Mechanical Design Data and Machine-Element Reference: Single-Phase Motor Type Comparison

Single-Phase Motor Type Comparison

Circlip Type Comparison

Seal Lip Material Comparison

Single-Phase Motor Selection Flowchart

flowchart TD
    A[Application Requirement] --> B{Starting Torque Needed?}
    B -->|Low - Fan Duty Only| C[Permanently Connected Capacitor]
    B -->|High| D{Running Efficiency Critical?}
    D -->|No - Standard Duty| E[Capacitor Start / Induction Run]
    D -->|Yes - Demanding Duty| F[Capacitor Start / Capacitor Run]
    C --> G{Speed Requirement?}
    E --> G
    F --> G
    G -->|High Speed ~3000 RPM| H[Two-Pole Motor]
    G -->|Standard Speed ~1500 RPM| I[Four-Pole Motor]
    H --> J[Select Frame Size in the supplied reference]
    I --> J
    J --> K[Verify Mounting Configuration: B3 Foot or B5 Flange]

Shaft Component Retention — Circlip Selection Process

flowchart TD
    A[Component Requires Axial Retention] --> B{Retention Location?}
    B -->|Inside Bore| C[Internal Circlip - Type 1300]
    B -->|On Shaft| D{Groove Possible?}
    D -->|Yes| E{Repetitive Disassembly Needed?}
    D -->|No| F[E-Clip - Type 1500 Push-On]
    E -->|Yes| G[External Circlip - Type 1400 with Lugs]
    E -->|No| H[No-Groove Type 1465 or E-Clip]
    C --> I[Determine Size from Shaft/Bore Tables]
    G --> I
    F --> I
    H --> I
    I --> J[Check Thrust Load: T_c and T_g]
    J --> K{Shaft Material ≠ 300 MPa Yield?}
    K -->|Yes| L[Apply Correction Factor to T_g]
    K -->|No| M[Use Lower of T_c and T_g]
    L --> M
    M --> N[Select Circlip Material for Environment]
    N --> O[Check Galvanic Compatibility with Groove Material]

Radial Shaft Seal Selection Process

flowchart TD
    A[Seal Required for Rotating Shaft] --> B[Determine Shaft Diameter]
    B --> C[Determine Operating Temperature]
    C --> D[Determine Shaft Speed / Surface Speed]
    D --> E[Determine Pressure Requirements]
    E --> F[Determine Media - Oil / Grease / Chemical]
    F --> G{Select Lip Material by Temperature & Media}
    G --> H[Select Seal Group in the supplied reference]
    H --> I[Verify from Operating Conditions Table]
    I --> J[Check Shaft Tolerance per ISO]
    J --> K[Check Shaft Finish - 10-20 µinch Ra]
    K --> L[Check Bore Tolerance per ISO/H8]
    L --> M[Verify Shaft Hardness ≥ Rc30]
    M --> N[Check Misalignment: STBM and DRO]
    N --> O[Confirm Seal Size from Catalogue Tables]

Seal Anatomy — Component Relationships

flowchart LR
    A[Outer Case / Shell] -->|Press-fits into| B[Bore Housing]
    C[Sealing Lip] -->|Contacts| D[Rotating Shaft]
    E[Garter Spring] -->|Maintains pressure on| C
    F[Inner Shell] -->|Protects| C
    G[Dust Lip] -->|Excludes| H[External Contaminants]
    A --- C
    A --- E
    A --- F
    A --- G

Key Terms Glossary

• B3 Mounting — foot-mounted motor configuration; motor bolted to base via feet
• B5 Mounting — flange-mounted motor configuration; motor attached via drive-end flange
• Bore Tolerance — the allowable dimensional variation of the housing bore into which a seal or bearing is fitted
• Capacitor Start / Capacitor Run — single-phase motor using both a start and run capacitor for optimum torque and efficiency
• Capacitor Start / Induction Run — single-phase motor using a start capacitor that disconnects at speed
• Circlip — a retaining ring (snap ring) that fits into a groove to prevent axial movement
• DRO (Dynamic Run-Out) — the deviation of a shaft from its true centre of rotation during operation
• E-Clip — a push-on external retaining clip that does not require a machined groove
• Fluoroelastomer — a premium seal lip material offering the widest temperature and chemical resistance range
• Full Load Torque — the torque output of a motor at its rated full load speed
• Galvanic Corrosion — electrochemical corrosion between dissimilar metals in electrical contact, accelerated by an electrolyte
• Garter Spring — a circular spring inside a radial shaft seal that maintains lip contact pressure on the shaft
• Key — a machine element inserted between a shaft and hub to transmit torque
• Keyway — the slot or groove machined into a shaft or hub to receive a key
• Lip Code — a letter designation identifying the elastomer material of a seal's sealing lip
• Nitrile (Buna-N) — the most commonly used seal lip material; good for mineral oils and greases
• Permanently Connected Capacitor — single-phase motor with a run capacitor always in circuit; suitable for fan duty only
• Power Factor — the ratio of real (useful) power to apparent power in an AC circuit
• Radial Shaft Seal — a dynamic seal that creates a barrier between a rotating shaft and a stationary housing
• STBM (Shaft-to-Bore Misalignment) — the static offset of the shaft centreline from the bore centreline
• Synchronous Speed — the theoretical speed of an AC motor determined by supply frequency and pole count (e.g., 3000 RPM for 2-pole at 50 Hz)
• T_c — maximum safe thrust load on the circlip itself
• T_g — maximum safe thrust load on the groove in the shaft or bore
• TIR (Total Indicator Reading) — the full range of dial indicator movement when measuring eccentricity or run-out

