Environmental Protection in Sliding Bearings
We provide custom manufacturing of finished bronze parts and self-lubricating bronze, precisely based on our clients’ drawings.
Environmental Protection in Sliding Bearings: What to Measure First
Most writing on environmental protection in sliding bearings stops at intentions. This page takes the measurable route: how much lubricant a greased plain bearing consumes, where it ends up, what friction costs in energy, and how much material leaves as scrap. Where a self-lubricating bronze bushing improves those numbers we say by how much and under which conditions; where it makes them worse, we say that too. The figures are typical ranges — take your own baseline first.
Where the environmental load comes from
A sliding bearing touches the environment in five places, only one of which is the lubricant you buy.
| Source | What drives it | Typical order of magnitude | How to measure it |
|---|---|---|---|
| Lubricant purchased | Lube points × dose per point × intervals per year | A point greased weekly at 2–5 g uses about 0.1–0.3 kg/a (0.2–0.7 lb/a); 100 points greased monthly at 5–10 g use 6–12 kg/a (13–26 lb/a) | Lubrication schedule; weigh a few metered gun strokes |
| Lubricant lost to the surroundings | Over-greasing, seal leakage, washout, spillage | Varies widely with housekeeping; often a large share of the applied volume | Weigh trays under sample points for a month |
| Energy lost to friction | Friction coefficient × load × velocity × hours | About 0.001–0.01 with a full oil film; about 0.05–0.20 in boundary or dry sliding | Motor current at fixed duty |
| Replacement parts | Wear life and intervention interval | A 6-month to 24-month change-out removes about three quarters of the parts over four years | Maintenance records per bearing location |
| End of life | Alloy type and contamination | Bronze carries scrap value; oily rags and swabs need controlled disposal | Weigh scrap by alloy family; ask for the settlement sheet |
The clear gains are usually in the first, second and fourth rows — the last especially where the duty is slow or hard to reach. The third row can move the wrong way.
What a self-lubricating bronze bushing changes
Graphite-plugged bronze removes the external lubricant from a bearing location and replaces it with a solid film generated as the shaft slides. The comparison below keeps both columns on the same duty: slow to moderate speed, high load, and an environment that either washes grease out or makes relubrication awkward.
| Factor | Greased bronze bushing | Graphite-plugged bronze bushing | Comment |
|---|---|---|---|
| External lubricant | Required at set intervals | None during service | Removes purchase, handling and disposal |
| Leakage and housekeeping | Possible at seals and after over-greasing | No free oil or grease | Relevant in food, textile, paper and water contact |
| Friction coefficient | About 0.001–0.01 with a full film; 0.05–0.15 boundary | About 0.10–0.20 running dry | At low speed the film rarely forms, so the gap narrows |
| Heat removal | Oil carries heat away | Through shaft and housing | This is what sets the PV ceiling |
| Sliding speed | High, once the film forms | Low, typically a fraction of a metre per second | Check PV before converting a rotating shaft |
| Temperature range | Limited by the grease or oil | Commonly to about 300 °C (570 °F) | Confirm against the material certificate |
| Service interval | Set by schedule and by wear | Set by wear only | The gain is largest where access is difficult |
| End of life | Oily parts and cleaning waste | Dry parts to metal scrap | Sorting by alloy keeps the scrap value |
Two consequences follow from the friction row. On a rotating shaft that already runs on a proper oil film, switching to dry bronze raises friction losses rather than lowering them — keep the oil. On slow or oscillating duty, which covers most plain-bearing locations in heavy plant, the film never fully forms, so the gap narrows and the maintenance and cleanliness gains dominate. Material options for that duty are listed under cast bronze oilless materials and graphite bronze bushings.
Material choice, compliance and end of life
The compliance questions buyers raise are almost always about lead. Leaded bronzes earn their place on performance grounds: lead improves conformability, embeddability and behaviour during a lubrication upset. The counterweight is regulation — in the European market lead in products is restricted, with an exemption covering lead as an alloying element in copper alloys up to a defined weight percentage whose scope and review status change over time, so the current text has to be checked. Lead also appears on the candidate list of substances of very high concern, which brings communication duties along the supply chain. Nothing here is legal advice.
