Overrunning Sprag Clutches for Printing & Converting Machines

GMN Overrunning Sprag Clutches Keep It Tight for Printing & Flexible Material Converting Machines

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In the world of flexography and converting machines, the name of the game is keeping a taut line. Whether your material is paper, tissue, foil, film, or another non-woven flexible material, maintaining correct tension can be the difference between success and failure, that tension often comes down to the torque control mechanisms in the drives. It’s common for drives throughout the process line, including in the unwinders and rewinders, to incorporate roller ramp or sprag clutches, also known as “cam clutches.” These clutches enable the drives to maintain a constant torque in one direction but can also overrun in the other direction.

Roller Ramp vs Sprag Clutch Designs

Roller ramp and sprag clutches both achieve the same goal, transferring torque in one direction and freewheeling in the other direction, but they go about it in very different ways.

As their name implies, roller ramp clutches have ramps on the inner rings that wedge the rollers in place against the smooth outer ring. Overrunning sprag clutches have sprag elements that are larger than the gap between a smooth inner and outer race and have curved surfaces that engage against the inner and outer race almost instantaneously when torque is transmitted.

Benefits of an Overrunning Sprag Clutch

These differences may seem minor, but the impact they have on the design and performance of the system are anything but. Consider these advantages of using a sprag clutch:

• More compact design. Because there are no ramps, sprag clutches don’t require nearly as much space. This means that the radial space allotment to the clutches can be much less for sprag clutches.
• Higher number of engagement elements. In roller ramp clutches, the amount of space needed for the ramps limits how many rollers can be used for a given clutch. Since sprags don’t need nearly as much space numerous sprags can fit in the space required for a single roller in a roller. More sprags mean there are more elements to transfer torque which corresponds to a higher torque capacity.
• Less rotation for engagement. For roller ramp clutches to engage, the rollers have to move up the ramp and be wedged between the ramp and the outer ring. All the sprags have to do is twist slightly. That means the amount of rotation before the clamping element engages is less for a sprag clutch.

GMN offers a wide range of sprag clutches to serve all types of specific applications, such as overrunning, in the printing and flexible material converting industry, especially with winders, slitters, rolling mills, and levelers.

One series, the FND 400, has become the go-to clutch for the industry because of its many unique features compared to GMN’s other clutches:

• Hardened races with a keyway on the inner ring. No need for special shaft and housing requirements. Just press the clutch in and secure it with a key to the shaft.
• Built in bearing support. These clutches come with a ball bearing on one side and a roller bearing on the other to side to provide radial and some axial load support to the clutch.
• Sealed with oil lubrication. Grease has a shelf and operating life limitation. Instead, these clutches are sealed with an oil lubrication to keep running for years without the need to change the lubrication.

Slug	GMN Series	Part No	Spring Type	Inner Diameter d [mm]	Outer Diameter D [mm]	Width b [mm]	Torque M [Nm]
sc-fnd-437-z-complete-freewheel-clutch	FND	437 Z	Tension	15	41	34	161
sc-fnd-442-z-complete-freewheel-clutch	FND	442 Z	Tension	20	46	34	208
sc-fnd-453-z-complete-freewheel-clutch	FND	453 Z	Tension	25	58	34	314
sc-fnd-459-z-complete-freewheel-clutch	FND	459 Z	Tension	30	64	34	381
sc-fnd-463-z-complete-freewheel-clutch	FND	463 Z	Tension	35	68	34	428
sc-fnd-470-z-complete-freewheel-clutch	FND	470 Z	Tension	40	75	34	509
sc-fnd-473-z-complete-freewheel-clutch	FND	473 Z	Tension	45	78	34	543
sc-fnd-437-m-complete-freewheel-clutch	FND	437 M	Meander	15	41	34	176
sc-fnd-442-m-complete-freewheel-clutch	FND	442 M	Meander	20	46	34	223
sc-fnd-453-m-complete-freewheel-clutch	FND	453 M	Meander	25	58	34	343
sc-fnd-459-m-complete-freewheel-clutch	FND	459 M	Meander	30	64	34	411
sc-fnd-463-m-complete-freewheel-clutch	FND	463 M	Meander	35	68	34	462
sc-fnd-470-m-complete-freewheel-clutch	FND	470 M	Meander	40	75	34	550
sc-fnd-473-m-complete-freewheel-clutch	FND	473 M	Meander	45	78	34	588