For a conveyor that runs many hours, a helical or helical-bevel gearbox is usually the better engineering choice. Its higher efficiency reduces electricity losses and heat over the machine’s life. A worm gearbox is often the better fit when you need a compact 90-degree drive, a high reduction ratio in one stage, quiet operation, shock tolerance or conditional resistance to back-driving.
For a lift or hoist, neither gearbox type is safe to select by label alone. Confirm the exact unit’s back-driving behavior, thermal and load ratings, and braking requirements. A gearbox that happens to resist back-driving must not be treated as the sole device holding a suspended load; use the rated mechanical or electromagnetic brake and the other safeguards required by the design.
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The short decision guide
| Requirement | Best starting point | Reason and qualification |
|---|---|---|
| Horizontal conveyor running many hours per day | Helical or helical-bevel | Higher efficiency and better thermal behavior usually lower operating cost and heat accumulation. |
| Inclined conveyor where rollback matters | Helical with a rated brake, or a verified self-locking worm | Self-locking is conditional on the worm geometry, ratio, friction, lubrication, load and operating conditions; it is not automatic. |
| Very compact 90-degree layout | Worm, or bevel-helical if its efficiency justifies the extra size or cost | Worm units naturally provide right-angle output in a compact package. |
| Very high reduction in one stage | Worm | Worm units commonly cover high single-stage ratios; helical reducers normally add stages for the same reduction. |
| Lift or hoist with a suspended load | Whichever exact model passes the safety review, with a rated brake | Verify back-driving and stopping performance for the selected unit, orientation and load. Do not rely on a generic “self-locking” claim. |
The right answer depends on duty cycle, speed, torque, ratio, shaft arrangement, ambient temperature, starting frequency, shock loading and the consequences of a stopped motor. Compare the complete installed system rather than the gearbox purchase price.
How the two gearboxes transmit torque
Worm gearbox: sliding contact and a compact right angle
A worm drive uses a screw-like worm that meshes with a toothed wheel. The worm and wheel slide against one another over much of the contact path. That sliding makes it possible to obtain a large reduction in one stage and to place the input and output shafts at 90 degrees, often in a small housing.
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The same sliding creates friction. Losses become heat in the lubricant and housing, and efficiency changes with ratio, input speed, load, temperature, lubricant and break-in condition. A rough efficiency assumption can therefore produce a misleading comparison; Nidec Drive Technology America cautions that worm efficiency should be evaluated for the actual operating point.
Helical gearbox: progressively meshing angled teeth
Helical gears have teeth cut at an angle. The teeth enter and leave mesh progressively instead of engaging across their full width at once. Contact is more rolling-dominant than in a worm set, so sliding losses are generally lower, noise is typically low and the gearbox can reject more of its input power as useful output.
Helical teeth create axial thrust as well as radial load. The reducer’s bearings and the driven machine’s mounting must be rated for those forces. Large reductions normally require two or more helical stages, which increases length, parts count or cost. A bevel-helical arrangement can provide a right-angle output when a plain inline or parallel-shaft helical unit will not fit.
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| Characteristic | Worm gearbox | Helical gearbox |
|---|---|---|
| Illustrative efficiency range | 50–90%, depending on design and operating point | 95–99% in one manufacturer comparison; Nercon reports 94–98% per helical stage |
| Published conveyor example | Approximately 64% at 30 RPM output and a 60:1 ratio in a Nercon example (2015) | 94–98% per stage in the same published guidance |
| Common single-stage ratio range | 5:1–100:1 | 1.5:1–10:1; multiple stages are used for larger reductions |
| Heat behavior | More frictional heat, especially at high ratio, speed or continuous duty | Lower losses per stage generally make continuous operation easier to cool |
These figures are illustrative published ranges, not guarantees for a particular reducer. A 64% efficient drive turns a much larger share of motor input into heat than a 94–98% drive. Over thousands of conveyor hours, that difference affects motor electricity, enclosure temperature, lubricant life and the risk of thermal overload. Ask the supplier for the selected model’s efficiency curve and thermal rating at your speed, ratio, load and ambient temperature.
Do not multiply stage efficiencies casually. A multistage helical reducer’s total efficiency is the product of the individual stage efficiencies plus bearing and seal losses. Conversely, a worm’s efficiency can improve or deteriorate materially with lead angle, speed, load, lubricant and temperature. Use the manufacturer’s data at the actual duty point.
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Choosing a gearbox for conveyors
Continuous horizontal conveyors
Start with a helical or helical-bevel reducer when the conveyor runs for long shifts or around the clock and the shaft arrangement permits it. The higher efficiency limits heat buildup and reduces the recurring electricity penalty. Confirm service factor for starts, stops, accumulated product, belt tension and any jam or overload condition.
