SS316L Seamed Dry Self-Lubricating Bushings for Gear Pumps
SS316L Seamed Dry Self-Lubricating Bushings for Gear Pumps
High-Performance Self-Lubricating Bronze Bushing Solutions & Technologies. Minimize downtime, extend service life, and reduce costs for dynamic applications.
Plain Bearing Materials · Rotary Positive Displacement Pumps
SS316L Seamed Dry Self-Lubricating Bushings for Gear Pumps: Steel–Bronze–PTFE Wrapped Bearing Material and Selection Guide
A seamed (wrapped) dry-running self-lubricating bushing built on an SS316L stainless backing, a sintered bronze interlayer and a pigmented PTFE-based sliding layer is the standard thin-wall solution for gear pump journals handling low-lubricity, corrosive or high-temperature liquids. This guide sets out the verifiable material data, the published performance envelope, the chemical and thermal boundaries that actually govern service life, a gear-pump selection matrix, and the regulatory frameworks that apply — together with an explicit statement of what this document does not certify.
1. What this bushing is, and the terminology that matters
A wrapped bushing is a thin-wall plain bearing rolled from a flat composite strip. The composite is a three-layer metal-polymer construction:
- Backing — steel or stainless steel strip carrying the mechanical strength and the press-fit interference. Here: SS316L.
- Interlayer — a porous sintered tin bronze (CuSn8 or CuSn10 class) bonded to the backing. It anchors the polymer, conducts frictional heat into the housing, and provides a reservoir into which the sliding-layer compound is impregnated.
- Sliding layer — a PTFE-based compound with fillers, applied over and into the bronze. This is the layer that runs against the shaft and forms the transfer film.
On the word “seamed.” ISO 3547-1 states that in its free state a wrapped bushing might not be exactly cylindrical and its split can be open; after it has been pressed into its housing, in general, a wrapped bushing is round and its split is closed. Wrapped bushes can be closed by an interlocked split, and the design of the split is left at the manufacturer’s discretion. In practical terms “seamed” means the bushing is rolled from strip and carries a longitudinal split (either a plain butt joint or an interlocked/clinch joint), as opposed to a seamless machined or drawn sleeve. The split is a normal feature of the product family, not a defect — but the joint geometry is supplier-specific and should be part of the drawing specification.
1.1 Designation equivalence for the stainless backing
| System | Designation | Remark |
|---|---|---|
| UNS / ASTM | S31603 | Low-carbon molybdenum-bearing austenitic grade |
| EN / DIN | 1.4404 · X2CrNiMo17-12-2 | Per EN 10088-2 (sheet, plate and strip) |
| JIS | SUS316L | Commonly cited equivalence |
| GB/T | 022Cr17Ni12Mo2 | Commonly cited equivalence; verify against current GB/T 20878 |
| ISO 15510 | X2CrNiMo17-12-2 | ISO designation for the composition |
1.2 On the red colour of the sliding layer
Some PTFE-lined wrapped bushings are supplied with a red-pigmented sliding layer. Two points should be kept separate:
- Colour is an identification feature, not a performance property. Pigments are used in PTFE parts for identification, brand differentiation and stain masking, and they are not a functional property of the compound. Bronze-filled PTFE is naturally brown, so colour alone cannot be used to identify a formulation or a performance class.
- The pigment has a compliance dimension. Some red and brown PTFE pigments are based on iron oxide, while certain other red and yellow pigments (cadmium-based) and chrome-based pigments carry RoHS and hexavalent-chromium concerns. If the pigment matters for the application — because of a chemical, potable-water, food-contact or customer substance-restriction requirement — the pigment chemistry must be declared in writing by the supplier. Do not infer it from the colour.
Note: no food-contact, potable-water or medical suitability is implied by the colour or by this document. See section 11.
