Pillow Block Housings

What is a pillow block housing?

A pillow block housing is a mounting block that holds a bearing and bolts to a flat surface, so a shaft can be supported parallel to that surface. It provides a ready-made seat for the bearing, a way to fix it to the machine, and usually a way to seal and lubricate it. Pillow blocks are one of the most common ways of supporting shafts on conveyors, fans, and general machinery.

There are two main families:

• Pillow block units, which hold an insert bearing with a spherical outer ring and are bolted down as a complete unit
• Split plummer block housings, which have a removable cap and hold a separate bearing, usually a self-aligning ball or spherical roller bearing.

A standard pillow block unit has four main parts:

• A housing with a two-bolt base, usually made of cast iron
• An insert bearing, which is a deep groove ball bearing with a spherical outer ring and an extended inner ring
• A locking method, such as grub screws or an eccentric collar, which fixes the bearing to the shaft
• Seals on the insert bearing, and usually a grease nipple on the housing.

The spherical seat in the housing lets the insert bearing self-align.

• The spherical outer ring of the insert sits in a matching spherical bore in the housing.
• This allows the bearing to adjust to small mounting errors and shaft deflection when it is fitted.

Why are pillow block housings essential?

They make supporting a shaft quick and simple. Instead of machining a housing, a pillow block unit is bolted to the frame, slid onto the shaft, and locked in place. The self-aligning seat means two pillow blocks on the same shaft do not need to be perfectly lined up, which saves time during installation.

Split plummer blocks do the same job for heavier loads and larger shafts. The removable cap makes it easy to fit, inspect, and replace the bearing without removing the housing from the machine. Both types come in standard sizes, so they are easy to source and replace.

Typical applications include:

• Conveyors and material handling
• Fans and blowers
• Agricultural machinery
• Food and beverage processing
• Pumps and compressors
• Mining and quarrying equipment
• Woodworking and sawmill machinery
• Packaging machines
• Paper and textile machinery

The main types of pillow block housings

• Cast iron pillow block units - These are the standard design and by far the most common. They are strong, rigid, and suited to most industrial applications.
• Pressed steel pillow block units - These are lighter and lower in cost, and suit lighter loads and speeds.
• Thermoplastic pillow block units - These have a housing made of glass-filled nylon or a similar polymer. They are light, corrosion resistant, and non-metallic, but not suited to high temperatures or heavy loads.
• Stainless steel pillow block units - These have a stainless steel housing and insert bearing, for washdown, food, and corrosive environments.
• Split plummer block housings - These have a cap that bolts onto a base, and hold a self-aligning ball bearing or spherical roller bearing, often on an adapter sleeve. They are used for heavier loads and larger shafts.
• Solid plummer block housings - These are one-piece housings for heavy-duty applications, where the bearing is fitted from the end.

Locking methods for pillow block units include:

• Grub screw locking - Two grub screws in the inner ring press onto the shaft. Simple and works in both directions of rotation.
• Eccentric collar locking - A collar is turned onto the inner ring and locked with a grub screw. It grips the shaft without marking it, but is best suited to drives that run in one direction.
• Adapter sleeve locking - The bearing is clamped onto the shaft with a tapered sleeve and nut. It gives the best concentricity and suits reversing drives and higher speeds.

How to choose the right pillow block housing?

• Shaft size - The bore of the insert bearing or bearing must match the shaft diameter. Check whether the shaft is metric or inch, as they are not interchangeable.
• Load and speed - Choose a cast iron unit or plummer block for heavier loads, and a pressed steel or thermoplastic unit for lighter duty. For high loads or large shafts, use a split plummer block with a spherical roller bearing.
• Centre height and mounting - Check the centre height (from the base to the middle of the shaft), the bolt hole spacing, and the overall length suit the frame.
• Locking method - Use grub screws for general use, an eccentric collar where the shaft must not be marked and the drive runs in one direction, or an adapter sleeve for reversing drives and higher speeds.
• Environment - Use stainless steel or thermoplastic housings for wet, washdown, or corrosive conditions. Add end covers or extra seals in very dirty conditions.
• Locating or non-locating - On a shaft with two housings, one should locate the shaft axially and the other should allow it to move with thermal expansion. On plummer blocks, this is usually set with locating rings.

Essential references and specialised ranges

How the numbering works:

Pillow block unit numbers combine the insert bearing and housing:

The first two letters, UC. Identify the insert bearing type, a grub screw locking insert with an extended inner ring.

The next letter or letters identify the housing: P = pillow block (for example, UCP).

The digits give the series and bore. The 2 series is the standard series and 3 is heavier. The last two digits are the bore code, so 05 × 5 = 25mm.

For example, UCP205 is a cast iron pillow block unit with a UC205 insert for a 25mm shaft. The housing on its own is a P205.

Inch bore versions add a suffix showing the bore in sixteenths of an inch, so a UCP205-16 fits a 1 inch shaft.

Split plummer block housings use their own series, such as SN, SNL, and SD. These are sized to suit a particular bearing and shaft, so always check the bearing reference and shaft diameter before ordering.

Suffixes:

E = eccentric collar locking insert (for example, UC205E)

-16, -20, and similar = inch bore in sixteenths of an inch (for example, -16 = 1 inch)

Suffix codes vary between manufacturers, so check the supplier’s catalogue for the exact meaning.

FAQ - All you need to know about pillow block housings

What is the difference between a pillow block and a plummer block?

The terms are often used for the same thing. Pillow block usually means a complete unit with an insert bearing, which is bolted down as one piece. Plummer block usually means a split housing with a removable cap, which holds a separate bearing.

Can I buy the housing and insert bearing separately?

Yes. Housings and insert bearings are sold separately as well as together as units. Make sure the insert bearing matches the housing size, so the spherical outer ring fits the housing seat correctly.

What is the difference between grub screw and eccentric collar locking?

Grub screw locking uses two screws in the inner ring that press onto the shaft. Eccentric collar locking uses a collar that is turned onto the inner ring to grip the shaft. Eccentric collars do not mark the shaft but are best suited to drives that run in one direction.

Do pillow block housings need lubrication?

Most pillow block units are supplied pre-greased, and many have a grease nipple so the bearing can be relubricated. Relubricate slowly with the correct grease, as too much can damage the seals. Split plummer blocks are usually packed with grease when the bearing is fitted, and can be relubricated through a grease nipple in the cap.

Can I replace a pillow block myself?

In most cases, yes. Loosen the locking screws or collar, undo the mounting bolts, and slide the old unit off the shaft. Clean the shaft and remove any burrs, then slide the new unit on, bolt it down, and lock it to the shaft last, once both housings are aligned. Never hammer on the housing or bearing.

How do I identify a pillow block I need to replace?

The reference is usually cast into the housing and marked on the insert bearing. If the markings are worn away, measure the shaft diameter, centre height, bolt hole spacing, and overall length. Also note the locking method and housing material.

How can I tell if a pillow block is worn or failing?

Warning signs include:

• Grinding, rumbling, or squealing noises
• Increased vibration
• The bearing running hot
• Play in the shaft
• Grease leaking from the seals
• A cracked or damaged housing
• The insert bearing turning in the housing, or the shaft turning in the bearing