E-Mail: aavolyn@bellatlantic.net

Bronze material has been widely used in reciprocating gas compressors for piston rings,
packing rings and oil scrapers. The performance has been excellent in lubricated
applications. It is a must in the very high pressures (over 5000 PSI). However, as many have
found lately, all bronze materials are not the same.

Originally, packing rings and segmented compressor piston rings were manufactured from a
quality high-lead bronze sand castings which gives the best physical properties for both
frictional heat and good bearing life. With the difficulty in obtaining sand castings, some ring
suppliers have gone to the readily available centrifugally cast bronze bar stock SAE-660. The
two materials are very close in appearance. However, the difference is in the service.
Greater rod wear and cylinder wear are experienced over a period of time with SAE-660.

Cause/Effect:
A. Reduced quantities of lead in the mix increases the frictional heat at the sealing area
B. Presence of zinc makes the metal harder
C. Increased density due to centrifugal molding techniques. This also affects frictional
properties because of the lead dispersion and particle size.

Below compare the physical properties of the two materials. You can readily see the
frictional properties and the hardness are different. This is what makes the SAE-660
inadequate in packing, segmented piston rings and oil wiper applications. Note: SAE-660
does perform well for one piece piston rings because it provides excellent tensioning
properties which offset its frictional limitations.

When comparing the microscopic cross sections of the two materials, you will see a very
homogenous mixture of the lead, bronze, copper, zinc and tin in the SAE-660. The SAE-64
high lead bronze sand casting has large lead particles interspersed throughout in an uneven
manner. However, it is the very lead particles interspersed in the bronze sand casting that
give you good frictional properties and minimize the rubbing action at the mating surface and
the wear on the shaft and cylinder wall.

The SAE-64 high lead sand casting is a more expensive material because of the high
percentage of tin, but it more than makes up for slightly additional cost in the life of the seal
and the increased life of the mating surface. AAVOLYN strongly recommends that the
SAE-64 be specified in all packing and compressor ring applications

616 ORANGE ST.

P.O. BOX 1097

MILLVILLE, NJ 08332

Telephone: 856-327-8040

Fax: 856-327-9595

E-Mail: aavolyn@bellatlantic.net