2. Why this construction is used in gear pumps
Gear pumps in chemical and process service present a combination of conditions that is hostile to conventional bearing arrangements:
| Condition in service | Consequence for the bearing | What the composite provides |
|---|---|---|
| Low-lubricity pumped liquid (light hydrocarbons, LPG, solvents, refrigerants, CO2, water, alcohols) | The hydrodynamic film generated by these liquids cannot reliably separate the surfaces; metal-to-metal contact, galling or seizing can follow | A solid-lubricant PTFE sliding layer that runs on a transfer film rather than on a fluid film; tolerant of boundary and mixed lubrication at start-up, low speed and starved suction |
| Solvents and water that wash grease out | Relubrication intervals collapse; the bearing becomes effectively dry | Dry-running capability; no external lubricant to be displaced |
| Corrosive media, marine atmosphere, frequent wash-down | A plated carbon-steel backing corrodes on its outside diameter; corrosion products occupy a larger volume than the steel consumed, so a thin-wall bush can swell inward, lose running clearance and seize | SS316L backing resists external attack and reduces galvanic interaction with stainless or aluminium housings |
| Wide viscosity range (published chemical gear-pump data: roughly 0.3 to 1 000 000 mPa·s) | Bearing load and speed vary enormously across the operating map | Two published limits — load and PV — can both be checked against the actual duty point |
| High media temperature (published pump data up to about 320 °C, with one manufacturer to 350 °C) | The polymer, not the steel, sets the ceiling | PTFE-based layer rated to about 280 °C continuous — but see the thermal warning in section 6 |
| Compact pump frames with pressure-loaded bearing blocks and thin-wall bores | No space for rolling bearings; the bush also acts as the axial pressure-compensation element | Thin wall, press-fit into an H7 bore, no axial retention hardware required |
3. Material data — SS316L backing
3.1 Chemical composition
| Element | ASTM A240 (316L) | EN 10088-2 (1.4404) | Comment |
|---|---|---|---|
| Carbon (C) | ≤ 0.030 | ≤ 0.030 | The defining “L” limit; limits sensitisation in the heat-affected zone of welded parts |
| Chromium (Cr) | 16.0 – 18.0 | 16.5 – 18.5 | |
| Nickel (Ni) | 10.0 – 14.0 | 10.0 – 13.0 | |
| Molybdenum (Mo) | 2.00 – 3.00 | 2.00 – 2.50 | Drives pitting resistance |
| Manganese (Mn) | ≤ 2.00 | ≤ 2.00 | |
| Silicon (Si) | ≤ 0.75 | ≤ 1.00 | |
| Phosphorus (P) | ≤ 0.045 | ≤ 0.045 | |
| Sulfur (S) | ≤ 0.030 | ≤ 0.015 | EN limit is tighter |
| Nitrogen (N) | ≤ 0.10 | ≤ 0.11 | Sources differ on the EN figure (0.10 vs 0.11); use the current EN 10088-2 table |
3.2 Mechanical and physical properties
| Property | Value | Condition / source basis |
|---|---|---|
| Tensile strength Rm | ≥ 485 MPa | ASTM A240 minimum, annealed |
| Tensile strength Rm | 530 – 680 MPa | EN 10088-2 cold-rolled strip, solution annealed, thickness ≤ 8 mm |
| 0.2% proof strength Rp0.2 | ≥ 170 MPa | ASTM A240 minimum, annealed |
| 0.2% proof strength Rp0.2 | ≥ 240 MPa | EN 10088-2 cold-rolled strip, solution annealed |
| Elongation after fracture | ≥ 40% | Both specifications, annealed |
| Hardness | ≤ 95 HRB / ≤ 217 HB | ASTM A240 maximum, annealed |
| Density | 8.0 g/cm³ | Annealed, 20 °C |
| Thermal conductivity | 15 W/m·K at 20 °C; 16.3 W/m·K at 100 °C | Annealed |
| Modulus of elasticity | 200 GPa | Annealed |
| Specific heat capacity | 500 J/kg·K | Annealed |
| Coefficient of thermal expansion | 16.0 × 10−6/K (20–100 °C); 17.0 × 10−6/K (20–300 °C) | Annealed |
| Electrical resistivity | 0.75 Ω·mm²/m | Annealed |
| Melting range | about 1375 – 1400 °C | Typical value from grade data; not a specification limit |
| Magnetic response | Non-magnetic in the annealed condition; may become slightly magnetisable after cold forming | Qualitative |
3.3 Corrosion and temperature limits
- Pitting resistance: PREN = %Cr + 3.3 × %Mo + 16 × %N. For the 1.4401/1.4404 family published values span about 23 to 28; a typical 316L composition (about 17.2% Cr, 2.1% Mo, 0.04% N) gives roughly 24 to 25.
- Chloride limits: 316L is subject to pitting and crevice attack in warm chloride environments and to stress-corrosion cracking above roughly 60 °C. Indicative guidance places ambient-temperature service near 1000 mg/L chloride and about 500 mg/L at 60 °C. These are indicative, not design limits.
- Sensitisation: carbide precipitation is reported over about 425 to 860 °C. The low-carbon L grade avoids sensitisation in the heat-affected zone, so no post-weld heat treatment is normally required.