Quick Revision

• Single-phase motors: permanently connected capacitor (fan duty, low start torque), capacitor start/induction run (high start torque, moderate efficiency), capacitor start/capacitor run (high start torque, best efficiency)
• Two-pole = 3000 RPM synchronous; four-pole = 1500 RPM synchronous (at 50 Hz)
• Motor mounting: B3 = foot mount; B5 = flange mount
• Standard key sizes increase with shaft diameter — always refer to the shaft-to-key sizing table
• Keyway stress rules: shear = 0.75 × tensile; bearing = 1.5 × tensile
• Common shaft materials: plain carbon steel (1020–1045), stainless (304, 316, 420, 431), alloy (4140, 4340)
• Circlip types: 1300 (internal with lugs), 1400 (external with lugs), 1500/E-clip (push-on, no groove)
• Circlip thrust design: always use the lower of T_c (circlip load) and T_g (groove load)
• For non-300 MPa shaft material, multiply T_g by (yield point / 300)
• Check galvanic corrosion compatibility between circlip material/finish and groove material
• Seal lip material selection: R (nitrile, general purpose), V (fluoroelastomer, premium), S (silicone, wide temp), T (TFE, widest chemical resistance)
• Shaft finish for seals: 10–20 microinches Ra (0.25–0.50 µm), plunge ground, zero lead angle
• Shaft hardness for seals: minimum Rockwell C30
• Bore tolerance per ISO/H8; bore finish 125 microinches Ra (3.2 µm) or smoother
• Seal surface speed (FPM) is a better selection criterion than RPM
• STBM = static misalignment; DRO = dynamic run-out; both measured as half of TIR

POWER TRANSMISSION: GEARS & GEARBOXES

Worm Gearboxes & Geared Motor Units

Overview

This document covers worm gearbox selection and specification, including single and double reduction configurations, and geared motor unit selection for industrial drive applications. It provides comprehensive rating data for various nominal gear ratios, centre distances, input speeds, and mounting configurations, along with a step-by-step method for selecting an appropriate geared motor unit based on application requirements such as torque, speed, load classification, overhung load, and thrust load.

Key Concepts

• Worm Gearbox: A gear system using a worm (screw-type gear) meshing with a worm wheel to achieve high reduction ratios in a compact form
• Nominal Ratio: The designed speed reduction ratio between input and output shafts (e.g., 40:1, 50:1, 60:1, 70:1)
• Centre Distance: The distance between the centrelines of the worm shaft and the wheel shaft; determines gearbox physical size and torque capacity
• Thermal Rating: The maximum continuous input power (kW) a gearbox can handle without exceeding safe operating temperatures under standard conditions
• Mechanical Rating: The maximum input power (kW) based on the strength of the gears, shafts, and bearings — typically higher than thermal rating
• Efficiency (%): The ratio of output power to input power; worm gearboxes have lower efficiency at higher ratios due to sliding contact
• Output Torque (Nm): The rotational force available at the output shaft — specified for both thermal and mechanical limits
• Single Reduction: One worm and wheel pair providing a single stage of speed reduction
• Double Reduction: Two stages of worm and wheel reduction in series for very high overall ratios
• Overhung Load (OHL): A radial force applied to the output shaft by an attached mechanism (e.g., pulley, sprocket, gear)
• Axial (Thrust) Load: A force acting along the axis of the output shaft, caused by mechanisms such as helical gears
• Drive Classification: A rating system (1 to 4) that accounts for the severity of service based on load type and operating hours
• Load Classification: Categorisation of driven machinery as Steady (S), Medium Impulsive (M), or Highly Impulsive (H)
• Geared Motor Unit: A pre-assembled combination of an electric motor and a gearbox, designed as a compact drive solution
• Force Feed Lubrication: Required for operation in shaded (high-load) areas of rating tables; uses a pump to circulate lubricant
• Oil Cooler: External cooling device that allows higher ratings beyond standard thermal limits
• Taper Lock Bush: A mechanical fastening method for mounting pulleys, sprockets, or gears onto shafts using a tapered interference fit

