Arm (Stick): Component Specs, Materials & Applications

Component Specifications

Definition

The arm, also known as the stick or dipper, is a pivotal structural member in excavator work equipment assemblies. It functions as the intermediate linkage between the boom and the attachment (typically a bucket), translating hydraulic cylinder force into controlled linear and rotational motion. Its primary role is to provide the necessary reach, leverage, and force application for digging, lifting, and material placement tasks. The component's geometry, pin connections, and structural integrity directly influence the machine's digging depth, breakout force, and overall operational envelope.

Working Principle

The arm operates on lever and linkage principles. It is connected to the boom via a pivot pin at its proximal end and to the bucket via another pivot pin at its distal end. One or more hydraulic cylinders (the arm cylinder) are mounted between the boom and the arm. When hydraulic pressure is applied to extend or retract this cylinder, it exerts a force on the arm, causing it to rotate about its boom connection pin. This rotation moves the attached bucket in an arc, enabling the digging (crowd) and dumping motions. The mechanical advantage is determined by the cylinder mounting points and the arm's geometry.

Materials

High-strength, low-alloy (HSLA) steel plate (e.g., ASTM A572 Grade 50 or equivalent, with yield strength ≥ 345 MPa). Critical weld areas and pin bosses may use higher-grade steel or undergo specific heat treatment (quenching and tempering) for enhanced wear resistance and fatigue life.

Technical Parameters

Parameter	Typical range	Notes & selection driver
Weight	Machine-dependent (e.g., 500kg - 5000kg+)
Safety Factor	Typically ≥ 3:1 for structural yield
Main Pin Diameter	e.g., 80mm - 200mm
Length (Pin To Pin)	Varies by machine class (e.g., 2.5m - 7m+)
Maximum Design Load	Based on machine's rated lift capacity at specified radius
Arm Cylinder Bore/Stroke	Machine-specific (e.g., 140mm / 1200mm)

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

ISO 2867, ISO 10261, ISO 10567, DIN 15018, DIN EN 13001

Parent Products

This component is used in the following industrial products

Work Equipment (Boom, Arm, Bucket)

The primary digging and material handling assembly of a mining excavator, consisting of boom, arm, and bucket components.

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Engineering Analysis

Risks & Mitigation

Structural fatigue and crack propagation leading to catastrophic failure
Pin and bushing wear causing poor control and increased stress
Overload scenarios from improper use or attachment
Corrosion in harsh environments reducing wall thickness

FMEA Triads

Trigger: Cyclic stress exceeding material endurance limit at stress concentrators (weld toes, sharp corners).
Failure: Fatigue crack initiation and propagation, leading to complete fracture of the arm.
Mitigation: Implement robust design with smooth transitions, proper weld profiles (grind toes), use of HSLA steel with good fatigue properties, and enforce regular NDT (Ultrasonic, Magnetic Particle) inspections on high-stress areas.

Trigger: Abrasive wear and lack of lubrication at pivot pin connections.
Failure: Excessive clearance between pin and bushing, leading to impact loads, poor machine control, and accelerated wear on other components.
Mitigation: Use hardened and ground pins with replaceable lubricated bushings, enforce strict greasing schedules per OEM manual, and monitor for abnormal play during pre-operation checks.

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

Dimensional tolerances for pin holes per ISO 2867 (e.g., H8 for bore). Straightness and parallelism tolerances critical for cylinder alignment. Weld quality per ISO 5817 Level B.

Test Method

Non-Destructive Testing (NDT): Ultrasonic Testing (UT) for internal flaws, Magnetic Particle Inspection (MPI) for surface cracks on critical welds. Load testing via strain gauging to verify stress distribution under simulated working loads.

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

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Inspection readiness

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Supplier transparency

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Manufacturers of Arm (Stick)

Manufacturer profiles associated with Arm (Stick).

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Compiled and source-reviewed by the CNFX editorial team. Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review

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Frequently Asked Questions

What is the difference between an arm and a boom on an excavator?

The boom is the primary, longest structural member attached directly to the excavator's house (upper structure). The arm (stick) is attached to the end of the boom and connects to the bucket. The boom provides vertical reach and lift height, while the arm provides horizontal reach and controls the digging (crowd) motion.

What causes cracks to form in an excavator arm?

Cracks typically initiate due to cyclic fatigue from repetitive loading/unloading during digging, material defects, stress concentrations at weld joints or sharp geometry changes, or overload conditions exceeding design limits. Improper welding repairs can also be a significant cause.

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records. See the editorial policy.

Preliminary Technical Classification

This page supports structured research, RFQ preparation, and supplier evaluation. It does not replace buyer-led supplier qualification, standards review, or technical approval.

Arm (Stick)