SNUB PULLEY
CONVEYOR SNUB PULLEY
A snub pulley sits immediately next to the drive pulley and deflects the belt so it wraps further around the drive. That extra wrap angle is the whole purpose: the traction a drive can transmit before the belt slips rises with the wrap angle, so a snub pulley buys traction without raising belt tension. It transmits no drive torque itself.
BisonConvey snub pulleys are precision-machined from carbon steel and supplied with a plain steel face or rubber lagging. Because a snub runs against the clean (pulley-side) face of the belt near the drive, lagging is specified where wet or sticky carryback would otherwise build up. Diameters run from 200 mm to 630 mm β smaller than the drive it serves, since it only deflects the belt rather than carrying the load.
- ISO 9001:2015
- SGS Certified
- CE
- OHSAS 18001
- ISO 14001
- Β· 30+ Countries
- Β· Since 2005
TECHNICAL DATA
WHY CHOOSE THIS PRODUCT
- Increases drive-pulley wrap angle for higher transmissible traction
- Solves belt slip without raising belt tension or belt-cover wear
- Transmits no drive torque β a routing component, not a drive
- Optional rubber lagging sheds carryback on the clean side of the belt
- Compact diameter suits the tight space beside a drive pulley
- Precision-balanced shells for stable running at speed
APPLICATIONS
How to Read a Snub Pulley Specification
A snub pulley is specified around one number that no other pulley cares about: how much wrap angle it adds at the drive. A typical spec reads Γ 400 Β· targets 210Β° drive wrap Β· clean side Β· plain or lagged Β· dynamic balancing.
- Γ 400
- Pulley diameterFrom 200 to 630 mm, usually smaller than the drive pulley it serves because it only deflects the belt. It must still clear the belt's minimum bend radius β a snub too small for the carcass fatigues the belt at every pass.
- 210Β°
- Target drive wrap angleThe whole reason the snub exists. A plain drive gives roughly 180Β° of wrap; a snub deflects the belt to push that toward 200-240Β°, and the transmissible traction rises with it. This target, not the snub's own size, is what the geometry is designed around.
- Clean side
- Belt side contactedThe snub runs against the clean (pulley-side) face of the belt near the drive. That side is usually cleaner than the carrying side, but in wet or sticky duty carryback still reaches it β which is when lagging earns its place.
- Plain / lagged
- Surface treatmentPlain steel or rubber lagging. The snub transmits no torque, so lagging is not for grip; it is for shedding build-up that would otherwise create a high spot and disturb tracking near the drive.
- Dynamic
- Balancing gradeDynamic balancing matters more as belt speed rises. A snub sits in the highest-tension part of the conveyor, next to the drive, so an unbalanced one induces vibration exactly where the system can least tolerate it.
The transmissible traction of a drive rises with both the friction coefficient at the belt-pulley interface and the wrap angle. A snub pulley is the wrap-angle lever; lagging the drive is the friction lever. They solve the same slip problem, and the cheaper of the two on a given conveyor is worth checking before defaulting to either.
Snub Pulley Selection Guide
A snub pulley is bought to solve one problem: the drive cannot transmit the required traction and the belt slips. Confirm that is the problem, then size the geometry.
Confirm the problem is drive slip, not something else
Belt slip at the drive shows as squeal, belt-speed loss under load, or scorching of the belt bottom cover. If that is what you have, a snub is one of three levers β more wrap, better lagging, or a dual drive. If the belt is mistracking or spilling rather than slipping, a snub is not the answer.
Calculate belt tensionDecide between wrap angle and lagging
Transmissible traction rises with both wrap angle and friction. A snub adds wrap; lagging the drive adds friction. On a conveyor with room beside the drive, a snub is often the cheaper first move; where space is tight, better lagging may win. Calculate the tensions and check which closes the gap.
Set the diameter from the belt carcass
Even though the snub carries no load, the belt still bends around it, so minimum diameter is governed by the carcass exactly as for any pulley. A heavier carcass or a steel cord belt needs a larger snub. Undersizing to fit the space beside the drive puts a fatigue cycle into the belt.
