EP3398870B1 - Plastic pallet with stiffening structure - Google Patents

Description

Field of the Invention

The invention relates to a plastic pallet, which initially comprises a deck for storing objects to be transported, and feet which are designed to protrude from the underside of the deck. The plastic pallet also includes runners, which are each connected to each other at least two feet on their undersides, ie on the side opposite the deck. Finally, the plastic pallet also comprises at least one stiffening structure, which in turn comprises lower spars arranged in the runners and upper spars lying exactly above the lower spars and spaced apart from them and running parallel. The upper spars can be arranged in the deck in the area between a top and bottom of the deck, or also below the bottom of the deck.

In addition to the classic wooden pallets, plastic pallets for the transport and storage of goods are playing an increasingly important role today. Advantages are, for example, the lower weight and the possibility to form almost any pallet structure with the help of injection molding techniques, so that a high degree of individuality can be achieved and customer-specific requirements can be met. In addition, recyclate can be used to manufacture many types of pallets, unless special hygiene regulations are to be observed. It is also possible to use additives such as reinforcing fibers. The deck can have a continuous, closed loading area, but the loading area can also be formed by a lattice or rib structure.

On the underside of the deck, ie facing the floor, feet are formed projecting downwards. They have a height that allows the pallet to be picked up and transported with the fork of a forklift, the fork moves into the spaces between your feet. At the same time, however, the feet must also be able to support the permissible weight of the pallet with goods stored on it, without the material showing signs of fatigue. Although it is possible to manufacture the feet separately from a material with a higher impact strength, this type of production is more expensive compared to the one-piece production of a pallet, since more tools have to be kept available and the pallet then has to be assembled.

For the transport on roller and chain conveyors on the one hand and to increase the stability on the other hand, plastic pallets often also include runners which are each connected to one another on the undersides of at least two feet. Mostly the runners are arranged parallel to each other, in the case of rectangular pallets their longitudinal direction is usually parallel to the narrower edge of the pallet, but this is not mandatory, and a connection of the feet along the longer edge is also possible. All-round runners can also be used, i.e. Skids that also connect the feet together along the longer edge of the pallet.

Plastic pallets also have disadvantages compared to wooden or metal pallets. One disadvantage is that plastic pallets tend to deform more than wooden pallets under load. In the worst case, this can lead to irreversible deformations. If goods with a high but still permissible mass are placed on the pallets, this leads to a deflection of the deck, whereby the feet with the runners molded onto them also deform slightly or bear their share of the deflection by the feet on their top Tilt inwards towards the middle of the deck, but strive outwards on the underside. This results in shear, bending and shear forces that can only be insufficiently reversibly absorbed by the pallet.

State of the art

In order to reduce the deformation under load, it is known in the prior 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 describes a plastic pallet that can be assembled from several parts, in the deck of which metal rods are inserted in the longitudinal direction to increase the bending rigidity. The metal bars are arranged transversely to the longitudinal direction of the runners. They reinforce the cover structure and are parallel to each other without being connected.

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

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

In the DE 10 2011 052958 A1 describes a pallet composed of several parts, in which foot elements are arched and arranged crosswise. On its side facing the deck, in the region of the apex of the arches, support rods are used which extend over the length of the foot elements and which can also be made of metal. The grid-like arrangement increases the load-bearing capacity of the pallet. Also in the DE 43 36 469 A1 describes a plastic pallet in which the cover structure is reinforced with a frame made of reinforcing tubes, which can be made of steel, for example.

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 floor. According to the in Fig. 1-3 In the embodiment shown, the reinforcement elements, which can be formed from a rod-shaped or rod-shaped material, form a lattice structure in the deck, and two reinforcement elements arranged one above the other lie parallel to one another along the narrow side of the pallet, one element being embedded in the deck below the surface thereof and the other in the bottom of the skid. However, the reinforcement elements are not in direct contact with one another, they are not connected to one another.