- Oxidation in air: about 925 °C continuous and 870 °C intermittent. These figures are far above what the polymer sliding layer can survive; the composite limit is set by the polymer.
4. Material data — sintered bronze interlayer and PTFE sliding layer
4.1 Sintered bronze interlayer
| Property | CuSn8 (CW453K / UNS C52100) | Comment |
|---|---|---|
| Tin | 7.5 – 8.5% | ASTM B103/B103M gives C52100 at Sn 7.0–9.0% |
| Phosphorus | 0.01 – 0.40% | ASTM B103/B103M: C52100 at P 0.03–0.35% |
| Lead | ≤ 0.02% | Relevant to RoHS discussion in section 10 |
| Density | 8.8 g/cm³ | Wrought value |
| Thermal conductivity | 46 – 67 W/m·K | Published values differ between producers (about 46, 58 and 67 W/m·K); a porous sintered layer will be lower |
| Melting range | about 960 – 1040 °C | Producers quote either a single value near 1040 °C or a 960–1020 °C range |
| Specific heat capacity | 377 J/kg·K | |
| CTE (20–300 °C) | 18.5 × 10−6/K | |
| Modulus of elasticity | 115 GPa | |
| Hardness (ISO 3547-4) | about 150 HB | ISO 3547-4 lists CuSn8P at 150 HB and refers to ISO 4383 for multilayer bearing materials |
4.2 PTFE-based sliding layer
| Property | Value |
|---|---|
| Density | 2.13 – 2.19 g/cm³ |
| Crystal melting point | 327 °C |
| Continuous service temperature | 260 °C |
| Short-term service temperature | about 300 °C |
| Minimum service temperature | about −200 °C |
| Thermal conductivity | 0.24 W/m·K |
| Thermal decomposition in air | about 505 °C (some sources report pyrolysis above 400 °C) |
| Coefficient of friction against steel, dry | about 0.06 dynamic / 0.08 static unfilled; 0.02 to 0.10 by ASTM D1894 |
| Cold flow under 14.2 MPa at 23 °C | 11.8% deformation after 1 h; 14.3% after 24 h; 7.9% permanent set |
The cold-flow figures explain why the sliding layer is always a filled compound rather than neat PTFE. Fillers used in bearing-grade PTFE compounds include bronze, glass fibre, carbon, graphite, MoS2, PEEK, zinc sulfide, stainless steel and inorganic pigments. One published lead-free sliding-layer composition for this product family is 80–86% PTFE, MoS2 up to 8%, other fillers up to 5.5%, Sn 7–12%, balance copper — useful as an indication of the formulation space, not as a specification.
5. Construction, dimensions and fitting
| Item | Published range | Note |
|---|---|---|
| Steel backing thickness | 0.7 – 2.3 mm | Total bush wall commonly 0.3 to 3.0 mm |
| Sintered bronze interlayer | 0.20 – 0.35 mm | Porosity commonly reported at 25 to 40% |
| PTFE-based sliding layer | 0.01 – 0.05 mm running-in overlay on a 0.2 – 0.4 mm impregnated layer | Some sources define only the overlay (0.01–0.03 mm); others quote the whole impregnated sliding layer (0.2–0.4 mm). Both are in circulation |
| Transfer film on the shaft | 0.5 – 2 µm | Formed during running-in |
| Backing thermal conductivity | over 42 W/m·K (steel); over 70 W/m·K (bronze back) | Affects how much frictional heat leaves through the housing |
| Housing bore tolerance (ISO 3547-1) | H7 for d > 4 mm; H6 for d ≤ 4 mm | |
| Housing bore surface roughness | Ra 1.6 – 3.2 µm | ISO 3547-1 recommendation |
| Shaft surface roughness, dry running | Ra 0.2 – 0.5 µm | ISO 3547-1 recommends 0.2–0.4 µm; a widely used product datasheet states 0.4 ± 0.1 µm |
| Shaft surface roughness, lubricated | Ra 0.05 – 0.40 µm | |
| Shaft hardness | over 200 HB recommended | Unhardened shafts are usable; a hardened shaft extends bearing life. Hardness of 45 HRC and above is used in clean service, higher in contaminated service |
