GB2128957A

GB2128957A - A boom, for example for lifting apparatus, a platform hoist, or a dredger

Info

Publication number: GB2128957A
Application number: GB08328481A
Authority: GB
Inventors: Dieter Althoff
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-10-27
Filing date: 1983-10-25
Publication date: 1984-05-10
Also published as: IT8312652A1; FR2535301A1; GB2128957B; DD215518A5; GB8328481D0; FR2535301B1; IT8312652A0; IT1171241B

Abstract

A boom comprises one, or more than one, box girder (18) whose longitudinal edges are formed by rods (21, 22, 23) designed to take up the major portion of the forces of tension and compression to which the box girder is subject. The rods (21, 22, 23) are connected with metal plates (25, 26, 27) which are reinforced by metal strips or bands (27) only for taking up forces of compression, the rods being sufficiently thin that they form bulges under loads for which the boom is designed. As shown the cross-section of the boom is an equilateral triangle, though it may be a square, rectangle or trapezium. <IMAGE>

Description

SPECIFICATION A boom, for example for lifting apparatus, a platform hoist, or a dredger This invention relates to a boom, for example for lifting apparatus, a platform hoist, or a dredger, the boom having at least one hollow box girder with walls formed by metal plates connected to corner reinforcements.

It is an object of the invention to provide such a boom which may be of reduced weight for taking up a given bending stress produced by load on the boom (for example by a load suspended from the boom) or by lateral forces.

According to this invention there is provided a boom having at least one hollow box girder with walls formed by metal plates connected to corner reinforcements, wherein: i) The corner reinforcements take up the major part of the forces of tension and compression to which the or each box girder is subject; ii) Elongate elements attached to the metal plates keep the corner reinforcements apart, which elongate elements extend from each corner reinforcement to adjacent corner reinforcements thereby subdividing all the metal plates into areas reinforced along their edges; and iii) The metal plates are sufficiently thin that they form bulges under loads envisaged for the boom.

The corner reinforcements may be provided without substantial increase in weight if they are suitably designed, e.g. in the form of tubes. Since all the metal plates are sufficiently thin that they form bulges under the loads for which the boom is intended, a reduction in the weight of the box girder or girders and hence of the boom is achieved.

Since the elongate elements connected to the thin metal plates, e.g. welded to the plates, subdivide the plates into separate areas reinforced at their edges, it is possible to define the bulges so that they form diagonal tension braces, in much the same way as bracing wires, by which the bearing capacity of the girder is maintained even after formation of the bulges.

An embodiment of the invention will now be described by way of example, with reference to the drawings, in which: Figure 1 is a perspective view of a mobile platform hoist with a telescopic boom; Figure 2 is a side elevation of the boom of Fig. 1, with parts broken away; Figure 3 is a section taken on the plane Ill-Ill of Fig. 2; and Figure 4 is a view partly in section and partly in elevation taken at the point A in Fig.

2 and corresponding to a section on the plane IV-IV of Fig. 3.

Referring to the drawings, a platform hoist has a telescopic boom 1 5 carrying at its free end an elevated platform 1 6 and connected to a cabin, housing or upper chassis 1 2 at a horizontal pivotal axis 13, while the cabin 1 2 is mounted on a chassis or undercarriage 11 in such manner as to be rotatable about a vertical axis. The boom 1 5 may be pivoted about the axis 1 3 by means of a jack 14. The boom 1 5 has three trihedral box girders, 17, 1 8 and 1 9 each of triangular section and fitting telescopically one inside the other and which are connected together and to a drive (not shown) in known manner so that they may be telescopically extended.

