DE9113981U1 - Telescopic boom for mobile cranes or similar - Google Patents

Description

11.11.1991 91-1592 G-ei

Liebherr-Werk Ehingen GmbH, 7930 Ehingen/Donau

Telescopic boom for mobile cranes etc.

The invention relates to a telescopic boom for mobile cranes or the like, consisting of an outer pivot piece pivoted on the vehicle or its superstructure, in which several telescopically collapsible and extendable telescopic sections are held, whereby each section is provided with bearings for the section guided in it and can be locked with this section, and whereby a hydraulic pressure medium piston-cylinder unit is provided for extending and retracting the individual sections.

In a telescopic boom of this type, known for example from DE-PS 21 48 966, the individual telescopic sections have a substantially box-like profile, with the lower chords of the individual sections having flat V-shaped profiles or flat channel-shaped profiles, which are formed by legs angled from a flat central web part. These lower chords are welded to the edge areas of the downward-pointing legs of U-shaped profile parts with rounded corner areas between their web parts and legs to form box-shaped profiles, with the area of the

In addition, stiffening strut-like sheets can be welded into the welded joints. The individual telescopic sections are supported on the channel-shaped profiled lower chords according to the pressure distribution ratio known from DE-PS 21 48 966, whereby in the area of the upper rounded corners of the box profiles the bearing forces are transmitted by rollers or appropriately shaped bearing shoes. In order to protect the side walls of the U-shaped profile part against dents, U-shaped profiled buckling stiffeners are welded onto the inside or outside of the legs of the profile. The lower chord, which is mainly loaded by bending forces, is stiffened and protected against dents by its V-shape or the two longitudinal bends that form the channel shape.

Despite the welded-in buckling stiffeners and the bend lines, the well-known telescopic boom is not only sensitive to buckling, but also requires a lot of effort to manufacture due to its complicated cross-sectional shape. Telescopic booms are not only subjected to bending, but also to torsion. The bearing elements arranged in the lower chord with a grooved or V-shaped cross-section counteract any twisting. However, if the telescopic boom is equipped with a luffing needle, it is braced via a rear α-frame or similar using guy ropes, so that a guide that transmits torsional forces in the bearing elements of the V-shaped lower chords can be canceled out if the moment acting to the rear is equal to or greater than the moment acting to the front and resulting from the load and needle boom weight.

In order to give a telescopic boom sufficient torsional rigidity independent of its sliding bearing, it is known to bolt the individual boom sections together and additionally provide them with lateral guide bearings.

The object of the invention is to provide a telescopic boom of the

to create a device of the type described above which is characterized by a simple and economically producible construction with high bending stiffness of its individual sections.

According to the invention, this object is achieved in that the individual sections have round profiles. Such round profiles can be manufactured in a simple and economical manner using known pipe manufacturing processes. Round profiles not only have favorable area inertia and section moments, so that they have a high degree of bending stiffness, their round cross-section also offers a high degree of protection against dents, without the profiles having to be additionally protected against dents. Round profiles can be conveniently provided with all-round bearings, so that good bearing of the individual sections in one another is guaranteed even when the telescopic booms are provided with rocking needles and additionally braced. In addition, the required torsional stiffness is ensured by locking or bolting the individual sections together both in the retracted and extended state.

The individual shots can have circular profiles.

Of particular advantage, however, are shots with elliptical profiles, which have large area moments of inertia in the direction of their long axis, which are arranged vertically.

When using elliptical profiles, the ratio of the long to the short axes of the profiles preferably decreases from section to section from outside to inside, so that lateral crescent-shaped spaces are formed between the individual sections in which cables for the energy supply can be laid.

Even if the inner shots have elliptical profiles, the outer shot can have a circular profile.

