EP3398870A1 - Plastic pallet with stiffening structure - Google Patents

Abstract

The invention relates to a plastic pallet comprising a deck (1) for storing objects to be transported, feet (3) projecting from a deck underside, and runners (4) each having at least two feet (3) on their undersides are formed connecting comprises. The plastic pallet also comprises at least one stiffening structure (5), which in turn in the runners (4) arranged lower spars (6) and spaced therefrom arranged upper spars (7), which are arranged parallel to the lower spars (6) extending parallel thereto, includes. According to the invention, the at least one stiffening structure (5) has rungs (8), each with a predominantly closed surface, which connect the lower spars (6) in the feet (3) with the upper spars (7). The rungs (8) are integrally formed on the spars (6,7) or connected to these in each case via contact surfaces cohesively, non-positively or positively. In this way, the flexural rigidity of the plastic pallet and its shear strength is increased in a plane parallel to the top surface (2).

Description

Field of the invention

The invention relates to a plastic pallet, which initially comprises a deck for the storage of objects to be transported and feet, which are formed projecting from a deck underside. The plastic pallet also includes skids, which are each at least two feet on the undersides, ie on the opposite side of the deck, connected to each other. Finally, the plastic pallet also comprises at least one stiffening structure, which in turn comprises arranged in the runners lower spars and just above the lower spars lying and spaced therefrom arranged and extending parallel upper spars. The upper spars may be arranged in the deck in the area between a deck top and the deck bottom, or below the deck bottom.

In addition to the classic wooden pallets, plastic pallets are becoming increasingly important for the transport and storage of goods nowadays. Advantageously, for example, the lower weight and the ability to form almost any pallet structure using injection molding techniques, so that here reaches a high degree of individuality and can be particularly tailored to customer-specific needs. In addition, recyclates can be used to manufacture many types of pallets, unless specific hygiene requirements are met. The use of additives such as reinforcing fibers is possible. The deck can have a continuous, closed loading area, but the loading area can also be formed by a grid or ribbed structure.

At the bottom of the deck, ie facing the floor, feet are formed projecting down. They have a height that allows the pallet to be picked up and transported with the forks of a forklift, and the fork moves into the spaces between them between the feet. At the same time, however, the feet must also be able to support the allowable weight of the pallet with stored goods without fatigue of the material. Although it is possible to make the feet separately from a material with a higher impact strength, but this type of production is more expensive compared to the one-piece production of a pallet, as more tools must be kept and the pallet must then be assembled.

For transport on roller and chain conveyors on the one hand and to increase the stability on the other hand, plastic pallets often include skids, which are each at least two feet connected to each other at their bottom sides. Most of the runners are arranged parallel to each other in rectangular pallets their longitudinal direction is usually parallel to the narrower edge of the pallet, but this is not mandatory, a connection of the feet along the longer edge is possible. Circumferential runners can also be used, i. Skids, which additionally connect the feet along the longer edge of the pallet.

However, plastic pallets also have disadvantages compared to wood or metal pallets. One disadvantage is that plastic pallets tend to deform more under load than wood pallets. At worst, this can lead to irreversible deformations. If goods with high, but still permissible mass parked on the pallets, this leads to a deflection of the deck, with the feet with molded-on runners easily deform or wear their share of the deflection by the feet on their top lean inward toward the center of the deck, but on the underside, they strive outwards. It thus thrust, bending and shear forces occur, which can be absorbed only insufficiently reversible by the pallet.

State of the art

In order to reduce the deformation under load, it is known in the art to reinforce plastic pallets with stiffening structures, in particular to increase the flexural rigidity of the pallets.

For example, in the DE 20 2015 100 355 U1 a composite of several parts plastic pallet described in the deck in the longitudinal direction to increase the bending stiffness metal rods are used. The metal rods are arranged here transversely to the longitudinal direction of the runners. They reinforce the deck structure and lie parallel to each other without being connected.

In the DE 10 2014 007 079 A1 describes a two-part plastic pallet with reinforcing profiles, which have the function of stiffening elements. The stiffening elements are rod-like and are inserted separately in the runners. Here, the runner structure is reinforced in the area of the ground level.

In the DE 10 2011 103 359 A1 shows Fig. 8 a plastic pallet in which reinforcing elements are arranged in the corners. Except for the non-interconnected reinforcing elements, which are also referred to as fittings, the pallet is made in one piece. The reinforcing elements extend in the finished pallet from the deck to the floor and are not interconnected. The attachment of the reinforcing elements exclusively in the corners serves to increase the wear resistance.

In the DE 10 2011 052958 A1 is described a composite of several parts range, are formed in the foot members arc-shaped and arranged crosswise. On their side facing the deck, in the region of the apex of the arches, support rods extending over the length of the base elements are used, which can also be made of metal. The lattice-shaped arrangement increases the load bearing capacity of the pallet. Also in the DE 43 36 469 A1 is a plastic pallet described in which the cover structure with a framework of reinforcing tubes, which may be made of steel, for example, is reinforced.

In the DE 20 2007 000 985 U1 describes a plastic pallet, which is provided with reinforcements both in the area below the deck and in the area of the feet just above the ground. According to the in Fig. 1-3 In the embodiment shown, the reinforcing elements, which may be formed from a rod-shaped or bar-shaped material, form a grid structure in the deck, and along the narrow side of the pallet two reinforcing elements arranged one above the other are parallel to one another, wherein the one element is embedded beneath the surface of the deck and the other in the bottom of the skid. However, the reinforcing elements are not in direct contact with each other, they are not connected to each other.

