The importance of turning the center of the machine (centering)
1.1 What is a match (centering)?
Concentricity is the alignment of the operational centerlines of the two devices that will be linked together, making it a straight line.
1.2 The purpose of mind (centering) is to:
消除 Eliminate unnecessary stress in radial and axial directions of the bearing, extend the bearing life and the normal operation of the shaft.
é¿å… Avoid the vibration caused by poor mind, reduce the vibration of mechanical components.
é¿å… Avoid premature damage to bearings and shaft seals
 Avoid premature wear of the coupling
é¿å… Avoid energy loss (precise alignment can save about 5%~10% of energy)
延长 Extend the life of equipment and its components
In short: the purpose of correct alignment (centering) is to extend the mechanical operating life
According to the statistics of the experiment, the bad rate of the heart (centering) decreases the bearing life to the third power, for example,
A 2x misalignment (centering) defect will leave the bearing life to 1/8 (23=2x2x2=8), and 3x misalignment (centering) will degrade the bearing life by 1/27. (33=3×3×3=27), and so on.
1.3 Heart (Centering) Bad Symptoms
æ Early damage to bearings, shaft seals, couplings, and shafts.
轴承 Bearings generate one or double frequency large vibrations in the axial and radial directions.
轴承 Bearings have high temperature or even large amounts of lubricating oil.
基础 Foundation pile screws loose.
过 Coupling clearance is too large or broken.
è” Couplings have a high temperature and the rubber-plastic coupling has a powder discharge.
å Motor running current is high.
轴承 Bearing damage is 180 degrees and symmetrical wear inside and outside on the track.
1.4 Spindle Centering (Centering) Precautions
First, check the surface of the base, fixing screws, adjusting screws and couplings.
Second, check the radial, axial movement or shaft bending deformation of the shaft.
Third, check the soft feet, including: bad foot processing or corrosion, base corrosion, gasket corrosion, pipeline stress, etc. These items should be excluded before the center of mind (centering) in advance.
Fourth, the installation of the centering (centering) tool should avoid loosening or deflection.
Fifth, try to use a good stainless steel gasket, if not pre-cut gasket, cutting should avoid the appearance of flash.
Sixth, after the heart, when the need to adjust the height is quite high, it is recommended to use a thicker gasket, the total number of pads per foot pad should not exceed four.
Related definitions and conditions for the mind (centering)
2.1 Definitions of Heart (Centering)
1. Good heart (centering)
2. Parallel misalignment
3. Symmetrical angular misalignment
4. Asymmetric angular misalignment
Ways to check your heart condition
How can I know if my heart is bad? When machine equipment vibration is quite large, and we suspect that it is caused by bad heart, apart from using vibration analysis, the simplest method is to use the scale directly. The lower left figure can be used to check the angular misalignment, and the lower right figure can be used to check the parallel misalignment.
Tolerance of center (centering)
good
Shang Ke
level
Row
Partial
difference
Do not
Correct
heart
Speed ​​(rpm)
Mils
Mm
Mils
Mm
0000~1000
3.0
0.07
5.0
0.13
1000~2000
2.0
0.05
4.0
0.10
2000~3000
1.5
0.03
3.0
0.07
3000~4000
1.0
0.02
2.0
0.04
4000~5000
0.5
0.01
1.5
0.03
5000~6000
<0.5
<0.01
<1.5
<0.03
angle
degree
Partial
difference
Do not
Correct
heart
Speed ​​(rpm)
Mils/in
Mm/100mm
Mils/in
Mm/100mm
0000~1000
0.6
0.06
1.0
0.10
1000~2000
0.5
0.05
0.8
0.08
2000~3000 0.4 0.040.7
0.07
3000~4000 0.30.03
0,6
0.06
4000~50000.2
0,02
0.5
0.05
5000~60000.1
0,01
0.4
0.04
The following is a description of the most commonly used Reverse Indicator centering (centering) method, Rim and Face centering method, and laser precision centering (centering):
2.3 Most of the people who are not aware of the importance of the centering (centering) method use the visual measurement method and the ruler method to compare the deviation of the height of the two sides of the coupling, but due to the machining accuracy The relationship with the visual deviation often fails to achieve a good centering (centering) condition of the device. Therefore, the best use of the mind work scale or the more sophisticated laser alignment (centering) tool, the use of the scale to the heart There are many ways to (centering), including:
1. Reverse Indicator
2. Rim and Face centering (centering) method
3. Across-the-Flex-Element centering (centering) method
4. Double Indicator heart (centering) method
5. Continuous shaft centering method
1.Reverse Indicator When using the scale method to implement the centering (centering) method, it is best to use grid paper, ruler, and pen to assist, which will make the centering (centering) work more Complete soon. As shown in the figure below, after the equivalent table is set up, measure the distance between the two gauges, the distance from the scale to the front of the motor, and the distance from the front to the rear of the motor. Then draw a vertical adjustment line on the square paper and scale it. Mark each point and distance.
