Komatsu 20Y3007201 PC200-7/8 Carrier Roller Assy/Crawler excavator undercarriage components manufacture and supplier
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Product Specifications
Technical Description: Komatsu PC200-7/8 Track-Type Excavator Carrier Roller Assembly
1.0 Introduction and Functional Overview
DPW Parts' Carrier Roller Assembly, also known as the upper roller or top roller, is an essential component of the Komatsu PC200-7/8's undercarriage system. Positioned on the upper section of the track frame, its primary functions are distinct from, yet complementary to, the bottom rollers.
Upper Track Support: It supports the weight of the track chain's upper strand (the return side) as it travels back from the front idler to the sprocket.
Track Alignment and Stabilization: It maintains the vertical alignment of the upper track strand, preventing excessive vertical whip, bounce, and lateral sway during machine travel, especially at higher speeds or over rough ground.
Reduction of Frictional Drag: By supporting the track's return run, it minimizes contact and frictional drag between the track chain and the track frame, improving efficiency and reducing power loss.
Containment and Guidance: It works in concert with the track guides (or grousers) on the track chain to keep the track properly centered on the track frame, preventing derailment.
A well-maintained carrier roller assembly is crucial for smooth track operation, reduced vibration, and the prevention of abnormal wear on the track chain links and bushings.
2.0 Major Components and Their Detailed Specifications
The assembly is a self-contained, pre-lubricated unit designed for durability and serviceability.
2.1 Roller Shell (or Housing)
Material & Construction: Manufactured from a high-carbon, heat-treated alloy steel forging or casting. This provides superior strength and exceptional resistance to impact and abrasive wear.
Design: Typically features a double-flange design. The two integral, robust flanges run against the inner surfaces of the track chain links, providing precise lateral guidance and containing the track.
Running Surface: The outer diameter (O.D.) is precision-machined and undergoes induction hardening. This creates a deep, hardened layer to withstand the constant rolling contact with the track chain bushings.
Internal Bore: The bore is machined to a precise tolerance to provide a secure interference fit for the sealed bearing cartridge.
2.2 Sealed Cartridge Bearing Assembly
Komatsu utilizes a "sealed and lubricated for life" cartridge bearing system, which is a key feature for reliability and minimal maintenance.
Bearing Type: The assembly contains a pair of pre-adjusted Tapered Roller Bearings. This configuration is selected for its ability to handle significant radial loads from the track weight and substantial axial (thrust) loads generated during machine turning and side-sloping.
Bearing Cartridge: The bearings are pre-greased, pre-set, and housed within a single, sealed steel cartridge. This unitized design ensures proper internal alignment, simplifies installation and replacement, and prevents improper field adjustment.
Lubricant: The cartridge is packed with a high-quality, high-temperature, extreme-pressure (EP) lithium soap-based grease, sufficient for the projected service life of the roller.
2.3 Multi-Stage Sealing System
The integrity of the sealing system is the primary determinant of the roller's service life. The PC200-7/8 carrier roller employs a sophisticated, multi-barrier seal.
Primary Seal: A Spring-Loaded Radial Lip Seal forms the primary fluid-tight barrier. It is typically made of advanced materials like Nitrile (NBR) or Fluoroelastomer (FKM/Viton) for excellent resistance to grease, heat, and water.
Labyrinth Seal: An external, multi-path "labyrinth" seal is created between the roller shell and the Flange of the Axle Pin. This complex, tortuous path is the first line of defense, designed to trap and expel contaminants.
Dust Lip / Excluder: An outward-facing, secondary rubber or polyurethane lip acts as a scraper, actively removing coarse mud, clay, and debris before they can enter the labyrinth passage.
2.4 Axle Pin (Shaft) and Mounting Bracket
Axle Pin: This is the stationary, high-strength alloy steel shaft. It is hardened and ground to provide a perfect, wear-resistant surface for the inner bearing race and the seal lips.
Mounting: The axle pin is either an integral part of a Carrier Roller Bracket or is pressed into it. This bracket is then bolted directly to the vertical surface of the track frame using high-tensile cap screws. This bolted design allows for straightforward replacement and adjustment of the roller's lateral position.
3.0 Operational Context and Wear Characteristics
3.1 Load and Service Conditions:
Unlike bottom rollers, carrier rollers are not subjected to direct ground impact. However, they are under constant load from the track's weight and experience significant shock loads from the track's engagement with the sprocket and the slapping action of the return strand.
3.2 Common Wear Patterns and Failure Modes:
Flange Wear: Gradual wear on the guiding surfaces of the flanges. Severe wear can lead to increased track lateral movement and potential contact with the track frame.
Running Surface Wear: A reduction in the roller's outer diameter (O.D.). While less severe than on bottom rollers, excessive O.D. wear can contribute to increased track sag and vibration.
Bearing Failure: The most common cause of carrier roller failure. Symptoms include:
Seizure: The roller stops rotating, leading to rapid, grinding wear on the roller surface and the track bushing O.D.
Excessive Play: Worn bearings allow the roller to wobble, causing irregular wear patterns and noise.
Cause: Seal failure is the primary precursor, allowing abrasive contaminants to enter the bearing assembly, destroying the grease and causing accelerated wear.
4.0 Maintenance, Inspection, and Replacement
Regular Inspection: During walk-around inspections, check that all carrier rollers rotate freely. Listen for grinding or rumbling noises during operation, which indicate failed bearings.
Wear Measurement: Use calipers to measure flange width and roller O.D. Compare against the manufacturer's specified "wear limits" provided in the Komatsu service manual. Replacement is recommended before reaching these limits.
Replacement Procedure:
Clean the area around the mounting bolts thoroughly.
Remove the mounting bolts securing the carrier roller bracket to the track frame.
The entire assembly (roller and bracket) can be removed. In some cases, a pry bar or slide hammer may be necessary if the bracket is corroded in place.
Install the new assembly, ensuring the mounting surfaces are clean. Torque the bolts to the specified value in a crisscross pattern.