| Bore-after-mounting deviation (ISO 3547-1, one series) | +0.036/0 up to 10 mm; +0.043/0 for 10–18; +0.052/0 for 18–30; +0.062/0 for 30–50; +0.074/0 for 50–80; +0.087/0 for 80–120; +0.100/0 for 120–175 | Confirm the tolerance series on the drawing, since ISO 3547-1 carries more than one |
| Concentricity of inside to outside diameter | 0.05 mm | Unless otherwise agreed |
6. Published performance envelope
| Parameter | Published range | Comment |
|---|---|---|
| Maximum static load | 137 – 250 MPa | |
| Maximum dynamic load | 49 – 140 MPa | The lower figure is a normal-duty allowable, the higher a stated maximum |
| Maximum sliding speed, dry | 0.65 – 2.5 m/s | Sources note that speeds above about 2.5 m/s can lead to overheating and that a running-in procedure can help |
| Maximum sliding speed, oil lubricated | up to 5.0 m/s | |
| Maximum PV, dry, continuous | 0.5 – 1.8 MPa·m/s | |
| Maximum PV, dry, intermittent or short-term | 1.0 – 3.6 MPa·m/s | |
| Maximum PV, oil lubricated | about 10 MPa·m/s | |
| Coefficient of friction, dry | 0.03 – 0.25 | Lowest at high load and low speed; rises toward the low-load end |
| Coefficient of friction, oil lubricated | 0.02 – 0.08 | |
| Service temperature | −200 to +280 °C | Set by the polymer, not the steel |
6.1 Temperature de-rating
Published de-rating for this product family is given as a life factor rather than as a PV curve. One handbook gives, for dry continuous operation with average heat dissipation through the housing:
| Bearing temperature | 25 °C | 60 °C | 100 °C | 150 °C | 200 °C | 280 °C |
|---|---|---|---|---|---|---|
| Life factor | 1.0 | 0.8 | 0.6 | 0.4 | 0.2 | 0.1 |
Where the housing dissipates heat poorly the factors are lower (about 0.5, 0.4, 0.3, 0.2 and 0.1 at 25, 60, 100, 150 and 200 °C respectively), and intermittent dry operation with dwell periods roughly doubles them. This is the single most important derating consideration in a hot gear pump.
6.2 Worked first-order example
Consider an external gear pump on a viscous chemical duty with differential pressure 16 bar, gear width 40 mm and tip diameter 80 mm. A standard first-order estimate of the radial hydraulic load on the driven journal is:
F ≈ k × Δp × B × De, with k ≈ 0.85 for the driven gear and ≈ 0.75 for the drive gear, Δp in MPa, B and De in mm, giving F in newtons.
With Δp = 1.6 MPa: F ≈ 0.85 × 1.6 × 40 × 80 = 4352 N. For a journal of 40 mm diameter in a 40 mm long bush, the projected bearing pressure is P = 4352 / (40 × 40) = 2.72 MPa. At 300 min−1 the sliding speed is v = π × 0.040 × 300 / 60 = 0.63 m/s, so PV ≈ 1.71 MPa·m/s.
Interpretation: 1.71 MPa·m/s sits above the most conservative published continuous dry limit (0.5 MPa·m/s) and inside the least conservative continuous limit (1.8 MPa·m/s). That spread is the whole point: the number is meaningless without the supplier’s own PV data and application factors, and without stating whether the journal runs dry, boundary-lubricated by the pumped liquid, or fully flooded. At 150 °C the temperature life factor is 0.4, so the same duty point would need to be re-evaluated with a fourfold reduction in expected life.
A consequence worth stating explicitly: most journal loads in a high-pressure gear pump exceed what any dry PV rating allows, because in normal operation the journal is lubricated by the pumped liquid. The dry-running rating of this bushing is therefore a transient and upset capability — start-up, loss of suction, low-lubricity media, slow roll on standby — not the steady-state design limit.