Single Reduction Worm Gearbox Ratings

Nominal Ratio 40:1

• Input Speed: 1800 rev/min (output 45 rev/min) down to 100 rev/min (output 2.5 rev/min)
• Centre Distances Available: 10, 12, 14, 17, 20, 24, 28 (units correspond to shaft separation)
• Key Observations:
  • At 1800 rev/min input, thermal input ranges from 28 kW (CD 10) to 216 kW (CD 28), mechanical input from 33 kW to 372 kW
  • Efficiency improves with increasing centre distance: 86% (CD 10) to 89% (CD 28) at 1800 rev/min input
  • At lower input speeds (e.g., 500 rev/min), thermal input drops significantly (10–105 kW), but mechanical input becomes proportionally larger relative to thermal
  • At 100 rev/min input, only mechanical ratings are listed (no thermal rating), with efficiency dropping to 68–77%
  • Maximum output torque (single key): ranges from 11,200 Nm (CD 10) to 72,000 Nm (CD 28)
  • Maximum output torque (standard shaft): ranges from 15,800 Nm (CD 10) to 146,400 Nm (CD 28)

Nominal Ratio 50:1

• Input Speed: 1800 rev/min (output 36 rev/min) down to 100 rev/min (output 2 rev/min)
• Key Observations:
  • Thermal input ratings are lower than 40:1 at the same centre distance due to increased sliding losses
  • At 1800 rev/min, thermal input ranges from 23 kW (CD 10) to 170 kW (CD 28)
  • Efficiency is lower than 40:1: 83–86% at 1800 rev/min, dropping to 64–72% at 100 rev/min
  • At 250 rev/min input, efficiency drops to 70–78%
  • Maximum output torque values remain the same as 40:1 (they are gearbox-size dependent, not ratio dependent)

Nominal Ratio 60:1

• Input Speed: 1800 rev/min (output 30 rev/min) down to 100 rev/min (output 1.6 rev/min)
• Key Observations:
  • Further reduction in thermal input compared to 50:1: 21 kW (CD 10) to 149 kW (CD 28) at 1800 rev/min
  • Efficiency continues to decrease: 81–84% at 1800 rev/min, down to 61–69% at 100 rev/min
  • Mechanical ratings become increasingly dominant at low input speeds
  • At 250 rev/min input, efficiency is 67–75%

Nominal Ratio 70:1

• Input Speed: 1800 rev/min (output 25.7 rev/min) down to 100 rev/min (output 1.4 rev/min)
• Key Observations:
  • Lowest thermal input ratings among the four ratios: 18 kW (CD 10) to 133 kW (CD 28) at 1800 rev/min
  • Efficiency is the lowest: 78–82% at 1800 rev/min, dropping to 55–65% at 100 rev/min
  • At very low input speeds (100 rev/min), efficiency can be as low as 55%
  • Higher ratios generate more heat due to greater sliding between worm and wheel

General Trends Across Ratios

Important Notes from Rating Tables

• Ratings in shaded areas require force feed lubrication
• All ratings are based on mineral oils; synthetic lubricant ratings available on request
• Oil coolers can provide higher ratings than those listed
• Two keys must be specified for the wheel and output shaft when maximum output torque for single key is exceeded
• High tensile steel output shaft must be specified when maximum output torque for standard shaft is exceeded

Double Reduction Worm Gearbox Ratings (Mineral Oil)

Input Speed: 1450 rev/min

• Nominal Ratios Available: 75:1 to 4900:1
• Output Speeds: 19.0 rev/min (ratio 75) down to 0.30 rev/min (ratio 4900)
• Centre Distances Available: 10, 12, 14, 17, 20, 24, 28
• Key Observations:
  • At ratio 75, input power ranges from 14.7 kW (CD 10) to 156 kW (CD 28), efficiency 83–88%
  • At ratio 150, input power ranges from 13.3 kW (CD 10) to 186 kW (CD 28), efficiency 79–83%
  • At ratio 500, input power ranges from 6.2 kW (CD 10) to 68.2 kW (CD 28), efficiency 67–76%
  • At ratio 1000, input power ranges from 4.1 kW (CD 10) to 37 kW (CD 28), efficiency 59–70%
  • At ratio 4900, input power ranges from 1.2 kW (CD 10) to 12.0 kW (CD 28), efficiency 33–43%
  • Output torque reaches maximum capacity at larger centre distances (up to 165,000 Nm at CD 28)
  • Efficiency drops dramatically at very high ratios — as low as 33% at ratio 4900, CD 10

