ES2670924T3 - Heavy Duty Telescopic Arm - Google Patents

Abstract

A high-strength telescopic arm, comprising a plurality of coaxial sections (3) with sizes in sustained decrease and that are inserted into each other that can slide relative to each other, and thanks to a suitable drive mechanism, are you can move the arm (1) from the initial position to the operating position, and vice versa; each section (3) comprises, in cross section, an upper part (3a) a lower part (3b) lateral parts (3c, 3d) between them; each section (3) comprises a plurality of straight segments (5) arranged in a sequence; each straight segment (5) having a length (b), a thickness (t1) and two ends (6a, 6b); each end (6a, 6b) of the straight segment (5) being connected to one end (6a, 6b) of an adjacent straight section (5) to form a closed section (3); characterized in that all straight segments (5) have the same thickness (tl); because it also comprises, at the bottom of the section subjected to compression, only a welding joint (11) that joins two adjacent straight segments (5) or two halves of segments (5a, 5b) that form a single segment ( 5) and are provided on the axis of symmetry (Y) of the section; because the number of straight segments (5) of the lower part of the section is equal to or greater than three; and because it is completely made entirely of a material with an elasticity limit of more than 800 MPA (N / mm2).

Description

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DESCRIPTION

Heavy Duty Telescopic Arm

The present invention relates to a high-strength telescopic arm, in particular for mobile cranes, and a process for manufacturing the arm.

As is known, mobile cranes, for example, mounted on vehicles, have a telescopic arm that can be easily transported in the initial position completely retracted, and which, in the operating conditions, can be extended to great heights, to lift and move loads heavy

In the most common operating condition, the weight is fixed to the end of the crane arm, and the arm is mainly subjected to a flexural load.

Loading of the indicated type results in the formation of tensile stresses in the upper part of the arm, and compression stresses in the lower part. Therefore, the arm section must have a size that guarantees a safety margin in the presence of the maximum tensile and compressive stresses allowed, respectively in the upper and lower areas of the section.

In particular, sections are known that are hexagonal and have walls with a constant thickness, which are usually obtained from a single sheet of metal that is folded and welded.

A hexagonal section manufactured using high strength materials does not provide the best results in terms of weight, size, cost, rigidity, flexural strength, shear strength, resistance to normal and buckling stress.

A very small thickness can lead to instability in the form of the lower panels of the arm, subjected to compression, and in the side panels subjected to bending and shearing, according to a phenomenon known to those skilled in the field as buckling. of thin section panels.

Sections with a small number of straight segments with a significant length, including the hexagonal section, do not allow a reduction in thickness that could provide clear advantages in terms of weight, because if the proportion between the thickness of each compressed segment and the segment length is less than a given value, its safety in terms of buckling resistance or form instability can no longer be guaranteed.

Therefore, even if the use of the most recent special steels, with good structural specifications, would allow a reduction in the thickness of the walls, with respect to the resistance to pure bending, and therefore the total arm weight .

This is not possible due to the instability phenomena mentioned above, unless the section size is optimized.

Together with the solution just presented, telescopic arm sections formed from curved segments are known, at least in the compressed areas. As is known, a curvature has good properties with respect to the stability of the shape.

The section of a telescopic arm for a crane of the type mentioned above is described in US-6,098,824. This section comprises an inverted U-shaped upper portion, formed from a flat upper wall and two side walls extending from the upper to the lower part towards the margins of the upper wall end, and a lower, welded portion to the upper portion, which has a concave-convex wall, with a greater thickness and consisting of adjacent arcuate segments arranged in a sequence.

However, the production of arms with sections of this type is very complex and expensive, since the entire metal sheet in the area that will be subjected to compression must be processed to provide it with an arcuate shape.

In addition, this process involves prolonged construction times when compared to simple folding along pre-established lines for the construction of polygonal sections with straight sides, such as the hexagonal described above.

The aspiration of the present invention is therefore to overcome the drawbacks mentioned above.

In particular, the aspiration of the present invention is to provide a telescopic arm with a good resistance to shape instability and whose weight is contained.

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The aspiration of the present invention is also to provide a telescopic arm that is easy to produce.

Another aspiration of the present invention is to provide a quick and economical process for the production of a telescopic arm of the type mentioned above.

US 4171597 discloses a crane boom whose telescopic sections have upper and lower flanges and lateral networks that are provided with a thinner plate than that of the flanges. In US 4171597 the segments of the lower compressed part of the section are only three in number, with the widest and thickest flat flange assuming most of the resistance of the section with respect to buckling.

GB 2342603 is related to a method of manufacturing an angled aluminum pipe in which the cross-section of the back member that ultimately results from the disclosed process is quadrangular in shape.

These aspirations and others, which will be more evident in the description that follows, are achieved by a high-strength telescopic arm as described in the claims herein.