A worm reducer can still be sensible for a short or intermittent conveyor, a machine with a very tight right-angle footprint, or a line where low initial cost and quiet shock-tolerant operation outweigh energy losses. Check its thermal capacity rather than assuming that the motor’s nameplate power is enough.
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An incline introduces a rollback question whenever motor torque disappears. A worm may resist back-driving in some combinations of lead angle, ratio, friction and load. That behavior is conditional, can change with wear and lubrication, and may disappear under vibration or a different orientation. Specify a brake or other anti-rollback device unless the manufacturer has documented the required holding performance for the exact reducer and conveyor.
Helical drives are not inherently self-locking. If an inclined conveyor uses one, size a spring-applied or otherwise suitable brake for the stopping and holding duty, and coordinate it with the conveyor’s emergency-stop and control logic.
Shock, starts and reversing
Worm sets can absorb certain shock loads because of their sliding contact and compact construction, but the allowable shock, overhung load and starts per hour are model-specific. Helical drives transmit torque efficiently but still need a service factor for impact, frequent reversing and high acceleration. Obtain permissible overhung and thrust loads, starting torque limits and brake-cycle ratings from the reducer supplier.
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Choosing a gearbox for a lift or hoist
A lift is a safety-critical application because a loss of motor torque can allow a suspended load to move. Start with the load path and required stopping performance, then select the gearbox and brake as a coordinated system.
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In theory, a worm gear is considered self-locking when the coefficient of friction between the gear and worm is greater than the tangent of the worm’s helix angle. Nidec Drive Technology America states: “In theory, as long as the coefficient of friction between the gear and the worm is larger than the tangent of the worm’s helix angle, the worm gear is considered self-locking and will not back drive.”
That is a condition, not a universal rating. Innomotics notes that helical-worm units are not universally self-locking, and SEW-EURODRIVE relates self-locking to stage efficiency and ratio. Actual back-driving depends on the exact gear geometry, ratio, lubricant viscosity, temperature, wear, load direction, vibration and installation orientation. A unit that resists back-driving when new and cool may behave differently after warming or wear.
Required lift safeguards
- Obtain the manufacturer’s back-driving or holding data for the exact model, ratio, orientation and load direction.
- Use a brake rated to hold and stop the maximum suspended load, including the required safety factor and stopping cycles.
- Verify brake torque, release voltage, response time, wear adjustment and the behavior on power loss.
- Include the applicable overspeed, limit, overload, emergency-stop and mechanical load-retention controls for the lift design and jurisdiction.
- Have a qualified engineer validate the complete load path, not just the gearbox catalog selection.
If a lift must remain stationary when the motor is de-energized, design that requirement around the rated brake and safety system. Treat any gearbox self-locking effect as an additional characteristic only after it has been documented and tested.
Mechanical and installation differences
| Factor | Worm | Helical or bevel-helical |
|---|---|---|
| Shaft arrangement | Naturally 90-degree input/output; compact footprint | Usually inline or parallel shaft; bevel-helical versions provide right-angle output |
| Reduction strategy | High ratio commonly available in one stage | Lower ratio per stage; larger reductions normally need multiple stages |
| Contact and noise | Sliding contact; generally quiet and able to tolerate some shock | Progressive tooth engagement; typically smooth and low-noise |
| Backlash and holding | Backlash and self-locking behavior vary by model and wear | Not inherently self-locking; brake normally provides holding |
| Loads on bearings | Model-specific radial and thrust loads | Helical tooth angle creates axial thrust that bearings must carry |
Mounting orientation affects oil level, seal loading and cooling. Check the installation drawing for approved orientations, shaft overhung load, coupling alignment, foundation stiffness and the required lubricant. A right-angle worm can save space but may need more cooling capacity than a similarly powered helical unit.
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Total cost of ownership
The lowest purchase price is not necessarily the lowest-cost drive. Compare these items over the planned service life:
- Electricity: motor input power includes gearbox losses, so a less efficient reducer costs more whenever the conveyor is running.
- Heat management: frictional heat can require larger housings, fans, oil coolers or reduced ambient-temperature limits.
- Lubrication: confirm oil type, fill level, break-in procedure, inspection interval and replacement interval. Mixing incompatible lubricants can damage seals or gears.
- Parts and maintenance: include seals, bearings, worm wheels, brakes and the labor needed to change them.
- Downtime: estimate the cost of a failed reducer, a thermal trip, a brake adjustment or a difficult-to-access installation.
- Safety hardware: an inclined conveyor or lift may require a brake, backstop, guarding and controls regardless of gearbox type.
