FR2680758A1 - Lightweight plastic pallet prodn. - Google Patents

Abstract

A lightweight pallet includes a flat load carrying surface and feet projecting from one side along two parallel edges and also symmetrically in lines parallel to the edges. The feet in each line are connected by a flat strip along the feet bases. The complete pallet including the load carrying surface, feet and connecting strips are mfd. in one injection moulding operation. Hollow chambers are formed inside the rectangular profiled feet which are completely enclosed on all sides. Hollow chambers are produced during moulding by moving wall areas of the tool during the holding pressure phase to increase cavity volume and injecting high pressure gas.

Description

Flat pallet.

 The invention relates to a flat pallet with a substantially flat loading surface, on one side of which prominent feet, mainly in the vicinity of two parallel edges, and possibly also between these, in another parallel alignment, the feet d 'a row of feet being connected at their end opposite to the loading surface by a substantially flat board.

 Such flat pallets are known in many models in the current art. We are currently in the habit of manufacturing such wooden pallets. The loading surface is then formed of several wooden boards parallel to each other. In the vicinity of the longitudinal edges of the loading surface, other wooden boards are provided which extend transversely to the first, and in the vicinity of the corners, and possibly also in the middle of the pallet, wooden legs are attached to these second boards, these feet being in turn connected in rows by boards nailed from below.

 We also already know of such pallets in which the feet are formed from pieces of steel bent into a U, the rest of the components being made of wood, as before. These pallets are used as so-called four-way pallets, because the forks of a forklift can grab from below and lift the rectangular pallet, from each of its four sides.

 Based on this state of the art, the object of the invention is to create a very light, extremely robust and inexpensive palette to manufacture.

 To achieve this object, the invention proposes to form the pallet in one piece, with the loading surface, the feet and the boards, made of synthetic material (injection molded), and at least the feet have walls lateral, head and bottom which form closed hollow volumes.

 The single-piece shaping of synthetic material greatly facilitates manufacture, and the necessary stability and resistance of the feet is obtained by making the feet in the form of closed hollow volumes. At the same time, this measure results in a considerable saving in weight, as well as a reduction in the duration of the cycles, since massive feet made of synthetic material would require considerably higher quantities of raw materials and considerably longer cooling times.

 In a preferred embodiment, the legs have a cross section in the form of a flat rectangle whose corners are optionally rounded.

 Despite a small footprint, this provides sufficient rigidity and loading capacity.

 It is preferable to place the upper wall or head of the feet in the plane of the pallet loading surface.

 It is further planned to align in the vicinity of each corner a long side wall and a short side wall on the side edges of the loading surface.

 This embodiment allows a perfect connection of the feet to the loading surface, which reinforces the rigidity and the wear resistance of the pallet.

 It is also planned to produce the board which connects the feet of a row of feet, preferably in the form of a board with profiled ribs completely surrounding the side wall and / or the bottom wall of the feet, the profiled ribs being open on the side of the board opposite the loading surface.

 This measure serves to further increase the rigidity.

 It is planned to preferably give the board a cross section whose profile is in the form of a flat triangle.

 It is thus guaranteed that the board does not constitute an obstacle against which the fork of the lifting machine would abut when it is inserted, but that the rising sides of the triangle have a guiding effect on the fork.

 To further increase the reinforcement, it is expected that the board has, near or at the top of the triangle, a closed hollow channel which connects the molded feet on the board near their bottom, the hollow channel being on the closed side. at the ends by parts of the lateral wall of the feet.

 Following these measures, the board can be made with a small wall thickness, which allows weight savings and a reduction in costs (material expenditure and cooling times).

 In addition, for the purpose of reinforcement, provision is made to extend the hollow sections between the faces of the legs which are turned towards one another, the side walls of the legs forming the covering surfaces of the hollow sections.

 For the same purpose, provision is made to form additional hollow sections parallel to the hollow sections connecting the feet, symmetrically therebetween.

 Still for the same purpose, provision can be made for placing a lateral face of the hollow sections in the loading surface of the pallet.

 The invention further relates to a method of manufacturing such a pallet of thermoplastic material, in which a fluid thermoplastic material is injected under high pressure into a closed casting mold, formed of at least two half-molds, to fill this last, with addition of molten thermoplastic material, during the solidification phase, to compensate for the shrinkage caused by solidification (second pressure phase), characterized in that, with a view to the formation of the hollow profile in a part of the flat pallet, the mold surrounding this part is enlarged by displacement of a part of the wall of the mold during the secondary pressure phase, gas under high pressure is injected during the secondary pressure phase, into the thermoplastic material which is there and which is still molten or pasty at least at the core, so that the film of thermoplastic material already frozen near the wall part which is displaced, follows the displaced part of the wall, is pressed against it while at the same time forming a hollow space, the mass of the still fluid or pasty core of this part connecting the material slots continuously between the plastic part formed in this region, and the part of the part made of thermoplastic material displaced towards the displaced part of the wall.

 The object of the method is to provide the possibility of producing flat pallets with closed internal recesses, and this in a particularly simple manner and in a simplified constructive implementation.

