basic Pnumatics

Pneumatics is a branch of technology, which deals with the study and application of use of pressurized gas to affect mechanical motion. Pneumatics is used in applications where only a fair accuracy of control is needed with medium pressure. Cylinders and other pneumatic devices are powered by a compressor, which compresses the gas/air. Generally most of the pneumatic systems (mostly I factories) use compressed air as a sustainable supply of compressed air could be obtained by atmospheric air. Smaller or stand-alone systems can use other compressed gases which are an asphyxiation hazard, such as nitrogen - often referred to as OFN (oxygen-free nitrogen), when supplied in cylinders.
  
Pneumatic systems are extensively used in industry, where factories are commonly plumbed with compressed air or other compressed inert gases. This is because a centrally-located and electrically-powered compressor that powers cylinders and other pneumatic devices through solenoid valves is often able to provide motive power in a cheaper, safer, more flexible, and more reliable way than a large number of electric motors and actuators.  Pneumatics also has applications in dentistry, construction, mining, and other areas.

In many industrial applications pneumatic logic systems are often used to control industrial processes, consisting of primary logic units such as And Units, Or Units, Relay or Booster' Units, Latching Units, Timer' Units, Sorteberg relay ,fluidics amplifiers with no moving parts other than the air itself. Pneumatic logic is a reliable and functional control method for industrial processes. In recent years, these systems have largely been replaced by electrical control systems, due to the smaller size and lower cost of electrical components. Pneumatic devices are still used in processes where compressed air is the only energy source available or upgrade cost, safety, and other considerations outweigh the advantage of modern digital control.

Pneumatic systems are widely used in industry due to the many advantages they provide.

Advantages of Pneumatic Systems over the other systems. 

 

·         Most pneumatic circuits run at low power -- usually around 2 to 3 horsepower. One of the main advantages of air-operated circuits is their low initial cost. Because air systems operate at relatively low pressure, the components can be made of relatively inexpensive material -- often by mass production processes such as plastic injection molding, or zinc or aluminum die-casting. Either process cuts secondary machining operations and cost.

·         Another main advantage of pneumatics is the simplicity of design. Pneumatics is easy to install and have useful mechanical movements. For an instance Straight-line movements can be obtained without further adjustments, such as levers, cams...etc.

·         Air-driven machines are usually quieter than their hydraulic counterparts. This is mainly because the power source (the air compressor) is installed remotely from the machine in an enclosure that helps contain its noise.

·         Pneumatic systems are highly reliable and need very little maintenance but operate continuously with high reliability. Air /gas used as the working fluid is less likely to damage the equipments since gas are good in absorption of shock, and excessive forces, but hydraulics react directly transferring the stress to mechanical parts.

·         Cleanliness of the work place is another main advantage as working fluid is purified air.. Also, since is used no risk of toxic hazards to machines or humans. This cleanliness factor is at most important in some industries like pharmaceutical.

·         Easy to move around (portability) is another factor. Air is very light compared with other fluids, which are very heavy. They don't need high power to transfer. Air is easily obtainable from atmosphere and can be used with little purification. Air can be pumped to long distances in pipelines, so can control pneumatic equipments for long distances. This makes central controlling possible. These also require no return line, so easy to manage and cost effective.

·         Safety of the work place is a major consideration in any industry. Pneumatic controls have high safety profile due to many reasons. Air used in these is fire proof, and less vulnerable to explosions and electric hazards. These are adoptable in extreme weather conditions, and we can rely on their continuous operation. This is because compressed air can stay in good condition in high temperature fluctuations, unlike hydraulic systems that tend to freeze or boil in these situations.

 

BALANCING OF ROTATING MASS

Introduction

If the mass center of a component of mass 'm' is rotating at an angular velocity   at a

distance 'r' from the axis of rotation, then the component is subjected to force of mr2

The 'out of balance' forces increase bearing loads, and introduce stresses in the rotor and

framework of a machine. These so called 'inertial forces' may introduce dangerous

vibrations, structural failure or unacceptable noise, and may limit the operating speed

range of a machine. The magnitude of these forces may be reduced or eliminated in the

design stage by 'balancing' the effects of the various mass elements of the device.

