Tech Insights · 2026-10-10

Bearing Housing Selection for Belt Conveyors: Pillow Block, Flanged and Take-Up Types

Updated for plant engineers and procurement teams · Hebei Xiangming

A pillow block bearing housing is one of the cheapest machined parts on a conveyor, and it is very often the part that decides whether the bearing inside ever reaches its rated life. The housing has four jobs: hold the shaft in position, carry the load into the structure, keep the grease in, and keep dust and water out. Two of those four are structural and two are sealing — and on a bulk handling line the sealing pair does most of the life-determining work. Yet in most spares enquiries the housing is ordered as "UCP 208, cast iron", with nothing said about the seal, the shaft tolerance or the centre height, and the replacement that arrives is dimensionally close but fails in a fraction of the original's service hours. This guide sets out the housing families used on belt conveyors, how sealed bearing housings differ in seal architecture, how shaft fit and locking are specified, and what data you need to send a factory so that the spare you buy is genuinely interchangeable.

1. What a bearing housing actually does

A rolling bearing is a precision component that is remarkably tolerant of load and remarkably intolerant of its surroundings. It will carry a large radial load indefinitely if it is held round, kept lubricated and kept clean. The housing is what makes those three conditions true.

• Locating the shaft. The housing bore holds the bearing outer ring concentric with the shaft axis. If the bore is out of round, or the mounting face is not flat, the outer ring is squeezed into an oval and the bearing is destroyed from the outside — the failure mode that looks like a bearing defect but is a housing defect.
• Transferring load to structure. Belt tension, pulley weight and impact load all arrive at the shaft and must leave through the housing feet or flange into the frame. This is why housing material and bolt pattern are not cosmetic.
• Keeping lubricant in. A housing with a grease cavity and a correctly positioned grease nipple maintains a reservoir; a dry housing relies entirely on the grease packed into the bearing at assembly.
• Keeping contaminant out. This is where a non contact labyrinth seal, a lip seal or a taconite seal earns or loses its cost, and it is the subject of section 3.

When a conveyor is designed, the housing is usually selected last, from the shaft diameter. That is the wrong order. Select the seal arrangement first, then the housing family, then the size — because the seal arrangement is set by the environment and cannot be upgraded later without changing the housing.

2. The housing families used on belt conveyors

Most conveyor-duty housings belong to the insert-bearing family (a self-aligning ball or spherical roller bearing with a spherical outside surface, sitting in a matching spherical bore in the housing). The letter code after "UC" describes the mounting form.

The distinction that matters most in practice is between the insert-bearing pillow block family (UCP and its relatives, used up to roughly 100 mm shaft) and the split plummer block family (SN/SNL, used above that, where a spherical roller bearing is needed to carry the bending of a long pulley shaft). Below the split-housing threshold the bearing is mounted complete with the housing; above it, bearing, sleeve, seals and housing are specified as separate line items. Pulley shaft sizing and the resulting bearing choice are covered in our pulley selection guide.

3. Seal architecture: where service life is won

Dust and water ingress cause the majority of premature bearing failures on conveyors, well ahead of genuine fatigue. The seal is therefore not an accessory — it is the specification. There are three architectures in common conveyor use.

Contact lip seal

A rubber lip runs on a ground journal on the shaft or on the bearing inner ring. It is cheap, effective against both dust and water, and it is the default on general-duty insert bearings. Its two costs are permanent: the lip adds friction — measurable drag and heat, worth a small but real efficiency penalty on a long line with hundreds of idlers — and it wears, because it is a rubbing contact. Once the lip has worn a groove in the journal, sealing is gone.

Non-contact labyrinth seal

A non-contact labyrinth has no rubbing part: concentric or interleaved rings form a tortuous path that grease has to work outwards through and dust has to work inwards through. Because nothing rubs, there is no wear, no measurable drag, no heat generation and no surface-speed limit — which is exactly why labyrinth sealing is the right answer at higher rotational speeds and on long idler runs where drag is multiplied by hundreds of rolls. The trade-off is that the labyrinth only holds as long as it is periodically purged with grease: the grease that fills the path is the seal. In very fine, dry dust, or under high-pressure washdown, a labyrinth on its own is not enough and needs an auxiliary stage.

