reverse dial indicator method.doc

LESSON

4LECTURE

REVERSE DIAL INDICATOR ALIGNMENT METHOD

SUB-OBJECTIVE

At the end of this lesson the trainee will be able to performed coupling alignment by the dial indicator reverse method.

1.0 INTRODUCTION

The dial indicator reverse method of shaft alignment is the most accurate procedure. By using conventional tools and instrument, achieve a great amount of accuracy in minimum time. In this method two dial indicator are fixed on the both coupling’s rims, just exactly reverse to each other, and all reading taken on the two coupling rims. As mention in Fig. 4-1.

Since the face reading does not involve in this procedure, the thrust and axial float does not affect the reading obtained and that is the major advantage of this procedure.

2.0 WHERE THIS PROCEDURE APPLIED

Since this procedure of alignment have many advantages and use of this procedure a is limited only by the characteristics of the unit itself. Here are some advantages and use limits. Considered these as a general.

Fig. 4-1. Reverse Indicator Method.

1. This method is preferred when the distance between the adjacent shaft ends greater than one half the coupling diameter.

1. It is preferred especially for large equipment operating at high speed.

ADVANCED1 COURSE MECHANICAL MAINTENANCELESSON 4 PAGE 1 MACHINE ALIGNMENT

1. This method is also preferred when coupling run-out cannot be eliminate.

1. When one or both shafts have end float or have axial movement of the shaft.

1. also preferred, when gear type couplings are used.

1. More over this procedure can be used for all kind of equipment due to its accuracy in a very short time.

3.0 DETAILED STEPS OF PROCEDURE

Any procedure that is effective has a definite outline. It was proven in the Two Indicator Method and will be proven in this procedure. Since both are procedures to achieve alignment of two rotating shafts, each has steps that are common to each other. The discussion of the steps in the previous procedure are applicable to this procedure.

3.1 LOCK OUT

3.2 CLEAN FEET & PADS

3.3 DETERMINE INDICATOR SAG & RECORD

If using two brackets, check the sag for both brackets list the sag for the driver to driver bracket.

3.4 PROVIDE FOR COUPLING GAP

3.5 ROUGH ALIGN

3.6 ELIMINATE SOFT FOOT

3.7 COMPLETE RECORD SHEET WITH INFORMATION & DIMENSION

1) Measured the distance from the bracket to the post and record as mention in Fig. 4-2.

2) Measure the distance from the center of the bracket to center of the in board feet and record it.

3) Measure the distance from the center of the bracket to center of the out board feet and record it

3.8 TAKE A ROUGH ALIGNMENT BY STRAIGHT EDGE AND MINIMIZE THE SIDE TO SIDE DIFFERENCE UP TO THE POSSIBLE LIMITS

3.9 TAKE READINGS

1) First of all dial indicators are attached to each half coupling hub using brackets - see Figure 4 -2. The indicator on the stationary machine hub (usually the driven machine) is set to zero at point 1. The indicator on the moveable machine hub

MECHANICAL MAINTENANCE ADVANCED COURSE MACHINE ALIGNMENT LESSON 4 PAGE 2

(usually the driver) is set to zero at point 2. Points 1 and 2 must be 180° apart.

2) Both shafts are turned together clockwise 90° and indicator readings are recorded. This process is repeated until four sets of readings on each hub are recorded. The readings are checked for consistency, and another entire set of readings is taken. If readings are not repeatable, the problem must be found and eliminated in the machinery, the tools, or the method.


Equipment I.D. : __________________ Date______________________

Type of Unit : __________________ Date of Last Alignment______

Running Sped : ___________________ KW:______________________

Coupling : Manufacturer ___________ Type: _____________________

Coupling Manufacturer’s tolerances : Angular ________Parallel _________

Notes:_______________________________________________________

____________________________________________________________

Coupling Bracket I.D.: ______________ Bracket Deflection: __________

Movable Machine: _________________ Stationary Machine: _________

Fig. 4-2. Alignment Record Sheet.


Fig. 4 -2. Position of Brackets Viewer.

3.10 CORRECT FOR SAG

From previous discussions we know that indicator bracket sag only directly affects the bottom OD reading. We also know that it is a negative value. To correct for sag we simply subtract it, algebraically, from the bottom OD reading. Each bracket has a different value for sag and each must be handled independently.


4.0 USING ANALYTICAL METHOD FOR CALCULATING SHIMS (FOLLOW THE FIG. 4 -4)

Fig. 4 -4. Sample diagram of reading and shaft positions.

