Pneumatics & Hydraulics Technology Chapter 1 Pneumatics Overview Instructor: Phan Thi Thu Thuy Higher Engineering Education Alliance Program Contents 1 Overview of pneumatics Definition of pneumatics History of pneumatics Applications of pneumatics Advantages and Disadvantages 2 Fundamentals of pneumatics Physical properties of air Characteristics of air Control theory 2 Objectives 1. Be able to write pneumatics branch after attending a lecture within 3 minutes 2. Given lecture note, be able to list at least 5 applications of pneumatics within 3 minutes 3. Given lecture note, be able to discuss 5 advantages and 4 disadvantages of pneumatics system within 10 minutes 4. Given lecture note, be able to define 3 gas laws and 3 equations with 100% accuracy. 3 1 Overview of pneumatics Definition of pneumatics History of pneumatics Applications of pneumatics Advantages and Disadvantages 4 Definition of pneumatics 60 AD - Pneumatics (from the Greek πνευματικός pneumatikos, coming from the wind) is the use of pressurized gas to do work in science and technology. Pneumatics is a branch of technology, which deals with the study and application of use of pressurized gas to affect mechanical motion 5 History of pneumatics It was near the end of the 17th Century that Torricelli, Mariotte and later, Bernoulli carried on experiments to study the elements of pressure or force in the discharge of water through orifices in the sides of tanks and through short pipes. In that same period the French scientist, Blaise Pascal, evolved the fundamental law for the science of hydraulics. 6 History of pneumatics Establishment of Industry Standards During the last forty years and particularly during the period of World War II, the use of fluid power has grown by leaps and bounds and among many fields of application a most important one has been that of production machinery. In fact, by 1951 applications in this field had increased so rapidly that a number of conferences were held in Detroit, Michigan, for the purpose of establishing a set of standard for industrial hydraulics and pneumatic equipment. These are now well known as the “Joint Industry Conference Standards for Industrial Equipment” 7 History of pneumatics Establishment of Industry Standards Represented in these conferences: - Hydraulic equipment manufactures, - Pneumatic equipment manufactures, - Machine tool builders, - Packing and seal manufacturers, - Press manufacturers, - Resistance welding manufacturers, - Tubing and fitting manufacturers - And industrial users. 8 History of pneumatics Establishment of Industry Standards In 1966, a new set of graphic standards was released by the United States of America Standards Institute. The Institute changed its name to the American National Standards Institute, Inc., on Oct 6, 1969. Through their use, the maintenance man can readily trace the flow of fluids through the controls without reference to the control manufacturer’s catalogs. This is great timesaver, especially on complicated layouts. Today, many machines containing fluid power systems have their circuit diagrams attached. 9 Applications of pneumatics Pneumatic components can perform the following types of motion: - Linear: moving in a straight line such as on a paper trimmer - Rotary: turning round in a circle, such as a wheel turning, gear, roller Pneumatics is used in carrying out machining and working operations: - Drilling - Finishing - Turning - Forming - Milling - Quality control - Sawing 11 Applications of pneumatics Some industrial applications employing pneumatics are listed below: General methods of material handling: - Clamping - Shifting - Positioning - Orienting 12 Applications of pneumatics General applications: - Packaging - Feeding - Metering - Door or chute control - Transfer of materials - Turning and inverting of parts - Sorting of parts - Stacking of components - Stamping and embossing of components 13 Applications of pneumatics S1 S2 S4 Cylinder A S3 Cylinder B Transfer station Parts are to be transferred from vertical magazine to a processing station 14 Applications of pneumatics Mps transfer / FESTO MPS system Robot Station with Assembly Tripod EXPT - the parallel kinematic robots Festo_Exohand Festo_MultiChoice Gripper 15 Test question Machines spray markings onto roads Automatic dumpling manufacturing system Rubbish sytem Name at least 4 applications of pneumatics in 3 video clips ? 