Cylindrical Iron Bushings FP20

FP20 works as a self-lubricating bearing because roughly 20-25% of its volume is interconnected porosity flooded with oil. At rest, capillary action holds the oil within the pore network. When the shaft turns, two effects release it: frictional heat expands the oil more than the surrounding iron matrix, and the converging gap between shaft and bore generates a local hydrodynamic pressure that draws lubricant out of the pores at the load zone. A thin film is pumped onto the sliding surface, so the shaft rides largely on oil rather than on dry metal, keeping friction and wear low.

When rotation stops and the bush cools, the pressure and thermal drivers reverse and the same capillary action reabsorbs the surface oil back into the porosity — the reservoir is recharged for the next cycle. Because the lubricant is stored inside the bearing wall, no external oiling, greasing or maintenance is normally required over the service life, and the bush tolerates start-stop and oscillating duty where a fresh film must form repeatedly. The dense iron matrix gives FP20 its load-bearing hardness, while the retained pore volume sets how much oil is available to feed the interface.

These bushes are located solely by an interference (press) fit; the plain cylindrical form has no flange, so the housing carries all radial reaction and any axial retention is by the fit alone. Press into a clean, chamfered housing bore machined to roughly H7. Use a piloted arbor or insertion mandrel and press squarely — never drive the bush in with direct hammer blows, which brinell the sintered face and can distort the sleeve. A lead-in chamfer on both the housing mouth and the shaft end helps the bush enter without shaving.

• Bore closes after fitting: pressing into the housing shrinks the bore by a fraction of the diametral interference, so the finished running clearance must be planned around the after-fit bore, not the free size. Thicker-walled sizes at the large end (up to 10 mm wall) close less than the thin 1.5 mm miniature.
• Do not ream, hone or machine the bore: cutting smears the surface and closes the interconnected pores, destroying the self-lubricating action. If the bore must be brought back to size, use a polished ball or burnishing pin to size by displacement, which re-opens rather than closes the porosity.
• Shaft: a ground steel shaft, typically h6/g6 with a fine finish, gives the best film formation and life; harder, smoother shafts suit the iron matrix well.
• Handling: keep the bushes in their oiled packaging until fitting, and do not degrease or solvent-wash them — that strips the impregnated oil. Store flat and clean.

Choose the FP20 sintered iron cylindrical bush when cost, hardness and steady low-to-moderate-speed load capacity matter more than top speed or corrosion resistance. Against a hardened or ground steel shaft, FP20 typically outperforms bronze on price and on resistance to high specific and intermittent loads, making it ideal for motors, appliances and oscillating linkages. Prefer BP25 sintered bronze instead where sliding speeds are higher, quieter running is required, or the environment is wet, corrosive, marine or food-adjacent — bronze tolerates faster surface speeds and resists corrosion better. Within the cylindrical family, use this straight bush wherever the bearing takes purely radial load and needs no thrust face; if the design must also locate a shaft axially or react a light thrust, select a flanged variant rather than a plain sleeve. With 91 sizes from Ø3 to Ø100 mm bore, this range covers everything from miniature instrument spindles to heavy Ø100 mm shafts from a single material class.