EP0649794A1 - Plastic pallet and method of manufacturing the same - Google Patents

Abstract

The invention relates to a plastic pallet. It includes, in combination, an upper element or a central element provided with an array of stiffening grooves and a plurality of feet (mounts) (4,5,6,7,8) constituted by a set of vertical walls and of hollow longitudinal members (9,10,11) produced by extrusion, these being fastened, for example by welding or adhesive bonding, to the lower part of a series of aligned feet (6,7,8). The invention also relates to the method of manufacturing such a pallet. <IMAGE>

Description

The present invention relates to a new plastic pallet and its manufacturing process.

We know that pallets are kinds of trays intended to support various goods in particular for their transport and storage.

These trays are provided with feet or studs, generally nine in number, leaving between them spaces intended to receive the forks of a forklift or a pallet truck in order to allow movement from one place to another of the pallet and the goods it supports.

It is also known that there are standards which define the different dimensions of the pallets as well as the resistance which they must present with respect to the different forces which are applied to them.

The most commonly used pallets are wooden pallets which have the advantage of a low cost price, but which have the disadvantage of having a limited lifespan, a high weight and soiling quickly so that they are difficult to use in certain industries such as the food or pharmaceutical industries.

Plastic pallets are also known which have the double disadvantage of being of a much higher price than that of wooden pallets, and of not being able to meet the standards in force, that is to say that they do not have mechanical strength sufficient, either that their plate or their studs do not meet the requirements of these standards.

Following numerous studies, the applicant company has imagined a new plastic pallet which makes it possible to meet the standards in force and which has the advantage of being simple and inexpensive to manufacture, which allows it to be economically competitive with wooden pallets, without having the disadvantages.

The subject of the present invention is a plastic pallet, characterized in that it comprises, in combination, an upper element or a median element provided with a network of ribs of stiffening and a plurality of studs constituted by a set of vertical walls, and hollow beams produced by extrusion which are secured for example by welding or gluing to the lower part of a series of aligned studs.

According to a first embodiment, the pallet according to the invention comprises an upper element which has the particularity of being constituted by a substantially flat plate which is extended perpendicularly downwards by a plurality of stiffening ribs connected laterally to each other as well as by partitions also laterally connected to each other to form studs.

This upper element can be easily produced by a conventional injection molding process which consists in sending a thermoplastic material in the pasty state under high pressure into a mold of corresponding shape.

This upper element can also be produced by an injection-compression process which consists in injecting the thermoplastic material under a relatively low pressure into a half-opened mold, then in closing the mold, which has the effect of strongly compressing the plastic material to inside the mold and give it the shape it should have.

The upper element of the pallet can also be produced by a similar process called extrusion-compression, according to which the elements of the mold are separated from one another, the thermoplastic material extruded is deposited in the part bottom of the mold, then the mold is closed by applying its upper part to its lower part so as to compress the plastic.

According to the invention, the side members are advantageously obtained by continuous extrusion of a hollow plastic profile which preferably comprises at least one vertical rib which contributes to its stiffening.

The beams that are used for the realization of the pallet are sections cut to the desired length in the extruded profiles in question.

It can be seen that these beams can be obtained in a simple and economical manner.

According to a preferred embodiment of the invention, the side members comprise at least one vertical partition which makes them more rigid.

In addition, it is very easy to considerably increase their mechanical characteristics by placing inside one or more of their internal cavities, a reinforcing element such as for example a tube, a metal profile or a bar of wood.

The welding or bonding of the beams under the studs of the upper or middle element of the pallet according to the invention is easily carried out while having excellent mechanical characteristics.

Indeed, the lower end of the studs which is formed by the edge of the partitions of the latter comes to bear without difficulty on the upper face of the beams, which allows easy welding and avoids any problem of precise positioning.

Thus, for example, the welding of the side members on the lower surface of the studs can advantageously be carried out according to the invention by vibration welding.

It is known that this welding process is implemented by vibrating one of the parts to be welded while it is applied against the other so as to cause a local rise in temperature which causes the plastic material of the two parts to melt and thus allows to weld them.

This method can be easily implemented for fixing the side members because the welding can be carried out by slight relative displacements between the lower edge of the partitions constituting the studs, and the upper smooth surface of the side members.

