JPH06313325A - Boom member of working machine for construction machine - Google Patents

Abstract

PURPOSE:To ease stress concentration to a corner part and to improve durability against a compound bending and twisting load by forming the sheet metal composition part of a boom member to have a square section and the corner part to be circular. CONSTITUTION:A base end member 1 connected to the base pedestal of a power shovel and a top member 2 connecting an arm are severally welded to both the ends of a dogleg-shapedly bent boom member 3 and joined, and the middle of the member 3 is provided with a middle member 4 to mutually connect a boom cylinder and an arm cylinder. Next, the members 5a, 5b on both the sides of the member 3 are tapered pipe-shapedly formed, and a tapered round pipe is machined by extension roll forming and press forming to form each flat section 6 whose width becomes wider as it becomes thicker on both its sides. Thus when working load acts on the member 3, the sectional form of the corner part turns into a circular shape, and stress concentration in the corner part is eased because of having no welded part, and durability against a compound bending and twisting load can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boom member used as a constituent member of a construction machine working machine such as a power shovel.

[0002]

2. Description of the Related Art FIG. 11 shows a conventional boom member a of a power shovel, for example, and its cross-sectional structure is as shown in FIG. The parts were joined by fillet welding or groove fillet welding from the outside.

[0003]

As a result of analyzing the stress distribution in the cross-sectional shape when a combined load of bending and twisting is applied to the boom member a having the above-described structure, it is possible to compress both the one opposing corner and the other. It was found that high tensile stresses were generated in both of the opposite corners. However, since there is a welded joint at each corner of the conventional boom member described above, stress concentration occurs there. (1) Durability is reduced due to welding defects, etc. (2) Even if there is no welding defect, the welded portion is always Due to the notch, the durability of this part is much lower than the other base metal parts.

The present invention has been made in view of the above, and by eliminating the welding of the corner portion, which is the most difficult in terms of strength, and using this corner portion as the base material and making it into an arc shape, It is possible to reduce stress concentration and improve durability against a combined load of bending and twisting. Also, with the improvement of the strength of the above corners, it is possible to reduce the plate thickness together with other base materials with a margin. It is an object of the present invention to provide a boom member for a working machine for construction machinery, which can be made lighter.

[0005]

In order to achieve the above object, a boom member of a construction machine working machine according to the present invention is a boom of a construction machine working machine having connecting portions at both ends of the boom member. The sheet metal forming portion of the boom member has a square cross section and the corner portion has an arc shape. Further, the above-mentioned sheet metal constituent part has a welded structure, and its welding line is provided in the central part of the plane part of the sectional shape.

[0006]

[Operation] When a work load is applied to the boom member,
Large stress acts on the corner of this cross-sectional shape,
Since this portion is arcuate and there is no welded portion, stress concentration on this corner portion is alleviated.

[0007]

EXAMPLES Examples of the present invention will be described with reference to FIGS. 1 to 10. This embodiment is for a boom member of a power shovel. 1 and 2 (a),
(B) and (c) show the first embodiment of the present invention.
In the figure, 1 is a base end member for connecting a boom member to the base side of a power shovel, 2 is a tip member for connecting an arm, and both members 1 and 2 are both ends of a boom member 3 curved in a dogleg shape. It is connected by welding. An intermediate member 4 that connects the boom cylinder and the arm cylinder is provided at the intermediate portion of the boom member 3. The base member 1, the tip member 2, and the intermediate member 4 are made of cast metal.

Both side members 5a, 5 of the boom member 3 are also provided.
Each of b has a tapered tube structure, and a flattened portion 6 having a width that becomes wider as it becomes thicker is formed on both side surfaces by the roll forming and the press forming of the tapered round tube,
As shown in FIGS. 2A, 2 </ b> B, and 2 </ b> C, the cross-sectional shape of the thin portion welded to the base member 1 and the tip member 2 is circular, and the thin portion is welded to the intermediate member 4. As it goes to the thicker part, it becomes a long quadrilateral with the corner part arcuate.

In the first embodiment, the both side members 5a and 5b may be formed by pressing a tapered round tube.

