Abstract of Mechanical Lab

From this lab we will learn about the bearing reaction forces which occur in a dynamically unbalanced rotating system through the use of piezoelectric force transducer. Firstly, we find the empirical equation from the given data then compare the theoretical equation with the experimental equation. Balancing of the rotating parts of the single engine, high speed of engine and rotating shaft which was used in the industrial machine these are can be measured by using reaction force. Dynamic unbalance is basically the force which exerted to the rotating parts of the machine and it is directly proportional to the square of the rotational machine. When the rotating parts of the system are unbalanced so this means the vibration in the system will be increased in great amount. The main job is that you have to remove these vibrations from the rotating bodies, for this you must have to balance the rotating parts. This is the main motivation we will get from this mechanical lab.

The main work is that you have to remove the vibration from the rotating bodies because these vibrations in the rotating body decrease the efficiency of the rotating bodies.  If the efficiency of the rotation body decreases so this means the errors increases and these errors are increase with unbalanced.  The scope of this lab is that we need to work on how to remove the vibration from the rotating body. Vibration in the machine can reduce its efficiency because it increases noise and discomfort. This technique is used in heavy industrial machines like turbine, electric generator. The main approach of this lab is that we will work on how to remove the unbalance in the rotating parts of the machine. Due to its wide application of force transducer in many apparatuses and many instruments like accelerometer, pressure gauge, and many other devised. Mostly used transducer is vibratory type due to satisfactory and suitable. Due to the advancement in the technology in the apparatus; force transducers are also employed by the technology. Now transducers are employed by minimum weight, size and of electrical power requirements from which we get more advantages. Now transducers are employed by sensors. This new invention of sensing makes it more efficient and long stability. The intended results that will be achieved from this lab are include we will find out the empirical equation from the given data and this data is compared with the experimental data.

Introduction of Mechanical Lab

In industrial machines like steam and gas turbines, turbo generator and in internal combustion in these entire rotating shafts is employed with the system. This increases its power, efficiency and speed. Which makes the design of unbalanced rotation and makes its study easy, this system consists of shafts, and two balanced wheels. When the wheel is rotating at a constant angular velocity ω, the small eccentric
mass m will produce a radial force Fm

In this equation

m = the mass of object

r = the distance of the object to the center of the shaft

ω = the angular frequency of the motor
rω2 = the acceleration in the normal or radial direction

By Summing moments about the bearing closest to the motor, results in the following equations

By putting the values 

In the equation A

L = length of the shaft between the bearings

b = distance from the bearings to the unbalanced disk

 = peak force at the location of the force transducer

Equipment of Mechanical Lab

1.  Rotor mounted in bearings

2.  12 inch steel scale
3.  Charge amplifier
4.  Multi-meter
5.  Balance transducer

Theory of Mechanical Lab

Force

                The exertion of pressure on the body the pressure may be for pulling towards or away from the object. In mechanical the force involves in contact with the other object, these forces are different from the other four natural forces.

Frequency

The mechanical forces increases frequency in the rotating bodies, the mechanical resonance has the tendency of a simple mechanical system to respond at greater amplitude. The frequency of oscillation must match with the system natural frequency.

Bearing Reaction Forces of Mechanical Lab

As force which acts in opposite to the direction of a action force is called reaction force. Reaction force is also known as friction force this is due to adhesion and interaction of surface due to sliding. These reaction moment and reaction force are due to the applied force. 

Working principle of piezoelectric force transducer of Mechanical Lab

Working principle of the piezoelectric transducers is piezoelectric effect. Electric voltage will be produced by applying forces or mechanical stress on plane and certain material. Output in the form of voltage is directly proportional applied force and stress and also this output voltage is in DC voltage form.

Unbalanced system of Mechanical Lab

 When the system will rotate then tensional forces will produce that are perpendicular to the axis of rotation. These are only occurring in unbalanced system.