16 Advantages 1. Availability: Air is available practically everywhere in unlimited quantities. 2. Transportation: Air can be easily transported in pipelines, even over large distance. Not necessary to return the compress air. 3. Storage: Air compressor need not be in continuous operation. Compressed air can be stored in a reservoir and removed as required. In addition, the reservoir can be transportable. 17 Advantages 4. Temperature: Compressed air is relatively insensitive to temperature fluctuations. This ensures reliable operation, even under extreme conditions. 5. Explosion proof: No risk of explosion or fire; expensive protection against explosion is not required 18 Advantages 6. Cleanliness: Unlubricated exhaust air is clean. Any unlubricated air which escapes through leaking pipes or components does not cause contamination. This is an important point when considering the food, wood and textile industries. 7. Components: The operating components are of simple construction and are therefore relatively inexpensive. 19 Advantages 8. Speed: Compressed air is a very very fast working medium; cylinders have working speed of 1- 2 m/s. This enables high working speeds to be attained. 9. Adjustable: With compressed air components, speeds and forces are infinitely variable. 10. Overload safe: Pneumatic tools and operating components can be loaded to the point of stopping and are therefore overload safe. 20 Disadvantages 1. Preparation: require to remove dirt and humidity 2. Compressible: Not possible to achieve uniform and constant piston speeds 3. Force requirement: low working loads; the require output force is economical only up to about 20 KN to 30 KN; commonly used working pressure of 7 bar 4. Exhaust air: Noisy; the oil mist with compressed air escapes with the exhaust to the atmosphere 21 Dirt and Moisture are damaging Moisture in compressed air used in a manufacturing plant causes problems in the operation of pneumatic systems, solenoid valves and air motors and can adversely affect the process or product being manufactured. For many years, problems from moisture in compressed air lines were simply tolerated as unavoidable. Moisture: Causes corrosion of air or gas operated instruments, giving false readings, interrupting or shutting down plant processes. Causes rust and increased wear of moving parts in production equipment as it washes away lubrication Can freeze in control lines in cold weather, which may cause faulty operation of controls Can endanger process industries where many operations are dependent upon the proper functioning of pneumatic controls. The malfunctioning of these controls due to rust, scale, and clogged orifices can result in damage to product or in costly shutdowns 22 2 Fundamentals of pneumatics Physical properties of air Characteristics of air Control theory 23 Physical properties of air 24 Physical properties of air Composition of air The surface of the globe is entirely covered by a mantle of air. It is an abundant gas mixture with the following composition. Composition by Volume Nitrogen 78.09% N2 Oxygen 20.95% O2 Argon 0.93% Ar Others 0.03% 25 Atmospheric pressure The atmospheric pressure is caused by the weight of air above us It gets less as we climb a mountain, more as we descend into a mine The pressure value is also influenced by changing weather conditions 26 Atmospheric pressure We see values of atmospheric pressure on a weather map The lines called isobars show contours of pressure in millibar These help predict the wind direction and force 1015 mb 1012 mb 1008 mb 1000 mb 996 mb LOW 28 Atmosphere and vacuum The power of atmospheric pressure is apparent in industry where pick and place suction cups and vacuum forming machines are used Air is removed from one side allowing atmospheric pressure on the other to do the work 