Input Speed: 960 rev/min

• Same ratio and centre distance options as 1450 rev/min
• Key Observations:
  • Input power ratings are lower than at 1450 rev/min across all configurations
  • At ratio 75, input power ranges from 11.9 kW (CD 10) to 119 kW (CD 28), efficiency 81–87%
  • At ratio 500, input power ranges from 4.6 kW (CD 10) to 44.3 kW (CD 28), efficiency 64–74%
  • At ratio 4900, input power ranges from 0.9 kW (CD 10) to 8.2 kW (CD 28), efficiency 31–40%
  • Output torque values reach the same maximums as 1450 rev/min tables
  • Efficiency is slightly lower at 960 rev/min compared to 1450 rev/min for the same ratio

Gearbox Dimensions and Configurations

Mounting Types

Unit Size Range

• Available sizes: 10, 12, 14, 17 (single reduction also includes 20, 24, 28)
• Sizes are designated by centre distance number
• Double reduction units add a second worm/wheel stage, increasing overall envelope

Key Dimensional Parameters

• A — Overall length (mm)
• B — Height to shaft centre (mm)
• C — Width across mounting feet (mm)
• D — Mounting foot length (mm)
• F — Mounting hole pattern (format: pitch × number / bolt size)
• G — Output shaft details (bore, keyway, etc.)
• H, J — Additional envelope dimensions
• K — Bolt hole size (for mounting)
• Oil Capacity — Approximate litres of lubricant required
• Weight — Approximate mass in kg (quoted without oil)

Wormshaft and Wheelshaft Details

• E1 — Wormshaft diameter
• V1 — Wormshaft length
• W1 — Wormshaft bearing span
• X1, X2 — Wormshaft extension details
• Tapped Hole — Thread size for input shaft connection (e.g., M20×42, M24×50, M30×60)
• E2 — Wheelshaft (output) diameter
• V2 — Wheelshaft length
• W2 — Wheelshaft bearing span
• Y1, Y2 — Wheelshaft extension details

Dimensional Data Summary (Single Reduction — Foot Mounted Underdriven)

Important Configuration Notes

• Non-reversible units require a sprag clutch backstop to be fitted
• Units with central mounting pads use a bolt hole diameter designated as dimension K
• Shaft-mounted types use output sleeve details instead of foot mounting dimensions
• For units with flange mounting motors, refer to separate motor-specific data
• Double reduction units have two output keys as a standard feature
• Second reduction units may have blank central mounting pads

Geared Motor Units

Overview

• Designed for relatively low power applications (approximately 0.1 to 4.0 kW motor power input)
• Only foot-mounted geared motor units are covered; output is via bored bush with key or output shaft extension
• Units can also be specified as a free-standing unit (gearbox without motor) coupled to a designer's chosen motor
• Five gearbox sizes available (designated by frame size number: 11, 17, 22, 26, 30)
• 12 gear ratios available per size, ranging from 5:1 to 70:1
• All units fitted with 4-pole motors (nominal speed 1400–1420 rev/min), giving output speeds from 288 rev/min down to 20 rev/min
• 11 motor sizes available, ranging from 0.12 kW to 4.0 kW
• Each gearbox size can be fitted with multiple motor sizes according to power requirements
• Total of 104 power and speed combinations available

Note: The smallest motor size (0.12 kW) is not a preferred size and may have extended lead times.

