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Intentional Slipping is a Good Thing

( 01/23/2019 ) Written by: Tim Kubat

We previously talked about how important it is to insist on flexible couplings when you purchase heavy equipment.  Continuous vibration and intermittent shocks can cause numerous difficulties – from gear tooth fatigue to broken driveshafts—and flexible couplings can prevent these problems by reducing the vibration transmitted to downstream components.

LORD Corporation’s LCD Flywheel Coupling, which connects the engine and transmission, or gear box, generator or hydraulic pumps, also features a built-in “slip” aspect that helps protect against expensive breaks, and is rated to three times the expected torque value.

If your heavy equipment does not include a flexible coupling, there are metal-to-metal contact surfaces experiencing repeated relative surface motion induced by vibration, which causes fretting.  Fretting downgrades the surface layer producing increased roughness and pitting, which reduces the fatigue strength of the component, and eventually results in damage.  This translates into increased maintenance time and costs.

LCD couplings absorb vibratory torque, relieving 90% of the repetitive vibration transmitted through the connected parts so fretting is essentially reduced. 


Our LCD coupling also includes an inner elastomeric ring that “slips” during torque overload sessions to protect components.  The ring will intentionally slip for a millisecond to absorb the energy created during high torque spikes (an example would be shifting from one gear to the next).  Essentially, the magnitude of the peak torque is limited by the torque value that the rubber ring slips at – the torque value is held constant.



In the graph below you can see the slip torque is at least three times the rated torque.  When the rubber ring slips, the maximum torque transmitted to the driveline components is limited as the energy is absorbed by displacement of the rubber ring.


The slipping feature acts as a safety fuse, protecting downstream items/connections, as the coupling transfers the torque energy into displacement energy, which reduces the torque value instead of transferring it to the drive train.  *However, it should be noted that this slipping generates heat and continuous running at overload could damage the coupling.

Flexible couplings are particularly successful for diesel driven applications and are an example of a small upfront cost that pays big dividends later. Look for them as part of your due diligence prior to buying heavy equipment.


Tim Kubat

Tim Kubat is a Principal Engineer in the LORD Industrial Equipment Team, focusing on drivetrains and other applications for agricultural and construction vehicles. He holds three patents for elastomeric designs used in the off-highway market.

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