet, according to claims 1 or 2, characterized in that: the inside of the mold is depressed to improve the fluid flow of the pasty mass in order to fill the mold. 4. Device for the manufacture of a composite wood pallet, said composite wood consisting of a mixture composed of at least wood fibers derived from wood or the like and a binder of a thermoplastic material, said device comprising means for preparing said mixture, including means for mixing the components and means for raising the temperature of the mixture beyond the melting point of the thermoplastic material and means for injecting the pasty mixture into a mold corresponding to the profile of said pallet and means for cooling the injected pallet below the melting temperature of the thermoplastic material, characterized in that: The means for injecting the pasty mixture into a mold corresponding to the profile of said pallet (20) comprise an injection circuit (10) comprising a plurality of injection points (11) arranged on the mold in predetermined locations, Said injection points (11) are located on the mold in predetermined locations defined so that the path traveled by the pasty mass injected from its injection point to the furthest place in the mold is substantially the same. even at any point of injection, The supply circuit (10) of the pasty mass at the said injection points (11) comprises several branches of tubings (12, 15, 17), and - Said tubing branches (12, 115, 17) of the feed circuit (10) of the pasty mass are arranged so that the flow of said pasty mass is substantially the same at the inlet of each injection point. 5. Device according to claim 3, characterized in that: said injection circuit comprises at least two stages, the first of which consists of a branch of single inlet manifold (17) of pasty mass, the second stage comprises at least two separate branches of tubes (15; 12), arranged to be fed in such a way that each of said at least two branches of tubings (15; 12) are supplied with the same quantity of pasty mass, during the same time, each of said at least two branches of tubings (15; an outlet constituting an injection point (13; 11) in said mold, the sections of said second stage tubing branches being such that the sum of the pasty masses they transfer is equal to the sum of pasty mass passing through the branch of tubing arrival. 6. Injection mold for the manufacture of a composite wood pallet, characterized in that it comprises an injection circuit arranged to feed the mold with a pasty composite wood mass through a plurality of injection points each of said injection points being connected to an inlet pipe which brings the pasty mass through an injection circuit comprising at least two stages, each of said stages being arranged to distribute the pasty mass identically at the points of injecting said plurality of injection points.