In the WO 2007/019833 A1 describes a plastic pallet in which reinforcing elements are arranged below the base plate of the pallet in the area of the feet and within the deck. Here they show Fig. 9-11 a pallet consisting of a deck and feet attached to it, with three of the feet along the longer side of the pallet being connected in the runners by foot rails, which may be made of sheet steel. Reinforcing elements made of sheet steel are also arranged in the deck in the manner of a lattice, the crossing points of the longitudinal struts and cross struts are in the area of the feet. There the lattice structure is connected to the foot rails by means of webs, none of which are related to the type of connection further statement is made. As a preferred material for those in the WO 2007/019833 A1 The pallet described is called styrofoam and the lattice structure serves to increase the dimensional stability. The longitudinal and transverse struts arranged in the deck as well as the webs in the feet have a large number of recesses which are lined up to ensure that the plastic of the pallet can penetrate them completely; In this way, the connection with the plastic can be improved and the stability of the overall construct compared to a simple polystyrene pallet can be increased. The large number of recesses also ensures that the weight of the pallet does not increase excessively compared to a pure polystyrene pallet.

Such a structure of the stiffening elements with recesses is very advantageous with regard to the weight and the connection with the plastic and increases the stability with regard to a direct load from above, but is hardly able to cope with a load due to shear forces. The connection of the longitudinal or transverse struts with the foot rails via the struts is also only achieved through the composite in the plastic, so that the pallet can only withstand low bending and shear forces.

In the JP S56 123248 A describes a plastic pallet comprising a deck, feet and runners. The range also includes a stiffening structure with lower spars, upper spars and rungs that connect the lower and upper spars.

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 increased strength against bending and shear forces and, consequently, less deflection.

This object is achieved in a plastic pallet of the type described above by the alternative combinations of features according to claim 1. The at least one stiffening structure has rungs, each with a predominantly closed surface, which connect the lower bars in the feet to the upper bars. The rungs are formed in one piece on the spars or are preferably connected to them by means of contact surfaces in a cohesive manner, or also non-positively or positively, wherein the types of connection can also be combined, and both types of rungs can be realized on a stiffening structure. These measures increase 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 compared to pallets known in the prior art. With a predominantly closed surface, the proportion of openings in the rungs 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 percentage of openings is usually less than 10% of the surface.

The at least one stiffening structure is thus designed as a ladder-shaped structure with bars and rungs, the bars being firmly and preferably permanently connected to the rungs so that the ladder-shaped structure is able to absorb correspondingly high shear forces. The firm and preferably non-detachable connection, which is inevitably present when the rungs and the spars are made in one piece and, in the case of designs in which the rungs are not formed on spars, is preferably achieved by flat material connection, for example by gluing, but particularly preferably by welding. is only a partial aspect. To increase the bending stiffness or shear strength, it is also essential that the rungs have a predominantly closed surface.For example, in the case of plate-shaped rungs, this means that as few openings or recesses are formed in the plate-shaped rung parts as necessary, but in any case less occupy 50% of the total surface of the plate-shaped rung part, since a large number of such recesses reduce the shear strength. If possible, such openings should be avoided. As a rule, the plate-shaped rung parts therefore either have no openings or only one, two or three openings through which, for example, optional cross struts can be inserted to form a lattice structure. If no cross struts are to be used, the ladder-shaped stiffening structures therefore preferably have no openings.

There are various options for connecting the stiffening structures to the pallet or inserting them into the pallet. For example, they can already be used in the mold during manufacture, for example an injection mold, so that the stiffening structure is almost completely enclosed by the hardened plastic. In this way, a firm fit can be guaranteed. In order to be able to replace the stiffening structures in the event of wear, they can also be inserted from below or above into 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. However, the pallet is preferably designed in several parts, and the stiffening structures are inserted into the runners, possibly connected via cross struts, before the deck is placed on the runners and connected to it, for example, by means of snap locks or force-fit or material-locking.

In a simple embodiment, the stiffening structure can, for example, be made in one piece from steel strip, the spaces between the rungs being punched out, milled or introduced into the stiffening structure in another manner which is suitable in terms of processing technology. 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 the case preferably - is made of metal, in particular steel, this can lead to the mass of the plastic pallet with stiffening structures being higher than the mass of a comparable wooden pallet so that's an essential one The advantage of the plastic material would be lost. On the other hand, a sheet that is too thin as a ladder-shaped stiffening structure cannot produce the required shear strength. Instead of metal, the ladder-shaped stiffening structure can also be made from other materials that can provide the necessary flexural and shear rigidity 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 if, in particular, the spars have a corresponding thickness, whereas the rungs can be designed with a smaller thickness. In a preferred embodiment, the spars therefore have a predetermined thickness, which can be determined, for example, on the basis of the required shear strength. The thickness of the spars is understood to mean the extension of the spars perpendicular to their longitudinal direction and perpendicular to the longitudinal direction of the rungs in the ladder-shaped structure. By making the spars thicker, material and weight can be saved significantly without sacrificing shear strength.

