EPNMRV Aluminium Worm Gearbox Series

Worm gear efficiency is determined primarily by the worm lead angle, which is a function of the number of thread starts and the gear ratio. Higher lead angles (more thread starts, lower ratios) produce higher efficiency. Lower lead angles (single-start worm, high ratios) produce lower efficiency but enable self-locking.

Across the EPNMRV range, typical dynamic efficiency (measured at 1,400 RPM input speed, steady state, oil temperature stabilised) follows this general pattern:

• Ratios 5:1 to 10:1 (multi-start worm): 85-90% efficiency
• Ratios 15:1 to 20:1 (double-start worm): 78-85% efficiency
• Ratios 25:1 to 30:1 (single-start worm): 65-75% efficiency
• Ratios 40:1 to 60:1 (single-start worm): 50-65% efficiency
• Ratios 80:1 to 100:1 (single-start worm): below 50% efficiency

Published efficiency values are measured under ideal conditions. Real-world efficiency is affected by running-in period (5-10% lower for the first 100-200 hours), partial-load operation, ambient temperature, and lubricant condition. For the exact efficiency values of each model at each ratio, refer to the Gear Parameters tab on the individual model page.

Self-locking is the ability of the worm gear to prevent the load from back-driving the motor when power is removed. It occurs when the friction at the worm-to-wheel contact exceeds the driving force of the load acting on the worm wheel.

Dynamic Self-Locking

Occurs when the motor is suddenly de-energised and the output must stop. The condition for dynamic self-locking is a dynamic efficiency below 0.5 (50%). In the EPNMRV range, this is reliably achieved at ratios of 40:1 and above with a single-start worm. At ratios of 25:1 to 30:1, self-locking is marginal and should not be relied upon without additional verification.

Static Self-Locking

Occurs when the gearbox is at rest and the load attempts to rotate the output shaft. The condition is a static efficiency below 0.5. Static efficiency is typically lower than dynamic efficiency, so a gearbox that self-locks dynamically will generally also self-lock statically.

Important Limitation

Self-locking should never be used as the sole safety mechanism for suspended loads or personnel-carrying applications. Vibration, shock loads, and temperature changes can temporarily reduce friction at the worm-to-wheel interface, potentially allowing the load to creep. For safety-critical applications, always install a separate holding brake or mechanical backstop in addition to worm gear self-locking.

Each EPNMRV model page contains a Selection Table showing the available combinations of input power, ratio, output speed, output torque, radial load capacity, and service factor. Follow this process to select the correct model and ratio:

Step 1: Define Your Output Requirements

Determine the required output torque (Nm) and output speed (RPM) at the driven shaft under worst-case operating conditions.

Step 2: Determine the Service Factor

Identify your load class: A (uniform, fs >= 1.0), B (moderate shock, fs >= 1.25), or C (heavy shock, fs >= 1.75). The service factor accounts for shock loading, start-stop frequency, and daily operating hours.

Step 3: Enter the Selection Table

Find a row where the output torque meets or exceeds your requirement AND the service factor (fs) meets or exceeds your load class. The corresponding input power, ratio, and model number define your selection.

Step 4: Verify Thermal Capacity

If the gearbox will run continuously in ambient temperatures above 30 degrees C, verify that the thermal power rating at your site temperature is sufficient. Contact our engineers for thermal rating verification at your specific ambient conditions.

Step 5: Confirm Mounting and Shaft Configuration

Check the Dimensions tab for housing mounting dimensions and the Output Shaft tab for shaft diameter and keyway. Verify the IEC motor flange code matches your motor. Specify the mounting orientation (B3, B6, B7, B8, V5, or V6) at time of order.

All EPNMRV gearboxes ship factory-filled with synthetic PAO 220 gear oil. For standard operating conditions (ambient temperature below 40 degrees C, continuous duty), this lubricant is suitable for the life of the gearbox with changes at 10,000-hour or 24-month intervals.

In Australian conditions where ambient temperatures regularly exceed 40 degrees C — particularly in the Pilbara, Bowen Basin, and inland New South Wales — oil change intervals should be halved (5,000 hours or 12 months). In dusty environments such as quarries and mine sites, fit a desiccant breather and monitor oil particulate count at 3-month intervals.

Do not use conventional sulphur-phosphorus EP additives formulated for steel-on-steel gears. These will chemically attack the bronze worm wheel, causing accelerated corrosive wear. Use only EP additives specifically formulated for bronze-on-steel worm gear contact.

Series Variants

• EPNMRV — Hollow input (IEC flange motor connection) + solid output shaft
• EPNRV — Solid input shaft (no flange) + solid output shaft
• EPNMRV-E — Hollow input (IEC flange) + worm shaft extending to rear (double-ended)
• EPNRV-E — Solid input + worm shaft extending to rear

Output Shaft Options

• DZ (single-side) — Standard solid output shaft, one side
• SZ (double-side) — Output shaft extending both sides of the housing
• F — Low-profile output flange
• FL — High-profile output flange

Optional Upgrades

• Viton (FKM) seals for high-temperature or chemical environments
• IP65 enhanced sealing
• FDA H1 food-grade lubricant
• Epoxy coating for corrosive atmospheres
• Torque arm for hollow-shaft mounting

Specify all options when requesting a quote.