Keyway: Component Specs, Materials & Applications

Component Specifications

Definition

A keyway is a longitudinal groove or slot precisely machined into the bore of a hub or the surface of a shaft, designed to house a parallel or Woodruff key. In polypropylene injection molded gear wheels, the keyway is typically molded into the gear hub during manufacturing to create a positive mechanical connection with the shaft, preventing relative rotation and ensuring accurate power transmission. The keyway's dimensions must maintain strict tolerances to match standard key sizes while accounting for material properties like shrinkage and thermal expansion in plastic components.

Working Principle

The keyway works by providing a recess for a key that fits into both the shaft and the hub of the gear wheel. When torque is applied, the key transmits rotational force from the shaft to the gear (or vice versa) through shear stress across the key's sides, preventing slippage. In polypropylene gears, the molded keyway must distribute stress evenly to avoid localized deformation or cracking, relying on the plastic's resilience and the key's mechanical interference fit.

Materials

Polypropylene (PP), typically homopolymer or copolymer grades with additives for enhanced strength, wear resistance, and dimensional stability. Common specifications include PP with 20-40% glass fiber reinforcement for improved mechanical properties, or mineral-filled PP for cost-effective applications. Material must comply with standards like ISO 1873-1 or ASTM D4101.

Technical Parameters

Parameter	Typical range	Notes & selection driver
Draft Angle	0.5-1° for mold release in injection molding
Hub Diameter	Matches standard shaft sizes (e.g., 10 mm, 12 mm, 15 mm)
Keyway Depth	Typically 0.5-2.0 mm, depending on shaft diameter and torque requirements
Keyway Width	Standard sizes per ISO 773: e.g., 3 mm, 4 mm, 5 mm
Surface Finish	Ra ≤ 3.2 μm to reduce stress concentrations
Tolerance Class	ISO 773 tolerance class H9 for plastic components

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 773, DIN 6885, ISO 286-2

Parent Products

This component is used in the following industrial products

Shaft Connection Hub

A mechanical component that connects the shaft to the blade holder or rotor assembly, transmitting torque and rotational motion.

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Engineering Analysis

Risks & Mitigation

Stress concentration at keyway corners leading to cracking
Wear and deformation under high torque loads
Misalignment due to molding defects or shrinkage
Thermal expansion mismatch with metal shafts causing looseness

FMEA Triads

Trigger: Sharp corners or inadequate fillet radius in keyway design
Failure: Crack initiation and propagation in polypropylene hub
Mitigation: Design keyways with minimum 0.5 mm radius fillets, use stress analysis software, and select reinforced PP grades

Trigger: Excessive torque exceeding material yield strength
Failure: Shear failure of keyway walls or key deformation
Mitigation: Calculate torque limits based on material properties, oversize keyway dimensions, or use metal inserts in high-load applications

Trigger: Molding defects like voids or sink marks in keyway area
Failure: Reduced mechanical strength and premature failure
Mitigation: Optimize injection molding parameters (pressure, temperature), ensure proper gate location, and implement quality control inspections

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

Keyway width tolerance: H9 per ISO 286-2, depth tolerance: ±0.1 mm for typical applications

Test Method

Dimensional verification using CMM or optical comparators, torque testing per ISO 5299, and visual inspection for defects per ASTM D2561

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

Verify equipment lists, process limits, capacity, and representative production evidence.

Inspection readiness

Confirm test methods, calibrated equipment, sampling plans, and traceable reports.

Supplier transparency

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Manufacturers of Keyway

Manufacturer profiles associated with Keyway.

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Frequently Asked Questions

Why use a keyway in plastic gears instead of other locking methods?

Keyways provide a cost-effective, standardized, and reliable method for torque transmission in plastic gears, offering easy assembly and disassembly while maintaining alignment. Alternatives like set screws or press fits may cause stress concentrations or damage in polypropylene.

How does polypropylene affect keyway design compared to metal?

Polypropylene has lower strength and higher thermal expansion than metals, requiring keyways to be designed with wider tolerances, rounded corners to reduce stress, and possible reinforcement (e.g., glass fiber) to prevent deformation under load.

What are common failure modes for keyways in plastic gears?

Common failures include cracking due to stress concentration at sharp corners, wear from key movement under cyclic loading, and deformation from excessive torque or thermal expansion mismatches with the shaft.

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.

Keyway