According to an inventive design, all boom sections are locked together in the extended and retracted state and that only one pressure medium piston cylinder unit is provided, which is connected at one end to the boom linkage of the outer section and which only extends and retracts one section that has previously been unlocked. This design ensures that the individual sections are connected to one another in a torsionally rigid manner by their constant locking. If a lock is released for the purpose of extending and retracting a section, these two sections are secured against twisting by this connecting pressure medium piston cylinder unit, whereby the pressure medium piston cylinder unit must be provided with a suitable anti-twisting device.

To lock the individual sections together and to extend and retract them, an arrangement can be selected as is known from the older, but not previously published utility model G 90 13 210.6. The piston rod of the piston-cylinder unit can therefore be conveniently linked to the boom linkage piece and a driver device for the individual sections can be arranged in the area of the end of the cylinder from which the piston rod emerges. With this design, only a length of the telescoping cylinder is subjected to buckling that corresponds to the extended part of the piston rod plus the necessary clamping length. Furthermore, the mounts for the coupling pieces of the driver device can be arranged at the inner ends of the telescopic sections. To extend and retract a section, only this is always coupled to the driver device, so that the control of the bolts is overall simpler and more manageable. The mounts for the coupling pieces of the driver device are conveniently provided on ring-shaped frame parts at the inner ends of the telescopic sections. These mounts are conveniently arranged in pairs opposite each other. They can consist of holes or bushings

for retractable bolts. The receptacles can advantageously be arranged in common planes parallel to the center line of the shots. This design allows the coupling pieces of the driver device on the telescopic cylinder, which will usually be bolts, to only be extended by the same amount to couple each of the shots, so that the driver device can be designed more simply overall and the coupling pieces or bolts for opposite receptacles can be located closer together. For a more detailed description of the devices for locking and unlocking the shots with each other and for extending and retracting the shots, reference is made to the older utility model G 90 13 210.6.

Since a pressure medium piston cylinder unit provided with an anti-twist device has only a limited torsional rigidity due to its elasticity, a further inventive design provides that a freely extending profile tube is non-rotatably articulated in the sections parallel to the pressure medium piston cylinder unit and is connected to the boom linkage piece, the length of which corresponds to the length of the outer section and on which the inner sections are guided by plain bearings so that they can be moved longitudinally but not rotated. On this profile tube, the individual sections, whose bolts, which also serve as anti-twist devices, are removed relative to one another, are guided to one another in a rotation-proof manner during extension and retraction. The control system used ensures that the sections that have been separated from one another are only completely pushed away from the profile tube that prevents rotation when they are bolted to the adjacent section or sections to prevent rotation.

The profile used to prevent rotation is preferably a square tube or a triangular tube.

According to a further development, it is planned that in the

middle areas of the crescent-shaped spaces in cross-section between the sections, which are arranged with supply lines stabilized by caterpillar-shaped chains. Caterpillar chains that guide supply lines in the form of loops or double loops are known and are not described in detail here. To guide the chains, box profiles with gaps can be provided on the outer walls of the sections that delimit the crescent-shaped spaces.

To lock the individual shots together, bolts that can be operated hydraulically or by compressed air and springs are conveniently provided on their collar-like, thickened end areas.

The bolts can be provided with conical or bevelled centerings that correct slight twisting during the extension and retraction of individual shots when locking.

According to a further embodiment, the object is achieved according to the invention in that the pivot piece and the sections consist of profiles, each of which has a lower round part and an upper half-box-shaped part in the horizontal position (pivoted towards the vehicle), the legs of which are connected to one another and pointing towards one another. In this embodiment of the profile according to the invention, an upper half-box-shaped profile is connected to a lower round profile in a horizontal dividing plane. The lower round profile can, for example, be a semicircular profile. Preferably, the lower profile part has the shape of approximately half an ellipse with the apex formed by the small radius. The profile according to the invention therefore consists of different profile parts in relation to its horizontal axis, while it is symmetrical about its vertical axis.