If the rungs are made in one piece on the spars, the spars and rungs merge into one another, which means that the rungs can be made thinner. If the rungs are cohesively, non-positively and / or positively connected to the spars via contact surfaces, the dimensions of the contact surfaces should be as large as possible, both in height - i.e. in the longitudinal direction of the bars - as well as perpendicular to it, with curved surfaces also being possible in principle perpendicular to the height.

In order to ensure a high degree of stability with regard to bending and shear strength, the rungs have a predetermined height in the longitudinal direction of the bars - the width in the case of ladder-shaped stiffening structures in the view - which corresponds to at least 80% of the width of the respective foot receiving the rung. For the sake of clarity, the term “height” was used to refer to a standing ladder-shaped structure; in the case of lying ladder-shaped structures, this corresponds to the width in the view. The height of the rungs is preferably selected so that the maximum available installation space in the respective foot - which is different for different feet on the same pallet - is used, i.e. in the case of an integral, non-positive or positive connection, the extension of the contact surfaces in the longitudinal direction of the bars preferably corresponds to the predetermined height.

The spars do not have to be made of solid material over the entire thickness, the spars can also be designed as hollow structures with different cross sections. The hollow structure is particularly advantageously composed of different surfaces, with at least one of the surfaces of each spar parallel to the top of the deck - ie perpendicular to the longitudinal direction the spars and rungs - is aligned, which also contributes to increasing stability. If hollow structures are used, 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 there is at least one surface - that of the crossbar of the "T" - parallel to the top of the deck.

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

If the rungs are cohesively connected to the spars designed as tubes with a square cross section, 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 extension 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 integral and flat connection.

However, the contact surfaces can also lie perpendicular to the top surface in the plane spanned by rungs and spars. In the case of pipes with a rectangular cross section, for example, small plates can then be welded to the spars without the plates having 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 securely connect the rungs and bars up to a predetermined maximum thrust and bending load Spars guarantee.

This also applies in the case of a non-positive or positive connection. The latter can be designed, for example, as a snap lock, the contact surfaces then corresponding to the surfaces of the lock in the case of rungs and spars, which lie against one another in the connected state. A correspondingly stable connection can be achieved, for example, if the snap closure is aligned along the longitudinal direction of the spars and extends over 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, preferably also over the entire height, and the spars can have corresponding receptacles.

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

In a particularly preferred embodiment, which is particularly suitable for very large quantities, the stiffening structure is designed as an extruded aluminum profile. In this case, the rungs are formed in one piece 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, and 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 formed in one piece as a tube with a square cross section, which is bent into the shape of two spars with rungs in between. In this way it is possible to design a stiffening structure with a maximum of three rungs, which are formed in one piece on the spars. Such a stiffening structure can be implemented in different ways, which differ primarily in the location of the two pipe ends in the stiffening structure. For example, it is possible to produce a structure designed in the manner of an "8" by seven-fold bending by 90 ° each. In a preferred embodiment, which only requires 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 integrally connected to each other and to the other, opposite spar. The connection is particularly preferably made over the entire thickness of the spar. This type of production makes it possible to provide the pipe ends with a further bend to increase the stability, so that the effective height of the rung increases in accordance with the width in the case of a lying ladder-shaped structure. This increases the stability with regard to bending and shear strength when forces are applied in the area of the middle foot. The integral 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 manufacture, since pipes with a square cross-section, for example with a cross-section of 20x20 mm and a wall thickness of 2 mm, are available on the market in large quantities. When manufacturing profiles, about a quarter of the cost is incurred by sawing the square tubes to cut them to length. These costs can be minimized by using a single, bent pipe.

In another embodiment, which is somewhat expensive to manufacture and is more expensive due to the more time-consuming production, the spars are also designed as tubes with a square cross section, but at least the inner rungs are designed as plate-shaped connecting elements, in which contact surfaces are provided on two opposite sides 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 is also possible. Sheet steel is particularly suitable as a material, but all other metals and metal alloys that meet the requirements can also be used.

