1.0 INTRODUCTION INTRODUCTION
In rotating machinery machinery is an intricate part in many mechanical systems. Many different industries utilize rotating machinery. For example, oil refining, the aerospace industry, the automotive industry, the cell phone industry, and the t he chemical production industry all use rotating machinery in the form of engines, turbines, compressors, and pumps. The aerospace industry in particular uses large turbines to create thrust for jet engines to propel aircraft. Since the turbine rotates with such high RPM’s, t he design of the turbine blade must be statically and dynamically balanced to prevent unwanted vibrations. In rotating machinery, vibrations are unwelcomed. unwelcomed. Vibrations can be hazardous and can make a pump or compressor compressor perform inefficiently. In some industries, vibrations are wanted. For instance, in regards to cell phone production; in today’s times most phones have a vibrate feature. These vibrations must be carefully calibrated to determine the best amount to get the right amount of vibrating force with using the least amount of energy since the battery life of most cellular phones needs to be conserved. A vibration is known as a mechanical phenomenon phenomenon in which movement movement or oscillation occurs around a certain equilibrium point. Vibrations are usually periodic oscillations of motion. The reason vibrations occur is because weight is not symmetrically distributed around a rotating part. This difference causes the mass rotating about the center of the equilibrium point to have uneven forces acting on that center point. Most rotating machines are calibrated calibrated to the highest degree to minimize vibrations, but wear on certain parts of the systems can cause vibrations to occur. For example, bearing wear is a major component to producing vibrations. Therefore, the balancing of high-speed equipment is especially important to decrease the vibrations. The condition of unbalance of a rotating body may be classified as static or dynamic unbalance. In the case of st atic unbalance, the unbalance appears in a single axial plane. In t he case of dynamic unbalance, the unbalance can be in different axial planes. As a result, while in rotation, the two unbalanced forces form a couple, which rocks the axis of rotation and causes undesirable vibration of the rotor, mounted in i ts bearings.So, a machine machine already already in operation will will need re-balancing re-balancing or a new machine machine when assembled assembled at its permanent location will need balancing so t hat any damage at the machine or incident i ncident can be avoid.
2.0 THEORETICAL THEORETICAL BACKGROUN B ACKGROUND D
The system of balancing discussed in this experiment was developed to satisfy the need to perform field balancing of equipment easily and accurately. Although there are many possible causes of vibration in rotating equipment, this technique t echnique will deal only with that component component of vibration, which occurs at running speed and is caused by a mass unbalance in the rotor. Let us now consider a single rigid rotating mass mounted in two supporting bearings and assume that the axis of rotation is horizontal. It can be shown that for the correct balance of such a rotor, two weights placed in different radial planes of the rotor are necessary and sufficient sufficient to balance the rotor. The vibratory motion of either bearing may be represented r epresented by three components, the horizontal and vertical radial components and the axial component. The purpose of balancing at running speed of the rotor is to reduce the greatest of these three components to a practical minimum. The other two components will be reduced to negligible amounts from their original magnitudes by this technique. Assume Assume in this example that the radial component is the greatest. Therefore, only this component will be measured measured and analyzed in this technique. It follows that if the vertical components of vibration of two points, one chosen on each bearing, are reduced to zero or near zero, the purpose of balancing has been accomplished accomplished and no vibration will be transmitted to the t he support structure. There are four variables to be dealt with when balancing any rigid rotor. They are the amount amount and position of the two two correction weights required to
balance the rotor. Each Each correction weight is located in one of the arbitrary chosen radial reference reference planes on the rotor. rotor. These reference reference planes planes are usually usually placed near near the support bearings. bearings. In general, general, the farther apart the radial reference planes are located, the smaller the required correction weight. This technique deals with these four variables simultaneously as the amount and position of the correction weight in the other reference plane. The data is very necessary to determine the magnitudes and position (angle) of the t he two correction weights are obtained by test runs, all at the same speed by measuring the vibration amplitude and phase angle at each bearing. Some commercial commercial equipment allows measurement measurement of the vibration amplitude and phase relative to a geometric trigger reference point on the rotor. Lacking Lacking the instrumentation instrumentation to measure measure the phase angle, this technique technique will obtain data to allow calculation of the phase angle. An important assumption made by this technique is that the system follows linear relationships such as the vibration amplitude is proportional to the force producing the vibration. vibration. This assumption assumption is reasonably valid. valid. Most simple rotors can be balanced balanced by applying this technique iteratively.
3.0 APPARATUS AND EXPERIMENTAL SETUP
1. TM102 static and dynamic balancing apparatus. 2. Steel balls. 3. Belt. 4. Pulley. 5. Weight bucket.
4. EXPERIMENTAL SETUP AND PROCEDURE 4.1 Experiment 1: Static Balance
1.The Perspex dome and shaft drive belt was removed. 2. The discs was removed from the four rectangular blocks using the smaller hexagon key. 3. The extension pulley was unclipped and was inserted it in the pulley end of the motor driven shaft. 4. The Wr of the blocks was measured (one block at a time) using the steel balls and weight bucket by recording the number of steel balls it takes to rotate a block 90°. 5. The demonstrator demonstrator gave the positions of three of of the blocks to be mounted on the shaft. shaft. 6. Using the calculation or drawing method, the position of the fourth block for the shaft to be in static balance was was determined. determined. 7. The shaft was verified has achieved achieved static balance by mounting the fourth block on the shaft according to your calculations/drawing. calculations/drawing.