7. Chemical and media limits
| Media group | Behaviour | Note |
|---|---|---|
| Water, alcohols, glycols, mineral and synthetic oils | Resistant | PTFE does not absorb water and does not swell |
| Acids and alkalis | Published data for this construction states it is not resistant to acidic media below pH 5 or alkaline media above pH 9 | This is a bronze-interlayer limitation. The bronze is encapsulated by the PTFE compound but remains exposed at cut edges, at the split, and through the porous structure |
| Oxidising acids and gases, free halides, ammonia, moist H2S | Not resistant | Applies to bronze-backed variants in particular |
| Strong acids, bases, solvents, hydrocarbons, hydrofluoric acid, aqua regia | PTFE itself is essentially inert | Applies to the polymer alone; the composite is a different question |
| Molten alkali metals (Na, K, Li), elemental fluorine especially at elevated temperature and pressure, ClF3, OF2, sodium–ammonia solutions, high-energy radiation | Attack PTFE | Standard PTFE exclusions |
| Alternating dry and wet service | Worst case for the sliding layer | Published relative-life guidance puts alternating dry/water service at about 20% while continuously-in-water service is quoted at about 200% of the base figure |
8. Application matrix — gear pumps
| Pump type / position | Typical condition | Load | Speed | Environment | Bushing recommendation |
|---|---|---|---|---|---|
| External gear pump, chemical process — drive and driven journals | Viscous polymers, resins, additives; up to about 100–120 bar differential | Medium to high | Low to medium | Non-corrosive to mildly corrosive | SS316L backing, sintered bronze, lead-free filled PTFE; verify PV and apply the temperature life factor |
| External gear pump — solvents, alcohols, esters, monomers | Low lubricity; lubricant wash-out | Low to medium | Low to medium | Aggressive to carbon steel | SS316L backing is the appropriate choice; confirm the sliding layer against the specific solvent at temperature |
| External gear pump — low-viscosity hydrocarbons, LPG, refrigerants, CO2 | Insufficient fluid film; risk of galling | Medium | Medium | Hydrocarbon | PTFE sliding layer for boundary-lubrication tolerance; evaluate the dry PV limit at start-up |
| Internal gear pump — high-temperature heat-transfer fluid | Media temperature beyond the PTFE continuous limit | Low to medium | Low | Hot, oxidising | Verify bush temperature, not bulk fluid temperature. Above about 260–280 °C consider alternative bearing materials |
| Gear pump with pressure-loaded bearing blocks | Bush acts as the axial compensation element as well as the journal bearing | High, pressure-dependent | Low to medium | Process fluid | Thin-wall wrapped bush with correct wall series; check bore closure under pressure load |
| Marine and wash-down duty — seawater, brine, humid salt atmosphere | External corrosion of the outside diameter | Low to medium | Low to medium | Chloride | SS316L backing; note the chloride and temperature limits in section 3.3 |
| Dosing and metering gear pumps — aggressive acids or caustics | pH below 5 or above 9 | Low | Very low | Corrosive | The bronze interlayer is the limiting element. Evaluate a bronze-free construction or a different bearing concept |
| Standby / intermittent duty with dry starts | Dry running at start-up | Medium | Low | Ambient | Dry-running PTFE layer with a defined running-in procedure |
9. Selection guide
9.1 Decision table
| If the condition is… | Then… |
|---|---|
| Pumped liquid has low lubricity, or the bearing can run dry at start-up | Choose a PTFE-based sliding layer rather than an acetal (POM) layered bearing |
| outside-diameter corrosion, wash-down or chloride exposure is present | Choose SS316L backing over plated carbon steel |
| Rotating rather than oscillating motion, with continuous sliding in one direction | Acetal-layered bearings with lubrication pockets are usually evaluated for the lubricated oscillating case; PTFE-layered bearings suit continuous rotation |
| Bearing temperature above about 150 °C | Apply the temperature life factor; above about 260 °C the polymer limit governs and alternatives are needed |
| Media pH below 5 or above 9 | Escalate to the supplier; the bronze interlayer is the constraint |
| Explosive atmosphere | Treat the polymer sliding layer as a potential friction, hot-surface and electrostatic ignition source and carry out an ignition hazard assessment on the complete pump |
| Lead restriction applies to the finished equipment | Specify a lead-free sliding layer and obtain a written substance declaration |
| Shaft hardness is below 200 HB or roughness is outside Ra 0.2–0.5 µm | Upgrade the shaft before upgrading the bearing material |
9.2 Backing and sliding-layer variants
| Variant | Strength | Limitation | Typical use |
|---|---|---|---|
| Carbon steel backing, Cu- or Zn-plated | Lowest cost; higher thermal conductivity than stainless | Plating offers limited salt-spray resistance; outside-diameter corrosion can close the bore | Dry, indoor, non-corrosive hydraulic service |
| SS316L backing | Corrosion resistance on the outside diameter, at cut edges and in wash-down; compatible with stainless and aluminium housings | Lower thermal conductivity than carbon steel, so frictional heat is removed less effectively through the housing; higher material cost | Chemical process, marine, food-plant wash-down, outdoor duty |
