Chain Damage

I. Five Common Forms of Chain Damage

II. Six Core Causes of Chain Damage (Full-Lifecycle Investigation)

1. Selection and Design Errors (Fundamental Issues)

• Load Mismatch: The rated tensile force of the selected chain is less than the actual working load (e.g., using a light-duty drive chain to convey heavy materials). Long-term overloading causes the chain plates and pins to bear tensile stress exceeding the limit, accelerating wear or breakage.

• Incorrect Pitch/Specification: The chain pitch does not match the sprocket (e.g., a 5-pitch sprocket with a 4-pitch chain), or the chain width is incompatible with the equipment guide rail (excessive width causes jamming, insufficient width causes misalignment), resulting in uneven force during meshing/operation.

• Insufficient Environmental Adaptability: Using ordinary carbon steel chains (without anti-corrosion treatment) in humid and corrosive environments (e.g., chemical industry, food processing), or using ordinary lubricating grease that is not high-temperature resistant in high-temperature environments (e.g., drying lines), leading to chain rust or lubrication failure.

2. Installation Deviations (Hidden Damage Triggers)

• Excessive Parallelism/Coaxiality Deviation: The axes of the driving and driven sprockets are not parallel (deviation ＞ 0.5mm/m), or the chain tensioning device is installed crookedly, causing the chain to bear force on one side during operation, leading to one-sided wear of chain plates and bending of pins.

• Improper Tension: Excessively loose chains (sag exceeds 2% of the center distance between two sprockets) are prone to tooth skipping and vibration during operation; excessively tight chains (no sag) cause excessive meshing pressure between the chain and sprocket, accelerating the wear rate of chain plates and rollers by more than 3 times.

• Misaligned Guide Devices: The guide rail of the conveyor chain is installed offset, causing the chain to rub against the edge of the guide rail during operation, scratching the side of the chain plate, and leading to deformation and breakage of the chain plate over time.

3. Lubrication Failure (Most Common Trigger)

• Infrequent Lubrication: The mating surfaces of the chain pins and bushings, as well as rollers and bushings, lack lubricating oil, resulting in direct metal-to-metal friction. The wear rate increases by 5-8 times, and metal debris is easily generated to aggravate "abrasive wear".

• Incorrect Lubrication Method: Using "grease application" for high-speed chains (linear speed ＞ 8m/s) (which cannot effectively penetrate into the fit clearance), or using "light oil spraying" for low-speed and heavy-load chains (the oil film is easily squeezed and broken).

• Incorrect Lubricating Oil Selection: Using ordinary mineral oil in humid environments (prone to emulsification and failure), or using lubricating oil without extreme pressure performance in heavy-load scenarios (unable to resist extrusion under heavy loads, leading to oil film breakage).

4. Working Condition and Environmental Factors (External Damage)

• Dust/Impurity Invasion: In dusty environments such as mining, construction, and grain processing, dust and particles enter the chain's fit clearances (pin-bushing, roller-bushing), forming "abrasives" that scratch the surfaces of pins and bushings in a short period.

• Impact Loads: "Sudden acceleration" during equipment startup, "bulk material dropping" during material conveying, or forced operation when the chain is jammed, causing the chain to bear instantaneous impact tension. Cracks form near the chain plate holes, eventually leading to breakage.

• Abnormal Temperature: High-temperature environments (e.g., forging workshops) reduce the strength of the chain material (the tensile strength of carbon steel chains decreases by 30% when the temperature exceeds 200℃), while low-temperature environments (＜ -10℃) make the chain material brittle and prone to breakage.

5. Sprocket Issues Causing Consecutive Damage

• Sprocket Tooth Surface Wear: After the sprocket tooth thickness decreases, it cannot effectively "hold" the rollers during meshing with the chain, causing the chain to slip and skip teeth during operation, and aggravating friction between the chain plates and the sprocket tooth surface.

• Sprocket Eccentricity/Runout: Excessive coaxiality deviation during sprocket installation leads to "eccentric rotation" during operation, generating periodic impacts on the chain and causing fatigue damage to the chain plates and loose pins.

• Sprocket Tooth Profile Deformation: After long-term use, the sprocket teeth become sharp or develop "reverse teeth", which "gnaw" the chain plates during meshing with the chain, causing edge deformation and cracking of the chain plates.

6. Improper Maintenance and Usage (Human Factors)

• Infrequent Inspection: Failure to inspect the chain pitch, chain plate thickness, and pin clearance according to the equipment manual (usually every 150-300 hours) results in missing the opportunity to repair early wear (e.g., when the pitch increases by 1%).

• Overload Usage: Forcing an increase in conveying capacity to improve output (e.g., exceeding 1.5 times the chain's rated load), or continuing forced operation without shutting down to clear material when the chain is jammed.

• Incomplete Replacement: Only replacing partially damaged chain links (e.g., replacing broken chain plates alone while retaining severely worn pins) leads to inconsistent fit clearances between new and old components, causing rapid damage to the new components.

III. Inspection and Maintenance Solutions for Chain Damage

1. Preliminary Inspection: Quickly Locate the Problem (Preliminary Judgment Can Be Made Without Disassembly)

• Visual Inspection: After shutting down the equipment, check if the chain has broken or deformed chain plates, rust, broken or seized rollers, and loose or exposed pins. Rotate the rollers by hand; if they cannot rotate, it indicates "roller seizure".