Such a weld would be very difficult, if not impossible, to be carried out if one wished to weld two pieces by their ends constituted by partitions or ribs, due to the fact that the vibrations would be such that the corresponding ribs of the two parts would cease to be opposite each other during vibration.

In addition, the realization of the pallet according to the invention makes it possible to obtain an upper plate which can have at will a continuous surface or a surface in which one has practiced orifices whose surface and number depend on the use that one wishes to make of the pallet.

In addition, the lower surface of the pallet, which is formed by the lower faces of the side members, also has flat surfaces of widths which are large enough to be able to meet standards and which allow stacking of pallets loaded with fragile products such as for example liquids contained in plastic bottles.

By choosing the number and the nature of the reinforcing elements which are engaged in the longitudinal cavities of the longitudinal members, it is possible without any difficulty to adapt the mechanical characteristics of the pallet to the use that must be made of it.

Such reinforcing elements must simply be slid into the corresponding cavities, their section being slightly smaller than that of the cavities.

These reinforcing elements are kept inside the cavities, for example using plastic end covers which are glued, welded or clipped to the end of the side members, which has the advantage of both immobilizing the reinforcing elements inside the side members and to prevent dirt from entering the inside of the side members.

According to a particular embodiment of the invention, the side members are closed at their ends by an element, for example of molded plastic, which has a cut upper angle in order to facilitate the introduction of the forks of the handling machine.

The pallets according to the invention can be produced with a very wide range of thermoplastic material, the strength of which can possibly be reinforced by fibers such as glass fibers.

Thus, for example, the upper and / or middle elements and the side members of the pallet can be made of high density polyethylene.

According to the invention, it is advantageous to produce cut sides on the upper corners of the side members so as to facilitate the introduction of the forks of the handling equipment between the studs.

For the same reason, it is also advantageous to produce cut sides on the angles of the studs between which the forks of the handling equipment must be introduced.

Always for the same reason, it is interesting to finish the reinforcement ribs which are below the upper plate by bevel cuts.

To reinforce the solidity of the upper element, it is advantageous for the partitions and the ribs to be connected to the underside of the plate by rounding in order to avoid too great a concentration of the stresses in the material.

According to a second embodiment, the pallet is constituted by the assembly of three types of elements, namely a median element which has on its underside studs for example such as those which have been described in the first embodiment , longitudinal members obtained by extrusion which are fixed to the studs and whose structure has been described in the first embodiment and an upper element which has at its top a flat surface to constitute the upper face of the pallet plate and which is joined has the middle element through vertical ribs.

In this second embodiment, the middle element is advantageously obtained by injection, injection-compression or extrusion-compression, as has been described above for obtaining the upper element of the first embodiment.

In a first preferred variant of this second embodiment, the median element comprises a plate constituting the lower face of the pallet plate which extends to its lower face by the vertical partitions constituting the studs and which extends to its upper face by vertical stiffening ribs, while the upper element is constituted by a plate constituting the upper face of the pallet plate, a plate which is provided on its lower face with vertical stiffening ribs whose configuration is the same as that of the stiffening ribs of the middle element, so that the upper element can be joined to the middle element by welding together the ends of the stiffening ribs, for example by the so-called mirror welding process.

In this variant, the plate of the median element may lie entirely in the plane of the underside of the pallet plate while the partitions forming the studs extend downward and are welded to the crosspieces by their ends as described in the first embodiment.

In this variant, the plate of the median element can also be located in the plane of the underside of the plate only outside the studs while this plate is offset at the base of the studs in line with the latter, the reinforcing partitions studs then extending upwards until they connect with the upper element.

In this first variant of the second embodiment, the upper element can advantageously be produced by injection, injection-compression or extrusion-compression.

In a second variant of the second embodiment, the upper ribs of the median element have a height which corresponds substantially to the thickness of the plate of the pallet, while the upper element essentially serves to constitute the upper face of the plate of the palette.

In this second variant, the median element can be produced by injection, injection-compression, or extrusion-compression.

In a third variant of this second embodiment, the median element consists of a plate which supports the studs on its lower face, which may have no ribs on its upper face.