The invention is now described with reference to the accompanying drawings, which illustrate several preferred embodiments of a telescopic arm.

- Figure 1 is a side view of a truck equipped with a crane with articulated arms with cross sections;

- Figure 2 is a perspective view of one of the tubes forming the trunks of the arm illustrated in Figure 1-; and that it is not part of the present invention;

- Figure 3 is a cross section along line III-III of the telescopic arm shown in Figure 1;

- Figure 4 is a cross section of a first embodiment that is not part of the invention of a telescopic arm trunk shown in Figure 1;

- Figure 5 is the cross section of a second embodiment that is not part of the invention of a trunk of the telescopic arm shown in Figure 1;

- Figure 6 is a cross section of a third embodiment of a telescopic arm trunk shown in Figure 1;

- Figure 7 is a cross section of a fourth embodiment of a telescopic arm trunk shown in Figure 1;

- Figure 8 is a cross section of a fifth embodiment that is not part of the invention of a telescopic arm trunk shown in Figure 1;

- Figure 9 is a sheet of metal used for the manufacture of a trunk of the telescopic arm;

- Figure 10 illustrates a folding operation that is carried out on the metal sheet shown in Figure 9, for manufacturing a trunk that is not part of the invention of the telescopic arm;

- Figure 11 is a side view of a truck equipped with a crane with a telescopic arm, known to those skilled in the field as "crane truck", with cross sections according to the present invention;

- Figures 12 to 20 illustrate the folding sequence for obtaining a 10-sided section according to the present invention;

- Figure 21 illustrates a six-sided section of an arm for a crane of the known type; Y

- Figure 22 illustrates a ten-sided section of an arm for a crane according to the present invention.

With reference to the attached drawings, the number 1 represents a telescopic arm for mobile cranes.

The telescopic arm 1 comprises a plurality of coaxial tubes 2 that form the arm trunks 1. They have sections 3 with steadily decreasing sizes and are inserted into each other. The tubes 2 can slide relative to each other, and thanks to a suitable drive mechanism, which is not illustrated, can move from the arm 1 from the initial position to the operating position, and vice versa.

Each tube 2 consists of a plurality of panels 4 that form the side wall of the tube 2.

Therefore, a generic cross section 3 of each tube 2 is formed by a plurality of straight segments 5 arranged in a sequence.

Each straight segment 5 has a length b and a thickness t1, t2 and is connected to the next segment 5 by one end 6a and to the previous segment 5 by the opposite end 6b, whereby it forms a closed polygonal section 3.

In addition, two adjacent segments 5 form an inwardly oriented angle a of section 3 that is less than one hundred eighty degrees, therefore, the inner edge 7 of section 3 consists of a concave line.

In all the illustrated embodiments, the number of straight segments 5, and therefore, the number of panels 4 forming each tube 2, is between seven and ten.

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Section 3 preferably has an axis of symmetry Y, therefore, the segments 5 in which it consists are distributed symmetrically with respect to the Y axis. In some embodiments, illustrated in Figures 4, 5, 6, 7 and 22, the segments 5 of each section will all have the same thickness t1.

The proportion between the thickness t1 and the length b of the sides of the section is preferably such that it allows a similar safety margin with respect to the resistance of the areas subjected to normal, shear and flexural stresses (i.e. particular sides) and resistance to form instability (i.e. buckling).

In the embodiments illustrated in Figures 4, 5, 6, 7 and 22, each tube 2 that is part of the telescopic arm 1 is made from a single rectangular sheet 8 of metal with a constant thickness t1, which also makes the construction of the particularly economic sections.

The metal sheet 8 is deformed along the fold lines 9 parallel to the longitudinal edges 10 of the sheet 8, which are substantially the same length as the tube 2 to be formed.

The folds are made in such a way that the two longitudinal edges 10 meet, until they touch.

Each fold line 9 of the metal sheet 8 delimits two adjacent panels 4 that form dihedral angles at less than one hundred and eighty degrees or, similarly in a section of the metal sheet 8 at a right angle to the edges longitudinal 10, two straight segments 5 of section 3.

To obtain several panels 4, which form the side wall of the tube 2, or the segments 5 of the section 3, with a number between seven and ten, the process comprises between seven and ten folding stages. Finally, the edges 10, which are touched, are joined by welding.

In a first embodiment that is not part of the invention, illustrated in Figure 4, section 3 consists of seven straight segments 5, arranged symmetrically with respect to an axis of symmetry Y of section 3 that coincides with the main direction of load application.

This seven-sided section 3 is obtained by folding the metal sheet 8 along seven parallel lines 9 to obtain six complete segments 5 and two halves of segments 5a, 5b.