The profile according to the invention is particularly advantageously

meets the requirements of a telescopic boom. During operation, the profiles of the individual sections of a telescopic boom are primarily subjected to tension in their upper area and to compression in their lower area, so that the lower area is very susceptible to buckling. In conventional profiles that either had a box shape or were provided with a lower V-shaped profile section based on a box shape, stiffening plates were welded into the profile on the inside and/or outside to increase the buckling resistance. The profile according to the invention meets the stresses of a telescopic boom in a particularly favorable manner because the lower area, which is very susceptible to buckling, consists of a round profile that is much less susceptible to buckling than box-shaped profiles.

The buckling sensitivity of the lower profile part increases with the increasing compressive stress, i.e. in the direction of the lower apex line. The design of the lower profile part in the form of a semi-ellipse is therefore particularly advantageous because this has the smallest radius of curvature in its apex area and therefore has the lowest buckling sensitivity in the area with the greatest compressive stress.

The legs of the upper profile section can be at right angles to the straight web section forming the upper chord. Since the upper profile section is subjected to tensile stress, the risk of buckling is low, so the straight profile legs are acceptable.

According to an advantageous embodiment, the legs of the upper profile part form an obtuse angle with the straight web part. Due to this obtuse angle, the round profile part extends into the upper area of the overall profile, so that the middle profile part in particular is less susceptible to dents. The lateral stress distribution is namely highest in the middle of the profile, which results in an increase in the compressive stress in this area. If the curvature is above

the profile center continues upwards, the buckling stiffness is improved in this area.

According to a further embodiment, the legs of the upper profile part form acute angles with the straight web part. This embodiment takes account of the lateral stress distribution, whereby the resulting risk of buckling in the lateral area can be taken into account by appropriate measures if necessary. For example, larger sheet thicknesses can be selected or buckling stiffeners can be welded in.

The obtuse and acute angles of the profile shapes described above need only deviate slightly from 90°.

In order to achieve a seamless transition between the two profile parts, the legs of the lower round profile part connect tangentially to the straight legs of the upper profile part.

The legs of the upper profile part are conveniently connected to the straight web part by rounded areas. This design makes it possible to arrange bearings in the rounded areas to guide and hold the telescopic section.

The special configurations described above for the overall round profile shapes can also be advantageously applied to the combined profile shapes, provided that the previously described configurations are not specifically related to the round profile shapes.

The combined profile shapes create a number of special advantages.

This means that the upper shell of each shot can be folded from one piece along its entire length, so that there are no

Weld seams and in particular no transverse weld seams are present. Such a one-piece design is particularly difficult for round and oval profile shapes due to the manufacturing equipment required.

The round lower shell, however, can be assembled from several parts that are welded together, depending on the production facilities available. This can be accepted because weld seams in compression areas are less problematic than in tension areas.

When manufacturing the boom sections, the upper shell can be
a straight plate can be placed on it and does not need, as with
a complete oval boom profile to be held in special facilities.

In practical crane operation, the semi-box-shaped upper
Profile part additional advantages, which consist in the fact that
the hoist rope can be placed on the wide upper belt without slipping sideways. Furthermore, the flat upper web part of the upper profile part is also useful for maintenance purposes, as it can be walked on safely. The upper profile part can also
can also be sprayed with a rough coating so that the required slip resistance is ensured when walking on it.

The arrangement of the bearings in the rounded area
between the upper straight bridge part and the legs of the
The upper profile section enables the straight side profile walls to be kept free of bearings so that they can be painted and labelled for corrosion protection.

Embodiments of the invention are described in more detail below with reference to the drawing.