A standing seam is understood to mean a 90 ° bend in the edge of the plate-shaped connecting element. The bent surface of the plate-shaped connecting element then forms the contact surface. The extension of the contact surface in the direction of the thickness of the spar is at least a quarter of the thickness. With a tube diameter of the square tube of about 2 cm, the bending edge is then at least 5 mm from the 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.e. 10 mm, ideally even the thickness of the tube corresponding to 20 mm from the edge of the plate-shaped connecting element, parallel to this.

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

A slightly less production-intensive variant, in which the high stability with regard to bending and shear strength is retained in the case of a stiffening structure with three rungs for the middle rung - which experience has shown that the greatest forces act on - consists in using the middle, inner rung as a plate-shaped connecting element designed as standing seams, as described above, but to bend the two outer rungs from a tube with a rectangular or square cross-section. In this case, the two spars and the two outer rungs are formed in one piece from a bent tube.

Further options for keeping the material consumption as low as possible with a high degree of stability with respect to bending and shearing are to use thinner sheets instead of thick sheets or thick stiffening structures, in which the bars are formed by bending along the longitudinal direction of the bars. In this way, folds can be formed on the spars. The incorporation of beads as a special form of bending is also possible as a reshaping which also serves to reinforce, beads can be introduced at any point in the longitudinal direction of the bars. The stiffening structure is in this Case formed as a rolled and bent metal profile with openings made between the rungs, which are formed in one piece on the spars. The bending takes place according to the longitudinal direction of the bars. Sheets of different thicknesses can be used here, depending on the required load capacity, for example sheets with a thickness of 1 mm to 4 mm. The stability of the stiffening structure is therefore not achieved here by the material thickness, but rather by the design of the spars by bending, as a result of which, in particular, a predetermined thickness can also be impressed on them. In the simplest case, when using metal profiles, the spars can be formed as standing seams at the profile edges. A higher stability is achieved by double standing seams, that is, by two transverse bends in the profile - with bending edges along the longitudinal direction of the spars - successive bends by 90 ° in the same orientation. The spars can also be designed as envelopes, ie as bends through 180 °. To further increase stability, it may be advantageous to combine standing seams and envelopes with one another. The openings are made between the rungs, for example by punching, cutting or milling. The rungs are preferably plate-shaped, that is to say they have a predetermined height in the longitudinal direction of the bars, which is close to the dimensions of the feet in the longitudinal direction of the bars. In the case of tapered feet, the shape of the plate forming the rung can also be adapted accordingly, for example in a trapezoidal shape.

It goes without saying 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 on their own 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 is explained in more detail below, for example with reference to the accompanying drawings, which also disclose features essential to the invention. Show it

Fig. 1

a plastic pallet with a ladder-shaped stiffening structure embedded in it,

Fig. 2

a plastic pallet without a deck with stiffening structures,

3a) -c)

a first embodiment of a stiffening structure,

4a) -c)

a second embodiment of a stiffening structure,

5a) -b)

a third embodiment of a stiffening structure,

Fig. 6

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

7a) -c)

a fourth embodiment of a stiffening structure,

8a) -c)

a fifth embodiment of a stiffening structure,

9a) -d)

a sixth embodiment of a stiffening structure,

10a) -b)

a seventh embodiment of a stiffening structure and

11a) -c)

an eighth embodiment of a stiffening structure.

Detailed description of the drawings

Fig. 1 shows a conventional plastic pallet, which comprises a deck 1 for storing objects to be transported. In the perspective view shown here, a top side 2 of the deck can be seen, opposite this is a bottom side of the deck, not shown, top side 2 and bottom side of the deck are spaced apart by the thickness of the deck. Feet 3 are formed protruding from the underside of the deck. In addition, the plastic pallet also includes runners 4, each of which is designed to connect at least two feet 3 on their undersides. The foremost segment of the plastic pallet - comprising three feet and the runners that connect the feet - is shown cut open here, so that a stiffening structure 5 arranged there - indicated by hatching - becomes visible. The stiffening structure 5, of which the pallet here has two in the outer runners, is here ladder-shaped and comprises lower spars 6 arranged in the runners 4 and spaced-apart upper spars 7, which are arranged above the lower spars 6 and run parallel to them , The upper spars can be arranged in a region between the top 2 of the deck and the underside of the deck in deck 1, but they can also be located below deck 1, as in FIG Fig. 1 shown as an example. If the upper spars 7 are arranged in the area between the upper side 2 of the cover and the lower side of the cover, 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 bars 6 in the feet 3 to the upper bars 7. The surface of the rungs is mostly closed, i.e. it does not have any openings or recesses, and if it does, the area of the openings or recesses is less than 50%, generally less than 10%, in proportion to the entire surface of the rungs 8. Recesses and openings are only made where this is necessary or sensible for manufacturing reasons.