4.1 VERTICAL MOVEMENT


0 BA is the bottom reading at coupling “A”1 BB is the bottom reading at coupling “B”2 D1 is the distance between couplings3 D2 is the distance between coupling “A” and front support feet of

movable machine..4 D3 is the distance between coupling “A” and back support feet of

moveable machine

Now:-

i. The shim correction required at front support feet.

ii. The shim correction require at back support feet.

4.2 HORIZONTAL MOVEMENT

Normally for the horizontal alignment, no need of calculation but if machine is large and have jack bolts then this calculation is helpful for accurate horizontal movement. For horizontal movement dial set “ZERO” at left side and take the reading on the right side of the coupling.

* RA is the right side reading on coupling “A”* RB is the right side reading on coupling “B”

iii. Movement required at front support feet.

iv. Movement required at back support feet


Example: Fig. 4 -5.

Fig. 4 -5.

VERTICAL MOVEMENT

Shim correction required at front support feet.

BA = -10 BB = + 20 D1 = 8” D2 = 12)D3 = 24”

Add 12.5 Thou shims at front support feet.

Shim correction required at back support feet.

Add 20 thou. Shims at back support feet.

Movement required at front support feet =

RA = R - L = -15 - (+5) = - 20RB = R - L = 6 - 14 = -8

= -21 + 10 = -11Move 11 thou. Towards right.

Movement required at back support feet =

= -32


Move 32 thou. Towards right.


5.0 USING GRAPHICAL ALIGNMENT METHOD FOLLOW FIG. 4 -6

PLOT DISPLACEMENT

A typical problem worked on graph paper would go as follows:

1) First, the size of the machine on the paper must be determined. Assume the length of the machine is 24 inch, from coupling “A” to the outboard (far) feet of machine “B”. You don’t need to consider the length of Machine “A”, only its coupling.

2) Using graph paper as shown in Fig. 4 -6 that has ten large square across eight squares can be used, by calling each one three inches. The machine will nearly fill the page across the top.

3) For vertical lines are need at their correct distance to represent coupling “A”, - the point at which the indicator button touches coupling “A”, coupling “B” Point at which the indicator button touches coupling “B”, the inboard feet and outboard feet of Machine “B”. Take the center lines of near foot and far foot bolts.

4) It is good practice to draw them as they are seen as shown in Fig. 4 -7 while working on the machine. In all cases machine “A” is fixed in position, while “B” is the one that will be moved to make corrections in alignment.

5) Make two circles for the readings. A coin, 5 Halala can be used for this. Write the dial indicator reading on the circles.

“LEFT” and “RIGHT” on the circles are found by looking from Machine “A” toward Machine “B”.


Fig. 4 -6. Graph paper.


Fig. 4 -7. Drawing of actual look.


6) Mark a horizontal line and identify it as Machine “A” “S” center line by marking a small line at the coupling line. Both indicator readings will be marked in relation to this line. Give each square a value of 0.010” (Each square vertically means 0.010”)

7) Taking the readings from the circles, the dial indicator at coupling “B” is lower than the center of line of Machine “A” (Remember “B” “PLUS” “BELOW”)

8) Divide the reading by 2 and make a mark below the line, nearly six squares down.

9) The dial indicator at coupling “A” showed + 0.122” at the bottom. The line for shaft “B” is higher at coupling “A” (Remember “A” “PLUS” “ABOVE”). Again divide the reading by two, and put a mark, 0.061”, or slightly more than six squares above the line.

10) Use a straight edge and draw a line to connect two marks, and extend the line over to the vertical lines for the feel. This represents the center line of machine “B”.

11) At the inboard foot, count off vertical squares and find that you will need about 0.120 “ of shims. Write 0.120” on the chart at that point.

12) At the outboard foot, count off squares and find that you will need about 0.301” of shims. Write 0.301” on the chart at the place.

The mounting bolts of machine “B” can now be loosened and the shims put in place. The alignment should now be much closer to perfection than before. It will not be completely “true” as there will be some error in extending bolts before taking the next reading.

The same vertical lines on the paper can be used for the next set of readings. The alignment should now be closer enough so that, if you want, you can increase your vertical scale.

Again the readings are written about the horizontal line that represents Machine “A”. The marks for Machine “B” are counted off by small squares, and will be half the amount of the reading. By extending the line from the marks, the amount of correction will be seen at the lines for the mounting feet as shown in Fig. 4 -8.


Fig. 4 -8.


reverse dial indicator method.doc

Documents