In this case, the upper element itself is constituted by a plate which constitutes the upper face of the plate and by stiffening ribs which are integral with the lower face of the plate and whose lower end is welded to the upper face. of the middle element, for example by the so-called mirror welding process or by vibration welding.

This upper element can also be produced in the form of an extruded rectangular profile with preferably vertical partitions.

In each of the three variants of this second embodiment, it is possible to engage in the spaces between two adjacent ribs of the upper element and / or of the median element, reinforcing members such as metal tubes or profiles and / or wooden bars.

Pallets according to the three variants of this second embodiment have the advantage of having smooth external surfaces and without recesses, which is important for keeping the pallets in a perfect state of cleanliness.

It is in fact understood that the lower end of the partitions constituting the studs is closed by the side members which can themselves be easily closed at their ends while the plates of the middle and upper elements give a continuous and closed surface to the lower and upper faces. from the pallet tray.

This advantage can also be obtained in the first embodiment using a plate, provided with orifices whose position and shape correspond to those of the studs, which are welded to the lower end of the ribs of stiffening of the upper element.

According to the invention, the peripheral partitions of the pads can have on at least part of their periphery a section in the form of Greek or corrugations so as to increase their resistance to crushing.

Due to their method of manufacture, the pallets according to the invention finally have the advantage of allowing easy differentiation of the different models, of their users or of their owners by using upper and / or median elements combined with spars of different colors, which allows the very wide variety of identifications desired in logistics.

It is even possible, thanks to the extrusion process of the side members and / or of the upper face of the plate of the pallet, to produce them in several colors, for example with strips of different colors.

This possibility gives the pallets according to the invention an important advantage due to the fact that in many cases they are rented pallets which are subjected to frequent movements and of which it must nevertheless be easy to identify the owner, which can be easily obtained by the invention.

Pallets, and in particular standard pallets, most often have a generally rectangular shape.

According to the invention, it is advantageous to arrange the side rails parallel to the long sides of the pallet, so as to benefit in this direction from the rigidity which is imparted by the side rails with possibly the reinforcing elements which they contain.

The mechanical strength required in the width direction can thus be more easily provided by the ribs of the middle or upper elements constituting the plate.

The rigidity in the direction of the short sides of the pallet can also be increased thanks to reinforcing elements placed between the ribs in the thickness of the plate.

The upper and / or middle elements of the pallet according to the invention can be produced either by a traditional injection process or by a gas-assisted injection process which allows a better distribution of the plastic material in the mold and the use of a lower power press. This process makes it possible to increase the rigidity of the pallet by increasing the moments of inertia for the same quantity of termoplastic material.

• la figure 1 représente une vue en perspective d'un mode de réalisation d'une palette selon l'invention,
• la figure 2 est une vue de dessus d'un quart de la palette de la figure 1,
• la figure 3 est une vue d'une section selon III-III de la figure 2,
• la figure 4 est une section selon IV-IV de la figure 2 représentée avec la nervure contiguë,
• la figure 5 est une vue selon V-V de la figure 2,
• la figure 6 est une vue schématique en perspective partielle à plus grande échelle représentant le raccordement d'un plot sur son longeron,
• la figure 7 est une vue en perspective partielle du dessous de l'élément supérieur de la palette de la figure 1.
• la figure 8 est une vue en coupe à travers un plot d'une variante du second mode de réalisation de l'invention,
• la figure 9 est une vue en coupe à travers un plot d'une autre variante du second mode de réalisation de l'invention, et
• les figures 10 et 11 sont d'autres variantes de réalisation de l'élément supérieur.

In order to better understand the invention we will now describe several embodiments taken as non-limiting examples and shown in the accompanying drawing in which:

• FIG. 1 represents a perspective view of an embodiment of a pallet according to the invention,
• FIG. 2 is a top view of a quarter of the pallet of FIG. 1,
• FIG. 3 is a view of a section along III-III of FIG. 2,
• FIG. 4 is a section on IV-IV of FIG. 2 shown with the contiguous rib,
• FIG. 5 is a view along VV of FIG. 2,
• FIG. 6 is a schematic partial perspective view on a larger scale showing the connection of a stud on its spar,
• FIG. 7 is a partial perspective view from below of the upper element of the pallet of FIG. 1.
• FIG. 8 is a sectional view through a stud of a variant of the second embodiment of the invention,
• FIG. 9 is a sectional view through a block of another variant of the second embodiment of the invention, and
• Figures 10 and 11 are other alternative embodiments of the upper element.

