GB2103575A - Booms for cranes or the like - Google Patents

Abstract

A boom for a crane or the like comprises four longitudinal stiffening members 16 interconnected with four substantially flat longitudinal plates 17 in such a way that the boom has a substantially diamond shaped cross-section. As shown the members 16 are of rectangular hollow. section butt welded by welds 18 on the outside of the boom to the plates 17 while diaphragm plates 20 also interconnect the members 16 at spaced locations along the boom either by welds or by bolting flanges 22 to the members 16. <IMAGE>

Description

SPECIFICATION Improvements in and relating to booms for cranes or the like The present invention relates to booms for cranes or the like particularly those having a box construction.

Box type booms, that is booms constructed from plate as distinguished from lattice type booms, are well known and are used for telescoping booms where the boom sections are comparatively short. The box construction is.normally rectilinear in cross-section aithough our British Patent No. 1,564,509 shows an octagonal construction which has certain advantages over the normal rectilinear shape. Certain disadvantages of the rectilinear shape are set out in our British Patent No.

1,564,509. A particular disadvantage of both rectilinear and octagonal boom construction is evident when the boom is lengthened. In this case, additional stiffening in the form of internal stiffening members has to be provided.

But then the assembly of boom components by welding standards require welds to run uninterrupted from end to end.

A boom for a crane or the like according to the invention comprises four longitudinal stiffening members spaced apart and four substantially flat longitudinal plates each welded between adjacent such stiffening members to form a boom with a substantially diamond shaped cross-section.

The stiffening members are preferably of rectangular hollow section.

The abutment between the plane longitudinal plates and the edges of the stiffening members enables a simple external butt weld to be run along the whole length of the boom without interruption which is simple to set up even with boom lengths of 20 m or more.

Considerable advantages of the present invention over rectangular section booms are the reduction of stress at the corners, elimination of internal fillets, reduction of distortion and easier and better welding during assembly.

Particular advantages of the present invention over octagonal section booms are that the plates between the stiffening members are narrower than the side plates of the octagonal section which reduces the buckling factor, the construction enables easier construction along the boom were the cross-sectional area varies and particularly at the boom foot where there is a large change in cross-sectional area, the stiffening member construction where this is of hollow section is less prone to corrosion and damage, the stress fluctuation at maximum stress position particularly during whip is improved, and the quality and dimensioning control is easier particularly if the boom is made as a single component.

Whilst the boom is particularly suitable for cranes and mobile cranes it can be sed for example on access platforms (aerial lifts) or on other apparatus using similar booms and the expression "cranes and the like" is to be interpreted accordingly.

An embodiment of the invention will now be described by way of example withrnfer- ence to the accompanying drawings in which Figure 1 is a side elevation of an example of a boom of the invention.

Figure 2 is a top elevation of the boom of Fig. 1; Figure 3 is a cross-section of the boom of Fig. 1 to an enlarged scale taken at a position A-A along the boom where there is a diaphragm plate, and Figure 4 is a diaphragm of stress distribution in the boom of Fig. 1 caused by normal and lateral bending moments.

In Figs. 1 and 2, a boom 10 is shown with a narrowing foot portion 11 and a slightly graduated main portion 1 2.

The boom construction which can be seen in Fig. 3 is extremely simple and comprises four rectangular hollow section stiffening members 1 6 interconnected by plane plates 1 7 which are butt welded, by welds 1 8 on the outside of the boom, to the members 16.

Diaphragm plates 20 also interconnect the members 1 6 at spaced locations along the boom. The diaphragm plates 20 have location flanges 22 welded to them which are channeled to provide location webs 24 at each side. The diaphragm plates 20 are connected to the members 1 6 suitably by welds 26 between the webs 24 and the stiffening members 1 6 or by bolting flanges 22 to members 16.

To assemble the boom the diaphragm plates are set up at the predetermined spaced locations and the members 1 6 are attached to them. The plates 1 7 are then butt welded between the members 1 6 taking advantage of the natural presentation formed by the angle between the edge of each plate 1 7 and the mating surface of each member 16. In order to hold the plates 1 7 in contact with the members 1 6 for welding, the plates may be dogged to the diaphragm plates which eliminates the necessity for tack welding.

Referring back to Fig. 3, it will be seen that the plates 1 7 conform to a diamond shaped parallelogram, the base angle being 65 and the side being 115 to 120 but these can be varied dependent on the loading conditions, the minimum base angle being 60e but the normal base angle being between 62 and 69'.

The stress distribution in the boom is shown in Fig. 4 where it will be seen to be substantially symmetrical both for stresses caused by boom whip, that is lateral stress and stresses caused by normal boom loading, that is stresses due to the boom weight and boom load. With this diamond shaped construction it can be seen that the maximum stresses FXX and FYY are never combined in full as they are in a rectangular construction, the corner joint of a rectangular construction having imposed stresses of FXX + FYY. In the present diamond construction the imposed stresses at the lowest joint at FXX + K (FYY) where K is typically 0.25 to 0.3. This lower variation in stress is of great significance when fatigue life is a prime consideration.

Claims (7)

1. A boom for a crane of the like comprising four longitudinal stiffening members spaced apart and four substantially flat longitudinal plates each welded between adjacent stiffening members to form a boom with a substantially diamond shaped cross-section.

2. A boom as claimed in Claim 1 in which the stiffening members are of rectangular hollow section.

3. A boom as claimed in either Claim 1 or Claim 2 in which the welds connecting each longitudinal plate to adjacent stiffening members, are an external butt weld running along the length of the boom.

4. A boom as claimed in any one of the preceding claims having transverse horizontal plates extending transversely to the stiffening members and welded thereto at spaced locations along the boom.

5. A boom as claimed in Claim 4 in which the 'transverse' plates have location plates to mate with the stiffening members to which they are to be attached.

6. A crane or the like provided with a boom as claimed in any one of the preceding claims.

7. A boom for a crane or the like substantially as hereinbefore described with reference to the accompanying drawings.