4.2 Experiment 2: Dynamic 4.2.1 Experimental Determination of Wr Values
1.The Perspex dome and shaft drive belt. Was removed. 2.The extension pulley was unclipped and inserted it in the pulley end of the motor driven shaft. 3.The apparatus was moved to the edge of the table or bench. There was ensured are no obstructions to the movement of the weight buckets. 4. The eccentric disc was inserted with the smallest hole into one of the rectangular blocks. The block was clamped to the shaft such that t hat the protractor scale reading is 0°. This was called block 1. 5. The steel balls was gradually added to one of the weight buckets until the block has moved through 90°. This is proportional to t o the out-of-balance moment of the block (Wr). An eccentric disc was fit to each block and the above procedure was repeated for each block in turn. The results were entered in a table similar to Table 1. 6. The extension shaft was removed and replaced it in its mounting clip.
5.0RESULTS AND DISCUSSION: 5.1 RESULTS.
Static Balancing. The steel balls gradually added to one of the weight buckets until the block has moved through 90°. This is proportional to the out-of-balance moment moment of the block (Wr). The results were filled in a table Table 1. Table 1: Experimental Experimental results
90
85
78
67
Table 2 presents the results for the t he static balancing of the system. The vector diagrams produced are also shown below Block Number
Wr (balls)
1 2 3 4 Table 2. Results from vector vector diagram for static balancing
Angular Position (degrees) 90 85 78 67
0 135 210.5 222.8
Using the calculation or drawing method, the position of the fourth block for the shaft to be in static balance was was determined As As previously noted, noted, the equations are simplified considerably by by taking moments about the first mass. The appropriate equations for a four-mass system are:
Horizontal moments about mass 1
− + + 4 4 4 = 0 −11785( −11785 (180 − 135 135 ) + 578 578 ((270 270 − 210. 210.5 5) + 13967 13967 ((360 − 4 ) = 0 −703 −7032. 2.17 17 + 197. 197.93 93 + 9313 9313 cos cos (3 6 0 − 4 ) = 0 4 = 222.79
210.5° Weight 3
135°
222.7°
Weight 2
Weight 4
0° Weight 1
Figure 7. Vector Diagram of block arrangement
Dynamic Balancing. Following the rearrangement rearrangement of the block, so that t hat the shaft was statically balanced, there was a noticeable difference difference in the behaviour of the system. It was tested to determine the degree improvement improvement of balance by eye and applying a force and moving the position of the shaft by hand. Before the eccentric masses were moved the system was also tested using this method. The unbalanced system would not remain in any position placed and after being moved to a new position rotated quickly quickly following release, release, eventually eventually returning to the same same position of rest. Only Only a slight displacement was required to cause the system to rotate. The force required to rotate the shaft was relatively large meaning that the shaft felt ‘heavy’. Once the masses had been rearranged into a statically balanced orientation, the shaft rotated slowly when a force was applied by hand and soon came to rest. The system would also remain at any angle to which it was placed, the system was generally easier to move and seemed ‘lighter’. Table 3 below shows the results calculated for the dynamic balancing of the system using table provided in the manual manual and less vibration obtained using using below configuration. configuration.
Mass Number 1 2 3 4
Angular Position (degrees)
Wr (balls) 90 85 78 67
Axial Position (mm) 0 150 190 333
5 105 25 142
5.2 DISCUSSION
The four-mass system was successfully achieve the balance state. This is because from our observation the system stay static when we rotate the rotor. From this experiment the four blocks have their own mass and we arrange it in specific distance on the rotor. To achieve the balance state we must get the right angle for each block with some reference from the lab manual. After arrange the block according according to the references references we successful successful get get the balance four-mass system system where static static in any direction when it rotating. Static balance refers refers to the t he ability of a stationary on object to its balance. This happens when the objects center of gravity is on the axis of rotation. Whereas dynamic dynamic balance is the ability of an object to balance whilst in motion or when switching between positions. For the dynamically balance test we also get that the four-mass system have achieve it balance state. state. We said that because when we run the TM102 static static and dynamic dynamic balancing apparatus we observe that less vibration on the machine. This prove that the arrangement of the four blocks on the four-mass system well balanced. A rotating system of mass is in dynamic balance when the rotation does not produce any resultant centrifugal force or couple. The system rotates without requiring the application of any external force or couple, other than that required to support its weight.
6.0 CONCLUSION
There are few reasons to an unbalanced rotating machinery. They are mainly due to uneven distribution of mass either of the material itself or the whole assembly. Other than that, the shape of the rotating parts can also affect the balancing. An unbalanced rotating machinery machinery will create a lot of consequences consequenc es such as shorter lifespan, energy consumption and failure of parts. Balancing can also involves shifting the center of gravity t owards the center of rotation. Dynamic balancing is when the rotating system doesn’t yield any other force or couple. Other than the force that is needed the system will rotate without the need for any additional external force or pressure to be applied. Finally ,to avoid the machine or the apparatus vibrates we must make sure the load or masses are in stable or balanced which which this is the main main factor of the vibration. vibration.
7.0 References
1. https://www.tecqu https://www.tecquipment.com ipment.com/static-and-dynam /static-and-dynamic-balancing ic-balancing 2. https://www.cours https://www.coursehero.com ehero.com/file/10316043/Static-and/file/10316043/Static-and-Dynamic-B Dynamic-Balancing-Expe alancing-Experiment/ riment/ 3. http://www.polylabindia http://www.polylabindia.com/static.com/static-dynamic-balan dynamic-balancing-appara cing-apparatus-1787517.html tus-1787517.html