Check minimum pulley diameterChoose lagging for the conditions, not for grip
The snub transmits no torque, so it never needs lagging for traction. Specify lagging only where the clean side of the belt runs wet or sticky and carryback would build up on a plain steel face. In clean, dry duty plain steel is correct and cheaper.
Confirm shaft, bearings and balancing for the position
The resultant load on a snub comes from belt tension and the deflection angle. Size the shaft and bearings from that resultant, and specify a balance grade to suit belt speed β the snub sits in the high-tension zone next to the drive, where vibration is least welcome.
Common Specification Mistakes
Four errors that recur on snub pulley enquiries. The first is the most common: reaching for a snub before confirming the problem it solves.
Fitting a snub when the belt is not actually slipping
A snub solves drive slip and nothing else. If the belt is mistracking, spilling or wearing rather than slipping at the drive, a snub changes nothing. Confirm the failure mode β squeal, speed loss under load, bottom-cover scorching β before assuming a wrap-angle problem.
Undersizing the diameter to fit beside the drive
The space next to a drive pulley is tight, which tempts a small snub. But the belt carcass sets the minimum diameter regardless of position. A snub smaller than the carcass allows fatigues the belt every pass, and the failure appears in the belt, not the snub.
Lagging a snub for traction it does not transmit
A snub transmits no drive torque, so lagging it for grip is spending money on a property that does nothing here. Lagging is justified only to shed carryback on the clean side in wet or sticky duty. Specifying it for traction confuses the snub with the drive.
Ignoring balancing next to the drive
The snub sits in the highest-tension part of the conveyor. An unbalanced snub at speed induces vibration exactly where the drive, its bearings and the structure can least absorb it. Specify a balance grade from belt speed rather than treating it as optional at this position.
FREQUENTLY ASKED QUESTIONS
What does a snub pulley actually do?
It deflects the belt so it wraps further around the drive pulley. The traction a drive can transmit before the belt slips rises with the wrap angle, so a snub pulley increases the drive's grip without increasing belt tension. It transmits no drive torque of its own β it is a geometry component that helps the drive.
What is the difference between a snub pulley and a bend pulley?
A bend pulley changes the direction of the belt along its path β routing the return strand around an obstacle, for example. A snub pulley sits specifically next to the drive and pushes the belt into it to increase the wrap angle. Both are non-drive pulleys, but the bend routes the belt and the snub boosts the drive. It is a common source of confusion because a snub is, geometrically, a small bend placed for a specific job.
How much wrap angle does a snub pulley add?
It depends on the geometry, but a plain drive pulley gives roughly 180Β° of belt wrap, and a snub is typically arranged to push that toward 200-240Β°. The exact figure is set by the position and diameter of the snub relative to the drive. More wrap means more transmissible traction, up to the practical limits of the layout.
Does a snub pulley need rubber lagging?
Not for traction β it transmits no drive torque, so grip is irrelevant to it. Lagging is worth specifying only where the snub runs against a wet or sticky belt and carryback would accumulate on a plain steel face, because build-up creates a high spot that disturbs tracking right next to the drive. In clean dry duty plain steel is the correct, cheaper choice.
Snub pulley or better lagging β which fixes belt slip?
Both can, because transmissible traction rises with both wrap angle and friction. A snub adds wrap; re-lagging the drive with a grooved or ceramic surface adds friction. Which is cheaper depends on the conveyor β a snub needs room beside the drive, lagging needs none. Calculate the drive tensions and see which lever closes the gap, rather than defaulting to one.
Can a snub pulley be undersized to fit the space?
It should not be. The belt bends around a snub just as it does around any pulley, so the minimum diameter is set by the belt carcass, not by the space available. A snub chosen too small to fit beside the drive imposes a fatigue cycle on the belt at every revolution, and the damage shows up as carcass failure rather than snub wear.
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Download the CONVEYOR SNUB PULLEY spec sheet
Full specifications, cover grades, tensile classes, and application recommendations β one PDF to share with your engineering team or procurement.
PDF Β· A4 Β· English
