Dial indicators

The Rockwed testing machine is thus a framework permitting stable support of the workpiece on one side and means to impress the indenter under specified load on the other. A dial indicator attached to the indenter spindle is used to read directly the depth of indentation in hardness numbers. 

Barcol Indenter. The Barcol hardness tester is a hand-held, spring-loaded instmment with a steel indenter developed for use on hard plastics and soft metals (ASTM D2583) (2). In use the indenter is forced into the sample surface and a hardness number is read direcdy off the integral dial indicator caUbrated on a 0 to 100 scale. Barcol hardness numbers do not relate to nor can they be converted to other hardness scales. The Barcol instmment is caUbrated at each use by indenting an aluminum ahoy standard disk suppHed with it. The Barcol test is relatively insensitive to surface condition but may be affected by test sample size and thickness. 

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 is the most popular method used in industry tttday because the investment in equipment is moderate and its effectiveness is proven. This method uses two dial indicators, one on the pump shaft and the other on the motor shaft. 

Sometimes in practice the dial indicators are mounted on the couplings, but it is best to mount and fix the indicatttrs onto the shafts because the couplings may be eeeentrie to the shaft centerlines. Rotate the shafts and obtain the displacement readings. Project these readings graphically (tr mathematically to the motor base t(t determine the adjustments required, and the spacing shims under each foot. 

To check for soft foot, place a dial indicator onto the machinery foot, and loosening the base bolt. If the indicator moves more than 0.002 inches, the foot is soft and it should be corrected. Go through the same procedure on the remaining feet one at a time. 

To correct soft foot, place shims under the foot in the thickness corresponding to the movement of the dial indicator. 

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

This dial indicator is fixed to the volute mounting adapter collar of the pump and the needle is on the shaft (Figure 14-21). The shaft should be moved radially by hand (see the arrows) up and down. Note the movement in the indicator. This is a check of the radial tolerance in the bearing. Some people use the word run out . Radial dellection causes misalignment of the rotating and stationary faces of the mechanical seal. This shortens the seal life by eausing drive pins and springs to wear and rub in relative motion. 

Install the pump back plate and seal chamber assembly. Mount the dial indicator on the shaft and place the needle onto the outer diameter of the lip or face of the seal chamber (Figure 14-24). An alternate method would be to place the indicator needle inside the seal chamber bore. Rotate the shaft. This will verify that the shaft is concentric with the seal chamber bore. If it is not concentric, the seal may rub against the bore when the pump is started. 

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. 

Figure 18-17. Graphic plotting for reverse-dial indicator method.

Hot alignment check. This technique attempts to determine actual alignment status when the machines are hot. When the machines are running, it is impossible to use dial indicator techniques on the shafts. 

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

From a practical standpoint, it is often difficult or undesirable to position the stems of the dial indicators at 90° angles to the rim and/or face surfaces of the coupling halves. For this reason, brackets are used to mount the devices on the shaft or a non-movable part of the coupling to facilitate taking readings and to insure greater accuracy. This is a valid method because any object that... 

The length of side b is measured with a tape measure and the length of side a is measured with a device such as a dial indicator. Note that this diagram assumes the coupling is centered on the shaft and that its center-line is the same as the shaft s. Angle A in degrees is calculated by ... 

Always position the stem of the dial indicator so that it is perpendicular to the surface against which it will rest. Erroneous readings will result if the stem is not placed at a 90° angle to the surface. 

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. 

Secure a dial-indicator holder to the base of the stationary machine and the MTBS. The stem of the dial... 

Set the dial indicator to zero. Completely loosen the hold-down nut on the foot to be checked. Watch the dial indicator closely for foot movement during the loosening process. 

If the foot rises from the base when the hold-down nut is loosened, place beneath the foot an amount of shim stock equal to the amount of deflection shown on the dial indicator. 

Move the dial indicator and holder to the next foot to be checked and repeat the process. Note The nuts on all of the other feet must remain securely tightened when a foot is being checked for a soft-foot condition. 

Indicator sag is best determined by mounting the dial indicator on a piece of straight pipe of the same length as in the actual application. Zero the dial indicator at the 12 o clock, or upright, position and then rotate 180° to the 6 o clock position. The reading obtained, which will be a negative number, is the measure of the mounting-bracket indicator sag for 180° of rotation and is called the sag factor. 

Indicator sag is the term used to describe the bending of the mounting hardware as the dial indicator is rotated... 

There are two primary methods of aligning machine trains dial indicator alignment and optical, or laser, alignment. This section provides an overview of each, with an emphasis on dial-indicator methods. 

Dial-indicator methods (i.e., reverse-dial indicator and the two variations of the rim-and-face method) use the same type of dial indicators and mounting equipment. However, the number of indicators and their orientations on the shaft are different. The optical technique does not use this device to make measurements, but uses laser transmitters and sensors. 

While the dial-indicator and optical methods differ in the equipment and/or equipment setup used to align machine components, the theory on which they are based is essentially identical. Each method measures the offset and angularity of the shafts of movable components in reference to a pre-selected stationary component. Each assumes that the stationary unit is properly installed and that good mounting, shimming, and bolting techniques are used on all machine components. 

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. 

If the distance between the points of contact of the two dial indicators set up to take rim readings for the indicator reverse method is larger than one-half the diameter of travel of the dial indicator set up to take face readings for the two-indicator method, the indicator reverse method should be used. 

This mle is because misalignment is more apparent (i.e., dial indicator reading will be larger) under these circumstances and, therefore, corrections will be more accurate. 

Dial indicators and mounting hardware are the equipment needed to take alignment readings. 

Dial indicators Figure 54.15 shows a common dial indicator, which is also called a mnout gage. A dial indicator is an instmment with either jeweled or plain bearings, precisely finished gears, pinions, and other precision parts designed to produce accurate measurements. It is possible to take measurements ranging from one-thousandth (0.001 inch or one mil) to 50 millionths of an inch. 

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