The rungs 8 are either formed in one piece on the lower spars 6 or the upper spars 7, or they are each integrally connected to them via contact surfaces. Depending on the configuration, some of the rungs 8 can also be integrally formed on one or both spars and other rungs can be integrally connected to the spars 6, 7. The type of material bond is chosen depending on the material. In the case of metallic stiffening structures 5, welding is particularly suitable here. Dependent on From the material - for example, carbon fiber and glass fiber reinforced plastics can also be used for the stiffening structure - other types of connection can also be useful, for example non-positive or positive connections, whereby all types of positive locking can also be combined with one another.

Due to the one-piece design of the rungs 8 on the spars 6 and 7 or by the integral connection via 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 strength of the plastic pallet is parallel to the top 2 of the deck Level increased.

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

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

With the aid of the stiffening structures 5, it is possible to reduce the deflection to the extent which is also considered to be permissible in the case of wooden pallets of comparable size, or to even smaller dimensions. The thicker the stiffening structures - by thickness is meant the expansion perpendicular to the longitudinal direction of the bars and perpendicular to the longitudinal direction of the rungs - the higher the shear and bending stiffness, but this goes hand in hand with a higher mass. Although plastic pallets are lighter than wooden pallets of the same size, the weight of comparable wooden pallets can be exceeded if the stiffening structures 5 are correspondingly thick, as a result of which a significant advantage of plastic pallets would be eliminated.

On the other hand, if one chooses the thickness of the lower bars 6, the upper bars 7 and the rungs 8 too small, for example as a pure sheet with a constant thickness, this cannot achieve the necessary shear stiffness if the thickness is too small. For this reason, at least the upper bars 6 and the lower bars 7 have a predetermined thickness.

In the case of a cohesive connection of the rungs 8 to the spars 6, 7 via contact surfaces, and also in the case of a non-positive or positive connection, the size of the contact surfaces is selected or specified as a function of a predetermined maximum bending and shear load on the plastic pallet As a rule, the contact areas should be as large as possible in terms of construction.

In the longitudinal direction of the bars 6, 7, the rungs 8 have a predetermined height in order to increase the shear stiffness and bending stiffness in the longitudinal direction of the bars 6, 7, which height is based on the width of the feet; it should be at least 80% of the width of the respective bar receiving the rung Foot. Here the expression "height" is used in reference to a standing ladder; it corresponds to the width for a lying structure. If the rungs 8 are connected to the spars 6, 7 via contact surfaces, the extension of the contact surfaces in the longitudinal direction of the spars 6, 7 preferably corresponds to the predetermined height.

Many design variants are possible for the design of the spars 6 and 7, for example the lower spar 6 and / or the upper spar 7 can be assembled as hollow structures from different surfaces, for example they can be tubes with the cross section of a square, in particular a trapezoid , Rectangle or square, which facilitates the connection of the contact surfaces; but a configuration as a T-beam or as a double-T beam is also conceivable. At least one of the surfaces of each spar (6, 7) is then preferably oriented perpendicular to the longitudinal direction of the respective spar 6, 7 and perpendicular to the longitudinal direction of the rungs 8. Contact surfaces can then be formed on these surfaces, in particular for the material bond.

In the case of a cohesive connection of the rungs 8 to the spars 6, 7, the contact surface is therefore preferably in a plane to the longitudinal direction of the rungs 8 and the spars 6, 7. The extent of the contact surface in the direction of the thickness should then generally be more than that Be half the thickness. Depending on the design, the rungs 8 can also have a smaller thickness, for example, in the case of a sheet metal construction, a thickness corresponding to the sheet metal thickness.