We see in Figure 1 the upper element 1 of the pallet which is constituted by a plate 2, substantially planar, provided at its lower part with nine studs among which the peripheral studs 4, 5, 6, 7 have simply been shown and 8.

We also see in Figure 1, how a beam 9 is secured to the lower part of the pads 6, 7 and 8.

Similarly, longitudinal members 10 and 11 join the lower parts of the pads which are in alignment with the pads 4 and 5.

Partially shown in FIG. 1 is how the plate 2 can be provided with orifices 3, the dimensions of which can be chosen as a function of the nature of the products which are intended to be placed on the pallet.

The advantage of these orifices 3 is to lighten the pallet, but it is clear that when it is desired to put fragile products such as products in bags on the pallet, it is advantageous to limit the size of these orifices for avoid damaging them.

FIG. 2 is a top view of the lower quarter of the pallet in FIG. 1.

We find in this figure the plate 2 as well as the orifices 3.

We see in broken lines the top of the stud 6 as well as half of the top of the studs 5 and 7.

The pads 5, 6 and 7 are constituted by peripheral partitions 12, and central partitions 13, which are joined laterally to one another and which, at their upper part, are integral with the plate 2. The central partitions 13 could also be positioned according to radial directions, for example along diagonals.

Alternatively, the peripheral partitions 12 may have, for example on their faces facing outwards from the palette, Greek-shaped or wavy sections to increase their resistance to crushing.

Also shown in broken lines in Figure 2, the ribs 14 which are arranged parallel to the width of the pallet and the ribs 15 which are arranged parallel to the length of the pallet.

A rib 16 which goes around the plate 2 has also been shown in broken lines.

Like the partitions 12 and 13 which constitute the studs, the ribs 14, 15 and 16 are integral with the underside of the plate 2, of which they provide rigidity and mechanical solidity.

Note in Figure 2 that according to a preferred embodiment of the invention the studs have cut sides 17 to facilitate the introduction between them of the forks of the forklift.

There is shown in Figure 7 the upper element of the pallet according to the invention which has been turned over so that one can see the partitions which constitute the studs, as well as the ribs.

This figure 7 clearly shows how the lower ends of the peripheral partitions 12 and of the internal partitions 13 which constitute the studs are made up.

We also see the cut sides 17 which are made on the periphery of the studs to allow easier engagement of the forks of the forklift.

Finally, we see in FIG. 7 the arrangement of the ribs 14 and 15 as well as the peripheral rib 16.

It is understood that, taking into account this particular structure of the upper element of the pallet, it is possible to manufacture the latter without this posing any particular difficulty because the partitions and the ribs are all directed perpendicular to the plate 2.

FIG. 3 represents a section along III-III of FIG. 2, on which we find the plate 2, the orifices 3, as well as the transverse ribs 14 and the peripheral rib 16.

Note that the peripheral rib 16 and the last transverse rib 14a have a height less than the other transverse ribs 14 so as to facilitate engagement Forks of a forklift in the free spaces between the studs.

Figure 4 is a section along IV-IV of Figure 2 which corresponds to Figure 3, except that there is shown in addition the longitudinal rib 15 and that the section was made outside the orifices 3.

We see in Figure 4 how the longitudinal rib 15 is cut at a bevel at its end to join the rib 14 a to the rib 14 which is adjacent to it.

In FIG. 5 which is a section along V-V in FIG. 2, we find the peripheral partitions 12 as well as the central partitions 13 of the studs 5 and 6. We also find in this figure a longitudinal rib 15 as well as the transverse ribs 14.

FIG. 6 is a perspective view of the lower part of the stud 6 which rests on its spar 9.

In the embodiment shown, the spar 9 is constituted by a generally trapezoidal profile, comprising a lower face 18 intended to rest on the ground or on the products supported by another pallet and an upper face 19 intended to be connected with the lower part of the partitions 12, 13 and 17 which constitute the stud 6.

