Cylindrical Bronze Bushings BP25 — 16 to 32

BP25 sintered bronze is produced by compacting and sintering bronze powder, which leaves a controlled network of interconnected pores — typically around 20–25% of the material volume — that is then vacuum/pressure-impregnated with lubricating oil. In service, the oil is held in this porous matrix by capillary action. When the shaft rotates, frictional heat and the hydrodynamic action of the moving journal draw a thin film of oil out of the pores and onto the bearing surface; when motion stops and the bush cools, capillary forces draw the oil back into the porosity. This continuous, reversible exchange forms a self-replenishing lubricating film and is what makes the bearing effectively maintenance-free over its normal working life.

Because the lubricant is stored within the wall of the bush, thicker-walled variants in this range (such as the 4 mm wall of the Ø32 × Ø40 size) hold a larger oil reservoir than the thin-walled small sizes, while longer bushes distribute the shaft load over greater projected area and generate a more stable film. The mechanism performs best at moderate sliding speeds and steady loads, where the pumping action stays in balance; very slow oscillation, frequent stop-start duty, or shock loading reduce hydrodynamic pumping and rely more heavily on the boundary-lubrication reserve held in the pores.

Sintered bushings are normally retained by an interference (press) fit into a rigid housing; the housing bore effectively sizes the bush, since a correctly toleranced press fit closes the sintered sleeve down to its final running clearance. Observe the following:

• Use a properly aligned arbor press with a piloted mandrel that bears on the full end face of the bush — never hammer directly on the sintered material, which can chip pores closed or fracture the wall.
• Provide a lead-in chamfer on the housing bore and keep the bush square to the bore to avoid cocking during entry; the shorter 16 mm-length variants are more prone to tilting than the longer 50 mm sizes.
• Do not ream or machine the bore after fitting where avoidable — cutting smears metal over the surface pores and can seal the oil paths. If sizing is unavoidable, use a burnishing/ball-sizing tool rather than a cutting reamer to preserve porosity and set the final bore.
• Check running clearance after fitting against the intended shaft; the press fit will have reduced the free inside diameter.
• The bushes are supplied pre-impregnated — handle with clean gloves, avoid degreasing solvents that would strip the stored oil, and store in clean, dry conditions until use.

Choose a variant from this BP25 16–32 group when you need a compact, flangeless, maintenance-free journal bearing in the medium bore range and the load is spread axially rather than taken as a thrust face. Pick a shorter length (for example the Ø16 × Ø20 × 16 mm size) for space-constrained pivots and light guiding, and a longer length (such as the Ø32 × Ø40 × 50 mm size) where a higher length-to-diameter ratio, greater projected bearing area and a larger internal oil reservoir are wanted for steadier running. If your design needs an integral thrust shoulder to locate the shaft axially or to react end loads, select a flanged sintered bush instead of these cylindrical types. Where duty involves higher temperatures, heavier or shock loading, or a corrosive/abrasive environment, consider the sintered-iron (FP20) or alloy (SO16) material families rather than BP25 bronze. Confirm the exact bore, outside diameter and length against your housing and shaft before ordering, and specify the running clearance required for your speed and temperature.