FIGS. 3, 4 (a), 4 (b) and 4 (c) show a second embodiment of the present invention, in which the boom member 3a has a tubular structure as a whole. Brackets 7 and 8 for the boom recinder and the arm cylinder are welded to each other. The boom member 3a is formed by swaging both sides of a steel pipe having a circular cross section into a tapered shape, and further heating the middle portion by high frequency heating to bend it into a dogleg shape. The cross-sectional shape of each part is a quadrangular shape whose corners are arcuate as shown in FIGS. 4 (a), (b), and (c).

FIGS. 5 and 6 show a third embodiment of the present invention, in which the boom member 3b comprises U-shaped members 9a and 9b formed by forming a plate material into a U-shaped cross section by a general press. They are joined to each other by welding, and their cross-sectional shapes are shown in FIGS. 6 (a) and 6 (b).
As shown in FIG.
9 and has a square cross section in which the corner portion has an arc shape. Cylinder brackets 7 and 8 are welded to the middle portion of the boom member 3b.

FIG. 7 shows a fourth embodiment in which the entire boom has a sheet metal structure and a boom member 3c having the same structure as the boom member 3b in the third embodiment has a steel pipe at the base end thereof. The base connecting member 10 and the arm connecting member 11 made of sheet metal are welded to the tip.

In both the third and fourth embodiments,
You may make it interpose the intermediate member made from a casting which has the brackets 7 and 8 in the intermediate part of the boom members 3b and 3c.

8, FIG. 9, FIG. 10 (a), (b),
(C) shows a fifth embodiment of the present invention, in which the boom member 3d is constituted by an integral tubular body. The boom member 3d has a round tube having a square cross section with a narrowed middle portion and an arced corner portion as shown in FIGS. 9, 10 (a) and 10 (b).

In each of the above embodiments, the boom members 3, 3
When a work load is applied to a, 3b, 3c, and 3d, a large stress acts on the corner portion of the cross-sectional shape, but because this portion is arcuate and there is no welded portion, Stress concentration on the corners is reduced.

[0016]

According to the present invention, welding of the corner portion, which is the most difficult in terms of strength, is eliminated, and this corner portion is used as a base material and has an arc shape, so that stress concentration on this portion is relaxed. As a result, the durability against the combined load of bending and twisting can be improved. Further, as the strength of the corner portion is improved, the plate thickness can be reduced together with the other base material portion having a margin, and the weight can be reduced.

[Brief description of drawings]

FIG. 1 is an overall perspective view showing a first embodiment of the present invention.

2 (a), (b) and (c) are cross-sectional views of respective portions A, B and C of FIG.

FIG. 3 is an overall perspective view showing a second embodiment of the present invention.

4 (a), (b), and (c) are cross-sectional views of respective portions A, B, and C of FIG.

FIG. 5 is an overall perspective view showing a third embodiment of the present invention.

6A and 6B are cross-sectional views taken along lines A and B of FIG.

FIG. 7 is an overall perspective view showing a fourth embodiment of the present invention.

FIG. 8 is a side view showing a fifth embodiment of the present invention.

FIG. 9 is a top view showing a fifth embodiment of the present invention.

10 (a) and 10 (b) are cross-sectional views of respective portions A and B in FIG.

FIG. 11 is a side view showing a conventional example.

FIG. 12 is a sectional view of a conventional example.

[Explanation of symbols]

1 ... Base end member, 2 ... Tip member, 3, 3a, 3b, 3c,
3d ... Boom member, 4 ... Intermediate member, 5a, 5b ... Both side members, 6 ... Plane part, 7, 8 ... Bracket, 9 ... Welding line, 9
a, 9b ... U-shaped member, 10 ... Base end connecting member, 11 ... Arm connecting member.

Claims (2)

[Claims] 1. A boom of a construction machine working machine having connecting portions at both ends of a boom member, wherein a sheet metal forming portion of the boom member has a square cross section and a corner portion has an arc shape. Boom members for construction machinery. 2. The boom member for a working machine for construction machinery according to claim 1, wherein the sheet metal constituting portion is provided in a welded structure, and a welding line thereof is provided in a central portion of a plane portion having a sectional shape.