The spar 9 has a generally trapezoidal shape which corresponds to the shape of the lower part of the partitions 12, 13 and 17 which constitute the stud 6, so as to ensure proper positioning of the stud on the spar.

We also see in Figure 6, how the spar has four vertical partitions 20, 21, 22 and 23 which define five channels inside the spar.

It can also be seen how, according to a preferred embodiment of the invention, a reinforcement element 24, constituted for example by a metal tube, is engaged in the central recess of the beam between the walls 21 and 22.

The reinforcing element can be, if desired, immobilized in the beam, for example by a slight deformation or withdrawal of the plastic material or by the fact that the reinforcing element is supported on ribs or extra thicknesses present on the inner surface of the spar.

As indicated above, the upper element of the pallet can be produced for example by injection, by injection-compression or extrusion-compression.

The number and dimensions of the ribs which are located on the underside of the upper element are chosen according to the mechanical strength which it is desired to impart to the pallet.

Given their profile, the beams can be easily obtained by extrusion to then be cut to the desired length.

The assembly of the beams on the studs can easily be carried out by a vibration welding process, which consists in applying the studs on the beam by vibrating one part with respect to the other so as to cause heating and melting partial of the two parts, which ensures their welding.

FIG. 6 shows how it is possible to close the recesses of the beam with the aid of a plate 25, for example made of plastic, which can be easily glued, clipped or welded, for example to the mirror, at each end of the beams in order to maintain the frame 24 in the beam and to prevent dirt from entering inside the latter.

There is shown in Figure 8, a first variant of the second embodiment of the invention which comprises a median element provided with a plate 26 which has on its underside the partitions 12 and 13 which constitute a stud. The ends of the partitions 12 and 13 are welded at 30, for example by vibration, to a beam 9 which is produced by extrusion.

As explained above, this spar 9 comprises a metal reinforcing tube 24 between two vertical partitions 21 and 22.

The plate 26 of the median element has on its upper part a series of vertical stiffening ribs of which only the peripheral rib 27 has been shown, the other ribs being hidden by the reinforcing tube 28 which is located between two ribs at the upper part of the median element, being covered by the upper element 29 which is welded at 30 by the end of its ribs to the ends of the ribs disposed at the upper part of the plate 26 of the median element, as shown in 30.

As shown in Figure 8, the reinforcing members which are arranged between the middle and upper elements are advantageously arranged perpendicular to the direction of the side members 9 so as to stiffen the pallet in both directions.

FIG. 9 represents a variant of FIG. 8 in which the plate 26 of the median element is offset downwards at the lower end of the studs to form a bearing surface 31 which comes to bear on the upper part of the side member 9.

The spar 9 is here reinforced by a wooden frame 24 a .

Also shown schematically in Figure 9 the reinforcing member 28 which is disposed between two ribs located above the plate 26 of the median element.

In this embodiment, the upper element 29 is constituted by a section of rectangular section which is provided with partitions 32 and which can be easily obtained by extrusion.

This profile 29 can be easily welded at 30 to the end of the upper ribs, for example using a vibration welding process.

There is shown in Figure 10, a variant of Figure 8 in which the plate 26 has vertical ribs which extend to the upper surface of the pallet which is constituted by a simple plastic plate 33 which is fixed by weld in 30 at the upper end 30 of the vertical ribs of the median element.

This welding can advantageously be carried out by the vibration welding process.

Finally, FIG. 11 represents another variant in which the plate 26 of the median element has no rib at its upper part, while the upper element 29 is provided with ribs 32 whose ends are welded at 30 on the face upper plate 26 of the middle element, this welding can advantageously be carried out by vibration.

Of course, in the embodiments of Figures 10 and 11, reinforcing members can also be placed between the ribs before the median element and the superior element meet.

It is understood that the embodiments which have been described have no limiting character and that they can receive any desirable modifications or adaptations without departing from the scope of the invention.