Additionally, extra balance masses may deliberately added to a rotating system in order

to cancel out the residual design imbalance.

This experiment involves the balancing of a number of known out of balance masses on a

shaft.

There are two types of balancing.

Static and Dynamic Balance

So far we have considered the case of a wheel, which approximates to a simple disc, having all its mass in or near one plane. If this is statically balanced in the way described, it will run at any speed without vibration. But in a rotating body having a fairly considerable axial length, such as a cylinder, it is important that any local unbalanced mass should be balanced out by a mass as nearly in the same cross plane as possible.

The static method of balancing, in this case, is not reliable because it gives no indication of the position of the bias in relation to axial length. Thus the cylindrical rotor, an armature shaft for instance, shown in Fig. 2, may be heavy at the point A, as indicated by a static balancing test. If this unbalanced mass is counteracted by a weight applied at the point B, the rotor will appear to be in correct balance; but when running at high speed, the effect of the two unbalanced masses will cause local reactions R-R which tend to rock the shaft along its length, or in other words to set up a "couple." In practice, the effect of this may be worse than that of a single unbalanced force which tends to vibrate the structure bodily, and it is often much more difficult to detect and correct.

The method usually employed for dynamic balancing is to mount the shaft in bearings on a frame which is resiliently mounted, usually by some form of spring suspension, so that it is capable of being displaced in any plane by the effect of unbalanced forces. Means are provided for locking the frame while the shaft is run up to a fair speed by any convenient means, after which it is released and allowed to vibrate or oscillate under the effect of the unbalanced forces. In modern dynamic balancing machines, 

indicating or recording devices are provided to show the position and extent of the unbalanced masses. While it would not be impossible to construct a simple dynamic balancing rig in the home workshop, most of the problems involved in small machines can be dealt with by careful consideration of design, and accuracy in construction of moving parts. It may be mentioned that even the balancing machine, unless of very complex design, may leave certain important considerations out of account.

For instance, suppose that a rotor having an unbalanced mass at J (Fig. 3A) is balanced by adding two smaller masses at the points K, L. The rotor is then in correct dynamic balance, and in the case of a fairly rigid component, such as an armature, it will be perfectly satisfactory in practice. But suppose the same principle is applied to a non-rigid component, such as a crankshaft; in this case, the cancelling masses, being in different planes, exert bending stresses on the shaft, and the latter may be deflected, thereby altering the moment of the masses and putting the system out of balance

Applications use rotating balancing to maintain there characters properly

1.       Engine crank shaft

2.       Automobile wheel

3.       Grinding wheels

4.       Steam turbines and runners

5.       Compressors

6.       Washing machines

7.       Air craft propellers

Types of Balancing

There are two forms of balancing: static and dynamic.
Static balancing is done by holding the component at its axis, then compensating (by removal or addition of mass) for the "heavy" side of the component. During Static balancing, the component is not rotating, hence "static".  Static balancing is typically done on "flat" parts, or parts that have a large diameter to axial length ratio (pancake like parts, such as fans, pulleys, wheels).
Dynamic balancing is done on parts that are long compared to their diameters such as rotor assemblies.  These parts require balancing to be done in two planes since the actual imbalance will intersect the centerline/axis.  Unless both ends of the part are balanced, mass imbalance will continue to exist.  Rotor assemblies that MCE manufactures are balanced dynamically (in two planes).
Balancing can be achieved by the addition or removal of mass in certain locations.  MCE only provides balancing by use of mass removal which is achieved by abrasive material removal or by drilling/machining.  Note that when designing your part, take into account that material removal will be required and allow for extra material such as a balancing ring or thicker flanges than required by design to achieve mechanical structural integrity.

Why we need Balancing of rotating Masses

1. It will reduce the unwanted vibrations

2. it reduce the energy waste so it will increase the efficiency of the machine.

3. Vibrating parts wear quickly . so balancing is so important to have a long life time for the sfats.

4. When shaft is unbalanced it bends when it’s rotating so it s subjected to compression and expansio  alternatively so it fails easily.

5.Bearing wear due to large forces on them