Page 39 - The Tribology Handbook

A6 Porous meta I bearings

Composition and porosity
The graphited tin bronze (No. 1 in Table 6.1) is the gen- iron-based alloys can be used. Soft iron (No. 5) has a low
eral purpose alloy and gives a good balance between safety factor against oil starvation, especially with soft
strength, wear resistance, conformability and ease ofmanu- steel shafts. Graphite (Nos. 6 and 10) improves this, but
facture. Softer versions have lead (No. 4) or reduced tin (No. reduces the strength unless the iron is carburised during
2). Graphite increases the safety factor if oil replenishment sintering (No. 11). Copper (Nos. 7, 8 and 9) increases the
is forgotten, and the high graphite version (No. 3) gives strength and safety factor. If combined with carbon (Nos.
some dry lubrication properties at the expense of strength. 12, 13 and 14) it gives the greatest strength especially after
Where rusting is not a problem, the cheaper and stronger heat treatment.

Table 6.1 Typical specifications for porous metal bearing materials

No. rd Composition Notes on composition
Fig. 6.2
1 89/10/1 Cu/Sn/graphite General purpose bronze (normally supplied unless otherwise specified).
Reasonably tolerant to unhardened shafts
2 91/8/1 Cu/Sn/graphite Lower tin bronze. Reduced cost. Softer
3 85/10/5 Cu/Sn/graphite High graphite bronze. Low loads. Increased tolerance towards oil starvation
4 86/10/3/1 Cu/Sn/Pb/graphite Leaded bronze. Softer. Increased tolerance towards misalignment

5 >99% iron (soft) Soft iron. Cheaper than bronze. Unsuitable for corrosive conditions. Hardened shafts
preferred
6 97$/2+ Felgraphite Graphite improves marginal lubrication and increases tolerance towards unhardened
shafts

7 98/2 Fe/Cu Increasing copper content increases strength and cost. This series forms the most
popular range of porous iron bearings. Hardened shafts preferred
8 2% to 25% Cu in Fe
9 75/25 Fe/Cu
10 8911012 Fe/Cu/graphite High graphite improves marginal lubrication and increases tolerance towards
unhardened shafts

I1 99/0.4 Fe/C Copper free, hardened steel material
12 97/2/0.7 Fe/Cu/C Hardened high strength porous steels. Increasing copper content gives
increasing strength and cost
13 2% to 10% Cu in 0.7 C/Fe
14 89/ 10/0.7 Fe/Cu/C

Nofe: These typical specifications are examples ofmaterials listed in various relevant standards such as: IS0 5755/1, BS 5600/5/1, DIN 30
910/3, MPIF/35, ASTM B 438, ASTM 439. Most manufacturers offer a wide choice of compositions and porosities.

A6.4