I. Overview and Function of High-Strength, Compact Chains for Mining Applications

Based on the actual operating conditions of circular-link chains in coal mine shafts, we have modified the traditional geometric shape and related dimensions of mining circular-link chains to design a new chain link geometry and chain structure. The compact chain consists of vertical links and flat links. The dimensions and profile of the flat links are consistent with those of conventional mining circular-link chains. The vertical links feature flattened sides and an outer width smaller than that of high-strength mining circular-link chains. The modification of the vertical link shape significantly reduces stress concentration on the chain links, thereby extending the service life of the chain. Consequently, without altering the dimensions of the conveyor trough, it is possible to upgrade the conveyor’s power and enhance its conveying capacity. Meanwhile, since the straight arms of the vertical links make surface contact with the bottom plate of the conveyor trough—rather than the line contact characteristic of conventional circular-link chains—this change improves wear resistance.

II. Market Analysis of Compact Chains

With the country’s ongoing efforts to regulate and restructure coal mining operations and its increasing investment in technology, the adoption rate of fully mechanized mining is steadily rising. Since large-specification, high-strength round-link chains are capital-intensive products with high technological content, nearly 80% of the market share for these large-specification, high-strength compact chains currently relies on imports. However, as imported equipment is gradually introduced, the domestic production rate continues to rise, and both quality and manufacturing processes keep improving—coupled with price advantages—replacing imports is only a matter of time.

III. There are two main types of compact chain production processes:

Type 1: The vertical ring is formed by extrusion—material feeding → individual vertical rings are linked into chains → vertical rings are blast-cleaned → vertical rings are welded → vertical rings are heated → vertical rings are extruded into shape → flat rings and vertical rings are knitted together → blast-cleaning → flat rings are welded → stretched to the specified dimensions → heat-treated → pre-stretched for strengthening and shaping → inspection → pairing → warehousing

The second method involves forging and pressing the vertical links: material cutting → weaving the flat rings and vertical links together → shot blasting → welding the flat rings → primary stretching to the specified dimensions → heat treatment → secondary pre-stretching for strengthening and shaping → inspection → pairing → warehousing. The high-strength compact chain for mining is a new type of product. What distinguishes it from conventional chains is that it is composed of interconnected vertical and flat rings; therefore, the weaving process used in its production is entirely different from that employed for traditional chains.

The first production process is the one currently adopted by most domestic manufacturers of round-link chains. In this process, the vertical links are formed using a hydraulic press. The key manufacturers in this category include Jiangsu Gelin Machinery Co., Ltd., Tiandi Beniu, and Germany’s ThyssenKrupp. The second production process primarily involves forging vertical links using die-forging equipment. Major manufacturers in this category include Zhangjiakou Parsons Coal Machinery Co., Ltd., Jiangsu Gelin Machinery Co., Ltd., Germany’s ThyssenKrupp, and Poland’s Huaxing. Both of these production processes require specially designed chain-linking equipment; each chain link must be formed through two separate workstations. Consequently, both the linking process itself and the associated tooling and molds need to be redesigned from scratch. Moreover, whether the links are forged or extruded, they all feature variable cross-sections. Unlike welded links, their geometric shapes and cross-sectional profiles differ significantly, resulting in varying degrees of deformation. Therefore, extensive process trials are necessary to determine precise dimensional requirements and ensure compliance with standard specifications. However, equally problematic is the inconsistency in pitch—a fundamental issue facing compact chains today. Particularly in the second production process, since the forged vertical links differ from traditional chain links, there remain shortcomings in terms of raw material selection and dimensional tolerance accuracy.

The third method involves directly forging bar stock. Domestically, some manufacturers have adopted the production process developed by Poland’s Huaxing, which first uses die forging to flatten both ends and the central portion of the bar stock. The flattened bars are then linked together using a chain-link machine and subsequently welded.

The development of high-strength compact links for mining applications builds upon the foundation of high-strength round-link chains used in mining. The dimensions, shapes, and structural configurations of the chain links have been optimized. These improvements and optimizations were made based on the results of stress analysis of the chains and taking into account the increased power requirements of coal-mining equipment, while also considering the limited space available underground in coal mines.

The increasing specifications of high-strength, compact chains and round-link chains for mining applications, coupled with changes in their structural designs and rising requirements for mechanical performance, have spurred the rapid development of chain-manufacturing equipment and process technologies in China.