30 The Story of Otto von Guericke's 1654 demonstration of the power of a vacuum at the bottom of a sea of air. Clip 1 Clip 2 Clip 3 In 1654 Otto von Guericke gave the citizens of Magdeburg a remarkable lesson in the force of the atmosphere. He machined two hollow hemispheres, twenty inches in diameter, so they fit snuggly into a sealed sphere. He pumped the air out of it. Then he put sixteen horses, eight on each side, to the task of pulling the halves apart. The horses couldn't, of course. It would've taken a force of over two tons to separate the halves. ... John Lienhard, at the University of Houston, where we're interested in the way inventive minds work. 31 Physical properties of air Base Quantities Unit Symbol Units and Units symbols Technical system System SI Length L Metre (m) Metre (m) Mass m Kp.s2/m Kilogram (kg) Time t Second (s) Second (s) Temperature T Degree Celsius (0C) Kelvin (K) 32 Physical properties of air Derived Quantities Unit Symbol Derived Units and Units symbols Technical system System SI Force F Kilopond (kp) Newton (N) = 1 kg.m/s2 Area A Square metre (m2) Square metre (m2) Volume V Cubic metre (m3) Cubic metre (m3) Flowrate Q (m3/s) (m3/s) Pressure P Atmosphere (at) Pascal (Pa) 1 Pa = 1 N/m2 1 bar = 105 Pa 33 Pressure 1 bar = 105N/m2 (Newtons per square metre) 1 bar = 10 N/cm2 For measuring lower pressures the millibar (mbar) is used 1000 mbar = 1 bar For measurements in pounds per square inch (psi) 1 psi = 68.95mbar 14.5 psi = 1bar F P A (N/m2) 34 Pressure units There are many units of pressure measurement. Some of these and their equivalents are listed below. 1 bar = 105 N/m2 1 bar = 100 kPa 1 bar = 14.50 psi 1 bar = 10197 kgf/m2 1 mm Hg = 1.334 mbar approx. 1 mm H2O = 0.0979 mbar approx. 1 Torr = 1mmHg abs (for vacuum) 35 Pressure Unit Conversion Table Pa bar Pa 1 1x10-5 bar 1x105 1 KG/cm2 9,80665x104 9.80665x10-1 KG/cm2 atm mmH20 mmHg psi 1,01972x10-5 9,86923x10-6 1,01972x10-1 7,50062x10-3 1,45038x10-8 9,86923x10-1 1,01972x104 7,50062x102 1,45048x10 1 9,67841x10-1 1x104 7,35559x102 1,42234x10 7,60x102 1,46960x10 1,01972 atm 1,01325x105 1,01325 1,03323 1 1,03323x104 mmH20 9,80665 9,80665x10-5 1x10-4 9,67841x10-5 1 7,35559x10-2 1,42234x10-3 mmHg 1,33322x102 1,33322x10-5 1,35951x10-3 1,31579x10-3 1,35951x10-3 1 1,93368x10-2 psi 6,89473x103 6,89473x10-2 7,03065x10-2 6,80457x10-2 7,03067x102 5,17147x10 1 36 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Gauge pressure bar g Pressures are in “bar g” gauge pressure (the value above atmosphere) Zero gauge pressure is atmospheric pressure Absolute pressures are used for calculations Pa = Pg + atmosphere For quick calculations assume 1 atmosphere is 1000 mbar For standard calculations 1 atmosphere is 1013 mbar Absolute pressure bar a Industrial compressed air 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Extended Industrial range Typical Industrial range Low range Atmosphere Full vacuum 37 Characteristics of air 38 Characteristics of air In common with all gases, air has no particular shape. Its shape changes with the slightest resistance, i.e. its assume the shape of its surroundings. Air can be compressed and it endeavours to expand. 39 The gas laws For any given mass of air the variable properties are pressure, volume and temperature. By assuming one of the three variables to be held at a constant value, we will look at the relationship between the other two for each case Constant temperature Constant pressure P.V = constant V (Boyle’s law ) = constant (Charles’ law) = constant (Boyle’s law and Charles’ law = combined gas law) T Constant volume P T 40 Constant Temperature 41 Constant temperature Boyle’s law states: the product of absolute pressure and volume of a given mass of gas remains constant if the temperature of the gas remains constant. This process is called isothermal (constant temperature). It must be slow enough for heat to flow out of and in to the air as it is compressed and expanded. Pressure P bar absolute 16 14 12 10 8 6 4 2 0 0 2 4 6 8 10 12 14 16 Volume V P1.V1 = P2.V2 = constant 42 Constant temperature Boyle’s law states: the product of absolute