In the WO 2007/019833 A1 a plastic pallet is described in which reinforcing elements are arranged below the base plate of the pallet in the region of the feet and within the deck. Here show the Fig. 9-11 a pallet of a deck and feet attached thereto, wherein each three of the feet along the longer side of the pallet are connected by foot rails, which may consist of sheet steel, in the runners. In the deck also made of steel sheet reinforcing elements are arranged in the manner of a grid, the crossing points of the longitudinal struts and cross struts are in the feet. There, the grid structure is connected via webs with the foot rails, wherein on the type of connection no closer statement is made. As a preferred material for in the WO 2007/019833 A1 pallet described is called Styrofoam and the lattice structure serves to increase the dimensional stability. The arranged in the deck longitudinal and transverse struts and the webs in the feet have a plurality of juxtaposed recesses, which should ensure that they can be completely penetrated by the plastic of the pallet; In this way, the compound can be improved with the plastic and the stability of the overall construct compared to a simple Styrofoam palette can be increased. The high number of recesses also ensures that the weight of the pallet does not increase excessively compared to a pure polystyrene pallet.

Although such a structure of the stiffening elements with recesses is very advantageous in terms of weight and the connection with the plastic and increases the stability with respect to a direct load from above, but is hardly cope with a load by shear forces. The connection of the longitudinal or transverse struts with the foot rails on the struts also comes about only by the composite in the plastic, so that the range can withstand only low bending and shearing forces.

Description of the invention

The object of the invention is, therefore, to develop a pallet which, compared to the pallets known in the prior art, has an increased resistance to bending and shearing forces and, consequently, a lower deflection.

This object is achieved in a plastic pallet of the type described above in that the at least one stiffening structure has rungs each with predominantly closed surface, which connect the lower spars in the feet with the upper spars. In this case, the sprouts are integrally formed on the spars or preferably integrally connected thereto via contact surfaces cohesively, or positively or positively, wherein the connection types can also be combined, and where quite both types of sprouts can be realized on a stiffening structure. By these measures, the flexural rigidity of the pallet on the one hand and the shear strength of the pallet in a plane parallel to the top of the deck, on the other hand, is increased over pallets known in the art. In a predominantly closed surface, the proportion of openings in the sprouts is less than 50%, usually less than 25%. Recesses and openings are only where it is necessary or advantageous for manufacturing reasons. In fact, the proportion of openings is therefore usually less than 10% of the surface area.

The at least one stiffening structure is thus designed as a ladder-shaped structure with spars and bars, wherein the spars are connected to the sprouts and fixed and preferably inseparable, so that the ladder-shaped structure is able to absorb correspondingly high shear forces. The solid and preferably insoluble compound which is inevitably present in integral formation of the rungs and the spars and in embodiments in which the sprouts are not formed on spars, is preferably achieved by flat material bond, for example by gluing, but more preferably by welding is only a partial aspect. To increase the flexural rigidity or shear strength is also essential that the sprouts have a predominantly closed surface, for example, this means that as little openings or recesses are formed in the plate-shaped sprout parts as necessary, but in each case less than 50% of the entire surface of the plate-shaped spine part occupy, because a plurality of such recesses reduce the shear strength. If possible, such openings should be avoided. As a rule, the plate-shaped sprout parts therefore either have no openings, or only one, two or three openings through which, for example, optional transverse struts can be inserted to form a grid structure. If no transverse struts are to be used, the ladder-shaped stiffening structures therefore preferably have no openings.

In order to connect or insert the stiffening structures with the pallet, there are various possibilities. For example, they can be used in the mold, for example an injection mold, during production, so that the stiffening structure is almost completely enclosed by the cured plastic. In this way, especially a tight fit can be guaranteed. In order to replace the stiffening structures in the event of wear, it can also be inserted from below or above in the pallet or the feet of a one-piece pallet. The connection with the plastic of the pallet can then also be non-positive and / or positive. Preferably, however, the pallet is made of several parts, and the stiffening structures are - possibly connected via crossbars - used in the runners before the deck is placed on the runners and with this example via snap closures or kraftform- or cohesively connected.

In a simple embodiment, the stiffening structure can for example be made in one piece from strip steel, wherein the spaces between the rungs are punched out, milled or introduced into the stiffening structure in other, technically suitable manner. The thicker the tape is chosen, the more the shear strength is increased. At the same time, however, the mass of the plastic pallet is increased and if the ladder-shaped stiffening structure - as is preferably the case - made of metal, especially steel, this can lead to the mass of the plastic pallet with stiffening structures is higher than the mass of a comparable wooden pallet so that is an essential one Advantage of the material plastic would be lost. Too thin a sheet as a ladder-shaped stiffening structure on the other hand can not produce the required shear strength. Instead of metal, the ladder-shaped stiffening structure can also be made of other materials that can provide the necessary bending and shear stiffness of the pallet. For example, glass fiber or carbon fiber reinforced plastics are also suitable.

However, it has been found that a sufficiently high shear strength can be produced, in particular, the spars have a corresponding thickness, whereas the sprouts can be made with a smaller thickness. In a preferred embodiment, therefore, the spars on a predetermined thickness, which can be set, for example, based on the required shear strength. The thickness of the spars is understood to mean the extent of the spars perpendicular to their longitudinal direction and perpendicular to the longitudinal direction of the sprouts in the ladder-shaped structure. By only making the spars thicker, it is possible to significantly reduce material and thus weight without sacrificing shear strength.