The two halves of segments 5a, 5b are joined and welded along the edges, keeping them in the same plane, to form a single segment 5, with a weld joint 11 on the axis of symmetry Y of section 3. A second embodiment that is not part of the invention, illustrated in Figure 5, comprises a section 3 consisting of eight straight segments 5, again arranged symmetrically with respect to an axis of symmetry Y of section 3.

The eight-sided section 3 is obtained by folding the metal sheet 8 along eight parallel lines 9 to obtain seven complete segments 5 and two halves of segments 5a, 5b.

As already indicated, the two halves of segments 5a, 5b are joined and welded along the edges, keeping them in the same plane, to form a single segment 5, with a welding joint 11 on the axis of symmetry And from section 3.

A third embodiment, illustrated in Figure 6, comprises a section 3 consisting of nine straight segments 5, again arranged symmetrically and manufactured using the same procedure that was used for the first two.

Finally, a fourth embodiment, illustrated in Figure 7, consists of ten segments.

Section 3 is obtained by folding the metal sheet 8 along nine parallel lines 9 to obtain ten complete segments 5. The terminal segments 5 are joined at a given angle to and welded along the edges 10a, 10b, leaving weld joint 11 at the edge.

The folding process, which is common for all the aforementioned embodiments, is carried out by placing the metal sheet 8 on a die 12 and pressing it along the folding lines 9 with a punch or a blade 13.

In order to use the blade 13 in all the folding lines 9, a first set of folds is made in succession, starting from a longitudinal edge 10 towards the inside of the metal sheet, then moving towards a second set, starting from the edge longitudinal opposite 10 and continuing until the final folding of the first set. Thus, as illustrated in Figure 10, which illustrates a section that is not a part of the invention, the blade 13 can be removed after the last folding, from the gap left by the metal sheet 8 between the two edges. longitudinal 10 that practically touch. Figures 12 to 20 illustrate the folding sequence used to obtain a 10-sided section.

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The sides are marked with capital letters from "A" to "J" and are obtained by first folding the part of the right side of the section (Figures 12 - 15), after the part of the left side of the section (Figures 16-19), and then performing a lateral central folding opposite the gap left by the metal sheet.

Again, the blade 13 can be removed after the final folding has been made of the gap left by the metal sheet between the two longitudinal edges that are practically in contact. In addition, since it is straight, the blade 13 is cheaper than the curved blades and can be used in all sections, both large and small, because special curved shapes on the blades are not necessary for extraction from the profile being folding.

Advantageously, as an additional guarantee of shape stability or buckling resistance, part 14b of section 3, which essentially supports compression loads, can be formed with a segment 5 of a thickness t2 greater than segment 5 of a thickness t1 for the rest of part 14a, designed to withstand only tensile and shear loads.

In other words, at least two of the straight segments 5 have a thickness t2 that is different from the thickness t1 of the rest of the segments 5. Therefore, about half of section 3, considered along the axis of symmetry And, in an embodiment illustrated in Figure 8 which is not a part of the invention, it consists of a sheet metal that is thicker than the other half.

The precise calculation is made with reference to the neutral axis of the section, which also depends on the thickness, according to known processes that are not described here.

Given the presence of two different thicknesses t2, section 3, in the above-mentioned embodiment, is obtained from a pair of metal sheets 8a, 8b.

Each metal sheet of the pair 8a, 8b is folded along a plurality of folding lines 9, according to the process mentioned above, without contacting the longitudinal edges 10a, 10b of each sheet 8a, 8b, but leaving that the distance between the two edges 10a of the first sheet 8a is equal to the distance between the two edges 10b of the second sheet 8b.

Advantageously, to obtain a closed section 3 consisting of between seven and ten segments 5, the sum of the fold lines 9 of the first and the second sheet 8a, 8b must be between five and ten. Therefore, the two sheets 8a, 8b are joined so that the longitudinal edges 10a of the first sheet and 10b of the second sheet are touched, forming the tube 2 with a polygonal cross-section.

Then, the edges 10a, 10b of the two sheets 8a, 8b are welded together.

Advantageously, the weld joint 11 is at the bottom of section 3, subjected to compression, because it improves its stress resistance characteristics.

Figures 21 and 22 illustrate two embodiments of sections of a crane arm, a six-sided section 15 of the known type, and the other, a ten-sided section 16 according to the present invention.

These sections 15, 16 are shown by way of example to help provide a clear explanation of the inventive concept, but without limiting its scope, which extends to all embodiments covered by the inventive concept expressed in the description and in the claims.

Both sections 15, 16 have maximum dimensions inside a marked rectangle 27 having a width of 305 mm and a height of 450 mm. Both sections have the same coefficient of bending inertia in the vertical plane (W - 759 cm3) and the same buckling resistance.

The overall dimensions of section 15 are a height of 477.5 mm and a width of 235 mm.

It consists of six sides with reciprocal angles at 120 degrees. The sides 15a are 288 mm long, and the upper and lower sides 15b are 103 mm long. The radius of the sides is 21 mm.

