Failure Mechanisms Guide

GMN Bearing USA’s ABEC 7 high precision ball bearings are made for high speed and heavy load applications.

GMN angular contact bearings (spindle bearings) are expertly crafted for speed, precision, & accuracy.

GMN radial ball bearings are versatile, great in small spaces & when axial loads move in both directions.

We know that not every application requires super, high-precision bearings. We stock other industrial parts from quality brands.

Our one-way sprag clutches are great for applications with low to high torque capacity.

Includes built-in ball bearing support. Supports HEAVY loads & has a high torque capacity: 53 to 588 Nm. Bore (ID) sizes: 10 to 60 mm (0.393 to 2.362 in)

Includes built-in ball bearing support. Supports MEDIUM loads & low to medium torque capacity: 53 to 267 Nm. Bore (ID) sizes: 17 to 40 mm (0.669 to 1.57 in)

No built-in ball bearing support. Good for large orders & low to high torque needs: 1 to 2673 Nm. Bore (ID) sizes: 2 to 240 mm (0.078 to 9.448 in)

No built-in ball bearing support. Has no RPM limits & Supports high torque needs: 609 to 14,060 Nm. Bore (ID) sizes: 38.09 to 220 mm (1.499 to 8.66 in)

This heavy-duty clutch (aka a hold-back clutch) is good for high torque operations and ensures motion freezes in place. Bore (ID) sizes: 15 to 40 mm. (0.59 to 1.73 in)

Designed for HEAVY-DUTY applications that require tough durability.

Our non-contact labyrinth seals are the first line of protection for bearing systems.

The best protection for your bearing. Easy to install with a simple “drop-in” next to your bearing. No added space needed. CF seals offer 100% sealing efficiency against splashing liquids.

Protection against low contamination & splashing liquids.

Designed with grooves in the outer ring to offer more protection (than our L-type seal) against contamination and direct spray liquids. Liquid gets pushed out through outer grooves when in rotation.

Our GMN Gap Seals are plastic and a great choice for washdown applications, such as food conveyors and food manufacturing facilities

Overrunning Failure

The most common reason for overrunning failure is wear between the sprags and the mating surfaces. The sprags require a lubrication film to maintain separation between the sprag and the mating surfaces so that wear is minimized. However, if the lubrication is not sufficient to maintain a thick enough oil film to overcome the microscopic surface roughness of the sprag and the mating surface, then there can be some metal-to-metal contact.

The inside of a sprag clutch with a red circle indicating overrunning failure

This can happen with lubrication that doesn’t have a sufficient viscosity to work at the application operating temperatures. Additionally, if contamination is present in the application, the contaminants will bridge the oil film gap and can act as sandpaper against the sprag, speeding up the wear.

The wear will result in flat spots on the sprag that appear toward the back of the sprag engagement curve. Methods of correction include using proper lubrication with sufficient viscosity and ensuring the environment remains free from contamination.

Another potential cause for sprag failure in overrunning conditions can come from excessive application vibrations.

The springs in the sprag clutches are intended to ensure contact between the sprags and the mating surfaces. But, if the vibrations are significant enough, the forces generated from the vibrations can overcome the spring force and cause the sprag to hit the back of the sprag in front and possibly damage the cage. This can result in broken sprag toes and marks on the backs of the sprags in front as well as twisted cage separators.

If heavy vibration is unavoidable, the spring force can be increased on the sprag clutches to help overcome the vibration forces, however this may result in increased overrunning wear.

Loading Failure

Excessive Torque

If the application generates a torque that is above the maximum torque limit, the sprags will want to extend past the maximum point on the engagement curve and roll over. This will result in permanent destruction of the clutch.

This would be indicated by sprags laying down in the overloaded position, cage separators twisted or removed, and sprag toes damaged. To rectify this, the application needs to be designed to ensure that the maximum possible torque required is below the torque limit of the clutch.

GMN sprag clutches have a built-in safety to help prevent sprag rollover in excessive torque applications. At the point of maximum torque transmission, the engagement angle starts to increase, which causes the sprags to lose friction contact and slip instead of rolling over.

Even though this is part of the sprag design, it is still possible for the conditions to cause the sprags to roll over in an excessive torque situation, especially if it is a rapid torque transmission. (The sprags should not be relied upon to slip.)

Popping

The other type of loading failure is a phenomenon called popping. This happens at the point of transmission when the sprags go from overloading to transmitting torque.

Popping

As the sprags start to engage, they elastically deform the mating surface, building up potential energy. Something can happen to cause the contact to not be maintained and that built-up energy acts as a spring that rapidly propels the sprags forward creating a “popping” sound.

This can result in damaged sprag toes, marks on the back of the sprags from the toes of the sprags behind hitting the sprags in front, and twisted cage separators.

The most common cause for popping is improper lubrication, mainly the presence of extra pressure additives. If the sprags are unable to break through the oil film when they engage, that film will cause the sprags to slip and spring forward.

Other potential causes for popping and overloading failure can be improper mating surface tolerances as well as incorrect mating surface material, hardness, and hardness depth.

Cage Failure

The inside of a sprag clutch with a red circle indicating where cage failure occurred

Cage failure is almost never due to a problem with the cage. The purpose of the cage is to evenly space out the sprags to enable proper torque transfer. No loading should ever be placed on the cage.

If the application is designed correctly, the cages should never experience conditions that cause it to fail. If cage failure occurs, it is typically the symptom of one of the failures mentioned above.

If the conditions that are causing the cages to fail are unavoidable, it is possible to make alterations to the cage design to help ensure clutch success. This can include making the cage thicker or changing cage materials.

If you are experiencing one of the sprag clutch failure symptoms above, contact us for assistance.

Check out our Sprag Clutch Guide resources below for more information.

Overrunning Failure

Loading Failure

Excessive Torque

Popping

Cage Failure

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