• Operation Test: After starting the equipment, listen for abnormal noises ("clunking" may indicate tooth skipping, "sharp friction sound" may indicate lubrication failure, "metal impact sound" may indicate loose pins). Observe if the chain has obvious vibration or misalignment, or if there is a tendency to "fall off the sprocket" during meshing with the sprocket.

• Dimensional Measurement:

1. Pitch Measurement: Use a caliper to measure the total length of 10 standard pitches (compare with the standard value of a new chain); a deviation exceeding 1% indicates "chain elongation".

2. Chain Plate Thickness Measurement: Measure the thickness of the inner and outer chain plates; if it is less than 80% of the original thickness, replacement is required.

3. Clearance Measurement: Use a feeler gauge to measure the fit clearance between the pin and bushing; a clearance exceeding 0.2mm indicates severe wear.

2. Maintenance/Replacement Solutions: Handle According to Damage Severity

IV. Preventive Measures for Chain Damage (Extend Service Life by Over 60%)

1. Selection Stage: Adapt to Working Condition Requirements

• Select Based on Load: Choose the chain according to the actual working load × 1.2-1.5 safety factor. For hoisting chains and conveyor chains, additionally consider "dynamic load" (e.g., startup impact), and prioritize high-strength chains (e.g., 20Mn2 material, carburizing and quenching treatment).

• Select Based on Environment: Choose stainless steel chains (304/316) or galvanized chains for humid/corrosive environments, high-temperature resistant chains (e.g., nickel alloy material) for high-temperature environments (＞ 200℃), and "fully enclosed chains" (with dust covers) for dusty environments.

• Match with Sprockets: Ensure the chain pitch and number of teeth fully match the sprocket; the number of teeth of small sprockets is recommended to be ≥ 17 (too few teeth increase the chain wear rate); the center distance between the two sprockets is recommended to be 30-50 times the chain pitch (avoid excessive shortness leading to frequent chain bending).

2. Installation Stage: Ensure Accurate Fit

• Calibrate Parallelism and Coaxiality: Use a laser alignment tool or level to calibrate the axes of the driving and driven sprockets, with parallelism deviation ≤ 0.3mm/m and coaxiality deviation ≤ 0.1mm.

• Control Tension: After installation, press the middle of the chain by hand; the sag should meet the standard (e.g., 5-10mm sag for a chain with a 1m center distance). For automatic tensioning devices, adjust the tension force (avoid excessive or insufficient tension).

• Install Guide Devices: Install guide rails for conveyor chains, with a clearance of 0.5-1mm between the guide rail and the chain to avoid chain misalignment; for long-distance conveyor chains (＞ 10m), install a guide wheel every 3-5m to reduce chain vibration.

3. Lubrication Management: Core Protection Method

• Develop a Lubrication Cycle: Lubricate every 200-300 hours in light-load/clean environments, every 100-150 hours in heavy-load/dusty/humid environments, and shorten the lubrication cycle (e.g., every 80 hours) in high-temperature environments.

• Select the Right Lubricating Oil and Method:

• Low-speed and heavy-load (linear speed ＜ 3m/s): Use 150#-220# extreme-pressure gear oil, with "soak lubrication" or "drop lubrication";

• Medium-speed and medium-load (linear speed 3-8m/s): Use 46#-68# anti-wear hydraulic oil, with "spray lubrication";

• High-speed and light-load (linear speed ＞ 8m/s): Use 32#-46# light lubricating oil, with "oil mist lubrication";

• Humid environments: Use waterproof lithium-based grease (avoid emulsification); high-temperature environments: Use high-temperature synthetic lubricating grease (temperature resistance ＞ 250℃).

• Ensure Adequate Lubrication: Run the chain slowly during lubrication to ensure the lubricating oil penetrates the fit clearances of the pin-bushing and roller-bushing; avoid only applying lubricant to the chain plate surface (which has no actual protective effect).

4. Daily Maintenance: Identify Hidden Risks in Advance

• Daily Inspection: Check the chain for abnormal noises, vibration, and rust once per shift (8 hours); check if the rollers rotate flexibly and if the chain plates have cracks.

• Regular Testing: Measure the chain pitch (total length of 10 links) and chain plate thickness with a caliper every month; test the actual tensile strength of the chain with a tension meter every quarter (replace if it is less than 80% of the rated value).

• Cleaning and Maintenance: In dusty environments, use compressed air to blow off dust on the chain surface every 200 hours, then clean with kerosene and re-lubricate; in humid environments, check the chain for rust once a week, and if rust is found, polish it with sandpaper and apply anti-rust oil in a timely manner.

5. Usage Specifications: Avoid Human-Induced Damage

• Prohibit Overload Usage: Strictly operate according to the chain's rated load; avoid sudden load increases (e.g., prohibit stacking excessive materials on the conveyor chain at one time).

• Smooth Startup and Shutdown: Accelerate slowly when starting the equipment (e.g., control the motor speed with a frequency converter); run without load for 1-2 minutes before shutdown to avoid sudden start-stop and resulting impact loads.

• Handle Jamming Timely: Immediately shut down the equipment when the chain is jammed, clean the material before restarting, and prohibit forced operation (to avoid chain plate breakage).