Geared Motor Unit Selection Method

Step 1: Establish Mechanical Data

• Determine the type of output (driven) machinery
• Establish maximum (design) torque, power, and speed (including tolerance range on speed if given)
• Determine duration of service: continuous or intermittent
• Determine average number of hours per day of operation

Step 2: Determine Load Classification

• From the load classification table, identify whether the driven machinery is:
  • S (Steady) — e.g., conveyors (uniformly loaded), fans, generators
  • M (Medium Impulsive) — e.g., car dumpers, dough mixers, machine tools, textile dryers
  • H (Highly Impulsive) — e.g., crushers, hammer mills, rubber mills, tumbling barrels

Step 3: Determine Drive Classification

• Cross-reference:
  • Load classification (S, M, or H) from Step 2
  • Average hours per day of operation (Under 3 hours, 3–10 hours, Over 10 hours)
• This yields a Drive Classification number from 1 to 4

Step 4: Select Unit from Data Tables

• Using the drive classification from Step 3, go to the appropriate data table
• Select the unit based on required output speed and output power (or torque)
• The data tables provide: output power (kW), output torque (Nm), and recommended gearbox size for each motor power and gear ratio

Step 5: Check Overhung Load

• If a gear, pulley, chain-wheel, flywheel, or other mechanism is directly attached to the output shaft, calculate the overhung load (radial force on the shaft)
• Use the approximate formula:

$$F = \frac{2 \cdot f \cdot T}{d} = \frac{60 \cdot f \cdot P}{\pi \cdot d \cdot N}$$

Where:

• F = overhung load (N)

• T = output shaft torque (Nm) — use design value, not selection table value

• P = output shaft power (W) — use design value, not selection table value

• d = pitch circle diameter (PCD) of pulley, sprocket, or gear (m)

• N = output shaft speed (rev/min)

• f = drive application factor:

  • 1.0 for chain drive or toothed belt
  • 1.25 for gear drive
  • 1.5 for vee (wedge) belt
  • 2.0 for flat friction belt

• Compare calculated overhung load to the allowable overhung load from the capacity table

• Overhung load capacities assume the load is applied mid-way along the shaft (at dimension A)

• If the allowable value is exceeded, either choose a larger unit or use an intermediate shaft (layshaft) with its own bearings and a flexible coupling

Step 6: Check Thrust (Axial) Load

• If a helical gear or other mechanism creates an axial load on the output shaft, verify it does not exceed the allowable axial load from the capacity table
• If exceeded, choose a larger gearbox or use an intermediate shaft with bearings to absorb the axial load

Step 7: Check Output Shaft Dimensions

• Verify the output shaft diameter is suitable for the attached mechanism (e.g., bore of pulley or sprocket)
• Check mounting bolt sizes, bolt hole locations, and centre distances from the dimension data

Step 8: Specify the Unit

• Specify: gearbox size, gear ratio, output speed, and motor details (frame size, power rating)
• Motor data includes: rated speed, current at rated voltage, moment of inertia, and rotor mass

Motor Ratings and Performance Data

Motor Flange and Shaft Dimensions

Overhung Load Capacities (N)

• Load capacities assume resultant load applied mid-way along the shaft (dimension A)
• Dimension A varies by gearbox size: 60 mm (Size 11), 75 mm (Size 17), 95 mm (Size 22), 115 mm (Size 26), 140 mm (Size 30)

Service Factors

Starts per Hour Factor (f_s)

Worked Example: Geared Motor Unit Selection

Problem: An industrial textile dryer operates for 12 hours/day, driven by a geared motor unit via a wedge belt drive. The wedge belt pulley has a PCD of 160 mm and will be attached to the output shaft via a taper lock bush with a maximum bore size of 50 mm. The torque at the pulley is 200 Nm and the required speed is 35 ± 2 rev/min.

Solution:

1. Output torque = 200 Nm at 35 ± 2 rev/min

   • Required output power: P = T × ω = 200 × (π × 35 / 30) = 0.733 kW

2. Load classification: Textile dryer = M (Medium Impulsive)

3. Drive classification: Load M, 12 hrs/day (over 10 hours) → Drive Classification 3

4. Unit selection: From Drive Classification 3 data table, select a unit with output speed 36 rev/min, ratio 40:1, output torque 225 Nm — output speed 36 rev/min is within the tolerance of 35 ± 2 rev/min. Unit size: Size 30.

5. Overhung load check:

   • F = (2 × f × T) / d = (2 × 1.5 × 200) / 0.16 = 3750 N
   • Allowable OHL for Size 30 at 50 rev/min = 6900 N; at 25 rev/min = 7000 N
   • 3750 N < 6900 N → OK, no interpolation necessary

6. Thrust load: No helical gear → No axial load → OK

7. Output shaft diameter: Size 30 output shaft = 40 mm (nominal)

   • Maximum pulley bore = 50 mm → 40 mm < 50 mm → OK
   • Bolt holes: 14.5 mm diameter → use M14 bolts
   • Bolt hole centre distances: 160 mm (side) and 130 mm (end)

8. Specification: Size 30, Ratio 40:1, Output Speed 36 rev/min, D90S frame motor (1.1 kW)

Single vs Double Reduction Gearboxes