For a duty-cycle comparison, request losses and thermal limits at the actual output speed and torque rather than relying on a headline efficiency range. A worm’s lower first cost can be offset by years of additional electricity and heat-related maintenance; a multistage helical unit’s higher purchase price can be justified by continuous operation.
A practical selection procedure
- Define the driven load. Record conveyor belt pull or lift load, drum or pulley diameter, incline, acceleration time, starts per hour, reversing, shock and the maximum overhung and thrust loads.
- Calculate output speed and torque. State the required speed at the shaft, not just the motor speed. Include acceleration torque, friction, gravity on an incline and the desired service factor.
- Choose the shaft layout. Decide whether inline, parallel-shaft or right-angle output fits the frame. If right-angle is mandatory, compare a compact worm with a bevel-helical alternative.
- Shortlist ratio and motor combinations. Use the reducer’s actual ratio, rated output torque and permissible input speed. Do not infer a model’s rating from a similarly named series.
- Check efficiency and thermal rating. Obtain the manufacturer’s efficiency curve, thermal capacity and ambient-temperature limit at the intended duty cycle.
- Check mechanical ratings. Verify service factor, radial and axial loads, shaft diameter, coupling fit, shock rating and allowable starts or reversals.
- Address holding and stopping. For an incline or lift, specify brake torque, stopping time and power-loss behavior. Require written back-driving data for the exact worm unit if self-locking is part of the concept.
- Confirm lubrication and mounting. Match oil or grease, fill quantity, orientation, sealing, cooling and maintenance access to the installation drawing.
- Compare life-cycle cost. Add purchase, motor energy, cooling, lubricant, replacement parts, brake maintenance and the financial impact of downtime.
- Commission and verify. Check running temperature, noise, vibration, current, brake release and stopping behavior under the real load. Record baseline values for future maintenance.
Common selection mistakes and fixes
“A worm is self-locking, so no brake is needed.”
Why it fails: self-locking depends on geometry, friction, ratio, lubricant, temperature, wear and load direction. Fix: use a rated brake and obtain model-specific back-driving data.
“The gearbox efficiency is one fixed percentage.”
Why it fails: worm losses vary substantially with speed, ratio, load and temperature, while multistage helical efficiency must account for every stage and bearing loss. Fix: request an efficiency curve and thermal rating at the operating point.
“The motor has enough horsepower, so the reducer is suitable.”
Why it fails: output torque, service factor, starts, overhung load, thrust and thermal capacity can limit a reducer before motor power does. Fix: size from the driven load and verify every mechanical rating.
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“A right-angle worm is always the smallest overall solution.”
Why it fails: a worm may need extra cooling or a larger frame for continuous duty, while a bevel-helical unit may deliver more output per unit of heat. Fix: compare the complete envelope, mounting, cooling and service access.
“An inclined conveyor only needs a gearbox that stops quickly.”
Why it fails: stopping and holding are different requirements, especially after power loss. Fix: specify anti-rollback hardware, brake torque and control interlocks separately.
Bottom-line recommendations by application
- Long-running horizontal conveyor: select a helical reducer first, then confirm ratio, thermal capacity, service factor and shaft loads.
- Right-angle conveyor with intermittent duty: a worm reducer may offer the best packaging and purchase-cost balance if its thermal rating is adequate.
- High-ratio, low-speed conveyor: compare a single-stage worm with a multistage helical or bevel-helical unit using life-cycle energy and heat, not ratio alone.
- Inclined conveyor: choose the architecture that fits the layout, but make rollback protection a separately verified brake or backstop requirement.
- Lift or hoist: select the exact gearbox, brake and safety controls as one engineered system; never rely on a generic worm “self-locking” label.
Frequently Asked Questions
Can a helical gearbox be used in a right-angle conveyor drive?
Yes. A bevel-helical reducer provides a right-angle layout while retaining the helical tooth stages’ efficiency advantages. Confirm its envelope, ratio, axial and radial load ratings, and thermal rating against the worm alternative.
Does a higher worm ratio always mean lower efficiency?
Not as a universal rule, but worm efficiency generally changes with ratio, lead angle, speed, load, lubricant and temperature. Use the selected manufacturer’s efficiency data at the actual operating point rather than inferring performance from ratio alone.
What information should I send a gearbox supplier?
Provide motor speed and power, required output speed and torque, duty hours, starts and reversals per hour, conveyor incline or lift load, acceleration, shock, ambient temperature, shaft layout, mounting orientation, overhung and thrust loads, and whether a brake or verified anti-rollback function is required.
Can I replace a worm reducer with a helical reducer without changing the machine?
Usually not as a direct swap. Shaft position, flange or foot mounts, output speed, rotation, coupling, lubrication, axial loads and brake arrangement may all change. Treat it as a mechanical redesign and verify alignment and guarding before installation.
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