If the sprouts are made in one piece on the spars, spars and sprouts merge, the sprouts can therefore be made thinner. If the rungs are connected in a material-locking, frictional and / or form-fitting manner to the bars via contact surfaces, the contact surfaces are selected to be as large as possible in their extent, both at height - ie. in the longitudinal direction of the spars - as well as perpendicular to it, in principle, also perpendicular to the height of curved surfaces in question.

In order to ensure a high stability in bending and shear strength, the rungs in the longitudinal direction of the spars a predetermined height - with lying ladder-shaped stiffening structures in the view the width - on, which corresponds to at least 80% of the width of the respective, in rung-receiving foot. For the sake of clarity, the term "height" has been referred to a standing, ladder-like structure; in the case of horizontal ladder-shaped structures, this corresponds to the widthwise view. Preferably, the height of the rungs is chosen so that the maximum available space in the foot - which are different for different feet on the same pallet - is utilized, i. in the case of a cohesive, non-positive or positive connection, the extension of the contact surfaces in the longitudinal direction of the spars preferably corresponds to the predetermined height.

The spars do not have to be solid over the entire thickness of material, the spars can also be designed as hollow structures with different cross-sections. Particularly advantageously, the hollow structure is composed of different surfaces, wherein at least one of the surfaces of a spar parallel to the top surface - ie perpendicular to the longitudinal direction the spars and sprouts - is aligned, which also contributes to increase the stability. In the case of using hollow structures, the spars are designed, for example, as tubes with the cross-section of a quadrilateral, for example a trapezoid, rectangle or square, and accordingly comprise four surfaces. Alternatively, they can also be designed as a T-beam or as a double T-beam, here too, at least one surface - that of the crossbar of the "T" - is parallel to the top surface.

In this way, a high stability of the stiffening structure with respect to bending and shearing in the pallet perpendicular to the direction of the runners, ie perpendicular to a plane in which the ladder-shaped structure is achieved, can be achieved.

If the rungs are firmly bonded to the spars formed as tubes having a quadrangular cross-section via contact surfaces, then these contact surfaces are preferably parallel to the top surface and the extent of the contact surface in the direction of the thickness of the spars is at least a quarter of the thickness, but preferably at least half the thickness , However, the expansion of the contact surface in the direction of the thickness particularly preferably corresponds to the entire thickness, this guarantees the best possible stability of the cohesive and planar connection.

However, the contact surfaces can also be perpendicular to the top surface in the spanned by sprouts and spars plane, in tubes with rectangular cross-section then small plates can be welded to the spars, for example, without the plates would have to be bent. Depending on the shape of the spars, the contact surfaces can also have any other shape or protrude at a different angle, it is important that the contact surfaces are chosen so large that they up to a predetermined maximum thrust and bending load a secure connection of sprouts and Holmen guarantee.

This also applies in the case of a non-positive or positive connection. The latter can for example be designed as a snap closure, wherein the contact surfaces then correspond to the surfaces of the closure in sprouts and spars, which lie in the connected state to each other. A correspondingly stable connection can be achieved, for example, if the snap closure is aligned along the longitudinal direction of the spars and extends beyond the predetermined height.

In order to produce a sufficiently stable non-positive connection, the rungs can be wedge-shaped on their sides facing the spars, for example-also here preferably over the entire height-and the spars have corresponding receptacles.

The ladder-shaped stiffening structure can be realized in various ways, particularly advantageous embodiments are described below.

In a particularly preferred embodiment, which is particularly suitable for very high numbers, the stiffening structure is designed as an aluminum extruded profile. The sprouts are in this case formed integrally on the spars. Openings are made between the rungs, for example by punching or milling, through which the tines of a forklift can enter. Aluminum has the advantage that it is a light metal, moreover, no corrosion protection is necessary.

In a further preferred embodiment, which is particularly suitable for smaller and medium quantities of less than 10,000, the stiffening structure is integrally formed as a tube with a square cross section, which is bent in the shape of two spars with intermediate rungs. In this way, it is possible to make a stiffening structure with a maximum of three rungs, which are integrally formed on the spars. Such a stiffening structure can be realized in various ways, which differ mainly by where the two pipe ends are arranged in the stiffening structure. By way of example, it is possible to produce a structure designed in the manner of an "8" by sevenfold bending by 90 ° in each case. In a preferred embodiment, which requires only six bends, the two ends of the tube are bent from one of the spars to the other, opposite spar and form the middle rung. The pipe ends are cohesively connected to each other and to the other, opposite spar. The compound is particularly preferably over the entire thickness of the spar. This type of manufacture makes it possible to provide the tube ends with a further bend for increased stability, so that the effective height of the rung, corresponding to the width of a lying ladder-shaped structure, grows. This increases the stability in terms of bending and shear strength when forces in the area of the middle foot attack. The cohesive connection is particularly preferably produced by welding, the welds are then protected against corrosion, for example by galvanizing. Basically, this profile is relatively inexpensive to produce, since tubes with square cross section, for example, with a cross section of 20x20 mm and a wall thickness of 2 mm, are available in large quantities on the market. In the production of profiles, about a quarter of the costs incurred by sawing the square tubes in order to cut them. By using a single curved tube, these costs can be minimized.

