Page 309 - Reciprocating Compressors Operation Maintenance

294* Reciprocating Compressors: Operation and Maintenance

cracks. This inspection should also be repeated on final-ground, plated sur-
faces. No circumferential cracks or indication should be permitted.
Note: The use of bronze packing rings with chrome plated piston rods
is to be avoided because it leads to scoring of rods. If the compressor
uses bronze packing, chrome plating of piston rods should not be done.
Caution: All previous plating or spray must be removed before replat-
ing or spraying. DO NOT attempt to chrome plate or spray over surfaces
previously coated with fuseable alloy. Also, do not attempt to recoat fuse-
able alloy piston rods with any coating including fuseable alloy.
Regrind piston rods after coating or plating to size. Specify 16 RMS
finish for lubricated service and 8 RMS finish for nonlubncated service.
Bent rods may be straightened only if they have not been coated or plated.

Piston rods may be manufactured if proper attention is paid to selec-
tion of material, machining accuracies, heat treatment of materials, sur-
face treatments, and surface finishes.
Note: Do not attempt to manufacture piston rod without first asking
questions and consultation on the various aspects of piston rods.
Before deciding to manufacture piston rods, the following factors
should be considered:

1. Determine operating conditions of compressor.
2. Material may be substituted from original design but only after con-
sultation. Do not substitute new specifications without questions.
Ask questions!! Many times the reasons for designs are not known
and certain changes may be dangerous.
3. Coatings may be applied to piston rods that had originally been fur-
nished without these coatings.
4. Threads on piston rods are now made either by grinding or rolling.
Rolled thread is superior in that it eliminates high stresses at the root
of the threads. There are few, if any, repair service facilities that
have thread rolling equipment; therefore, this work must be subcon-
tracted. Do not attempt to substitute cut threads without consultation
and knowing all details of the compressor design.

In some cases, it is possible to use cut threads (on lathe, not die cut)
but considerable prior investigation will be required. Modern designs