Gear reduction unit

01

Select by torque, speed and service factor

Boston Gear's 600 Series catalog says selecting a speed reducer needs three pieces of application information: the service factor or AGMA class of service, the output horsepower or torque, and the output speed or ratio. Design horsepower is application horsepower times the service factor, and design torque is application torque times the service factor; the reducer is then chosen from rating tables to meet output speed, service class and torque. [1]

Its service factor table gives 1.00 for AGMA Class I (moderate shock for no more than 15 minutes in 2 hours, or uniform load up to 10 hours a day); 1.25 and 1.50 for Class II (moderate shock up to 10 hours a day or uniform load over 10 hours; heavy shock for no more than 15 minutes in 2 hours or moderate shock over 10 hours); and 1.75 and 2.00 for Class III (heavy shock up to and over 10 hours a day). [1]

Its worked example takes a continuous-duty concrete mixer needing 8,000 lb-in at about 35 rpm for up to 8 hours a day, driven at 1,160 rpm, applies a 1.25 service factor to get 10,000 lb-in design torque, and selects a unit rated at or above that. It adds that an auxiliary drive such as a 3:1 chain reduces the torque needed at the reducer output in proportion. [1]

Editorial calculation: 10,000 lb-in is about 1,130 N·m; 1,160 rpm in to about 35 rpm out implies a ratio of about 33:1. [1]

Give the supplier the driven machine and its load type (uniform, moderate or heavy shock), hours per day, required output torque and speed, input speed and motor or input type, reduction ratio, mounting (foot, flange, shaft-mounted) and position, shaft arrangement, overhung or thrust loads, ambient conditions, lubrication and backstop needs.

02

Fix stages, input, mounting, loads and lubrication

Boston Gear offers its 600 Series helical gear speed reducers in single reduction and in double and triple reduction, as flanged (F600B) and non-flanged (600B) versions, with ordering codes covering reducer size, ratio, reduction stages, lubrication and NEMA motor mounting; backstops and other special needs require factory consultation. It warns that overhung shaft load must be checked when belt or chain drives are used to avoid premature shaft or bearing failure, and gives mounting positions and lubricants in the catalog. [1]

Flender describes its industrial gear units as available in single-stage and multi-stage designs for a wide range of applications. [2]

SEW-EURODRIVE's documentation calculates the overhung load F_R (N) on the gear unit shaft from the operating torque on the low-speed shaft (Nm), the mean diameter d₀ (mm) of the mounted transmission element and a transmission element factor f_Z that it says must be applied: 1.15 for gear wheels with fewer than 17 teeth, 1.40 for sprockets with fewer than 13 teeth, 1.25 for sprockets with fewer than 20 teeth, 1.75 for narrow V-belt pulleys, 2.50 for flat V-belt pulleys and 1.50 for toothed belt pulleys, the belt factors reflecting the influence of pre-tensioning. [4]

Editorial calculation: an output torque of 500 Nm (assumed) on a 200 mm mean-diameter element gives a tangential force of 2 × 500 / 0.200 = 5,000 N; with SEW's factor this is about 5,750 N for a small gear, 6,250 N for a sprocket under 20 teeth and 8,750 N for a narrow V-belt pulley, so a belt drive needs about 1.75 / 1.15 ≈ 1.5 times the shaft load capacity of a small-gear drive at the same torque and diameter. [4]

03

Compare efficiency by gear type before choosing

The US Department of Energy's guidebook Continuous energy improvement in motor driven systems (Advanced Manufacturing Office, 2014) defines gear reducer efficiency as output shaft power divided by input shaft power, with losses from tooth friction, lubricant churning, seals and windage, and notes that a 20:1 reducer multiplies motor torque by 20. Its Table 8-1 gives ratio and efficiency ranges by gear type. [3]

The guidebook explains that worm gears lose efficiency because of sliding rather than rolling contact, that their efficiency depends on ratio, output speed and motor rating and falls at lower input speed and partial load, and that they run hotter than other types; switching from mineral to synthetic lubricant can raise efficiency and extend life. It lists low first cost, compactness, high reduction, quiet running, overload capacity and self-locking as reasons worm gears are specified. It also notes that makers' catalogues may not state reducer efficiency, which can be derived from catalogue performance values. [3]

Editorial calculation: for a 10 hp (7.46 kW) drive at 75% load running 8,000 h a year (about 44,700 kWh at the gear input), moving from 80% to 95% gearbox efficiency cuts input energy by 1 − 0.80/0.95 ≈ 16%, about 7,100 kWh a year, using the DOE guidebook's savings formula.

Ask the supplier for gearbox efficiency at your ratio, speed and load (not only at rated load), the lubricant type, and the thermal rating, and compare helical or helical-bevel with worm options on lifetime energy.

04

Find gear reduction unit manufacturers

The manufacturer card below states what the reviewed source shows.

Ask any supplier for rated output torque and power at your speed and service factor, exact ratio, number of stages, efficiency, thermal rating, overhung and thrust load capacity, backlash, housing material, mounting positions, lubricant type and quantity, seals, weight and dimensions.

05

Trace what each part does

This is a functional reference built from the sources cited; it is not one maker's specification.

06

Fill the specification fields with values for your order

A gear reducer quotation needs values for your drive. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the load, speed and mounting data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Machine: [type; load class]
Duty: [hours per day; starts]
Output: [torque; rpm]
Input: [motor kW; rpm; flange]
Ratio: [required]
Mounting: [foot; flange; shaft; position]
Loads: [overhung; thrust]
Options: [backstop; lubrication]

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