Alignment reverse-dial indicator

Cold alignment. There are two predominant techniques used for cold alignment. These are (1) the face-OD method, and (2) the reverse-dial indicator method. Both these techniques utilize dial indicators. For highspeed turbomachinery, the reverse-dial indicator method is the superior method and should be used. 

There are three primary methods of aligning machine trains with dial indicators reverse-dial indicator method, also called indicator-reverse method, and two variations of the rim-and-face method. 

Reverse-dial indicator method (also referred to as indicator-reverse method) is the most accurate form of mechanical alignment. This technique measures offset at two points and the amount of horizontal and vertical correction for offset and angularity is calculated. Rim readings are taken simultaneously at each of the four positions (12, 3, 6, and 9 o clock) for the movable machine (MTBS/MTBM) and the stationary machine. The... 

As with the reverse dial indicator method, the measuring device used for rim-and-face alignment is also a dial indicator. The fixture has two runout indicators mounted on a common arm as opposed to reverse-dial fixtures, which have two runout indicators mounted on two separate arms. 

Rim-and-face alignment is subject to the same errors as those of the reverse-dial indicator system. As with that system, care must be taken to insure proper orientation with the equipment and accurate recording of the data. 

Most of the optical-alignment systems incorporate a micro-processing unit, which eliminates recording errors commonly found with reverse-dial indicator and rim-and-face methods. Optical systems automatically maintain the proper orientation and provide accurate offset and angularity data, virtually eliminating operator error. 

With horizontally mounted units, it is possible to correct both angularity and offset with one adjustment. In order to compute the adjustments needed to achieve the desired alignment, it is necessary to establish three horizontal measurements. These measurements are critical to the success of any alignment and must be accurate to within f inch (see Figure 54.20). Again, the procedure described here is for the reverse dial indicator method (see Figure 54.16). 

Figure 54.20 Reverse-dial indicator alignment setup...

The following procedure can be used on vertical units to obtain angularity and offset values needed to compare with recommended manufacturer s (i.e., desired) tolerances in order to determine if a unit is out of alignment. Perform an alignment check on the unit using the reverse-dial indicator method. 

The graphical plotting technique for computing initial alignment can be performed with any of the three types of measurement fixtures (i.e. reverse dial indicator, rim-and-face, or optical). The following steps should be followed when plotting alignment problems ... 

There are three methods of aligning machinery with dial indicators. These methods are (1) two-indicator method with readings taken at the stationary machine, (2) two-indicator method with readings taken at the machine to be shimmed, and (3) indicator reverse method. Methods 1 and 2 are often considered to be one method, which is referred to as rim-and-face. 

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