The "Chassis Frame" of Excavators is the Undercarriage Components!

I. Understanding Undercarriage Components: The "Chassis Frame" of Excavators—You Can't Move or Stand Firm Without Them!

   Undercarriage components are the core executive parts of an excavator's chassis. Simply put, "the drive sprocket transmits power, the idler sets the direction, the track rollers support the weight, the carrier rollers prevent deviation, and the tracks grip the ground." Only when these 5 components work together can the machine move flexibly. To understand the undercarriage components, you just need to remember the function and principle of each part:

1. Structure and Core Principles: 5 Components with Clear Division of Labor—None Can Be Missing

(1) Track Rollers: "Chassis Jacks" That Support the Entire Machine's Weight

• Structure: Cylindrical metal wheels with internal bearings and seals. The wheel surface has wear-resistant patterns. They are installed on the track frames on both sides of the chassis. A 20-ton excavator usually has 6-8 track rollers.

• Principle: They directly contact the inner side of the tracks and rotate with the track movement via bearings. At the same time, they support the entire weight of the excavator (for example, each track roller of a 20-ton machine bears a weight of 2-3 tons), preventing the machine body from directly pressing against the ground and sinking into the soil.

(2) Carrier Rollers: "Track Stabilizers" That Prevent Track Deviation

• Structure: Installed on the upper part of the chassis and below the boom. They are similar in shape to track rollers but smaller in size. An excavator usually has 2-4 carrier rollers.

• Principle: They fit closely to the upper inner surface of the tracks and guide the tracks to move in a straight line through their own rotation, preventing the tracks from arching upward or deviating during movement or turning (for example, when the machine rotates, the carrier rollers can "press" the tracks onto the correct path).

(3) Idlers: "Direction Calibrators" That Position the Track Movement Path

• Structure: Installed at the front end of the chassis. The middle of the wheel has a groove, and the track links can be clamped in the groove. There is a tension cylinder inside (connected to the track tensioning system).

• Principle: The tension cylinder adjusts the track tightness (keeping the track sag within 3-5 cm). At the same time, the wheel groove restricts the lateral movement of the tracks, ensuring the tracks always move along a fixed path and avoiding deviation or derailment.

(4) Drive Sprockets: "Power Transmission Wheels" That Drive Track Rotation

• Structure: Installed at the rear end of the chassis. The wheel surface has protruding "teeth" (which mesh with the holes of the track links) and is connected to the reducer of the track drive assembly.

• Principle: The power of the track drive assembly is transmitted to the drive sprockets through the reducer. When the drive sprockets rotate, the teeth "clamp" the holes of the track links, driving the entire track to rotate and thus pushing the machine forward or backward (for example, when the machine moves forward, the drive sprockets rotate clockwise, and the teeth pull the tracks to move backward, making the machine move forward).

(5) Tracks: "Ground Grip Belts" That Adapt to Complex Terrains

• Structure: Composed of multiple track shoes, track links, and bushings. The surface of the track shoes has anti-skid patterns (to enhance grip). The track links are connected into a ring via bushings and fit around the outside of the four wheels.

• Principle: By increasing the contact area with the ground (5-10 times larger than that of tires), the pressure of the machine on the ground is reduced (for example, on muddy ground, tracks will not sink, but tires will get stuck). At the same time, the anti-skid patterns can enhance grip, allowing the machine to move stably on steep slopes and gravel.

2. Importance: Without Undercarriage Components, an Excavator Is Just "Useless Metal That Can't Stand or Move"

• They Bear All the Weight: The undercarriage components together support the entire weight of the excavator (20-30 tons). The track rollers and tracks directly contact the ground. If the track rollers are damaged, the machine body will tilt and may even fail to support the weight.

• Flexible Movement Depends on Their Performance: The drive sprockets transmit power, the idlers set the direction, and the carrier rollers prevent deviation. Only when these 5 components work together can the machine turn flexibly and move quickly on the construction site. If the drive sprockets are worn out, the tracks cannot rotate, and the machine will be "stuck in place."

• Adapting to Working Conditions Relies on Their Durability: Construction sites are mostly gravel or muddy. The anti-skid patterns of the tracks and the wear-resistant wheels of the track rollers allow the machine to work in complex terrains. If the track shoes break, the machine will slip on steep slopes, and even safety accidents may occur.

• High Maintenance Costs—You Can't Afford to Repair Them When Damaged: A set of imported undercarriage components costs 11,500-21,800 US dollars, and domestic ones cost 4,350-11,500 US dollars. Maintenance also requires disassembling the chassis and hoisting the machine body, resulting in 3-5 days of downtime. The downtime cost is even higher than the maintenance cost.

II. The Undercarriage Components Fear These 5 Things the Most!

1. Not Cleaning Debris Stuck in Tracks: Damaging Track Rollers and Carrier Rollers

   Gravel, branches, and steel bars on the construction site are easy to get stuck in the gaps of track shoes or between the wheel systems (such as the gap between track rollers and tracks). If not cleaned in time, these debris will wear the surface of track rollers and the seals of carrier rollers like "sandpaper." For example, if gravel is stuck between track rollers and tracks, the wear-resistant layer of track rollers will be worn out in 1-2 weeks, leading to oil leakage. Replacing one track roller costs 215-430 US dollars.

2. Improper Track Tightness: Easy Wear of Idlers and Drive Sprockets

• Too Loose: If the track sag exceeds 5 cm, the tracks will shake up and down when the machine moves. The groove of the idler cannot stably clamp the tracks, which may cause track deviation and derailment, and also wear the rim of the idler.

