GEAR APPLICATION GUIDE · PLASTIC GEAR · PL01
Plastic Gears for Office Automation:
Material Selection and Noise Reduction
Office automation equipment — laser printers, copiers, scanners, fax machines, and paper shredders — uses plastic gears in almost every drive train stage. Their self-lubricating properties, lightweight, corrosion resistance, low noise, and low cost make plastic gears technically superior to steel alternatives in these applications. This guide covers material selection, tooth design, noise reduction and common failure modes for office automation plastic gear drives.
Module M0.3 – M2.5 · Injection Moulded
Printer · Copier · Scanner · Shredder Drive
Why Office Automation Uses Plastic Gears — Not Steel
The universal adoption of plastic gears in office automation equipment is not a cost-reduction compromise — it is the correct engineering choice driven by several performance requirements that steel gears cannot meet simultaneously. The most important is noise: a 45 dB(A) total printer operating noise budget leaves very little headroom for the gear drive train. Steel gears at the pitch line velocities and loads of a laser printer paper feed drive (typically 0.5–3 m/s, 0.5–2 Nm torque) generate 8–12 dB(A) more mesh noise than equivalent plastic gears because steel has very low internal damping. The viscoelastic damping of engineering polymers absorbs the impulsive mesh contact energy before it can be radiated as airborne noise from the gear body.
Korea Ever-Power’s plastic gears for office automation are injection moulded in POM (Delrin/Duracon), PA66/PA46 with glass or carbon fibre reinforcement, PPS and LCP for high-temperature printer components, and PEEK for the most demanding precision positioning applications. All plastic gear moulds for office automation are machined to ±0.002 mm tool accuracy to achieve the tooth profile tolerances needed for quiet gear drives in office equipment.
The self-lubricating property of POM and Nylon is equally important: laser printer paper paths, copier platen assemblies, and scanner optical rails cannot tolerate oil contamination. A steel gear drive in these assemblies would require grease or oil that, over the product lifetime, would inevitably migrate to contaminate paper, printed surfaces, or optical components. Plastic gears eliminate this lubricant exclusion zone entirely — no lubricant is needed, applied, or at risk of migrating.
Noise — The Dominant Requirement
Office equipment operating noise (IEC 62368-1 / ISO 7779) must be below 45–52 dB(A) for class A office environments. The gear drive train is a major noise source in printers and copiers. Plastic gears’ viscoelastic damping absorbs impulsive mesh contact energy, and their lower elastic modulus (POM: 3.2 GPa vs steel: 200 GPa) reduces the dynamic stiffness of the gear mesh — resulting in 8–12 dB(A) quieter operation than equivalent steel gears without any change to gear ratio, pitch line velocity, or transmitted torque. No comparable noise reduction technique for steel gears at these small modules and low loads is commercially practical.
Lubrication-Free Operation
POM and PA66 plastic gears run dry at friction coefficients of 0.10–0.25 against each other and 0.08–0.15 against steel — acceptable for the low-to-medium loads of office equipment drives without external lubrication. This eliminates the lubricant contamination risk to paper, printed media, and optical scanning components. It also eliminates periodic relubrication from the maintenance schedule — a practical requirement for office equipment that must operate for years without maintenance attention from users.
Low Inertia and Precision Positioning
Plastic gear density (POM: 1.41 g/cm³; PA66: 1.14 g/cm³) is 80–85% lower than steel (7.85 g/cm³). In a laser printer paper feed drive with dozens of small gears, the cumulative inertia reduction from plastic vs steel gears allows the stepper motor to achieve accurate step positioning at higher stepping frequencies — directly improving paper feed accuracy and print registration. The lower inertia also reduces motor current demand during stop-start cycling, enabling smaller, less costly stepper motors throughout the printer drive train.
Plastic Gear Material Selection for Office Automation
Office Automation Drive Applications
Plastic Gear Failure Modes and Solutions in Office Equipment
COMMON FAILURE MODES
- →Tooth root fatigue fracture: most common in shredder and heavy copier drives — occurs when design torque is exceeded by paper jam shock loads above the material’s fatigue limit. Prevent with PA66 GF30 or GF40 and a service factor ≥ 2.0 for jam reversal loads
- →Creep deformation: POM and PA66 creep under sustained load at elevated temperature — the tooth tip dimension changes over years of intermittent loading in warm printer environments. Select PA66 GF30 or PPS for drives in heated zones above 60°C
- →Moisture absorption distortion: unfilled PA66 absorbs 2.5% moisture by weight, causing tooth OD to increase by ~0.3 mm per 100 mm diameter — enough to increase backlash or cause gear binding. Specify PA66 GF30 (0.7% absorption) or POM (0.2%) for gears in high-humidity environments
- →Mould shrinkage tooth profile error: plastic gears shrink 0.5–2.5% during injection moulding cooling. Tooth profile accuracy depends on precisely compensating shrinkage in the mould tool. Korea Ever-Power compensates mould geometry by material-specific shrinkage calculation and validates tooth profile by CMM before accepting the mould for production
DESIGN RECOMMENDATIONS
- →Use helical teeth (helix 10°–20°): helical plastic gears are 4–6 dB(A) quieter than equivalent spur plastic gears at the same pitch line velocity — important for printer and copier noise specifications
- →Minimum 17 teeth on pinion: plastic gear pinions with fewer than 15 teeth suffer from root undercut in standard tooth proportions — use profile shift x ≥ +0.3 for pinions with 10–14 teeth to avoid root weakening
- →Gate location on mould: gate directly on the gear face introduces residual stress that distorts the tooth profile after moulding. Specify submarine or pinpoint gate in the hub area, with balanced runners for multi-cavity moulds
- →Steel core hub for bore accuracy: plastic gear bores >10 mm in diameter should use a moulded-in steel insert hub for bore accuracy, dimensional stability, and shaft fit retention — pure plastic bores creep under the shaft press-fit force over time
Frequently Asked Questions
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