Technical Analysis and Application Guide for Plum Couplings

Ⅰ. Core Features and Functional Advantages

1. Structural Design Excellence
   The plum coupling adopts a modular lubrication-free structure, eliminating the need for regular greasing. Power transmission is achieved through a high-strength polyurethane elastomer (plum pad), offering these key features:
   • Maintenance-Free Operation: No sliding components, eliminating risks of grease aging or leakage; supports 24/7 continuous operation.
   • High Reliability: Elastomer is wear- and oil-resistant (operating temperature: -30℃~+80℃), with torque capacity ranging from 5N·m to 20,000N·m—30% longer service life than traditional rigid couplings.
   • Superior Dynamic Performance: Provides vibration damping (damping ratio 0.15~0.25), shock absorption (efficiency ≥60%), and electrical insulation (insulation resistance ≥10MΩ), reducing shafting noise and vibration.
   • Strong Misalignment Compensation: Accommodates axial ±1.5mm, radial ±0.7mm, and angular ±1.5° deviations, adapting to installation errors and thermal expansion.
2. Flexible Functional Adjustment
   • Torque Adaptability: By selecting elastomers with different Shore hardness (70A~95A), torque capacity and damping characteristics can be linearly adjusted to suit precision drives (low damping) or impact-loading scenarios (high damping).
   • Lightweight Design: Radial dimensions are 60% smaller than traditional couplings, with moment of inertia as low as 0.01kg·m² (for φ50mm model), suitable for medium-to-high speed operations (max speed 8,000RPM).

Ⅱ. Installation Technical Specifications

Installation Steps (Axial Insertion Type)

1. Shaft End Preparation
   • Ensure shaft insertion dimensions meet design requirements: unilateral insertion depth is coupling unilateral length L1 ±0.5mm (axial tolerance ±0.3mm), with surface roughness ≤Ra3.2μm.
   • Clean the shaft surface and coupling inner bore with anhydrous ethanol, removing oil and debris. Apply a thin layer of molybdenum disulfide grease to reduce assembly resistance.
2. Precision Assembly Process
   • Interference Fit Handling: For interference >0.05mm between inner bore and shaft, avoid hammering. Use a hydraulic press (pressure ≤1.5x rated torque) or thermal installation (heat coupling to 80℃~100℃) to prevent elastomer deformation from impact.
   • Torque Control for Locking: Tighten locking screws with a digital torque wrench according to manufacturer specifications (e.g., M6 screw torque 8~10N·m), ensuring circumferential positioning accuracy ≤0.02mm/m.

Installation Precautions

• Safety during Disassembly: Operate after shutting down and disconnecting power. Loosen locking components in a diagonal sequence to prevent parts from ejecting.
• Startup Inspection: Run no-load for 5 minutes, checking radial runout ≤0.1mm and axial play ≤0.2mm. Confirm no abnormal vibration or noise.
• Vertical Installation Key Point: Ensure the coupling end face fully contacts the shaft shoulder (gap <0.05mm) to avoid uneven loading on the elastomer due to step misalignment.

Ⅲ. Maintenance and Wear Part Replacement

1. Routine Maintenance Guidelines

• Elastomer Inspection: Check every 200 operating hours for cracks (≥1mm), wear (thickness reduction >15%), or aging (surface hardening/cracking). Use an industrial endoscope for internal damage detection.
• Bolt Tightness Check: Recheck locking screw torque with a torque wrench during equipment patrols (allowable deviation ±5%) to prevent axial movement from looseness.

2. Plum Pad Replacement Strategy

• Replacement Interval: No fixed cycle; evaluate dynamically based on operating conditions:
  • Normal Conditions (light load, no 冲击): Replace annually or after 8,000 hours of operation.
  • Harsh Conditions (frequent start-stop, high 冲击): Inspect quarterly; replace immediately if elastomer wear reaches the warning level (remaining thickness <80%).
• Failure Risk Warnings:
  • Excessive misalignment (e.g., angular deviation >2°) causes unilateral stress concentration on the elastomer, accelerating tearing (life reduced to 1/5 of normal).
  • Unlevel equipment foundation (levelness >0.5mm/m) induces vibration, leading to fatigue fracture of plum claws (metal parts). Calibrate shaft alignment with a laser aligner (deviation ≤0.05mm).

3. Replacement Operation Specifications

• After removing old parts, clean the coupling body and check metal claws for deformation (flatness error >0.1mm requires correction or replacement).
• When installing a new elastomer, ensure full engagement with the 卡槽 (gap <0.1mm). Press symmetrically into place to avoid initial stress imbalance from skewing.

Ⅳ. Typical Failure Scenarios and Prevention