Different configurations 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 the shear strength 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 area of a rung 8 and Fig. 3c ) A perspective view of the stiffening structure, which is designed here as an extruded aluminum profile 10. The lower spar 6 and the upper spar 7 are each designed as a T-beam, the thickness of the spars 6, 7 can be, for example, 20 mm in the region of the crossbar of the "T". Since aluminum is a rustproof material, there is no need for separate corrosion protection. Openings 11 are made between the rungs 8, which in the assembled state are located between the feet of the plastic pallet and allow the fork of a forklift to enter. The rungs 8 are integrally formed on the bars 6, 7 and are plate-shaped. In the area below the upper spar 7, through holes 12 are optionally arranged, through which plastic can pass during manufacture in the case of a one-piece pallet in order to ensure a firm connection between the stiffening structure and the plastic pallet. The through holes 12 can also be used for another type of fastening, for example a mechanical one, if it should not be possible to clamp them in the framework structure of the plastic pallet, in which case no through holes 12 are required. In particular, the through holes 12 are also suitable for receiving optional cross struts 9 in order to fix them better and to produce a stiffening lattice structure in the plane of the deck 1, as in FIG Fig. 2 shown. Another advantage of using an extruded aluminum profile is the reduced mass. While a wooden pallet with the dimensions 800 mm x 1200 mm weighs 20-25kg, the mass of a pallet with the in Fig. 3a ) -c) shown profiles about 15-20kg.

A second embodiment of a stiffening structure, which is designed here as a further extruded aluminum profile 13, is shown Fig. 4a ) -C). Fig. 4a ) shows a side view of the extruded aluminum profile 13, Fig. 4b ) a cross section through the profile in the area of a rung 8 and Fig. 4c ) the aluminum extruded profile 13 in a perspective view. Here, too, 8 openings 11 are introduced between the rungs. The insertion can take place, for example, by punching, cutting or milling. That too Fig. 4 shown further aluminum extruded profile 13 has through holes 12. In contrast to the in Fig. 3 Extruded profile shown here, however, the lower spar 6 is designed as a tube with a square cross section and the upper spar as a double-T beam. It is, of course, also possible to design one of the spars as a T-beam here, just as one of the spars of the extruded aluminum profile 10, which in Fig. 3a ) -c) is shown as a double T-beam or as a tube 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 in the form of two bars 6, 7 with rungs 8 in between. It is a one-piece design with a maximum of three rungs 8, which is particularly suitable for smaller pallets. All rungs 8 are formed from the square tube 14. At the in Fig. 5 Example shown, the outer rungs 8 of the stiffening structure are formed by bending the tube 14 twice by 90 °. The middle or inner rung 8, on the other hand, is formed by the two pipe ends 15 being bent by one of the spars - here without restriction of generality from the upper spar 7 by 90 °, so that the middle rung 8 is created by the bend. The pipe ends 15 are also the opposite spar - here the lower spar 6 - integrally connected, for example by welding, here over the entire thickness of the lower spar 6. To increase the bending and shear rigidity and the stability of the stiffening structure, the tube ends 15 can also be integrally connected to each other A corresponding fixation in the plastic pallet in the middle foot can also be dispensed with.

A modification of this embodiment is in Figure 6 shown. The tube ends 15, which form the middle rung 8, are spread apart in their end regions here, so that the middle rung 8 takes the shape of a "Y". With one edge, the tube ends 15 are integrally connected to the opposite spar, here the lower spar 6, over the entire thickness of the spar. The edges in question are preferably provided with larger chamfers in order to provide a contact surface for the integral connection, which is more stable compared to a linear, one-dimensional connection. Here, too, the rungs 8 are formed in one piece on the lower spar 6 or on the upper spar 7, even if the pipe ends are integrally connected to the opposite spar in order to increase the rigidity. By spreading the pipe ends 15 in the "Y" shape, the shear stiffness in a plane parallel to the deck 1 or the bending stiffness perpendicular to the deck plane is compared to that in FIG Fig. 5 a) -b ) shown execution further increased.

Another version 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. In this fourth embodiment, too, the spars are designed as tubes with a square cross-section, the lower spar 6 and the upper spar 7 and the two outer rungs 8 are likewise formed in one piece from a bent tube 14. The two pipe ends 15 are integrally connected to one another in the area of one of the outer rungs 8. However, the pipe ends 15 can also meet at another point on one of the spars, for example in the area of the middle rung 8. The middle rung 8 is designed here as a plate-shaped connecting element 16, with the two opposite sides, namely the sides leading to the spars 6 and 7 have, contact surfaces are formed as standing seams.