pressure and volume of a given mass of gas remains constant if the temperature of the gas remains constant. This process is called isothermal (constant temperature). It must be slow enough for heat to flow out of and in to the air as it is compressed and expanded. Pressure P bar absolute 16 14 12 10 8 6 4 2 0 0 2 4 6 8 10 12 14 16 Volume V P1.V1 = P2.V2 = constant 43 Constant temperature Boyle’s law states: the product of absolute pressure and volume of a given mass of gas remains constant if the temperature of the gas remains constant. This process is called isothermal (constant temperature). It must be slow enough for heat to flow out of and in to the air as it is compressed and expanded. Pressure P bar absolute 16 14 12 10 8 6 4 2 0 0 2 4 6 8 10 12 14 16 Volume V P1.V1 = P2.V2 = constant 44 Constant temperature Boyle’s law states: the product of absolute pressure and volume of a given mass of gas remains constant if the temperature of the gas remains constant. This process is called isothermal (constant temperature). It must be slow enough for heat to flow out of and in to the air as it is compressed and expanded. Pressure P bar absolute 16 14 12 10 8 6 4 2 0 0 2 4 6 8 10 12 14 16 Volume V P1.V1 = P2.V2 = constant 45 Constant temperature Boyle’s law states: the product of absolute pressure and volume of a given mass of gas remains constant if the temperature of the gas remains constant. This process is called isothermal (constant temperature). It must be slow enough for heat to flow out of and in to the air as it is compressed and expanded. Pressure P bar absolute 16 14 12 10 8 6 4 2 0 0 2 4 6 8 10 12 14 16 Volume V P1.V1 = P2.V2 = constant 46 Constant Pressure 47 Constant pressure Charles’ law states: for a given mass of gas at constant pressure the volume is proportional to the absolute temperature. Assuming no friction a volume will change to maintain constant pressure. From an ambient of 20oC a change of 73.25oC will produce a 25% change of volume. 0o Celsius = 273K Temperature Celsius 100 80 60 40 20 293K 0 -20 -40 -60 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 Volume V1 V2 = =c T1(K) T2(K) 48 Constant pressure Charles’ law states: for a given mass of gas at constant pressure the volume is proportional to the absolute temperature. Assuming no friction a volume will change to maintain constant pressure. From an ambient of 20oC a change of 73.25oC will produce a 25% change of volume. 0o Celsius = 273K Temperature Celsius 100 366.25K 80 60 40 20 0 -20 -40 -60 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 Volume V1 V2 = =c T1(K) T2(K) 49 Constant pressure Charles’ law states: for a given mass of gas at constant pressure the volume is proportional to the absolute temperature. Assuming no friction a volume will change to maintain constant pressure. 0o Celsius = 273K Temperature Celsius 100 80 60 40 20 0 -20 -40 -60 219.75K 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 Volume V1 V2 = =c T1(K) T2(K) 50 Constant pressure Charles’ law states: for a Temperature Celsius given mass of gas at 100 366.25K constant pressure the 80 volume is proportional to 60 the absolute temperature. 40 Assuming no friction a 20 293K volume will change to 0 maintain constant pressure. -20 -40 From an ambient of 20oC a 219.75K -60 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 Volume change of 73.25oC will produce a 25% change of volume. V1 V2 = =c 0o Celsius = 273K T1(K) T2(K) 51 Constant volume 52 Constant volume From Boyle’s law and Charles’ Temperature law we can also see that if the Celsius volume of a given mass of air 100 80 were to be kept at a constant 60 value, the pressure will be 40 proportional to the absolute 20 temperature K. 0 -20 For a volume at 20oC and 10 -40 bar absolute a change in -60 5 0 o temperature of 60 C will produce a change in pressure of 2.05 bar 0oC = 273K 8 6 10 4 12 14 2 0 bar 16 bar absolute 10 15 20 P1 P2 = =c T1(K) T2(K) 53 Constant volume From Boyle’s law and Charles’ Temperature Celsius law we can also see that if the 100 volume of a given mass of air 80 were to be kept at a constant 60 40 value, the