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Torque Rating - Sizing / Selection


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Rated Torque - Gearbox Sizing and SelectionRated Torque - Gearbox Sizing and Selection

S-N curve for a typical ferrous material (steel)

Fatigue phenomena of ferrous materials

Material fatigues after a limited numberof stress (load) cycles the, unless the

stress is limited to a stress level below

the Endurance Limit

At the Endurance Limit corresponding

stress level the material does not

fatigue it can endure unlimited load

cycles

The S - N curve shows, that the

transition to the Endurance Limit is at

2 x 106 1 x 107 Cycles N = 1 / SE N Number of cycles S Load (Stress)

E Exponent determines the

slope of the S-N curveFor the gears, and shafting is the value of

the exponent is between 8.7 und 84


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Bearing load ability

Rolling-element bearings (ball, roller, needle taper) do not have a defined

endurance limit.

Bearings are designed for a certain number of rotations / certain hours our

of L10 life

L10 life (90% survival probability; 10% failure )

L = (C / P) 3

N = 1 / SE N Number of cycles S Load (Stress)

E Exponent determines the

slope of the S-N curve

For the gears, and shafting is the value ofthe exponent is between 8.7 und 84

For bearings E =3 - 3.3.


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Proven gear design practice / recommended by standards ISO, DIN, AGMA, JIS,

Gears, shafts must be designed for endurance limit,

Nominal / Rated Torque shall be based on the endurance limit

Bearings shafts must be designed for certain hours life at defined (nominal

speed) and rated load

(For standard industrial gears AGMA recommends 5000 hrs L10 design life)


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NEUGART listed torque rating is the continuous duty torque (S1) - based on the endurance limit -

20 000 hrs L10 bearing life (planet needle bearing) at 100 rpm output speed ( PLS, WPLS, PLS-HP, PLF-HP, WPLE )

30 000 hrs L10 bearing life (planet needle bearing) at 100 rpm output speed ( PLE, PLFE, WPLE)

NEUGART developed a realistic, yet easy to use sizing and selection method to match up motors with

the appropriate size gearhead based on Inertia RatioInertia Ratio


Competitors,

almost all are listing purposely misleading and ill defined torque values such asNominal torque, Listed torque, Acceleration Torque etc. No clear reference is given at what

rpm and what L10 Bering life, frequently multiple values are listed

are recommending gearbox sizing and selection formulae using RMC (Root Mean Cube)load, (which is only applicable for rolling element bearing L10 life estimation) and fudge factors ;

are using artificially inflated torque ratings and in turn recommend in the sizing guidelines

to apply de-rating factors. RATING GAME


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Characteristic load cycle found in most

automation application

TTMM Motor Peak TorqueMotor Peak Torque

TTLRLR Non Dynamic Load TorqueNon Dynamic Load Torque

JJMM Motor Rotor InertiaMotor Rotor Inertia

JJLRLR

Load InertiaLoad Inertia

aa -- Angular AccelerationAngular Acceleration

(all referenced values to the motor shaft)(all referenced values to the motor shaft)

TM

- TLR

- JM

x a - JLR

x a = 0

a = (TM- TLR) / (JM+JLR)

TGR= TM- JMx a and (2a)

TGR= TLR+ JLRx

( TGR = (TM - TLR ) x (1- k ) + TLR with k = JM/ (JLR + JM )

InertiaMatchRatio IMR = JLR/ JM k = 1 / (IMR + 1)


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Determination of required gearbox torque rating if used servomotor is motor is

known

k = JM/ (JLR+ JM) = 1 / (IMR + 1)

TGR= (TM-TLR) x (1-k) + TLR

Example :

Inertial match JM=JLR IMR =1 k = JM/ (JLR+ JM)= 0.5


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