Technical Data  Mechanical protectors 　Selection

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Shock Guard 　Selection

Shock Guards are most effective as a safety device when they are installed closest to the driven machine where an overload is likely to occur.

In principle, avoid using the Shock Guard with personnel transport devices and lifting equipment.

If they are to be used, measures should be taken by the equipment side to prevent serious injury or death from falling objects.

1. Selecting the trip torque

TP = TL × S.F = 60000 × P 2π・n × S.F   TP = 974 × P n = × S.F

  • TP = Trip torque N・m{kgf・m}
  • TL = Load torque N・m{kgf・m}
  • P = Power transmission kW
  • S.F = Service factor
  • n = Speed r/min
  • (1) Set the trip torque equal to the maximum amount of torque that can be applied (limit value) based on such conditions as the strength of the machine and load.
  • (2) If the limit value is not clear, calculate the rated torque from the rated output and the shaft rpm onto which the Shock Guard will be installed. Then, multiply by the service factor in Table 1 depending on the operating conditions to determine the trip torque.
Table 1
S.F Operating conditions
1.25 Normal start/stop or intermittent movement
1.5 Severe shock load or forward/reverse movement

2. When the rpm is relatively high

When the rpm is relatively high (500 r/min or higher) or when the load inertia is large, depending on the motor’s starting torque, there is a chance the Shock Guard will trip.

In this case, determine the inertia ratio, calculate the torque acting on the Shock Guard during start-up, and multiply this by the service factor to obtain the trip torque.

K = IL + It Is   K = GD2L + GD2t GD2s   Tt = K・TS + TL 1 + K Tp = SF・Tt

  • K：Inertia ratio
  • Is：Moment of inertia on the drive side (kg・m2)
  • {GD2s：Drive side GD2(kgf・m2)}
  • IL：Moment of inertia on the load side (kg・m2)
  • {GD2L：GD2 of the load side (kgf・m2)}
  • It：Shock Guard moment of inertia (kg・m2)
  • {GD2t：Shock Guard GD2 (kgf・m2)}
  • Ts：Starting torque of the motor (N・m){kgf・m}
  • Tt：Torque acting on Shock Guard during start-up (N・m){kgf・m}
  • TL：Load torque (N・m){kgf・m}
  • TP：Trip torque (N・m){kgf・m}
  • S.F.：Service factor

Note )Use the equivalent value to the shaft in which the Shock Guard is installed for each moment of inertia, GD2, and torque value.

3. Precautions when deciding the trip torque

If the torque acting on the Shock Guard at start-up becomes larger than the load torque, the trip torque value will also become large, causing a problem in overload protection.
(The trip torque is too large for the load torque. )

In this case install the Shock Guard as close to the load side as possible.

4. Determination of model No.

Choose a model where the calculated trip torque is within the minimum to maximum torque range.

5. Check the bore diameter

Confirm that the shaft to which the Shock Guard will be installed is within the allowable bore diameter range of the selected Shock Guard model. (Refer to the dimensions table.)

If the shaft diameter is larger than the allowable bore range, select a model one size larger that uses a weak spring.

6. Confirming the rpm

Confirm that the Shock Guard rpm used is within the maximum rpm value in this catalog.

Notes for Design

  • * When selecting the size based on the torque, make sure that the preset torque is 80% or less of the upper limit of the Shock Guard’s torque capacity. This is to allow a margin for readjustment, considering the decline in torque due to wear after many years of use.
  • * When using an induction motor or a similar device as the drive motor, it’s important to consider the starting torque. In addition, if the machine generates strong vibrations, these vibrations should be considered when setting the torque. This is because the Shock Guard may trip in response to a momentary overload, resulting in a trip at a torque lower than the calculated torque.
  • * When using the Shock Guard in intermittent drive units such as indexers, if the difference between the set torque and the normal peak torque is small, load fluctuations during the operation will cause the drive balls to oscillate inside the pockets. This will result in mechanical vibration and abnormal wear inside the Shock Guard. Therefore, set the torque as high as possible within the range that can protect the equipment.
  • * Repeated trip accuracy is the value at the time of shipment.
  • * When using the Shock Guard with V-belt pulleys or timing pulleys, confirm that the radial load caused by belt tension does not exceed the allowable load. Contact a Tsubaki representative if the load exceeds the allowable load.
  • * Select the appropriate type according to your usage conditions after checking whether it satisfies the allowable values.
  • * The reset speed must be as low as possible. The reset speed varies depending on factors such as the inertia of the driven-side machinery, the elasticity of the drive side, and the torque setting of the Shock Guard. In most cases, 50 r/min or less should be sufficient. If it is impossible to reset at low speed, try “jogging” the motor.

⚠Do not manually reset the Shock Guard by turning the main unit or shaft as this can be dangerous.