 This method is further characterized in that in the vicinity of the hollow to be formed, the mold has a displaceable molding core whose front surface, located forward in the direction of its inward movement, forms the displaced part of the wall , while a pot-shaped crosspiece is formed when the molding core is pushed in, which is detached from the bottom, after the extraction of the molding core and after the supply of pressurized gas into the still liquid core or pasty bottom, a layer parallel to the bottom and to the front surface of the molding core and whose outer surface, which has just set, is pressed against the front surface of the molding core, the separation slots between the side walls of the crosspiece and the detached layer being closed by the remains of molten material from the thermoplastic mass, compressed by the gas under pressure against the walls of the hollow thus created, and still pre between the bottom and the detached layer.

 According to another characteristic of the process, the pressurized gas is brought into the hollow by a bore in the matrix or the moving part (core) of the mold.

 According to another characteristic of the process, the compressed gas is brought under a pressure higher than the injection pressure of the thermoplastic mass.

 According to another characteristic of the process, the compressed gas is brought under a pressure of about 200 bar, the thermoplastic mass being injected under a slightly lower pressure.

 According to another characteristic of the process, the bottom of the pot-shaped hollow is formed by injection, before the extraction of the molding core, at a wall thickness approximately twice the required thickness, it is detached using gas compressed about half the wall thickness, and this element is pressed against the front surface of the extracted molding core.

 According to another characteristic of the process, the duration of the secondary pressure phase, including the supply under pressure of the compressed gas, does not exceed the time available for shaping the thermoplastic product.

 According to another characteristic of the process, the compressed gas is supplied via a pipe separate from the supply pipe for the thermoplastic material.

The advantages and advantageous effects of the application of this process are described in the patent application.
P 40 34 663.3.

 An exemplary embodiment of the invention is presented in the drawing and is described below in more detail.

In the drawing:
Figure I shows in plan a flat pallet of dimensions 800 x 600 x 140, partially sectional view along line AA of Figure 3;
Figure 2, the same sectional view along line CC of Figure 1;
Figure 3, the same sectional view along line BB of Figure 1.

 The flat pallet has a loading surface 1 which is substantially flat and has openings, from which feet 2 project from one side, that is to say downwards in the position of use.

 Each foot is located in the vicinity of two parallel side edges, and the feet are arranged symmetrically between these edges, in parallel alignments.

 At their free end, opposite to the loading surface 1, the legs 2 of a row of legs are connected by a board 3 which is substantially flat.

 The flat pallet is molded in one piece by injection of synthetic material, with its loading surface 1, the feet 2 and the board 3. The feet 2 form a closed hollow volume 4, with side walls 5, upper walls or head, 6, and bottom or bottom walls ^ 7.

 The feet 2 are in cross section made in the approximate form of a flat rectangle with rounded corners, while the long sides of the rectangle of all the feet are oriented in parallel with each other and in parallel with the extension of a side wall. . The head wall 6 of the feet 2 is located in the plane of the loading surface 1. In the vicinity of each corner of the rectangular loading surface 1, a long and a short side wall 5 are aligned with the lateral edges of the surface loading 1, and other feet 2 are arranged in the middle of the pallet, in addition to the pairs of feet 2 at the corners.

 The board 3, which connects the feet 2 belonging to a row of feet, is produced in the form of a board with profiled ribs, as can be seen particularly clearly in FIG. 3. This board with profiled ribs encompasses the wall bottom 7 of the feet 2, which is an integral part thereof, while the profiled ribs are open on the side of the board which is opposite to the loading surface 1. The board 3 is in the form of a section in shape of a flat triangle and thus facilitates the insertion of the fork of a lifting machine. The board 3 also has, at the top of the triangle, a closed hollow channel 8 which connects the feet 2 molded on the board 3, near their bottom 7. The hollow channel 8 is closed at its ends by a part of the wall lateral of the feet.

 The loading surface 1 of the pallet is further reinforced by closed hollow sections 9 arranged on edge and extending parallel to the lateral edges. Each hollow section 9 extends between the side walls 5 facing one another of the feet 2, the side walls 5 of the feet 2 forming the covering surfaces used to close the hollow sections 9.

In addition, additional hollow sections 9 are formed in symmetrical positions between the hollow sections 9 connecting the feet 2. One of the side faces of each of these hollow sections 9 is located in the loading surface 1 of the pallet. The embodiment presented in the drawing allows manufacturing, economical in raw materials, pallets of high rigidity and large loading capacity; following the reinforcements made by the closed hollow sections, an overall material saving is also obtained in terms of wall thicknesses, which leads to savings in weight, materials and manufacturing costs.

 The invention is not limited to the exemplary embodiments, but can be modified in numerous ways without departing from the scope of its disclosure.

 All the new features and combinations of features disclosed in the description and / or the drawing are considered to be essential to the invention.

