Page 261 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair
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Power Transmission Gears   243

                  there is no starting and stopping, adequate clean oil is supplied, and the
                  speed is high enough to generate a hydrodynamic oil film. The journal
                  bearing can easily be manufactured in a split configuration for effortless
                  removal. Also, it can be repaired with a roll of  solder and an acetylene
                  torch when absolutely necessary, and machined in almost any shop where
                  an engine lathe of  sufficient size is available.
                    Unlike some machine bearings, gear bearings have imposed operating
                  loads in addition to loads due to rotor weights. These operating loads are
                  directly proportional to the transmitted torque, and since gears are basi-
                  cally constant torque machines, the bearing loads are basically constant.
                  Figure 6-22 is included to show the approximate bearing load directions for
                  speed reducers and increasers with single stage gearing. Bearing load magni-
                  tude and direction can be determined from many handbooks and are differ-
                  ent for each type of gearing. Thrust loads are produced by both single helical
                  and spiral bevel gearing; the direction of thrust changes with the direction of
                  rotation.


                                             Installation

                  Handling
                   A gear unit should always be moved by rolling on bars or skates or by
                 lifting it with slings through the lifting lugs or eye bolts found on all gear
                 units. Never lift or sharply pound on the shaft extensions or lubrication
                 piping as serious damage may result.
                   Most manufacturers’ gears are test run with a break-in oil that contains
                 a rust preventive which will protect the internal parts for at least  six
                 months under normal storage conditions after they leave the factory. Do
                 not store gear units outdoors unless covered. If the inoperative period is
                 greater than six months, special treatment is required (see “Inoperative
                 Periods” under “Lubrication”).

                 Foundation

                   The foundation under a gear unit has great bearing on the unit’s opera-
                 tion and life.  First of  all, proper alignment is absolutely essential for
                 long, trouble-free operation, and obviously, to maintain the alignment re-
                 quired for satisfactory operation, the gear unit must be securely mounted
                 to a suitable rigid foundation. lbo of the more commonly used founda-
                 tions are the concrete foundation and  soleplate combination, and the
                 common bedplate (baseplate).
                   The concrete foundation and soleplate combination is semi-permanent
                 and thereby allows for the removal of the gear housing at a later date
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