1. Rated Load Capacity

Definition:
The rated load capacity refers to the maximum weight of material (in tons or kilograms) that a loader can safely carry and transport under normal operating conditions. This value is determined by the manufacturer based on structural strength, hydraulic system capability, stability, and other factors.

Key Points:

• Testing Standards: Typically conducted according to ISO or GB standards on firm, level ground using standard bucket loads (e.g., gravel with a density of ~1.6–1.8 t/m³).

• Safety Limits: Overloading may cause tipping, structural deformation, or hydraulic system failure.

• Influencing Factors:

• Machine model (e.g., 3-ton, 5-ton loaders).

• Center of gravity (higher lift height reduces allowable load).

• Ground conditions (softer surfaces require reduced loads).

Example:
A 5-ton loader may have a rated capacity of 5,000 kg, but when the bucket is raised to maximum height, the safe load may drop below 3,000 kg.

2. Bucket Capacity

Definition:
Bucket capacity refers to the theoretical volume of material the bucket can hold (in m³), categorized into two standards:

• Struck Capacity (SAE Struck): Volume when material is level with the bucket edge (excluding piled material).

• Heaped Capacity (SAE Heaped): Additional volume from natural material spillage (typically 20%–30% larger than struck capacity).

Key Points:

• Matching Requirement: Bucket capacity must align with rated load capacity.

• Example: For a 5-ton rated load and material density of 1.6 t/m³, bucket capacity should be ≤3.1 m³ (5 ÷ 1.6 ≈ 3.1).

• Bucket Types:

• Standard Bucket: For general materials like soil and gravel.

• Rock Bucket: Reinforced structure, smaller capacity.

• Light-Duty Bucket: For low-density materials (e.g., wood chips, grain), larger capacity.

Example:
A loader with a 3.0 m³ struck / 3.6 m³ heaped capacity carrying gravel (density 1.7 t/m³) would weigh ~5.1 tons (3.0 × 1.7), requiring verification against the rated load limit.

3. Relationship & Selection Guidelines

Formula:
Rated Load Capacity ≥ Struck Bucket Capacity × Material Density
(For high-density materials like iron ore, choose smaller buckets; for low-density materials like coal, larger buckets are suitable.)

Safety Notes:

• Avoid mismatches (e.g., oversized bucket on a low-capacity loader).

• Account for fill efficiency (wet/loose materials may only achieve 70%–80% of theoretical capacity).

Industry Standards:

• ISO 7546:2010 (Loader Rated Load Testing).

• SAE J296 (Bucket Capacity Measurement).

By balancing load capacity and bucket size, operators can optimize both efficiency and safety.