Claims (19)

Claims  1. Flat pallet with a substantially flat loading surface and, on one side thereof, prominent feet, mainly in the vicinity of two parallel edges, and possibly also symmetrically between them, in another parallel alignment, the legs of a row of legs being connected at their end opposite to the loading surface by a substantially flat board, characterized in that the pallet is formed in one piece from synthetic material (injection molded), with the surface loading (1), the feet (2) and the boards (3), and that at least the feet (2) have side walls (5), head walls (6) and bottom walls (7 ) which form closed hollow volumes (4).  2. Flat pallet according to claim 1, characterized in that the feet (2) are made with a cross section in the form of a flat rectangle whose corners are optionally rounded.  3. Flat pallet according to claim 1 or 2, characterized in that the head wall (6) of the feet (2) is located in the plane of the loading surface (1) of the pallet.  4. Flat pallet according to one of claims 1 to 3, characterized in that in the vicinity of each corner of the rectangular loading surface, a long side wall (5) and a short side wall (5) are located in alignment on the side edges of the loading surface (1).  5. Flat pallet according to one of claims 1 to 4, characterized in that the board (3) which connects the feet (2) of a row of feet, is preferably in the form of a ribbed board profiles optionally comprising the side wall (5) and / or the bottom wall (7) of the legs (2), the profiled ribs being open on the side of the board opposite the loading surface (1).  6. Flat pallet according to one of claims 1 to 5, characterized in that the board (3) has a cross section whose profile is in the form of a flat triangle.  7. Flat pallet according to claim 5 or 6, characterized in that the board (3) has, near or on the top of the triangle, a closed hollow channel (8) which connects the feet (2) molded on the board (3) in the vicinity of their bottom (7), the hollow channel (8) being closed at its ends by parts of the side wall (5) of the feet (2).  8. Flat pallet according to one of claims 1 to 7, characterized in that the loading surface (1) of the pallet is reinforced by hollow profiles (9) closed, arranged on edge and extending parallel to the side edges .  9. Flat pallet according to claim 8, characterized in that the hollow sections (9) extend between the faces (5) of the feet (2) which are turned towards each other, the side walls (5) feet (2) forming the covering surfaces of the hollow sections (9).  10. Flat pallet according to claim 8 or 9, characterized in that additional hollow sections (9) are formed parallel to the hollow sections (9) connecting the feet (2), and symmetrically between the latter.  11. Flat pallet according to one of claims 8 to 10, characterized in that a side face of the hollow sections (9) is located in the loading surface (1) of the pallet.  12. Method of manufacturing a flat pallet according to one of claims 1 to 11, in thermoplastic material, in which a fluid thermoplastic material is injected under high pressure into a closed casting mold, formed of at least two half molds, to fill the latter, with addition of molten thermoplastic material, during the solidification phase, to compensate for the shrinkage caused by solidification (second pressure phase), characterized in that for the purpose of forming the hollow profile in a part of the flat pallet, the mold surrounding this part is enlarged by displacement of a part of the wall of the mold during the secondary pressure phase, gas under high pressure is injected during the secondary pressure phase, in the thermoplastic material which s '' there and which is still molten or pasty at least to the core, so that the film of thermoplastic material already frozen near the wall part which is displaced, follows the displaced wall part, is pressed against it while at the same time forming a hollow space, the mass of the still fluid or pasty core of this part connecting without interruption of material the separation slots between the plastic part formed in this region, and the part of the part made of thermoplastic material moved towards the displaced part of the wall.  13. The method of claim 12, characterized in that in the vicinity of the hollow to be formed, the mold has a movable molding core whose front surface, located forward in the direction of its movement inward, forms the part displaced from the wall, while a pot-shaped crosspiece is formed when the molding core is pushed in, which is detached from the bottom, after the extraction of the molding core and after the supply of pressurized gas into the still liquid or pasty core at the bottom, a layer parallel to the bottom and to the front surface of the molding core and whose outer surface, which has just set, is pressed against the front surface of the molding core, the separation slots between the side walls of the crosspiece and the detached layer being closed by the remains of molten material from the thermoplastic mass, compressed by the gas under pressure against the walls of the hollow thus created ed, and still present between the base and the detached layer.  14. Method according to claim 12 or 13, characterized in that the gas under pressure is brought into the hollow by a bore in the matrix or the moving part (core) of the mold.  15. Method according to one of claims 12 to 14, characterized in that the compressed gas is brought under a pressure greater than the injection pressure of the thermoplastic mass.  16. The method of claim 15, characterized in that the compressed gas is brought under a pressure of about 200 bar, the thermoplastic mass being injected under a slightly lower pressure.  17. Method according to one of claims 12 to 16, characterized in that the bottom of the pot-shaped hollow is formed by injection, before the extraction of the molding core, to a wall thickness approximately twice the thickness required, about half the wall thickness is detached using compressed gas, and this element is compressed against the front surface of the extracted molding core.  18. Method according to one of claims 12 to 17, characterized in that the duration of the secondary pressure phase, including the supply of compressed gas under pressure, does not exceed the time available for shaping the thermoplastic product.  19. Method according to one of claims 12 to 18, characterized in that the compressed gas is supplied via a pipe separate from the supply pipe of the thermoplastic material.