Dynamic unbalance of Mechanical Lab

The dynamic unbalance is one of the most common type of unbalance system in the mechanical system. When principal axis and rotating center line will not coincide then unbalance will form. Due to the rotating centerline, the principal axis will tilt and displaced from the center line. These unbalance is called dynamic unbalance.

Types of transducer of Mechanical Lab

There are some types of the transducer such as Mechanical transducer, Electrical transducer, light energy transducer, chemical energy transducer, thermal energy transducer, acoustic energy transducer, electromagnetic energy transducer etc.

Procedure of Mechanical Lab

 For starting the experimental procedure in the first step you have to measure the total weight of the bolt. Also you have to measure the weight of the nut and also two washers. Also you have to record all these values. In the next step you have to check the charge amplifier and also check the voltmeter through testing. If the reading of voltmeter is not ok so this means that your voltmeter is not ok for measure the required voltage. Turn on the force transducer and also apply force on it. Then after this the next step is most important because you have to convert these voltages reading from the force transducer into force. While recording we have seen that the value of force is so small because the value of voltage was in mili voltage so you have to multiply the force value with 10.  Suppose that the voltage value is 0.34 volts so after converting into force it becomes only 0.34 lb after multiply with 10 it become 3.4 lb. The reading of voltage must be set to DC. In the table three you have to record the bearing reaction force of the system without any mass for each specified frequency. Afterwards in the next step you have to put this mass in one hole and then measure the bearing force at constant frequency of 900 rpm. Then you have to measure and record the reading for seven holes and record the data in table 2. You must have to keep the speed of the motor constant and for achieving constant speed of the motor you have to turn on and off the motor and then after that you have to start the motor when you have move the mass of the bolt. You must have to be aware about the safety of using the motor by checking the bolt nut is tight and also the cage is closed before turning on the motor. After this in the next step you have to perform another test with the mass in the hole and also that had the highest reaction force from the last step. You must have to record these values in the table 3. In the next step you have to find the value of the true force and this that force which is with the bolt and minus it without the bolt. Through the help of free body diagram the theoretical peak force and be found easily with the help of transducer.

RESULTS:

Table #1 system specifications of Mechanical Lab

Calculations of Mechanical Lab

From the measured data so for the theoretical calculation we will consult the formula for finding the force.

Table #2: Reaction force for different mass locations at 700 rpm.

Table #3 Experimental data:

Graph between the Frequency and experimental force 

The graph between Frequency and theoretical force

EXPERIMENTAL REACTION FORCE VS RPM PLOT

DISCUSSION AND CONCLUSION on Mechanical Lab

From the above discussion it is concluded that for balancing the rotation machine is extremely necessary because if the rotation of the machine is not balance so this means that the voltages are not balanced. If the speed of the motor is not constant that’s means your rotating system is not balanced and if the rotating system is not balance so the mechanical force is not constant. The balancing of rotating parts is necessary for every engine but for high speed engines it becomes most important. Force exerted on the rotating parts is directly proportional to the square of the rotational speed, which is also known as omega.  Sometimes the rotating parts are not balanced then vibration caused in the machine which makes noise in the machine. The vibration in the rotating parts is not good for the machine because it decreases the efficiency of the machine. These vibrations can be balanced through the use of balanced key. It is the main key for conducting all functional movement of the rotating parts. Balancing is important in every aspect in the mechanical machines and also for doing any work. When we are running, walking and moving the balancing is very important. Soft bearing and hard bearing are two main types of balancing machine.

In this experiment the transducer we have used must be perfect and it is a force transducer the output of this force transducer is in the form of DC voltages. From the experiment we have seen that how to convert the voltages into force. In the experiment we have seen that after getting different force from different frequency from the experiment. From experiment we get that by increasing frequency there will be increase of force. This depends upon the number of holes in the nuts and from the experiment it is has been concluded that greater the number of hole so greater will be the force.

APPENDIX

Piezoelectric force transducer

Charge amplifier for piezoelectric force transducer

Double balanced mechanical seal

Force transducer circuit diagram

Force transducer block diagram