Stress-Relieved Weldment for Box Sections

Abstract

A structural member, such as an excavator boom, comprises four plates forming a box section secured together at each corner thereof by a weldment comprising an L-shaped angle bar disposed within the box section and a weld which penetrates into each adjacent pair of plates and into an apex of the angle bar.

Description

BACKGROUND OF THE INVENTION

Box sections employed in the structural members for heavy duty construction machines, such as the boom for a hydraulic excavator or the track roller frame for a track-type tractor, are subjected to torsional and bending loads of high magnitude. The box sections are normally fabricated from four load-bearing plates which are secured together at their corners by weldments. Due to the thickness of the plates and further due to the large weld areas required, backup means are oftentimes provided in the weldment to insure increased structurally integrity thereat.

Such conventional backup means are illustrated in hereinafter more fully described FIGS. 3 and 4 of applicant's drawings which disclose a roll-formed backup bridge 16a and a single backup plate 16b, respectively. Such conventional backup means induce high stress concentrations at the weldment and/or allow the weld to "blow through" the weldment, thus resulting in premature failure of the structural member.

SUMMARY OF THIS INVENTION

An object of this invention is to overcome the above, briefly described problems by providing an economical and non-complex stress relieved weldment for the corners of a box section which exhibits a high degree of structural integrity when subjected to heavy-duty use. The weldment comprises an L-shaped angle bar having a pair of legs each abutting inner surfaces of a respective member of the box section. Common weld means secure the members and the angle bar together.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects of this invention will become apparent from the following description and accompanying drawings wherein:

FIG. 1 illustrates a box section, such as the transverse cross-section through an excavator boom, a track roller frame or the like;

FIG. 2 is an enlarged view of a weldment employed at each corner of the box section with stress concentration lines superimposed thereon; and

FIGS. 3 and 4 are views similar to FIG. 2, but illustrating conventional weldments.

DETAILED DESCRIPTION

FIG. 1 illustrates a box section 10 of a structural member such as a boom employed on a hydraulic excavator, a track roller frame for a track-type tractor or the like. As illustrated, the corners of the metallic box section are each subjected to compressive and tensional forces C and T, respectively, when torsional or bending loads are imposed thereon. The torsional loads would normally tend to "rack" the box section whereas the bending loads would normally tend to induce the sides of the box section to "bulge out."

In order to counteract such tendencies, structural members or plates 11-14 of the box section are provided with a stress relieved weldment 15 at each corner thereof. As shown in FIG. 2, the weldment comprises an L-shaped angle bar 16 having a first leg 17 abutting inner surfaces of first plate 11 and a second leg 18 abutting inner surfaces of transversely disposed and adjacent second plate 12. The edge of the second plate, for example, is disposed in edge facing relationship relative to the inner surfaces of the first plate.

The angle bar may be initially tack-welded to one of the plates to provide for the weld backup function upon application of a common weld means 19 thereto. In the preferred embodiment of this invention, the legs of the angle bar are solely secured to the plates by the weld means and are not otherwise secured to the plates to aid in the hereinafter more fully described stress relieving function. The weld means is applied exteriorly of the box section to have its root penetrate generally downwardly through the lower end of plate 12, through an apex 20 of the angle bar and substantially into plate 11 (preferably to a depth of from one-eighth to one-third of the thickness of plate 11).

Since apex 20 of the angle bar provides a relatively large mass of material thereat, a weld arc of high amperage will not tend to burn through the weldment, beneath leg 17 of the angle bar. In addition, the substantial length of each leg 17 and 18 (preferably at least one-half of the thickness of an adjacent plate) eliminates weld "blow-through" even though a slight gap may form between leg 17 and plate 11. In the preferred embodiment of this invention, the thickness of each leg 17 and 18 is preferably selected from the range of from one-eighth to one-third of the thickness of each adjacent plate.

Such construction, in addition to the above described non-securance of substantial portions of legs 17 and 18 to the plates, provides some flexibility at the weldment to aid in reducing stress concentrations S.sub.1 thereat. Otherwise stated, an abrupt change in stiffness and geometric shape at the weldment would substantially increase such stress concentrations thereat.

FIG. 3 illustrates a corner of a conventional box section 10a wherein plates 11a and 12a are secured together by a weld 19a. Backup means, comprising a longitudinally extending ridge 16a is roll-formed on plate 11a to induce relatively high stress concentrations S.sub.2.

FIG. 4 illustrates a corner of a second conventional box section wherein a pair of plates 11b and 12b are secured together by a weld 19b and by a single backup plate 16b. The theoretical stress concentrations are illustrated at S.sub.3. A gap 21 is formed at the base of plate 16b to induce weld "blow-through" through the gap upon application of weld 19b.

It should be noted that the FIGS. 3 and 4 weldments inherently provide lesser degrees of structural integrity than applicant's weldment, illustrated in FIGS. 1 and 2. It should be further noted that during fabrication of the FIG. 1 box section, that the lower end of weldment 19 will tend to notch downwardly into plate 11, due to the low heat sink capability of angle bar 16.

Claims

What is claimed is:

1. A stress-relieved weldment comprising a pair of trasversely disposed first and second plates, with an edge of said second plate being disposed in edge facing relationship relative to the inner surfaces of said first plate,

an L-shaped angle bar having first and second legs abutting inner surfaces of said first and second plates, respectively, the thickness of each of the legs of said angle bar being from one-eighth to one-third of the thickness of a respective one of said plates and

common weld means securing said plates and said angle bar together wherein said weld means penetrates through said second plate and has a root that penetrates through an apex of said angle bar, joining the first and second legs thereof together, and into said first plate.

2. The weldment of claim 1 wherein the root of said weld means penetrates into said first plate at a depth which is from one-eighth to one-third of the thickness of said first plate.

3. The weldment of claim 1 wherein the length of each of said legs is at least one-half of the thickness of a respective underlying member.

4. The weldment of claim 1 wherein four of said plates form a rectangular box section have four corners therof each secured by a said, L-shaped angle bar and a said weld means.