Elsevier

Wear

Volume 306, Issues 1–2, 30 August 2013, Pages 131-137
Wear

Effect of hardness in shackle chain wear under harsh environmentally conditions

https://doi.org/10.1016/j.wear.2013.08.002Get rights and content

Highlights

  • Eight full scale wear experiments are performed on shackle chains splashed with seawater and sand.

  • Wear experiments (2×4) are performed on two commercially available materials: ‘normal’ material (=soft) and ‘wear resistant’ material (=hard).

  • The soft material wears faster (~1.5×) compared to the hard material.

  • The wear mechanism dependents on the tensile force: high forces generate ploughing; low forces give polishing wear and smearing.

Abstract

Industrial fishing (e.g. bottom trawling) uses shackle chains as a sea soil rake to increase the catch. Serving in such extreme conditions (seawater, sand) results in limited lifetimes less than 6 months. To increase the lifetime, hardened ‘wear resistant’ chains could be a possible alternative but quantitative data on their lifetime is unclear. In this study we quantified the wear rate and wear mechanism of two commercially available chain materials. The wear experiments performed on a custom designed full scale test rig show a significant difference between both materials. The hardened chains wear out ~1.5× less comparing with the ‘normal’ chains. The current investigation allows fishermen to make an economical trade-off between both types of chains.

Introduction

Shackle chains have a beneficial strength to flexibility ratio. They have a high strength in the longitudinal direction of the chain while being compliant in the two orthogonal directions. The advantage is due to its construction of the shackle chain; individual shackles are linked to each other and can move relatively to each other [1].

Typical industrial applications of shackle chains are hoisting and securing [2]. In offshore applications shackle chains are used in positioning buoys, oil platforms, to anchoring a ship, etc. [3]. In industrial offshore fishing multiple types of shackle chains and shackle nets are used, depending on the vessel and the used fishing technique.

One of the industrial fishing techniques used in the North Sea (Europe) is bottom trawling. The fishing technique is carried out by dragging a trawl just above the seabed (Fig. 1) and targets groundfish (halibut, sole …) and semi-pelagic species (cod, shrimp …). To increase the catch, the seabed is churned in front of the trawl, startling the ground fish and thus increasing the efficiency. The seabed is churned by ‘tickler chains’ which are ordinary shackle chains that plow through the seabed.

Tickler chains in industrial fishing suffer harsh conditions with a combination of sandy seabed and salty seawater. A combination of these conditions compared to dry conditions, abrasion and corrosion is evident in and results in accelerated wear.

Normal tickler chains have a service life (due to wear) of around 6 months with outliers of only 14 days.

Beside ‘normal’ shackle chains so called ‘wear resistant’ shackle chains are commercially available. The latter chains are more expensive but today nothing is quantified about their lifetime (or rate of wear) compared to the ‘normal’ tickler chains.

This investigation aims at identifying the performance of commercially available shackle chains used for industrial fishing. The synergetic effects of harsh conditions and material characterization will be studied to understand the wear behaviour of shackle chains. The experiments were performed at Soete Laboratory of Ghent University on a full scale chain wear tester. The experimental results will contribute to an economical trade-off between different types of shackle chains.

Section snippets

Test specimens

A common type of shackle is the round steel link normalized by DIN22252:2001, shown in Fig. 2. Geometrical characteristics of the shackle are the pitch p and the diameter of the bulk material d. The tested links (industrially used as tickler chain) have a pitch p=92 mm and diameter d=26 mm.

For a wear experiment two shackles are used, see Fig. 3. During testing, the shackles are linked with each other in longitudinal direction. Contact between both shackles takes place only at the curvature of the

Contact conditions during the wear experiment

During the experiment, the contact surface wears off and the initial contact conformity changes from Hertzian to conformal [6]. The associated contact conditions are calculated in Section 3.2. The curvatures of the surfaces change during the experiment and since they are not measured, it is not possible to calculate the contact stresses for conditions other than the initial contact.

The tensile force FT is applied in longitudinal direction on the left hand shackle. However, the normal force FN

Sample material

Two commercially available shackle chains with different material properties were tested. The hardness and microstructure of both materials were investigated and analysed. However, proprietary considerations concerning the composition and treatment of the ferrous alloys described in this work prevents providing a full characterization. Nevertheless, the unique experimental methods applied and the relationship of hardness and microstructure to wear under simulated conditions was felt to offer

Conclusion

The purpose of this study was to quantify the influence of steel hardness on the wear behaviour of shackle chains in the environment of seawater and sand. A dedicates full scale test rig is used to generate and quantify wear from a pair of shackles. Wear is observed at the contact area and is quantified by a mass reduction and dimensional change.

The measured hardness for material A is lower compared to the ‘wear resistant’ material B, respectively 158 and 419 HV10. A pair of shackles with a

Acknowledgement

The authors would like to acknowledge the support of the IWT (Agency for Innovation by Science and Technology—no. SB-091510). The IVLO (Institute for Agricultural and Fisheries Research) is recognized for the supply of the sample materials. Koen Van Minnebruggen is thanked for the metallographic assistance.

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