| Bronze backing | Higher thermal conductivity; resistant to water vapour and seawater | Not resistant to oxidising acids and gases, free halides, ammonia or moist H2S | Water and water-vapour service |
| PTFE-based sliding layer, lead-free | Wide temperature range, low friction, dry-running capability, broad chemical resistance of the polymer | Limited by the bronze interlayer in strongly acidic or alkaline media; cold flow under sustained load | Dry and boundary-lubricated rotation, gear pump journals |
| PTFE-based sliding layer containing lead | Higher published dry PV in some product data | Substance-restriction exposure under RoHS, ELV and customer banned-substance lists | Being phased out in most new designs |
| Acetal (POM) sliding layer with lubrication pockets | Suited to lubricated oscillating motion and to start-stop duty with relubrication | Depends on external lubrication; not a dry-running solution | Oscillating joints, greased pivots |
9.3 Failure modes and troubleshooting
| Symptom | Likely cause | First check |
|---|---|---|
| Rapid bore wear, clearance growth | Shaft too rough, PV above the rated envelope, abrasive contamination | Measure shaft Ra against the 0.2–0.5 µm range and recalculate PV at the real duty point |
| Scoring or seizure | Transfer film never formed; external grease applied to a dry-running grade; temperature beyond the polymer limit | Review the running-in procedure; confirm bearing temperature rather than fluid temperature |
| Bore closure and seizure without visible wear | Outside-diameter corrosion products expanding inward, or bore reduction under extreme pressure load on a pressure-loaded block | Inspect the outside diameter and the housing bore; review the backing material and the pressure-loading design |
| Bell-mouthing, uneven wear at the bush end | Misalignment or shaft deflection producing edge loading | Check housing alignment, shaft deflection under load and L/D ratio |
| Erosion or pitting of the sliding surface | Cavitation, entrained solids, or high-velocity leakage across the bush face | Review suction conditions, filtration and the pressure-compensation geometry |
| Short life in alternating wet and dry service | Transfer-film disruption in intermittent wetting | Establish whether service is continuously wet, continuously dry, or alternating; the alternating case carries a published life penalty |
10. Compliance and documentation
10.1 Frameworks that legitimately apply
| Framework | What it covers | Relevance here |
|---|---|---|
| ISO 3547 series, Plain bearings — Wrapped bushes | Part 1:2018 Dimensions; Part 2:2023 Test data for outside and inside diameters; Part 3:2017 Lubrication holes, grooves and indentations; Part 4:2017 Materials; Part 5:2020 Checking the outside diameter; Part 6:2020 Checking the inside diameter; Part 7:2020 Measurement of wall thickness of thin-walled bushes | Defines dimensions, tolerances, materials and inspection of the bush. It contains no PV, wear-life or seam-integrity performance criteria |
| EN 10204 | Type 2.1 — declaration of compliance with the order, without test results. Type 2.2 — compliance statement with results of non-specific inspection. Type 3.1 — results of specific inspection, validated by the manufacturer’s authorised inspection representative independent of the manufacturing department. Type 3.2 — prepared by that representative together with the purchaser’s representative or an inspector designated by official regulations | EN 10204 addresses metallic products. For a composite bush a 3.1 certificate normally covers the backing strip only. It is not a fitness-for-purpose certificate |
| API STD 676 | Positive displacement pumps — rotary, covering external gear, internal gear, lobe, vane and screw pumps for petroleum, petrochemical and gas industry service | Equipment-level pump specification; it does not approve a bearing material |
| ANSI/HI 3.1–3.5 and ANSI/HI 3.6 | Rotary pump nomenclature, definitions, application and operation; rotary pump tests | Testing and terminology for the complete pump |
| ATEX Directive 2014/34/EU | Equipment, protective systems, and components intended for use in potentially explosive atmospheres. Annex II requires that ignition sources including high surface temperatures be avoided, that electrostatic charges be prevented, that overheating caused by friction between rotating parts in contact be prevented at the design stage, and that instructions state maximum surface temperatures and other limit values | Applies to the complete pump placed on the market. A bushing is a component and carries no CE marking of its own |
| EN ISO 80079-36:2016 and EN ISO 80079-37:2016 | Non-electrical equipment for explosive atmospheres: basic method and requirements, and the types of protection constructional safety “c”, control of ignition source “b” and liquid immersion “k” applied to couplings, pumps, gearboxes, brakes and hydraulic or pneumatic motors | Ignition hazard assessment covers bearing overheating. Polymer parts must be assessed when incorporated into non-electrical equipment. A dry-running polymer sliding layer is both a friction and hot-surface source and an electrostatic source |
