Bearing Materials Compared: BP25 Bronze vs FP20 Iron vs SO16 Alloy vs Composite Plates

Matching the grade to the duty

Bushingo carries four distinct self-lubricating material families: BP25 sintered bronze, FP20 sintered iron, the SO16 alloy grade and composite friction plates. They share the same underlying principle of a solid or porous lubricant reservoir, but they differ in strength, speed capability, cost and the form in which they are supplied. Choosing well is mostly a matter of matching the material to the load, the sliding speed, the environment and whether the motion is rotary or flat.

BP25 sintered bronze: the general-purpose choice

BP25 is the classic oil-impregnated sintered bronze and the grade most engineers reach for first. Its tin-bronze base gives good corrosion resistance, a conformable and forgiving running surface, quiet operation and the highest speed capability of the porous grades. Bushingo offers BP25 across the widest size range in the catalogue: cylindrical bushes from 2 mm bore up to 125 mm, and flanged bushes from 3 mm bore to 60 mm with an integral collar for axial location. The recommended impregnation oil is TURBO T100.

As a typical class characteristic, sintered bronze of this type runs comfortably to around 100 degrees Celsius continuous on standard oil and suits low-to-moderate speed rotary and oscillating work. It is the natural pick for electric motors and fan assemblies, household and office equipment, small pumps, automotive ancillaries, gear-motor output shafts and general light machinery, wherever a clean, dry-running, maintenance-free bearing is preferred over a greased bush or a rolling-element bearing.

FP20 sintered iron: economical and load-tolerant

FP20 is the iron-based sintered grade. Its material cost is lower than bronze and its surface is harder, which makes it well suited to slower speeds, higher unit loads and intermittent or oscillating motion where a bronze bush would be over-specified. The trade-off is a lower top speed and a lower PV ceiling than bronze, and iron grades benefit from protection against corrosion in damp or wash-down environments. FP20 shares the TURBO T100 impregnation oil with BP25.

Bushingo supplies FP20 as cylindrical bushes from 3 mm bore to 100 mm and as flanged bushes from 3 mm to 60 mm. Typical applications include agricultural and construction machinery, hinges and pivots, pedal and lever mechanisms, seat and adjustment linkages, and other slow-moving, heavily loaded joints where economy and load capacity matter more than speed.

SO16 alloy: specialised blanks for bespoke bearings

SO16 is a specialised sintered alloy grade offered specifically as solid and hollow bearing blanks rather than as finished catalogue bushes. It is selected when the standard bronze and iron grades are not the best fit and a custom-machined bearing is required, and it is paired with its own dedicated impregnation oil, METADOP, rather than the TURBO T100 used for BP25 and FP20. Because it is supplied as blanks, SO16 is the route to a self-lubricating bearing in a non-standard bore, wall thickness or length.

The blank stock covers solid blanks with outside diameters from 20 mm to 145 mm in lengths from 40 mm to 120 mm, and hollow blanks with bores from 38 mm to 85 mm, outside diameters up to 175 mm and a standard 120 mm length. The same blank forms are also available in BP25 and FP20, so a bespoke bearing can be machined in whichever of the three grades best suits the duty. Confirmed material properties for a given SO16 application are quoted per project rather than stated as blanket ratings.

Composite self-lubricating friction plates: flat sliding, not rotary

The composite friction plates address a different problem from the cylindrical grades. Rather than a rotating shaft in a bore, they handle flat and linear sliding: wear pads, gib strips, slide ways, guide surfaces and die or mould guidance. They are supplied as self-lubricating composite plates measuring 375 by 375 mm in thicknesses from 4 mm to 20 mm, in the M10, M60 and M90 grade series, and are cut and drilled to shape by the user. Because the lubricant is carried within a composite matrix, these plates provide low-friction dry sliding across a broad flat contact area, which a cylindrical bush cannot do. Reach for a friction plate wherever the movement is planar and for a sintered bush wherever it is rotary or oscillating about a shaft.

The impregnation oils

The oil is part of the specification, not an afterthought, and the correct oil is matched to the grade and the environment:

Re-impregnating with the matching oil restores a bearing that has been degreased during cleaning, and selecting the food-grade or wide-temperature oil at the outset tailors an otherwise standard bush to a demanding environment.

Selection at a glance

A short decision path

• Rotary or oscillating shaft, general duty, moderate speed: choose BP25.
• Rotary or oscillating shaft, slow, heavily loaded, cost-sensitive: choose FP20.
• Non-standard bore, wall or length, or a special environment: machine from SO16, BP25 or FP20 blanks.
• Flat or linear sliding surface: choose a composite friction plate cut to size.

Where the choice is genuinely marginal, the relevant load, speed and temperature figures for a specific grade and size are confirmed per project so that the grade, the oil and the fit are settled together rather than in isolation.