Page 60 - Reciprocating Compressors Operation Maintenance

Design and Materials for Reciprocating Compressor Components 47

A knowledge of the materials used in the construction of the major
components of the heavy-duty water-cooled compressor will permit the
proper maintenance and repair of those components.
Frame or crankcase is a high-grade cast-iron casting similar to
ASTM class 40 or 50; it is designed with suitable supports or ribbing to
mount the compressor cylinders, crankshaft, and other running gear parts
and hold them in accurate alignment under the stresses imposed during
operation.
Crankshafts are made from carbon steel forgings or nodular iron
(ductile) castings. Most forgings are carbon steel conforming to AISI
1020, ASTM 668 for small shafts and AISI 1045, ASTM 668 class F for
large shafts. Nodular iron crankshafts conform to ASTM A-536 Grade
80-55-06. No hard surface treatment is used, and the shafts are not
dynamically balanced, unless they are used on compressors with rotative
speeds of 900 rpm and above.
Main bearings may be horizontally split shells made of steel or cast
iron, with a lining of babbitt. Some are made of aluminum without babbitt
or of a steel/bronze/babbitt tri-metal construction. The shells may have a
laminated shim placed between the halves to permit adjustment for wear.
On some smaller compressors, anti-friction roller bearings are used.
Connecting rod as shown in Figure 2-3 is a semi-marine type, made
from a low carbon steel forging. Oil under pressure is conducted from the

Connecting Rods

FIGURE 2-3. Connecting rods (Source: Dresser-Rand, Painted Post, New York).