| Alloy family | Engineering character | Compliance point to check | End of life |
|---|---|---|---|
| Leaded tin bronze (C93200 / CuSn7ZnPb type) | Forgiving of misalignment, good embeddability | Lead content against the copper-alloy exemption threshold | Recycled as leaded copper scrap; declare the grade |
| High-lead bronze (ZCuPb30 type) | High load capacity with poor lubrication | Usually the first alloy questioned in a review | Recycled, but documentation may be required |
| Aluminum bronze (CuAl10Fe, CuAl10Ni) | Strong, seawater resistant, low lead when specified accordingly | Nickel listings to check | Recycled as aluminum bronze scrap |
| Graphite-plugged brass or bronze | Solid lubricant embedded in the working surface | The matrix alloy governs, not the graphite | Dry parts, no oily waste |
| PTFE-lined or polymer composites | Low friction, no metal-to-metal contact | Fluoropolymer restrictions depend on the destination market | Usually not recyclable together with metals |
Copper alloys are among the most heavily recycled engineering materials, and secondary material supplies a large share of world copper use, so a bronze bushing arrives at end of life with value rather than a disposal cost. Three rules keep it: separate by alloy family, remove steel inserts, keep the parts dry — mixed or oily scrap is downgraded. Regulation and declaration practice are covered on our bronze bushing alloys and compliance and standards and certifications pages.
Limits: when an oilless bushing is the wrong answer
- PV above the material limit. For graphite-plugged bronze, dry PV limits are commonly about 1.0–1.6 MPa·m/s. Above that, wear accelerates.
- Continuous rotation at meaningful speed. Where a hydrodynamic film exists, oil is lower friction and better at carrying heat away.
- Heat with nowhere to go. Without oil, heat leaves through shaft and housing; a light housing or long duty cycle overheats the contact.
- Graphite dust is not acceptable — paint lines, clean rooms, electrical contacts, some food-contact surfaces.
- Abrasive slurry at the contact. Sand or scale cuts both parts. Filtration, flushing or a harder pairing is the fix.
- The existing bearing still has long remaining life. Replacing a serviceable part early spends new material before the old part has delivered its service.
- No wear monitoring. Dry bushings wear gradually, then faster; unmeasured, failure arrives as a seizure.
Selection and installation notes
- Record the baseline first. Annual grease volume at the affected points, hours between interventions, measured wear. Without it you cannot show whether a change helped.
- Calculate PV with margin using worst-case load and speed. See bushing material and housing practice.
- Check the shaft. A hardened shaft is normal, commonly above 300 HB, finished to about Ra 0.4–0.8 µm (16–32 µin).
- Hold the housing. A press fit in an H7 bore is standard. Thin walls take the shape of the housing, so an out-of-round bore gives an out-of-round bearing.
- Set the running clearance at typically 0.1–0.25% of shaft diameter, widened where thermal growth is expected.
- Dimension the plug layout for roughly 25–30% coverage of the working surface.
- Allow a run-in of a few hundred cycles at reduced load so the transfer film forms.
- Set the inspection interval from measured wear, not from the old lubrication interval.
- Plan the scrap route at specification time: segregate removed bushings by alloy and keep them dry.
In water or weather exposure, corrosion joins the list of constraints; see marine and offshore sliding bearings and water infrastructure bushings.
A comparison worth doing. Take one machine, list its lubrication points, and work out the annual volume, interventions and parts consumed. Convert the two points with the worst access and repeat the exercise a year later. See also oilless bushes vs traditional lubricated bearings.
Frequently asked questions
Does removing a grease point reduce total lubricant consumption?
At that location, yes — usually by the whole amount the point used. Two cautions: check whether other points on the machine dominate the total, and note that a dry bearing outside its PV envelope costs more in downtime and parts than the grease did.
Is a self-lubricating bushing automatically the lower-friction option?
No. A full hydrodynamic oil film has a lower friction coefficient than dry graphite bronze by roughly an order of magnitude. The advantage appears where the duty never builds a film: slow, oscillating, stop-start, or where the lubricant is washed out.
What happens to a removed bronze bushing?
Into the copper alloy scrap stream, normally with resale value. Segregate by alloy, remove steel inserts, keep the parts dry — mixed or oily scrap is downgraded. Ask the recycler for the assay and settlement sheet.
Do lead-bearing bronzes still make engineering sense?
In some duties, yes, where embeddability, conformability and behaviour during a lubrication upset matter. It then becomes a compliance question: confirm the current restriction status and exemption conditions for your market, and record the declared lead content on the drawing.
Assessing a switch to dry running?
Send the duty — load, speed or oscillation angle, temperature, medium and the current lubrication interval — and we will say whether a solid-lubricated bushing fits the envelope.