Taconite and multi-stage seals

For the worst environments — sinter plants, cement clinker, coal preparation, ore transfer points — a taconite arrangement adds a rotating flinger and an external labyrinth outside the housing, shielding the primary seal from direct impact of the contaminant. It costs more and adds axial length, which the frame must have room for. Triple-lip and felt-plus-labyrinth combinations sit between the two.

Match the seal to the environment, not to the catalogue: a washdown plant gets a lip or multi-stage seal regardless of drag; a high-speed idler line in dry bulk gets a labyrinth; a clinker transfer gets taconite. Once dust has crossed the seal, the bearing life collapse is described in our guide to contamination and L10 life, and the seal families themselves are compared in the sealed bearing housings article.

4. Shaft fit, tolerance and locking

A housing is only as good as the shaft it sits on. Three things must be right: the diameter tolerance, the locking method, and the geometry of the shoulders.

• Diameter tolerance. Conveyor shafts for insert bearings are normally finished to h6 (or j6 where a slightly tighter seat is wanted under vibration). A shaft that is undersized lets the inner ring creep on the shaft — fretting, heat, and a ruined shaft. A shaft that is oversized preloads the bearing and shortens its life. On idler shafts a turned finish of Ra 1.6 or better at the seal journal is part of the seal specification, not a nicety.
• Locking. Three common methods: set screw (two grub screws on the inner ring — simplest, adequate for light duty, prone to loosening under reversing load), eccentric locking collar (a cam collar that grips the shaft — better under vibration and reversing, standard on conveyor-duty insert bearings), and adapter or withdrawal sleeve for tapered-bore spherical roller bearings in split housings. Where the shaft is highly loaded or the direction reverses, an eccentric collar or adapter sleeve should be specified explicitly.
• Shoulder and concentricity. The shaft shoulder must locate the bearing without clamping it, and the two housing seats on a pulley shaft must be concentric. Over-constraining two fixed bearings against each other is a classic source of heat: one end should be a locating bearing and the other a floating one.

5. Sizing the bearing inside the housing

Bearing life is not a mystery; it is a ratio. The basic rating life L10 — the number of revolutions 90 % of a population of identical bearings will reach or exceed — is calculated from the ratio of the bearing's dynamic load rating C to the equivalent dynamic load P:

L10 = (C / P)^p × 10⁶ revolutions, with p = 3 for ball bearings and p = 10/3 for roller bearings.

Two consequences matter for conveyor work. First, life moves with the cube of load: reduce the load by 20 % and life roughly doubles, while a 20 % overload removes about half of it. Second, the contamination factor applied afterwards can be brutal — a bearing running in ingress-contaminated grease is routinely de-rated by a factor of three to ten. That is why choosing the correct housing seal is worth more than choosing a larger bearing. Target lives are 30 000–50 000 hours for general plant and 60 000–100 000 hours for overland and high-availability lines.

On the idler side the same housing logic appears in miniature: a pressed cup in the tube, a labyrinth or multi-stage seal, and a deep-groove ball bearing sized against roll load and speed. Roller load, spacing and roll selection are set out in our idler selection guide.

6. How to specify an interchangeable spare

"Interchangeable" has a precise meaning, and it is not "same bolt pattern". Two housings can share a bolt hole layout and still differ in the shaft centre height, which is the dimension that decides whether the shaft ends up where the belt expects it. When you ask a factory to match a housing, send these eight items:

1. Shaft diameter and tolerance at the bearing seat and at the seal journal.
2. Housing type and size code — UCP 208, UCF 210, UCT 206, SNL 517, and so on.
3. Bolt hole centres and bolt size, measured, not assumed.
4. Shaft centre height (the distance from the mounting face to the shaft axis).
5. Bearing designation — for example UC 208 or 22217 EK — so the internal clearance and cage are matched.
6. Seal arrangement — lip, non-contact labyrinth, two-stage or taconite — plus the grease nipple position and thread.
7. Housing material — grey cast iron (HT200 / GG20), ductile iron, cast steel or pressed steel — and any coating for a corrosive or washdown environment.
8. Duty data — radial load, axial load if any, speed, temperature range, and whether the location is washed down or buried in dust.

