Corrosion Causes and Protection Solutions for Underground Idlers in Coal Mines

In the complex underground environment of coal mines, the corrosion problem of belt conveyor idlers has become a key factor affecting equipment life and production efficiency. This paper deeply analyzes the three core causes of underground idler corrosion and proposes systematic solutions to provide operational protection guidelines for coal mining enterprises.

1. Three major causes of underground idler corrosion

(1). Chemical corrosion: synergistic erosion of acidic water and harmful gases

In the downhole environment, the coexistence of acidic water with harmful gases such as sulfur dioxide forms the chemical basis of idler corrosion. When the relative humidity of the air exceeds 90%, the water film formed on the metal surface dissolves the acid gas and forms a corrosive solution. Taking sulfur-containing mines as an example, the dissolved sulfur dioxide in the water film will react with iron to form ferrous sulfate, accelerating the dissolution of the metal matrix. This corrosion is hidden, initially manifested as surface rust spots, gradually developed into pitting pits, and eventually led to perforation of the cylinder skin.

(2). Electrochemical corrosion: the dual effect of metal potential difference and electrolyte

The potential difference between different metals in the idler assembly (such as the connection between carbon steel and copper parts) forms the primary cell effect in the presence of electrolyte. Taking the survey data of a coal mine as an example, the corrosion rate of carbon steel pipelines near copper valves is more than 3 times that of other parts. This corrosion is selective, and metals with lower potentials become anode-preferential dissolution. At the same time, the carbon particles in the coal dust adsorb corrosive gases and form local microcells, further aggravating the corrosion process.

(3). Environmental corrosion: the physicochemical compound of water film and coal dust

Continuous underground water spraying and coal dust accumulation constitute a unique corrosive environment. The presence of a water film not only dissolves corrosive substances, but also penetrates into metal crevices through capillary action. The accumulation of coal dust forms an insulation layer and prolongs the existence time of the water film. Experiments show that the corrosion rate of idlers in the dusty area is 2-3 times higher than that in the clean area. This kind of corrosion has regional characteristics, and mostly occurs at the connection of idler supports, welds and other structural weak parts.

2. Four technical paths of corrosion protection

(1). Material optimization: application practice of polymer materials

Ultra-high molecular weight polyethylene (UHMWPE) idlers achieve the unity of corrosion resistance and self-lubrication through molecular structure design. An application case of a coal mine shows that the service life of polymer idlers in acidic water environments is more than 5 times that of steel idlers. Its protection mechanism includes:

The tight arrangement of molecular chains forms a dense protective layer

Wear-resistant fillers such as silicon carbide are added to enhance surface hardness

Antistatic agent treatment eliminates the risk of static buildup

(2). Structural improvement: innovative design of sealing system

The new labyrinth seal structure blocks the intrusion of corrosive media with multiple protections:

The first rubber seal prevents large particles from entering

The intermediate air chamber forms a pressure equilibrium zone

The inner lip seal provides a dynamic seal

The salt spray test data of a certain model of idler shows that the sealing performance is improved by 300% and the bearing life is extended by 2 times.

(3). Surface treatment: application of composite protective coating

Nano-ceramic coating technology forms a protective layer of 50-100 μm on the metal surface through a plasma spraying process, with the following characteristics:

The hardness reaches HV800 or more, and the wear resistance is increased by 5 times

The porosity is less than 1%, effectively blocking corrosive media

The bonding strength with the matrix exceeds 20MPa

In the comparative test of sulfur-bearing mines, the corrosion rate of the coated idlers was reduced to 0.02mm/year.

(4). Maintenance strategy: the application of intelligent monitoring system

IoT-based idler health monitoring system enables precise maintenance through the following technologies:

Vibration sensors monitor bearing status in real time

The temperature sensor warns of abnormal heat

The corrosion rate prediction model warns 30 days in advance

After the application of a large coal mine, the idler replacement cycle was extended from 90 days to 180 days, and the maintenance cost was reduced by 40%.

3. The construction of a systematic protection system

(1). Protection design in the selection stage

Establish corrosive environment classification standards (such as C1-C5 levels)

Formulate a material selection matrix (e.g., C3 environment recommends polymer materials)

Design standardized interfaces to reduce structural gaps

(2). Control points in the installation stage

Laser centering instrument is used to ensure the installation accuracy (deviation < 0.5mm/m)

Use a torque wrench to standardize fastener installation

Implement dry air purge process

(3). Maintenance specifications in the operation stage

Formulate a hierarchical inspection system (daily/weekly/monthly inspection)

Development of special cleaning equipment (e.g. high-pressure gas-water combined cleaning machine)

Establish a corrosion database to achieve life prediction

Corrosion protection of underground idlers is a systematic project that requires collaborative innovation from multiple dimensions such as material science, structural design, and intelligent monitoring. With the application of new technologies such as nanotechnology and the Internet of Things, future corrosion protection will develop towards self-healing and intelligent early warning. Coal mining enterprises should establish a corrosion management system for the whole life cycle to achieve double improvement of safety and efficiency.