The plate-shaped connecting element 16 is here - in relation to the thickness of the lower spar 6 and the upper spar 7 - placed in the middle. The expansion 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 has to be cut to length only and bent only four times. Due to the plate-shaped connecting element, which can have a C or S shape in cross section, the shear strength and bending stiffness compared to the in Fig. 5 and Fig. 6 Embodiments shown further increased, since the plate-shaped connecting element 16 in the longitudinal direction of the spars can have the maximum height - in the view corresponding to the width - that 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 cannot be enlarged. The in the Fig. 7a ) -b) stiffening structure shown can also be used for pallets with more feet in one direction, since several of the plate-shaped connecting elements 16 can easily be placed 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 area of a rung 8 and Fig. 8c ) a perspective view. In contrast to that in Fig. 7 In the embodiment shown here, the outer rungs 8 are also designed as plate-shaped connecting elements 16 with standing seams 17 formed thereon to form the contact surfaces. The plate-shaped connecting elements 16 have a cross section - as in FIG Fig. 8c ) shown - 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 created from a pipe by sawing. In each case three - here identical - plate-shaped connecting elements 16 connect the upper spar 7 to the lower spar 6, the standing seams 17, which are formed on the plate-shaped elements 16 by bending, form the contact surfaces. Their extension in the direction of the thickness of the bars 6, 7 corresponds here to the total thickness of the bars 6 and 7. By means of the contact surfaces, the plate-shaped connecting elements are integrally connected to the bars 6 and 7. After the integral connection has been established, the stiffening structure must still be galvanized to protect it from corrosion.

Compared to the extruded aluminum profile variants described above, the in Fig. 5-8 Although the versions described are more complex to manufacture, they handle the material resources more gently, since there is practically no waste, whereas the Introduction of the opening 11 in the context of Fig. 3 and Fig. 4 described aluminum extruded profiles 10 and 13 a not inconsiderable proportion of material waste.

The Fig. 9-11 show further configurations for stiffening structures, all of which are formed in one piece from rolled and bent metal profiles, for example (steel) sheet metal or strip steel, openings 11 again being introduced between the rungs 8. In addition, these stiffening structures also have optional through holes 12. The configurations differ here only in the design of the lower spar 6 and the upper spar 7, which are formed on the profile edges by bending and are designed as standing seams, double standing seams, envelopes or combinations thereof. This in Fig. 9a ) in perspective view and in Fig. 9b ) The metal profile shown in cross section in the area of a rung 8 as a sixth embodiment of a stiffening structure has an upper spar 7 which is shaped identically to the lower spar 6. The spars are formed by a standing seam by 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 somewhat higher stability compared to an also possible "S" shape. All rungs 8 are plate-shaped and integrally formed on the bars 6 and 7.

That in the Fig. 10a ) perspective and in Fig. 10b ) In cross section in the area of a rung 8, the metal profile as the seventh embodiment of a stiffening structure has bars 6, 7 formed by other bending combinations. The plate-shaped rungs 8 are also integrally formed on the bars 6, 7, and in relation to the thickness of the bars 6 and 7 - in Fig. 10b ) according to the horizontal direction in the sheet plane - arranged in the middle. The upper spar 7, however, has a greater width - corresponding to the vertical direction in the sheet plane - than the lower spar 6. Here it can be used that the runners 4 should be kept flat on the one hand, but on the other hand for the upper spar 7 - with complete Enclosure through the plastic - almost the entire deck height can be used. This also increases stability. The spars 6, 7 are formed here by the combination of several bends by 90 ° (standing seams) and a bend by 180 ° (fold).