In another embodiment, which is somewhat expensive to manufacture and more expensive due to the time-consuming production, the spars are also formed as tubes with square cross-section, but at least the inner rungs are formed as plate-shaped connecting elements, in which on two opposite sides than contact surfaces Standing seams are formed. These are one-piece elements which are also commercially available as so-called C-profiles with a wall thickness of, for example, 2 mm, alternatively, production by cutting and bending from a straight sheet metal is also possible. As a material, in particular steel sheet in question, but also all other metals and metal alloys that meet the requirements can be used.

Under a standing seam is understood to be a bend of the edge of the plate-shaped connecting element by 90 °. The bent surface of the plate-shaped connecting element then forms the contact surface. The extent of the contact surface in the direction of the thickness of the spar is at least a quarter of the thickness. At a tube diameter of the square tube of about 2 cm, the bending edge is then at least 5mm from the peripheral edge of the plate-shaped connecting element. However, for a stable connection, it is advantageous to make the contact area as large as possible so that the bending edge is at least half, i. 10 mm, preferably even the thickness of the tube corresponding to 20 mm from the peripheral edge of the plate-shaped connecting element, is parallel to this.

A particularly stable, but also production-intensive variant is obtained if all sprouts are designed as such plate-shaped connecting elements, including the outer rungs. At the contact surfaces, the plate-shaped connecting elements are welded to the pipes, then the welds must be galvanized. Depending on the choice of material, it may also be necessary to galvanize the entire stiffening structure.

A somewhat less production-intensive variant, in which the high stability in terms of bending and shear resistance in the case of a stiffening structure with three sprouts for the middle rung - attack on the experience of the greatest forces - is preserved, is the middle, inner rung as a plate-shaped connecting element with designed as standing seams contact surfaces, as described above, but to make the two outer rungs of a tube with a rectangular or square cross section to bend. The two spars and the two outer rungs are in this case formed in one piece from a bent tube.

Other ways to minimize the material consumption with high stability with respect to bending and shearing, are to use instead of thick sheets or thick stiffening structures thinner sheets in which the spars are formed by bending along the longitudinal direction of the spars. In this way, folds can be formed on the spars. The introduction of beads as a special form of bending is possible as a stiffening serving as well, beads can be introduced at any point in the longitudinal direction of the spars in this. The stiffening structure is in this Case designed as a rolled and / or bent metal profile with between the rungs, which are integrally formed on the spars, introduced openings. The bending takes place in accordance with the longitudinal direction of the spars. Here, sheets of different thickness can be used, depending on the required load capacity, for example, sheets with thicknesses of 1 mm to 4 mm. The stability of the stiffening structure is thus not achieved here by the material thickness, but by the formation of the spars by bending, whereby they can be impressed in particular a predetermined thickness. When using metal profiles, the spars can be formed at the profile edges in the simplest case as standing seams. A higher stability is achieved by Doppelstehfalze, ie by two in the transverse direction of the profile - with bending edges along the longitudinal direction of the spars - in a short distance successive bends by 90 ° in the same orientation. The spars can also be designed as envelopes, ie as bends by 180 °. To further increase the stability, it may be advantageous to combine standing seams and envelopes. Between the rungs, the openings are introduced, this can be done for example by punching, cutting or milling. The rungs are preferably plate-shaped, so in the longitudinal direction of the spars on a predetermined height, which comes close to the dimensions of the feet in the longitudinal direction of the spars. With tapered feet, the shape of the plate forming the rung can be adjusted accordingly, for example in a trapezoidal shape.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the specified combinations but also in other combinations or alone, without departing from the scope of the present invention.

Brief description of the drawings

Fig. 1

eine Kunststoffpalette mit einer darin eingebetteten leiterförmigen Versteifungsstruktur,

Fig. 2

eine Kunststoffpalette ohne Deck mit Versteifungsstrukturen,

Fig. 3a)-c)

eine erste Ausgestaltung einer Versteifungsstruktur,

Fig. 4a)-c)

eine zweite Ausgestaltung einer Versteifungsstruktur,

Fig. 5a)-b)

eine dritte Ausgestaltung einer Versteifungsstruktur,

Fig. 6

eine Abwandlung der in Fig. 5 gezeigten Versteifungsstruktur,

Fig. 7a)-c)

eine vierte Ausgestaltung einer Versteifungsstruktur,

Fig. 8a)-c)

eine fünfte Ausgestaltung einer Versteifungsstruktur,

Fig. 9a)-d)

eine sechste Ausgestaltung einer Versteifungsstruktur,

Fig. 10a)-b)

eine siebte Ausgestaltung einer Versteifungsstruktur und

Fig. 11a)-c)

eine achte Ausgestaltung einer Versteifungsstruktur.

The invention will be explained in more detail for example with reference to the accompanying drawings, which also disclose characteristics essential to the invention. Show it

Fig. 1

a plastic pallet with a ladder-shaped stiffening structure embedded therein,

Fig. 2

a plastic pallet without deck with stiffening structures,

Fig. 3a) -c)

a first embodiment of a stiffening structure,

Fig. 4a) -c)

a second embodiment of a stiffening structure,

Fig. 5a) -b)

a third embodiment of a stiffening structure,

Fig. 6

a modification of the in Fig. 5 shown stiffening structure,

Fig. 7a) -c)

A fourth embodiment of a stiffening structure,

Fig. 8a) -c)

a fifth embodiment of a stiffening structure,

Fig. 9a) -d)

a sixth embodiment of a stiffening structure,

Fig. 10a) -b)

a seventh embodiment of a stiffening structure and

Fig. 11a) -c)

an eighth embodiment of a stiffening structure.