Fig. 1 a - &eegr; a telescopic boom in different

various extension states of its telescopic sections,

Fig. 2 a cross section through the telescope

leger according to Fig. 1 in a state in which all boom sections are telescoped in,

Fig. 3 a cross section through two interconnected

locked telescopic shots in the area of the end stiffening collar of the outer shot,

Fig. 3 a a cross section through two interconnected

locked telescopic sections in which the bearing segments are inserted from the front - the inner and outer shape of the bearing correspond to the elliptical shape of the inner and outer telescopic sections -,

Fig. 4 a top view of the collar-shaped

Locking area of two telescopic sections with each other according to Fig. 3,

Fig. 4 a is the top view corresponding to Fig. 3 a,

Fig. 5 shows a cross section corresponding to Fig. 2

cut through the pushed together telescopic boom sections,

Fig. 6 a cross section through the single-telescopic

copied boom sections with circular cross-section,

Fig. 7 a cross section through the outer

steering piece telescopic boom

sections with similar elliptical cross-sections, without built-in guides for the supply chains,

Fig. 8 a longitudinal section through the bearing

two telescopic sections in the extended state or by storing the first telescopic section in the boom linkage in the extended state,

Fig. 9 a cross section through the inner bearing

along the line IX-IX in Fig. 8,

Fig. 10 and 11 are representations corresponding to Fig. 8 and 9, but with a triangular anti-twist device ,

Fig. 12 a cross section through a telescope

shot or an outer link piece with a profile composed of a half-box-shaped part and a round part,

Fig. 12 a to

h diagrams showing the corresponding bending, bending tension, bending compression and the composite stresses,

Fig. 13 a cross section through a telescope

shot or an outer link piece with an upper half-box-shaped profile, the legs of which form obtuse angles with the web part, and a lower elliptical profile part,

Fig. 13 a to

13 h the corresponding bending, bending tension, bending

pressure and composite stress diagrams,

Fig. 14 a cross section through a telescope

shot or an outer link piece with a profile that is composed of an upper half-box-shaped profile, the legs of which form acute angles with the web part, and a lower elliptical profile,

Fig. 14 a to

14 h the corresponding bending, bending tension, bending

diagrams showing pressure and composite stresses.

As can be seen from Fig. 1, the outer linkage piece 1 of the telescopic boom 2 is provided with a joint piece 3, via which it is linked to the upper carriage of a crane, crane vehicle or the like. The piston rod of a hydraulic piston-cylinder unit 5 is linked to the part enclosed by the outer linkage piece 1 in the joint 4.

Parallel to the piston-cylinder unit 5, a square profile 6 is hinged above it to the boom linkage piece 4 in a torsion-proof manner.

The pivot piece and the other telescopic sections are provided with collar-like stiffeners 8-10 in the area of their ends, on which pressure medium piston cylinder units provided with locking bolts are arranged. The innermost telescopic section is provided with a roller head at its outer end, as can be seen from Fig. 1.

Fig. 2 shows an enlarged cross-section through the pushed-together sections of the telescopic boom. The inner sections 12, 13, 14, which have an elliptical shape, can be telescoped out from the outer boom linkage piece 1, which has a circular cross-section in the embodiment shown, with the ratio of their long to their short axes increasing from the outside to the inside. By increasing this ratio, crescent-shaped spaces 16 are formed between the side walls of the telescopic sections, in each of which profile boxes 17 with longitudinal slots can be arranged for caterpillar-like chains (not shown), which serve to guide and hold supply lines, for example hydraulic and electrical lines.

As can be seen from Fig. 2, the long axes of the elliptical profiles are reduced from shot to shot only by approximately equal and relatively small amounts, so that the bending stiffness of the shots only decreases by small amounts from shot to shot, since the area moment of inertia determining the bending stiffness is essentially determined by the long axes.

The piston rod of the single-stage hydraulic cylinder 18 is hinged to the lower fastening frame 3 of the boom linkage piece 1 in Fig. 1. The hydraulic cylinder is provided with a collar-like widening 19 in the area of its piston rod outlet end, from which the locking bolts 20 can be extended. These locking bolts move into receptacles 21 that are provided on each telescopic section. For a more detailed description of this arrangement, reference is made to Fig. 1 3 and the associated description of the utility model G 19 210.6.

