Cartridge Units

What is a cartridge unit?

A cartridge unit is a bearing unit with a cylindrical housing, designed to be pushed into a bored hole rather than bolted onto a surface. It has no flange or feet. Instead, the plain round outside of the housing fits into a bore in a machine frame, roller, or separate housing, and is held in place there. This lets a self-aligning insert bearing be used in places where a fixed bearing would normally be fitted.

A standard cartridge unit is made up of:

• A cylindrical housing, usually cast iron, with a machined outside diameter
• A self-aligning insert bearing, seated in a spherical bore in the centre of the housing
• A locking method, usually two grub screws, that fixes the insert to the shaft
• Seals on the insert bearing, and a grease nipple for relubrication.

The cylindrical housing is what makes a cartridge unit different.

• The machined outside diameter fits closely into a bore, so the unit sits on the exact centre line of the hole.
• Because there are no bolts or flanges, the unit takes up very little space around the shaft and can be fitted inside rollers, tubes, and deep housings.

Cartridge units are sold as complete units with the insert fitted, or as housings on their own so the insert can be replaced when it wears.

Why are cartridge units essential?

They make it possible to fit a self-aligning, sealed, ready-greased bearing into a simple bored hole. This is useful on rollers, idlers, and machine frames where a bolted housing would not fit, or where a standard bearing would need a precisely machined housing and accurate alignment.

The spherical seat lets the insert bearing align itself in the housing, so it copes with small errors between the bores at each end of a shaft. The insert can be removed and replaced on its own, and the grease nipple allows the bearing to be relubricated, which helps it last longer in dirty or wet conditions.

Typical applications include:

• Conveyor rollers and idlers
• Agricultural machinery, such as rollers and drums
• Fans and blowers
• Material handling equipment
• Packaging machines
• Printing and paper machinery
• Woodworking and sawmill machinery
• Food processing equipment

The main types of cartridge units

• Cast iron cartridge units - The standard design, with a cylindrical cast iron housing and a full width insert bearing locked with grub screws. Strong and suited to most applications.
• Cartridge units with eccentric collar inserts - These use an insert that locks to the shaft with an eccentric collar instead of grub screws. They grip the shaft without marking it, and suit drives that run in one direction.
• Heavy-duty cartridge units - These take a larger insert bearing for higher loads on the same shaft size.
• Stainless steel and thermoplastic cartridge units - Corrosion-resistant versions for food processing, washdown, and wet conditions.
• Metric and inch bore units - Cartridge units are available for both metric and inch shafts, often with the same outside diameter housing for a given size.

How to choose the right cartridge unit?

• Shaft size - Match the insert bearing bore to the shaft, and check whether the shaft is metric or inch.
• Housing outside diameter - The outside diameter of the cartridge must suit the bore it will fit into. Check the bore size and tolerance, as the fit decides how well the unit is held.
• Width - Check the housing width suits the depth of the bore or the space available.
• Axial location - Decide how the unit will be held in the bore. This can be a shoulder, a circlip, an end plate, or a clamping screw, depending on the design.
• Load - Standard units suit light-to-medium loads. For heavier loads, choose a heavy-duty unit.
• Conditions - Choose stainless steel or thermoplastic units for wet, corrosive, or washdown environments.

Essential references and specialised ranges

How the numbering works:

Cartridge unit references combine the insert bearing and the housing:

UC = insert bearing with grub screw locking and an extended inner ring

C = cylindrical cartridge housing

The digits = the series and bore code. Multiply the last two digits by five to get the bore in mm.

Examples:

UCC204 = cartridge unit for a 20mm shaft

UCC205 = cartridge unit for a 25mm shaft

UCC206 = cartridge unit for a 30mm shaft

C205 = the cartridge housing on its own, which takes a UC205 insert

Inch bore units add a suffix showing the bore in sixteenths of an inch:

UCC205-13 = 13/16 inch shaft

UCC205-16 = 1 inch shaft

The housing size stays the same for each series, so a UCC205 and a UCC205-16 both have a C205 housing with an 80mm outside diameter.

Suffixes:

-12, -13, -14, -16 and similar = inch bore in sixteenths of an inch

E = eccentric collar locking insert

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

FAQ - All you need to know about cartridge units

What is the difference between a cartridge unit and a flange unit?

A flange unit bolts onto a flat surface through holes in the flange. A cartridge unit has a plain cylindrical housing with no flange, and fits into a bored hole instead.

How is a cartridge unit held in place?

The housing is a close fit in its bore, and is usually held axially by a shoulder, a circlip, an end plate, or a clamping screw. The method depends on the machine design.

Can I replace just the insert bearing?

Yes. The insert bearing can be removed from the cartridge housing and replaced on its own, as long as the new insert has the same size and type.

Do cartridge units need lubrication?

Most cartridge units are supplied greased and have a grease nipple for relubrication. Regrease regularly in dusty, wet, or hot conditions, adding grease slowly until fresh grease just appears at the seals.

How do I fit a cartridge unit?

Make sure the bore is clean and free of burrs, then push the cartridge in squarely, pressing only on the housing and never on the insert bearing. Secure it axially, slide the shaft through, and lock the insert to the shaft last, once the shaft is in position and turns freely.

How do I identify a cartridge unit I need to replace?

The reference is usually marked on the housing and on the insert bearing. If it cannot be read, measure the shaft diameter, the outside diameter of the housing, and the housing width. Also note the locking method and whether there is a grease nipple.

What are the signs that a cartridge unit needs replacing?

Watch out for:

• Grinding, squealing, or rumbling from the bearing
• Increased vibration
• The housing running hot
• Play in the shaft
• Grease leaking past the seals
• The housing moving or turning in its bore
• The shaft slipping in the insert bearing