Procedures alignments

Interplanar Spacings. Diffractometer alignment procedures require the use of a well-prepared polycrystalline specimen. Two standard samples found to be suitable are silicon and a-quartz (including Novaculite). The 26 values of several of the most intense reflections for these materials are listed in Table 7.6 (Tables of Interplanar Spacings d vs. Diffraction Angle 26 for Selected Targets, Picker Nuclear, White Plains, N.Y., 1966). To convert to d for Ka or to d for Ka2, multiply the tabulated d value (Table 7.6) for Ka by the factor given below ... 

Prior to anv machineiy alignment procedure, it is imperative to check for machine pipe strain. This is accomplished by the placement of dial indicators on the shaft and then loosening the hold-down bolts. Movements of greater than 1 mil are considered indication of a pipe strain condition. 

This condition is probably misalignment, indicating a maintenance problem. The mechanic should be trained to correct this. Follow correct alignment procedures, as well as correct bolt torque procedures. 

This method is most usefiil when only one of the shafts can be rotated for the alignment procedure, or when the two shaft ends are very close to each other. Obtain the displacement readings with the dial on the rim (OD) of the coupling and the coupling face. Project these readings mathematically or graphically to the motor base to determine the required adjustments and shims for each foot. This method is not as precise and may have a built-in error, if the coupling center is eccentric from the shaft centerline. 

The alignment procedure should be repeated at various intervals to identify installation errors and compensate for equipment operation. This is the way to assure long equipment life. It is recommended to go through the alignment procedure and make corrections in the following stages ... 

Hot alignment Allow the equipment to run for three or four hours and come up to operating temperature, then shut-off the pump and repeat the alignment procedure with the equipment hot. 

During the alignment procedure, follow your plant loekout/tagout procedure to prevent accidents. 

Mount the dial indicators on the equipment in the same manner and distance required to perform the alignment procedure. 

This same procedure can be used during the actual alignment procedure to cancel bar deflection. 

Tools most commonly used for alignment procedures are dial indicators, adjustable parallels, taper gauges, feeler gauges, small-hole gauges, and outside micrometer calipers. 

Two perfectly aligned shafts are colinear and operate as a solid shaft when coupled. This condition is illustrated in Figure 54.1. However, it is extremely rare for two shafts to be perfectly aligned without an alignment procedure... 

Before starting the alignment procedure, check for soft-foot and correct the condition. 

Soft-foot is the condition when all four of a machine s feet do not support the weight of the machine. It is important to determine if this condition is present prior to performing shaft alignment on a piece of machinery. Not correcting soft-foot prior to alignment is a major cause of frustration and lost time during the aligning procedure. 

Dial-indicator readings taken as part of the alignment procedure can be different each time the hold-down nuts are tightened, loosened, and retightened. This can be extremely frustrating because each attempted correction can cause a soft-foot condition in another location. 

Number each machine foot in the sequence in which the hold-down nuts will be tightened during the alignment procedure. The numbers (1, 2, 3 and 4) should be permanently marked on, or near, the feet. 

Measurements taken with this device are based on a point of reference at the zero position, which is defined as the alignment fixture at the top of the shaft - referred to as the 12 o clock position. In order to perform the alignment procedure, readings also are required at the 3, 6, and 9 o clock positions. 

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