UCP200 Series Pillow Block Units are used for mounting a bearing on a machine frame that has no machined housing bore — the bearing, its housing, its seals and its shaft locking are supplied together as one bolt-down part. A wide inner ring insert bearing with a spherical outer surface sits in a matching housing seat: the unit finds its own alignment as it is bolted down, and locks to a plain commercial shaft with setscrews, an eccentric collar or an adapter sleeve. This page sets out the industries and machine positions where the type is specified, what has to be stated on the order, mounting practice, and the duties where a different bearing type is the correct answer. Boundary dimensions are to ISO 3228 / JIS B 1559. This series is catalogued from 12 mm to 90 mm bore; the full table of boundary dimensions is further down the page.
Typical Applications for UCP200 Series Pillow Block Units
The machine positions and sectors where this type is specified:
- Food and wet processing: stainless and thermoplastic housings with reinforced sealing, chosen for washdown rather than for load.
- Maintenance and repair (MRO): replacing a failed bearing where the original designation, clearance group and sealing have to be matched exactly.
- OEM machine building: designed-in shaft support on new equipment, specified from the load, speed and envelope at the design stage.
- Horizontal shafts on frames: bolted to a base below the shaft — the most common way to carry a conveyor or fan shaft on a weldment.
- Conveyors: head, tail and idler shafts, bolted straight onto the frame with no machined bearing seat anywhere in the assembly.
How to Specify UCP200 Series Pillow Block Units for Your Application
- Bore: Start from the bore the shaft or housing gives you — this series is catalogued from 12 mm to 90 mm — then check the outer diameter and width against the space available. The boundary dimensions are fixed by the standard, so they are the same from any manufacturer; the load ratings and limiting speeds are not, and belong to the specific bearing being supplied.
- Base height and bolt centers: Height to shaft center H and bolt hole centers J define the mounting; take them from the table before drilling the frame.
- Housing style: Pillow block (UCP, UCPA) for bolting to a horizontal surface below the shaft; two-bolt and square flange (UCFL, UCF) for bolting to a vertical face; take-up (UCT) where the shaft position has to be adjusted for belt or chain tension; cartridge for a bore in a plate; split plummer block where a large bearing must be inspected without dismantling the shaft.
- Shaft locking: Setscrews are the default and are adequate for one direction of rotation and moderate load. An eccentric collar grips better under reversing rotation. An adapter sleeve gives the most concentric grip and is used on larger shafts and where vibration is continuous.
- Housing material: Gray cast iron for general duty, pressed steel where weight and cost dominate, thermoplastic and stainless for washdown and corrosive environments. The housing material, not the bearing, decides where the unit can be used.
- Shaft tolerance: These units are made to fit a plain commercial shaft, typically h7 or h8 — not a ground bearing seat. Machining the shaft to a normal bearing fit is wrong here and prevents the locking device from working.
- Designation and suffixes: State the complete designation including every suffix. The base number gives the type and the boundary dimensions; the suffixes carry the sealing, the cage, the clearance group, the tolerance class and any special execution — and two bearings whose base numbers match but whose suffixes differ are not interchangeable.
- Clearance and tolerance: State the running clearance or fit class the assembly requires, together with the tolerances of the mating parts that produce it. For this type the clearance is created by the parts around the bearing rather than being built into it, which is precisely why it has to be written down.
- Seal or shield: State open, shielded (ZZ, 2Z) or sealed (2RS, 2RZ). A shield is non-contacting: it excludes coarse contamination and costs nothing in speed. A contact seal excludes fine dust and water and retains grease, but it rubs — it adds drag, raises the running temperature and lowers the permissible speed. Sealed bearings are also greased for life and cannot be relubricated.
- Cage material: State the cage. Pressed steel is the default and suits most duties; machined brass takes shock, high temperature and poor lubrication better and is used in large and heavily loaded bearings; polyamide is quiet, light and low-friction but has a temperature limit of about 120 °C and is attacked by aged oil. The cage is not a detail — it is the component that most often sets the real temperature limit of the bearing.
- Shaft and housing fit: Specify the seat tolerances, not just the bearing. The rule is that the ring which rotates relative to the load direction takes the interference fit: for a rotating inner ring under normal radial load the shaft seat is typically k5 or k6 with the housing bore H7, and where the outer ring rotates the interference moves to the housing (N7 or P7) with a clearance fit (g6) on the shaft. Heavier loads and hollow shafts move the fits tighter. A correctly chosen bearing in the wrong fit fails anyway — too loose and the ring creeps and frets its seat, too tight and the interference consumes the internal clearance and the bearing runs preloaded.
- Standard: Boundary dimensions are to ISO 3228 / JIS B 1559. Quoting the standard on the order guarantees the mounting dimensions are interchangeable between suppliers — it does not standardize load ratings, limiting speeds or internal design, which remain manufacturer-specific.
Mounting & Assembly Practice
- Bolt the unit down loosely, run the shaft through both units, then rotate the shaft to let the inserts find their alignment on the spherical seats before tightening the base bolts.
- Shim the bases to level rather than pulling the housings down onto an uneven surface. Bolting a pillow block onto a twisted base distorts the housing seat and preloads the insert.
- Tighten setscrews alternately to the specified torque with the shaft in its final position. Under-tightened setscrews let the inner ring creep on the shaft and polish it.
- Use the grease nipple. Almost all housed units are relubricatable by design, and the relubrication interval in a dirty or wet duty is short.
Common Selection Mistakes with UCP200 Series Pillow Block Units
- Treating the spherical seat as a continuous self-aligning feature. It takes up the initial misalignment on assembly and then stays where it settles — it is not a bearing that swivels every revolution.
- Specifying setscrew locking for a reversing drive, where the screws work loose and the inner ring fretting starts.
- Machining a precision seat onto the shaft, which leaves the insert bore loose on a shaft turned to a bearing fit rather than to the commercial size the unit expects.
- Sizing this bearing from the boundary dimensions alone. Load ratings and limiting speeds are manufacturer-specific for this series and are deliberately not published here — take them from the catalog of the bearing actually being supplied and calculate the life against them.
Where UCP200 Series Pillow Block Units Are Not the Right Choice
- Not for high speed. The insert bearing has wide internal clearance, a setscrew grip on a commercial shaft and contact seals, all of which limit speed well below a mounted deep groove bearing.
- Not for precision. The concentricity of a setscrew-locked insert on a commercial shaft is nothing like a bearing pressed onto a ground seat, and the runout carries straight into whatever the shaft drives.
- Not for heavy shock or high load. Where the load justifies it, use a plummer block with a proper spherical roller bearing rather than an insert unit.
- Not where the housing must locate the shaft accurately relative to the frame; the spherical seat exists precisely to give that up.
- The alignment capability is for a static angle between the shaft and the housing seat; it is not a licence to leave a shaft line unaligned, and it does not absorb misalignment that changes every revolution.