Claims (25)

Plastic pallet, characterized in that it comprises in combination an upper element or a median element provided with a network of stiffening ribs (14,15) and a plurality of studs (4,5,6,7, 8) constituted by a set of vertical walls and hollow beams (9,10,11) produced by extrusion which are fixed for example by welding or gluing to the lower part of a series of aligned pads (6,7,8) . Pallet according to claim 1, characterized in that the stiffening ribs (14,15) are connected laterally to each other as well as to the vertical walls (12,13) which constitute the studs (4,5,6,7,8 ). Pallet according to any one of the preceding claims, characterized in that the network of stiffening ribs (14,15) comprises ribs parallel to at least one of the sides of the pallet. Pallet according to any one of the preceding claims, characterized in that the hollow longitudinal members (9,10,11) are arranged at the lower part of the studs parallel to the long sides of the pallet. Pallet according to any one of the preceding claims, characterized in that the longitudinal members (9,10,11) comprise at least one vertical partition (20,21,22,23). Pallet according to any one of the preceding claims, characterized in that the longitudinal members (9,10,11) comprise in at least one of their longitudinal cavities a reinforcing element (24) constituted for example by a tube or a metal profile or a wooden bar. Pallet according to any one of the preceding claims, characterized in that the ends of the side members (9,10,11) are closed by a plate (25), for example made of plastic, which is welded, glued or clipped onto the stringers. Pallet according to any one of the preceding claims, characterized in that at least certain angles of the studs have a cutaway (17) to facilitate the introduction of the forks of the handling machines between the studs. Pallet according to any one of the preceding claims, characterized in that the peripheral walls (9) of the studs have, on at least part of their periphery, a section in the form of Greek or corrugations to increase their resistance to crushing . Pallet according to any one of the preceding claims, characterized in that the longitudinal members (9,10,11) have a substantially trapezoidal section whose upper corners have a cutaway to facilitate the introduction of the forks of the handling equipment between the studs. Pallet according to any one of the preceding claims, characterized in that the reinforcement ribs (16,14 a ) arranged on the periphery of the pallet have a height less than the other reinforcement ribs so as to facilitate the introduction of the forks handling equipment between the studs. Pallet according to any one of the preceding claims, characterized in that the ends of the reinforcing ribs are cut at a bevel to facilitate the introduction of the forks of the handling equipment between the studs. Pallet according to any one of the preceding claims, characterized in that the upper element (1) and / or the middle element and / or the side members (9,10,11) are produced using a plastic material containing fibers such as glass fibers or other reinforcing fillers. Pallet according to any one of the preceding claims, characterized in that it is constituted by an upper element comprising a plate which constitutes the upper face of the plate of the pallet and which is extended downwards by a network of stiffening ribs the ends of which are welded or glued to the side members. Pallet according to any one of claims 1 to 13, characterized in that it is constituted by the assembly of three types of elements, namely a median element which has studs on its underside, side members obtained by extrusion which are fixed to the lower part of the studs and an upper element which has at its top a flat surface to constitute the face upper part of the pallet plate, the upper element and the middle element being joined by vertical ribs. Pallet according to claim 15, characterized in that the vertical ribs which join the upper element to the middle element are secured by molding of the middle element. Pallet according to claim 15, characterized in that the vertical ribs which join the upper element to the middle element are integral for molding the upper element. Pallet according to claim 15, characterized in that the upper and middle elements each have stiffening ribs which are joined by welding or gluing at their ends. Pallet according to any one of claims 15 to 18, characterized in that it comprises at least one reinforcing element situated between two ribs between the upper and middle elements. Pallet according to claim 19, characterized in that the reinforcing elements are located perpendicular to the side members. Pallet according to any one of claims 19 or 20, characterized in that the reinforcing elements consist of profiles or metal tubes or wooden bars. Method of manufacturing a pallet according to any one of the preceding claims, characterized in that the upper element (1) and / or the middle element are produced by injection, gas-assisted injection, injection-compression or extrusion -compression of a thermoplastic material such as high density polyethylene. Method according to claim 22, characterized in that the longitudinal members (9,10,11) and / or the upper element are produced by extrusion and then cut to the desired length. Method according to either of Claims 22 and 23, characterized in that the longitudinal members (9,10,11) are fixed to the lower part of the studs (4,5,6,7,8) by vibration welding. Method according to any one of Claims 22 to 24, characterized in that the different parts are produced of the pallet with plastic materials of different colors to identify them for logistical purposes.

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