Detailed Engineering Analysis: Bent vs. Forged Chain Connectors & Localized Case Hardening Solutions

1. Advantages of Forged Chain Connectors (European Standard Practice)
(1) Grain Flow Optimization

The most critical advantage of forging is that the metal grain flow lines are directionally oriented to follow the geometric contour of the chain connector. For a connector subjected to complex stresses, forging ensures that the grain flow lines run continuously along the "U"‑shape profile, rather than being cut or interrupted. This directly translates into:

- Higher tensile and yield strength: Forged components exhibit significantly superior strength compared to bent parts made from the same material.

- Superior fatigue resistance: Under cyclic loading, the fatigue life of a forged connector is far longer than that of a bent counterpart.

- Better toughness and impact resistance.

(2) Material Density and Internal Defect Control

Forging eliminates internal porosity, voids, and segregation that may exist in bar stock or cast materials, resulting in a denser, more homogeneous microstructure.

(3) Dimensional Precision and Consistency

Precision die forging allows exact control over critical dimensions—including the oval cross‑section of the chain connector legs, the inner crown radius, and bore positions—ensuring proper fitment with the round chain links and bucket mounting holes.

2. Limitations of Bent Chain Connectors

(1) Grain Flow is Interrupted 

Bending is simply shaping a round steel bar into a "U" form. The original grain flow lines are deformed but cannot be optimally reoriented along the part contour as in forging. The stress concentration points (especially the inner bend radius) are precisely where the grain flow is weakest. 

(2) Fatigue Strength is Significantly Lower than Forged Parts

Industry literature clearly states: "Die‑forged chain connectors/shackles provide improved material strength compared to the conventional bar‑bending method." Under repeated tensile‑unloading cycles, the fatigue life of bent connectors is typically only 50%–70% of that of forged connectors. 

(3) Leg Cross‑Section is Circular, Not Oval

This is a critical point you raised. Bent connectors retain the original round cross‑section, whereas forged connectors can be designed with an oval cross‑section. The engineering advantages of an oval section are:

- Larger load‑bearing cross‑sectional area (for the same nominal diameter);

- Better fitment with bucket mounting holes, reducing play and wear;

- More uniform stress distribution, minimizing localized stress concentrations. 

(4) Poor Dimensional Consistency

The bending process is affected by material spring‑back, operator technique, and variations in bar stock, leading to greater dimensional scatter within a batch. 

3. Summary of Quality and Service Life Comparison   

For demanding cement plant bucket elevator applications involving high loads and continuous operation, forged chain connectors are the only technically sound choice for working with round link chains. Although bent chain connectors are cheaper, their deficiencies in strength and fatigue life will inevitably lead to more frequent replacements and higher downtime risks.
Same application can be found in slag removal conveyors in power plants.