| RoHS Directive 2011/65/EU | Restricts ten substances in electrical and electronic equipment, with 0.1% lead by weight in each homogeneous material | RoHS applies to electrical and electronic equipment. A bare bushing is outside its scope; a motorised pump unit can be in scope, typically in category 11. Copper alloys may rely on Annex III exemption 6(c), which permits up to 4% lead by weight in copper alloys and is subject to review dates that must be checked in the current Official Journal. There is no general exemption covering lead in bearing shells for this application; Annex III entry 42 covers lead in bearings and bushes of internal combustion engines only and is not applicable to gear pump bushes. A lead-free sliding layer avoids the question entirely |
| REACH Regulation (EC) 1907/2006 | Registration, evaluation, authorisation and restriction of chemical substances, including the SVHC candidate list | Substance declarations for the sliding-layer compound and the pigment must be requested from the supplier. No general SVHC statement covering this product family could be confirmed in this review; the candidate list changes, so verify at the date of purchase |
| POP Regulation (EU) 2019/1021, PFOA entry | PFOA, its salts and PFOA-related compounds; fluoropolymers of the form CF3[CF2]n–R′ with n above 16 are excluded from the definition of PFOA-related compounds. Unintentional trace contaminant limits are 0.025 mg/kg for PFOA and its salts and 1 mg/kg for PFOA-related compounds in substances, mixtures and articles | PTFE itself is not restricted under this entry, but trace-contaminant limits apply and specific exemptions have been deleted or have expired. Reputable suppliers provide a written statement |
10.2 Documentation to request with the order
- EN 10204 3.1 inspection certificate for the SS316L backing strip, with the specification and temper stated.
- Written confirmation of the sliding-layer compound: base polymer, filler system, lead-free status, and pigment chemistry for red-pigmented variants.
- RoHS, ELV and REACH SVHC declaration, with the date and the version of the candidate list referenced.
- PFOA / POP statement referencing Regulation (EU) 2019/1021 and the trace-contaminant limits.
- Dimensional statement against ISO 3547-1, including the wall-thickness series, outside-diameter tolerance and bore-after-mounting tolerance series.
- Manufacturer’s own PV, load, speed and temperature data with the application factors used to derive them.
- Installation instructions: housing bore tolerance and roughness, shaft tolerance, hardness and roughness, press-fit method, and the seam/joint type.
- Running-in procedure, where one is specified.
11. Scope limits of this document
This document is a materials-engineering reference. It deliberately does not extend into regulated application domains, and nothing in it should be read as a certification, approval or declaration of conformity for any of them:
- No military or defence conclusion. No defence standard, munitions-list classification, or export-control determination (ITAR, 22 CFR 120–130; EAR, 15 CFR 730–774) is made or implied.
- No automotive type approval. IATF 16949 is an organisation-level quality management system standard, not a product approval. No automotive homologation, PPAP or part approval is claimed.
- No food-contact conclusion. EC 1935/2004 is the framework regulation; EU 10/2011 covers plastic materials and articles and requires a written declaration of compliance supported by migration testing for the actual article under the actual contact conditions; US FDA 21 CFR 177.1550 covers perfluorocarbon resins only, with total extractives limited to 3.1 mg/dm² and fluoride to 0.46 mg/dm², and does not clear a filled PTFE compound or a metal-polymer bearing. Whether a specific filled fluoropolymer sliding layer falls within EU 10/2011 scope must be determined formulation by formulation. A red pigment carries no food-contact implication.
- No medical device conclusion. Neither EU MDR (EU) 2017/745 nor the US FDA medical device regulations are addressed. No biocompatibility, USP Class or implantable-device claim is made.
- No nuclear conclusion. ASME NQA-1 quality assurance requirements and the RCC-M design and construction rules for pressurised water reactor nuclear islands are outside the scope of this review. No nuclear safety-class or procurement-grade determination is made.
- No aviation airworthiness conclusion. No EASA Part 21 or FAA 14 CFR Part 21 design or production approval, no AS9100 aerospace quality management system claim, and no NADCAP special-process accreditation is claimed or implied. Material property data presented here is provided as a data source for engineering evaluation only and does not constitute an airworthiness finding, a certification basis, or any other certification conclusion.
- No explosive-atmosphere certification. ATEX 2014/34/EU and the EN ISO 80079 series are described for information. No equipment category, EPL, temperature class or type of protection is assigned to any product.
12. Frequently asked questions
What does “seamed” mean in a wrapped bushing, and does the seam weaken it?