Fig. 3 is a cross-section through the girders 1 8 and 19, one inside the other, showing their structure and hence also that of the girder 1 7 and the means for supporting and guiding the interengaging girders. Each girder 17, 1 8 and 1 9 comprises three parallel rods 21, 22 and 23 arranged at the corners of an equilateral triangular prism, the prisms of the girders fitting concentrically one inside the other. The rods of several girders situated at adjacent edges of the prisms have been given the same reference numeral. Each rod 21, 22 and 23 is a cylindrical tube.Each girder has its rods 21, 22 and 23 connected together by metal plates 24, 25 and 26 which meet the surfaces of the rods 21, 22 and 23 substantially tangentially and are welded to the rods so that the metal plates 24, 25 and 26 of each girder form the external surfaces of the prism while the "corners" are formed by approximately one third of the cylindrical surface of each rod 21, 22 and 23. The metal plates are sufficiently thin that they are in general only capable of absorbing forces of traction. In order to keep the rods apart, stiffeners in the form of metal bands or strips 27 and 28 are welded to the metal plates so as to extend transversely to the longitudinal axes of the rods 21, 22 and 23, the lengths of the strips 27 being at right angles to the rods while the lengths of the strips 28 are at an acute angle with the rods.The metal plates are thus subdivided into areas reinforced at their edges. This subdivision may be so arranged that bulges formed when a girder buckles under load take a particular form and direction, so that wave-shaped bulges are formed in which the crests of the wave extend diagonally from one corner of each area to the opposite corner, making an angle of about 45 with the forces of thrust which are substantially parallel to the rods 21, 22 and 23.

Such wave-shaped bulges form tension diagonals acting like bracing wires which connect two corners of the edge reinforcements of the individual areas formed by the rods 21, 22 and 23 and the strips 27 and 28. The bearing capacity of such a girder is thus maintained even after the plates have bulged and it may be further improved by firmly connecting the ends of the strips 27 and 28 to the rods 21, 22 and 23, e.g. by welding them thereto, although this is not always necessary. The rods 21, 22 and 23 form corner reinforcements for the box girders 17, 1 8 and 1 9 and are designed to take up the major part of the forces of tension and pressure to which each box girder is subject when the boom is under load.

In order to guide and support the telescopically interengaging girders during telescopic contraction or extension, plastic sliders 29 are disposed (Fig. 3) between adjacent rods having the same reference numerals. Sliders 29 are arranged at the outer end of the girder 17, at both ends of the girder 18, and at the inner end of girder 1 9 and (as will be explained with reference to Fig. 4) are attached to the respective girder so as to be axially fixed in relation thereto.In order that the girders may be fitted together substantially free from clearance, at least those sliders 29 which are accessible from outside at the outer ends of girders 1 7 and 18, each comprises two parts 31 and 32 (Fig. 4) which are in contact along planar sliding surfaces 33 and 34 set at an acute angle to the axes of the rods so that the two parts 31 and 32, cooperate like wedges. To provide surface contact against the cylindrical external surfaces of the rods 21, 22 and 23, the external surfaces of the sliders 29 (and hence of the parts 31 and 32) have concave cylindrical surfaces conforming to the surfaces of the rods, Fig. 3.As may be seen from Fig. 4, the parts 31 and 32 of each slider 29 at the outer ends of the girders 1 7 and 1 8 are situated between a stop 35 fixed to the outer end of a rod 21, 22, 23 and a stop 37 which is axially displaceable at the said outer end by means of a screw 36. The stop 37 enables the two parts 31 and 32 of a slider 29 to be pushed together so that adjacent rods may be kept apart at the required distance. This distance may be adjusted by means of a lock nut 30 cooperating with the screw 36 to form an adjustment device.

The boom 1 5 comprising the girders 17, 1 8 and 1 9 is attached to the cabin 1 2 in such manner that the rods 21 and 22 of all three girders form the boom compression member while the rod 23 forms the tension member.

The rods 21, 22 and 23 are so designed that the compression member in each case takes up the major part of the forces of compression while the tension member takes up the major part of the forces of tension or traction produced by a load acting on the boom. Shear or thrust forces are taken up by the metal plates 24, 25 and 26 which are reinforced by the stiffeners 27 and 28 and are sufficiently thin that they form bulges even under the weight of the boom if it is cantilevered horizontally (i.e. supported only at its lower end) without carrying a load. This state of stress or tension of thin plates with edge reinforcements subject to thrust is also referred to as "tension field" after a bulge has been formed.The plates could also be made somewhat thicker and/or the stiffeners or reinforcements 27 and 28 could be placed closer together so that bulges will only occur in the metal plates when the boom is subject to the loads for which it is designed.