Parallel to the piston-cylinder unit 5,18, the box profile 6 is pivotably but non-rotatably connected to the lower mounting frame 3 of the boom linkage 1. The individual telescopic

The telescopic sections 12-15 are provided with sliding bearings 24, which are arranged at the lower frame ends of all telescopic sections. The box profile 6 is guided in these sliding bearings. The sliding bearings 24 have only a relatively small axial length, so that when the telescopic sections are pushed in, they lie close to one another in the axial direction.

The individual sections are provided with all-round bearings in the manner shown in Fig. 3 and 4 or Fig. 3a and 4a, which consist of individual bearing segments 26 adapted to the cross-sectional shape, which can consist of a suitable plastic, such as polyamide, or other suitable bearing materials or even of composite materials.

Instead of bearings made up of individual bearing segments, continuous all-round bearings can also be provided.

A circumferential bearing is arranged on the inside of the end collar 27 that closes off the individual sections. Further bearings are located on the inner frame end of each telescopic section, as can be seen from Figs. 8 and 9.

Furthermore, hydraulic cylinders 28, 29 are arranged on opposite sides of the upper half of each stiffening collar 27, the pistons 30, 31 of which form or carry locking bolts. The individual telescopic sections are provided in a known manner with holes for the locking bolts 30, 31.

Fig. 5 again shows a cross-section through the round profiles of the telescopic shots.

All telescopic sections could also consist of round profiles as shown in Fig. 6. However, these round profiles have a smaller diameter than the elliptical profiles according to

Fig. 5 has the disadvantage that larger diameter gradations, which greatly reduce the bending stiffness, would have to be provided if supply lines were to be arranged in the annular spaces between the individual sections.

The single-stage piston-cylinder unit allows the individual sections to be extended to achieve the desired boom length. Regarding the adjustable different extension states of the individual telescopic sections, we refer to Fig. 10-19 of the utility model G 90 13 210.6 and the associated description, which also apply to the telescopic boom described here.

With the telescopic boom described above, the individual sections can be stored in one another with almost no play due to their round design, which is advantageous for the operation of the crane.

When extending the telescopic boom with the single-stage hydraulic cylinder, only the telescopic section that is being extended or retracted is unbolted. The section to be extended or retracted is connected to the hydraulic cylinder in the manner described during the process.

If the hydraulic cylinder and its piston rod do not ensure sufficient anti-twisting protection, this is achieved by the parallel profile described. This anti-twisting profile is preferably a large-volume square tube or triangular tube, which has a large polar area moment of inertia, so that the remaining torsional elasticity is negligible. Instead of a square tube, any other shape can be chosen, for example a triangular or hexagonal tube.

Shots made from round tubes can be manufactured inexpensively in the usual way. The elliptical cross-sections can also be

can be produced in a simple manner, for example, by subsequently compressing a round tube laterally using hydraulic presses so that the desired elliptical shape is created.

With the circular cross-sectional shape of the sections, which is the easiest to produce, the diameters of the sections are reduced relatively significantly if sufficiently large annular spaces are to be created for the arrangement of supply lines. This distance can be reduced to a favorable ratio if externally arranged cable drums are used, although these must also be protected against the effects of the weather.

The plastic bearings for the elliptical cross sections of the shots can be produced, for example, by copy milling. Circular bearings can be produced more easily by turning. The bearings can also be cast or pressed into molds.

The elliptical design of the individual shots also has the advantage that in the highly stressed lower and upper pressure areas, the buckling radius is smaller and thus the buckling resistance is greater. The larger buckling radius is in the middle, more neutral load zones.

As can be seen from Fig. 7, both the boom linkage piece and the sections that can be telescoped out from it can have similar elliptical profiles, so that elliptical annular spaces with the same width over their entire circumference are formed between the individual sections. If the individual sections are now mounted axially displaceably within one another by bearings of the type shown in Figs. 3, 8 and 9, the required torsional rigidity is already ensured, so that the box profile used for guidance can be dispensed with. Due to the fact that the individual sections are guided in one another in a way that prevents them from twisting, a design of this type can also be used for a

-17-locking of the individual shots to one another can be dispensed with.

