Solid Bearing Blanks FP20

Sintered iron is produced by compacting iron powder in a die and sintering it below the melting point, leaving a rigid metal skeleton threaded with roughly 20-25% interconnected porosity. That open pore network is vacuum-impregnated with lubricating oil, which is held in the body by capillary action and typically fills the majority of the available pore volume. In service the blank machined into a bearing works as a self-contained lubrication system: as the shaft rotates, frictional heat and the hydrodynamic pressure of the moving journal draw oil out of the pores and into the running clearance, forming a supporting film. When motion stops and the bearing cools, capillary forces and thermal contraction reabsorb the oil back into the porous structure, so it is retained rather than lost.

This cycle repeats without any external lubrication, which is why bearings cut from FP20 blanks run maintenance-free and dry to the touch. Critically, the porosity and its oil charge are distributed through the whole solid section, so when the customer bores the blank to the final inside diameter or turns the outside diameter, the freshly exposed working surface is just as oil-rich as the original skin. The self-lubricating function is a bulk property of the material, not a surface coating that machining would remove.

These blanks are supplied oversized for machining and must be finished to the target running clearance in-house. Observe the following when working and fitting them:

• Machine dry or with minimal cutting fluid. Use sharp tooling with light finishing cuts. Avoid flooding with coolant, which can wash oil from the surface pores; a light pass keeps the bore open and oil-rich.
• Do not smear the porosity. Blunt tools, excessive feed or aggressive burnishing can close the surface pores and blind the oil paths. Finish-bore rather than ream hard, and deburr gently.
• Allow for press-fit closure. When the finished bush is pressed into a rigid housing the bore contracts, so bore and check the inside diameter after fitting, or size the pre-fit bore to give the correct running clearance once installed. Provide a lead-in chamfer on the housing.
• Support the shaft correctly. Run against a smooth, hardened steel journal for best film formation and low wear.
• Re-oiling (optional). Machined blanks may be re-impregnated by soaking in warm bearing oil before assembly to top up any oil displaced during cutting.

Choose Solid Bearing Blanks FP20 when no standard finished bush matches your requirement and you intend to machine the bearing yourself — for a non-catalogue bore/OD pair, an integral flange, an unusual length, or several short bushes cut from one length. Within the self-lubricating family, select the FP20 iron grade over sintered bronze (BP25) when you want greater bulk strength, higher hardness and lower material cost, and can accept a slightly harder-running ferrous bearing against a steel shaft; prefer bronze blanks where softer, quieter running, better corrosion resistance or higher surface conformability matter more. Pick the smallest blank diameter and length that leave adequate machining allowance around your finished dimensions: the Ø 20 × 40 mm size for compact pivots and small bushes, stepping up through the range to the Ø 145 × 120 mm size for large sleeve bearings, thrust rings or batch-parted production. If your target size already exists as a finished FP20 bush, that ready-machined part will usually be the more economical choice than machining from solid.