What a housing does
A housing locates the bearing in the machine, carries the load into the frame, protects the bearing from dirt and often stores grease. In applications with a standard housed unit, the bearing is already pre-fitted: an insert bearing with a spherical outside surface sits in a matching seat inside the housing and can swivel slightly, which compensates for shaft misalignment at mounting. This is why housed units are popular for conveyors, fans and farm machinery, where frames are rarely perfectly aligned.
Housings also exist without insert bearings, in split or solid versions for large bearings. For a short introduction to the complete unit, see what is a pillow block bearing. This note is about the housing side of the assembly.
The main housing families
| Type | Common code | Mounting | Typical use |
|---|---|---|---|
| Pillow block | UCP, P | Two bolts through a base on a flat surface | Conveyor shafts, fans, general machinery |
| Square flange | UCF, F | Four bolts on a face, shaft passes through the frame wall | Frames, gearbox ends, agricultural equipment |
| Rhombic (diamond) flange | UCFL, FL | Two bolts on a face, space-saving | Light conveyors, packaging machinery |
| Take-up | UCT, T | Slides in a frame slot to tension a belt or chain | Belt conveyors, tensioned drives |
| Cartridge | UCC, C | Round body fitted in a bore or clamp | Tight spaces, centreline mounting |
| Split plummer | SN, SD and similar | Split casing with a base, fitted around a bearing | Heavy industry, fans, large shafts |
The letter codes follow industry convention: U for the insert shape, C for the cast housing, then the mounting type. The bore of an insert, such as the shaft size, is a separate part of the designation, and the full code is read the same way as other bearing designations. See designation guide for the general system.
Housing materials
- Grey cast iron (such as HT200). The standard, economical material for most pillow blocks and flange units. Strong in compression, good at damping vibration, brittle under shock.
- Ductile (spheroidal graphite) iron. Higher strength and toughness, selected for heavier loads and shock, and increasingly for agricultural duty.
- Pressed steel. Stamped housings are lighter and cheaper, suited to light loads and appliances, with less stiffness than cast.
- Stainless steel. For wash-down and food areas; pair with stainless inserts and suitable seals, as discussed in 440C stainless bearings.
- Thermoplastic. Moulded polymer housings with a stainless insert for wet, light-duty conveyors and food plants where rust is unacceptable.
Cast housings are usually painted or coated. Check the coating when the environment is corrosive, because bare cast iron rusts rapidly in damp storage and the coating is what protects it between delivery and installation.
How the insert locks to the shaft
Housed units differ most in how the inner ring grips the shaft, and this is a practical decision that often matters more than the housing shape.
- Grub (set) screw. Two screws in an extended inner ring bite the shaft. Simple and inexpensive, suitable for moderate loads and one rotation direction.
- Eccentric collar. A collar locks onto the inner ring with a twist action, good for shafts that rotate in one direction with stable load.
- Adapter sleeve. A tapered sleeve pulls the ring onto the shaft with even grip, which works for plain shafts and allows a looser shaft tolerance. See bearing accessories.
- Interference fit. A pressed fit on a ground shaft, for higher speed or load, requires proper tooling.
Grub screw units tend to loosen with vibration and reverse rotation, which is why heavier conveyor applications move to sleeves or collars. The type of lock needs to be part of the specification.
Lubrication, seals and relubrication
Many housed units are supplied pre-greased with a grease nipple, so that the user can add grease during service. Seal design in the insert, plus an end cover or a flinger ring, adds protection. In dusty sites, double-lip seals or multi-stage seals around the insert and a closed end cover protect the grease from contamination. For washdown, avoid ports and covers that collect water, and plan around the sealing described in bearing seal materials.
Relubrication is the most neglected part of a housed unit. A nipple that is never greased, or too much grease that burns the seals, shortens life. Intervals depend on speed, temperature and contamination, and a conservative first estimate comes from the supplier recommendation.
Common mounting mistakes
Most housed-unit problems come from installation, not from the product. Bolts tightened unevenly distort a cast base and pinch the insert. A housing mounted on a frame that is not flat transfers that error into the bearing as preload. Two housings on one shaft that are not aligned put bending into the shaft, which the self-aligning seat can only partly absorb. And a shaft that is oversize or out of round cannot be gripped properly by a set-screw insert.
A short checklist helps: check the frame surfaces for flatness, fit the shaft first, tighten the mounting bolts in a cross pattern to the torque in the datasheet, then lock the insert, and rotate the shaft by hand before power-up. On a fixed-and-floating arrangement, only one housing should be locked axially; the other must be able to move with thermal growth.
Choosing a housing for your application
Match the housing to the frame and the duty:
- Conveyors and bulk handling. Pillow blocks and take-up units with sleeves or collars, sealed inserts and end covers. See conveyor bearings.
- Agricultural machinery. Flange or pillow units in ductile iron with heavy seals and relubrication points; see agricultural machinery bearings.
- Fans and blowers. Split plummer blocks for large shafts, or pillow blocks with balanced shafts for smaller units.
- Light packaging and food lines. Stainless or polymer housings with sealed inserts and food-suitable grease.
Check the nominal dimensions of the bolt pattern and centre height, since they are standardised for common series but still vary between regions and plants. Confirm against the drawing and the supplier datasheet, and ask for a sample of the exact housing before ordering. Cast housings from partner plants are usually available in catalogue quantities, and the reference MOQ and lead times are on the MOQ and lead time page.
When you send a request, state the mounting type, shaft size and locking method, insert type and seal, housing material and finish, and the working conditions, through the quote form. The desk will propose matched housings and inserts and confirm the data in writing.