Many of the machines we use everyday are made possible by the bearing. Without bearings, lot of parts would wear out from friction and we would be constantly replacing the machine parts. We’ll explore how bearings work, some different kinds of bearings and explain their common uses.ApplicationsThe bearing has a very simple: Things roll better than they slide.
The wheels on your car are like big bearings. If you had something like skis instead of wheels, your car would be a lot more difficult to push down the road and more friction will be produced thus damaging the car. The friction between them causes a force that tends to slow them down.
the friction is greatly reduced if the two surfaces can roll over each other.The main function of a rotating shaft is to transmit power from one end of the line to the other. It needs a good supports to ensure stability and frictionless rotation which is provided by a bearing.Types of BearingThere are many types of bearings and each have different uses for different purposes. The types include ball bearings, roller bearings, ball thrust bearings, roller thrust bearings and tapered roller thrust bearings.
1) Ball Bearings a) Radial Ball Bearingb) Thrust Ball Bearing 2) Roller bearingsa) Radial roller bearings b) Thrust roller bearings Materials properties required for a good bearing are• Good fatigue strength• Enough compressive strength• Good corrosion resistance• Good thermal conductivity• Good embedding character• Material should be easily available and inexpensiveRoller bearings are usually fabricated of case hardened steels, surface hardened to Rockwell C 58- 63. Ball separators(i.e, cages) are normally made of low carbon steel, to use of elevated temperature upto 400o C, separators made of alloy steels may be used.Components of rolling bearings• 4 parts1) Inner ring2)Outer ring3) Rollers or balls4) Separator orretainerthe rolling contact bearings are made separately and they can be assembled with machine and disassembled from it whenever needed.Vibrations in bearingVibration can be a result of any manufacturing defect and can be complex to detect and monitor. Noise and vibration is becoming more critical in all types of equipment since it is often perceived to be synonymous with quality and often used for predictive maintenance. Heavy vibration and its counterpart, loud noise, can have an additive effect, and if your application is using many high vibration ball bearings, you may see significant noise or vibration in your application, and this may not be desirableGenerally, rolling bearings produce very little vibration when they are fault free and have distinctive characteristic frequencies when faults develop. A fault that begins as a single defect, e.
g. a spall on the raceway, is normally dominated As the damage worsens there is likely to be an increase in the characteristic defect frequencies and sidebands followed by a drop in these amplitudes and an increase in the broadband noise with considerable vibration at shaft rotational frequency. This is the simplest way of measuring vibration and usually consists of measuring the Root Mean Square (RMS) vibration of the bearing housing, or of some other point on the machine, with the transducer located as close to the bearing as possible. This technique involves measuring the vibration over a wide frequency range, e.g.
10-1000 Hz or 10-10000 Hz. The measurements can be trended over time and compared with known levels of vibration, or pre-alarm and alarm levels can be set to indicate a change in the machine condition. Accelerometer An accelerometer is an apparatus, either mechanical or electromechanical, for measuring acceleration or deceleration – that is, the rate of increase or decrease in the velocity of a moving object.
Important use of the accelerometers is to detect vibrations in machinery.The measurement of acceleration or one of its derivative properties such as vibration, shock, or tilt has become very commonplace in a wide range of products. The types of sensor used to measure acceleration, shock, or tilt include piezo film, electromechanical servo, piezoelectric, liquid tilt, bulk micromachined piezoresistive, capacitive, and surface micromachined capacitive. Each has distinct characteristics in output signal, development cost, and type of operating environment in which it best functions. What are accelerometers useful for?By measuring the amount of static acceleration due to gravity, the angle the device is tilted at with respect to the earth can be found. We can analyze the way the device is moving by sensing the amount of dynamic acceleration. An accelerometer is also useful to analyze problems such as vibration testing.
WorkingThe most commonly used device is the piezoelectric accelerometer. As the name suggests, it uses the principle of piezoelectric effect. The device consists of a piezoelectric quartz crystal on which an accelerative force, whose value is to be measured, is applied.
Due to the special self-generating property, the crystal produces a voltage that is proportional to the accelerative force. The working and the basic arrangement is shown in the figure below. As the device finds its application as a highly accurate vibration measuring device, it is also called a vibrating sensor. Vibration sensors are used for the measurement of vibration in bearings of heavy equipment and pressure lines.
The piezoelectric accelerometer can be classified into two. They are high impedance output accelerometer and low impedance accelerometer.