Definition:
For an excavator, basic structural components refer to:

1. Upper and lower turntables, main frame;

2. Boom, arm, and other structural members that do not require frequent short-cycle maintenance.

While these components are designed for long-term use, failures can still occur due to diverse operating conditions. Here, we focus on how to reduce and prevent problems, rather than detailed failure analysis of specific cases.

1. Manufacturing Considerations

• Stress Concentration:
  Every machine experiences stress concentrations during manufacturing, especially at welds. Welded steel plates generate internal forces, and these must be gradually relieved. Experienced workers know that some components (castings, structural plates) are stored for natural aging to relieve internal stresses before continuing with the next process—sometimes taking 2–3 years.

• Accelerated Stress Relief in Factories:
  To shorten aging cycles, professional factories may use artificial aging methods such as heat treatment, vibration, or sandblasting to reduce internal stress. Small factories often skip this due to cost, which is one reason for lower product quality.

• Design Life Trends:
  Modern excavators prioritize operator comfort, safety, and aesthetics over structural longevity. Some brands even deliberately design machines to last only a certain number of hours (e.g., 12,000 hours). Users must understand that even with careful operation, machines today are unlikely to reach the multi-decade service life of older models.

2. Common Failure Types

A. Weld Cracks

• Caused by manufacturing or excessive external stress.

• Can often be repaired professionally, but not with “quick welds” by unskilled personnel. Proper knowledge and technique are required.

B. Base Material Cracks

• Caused by material failure or excessive internal stress.

• These cannot be repaired in place; the affected component must be replaced.

3. Operating Considerations

• Do not use the excavator as a pickaxe or pry bar:
  Sudden impact loads on the boom or arm exceed design limits. Even if the overflow valve activates, repetitive impact cycles can cause cracks in the boom or arm. This is common in field operations when operators try to break hard rock with the bucket.

• Replace pins and bushings in pairs:

  • Worn pins are visible, but bushings wear as well. If a pin is worn, the corresponding bushing is almost certainly worn too.

  • Failure to replace bushings along with pins often leads to cracks in the boom or arm. Weld repairs in these cases are rarely successful and may deform the components.

• Cylinder Rod Failures:
  Some rod head failures are also linked to worn pins and bushings, highlighting the importance of maintaining proper fit and alignment.

4. Key Takeaways

1. Weld Cracks: Can be repaired professionally, but require proper technique.

2. Plate Cracks: Usually material or stress-induced; cannot be repaired in place—replacement is needed.

3. Avoid excessive impact: Using the excavator for “digging” rather than “excavating” leads to structural failure.

4. Pins and bushings: Always replace worn bushings along with pins to prevent secondary failures like arm or boom cracks.

5. Understand the limits: Modern machines may have intentionally shortened lifespans. Safe and proper operation is critical to maximizing usable life.

Summary:
The majority of base structural failures in excavators are due to external overloading or worn pin/bushing combinations, rather than poor design. Proper inspection, paired component replacement, and careful operation are essential to extend the life of these key components.