pressure will be 20 proportional to the absolute 0 temperature K. -20 o For a volume at 20 C and 10 -40 -60 bar absolute a change in 5 0 temperature of 60oC will produce a change in pressure of 2.05 bar 0oC = 273K 8 6 10 4 12 2 14 0 bar 16 bar absolute 10 15 20 P1 P2 = =c T1(K) T2(K) 54 Constant volume From Boyle’s law and Charles’ law we can also see Temperature Celsius that if the volume of a given 100 mass of air were to be kept at 80 a constant value, the 60 40 pressure will be proportional 20 to the absolute temperature 0 K. -20 For a volume at 20oC and 10 -40 bar absolute a change in -60 5 0 o temperature of 60 C will produce a change in pressure of 2.05 bar 0oC = 273K 8 6 10 4 12 14 2 0 bar 16 bar absolute 10 15 20 P1 P2 = =c T1(K) T2(K) 55 Constant volume From Boyle’s law and Temperature Celsius Charles’ law we can also see 100 that if the volume of a given 80 mass of air were to be kept at 60 40 a constant value, the 20 pressure will be proportional 0 to the absolute temperature -20 K. -40 -60 For a volume at 20oC and 10 5 0 bar absolute a change in temperature of 60oC will produce a change in pressure of 2.05 bar 0oC = 273K 8 6 10 4 12 14 2 0 bar 16 bar absolute 10 15 P1 P2 = =c T1(K) T2(K) 56 The general gas law The general gas law is a combination of Boyle’s law and Charles’ law where pressure, volume and temperature may all vary between states of a given mass of gas but their relationship result in a constant value. P1 .V1 P2 .V2 = T1 = constant T2 57 Test question Question 1: It says that, for an ideal gas at constant pressure, the volume is proportional to the ________ (in kelvins). Question 2: which gas law is stated as follows? The equation shows that, as absolute temperature increases, the volume of the gas also increases in proportion. Question 3: An ideal gas is contained in a volume V at temperature T. If the volume is doubled at constant pressure, the temperature will be: a. Unchanged b. Halved c. Doubled d. Unable to be determined without more information 58 Test question Question 4: An ideal gas is sealed in a container at constant volume. If the temperature T is increased to 4T, the pressure will be: a. Unchanged b. Increased to 4P c. Decreased by 4P d. Unable to be determined without more information Question 5: A sample of an ideal gas is held at constant temperature. If the pressure is decreased to 1/2 P, the volume will be: a. Increased to 2V b. Decreased to 1/2 V c. Unchanged d. Unable to be determined without more information 59 Pressure and force 60 Pressure and force Compressed air exerts a force of constant value to every internal contact surface of the pressure containing equipment. Liquid in a vessel will be pressurised and transmit this force For every bar of gauge pressure, 10 Newtons are exerted uniformly over each square centimetre. 61 Pressure and force The force contained by a cylinder barrel is the projected area multiplied by the pressure F P.A F .D .P 2 4 Dm P bar F : Force (N). D : Diameter of piston (m). P : Pressure(N/m2). 63 Pressure and force If both ports of a double acting cylinder are connected to the same pressure source, the cylinder will move out due to the difference in areas either side of the piston If a through rod cylinder is applied in this way it will be in balance and not move in either direction 64 Pressure and force In a balanced spool valve the pressure acting at any port will not cause the spool to move because the areas to the left and right are equal and will produce equal and opposite forces P1 and P2 are the supply and exhaust pressures P1 P2 65 Flow of compressed air 66 Flow units Flow is measured as a volume of free air per unit of time Popular units are : Litres or cubic decimetres per second l/s or dm3/s Cubic metres per minute m3/m Standard cubic feet per minute (same as cubic feet of free air) scfm 1 cubic foot 1 litre or cubic decimetre 1 m3/m = 35.31 scfm 1 dm3/s = 2.1 scfm 1 scfm = 0.472 l/s 1 scfm = 0.0283 m3/min 1 cubic metre or 1000 dm3 67 Free air flow The space between the bars represents the actual volume in the pipe occupied by 1 litre of free air at the respective absolute