On dimensional interchangeability, insert-bearing pillow blocks and flanges broadly follow ISO 3228 (cast and pressed housings for insert bearings) and the long-established UCP/UC series dimensions, which is why a UCP 208 from one maker generally drops onto another's base. Split plummer blocks follow ISO 113 (plummer block housings — boundary dimensions). Neither standard, however, makes the seal interchangeable: two dimensionally identical housings can leave the factory with completely different sealing performance. If the seal matters — and on a conveyor it does — specify it by architecture, not by part number.

7. The mistakes we see on real projects

• Ordering by part number alone. The number fixes the dimensions and says nothing about the seal, the clearance class or the locking method.
• Checking bolt centres, not centre height. The commonest reason a "correct" replacement still misaligns the belt.
• Shafts turned undersize. The inner ring creeps, frets and eventually spins; the housing is blamed.
• Two locating bearings on one shaft. Thermal expansion has nowhere to go and the bearings run hot.
• A labyrinth never purged. The seal empties, then it is no longer a seal.
• Washdown environment, standard lip seal, no end cover. Water enters along the shaft and emulsifies the grease in weeks.
• Housing mounted on an unpacked, uneven base. Tightening the bolts bends the housing and ovalises the bearing seat.

8. FAQ

What is a pillow block bearing housing?

A pillow block (also called a plummer block, UCP housing) is a foot-mounted housing with two bolt holes that holds a bearing with its shaft axis parallel to the mounting surface. It is the standard mounting for conveyor head, tail and snub pulleys because it is easy to install, easy to shim and easy to replace.

What is the difference between a contact seal and a non-contact labyrinth seal?

A contact lip seal rubs on the shaft: good barrier, low cost, but it wears, adds drag and has a surface-speed limit. A non-contact labyrinth has no rubbing part — no wear, no drag, no speed limit — and relies on a grease-filled tortuous path, so it must be periodically purged to keep working.

Which seal should I use on a conveyor idler?

For long idler runs in dry bulk, a non-contact labyrinth or two-stage labyrinth-plus-lip arrangement, because sealing drag multiplied over hundreds of rolls is a real energy cost. For wet, sticky or washdown duty, a multi-stage lip seal with an end cover is the safer choice.

How do I know if two bearing housings are interchangeable?

Match five dimensions, not one: shaft diameter, bolt hole centres, bolt size, shaft centre height, and bearing seat size. Matching the bolt pattern alone is the most common cause of a spare that fits the frame but misaligns the shaft.

What shaft tolerance does an insert bearing need?

Normally h6 for conveyor shafts up to about 80 mm, moving to j6, k6 or m6 as load and size increase, with an adapter sleeve for tapered-bore spherical roller bearings in split housings. The seal journal should be finished to Ra 1.6 µm or better.

How long should a conveyor bearing housing last?

The housing itself should outlast several bearing changes — it is a structural part. Service intervals are set by the bearing and the seal: with correct sealing and periodic relubrication, L10 lives of 30 000–100 000 hours are the normal design target.

Can HBXM supply housings and the matching shafts and bearings together?

Yes. We manufacture bearing housings, seals and the idler and pulley assemblies they go into, so the shaft tolerance, seal architecture and housing size are specified as one matched set. Send the shaft, load and environment data through the quote form.

Bottom line

Specify a bearing housing in this order: environment first, because it fixes the seal; then mounting form, because it fixes the housing family; then shaft tolerance and locking, because they decide whether the bearing grips or creeps; then size, from load and required L10. Only after those four are fixed does the part number matter. Do that and the housing stops being the cheapest thing that fails first. HBXM manufactures pillow block, flanged, take-up and split plummer block housings with lip, non-contact labyrinth and taconite sealing, together with the idlers, pulleys and frames they mount to — one-stop, specified as a matched package.

References & Sources

• ISO 113:2010. Rolling bearings — Plummer block housings — Boundary dimensions.
• ISO 3228:2013. Rolling bearings — Cast and pressed housings for insert bearings — Boundary dimensions and tolerances.
• ISO 281:2007. Rolling bearings — Dynamic load ratings and rating life.
• CEMA. Belt Conveyors for Bulk Materials, 7th ed. (2nd printing, 2020). Conveyor Equipment Manufacturers Association. ISBN 978-1891171-44-4.

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