Structurally Balanced Plastic Conveyor Chain

Abstract

A molded plastic conveyor chain link is constructed such that the pitch line of the link is offset upwardly from the horizontal centerline of the link. The relative increase in the volume of link material below the pitch line provides more nearly equal section moduli above and below the pitch line. As a result, the resistance of the chain link to transient bending stresses induced by variations in the line of chain pull vertically from the pitch line is substantially balanced.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention.

The present invention pertains to the art of flat top article carrying chains in which adjacent links having interfitting knuckles are pin connected to form a chain with a contiguous flat conveying surface. Such a chain is adapted to be sprocket driven and operated upon a pair of spaced parallel supporting strips or guideways. More particularly, this invention relates to improvements in links of such chains molded from plastic and to means for attaining a more structurally balanced design.

2. Description of the Prior Art.

Molded plastic conveyor chains are well known in the art and are used to convey a wide variety of articles in relatively light load applications. Each link of such a chain is generally of unitary construction and includes a flat, article carrying top plate, and link interconnecting means depending from the underside of the top plate and provided with lateral bores for the receipt of connecting pins, all in a manner known in the art and shown, for example in U. S. Pat. No. 2,911,091.

The link interconnecting means includes portions on both the forward and rearward edges of the link adapted to interfit with the complimentary portion of the next adjacent link such that the bores may be aligned for receipt of a connecting pin. Tensile strength and rigidity is incorporated into the link by providing interconnecting means comprising laterally spaced side bars or reinforcing ribs, which also serve as lateral guide means for the chain operating in the guideways. An example of this prior art construction is shown in U. S. Pat. No. 3,262,550, which patent further shows the adaptability of the side bars to operate to hold the links in a horizontal plane when the chain travels around a curve.

In prior art constructions, the pin receiving bores of the link are located such that the line extending longitudinally between their centers, called the pitch line, bisects the link section. Theoretically, then, chain pull occurs directly along the pitch line and there is no bending moment induced in the links by chain tension. Practically, however, variations in manufacturing, wear within the pin receiving bores through operation, and variations in the guideways and other conveyor structure cause the chain pull to be offset from the pitch line. As a result, a bending moment is induced and the link is subjected to a bending stress in addition to the normal tensile stress.

Since the chain pull offset may vary vertically from the pitch line in either direction and to varying distances, the type and intensity of the stress is not readily predictable. The construction of prior art links with the flat top plate molded integrally with the sidebars provides an upper link section with a relatively high section modulus and a consequent high resistance to bending stress.

The portion of the link below the pitch line, however, comprises only the lower portions of two spaced side bars. The section modulus, in comparison to the portion of the link above the pitch line, is very low, and the comparative bending stress induced by a given bending moment will be significantly greater below the pitch line than above it. In high load applications, transient bending moments in the chain links will thus create a critical bending stress situation first in the lower link portion.

SUMMARY OF THE INVENTION

In the present invention the section modulus of the link below the link pitch line is increased by the selective addition of material from which the link is molded. The material is added without changing the established standard link dimensions and without changing the operational characteristics of the chain. The resultant link has more nearly equal section moduli above and below the pitch line and the neutral axis is more nearly coincident therewith.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a front elevation of a conveyor chain link of the present invention.

FIG. 2 is a bottom plan view of the link shown in FIG. 1.

FIG. 3 is a side elevation of the link shown in FIG. 1.

FIG. 4 IS a sectional view taken on line 4--4 of FIG. 3 and additionally showing the spaced guideways over which the conveyor chain operates.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A molded plastic conveyor chain link 1 includes a flat, laterally elongated top plate 2 and a pair of integral, downwardly depending side bars 3. The side bars 3 are laterally spaced and extend rearwardly from the forward edge 4 of the link and are joined rearwardly of the trailing edge 5 by a barrel portion 6.

The spaced side bars 3 are provided, near their forward ends, with pin receiving bores 7. The barrel portion 6 joining the rearward ends of the side bars is provided with a bore 8 which is preferably flared at its ends or elongated in the direction of chain travel, as at 9. The links are assembled into a conveyor chain in a manner well known in the art by placing the barrel portion 6 of one link between the spaced side bars 3 of another link such that the bores 7 and 8 are aligned. A connecting pin (not shown) is inserted through the bores and its ends are held within the bores 7 by an interference fit. The fit of the pin in bore 8 is loose to allow articulation of the link relative to the adjacent interconnected link and the flared ends 9 allow side flexing of the chain for travel around a curve, all in a well known manner.

Referring particularly to FIGS. 3 and 4, the pitch line P of the link extends through the centers of the bores 7 and 8. By the addition of relatively large amounts of link material to the lower edges of the side bars 3, the link section below the pitch line is increased substantially. Thus, in the typical section shown in FIG. 4, the areas of the lower sections 10 below the axis A of the bores 7 (axis A being coplanar with pitch line P) are more nearly equal to the area of the upper section 11. The combined section modulus of the areas 10 is correspondingly increased and made to approach that of upper area 11.

The construction of the present invention takes advantage of the known side bar formation wherein the outer surfaces 12 thereof are downwardly divergent to engage correspondingly divergent surfaces 13 on the chain guideways 14. This downward widening of the side bar sections enables a relatively greater increase in section areas to be attained without as great a relative increase in the depth of the side bar below the pitch line. In this manner the desired approach toward a balance in the section moduli above and below the pitch line may be attained without extending the depths of the side bars beyond acceptable design limits.

Claims

1. A chain link of unitary construction including laterally spaced side bars having ends provided with aligned bores for the pins of the chain and a crosswise top plate merging with the side bars such that the upper surface of the plate is flush with the upper dimensions of the side bars, the improvement wherein the axes of said bores defining the pitch line of the chain are offset upwardly from the longitudinal centerline of the link whereby the effective section modulus of the link above and below the

3. The invention of claim 2 wherein the link is molded of plastic.