Make the two axes rotate synchronously, and read and record the scale values ​​of 0, 3, 6 and 9 o'clock directions sequentially (generally, the zero reading of the 0 o'clock direction is preferred), and then 0 pairs respectively. Half of the 6 o'clock difference is marked on the vertical adjustment line of the grid paper. Finally, connect the marked points on the vertical adjustment line and extend to the positions representing the front and rear feet of the motor, so that the motor can be read before The size of the rear foot should be adjusted vertically.
2. The only difference between Rim and Face method is that the two scales measure the coupling of the fixed side table, and the scale reading of the measuring end of the coupling represents the angular misalignment (centering ) Minus, the reading of the scale end of the measuring coupling represents the misalignment (centering) of the parallel misalignment. As with the Reverse Indicator centering (centering) method, after setting up the equivalent scale, measure the diameter of the coupling, the distance between the end face of the coupling to the forefoot of the motor, the distance from the front to the rear of the motor, and then draw two lines on the checkered paper. Straight lines (one for drawing angular deviation lines, one for drawing parallel and total deviation lines), and scale points and distances as shown in the figure below.
Read and record the values ​​of the two scales. First, the difference between 0 and 6 o'clock on the end face is marked on the vertical deviation line of the squared paper according to the proportion. Then, the scale on the end edge is 0 to 6 points. Half of the clock difference is indicated on the vertical parallel and total deviation line of the square paper, and then a straight line parallel to the angle deviation line is drawn from the marking point so that the size of the front and rear feet of the motor that should be adjusted in the vertical direction can be read. .
3. Laser precision centering (centering) method In the industry, lasers are increasingly used in processing and measurement, and are most often used in diode lasers and helium lasers for measurement purposes. It is generally lower than lasers for processing purposes, and the price is lower. The characteristics of lasers are beam directionality, good parallelism and long service life. Modern laser measuring instruments are not only precise, can simplify work, have high reliability, but also are light and inexpensive.
At present, the laser precision centering (centering) technology applied to the centering (centering) work is divided into two types. One is the double laser centering (centering) technique taken from the Reverse Indicator pairing principle and the other. A single-laser alignment (centering) technique based on the Rim and Face principle of centering (centering), both of which are now developed as visible lasers, making it easier for the laser to work on the center (centering) And accurate.
The steps of using the laser precise centering (centering) are the same as those described above. The difference is that we do not need to use paper or pen to draw the figure to calculate and adjust the size, but when using the laser to align the heart, the laser is used. Limiting the area of ​​the sensing panel usually requires a good rough centering (centering).
When purchasing a laser alignment (centering) instrument, special attention must be paid to the following points:
1. The problem of reproducibility of readings, especially under intense sunlight.
2. The laser sensing panel has a good filter and rate function options.
3. In addition to horizontal and vertical equipment for the heart function, it should have a soft foot detection function.
A good laser is a favorite, and its function also includes functions such as straightness, flatness, parallelism of the universal joint, and angle detection of the machine tool shaft.