• Too Tight: If the tracks are tight without sag, the tension cylinder of the idler will be in a high-pressure state for a long time, accelerating the aging of the cylinder seal. At the same time, the meshing pressure between the teeth of the drive sprocket and the track links will be too high, increasing the wear rate of both by 3 times. The drive sprocket will need to be replaced in one year.

3. Long-Term Operation on Sharp Gravel Ground: Easy Fracture of Track Shoes and Track Links

   When working in conditions with many sharp gravels such as mines and quarries, the surface of track shoes will be hit and scratched by gravel, and the bushings of track links will also be deformed by gravel extrusion. For example, if a track shoe is hit by a sharp stone and a gap is formed, continuing to use it will expand the gap and eventually cause fracture. Replacing one track shoe costs 115-215 US dollars, and replacing the entire set of track links costs 2,900-7,250 US dollars.

4. No Maintenance After Operation in Water or Humid Environments: Easy Rust of the Four Wheels

   After working on rainy days or wading in muddy ground, if the seals of track rollers and carrier rollers are damaged, water will enter the internal bearings, causing bearing rust. The teeth of idlers and drive sprockets will also rust due to contact with mud and water. Rusty bearings will get stuck and stop rotating, turning into "sliding friction," which wears the inner side of the tracks. One repair costs 290-725 US dollars.

5. Sudden Steering or Long-Term Single-Track Loading During Turning: Uneven Wear of Carrier Rollers and Drive Sprockets

• Sudden Steering: When the machine turns, suddenly operating the steering lever quickly will cause the tracks to exert a strong lateral impact on the carrier rollers, deforming the carrier roller shaft and making it unable to rotate normally.

• Single-Track Loading: For example, if one side of the track is pressed on a high platform for a long time during operation, the track rollers and drive sprockets on that side will bear double the weight, resulting in "uneven wear" (one side of the teeth is worn flat, while the other side is still intact). Eventually, the entire wheel system needs to be replaced, costing unnecessary money.

III. Cost-Performance Comparison of Undercarriage Components of Domestic and Foreign Excavator Brands

IV. Maintenance of Undercarriage Components

1. "Check 3 Points" Every Day: Detect Hidden Dangers Early

• Check Track Debris: Before starting the machine, use a shovel to clean gravel and branches in the gaps of track shoes and between the wheel systems to avoid debris wearing the components.

• Check Track Tightness: Park the machine on a flat ground and measure the track sag (press down from the middle of the upper part of the track; the sag distance should be 3-5 cm). If it is too loose or too tight, adjust the tension cylinder of the idler.

• Check Wheel System Oil Leakage/Rust: Check if there is oil stains at the seals of track rollers and carrier rollers (oil leakage will form oil spots on the ground) and if the teeth of idlers and drive sprockets are rusted. Deal with problems in a timely manner if found.

2. Regular Cleaning + Lubrication: Reduce Wear

• Cleaning: Rinse the tracks and wheel system with a high-pressure water gun every week to wash away the attached soil and gravel. Check the bushings of track links every 2 weeks and clean the sand and mud inside.

• Lubrication: Add grease to the bushings of track links every 500 hours to reduce friction between the bushings and track links and extend the service life of the tracks.

3. Choose Tracks According to Working Conditions: Avoid "Mismatch"

• Gravel/Mine: Choose tracks with reinforcing ribs and double-layer wear-resistant steel (such as Caterpillar reinforced tracks) to enhance impact resistance and wear resistance.

• Mud/Farmland: Choose wide tracks with deep patterns (such as Komatsu high-grip tracks) to increase the contact area and prevent getting stuck.

• Flat Ground/Municipal Work: Choose economical ordinary tracks (such as Sany Heavy Industry economical tracks) to reduce costs while meeting usage needs.

4. Standardize Operation: Avoid Sudden Movements and Single-Track Loading

• Slow Down When Turning: Push and release the steering lever slowly when turning to allow the tracks to turn smoothly, avoiding impact on carrier rollers and idlers.

• Avoid Single-Track Loading: Try to keep the load on both tracks balanced during operation and do not let one side of the track press on a high platform for a long time. When parking the machine, choose a flat ground and do not let the tracks stay in a twisted state for a long time.

5. Timely Maintenance After Wading/Humid Environments: Prevent Rust

• After working on rainy days or wading, rinse the wheel system and tracks with a high-pressure water gun and wipe off the surface moisture.

• Check the seals of track rollers and carrier rollers and replace them in time if damaged.

• Apply a layer of anti-rust oil on the tooth surface of idlers and drive sprockets to prevent rust.

V. Summary

The undercarriage components are the "chassis frame" of the excavator. Remember these 3 core points:

1. Understand the Division of Labor: The drive sprocket transmits power, the idler sets the direction, the track roller supports the weight, the carrier roller prevents deviation, and the track grips the ground. These 5 components work together, and none can be missing.

2. Avoid Risks: Prevent the 5 types of problems—debris stuck in tracks, improper tightness, sharp gravel impact, no maintenance after wading, and sudden steering—to avoid premature damage to the undercarriage components.

3. Master Maintenance: Do the 5 steps well—check debris and tightness every day, clean and lubricate regularly, choose tracks according to working conditions, standardize operation, and prevent rust after wading. This can extend the service life of the undercarriage components by 2 more years and reduce maintenance costs.

Well-maintained undercarriage components ensure the excavator moves stably, has strong adaptability, fewer faults, and high work efficiency. This is the real "cost reduction, efficiency improvement, and peace of mind"!