Application guide for SF-2 Series Bronze-Backed Composite Bushings to ISO 3547-1 / DIN 1494. The core duty of the type is providing a plain sliding bearing surface in a housing bore, carrying load with no rolling elements at all in the smallest possible radial section. A sleeve of bearing material — wrapped bronze, composite with a PTFE lining, sintered bronze carrying oil in its pores, or bronze with graphite plugs — takes its finished bore from the housing it is pressed into. The typical industries, the specification checklist, mounting practice and the exclusion cases are set out below. This series is catalogued from 12 mm to 50 mm bore; the full table of boundary dimensions is further down the page.
Typical Applications for SF-2 Series Bronze-Backed Composite Bushings
The machine positions and sectors where this type is specified:
- Pumps and fluid equipment: guide bushings running in the process fluid, where a greased bearing is not acceptable.
- Machine slides and dampers: guided sliding motion where a low, constant friction matters more than efficiency.
- Appliances and light mechanisms: quiet, cheap, low-load pivots in high volume.
- 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.
How to Specify SF-2 Series Bronze-Backed Composite Bushings for Your Application
- Bore: Start from the bore the shaft or housing gives you — this series is catalogued from 12 mm to 50 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.
- Lining and backing: A wrapped bushing is a steel or bronze backing strip with a bearing lining rolled into a sleeve. Specify the lining (PTFE composite, sintered bronze, POM) because it sets the pv limit, the temperature range and whether the bushing is lubricated or dry.
- Material and lining: Wrapped bronze for general duty with grease; a steel-backed PTFE composite for maintenance-free running; sintered bronze impregnated with oil where the pores supply the lubricant; solid bronze with graphite plugs for high load at high temperature. The material is the specification — everything else follows from it.
- pv limit: A plain bearing is rated by contact pressure multiplied by sliding speed. Check the load and speed combination against the pv limit for the specific liner, at the operating temperature; it is the number that decides whether the bushing survives.
- Running clearance: A wrapped bushing is supplied slightly oversize and takes its finished bore from the housing when it is pressed in. The housing bore tolerance and the shaft tolerance together produce the running clearance, so both belong on the drawing.
- 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.
- Sealing arrangement: This type is supplied open, so the sealing belongs to the housing around it. Specify the shaft seal, flinger or labyrinth that will keep the lubricant in and contamination out — with an open bearing, the sealing arrangement, not the bearing, decides how long it survives its environment.
- Cage: not applicable: This part has no cage and no rolling elements to separate, so the equivalent decision is the sliding material or liner. That is stated above, and it plays the same role: it is what sets the temperature limit and the lubrication requirement.
- 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 3547-1 / DIN 1494. 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
- Press in with a piloted mandrel over the full bore, square to the housing face. A bushing started at an angle shaves the housing bore and never seats.
- Do not ream or machine a wrapped composite bushing after fitting: the lining is thin, and cutting through it removes the bearing surface. The bore is produced by the press fit, by design.
- Specify the shaft finish and hardness — a plain bearing runs against the shaft, and a rough or soft shaft wears the bushing rather than the other way round.
- Where a lubrication groove or hole is provided, orient it into the unloaded zone; a groove in the load zone removes bearing area exactly where it is needed.
Common Selection Mistakes with SF-2 Series Bronze-Backed Composite Bushings
- Reaming a composite bushing to size after pressing it in, which cuts through the lining.
- Ignoring the pv limit and sizing on load alone, so the bushing survives the load and fails on sliding speed.
- Greasing a bushing whose lining is designed to run dry, which lets dust stick in the sliding gap.
- 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 SF-2 Series Bronze-Backed Composite Bushings Are Not the Right Choice
- Do not machine the bore after fitting — the lining is a few tenths of a millimetre thick and machining removes it.
- No misalignment capability whatsoever — a cylindrical bushing loads its edge as soon as the shaft tilts. Where the joint articulates, use a spherical plain bearing.
- Not for high speed at high load: the pv limit is reached long before any strength limit.
- Not for precision running clearance; the bore is created by the fit, and the clearance band is wider than a rolling bearing.
- Not where continuous low friction under load is required — starting friction is far higher than a rolling bearing, which is the usual reason a mechanism sticks.
- This type will not tolerate misalignment. The rolling or sliding contact is a line, so a fraction of a degree of tilt moves the whole load onto the end of the contact and the stress concentration there is what fails the bearing.