Each girder is highly resistant to torsion due to its triangular shape. Due to the distance between the rods 21 and 22 of the compression member, the girders are also highly resistant to bending under lateral forces, e.g.

wind. Since the inner girder, e.g. girder 1 9 in relation to its outer girder 1 8 or girder 1 8 in relation to its outer girder 17, is pressed against the slider 29 of the compression member of its outer girder, 1 8 or 17, when a load is applied, the connection between the girders remains substantially free from clearance even when lateral forces act on the boom 1 5. This is important, particularly in the case of an elevated platform, since the efficiency and quality of the work performed by the worker on the platform will not be impaired by movements of the platform 1 6 produced by clearances.

Due to the reduced weight of the boom achieved by the construction of the girders described above, a machine required for a particular purpose may be constructed with a lighter boom than one equipped with lattice girders, with the result that the form of construction of girders described above enables the whole machine to be manufactured more economically.

The embodiment described above is that of a telescopic boom for an elevating platform, but the invention may also be employed for the construction of a boom having only one girder, e.g. as in booms used for lifting appa ratus or dredgers. The invention is also applicable to a boom having a cross-section in the form of, for example, an equilateral triangle, a quadrangle (e.g. a square), a rectangle, or a trapezium. The rods may comprise tubes or any other, preferably hollow, section rods.

Claims

1. A boom, for example for lifting apparatus, a platform hoist or a dredger, having at least one hollow box girder with walls formed by metal plates connected to corner reinforce ments, wherein: i) the corner reinforcements take up the major part of the forces of tension and com pression to which the or each box girder is subject; ii) elongate elements attached to the metal plates keep the corner reinforcements apart, which elongate elements extend from each corner reinforcement to adjacent corner rein forcements thereby subdividing all the metal plates into areas reinforced along their edges; and iii) the metal plates are sufficiently thin that they form bulges under loads envisaged for the boom.

2. A boom according to claim 1, wherein the corner reinforcements are rods of a crosssection known to be resistant to bending.

3. A boom according to claim 2, wherein the or each box girder is trihedral and is so arranged in the boom that one corner reinforcement forms the tension member of the or each girder and the two other corner reinforcements form the compression member.

4. A boom according to claim 2 or claim 3, wherein the rods are tubular.

5. A boom according to any preceding claim, wherein the elongate elements are metal strips or bands welded to the respective metal plates.

6. A boom according to any preceding claim, wherein the elongate elements are connected to the corner reinforcements.

7. A boom according to any preceding claim, wherein the metal plates are sufficiently thin that when the boom is cantilevered horizontally, they bulge under their own weight.

8. A boom, for example for lifting apparatus, a platform hoist or a dredger, in which telescopically interengaging hollow box girders have walls formed by metal plates connected to corner reinforcements, wherein: i) the corner reinforcements of each girder take up the major part of the forces of tension and compression to which the girder is subject; ii) elongate elements attached to the metal plates keep the corner reinforcements apart, the elongate elements extending from each corner reinforcement to adjacent corner reinforcements of the same girder thereby subdividing the metal plates into areas reinforced along their edges; and iii) the metal plates are sufficiently thin that they form bulges under loads envisaged for the boom.

9. A boom according to claim 8, wherein the corner reinforcements of the telescopically interengaging box girders are spaced apart by sliders each comprising two parts in contact with each other along sliding surfaces which extend at an acute angle to the longitudinal axes of the corner reinforcements, and wherein an adjustment device is provided for at least one part of the sliding member for displacement thereof.

10. A boom according to claim 8 or claim 9, wherein the corner reinforcements are tubes to whose external surfaces the metal plates are welded.

11. A boom according to any of claims 8 to 10, wherein the metal plates are sufficiently thin that they bulge under their own weight when the boom is in a horizontal cantilevered position.

1 2. A boom constructed and arranged substantially as herein described and shown in the drawings.