Detailed description of the drawings

Fig. 1 shows a conventional plastic pallet, which includes a deck 1 for storage of objects to be transported. In the perspective view shown here, a top side 2 can be seen, this is opposite a deck underside, not shown, deck top 2 and bottom deck are spaced from each other by the thickness of the deck. From the top bottom downstanding feet 3 are formed. In addition, the plastic pallet also skids 4, which are each formed at least two feet 3 on the undersides connecting to each other. The foremost segment of the plastic pallet - comprising three feet and the runners that connect the feet - is shown here cut open, so that there - arranged by hatching - stiffening structure 5 is visible. The stiffening structure 5, of which the pallet here has two in the outer runners, is here ladder-shaped and comprises in the runners 4 arranged lower spars 6 and spaced therefrom arranged upper spars 7, which are arranged on the lower spars 6 extending parallel to these , The upper spars may be disposed in an area between the deck top 2 and the deck bottom in the deck 1, but may also be below the deck 1, as in FIG Fig. 1 exemplified, be arranged. In the case of an arrangement of the upper spars 7 in the area between the top side 2 and the underside of the deck, the stiffening structure 5 can then be completely enclosed by the plastic of the pallet in the case of a one-piece production.

The stiffening structure 5 is ladder-shaped and therefore has rungs 8 which connect the lower spars 6 in the feet 3 with the upper spars 7. The surface of the sprouts is predominantly closed, i. it has no openings or recesses, and if so, then the area of the openings or portions proportionately to the total surface of the rungs 8 is less than 50%, usually less than 10%. Recesses and openings are only applied where this is necessary or useful for manufacturing reasons.

The rungs 8 are either integrally formed on the lower bars 6 and the upper spars 7, or they are integrally connected to these respectively via contact surfaces. Depending on the configuration, some of the rungs 8 may be integrally formed on one or both spars and other sprouts may be connected to the spars 6, 7 cohesively. The type of fabric bond is chosen depending on the material. In the case of metallic stiffening structures 5, in particular a weld is suitable here. Dependent on Of the material - for example, can also be used carbon fiber and glass fiber reinforced plastics for the stiffening structure - other types of connection may prove useful, such as non-positive or positive connections, with all types of positive engagement can be combined.

Due to the one-piece design of the rungs 8 on the bars 6 and 7 or by the cohesive connection over larger contact surfaces on the one hand and by the predominantly closed surface of the rungs 8 on the other hand, the bending stiffness of the plastic pallet and in particular the shear resistance of the plastic pallet in parallel to the top 2 Level increased.

By using stiffening structures 5 formed in this way, it is possible to reduce the deflection of the plastic pallet with load bearing in the middle, for example from 22 mm to less than 10 mm for a plastic pallet measuring 1200 mm x 800 mm and 3 feet connected to runners. The shear stiffness is increased because shear forces are derived or absorbed by the stiffening structures 5, which may be made of metal in particular.

Fig. 2 shows a plastic pallet without deck, here only the feet 3 are molded with runners 4 molded thereto. In the outer two foot runner elements stiffening structures 5 are used. In addition, cross braces 9 are shown here, which further increase the stability of the plastic pallet. These transverse struts 9 may also be made of metal. However, they are purely optional and not absolutely necessary for achieving the desired effect. In the interest of the lowest possible mass of plastic pallet can be dispensed with the cross struts 9. They can be inserted into the pallet independently of the stiffening structures 5, but also be connected to them in a material-locking, positive-locking and / or non-positive manner, so as to form an even more stable structure. In the present case, the two outer transverse struts 9 are inserted through openings in the stiffening structures 5 and in the rungs 8 and form a grid with them. The middle cross strut 9 is only launched, but could also be integrated into the grid.

With the help of the stiffening structures 5, it is possible to reduce the deflection to the extent that is considered permissible even with wooden pallets of comparable size, or even to even smaller dimensions. The thicker the stiffening structures - with thickness is the extension perpendicular to the longitudinal direction of the spars and perpendicular to the longitudinal direction of the rungs meant - are, the higher the shear and bending stiffness, but this is associated with a higher mass. Although plastic pallets are in themselves lighter than wooden pallets of the same size, the weight of comparable wooden pallets can be exceeded in accordance with thick stiffening structures 5, whereby a significant advantage of plastic pallets fell away.

On the other hand, if, on the other hand, one chooses the thickness of the lower spars 6, the upper spars 7 and the sprouts 8 to be too small, for example as a pure sheet of constant thickness, this can not achieve the necessary shear stiffness if the thickness is too small. For this reason, at least the upper spars 6 and the lower spars 7 have a predetermined thickness.

In the case of a cohesive connection of the rungs 8 with the bars 6, 7 via contact surfaces, and also in the case of a non-positive or positive connection, the size of the contact surfaces depending on a predetermined maximum bending and thrust load of the plastic pallet is selected or specified, in As a rule, the contact surfaces should be chosen as large as structurally possible.

In the longitudinal direction of the spars 6, 7, the rungs 8 to increase the shear stiffness and flexural rigidity in the longitudinal direction of the spars 6, 7 a predetermined height, which is based on the width of the feet, it should be at least 80% of the width of the respective, the rung receiving Foot amount. Here, the term "height" is used in reference to a standing ladder, it corresponds to a horizontal structure with the width. In the case of a connection of the rungs 8 with the bars 6, 7 via contact surfaces corresponds to the extension of the contact surfaces in the longitudinal direction of the spars 6,7 preferably the predetermined height.

