Four types of torque ratings are given for most joint sizes.

Continuous torque (Tc) is the bearing life rating of the universal joint. This torque is based on the B-10 life of the universal joint bearings. The life torque values listed are based on 5000 hours B-10 bearing life at 3′ misalignment and 100 RPM. B-10 life is defined as the minimum life expectancy for a 90% probability of survival. Typically the average actual operating life of the bearings is 5X the calculated B-10 life.

Endurance Torque (Te) is the normal rating for fully reversed torque based on material strength.

Catalog Torque (Ts) is the short duration representing the capability of the joint to withstand stop-start service.

Peak Torque (Tcs) is the functional limit torque based on the yield strength capacity of the joint.

The torque ratings based on material strength. When approaching these limits the capacity of the desired flange connection should be verified. When the service torque (Tk) approaches the endurance torque (Te) or when the maximum torque approaches the peak torque capacity (Tcs) of the universal joint, a reinforced flange connection may be required. Please consult the factory for appropriate solutions.

Universal Joint Selection

I. Calculate application torque (Ta) and service torque (Tk).

Ta = HP(63025)/N
N = Speed (RPM)
Tk = Service Torque = Ta x Service Factor (Table 3)
Tk must be less than Te for reversing torque applications.

II. Check to see if life is sufficient.

Lh = [1.5×106/ [AxN] ] [Tc/Ta] 10/3
Lh = B-10 life in hours
A = operating angle in degrees
N = speed (RPM)
Tc = continuous torque
Ta = application torque

III. Duty Cycle: In application where the torque, speed and operating angle vary predictably during a typical load cycle or operational sequence, a duty cycle can be determined. First the load cycle must be analyzed and divided into groups of fixed combinations of torque, speed and operating angle. These groups represent percentages of the total operating time of the load cycle. Life expectancy can then be calculated using Miner’s Theory, which takes into account the cumulative effect resulting from operating at varying conditions.

Total Life Expectancy = N1/L1 + N2/L2 + N3/L3 + . . . + Nm/Lm
N1 = fraction of total, time at operating condition 1
L1 = life expectancy at operating condition 1 (hours)
M = total number of operating conditions

IV. Determine Peak Torque conditions.

Ts must exceed the short duration operating torque.

V. Other considerations: There are many other items that can determine the size of a universal joint.

These include:

  • Diameter and length limitations.
  • Bore size.
  • Equipment restrictions on forces and moments.
  • Speed limits (see tables 1 and 2)
    • due to mass acceleration as a function of misalignment
    • critical speed of center shaft

Telescopic splines are available on ST and SC designs. Telescopic sections are required for length compensation between two end connections. They will compensate for length changes due to machine articulation, temperature changes, frame flexure . . . etc.

For increased durability induction hardened, nitrided or coated splines may be required and are available on request.

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