Powder metallurgy oil-impregnated bearings are self-lubricating plain bearings made by pressing and sintering metal powder into a porous body, then vacuum-impregnating it with oil. The connected pores store the lubricant, heat during rotation pushes oil to the surface, and capillary action draws it back at rest, so the bearing runs maintenance-free in moderate speed and load conditions.
One bearing can run 100,000 hours in a fan motor and crush in a few thousand hours on heavy equipment. The bearing is the same. The duty cycle is not.
If you are choosing a bearing for a motor or a drive, this guide lays out the decision logic: how pores become an oil reservoir, how CuSn10 bronze differs from iron-based grades, how to check oil content and PV, and which assembly rules you cannot break. Yujiaxin Tech has delivered precision PM parts to appliance, automotive, and power-tool customers since 1998, with pressing, sintering, and impregnation under one roof.
Key takeaways
- Bronze bearings run 19-25% vol porosity and 18-25% vol oil content, the two sources of self-lubrication.
- Radial crushing strength is typically ≥150 MPa for bronze and ≥200 MPa for iron-based grades.
- PV is the binding selection limit: bronze runs about 1.6-1.8 N/mm²·m/s continuous, and above that the oil film breaks down.
- Shaft hardness should reach ≥HRC45 with roughness Ra 0.2-0.8 μm; press on the outer ring only and never solvent-clean the part.
A conventional plain bearing gets its oil from an external line or a grease cup, and it wears the moment supply stops. An oil-impregnated bearing stores oil inside itself. The connected pores left after sintering form the reservoir, and impregnation locks the oil into the matrix, so no external line is needed.
One point needs clearing up. Maintenance-free does not mean the oil lasts forever. The oil charge is fixed at the factory, and what it buys you is no relubrication schedule and no grease points to track, not an endless supply. In our delivery experience, intermittent service runs above 100,000 hours and continuous service roughly 10,000 to 30,000 hours, provided PV, temperature, and dust all stay inside the allowed window.
To see the whole powder metallurgy chain first, start with an overview of the six core PM processes.
Lubrication here is a closed loop. Three steps explain most of the selection numbers that follow.
Because the regime is mixed, low speed or light load can leave too little supply pressure, and shaft and bearing may touch directly, raising friction and temperature. That is why these bearings also have a minimum speed and load window.
Three systems cover three duty ranges, and picking the wrong family costs more than fine-tuning a parameter.
| System | Reference grades | Traits | Best for |
|---|---|---|---|
| Tin bronze CuSn10 (90Cu-10Sn) | SAE 841 / MPIF CT-1000 / ASTM B438 Gr1 Type2 / DIN 1850 / GB/T 5143 | Low friction, corrosion resistance, good heat conduction, embeds debris | Medium to high speed, light to medium load, low noise |
| Iron-based Fe-Cu(-C) | MPIF FC series / ASTM B439 | High strength, low cost, wear resistant | Low to medium speed, heavy load, mild shock |
| 316L stainless | Stainless PM grades | Corrosion resistance, hygiene | Wet, food, chemical, medical |
CuSn10 is the most common oil-impregnated bronze, about 90% copper and 10% tin, with density typically 6.4-6.8 g/cm³. The same material carries different names across standards, and SAE 841, MPIF CT-1000-K26, ASTM B438 Grade 1 Type 2, DIN 1850, and GB/T 5143 point to the same family. Iron-based grades run 5.6-6.6 g/cm³ density and can exceed 200 MPa crushing strength, at the cost of higher friction and noise.
Graphite bronze is a third route. Above roughly 3% graphite the bearing runs quieter, which suits oscillating duty, but load capacity drops.
Powder metallurgy oil-impregnated bearings trade these parameters against each other. None of them can be maxed out alone.
High speed wants low oil content (about 12-15%), and heavy load wants high oil content (about 20-25%). Oil content and speed move in opposite directions, and that rule is the one most often missed.
Selection runs in four checks, each tied to a number you can verify.
Keep the length-to-diameter ratio L/D between 1 and 1.5.
The pore structure is fixed in the first four steps. Mixing sets chemical uniformity, compaction sets green density, sintering sets pore connectivity and strength, and sizing corrects dimensions and tolerance. For the furnace side, see sintering temperature and atmosphere control, and for press pressure and tooling see the compaction process explained.
Vacuum impregnation is the last critical step. Parts go into a basket, the basket goes into an oil tank, vacuum pulls air from the pores, and restoring atmospheric pressure drives oil in. Oil choice follows the duty: mineral oil for -20 to +120 °C, synthetic oil to +150 °C, and anti-wear additives for heavy load. For the shapes we deliver, browse precision metal components.
Acceptance is not a formality. Five checks decide whether parts reach the assembly line.
| Check | Method | Typical range |
|---|---|---|
| Density | Archimedes method | Bronze 6.4-6.8 g/cm³ |
| Oil content | Mass or volume method | ≥19% vol (bronze) |
| Radial crushing strength | Crushing test | Bronze ≥150 MPa |
| Metallography and pores | Optical microscope | Pore distribution and connectivity |
| Dimensions and geometry | CMM | Per drawing datum |
Density by the Archimedes method is the most direct read on consolidation. Oil content is usually converted from a mass measurement and shows whether impregnation reached the target. Match grades and figures against the self-lubricating bearing tables in MPIF material standards.
Appliance motors are the largest home for powder metallurgy oil-impregnated bearings. Air-conditioner fans, washing machines, and juicer motors rely on them for quiet, maintenance-free running. Automotive use centers on wiper motors, seat motors, and small pumps, while power tools lean on them in drills, saws, and angle grinders. Within the global powder metallurgy market, bearings have long been one of the highest-volume product lines.
In 2024 a power-tool plant kept burning out angle-grinder bearings. Teardown showed the iron-based grade had too little PV margin, with duty load near the ceiling. After switching to an Fe-5Cu-3Gr-2MoS₂ mix, PV rose from 2.5 to 4.0 MPa·m/s and the return rate dropped.
Five failures cover most field problems, and each has its own fix:
Choosing a supplier is really a choice of process-chain completeness and data credibility.
Bring five duty figures to the first call and quotes arrive faster: shaft diameter and tolerance, speed, load direction and size, running mode (continuous or intermittent), and ambient temperature and media.
A source factory with a complete chain keeps mixing, pressing, sintering, sizing, impregnation, and inspection on one site, which keeps responsibility clear and lead time under control. For the inspection side, see quality control and inspection.
Conclusion: lining up the duty, the material, and the assembly
Getting powder metallurgy oil-impregnated bearings right depends on how the duty, the material, and the assembly line up. Keep PV, speed, and temperature inside the material limits. Pair the material with its parameters: bronze for medium-to-high speed and low noise, iron-based grades for heavy load at low speed, with oil content moving opposite to speed. Press the outer ring only, skip solvent cleaning, and leave the right clearance.
Get that alignment right and the maintenance-free promise holds. To receive samples and a capability list, send your duty data and our engineers will return a material recommendation, an oil-content plan, and a sample lead time. Request a sample and capability list from Yujiaxin Tech.
info@szyujiaxin.com 
中文
English
日本語
Deutsch
Русский
SHENZHEN YUJIAXIN TECH CO.,LTD.