For the design of the spars 6 and 7, many design variants are possible, for example, the lower beam 6 and / or the upper spar 7 can be composed of different surfaces as hollow structures, for example, they can be tubes with the cross section of a quadrilateral, especially a trapezoid , Rectangles or square forming, which facilitates the connection of the contact surfaces; but also a design as T-beam or as a double-T-beam is conceivable. At least one of the surfaces of a spar (6, 7) is then preferably aligned perpendicular to the longitudinal direction of the respective spar 6, 7 and perpendicular to the longitudinal direction of the rungs 8. On these surfaces can then be formed in particular for the material connection contact surfaces.

In the case of a cohesive connection of the rungs 8 with the bars 6, 7, therefore, the contact surface is preferably in a plane to the longitudinal direction of the rungs 8 and the spars 6, 7. The expansion of the contact surface in the thickness direction should then usually more than Half the thickness amount. The rungs 8 may also have a smaller thickness, depending on the embodiment, for example, in the case of an embodiment of a sheet, a thickness corresponding to the sheet thickness.

Various embodiments of stiffening structures 5 are described below with reference to FIG Fig. 3-11 explained.

Fig. 3a ) -c) show a first embodiment of a stiffening structure, as it can be used to increase the bending stiffness and shear resistance of the plastic pallet. Fig. 3a ) shows a view of the stiffening structure from the front, Fig. 3b ) A cross section through the stiffening structure in the region of a rung 8 and Fig. 3c ) is a perspective view of the stiffening structure, which is designed here as an aluminum extruded profile 10. The lower beam 6 and the upper beam 7 are each formed as a T-beam, the thickness of the spars 6, 7 may be, for example, 20 mm in the region of the crossbar of the "T". Since aluminum is a non-rusting material, special corrosion protection can be dispensed with. Between the rungs 8 openings 11 are introduced, which are in the assembled state between the feet of the plastic pallet and allow the entrance of the fork of a forklift. The rungs 8 are here integrally formed on the spars 6, 7 and plate-shaped. Passage holes 12 are optionally located in the area under the upper spar 7, through which plastic may pass during manufacture in the case of a one-piece pallet to provide a firm connection between the stiffening structure and the plastic pallet. The passage holes 12 can also be used for another type of attachment, for example a mechanical, provided that pinching in the framework structure of the plastic pallet should not be possible, in this case, no through holes 12 are required. In particular, however, the through-holes 12 are also suitable for accommodating optional transverse struts 9 in order to fix them better and to produce a stiffening grid structure in the plane of the deck 1, as in FIG Fig. 2 shown. An advantage of using an aluminum extruded profile is also in the reduced mass. While a wooden pallet measuring 800mm x 1200mm weighs 20-25kg, the mass of a pallet is the same as in Fig. 3a ) -c) shown profiles about 15-20kg.

A second embodiment of a stiffening structure, which is designed here as a further aluminum extruded profile 13, show Fig. 4a ) -C). Fig. 4a ) shows a view of the aluminum extruded profile 13 from the side, Fig. 4b ) A cross section through the profile in the region of a rung 8 and Fig. 4c ) the aluminum extruded profile 13 in a perspective view. Again, 8 openings 11 are introduced between the sprouts. The introduction can be done for example by punching, cutting or milling. Also in Fig. 4 shown further aluminum extruded profile 13 has through holes 12. Unlike the in Fig. 3 shown extruded here, however, the lower beam 6 is designed as a tube with a square cross section and the upper spar as a double-T-beam. It is of course possible to design one of the spars as a T-beam here, as well as one of the spars of the aluminum extruded profile 10, which in Fig. 3a ) -c), be configured as a double-T-beam or as a pipe with a square or rectangular cross-section.

A third embodiment is in Fig. 5a ) -b). This is a stiffening structure which is designed as a tube with a square cross section 14. The tube 14 is bent into the shape of two bars 6, 7 with intermediate rungs 8. It is a one-piece design with a maximum of three rungs 8, which is particularly suitable for smaller pallets. All sprouts 8 are formed from the square tube 14. At the in Fig. 5 As shown, the outer rungs 8 of the stiffening structure are formed by bending the tube 14 twice by 90 ° in each case. The middle or inner rung 8, however, is formed by the two pipe ends 15 are bent by one of the spars - here without limiting the generality of the upper beam 7 by 90 °, thus the middle rung 8 is formed by the bending the opposite spar - here the lower beam 6 - materially connected, for example by welding, here over the entire thickness of the lower beam 6. To increase the bending and shear stiffness and the stability of the stiffening structure, the pipe ends 15 may be connected to each other cohesively, at However, it can also be dispensed with a corresponding fixation in the plastic pallet in the middle foot.

A modification of this embodiment is in Figure 6 shown. The pipe ends 15, which form the middle rung 8, are spread away from each other here in their end regions, so that the middle rung 8 takes the form of a "Y". With one edge, the pipe ends 15 are each materially connected to the opposite spar, here the lower beam 6, over the entire thickness of the spar. The respective edges are preferably provided with larger bevels to a contact surface for the cohesive connection, which is more stable compared to a linear, one-dimensional connection. Again, the rungs 8 are integrally formed on the lower beam 6 and the upper spar 7, even if the pipe ends are connected to the opposite spar to increase the rigidity of material. Due to the spreading of the pipe ends 15 in "Y" shape, the shear stiffness in a plane parallel to the deck 1 or the bending stiffness perpendicular to the ceiling plane relative to the in Fig. 5a) -b) shown embodiment further increased.