A seamed bushing is rolled from flat composite strip and therefore carries a longitudinal split. Per ISO 3547-1, in its free state a wrapped bush might not be exactly cylindrical and its split can be open; after it has been pressed into its housing the bush is in general round and its split is closed. Interlocked splits are available and split design is at the manufacturer’s discretion. The seam is an inherent feature of the wrapped-bushing family. No primary source was found for a rule requiring the split to be oriented away from the load zone; where duty is severe, specify the joint type and confirm installation orientation with the supplier.
When is an SS316L backing worth specifying over carbon steel?
Whenever the outside diameter can be exposed to moisture, chlorides, wash-down, process splash or a corrosive atmosphere. The failure mechanism is specific: corrosion products occupy a larger volume than the steel they replace, so a thin-wall bush pressed into a housing can swell inward, lose running clearance and seize before any wear is visible. The trade-off is thermal — carbon steel conducts frictional heat away better than stainless — so a stainless-backed bush should be checked against the temperature life factor with that in mind.
Can the bushing run completely dry?
Yes as a capability, with limits. The published dry envelope for this family is roughly 0.65 to 2.5 m/s sliding speed and 0.5 to 3.6 MPa·m/s PV depending on the source and on whether operation is continuous or intermittent, and de-rating with temperature is severe: a published life factor drops from 1.0 at 25 °C to 0.4 at 150 °C and 0.1 at 280 °C. In a liquid pump the journal is normally lubricated by the pumped liquid, so the dry rating should be treated as an upset and start-up capability rather than a continuous design limit.
Does the red colour of the sliding layer mean anything technically?
It identifies the variant; it does not grade performance. Pigments in PTFE are used for identification and stain masking and are not a functional property, and bronze-filled PTFE is naturally brown, so colour cannot be used to infer a formulation. The pigment chemistry does have a substance-restriction dimension, since certain red pigments are cadmium- or chromium-based rather than iron-oxide based. If the pigment matters, require a written declaration.
Which documents should accompany a supply of these bushings?
An EN 10204 3.1 inspection certificate for the backing strip, a written statement of the sliding-layer compound including lead-free status and pigment chemistry, substance declarations covering RoHS, ELV and REACH SVHC with the candidate-list version, a POP/PFOA statement, a dimensional statement against ISO 3547-1, and the manufacturer’s own PV, load, speed and temperature data with the application factors used.
Is an ignition hazard assessment needed for explosive atmospheres?
Yes, at equipment level. EN ISO 80079-36 names bearing overheating among the ignition scenarios to be assessed and requires polymer parts to be assessed when incorporated into non-electrical equipment. A dry-running polymer sliding layer is a friction and hot-surface source and also an electrostatic source. The bushing is a component and carries no marking of its own; the assessment is performed on the complete pump.
Disclaimer
All data in this document is indicative and is compiled from published manufacturer datasheets, handbooks and publicly available standards documentation. Values for load, sliding speed, PV limit, friction coefficient and service life are bench-test results obtained on specific test rigs with specific counterfaces, and published values for nominally the same product family differ substantially. No figure in this document may be used as a design allowable without confirmation against the specific supplier’s test report for the exact article being purchased, and without validation under the actual operating conditions of the application.
Material designations and cross-references are given for convenience only; the controlling document is always the current edition of the cited specification. Where sources conflict, the conflict is stated in the text. Temper, condition and test method are stated wherever they materially affect a value.
No product names, trademarks or company names are used in this document, and no endorsement of any manufacturer or product is expressed or implied.
This document is provided as a data source for material property reference and engineering evaluation. It contains no military, defence, automotive, food-contact, medical device, nuclear or aviation airworthiness certification, approval or conformity conclusion, and no explosive-atmosphere equipment category, protection level or temperature class is assigned. Nothing here constitutes an airworthiness finding, a certification basis, or any other certification conclusion of any kind.
No warranty of fitness for a particular purpose is given. Fitness for purpose, compliance with the applicable directives and regulations, and suitability for the intended service remain the responsibility of the designer, the equipment manufacturer and the purchaser.
Document revision: 2026-09. Review before use; standards, exemption expiry dates and substance lists change.
Metal Bushing (Lubricated Metal) -Self-Lubricating Bushing Materials
Bushings are specialized, self-lubricating metal components widely utilized across various industries due to their durability and low maintenance requirements. Self-lubricating metal bushings are engineered to function without additional lubrication in numerous applications, thereby minimizing maintenance needs. These bushings are available in various series and configurations, such as flanged bushings and split bearings, to meet specific application requirements.
Metal-Polymer Anti-Friction Plain Bearings
Metal-Polymer Composite Self-lubricating Bushing Material
Steel Back + Porous Bronze Sinter + PTFE