Finally, an eighth version of a stiffening structure is shown in Fig. 11 shown. 11a) and 11b ) show the stiffening structure designed as a metal profile in perspective from two opposite sides, Fig. 11c ) shows the profile in cross-section in the area of a rung 8. Here too, the upper spar 7 is wider than the lower spar 6. Both spars 6, 7 are designed as double standing seams. Only two bends are required per spar here, making the stiffening structure comparatively easy to manufacture, but also offering 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 with a relatively low mass, so that the deflection in the middle is not greater than that of wooden pallets, but on the other hand the mass of the plastic pallet is Stiffening structures is even smaller than with 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 well 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

Square cross-section tube

15

pipe end

16

Plate-shaped connecting element

17

Standing Seam

Claims (9)

1. Plastic pallet, comprising

   - a deck (1) for storing objects to be transported,

   - feet (3) which are formed so as to protrude from a deck underside, and

   - runners (4) which are in each case designed to connect at least two feet (3) to one another on the undersides thereof,

   - at least one stiffening structure (5), comprising lower side rails (6) arranged in the runners (4) and upper side rails (7) arranged spaced apart therefrom, which are arranged above the lower side rails (6) running parallel thereto,

   - wherein the at least one stiffening structure (5) comprises rungs (8), each having a predominantly closed surface, which surfaces connect the lower side rails (6) in the feet (3) to the upper side pieces (7),

   - characterised in that

   - the rungs (8) are formed integrally on the side rails (6, 7) or are connected thereto in each case via contact surfaces by substance-to-substance bonding, by force-based engagement or by positive engagement,

   i the at least one stiffening structure (5) has rungs (8) exclusively formed integrally on the side rails (6, 7) and is formed as an extruded aluminium profile (10, 13) or as a rolled and bent metal profile, in each case with openings (11) introduced between the rungs (8), or

   ii the lower side rail (6) and the upper side rail (7) are designed as tubes (14) with a rectangular cross-section and at least the inner rungs (8) are designed as plate-shaped connecting elements (16), in which contact surfaces are integrally formed as standing seams on two opposing sides, or

   iii at least the lower side rail (6), the upper side rail (7) and the two outer rungs (8) are formed integrally from a bent tube (14) with a rectangular cross-section,

   - so that the bending stiffness the of pallet and the shear strength of the pallet are increased in a plane parallel to the deck upper side (2).
2. Plastic pallet according to claim 1, characterised in that the side rails (6, 7) have a predetermined thickness.
3. Plastic pallet according to claim 1 or 2, characterised in that in the case of a connection of the rungs (8) to the side rails (6, 7) by means of contact surfaces the size of the contact surface is predetermined as a function of a predetermined maximum bending and shear load of the plastic pallet.
4. Plastic pallet according to one of claims 1 to 3, characterised in that, in the longitudinal direction of the rungs (8), the side rails (6, 7) have a predetermined height which corresponds to at least 80% of the width of the respective foot (3) which receives the rung (8), wherein in the case of connection by substance-to-substance bonding, by force-based engagement or by positive engagement the extent of the contact surfaces in the longitudinal direction of the side rails corresponds to the predetermined height.
5. Plastic pallet according to one of claims 3 or 4, characterised in that in the case of connection by substance-to-substance bonding the side rails (6, 7) are formed as hollow structures assembled from various surfaces, preferably as tubes with the cross-section of a rectangle, or as T-beams or double T-beams, wherein in each case at least one of the surfaces of a respective side rail (6, 7) is aligned perpendicular to the longitudinal direction of the side rails (6, 7) and the rungs (8).
6. Plastic pallet according to claim 5, characterised in that in the case of connection by substance-to-substance bonding of the rungs (8) to the side rails (6, 7) the contact surfaces lie in a plane perpendicular to the longitudinal direction of the side rails (6, 7) and rungs (8) and the extent of the contact surfaces in the direction of the thickness preferably corresponds to at least half of the thickness, particularly preferably the entire thickness.
7. Plastic pallet according to claim 1, alternative iii, characterised in that the stiffening structure (5) has three rungs (8) formed integrally on the side rails, wherein the tube (14) is bent in the form of two side rails (6, 7) with rungs (8) located between them.
8. Plastic pallet according to claim 7, characterised in that the two tube ends (15) are bent from one of the side rails (6, 7) to the other, opposing side rail (7, 6) and form the middle rung (8), and are connected by substance-to-substance bonding to one another and to the other, opposing side rail (7, 6), preferably over the entire thickness of the side rail (7, 6) concerned.
9. Plastic pallet according to claim 1, alternative i, wherein the at least one stiffening structure (5) is designed as a rolled and bent metal profile, characterised in that the side rail (6, 7) are formed on the profile edges as standing seams, double standing seams, fold-overs or combinations thereof and/or the rungs (8) are plate-shaped.

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