Another embodiment for a stiffening structure is in Fig. 7 shown. Fig. 7a ) shows a projection view of the stiffening structure from the front and Fig. 7b ) a perspective view. Also in this fourth embodiment, the spars are formed as tubes with a square cross-section, the lower spar 6 and the upper spar 7 and the two outer rungs 8 are also formed integrally from a bent tube 14 here. The two pipe ends 15 are connected cohesively in the region of one of the outer rungs 8. However, the tube ends 15 may also meet at another location of one of the spars, for example in the region of the middle rung 8. The middle rung 8 is formed here as a plate-shaped connecting element 16, in which on two opposite sides, namely the sides, to the spars 6 and 7, contact surfaces are formed as standing seams.

The plate-shaped connecting element 16 is here - based on the thickness of the lower beam 6 and the upper spar 7 - placed centrally. The extent of the contact surfaces formed by the standing seams in the direction of the thickness here is half the thickness.

This fourth embodiment of a stiffening structure has a particularly good cost-benefit ratio, since on the one hand the square tube 14 only needs to be cut to length once and bent only four times. Due to the plate-shaped connecting element, which may have a C- or S-shape in cross-section, but the shear strength and bending stiffness compared to in Fig. 5 and Fig. 6 shown embodiments, since the plate-shaped connecting element 16 in the longitudinal direction of the spars, the maximum height - in the view corresponding to the width - may have, which just makes it possible to fully integrate it into the corresponding foot 3, whereas the width in the formation the middle rung 8 from the bent tube ends 15 is predetermined by the thickness of the square tube 14 and can not be increased. The in the Fig. 7a ) -b) stiffening structure can also be used for pallets with more feet in one direction, as readily several of the plate-shaped connecting elements 16 can be set as inner rungs between the integrally formed outer rungs.

Another - particularly stable - fifth embodiment of a stiffening structure for a plastic pallet is in Fig. 8 shown. Fig. 8a ) shows a side view of a stiffening structure lying on the outer edge of a spar, Fig. 8b ) the cross section in the region of a rung 8 and Fig. 8c ) a perspective view. Unlike the in Fig. 7 Shown here embodiment, the outer rungs 8 are formed as plate-shaped connecting elements 16 with molded-on standing seams 17 to form the contact surfaces. The plate-shaped connecting elements 16 have in cross-section - as in Fig. 8c ) - a "C" shape. The lower spar 6 and the upper spar 7 are also formed in this embodiment as a tube 14 with a square cross-section. They can be produced from a pipe by sawing. In each case three - here similar - plate-shaped connecting elements 16 connect the upper spar 7 with the lower spar 6, the standing seams 17, which are formed by bending against the plate-shaped elements 16, form the contact surfaces. Their extension in the direction of the thickness of the spars 6, 7 corresponds here to the entire thickness of the spars 6 and 7. By means of the contact surfaces, the plate-shaped connecting elements are integrally connected to the bars 6 and 7. After production of the cohesive connection, the stiffening structure must still be galvanized to protect against corrosion.

Compared to the above-described variants of extruded aluminum profile are in Fig. 5-8 Although described more elaborate in their production, but deal with the material resources, since there is virtually no waste, whereas in the Insertion of the opening 11 in connection with Fig. 3 and Fig. 4 described aluminum extrusions 10 and 13 a significant proportion of material waste accumulates.

The Fig. 9-11 show further embodiments of stiffening structures, which are all integrally formed from rolled and bent metal profile, for example (steel) sheet metal or strip steel, wherein between the rungs 8 openings 11 are again introduced. In addition, these stiffening structures also have optional through holes 12. The embodiments differ here only in the formation of the lower beam 6 and the upper spar 7, which are integrally formed on the profile edges by bending and as standing seams, double Stehfalze, envelopes or combinations thereof are formed. This in Fig. 9a ) in perspective view and in Fig. 9b ) in cross-section in the region of a rung 8 shown metal profile as the sixth embodiment of a stiffening structure has an upper spar 7 to the lower spar 6 identically shaped. The spars are formed by a standing seam of 90 ° and two envelopes, ie bends of 180 °, in the opposite orientation. The bends are arranged mirror-symmetrically to a horizontal plane in the sheet, so that the profile with the two standing seams forms a "C" shape, which offers a slightly higher stability over a likewise possible "S" shape. All rungs 8 are plate-shaped and integrally formed on the spars 6 and 7.

That in the Fig. 10a ) in perspective and in Fig. 10b ) in cross section in the region of a rung 8 shown metal profile as the seventh embodiment of a stiffening structure has trained by other bending combinations spars 6, 7. The plate-shaped rungs 8 are also integrally formed on the spars 6, 7, and in relation to the thickness of the spars 6 and 7 - in Fig. 10b ) according to the horizontal direction in the sheet plane - centered. However, the upper beam 7 has a greater width - corresponding to the vertical direction in the leaf level - than the lower beam 6. Here can be exploited that on the one hand the skids 4 should be kept flat, but on the other hand for the upper beam 7 - at more complete Enclosure through the plastic - almost the entire deck height can be used. This additionally increases the stability. The spars 6, 7 are here formed by the combination of several bends by 90 ° (standing seam) and a bend by 180 ° (envelope).