Fig. 12 shows the cross section through a telescopic section or an outer link piece of a telescopic boom, which consists of a lower semi-elliptical profile part 40 and an upper semi-box-shaped profile part 41, the legs of which are welded together in a horizontal parting plane by weld seams 42, 43. The legs 44, 45 of the upper semi-box-shaped profile part are connected to the upper web part 46 by curved areas 47, 48 with the bending radius RL. The lower profile part 40 is formed by a shell with a semi-elliptical cross section, whereby the profile shape can be described with a close approximation to an ellipse by the three radii ri, Rmi and Ri. For manufacturing reasons, a simplification can be made if the cross-sectional shape is only defined by the two radii ri and Rmi. The elliptical shape changes only slightly due to the described simplifications during production, although from a static point of view these can even be advantageous. This is because the area of the dent-resistant shell with the radius ri or the angle Ey2 becomes larger and the radius Rmi can be extended almost to the middle of the profile. This eliminates the larger and therefore less dent-resistant area with the radius Ri. This makes the lower shell 40 more dent-resistant overall, since the dent resistance decreases linearly with the increase in the radii.

The profile according to Fig. 13 differs from that according to Fig. 12 only in that the upper profile shell 41' has half-box-shaped profile legs 44' and 45', which enclose obtuse angles with the web part 46'.

The profile according to Fig. 14 has an upper shell 41" consisting of a half-box-shaped profile, the profile legs 44" and 45" of which form acute angles with the web part 46".

For the profiles according to Fig. 12-15, the structural centre

between dimensions Hl and H2 is the profile center. The lower part has the shape of a half ellipse, which simultaneously forms the lower structural profile shell. For manufacturing reasons, the lower part can be extended upwards by dimension V, whereby dimension H2 of the upper shell is shortened accordingly.

If the sheet thicknesses of the lower shell ti or t2 are matched to the thickness of the upper shell t3 and the profile heights Hl or H2 are adjusted so that the center of gravity is located near the center of the profile and the deviations B2 less than B or B2 greater than B of the profiles according to Fig. 13 or 14 are not greater than shown, the following stress ratios result, which are shown in the diagrams with the letters a to h:

The compressive stress (-) is often the most critical stress in thin-walled hollow profiles due to the risk of buckling. The greatest bending compressive stress is caused by the main load on the boom around the X-X axis (X direction) at the lower vertex of the radius ri. This is the same for the three profiles shown in Fig. 12 to 14.

The lateral loading or deflection of the boom around the Y-Y axis (Y direction) in both directions causes compressive or tensile stresses in the profile side walls, the magnitude of which is proportional to the distance to the Y-Y axis of inertia.

For all three profiles, these stresses are = 0 at the lower vertex, so that there is no change in the compressive stress from the X direction. At the upper edge of the profile, the stresses from the Y direction are reduced due to the radii RL.

Along the side wall upwards, the tensile and compressive stresses from the Y-direction add up to the bending stresses from

-19-the X-direction.

These stress ratios are shown for each of the three profiles in the corresponding diagrams.

In the profile according to Fig. 12, the build-up of compressive stress in the upper side wall, which is susceptible to buckling, is the lowest due to the uniform, lateral stress distribution in the upper half of the profile or the upper shell. The manufacture of this profile is simpler than that of the profiles according to Figs. 13 and 14, since the legs 44, 45 form right angles with the web part of the upper shell, which are easier to control in steel construction due to the available tools.

In the profile according to Fig. 13, the lateral stress distribution is highest in the middle of the profile, which results in an increase in the compressive stress in this area compared to the profile according to Fig. 12. However, since the radius Ri is continued upwards over the middle of the profile, the buckling resistance is improved, so that this is not disadvantageous.