The overall dimensions of section 16 are a height of 409.4 mm and a width of 304 mm.

It consists of ten sides. The sides 16a are 273 mm long and are at an angle of 115 degrees with respect to the upper and lower outer sides 16b, which are 70 mm long. The outer sides 16b are in turn at an angle of 162 ° 30 'with respect to the upper and lower inner sides 16c. The last sides 16c are at an angle of 165 degrees from each other with respect to the center line of section 16. The length of the sides 16c is such that it allows obtaining a section 16 with an overall width of 304 mm and is substantially 53 mm

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In both cases, sections 15 and 16 are created using a high strength material, marketed as Weldox 1100, a registered trademark of the company SSAB Oxelosund AB, which has an elasticity limit of 1100 MPA (N / mm2).

In the first short, section 15 is optimized in such a way that a thickness of at least 7 mm is required to obtain a sufficient elasticity and buckling resistance.

In the second case, section 16 is optimized so that a thickness of exactly 6 mm is required to obtain a sufficient elasticity and buckling resistance similar to those of section 15.

Thanks to the new ten-sided shape, the thickness of 6 mm is sufficient to obtain a similar safety coefficient against buckling of the sides of the section subjected to normal shear and flexural stresses. The example also shows how the ten-sided section is approximately 7% lighter, with the area of the ten-sided section being 73.9 cm2, compared to 79.6 cm2 in the area of the six-sided section.

In addition, compared to the six-sided section of the example, the ten-sided section is also 17% more resistant to bending in the horizontal plane, because the ten-sided section is wider, despite remaining in the dimensions of the example design.

The major advantages of the sections disclosed in the present invention are obtained with materials that have an elasticity limit of more than 800 MPA (N / mm2). Since the currently available materials reach elasticity limit values of 1100 MPA (N / mm2), this is the upper limit value. However, these advantages will also apply to future materials whose elasticity limit values are even higher.

Another possible use for the disclosed sections refers to materials with lower elasticity limit values of approximately 300-400 MPA (N / mm2).

With these materials, with a lower limit of elasticity, it is still possible to obtain advantages in terms of economic savings. Relatively large sections can be produced with thin sheets of metal, to obtain a reduction in the weight of the material used, and therefore, a cheaper construction.

The present invention provides important advantages. First, the entire section of the telescopic arm according to the present invention allows a reduction in thicknesses, and therefore, in the weight of the arm.

Thanks to its shape, the disclosed section guarantees a good safety margin with respect to possible instability in the areas that are compressed and in those subjected to bending and shearing, because it allows a similar safety coefficient with respect to both resistance as to the tendency to buckling.

It should also be appreciated that each arm trunk, with a section as described in the claims, is easily manufactured since it does not involve the production of profiles or arcuate shapes that are not straight.

In addition, the entire process is fast because the time required for the molding stage, during which the metal sheet is folded, is less than the time required to obtain semi-finished products with a curved section and two or more weld joints.

The process according to the present invention therefore allows the acceleration of production, with the consequent limitation in costs.

The described invention can be subjected to numerous modifications and variations without thereby departing from the scope of the inventive concept - described in the appended claims.

Claims (4)

5 10 fifteen twenty 25 1. A high-strength telescopic arm, comprising a plurality of coaxial sections (3) with steadily decreasing sizes and inserted into each other that can slide relative to each other, and thanks to a suitable drive mechanism , the arm (1) can be moved from the initial position to the operating position, and vice versa; each section (3) comprises, in cross section, an upper part (3a) a lower part (3b) lateral parts (3c, 3d) between them; each section (3) comprises a plurality of straight segments (5) arranged in a sequence; each straight segment (5) having a length (b), a thickness (t1) and two ends (6a, 6b); each end (6a, 6b) of the straight segment (5) being connected to one end (6a, 6b) of an adjacent straight section (5) to form a closed section (3); characterized in that all straight segments (5) have the same thickness (tl); because it also comprises, at the bottom of the section subjected to compression, only a welding joint (11) that joins two adjacent straight segments (5) or two halves of segments (5a, 5b) that form a single segment ( 5) and are provided on the axis of symmetry (Y) of the section; because the number of straight segments (5) of the lower part of the section is equal to or greater than three; and because it is completely made entirely of a material with an elasticity limit of more than 800 MPA (N / mm2). 2. The high-strength telescopic arm according to claim 1, characterized in that the number of straight segments (5) is between seven and ten. The high-strength telescopic arm according to any one of the preceding claims, characterized in that two adjacent straight segments (5) form an angle (a) opposite the inside of the closed section (3) that is less than or equal to one hundred eighty degrees . The high-strength telescopic arm according to any of the preceding claims, characterized in that the straight segments (5) are arranged symmetrically with respect to an axis of symmetry (Y) of the section (3) in its plane.