An eighth embodiment of a stiffening structure is finally in Fig. 11 shown. Fig. 11a) and Fig. 11b ) show the formed as a metal profile stiffening structure in perspective from two opposite sides, Fig. 11c ) shows the profile in cross section in the region of a rung 8. Again, the upper beam 7 is wider than the lower beam 6 executed. Both bars 6, 7 are formed as double standing seams. Pro Holm only two bends are needed here, the stiffening structure is thus relatively easy to produce, but also offers a very high bending and shear strength.

All profiles are characterized by the fact that they are able to give a plastic pallet the required bending and shear stiffness at relatively low mass, so that the deflection in the middle is not greater than wood pallets, but on the other hand with the mass of the plastic pallet Stiffening structures is even lower than in conventional wooden pallets of the same size. While the latter have a weight of 20-25 kg with dimensions of 1200 x 800 mm, it is possible with the invention presented here to keep the weight of the plastic pallets clearly below, at about 15-20 kg.

LIST OF REFERENCE NUMBERS

1

deck

2

Deck upper surface

3

foot

4

skid

5

stiffening structure

6

lower spar

7

upper spar

8th

rung

9

crossmember

10

Extruded aluminum profile

11

opening

12

Through hole

13

Extruded aluminum profile

14

Tube with square cross section

15

pipe end

16

Plate-shaped connecting element

17

Standing Seam

Claims (13)

Plastic pallet comprising a deck (1) for storage of objects to be transported, - Feet (3), which are formed projecting from a deck underside, and Skids (4), each of which has at least two feet (3) connected to one another at their lower sides, - At least one stiffening structure (5), comprising in the runners (4) arranged lower spars (6) and spaced therefrom arranged upper spars (7) which are arranged over the lower spars (6) parallel to these, characterized in that - The at least one stiffening structure (5) has rungs (8) each having a predominantly closed surface, which connect the lower spars (6) in the feet (3) with the upper spars (7), - Wherein the rungs (8) are integrally formed on the spars (6, 7) or connected to these in each case via contact surfaces cohesively, non-positively or positively, - Which increases the flexural rigidity of the pallet and the shear strength of the pallet in a plane parallel to the top (2) level. Plastic pallet according to claim 1, characterized in that the spars (6, 7) have a predetermined thickness. Plastic pallet according to claim 1 or 2, characterized in that in the case of a connection of the rungs (8) with the spars (6, 7) via contact surfaces, the size of the contact surfaces in dependence on a predetermined maximum bending and thrust load of the plastic pallet is specified. Plastic pallet according to one of claims 1 to 3, characterized in that the rungs (8) in the longitudinal direction of the spars (6, 7) have a predetermined height which at least 80% of the width of the respective, the rung (8) receiving the foot (3 ), wherein in the case of a cohesive, non-positive or positive connection, the extension of the contact surfaces in the longitudinal direction of the spars corresponds to the predetermined height. Plastic pallet according to one of claims 3 or 4, characterized in that the spars (6, 7) are formed as composed of different surfaces hollow structures, preferably formed as tubes with the cross section of a rectangle, or as a T-beam or double-T-beam are, wherein at least one of the surfaces of a spar (6, 7) is aligned perpendicular to the longitudinal direction of the spars (6, 7) and the rungs (8). Plastic pallet according to claim 5, characterized in that in the case of a cohesive connection of the rungs (8) with the bars (6, 7), the contact surfaces lie in a plane perpendicular to the longitudinal direction of the spars (6, 7) and rungs (8) and the Extension of the contact surfaces in the direction of the thickness is at least a quarter of the thickness, preferably at least half the thickness is, particularly preferably the entire thickness corresponds. Plastic pallet according to one of claims 1 to 5 with integrally formed on the spars (6, 7) rungs (8), characterized in that the at least one stiffening structure (5) as an aluminum extruded profile (10, 13) is formed with between the rungs (8) introduced openings (11). Plastic pallet according to one of claims 1 to 7, characterized in that at least the lower spar (6), the upper spar (7) and the two outer rungs (8) are integrally formed from a bent tube (14) with a square cross-section. Plastic pallet according to claim 8 with three integrally formed on the bars rungs, characterized in that the tube (14) in the shape of two bars (6, 7) is bent with intermediate rungs (8). Plastic pallet according to claim 9, characterized in that the two tube ends (15) of one of the spars (6, 7) to the other, opposite bar (7, 6) are bent and the middle rung (8) form, and cohesively with each other and with the other, opposite Holm (7, 6) are connected, preferably over the entire thickness of the respective spar (7, 6). Plastic pallet according to one of claims 1 to 5, characterized in that the lower spar (6) and the upper spar (7) are designed as tubes (14) with a square cross-section and at least the inner rungs (8) as plate-shaped connecting elements (16). are formed, in which contact surfaces are formed as standing seams on two opposite sides. Plastic pallet according to one of claims 1 to 4 with integrally formed on the spars (6, 7) rungs (8), characterized in that the at least one stiffening structure (5) as a rolled and bent metal profile with between the rungs (8) introduced Openings (11) is formed. Plastic pallet according to claim 12, characterized in that the spars (6, 7) on the profile edges as Stehfalze, double Stehfalze, envelopes or combinations thereof and / or the rungs (8) are plate-shaped.

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