Page 61 - Reciprocating Compressors Operation Maintenance

48 Reciprocating Compressors: Operation and Maintenance

crankpins to the crosshead pin. Similar to the main bearing, crankpin
bearings are babbitt-lined steel or cast-iron shells. They may be shim-
adjustable or shimless. In other designs, bearings are made from alu-
minum, bronze, or tri-metal construction.
The crosshead pin bushings are bronze, aluminum or babbitt-lined on
steel/cast-iron backing.
Crossheads, as illustrated in Figure 2-4, are generally made of cast
grey iron or nodular iron, but in some older designs cast steel is used.
Shoes or slippers of cast iron with babbitt overlay or shoes of aluminum
are bolted to the crosshead.

Top Crosshead
ShOS
Piston Rod
Lock Dowell

Crosshead
Pin Cap
Bottom I ^~~~~ i ' _ .. _ *~~*ffKfSSSlB!Vir~ SmattEnd
Crosshead—
Shoe
FIGURE 2-4. Crosshead with replaceable shoes (Source: Dresser-Rand, Painted
Post, New York).

The crosshead pin is made of steel and hardened to approximately 50
Re; it is tapered at the ends and held in place with caps. Other designs
have no taper and are free to rotate or "float," retained by lock rings.
The piston rod is threaded into the crosshead and is locked with a
dowel or set screws.
Other crosshead designs, such as the one in Figure 2-5, do not have
replaceable shoes or slippers but have the faces babbitted and machined
for a bearing surface. The crosshead pin is "floating"—it is not locked so
rotation is allowed, but it is restrained in the lateral direction by retaining
rings inserted in grooves in the pin. The total lateral movement of the pin
is .060" to .063".
Figure 2-6 shows a connecting rod, crosshead assembly, and all the
component parts of the connecting rod and the crosshead.