In the profile according to Fig. 14, the lateral stress curve has the highest value at the point where the radius RL begins. As the curvature ends below the center of the profile due to the radius R, the flat profile side that is not buckling-resistant is larger and is also shifted downwards. This area receives higher compressive stresses due to these influences. The less favorable buckling behavior must therefore be compensated for by appropriate measures (larger sheet thickness or buckling strips).

Claims (1)

11.11.1991 91-1592 G-ei Liebherr-Werk Ehingen GmbH, 7930 Ehingen/Donau Telescopic boom for mobile cranes etc. Protection claims : 1. Telescopic boom for cranes, preferably mobile cranes, consisting of an outer pivot piece mounted on the vehicle or its superstructure, in which several telescopic sections are mounted that can be pushed together and extended, each section being provided with bearings for the section guided in it and being lockable with this section, and a hydraulic pressure medium piston cylinder unit being provided for extending and retracting the individual sections, characterized, that the linkage and the shots have round profiles. 2. Telescopic boom according to claim 1, characterized in that the pivot piece and the sections have circular profiles. -2- 3. Telescopic boom according to claim 1, characterized in that the sections have elliptical or approximately oval profiles. 4. Telescopic boom according to claim 3, characterized in that the ratio of the long to the short axes of the elliptical profiles increases from section to section from outside to inside. 5. Telescopic boom according to claim 3 or 4, characterized in that the articulation piece forming the outer section has a circular profile. 6. Telescopic boom according to one of claims 1-5, characterized in that all boom sections are locked together in the extended and retracted state and that only one pressure medium piston-cylinder unit is provided, which is hinged at one end to the boom linkage piece of the outer section, and which only extends or retracts one section at a time, which has previously been unlocked. 7. Telescopic boom according to one of the preceding claims, characterized in that in the sections parallel to the pressure medium piston-cylinder unit, a freely extending profile tube is non-rotatably articulated to the boom articulation piece, the length of which corresponds to the length of the outer section and on which the inner sections are guided by sliding bearings so as to be longitudinally displaceable but non-rotatable. 8. Telescopic boom according to claim 7, characterized in that the profile tube is a square tube or a triangular tube. 9. Telescopic boom according to one of the preceding claims, characterized in that in the middle areas of the sick-shaped spaces between the sections -3- the supply lines are arranged stabilized by caterpillar-shaped chains. 10. Telescopic boom according to claim 9, characterized in that box profiles provided with gaps are provided for guiding the chains. 11. Telescopic boom according to one of the preceding claims, characterized in that bolts that can be actuated hydraulically or by compressed air and springs are provided on the collar-like thickened end regions of the sections for locking. 12. Telescopic boom according to claim 11, characterized in that the bolts are provided with conical or bevelled centerings. 13. Telescopic boom according to claim 3, characterized in that the articulation piece and the sections telescopically extending from it have similar elliptical or oval profiles. 14. Telescopic boom according to the preamble of claim 1, characterized in that the pivot piece and the sections consist of profiles, each of which in the horizontal position (pivoted towards the vehicle) has a lower round part and an upper half-box-shaped part, the oppositely directed legs of which are welded together. 15. Telescopic boom according to claim 14, characterized in that the lower profile part has approximately the shape of a half ellipse with the apex formed by the small radius. 16. Telescopic boom according to claim 15 or 16, characterized in that the legs of the lower round profile part are tangential to the straight legs of the upper profile part -4-connect. 17. Telescopic boom according to one of claims 14 to 16, characterized in that the legs of the upper profile part
be at right angles to the straight web part forming the upper chord. 18. Telescopic boom according to one of claims 14 to 16, characterized in that the legs of the upper profile part with
enclose obtuse angles with the straight web part. 19. Telescopic boom according to one of claims 14 to 16, characterized in that the legs of the upper profile part
are connected to the straight web part by rounded areas. 20. Telescopic boom according to one of claims 14 to 19, characterized by the characterizing features of one of claims 6, 7, 8 or 11.