pressures. Flow takes place as the result of a pressure differential, at 1bar absolute (0 bar gauge) there will be flow only to a vacuum pressure If the velocity were the same each case will flow twice the one above Volume (litre) Actual volume of 1 litre of free air at pressure 1.0 0.5 0.25 0.125 0.06325 0 Bar Pa Bar Pg 1 0 2 1 4 3 8 7 16 15 68 Control theory Control types according to DIN 19226 Form of information representation Pneumatic control system Signal flow and the control chain 69 Control theory Differentiation between the control systems can be made according to the following viewpoints. The following illustrations respresent the control types according to DIN 19226. There are three main groups. The categorisation of a control system to the three main groups depends on the problem definition. If it is a case of program control, the project designer has the choice of the three subgroups of program control . 70 Control types according to DIN 19226 71 Control types according to DIN 19226 Pilot control system There is always a clear relationship between the command or reference value and the output value provided disturbance variables do not cause any deviations. Pilot controls do not have a memory function. 72 Control types according to DIN 19226 Memory control system When the command or reference value is removed or cancelled, in particular after completion of the input signal, the output value achieved is retained (memorised). A different command value or an opposing input signal is required to return the output value to an initial value. Memory control systems always have a storage function. 73 Control types according to DIN 19226 Program control The three types of program control are: Step diagram control Sequence control system Time (schedule) control 74 Program control Step diagram control In the case of step diagram control, the reference variables are supplied by a program generator (program memory), whose output variables depend on the path travelled or the position of a moving part of the controlled system. 75 Program control Sequence control system The sequence program is stored in a program generator which runs through the program stepby-step according to the status attained by the system being controlled. This program may either be permanently installed or else read from punched cards, magnetic tapes or other suitable memories. 76 Program control Time (schedule) control In a time (schedule) control system, the command values are supplied by a time-dependent program generator. Characteristics of a timing control system are, thus, the existence of a program generator and a timedependent program sequence. Program generators may be : – Cam shafts – Cams – Punched cards – Punched tape – Programs in an electronic memory 77 Form of information representation Differentiation between the control systems: in the form of representation of information 78 Pneumatic control system 79 Signal flow and the control chain PNEUMATICS/HYDRAULICS - Cylinders - Motors - Indicators Directional Control Valves - Directional Control Valves - Non-return valves - Pressure valves - Switches - Pushbuttons - Limit switches - Program generators - Proximity signalers - Sensors Compressed air ELECTRICS/ ELECTRONICS ACTUATING DEVICES FINAL CONTROL ELEMENTS PROCESSING ELEMENTS (CONTROL ELEMENTS) INPUT ELEMENTS - Electric motor - Solenoids - Linear motors - Power contactors - Power transistors - Semiconductors - Contactors - Relays - Electronic Components - Switches - Pushbuttons - Limit switches - Program generators - Proximity signalers - Indicators - Generators Electrics/electronics energy 80 Pneumatic Circuit Diagram 1.5 Actuator A 1.4 Final control element S P 1.3 1.1 A B A Signal processor A 1.2 R Signal input P R P R 0.2 0.1 P A R Compressed air Energy supply (source) 81 Electro – pneumatic circuit diagram S1 Cylinder A S2 B A A Y1 S4 B Y2 S R S P +24V S3 Cylinder B 1 2 R P 3 4 5 6 7 8 Start S1 0V K1 S2 K3 K4 K1 K2 K2 S3 S4 K1 K2 K3 K4 Y1 Y2 82 Test question: Fill in the blanks Advantages of pneumatic system 83 Test question: Fill in the blanks Disadvantages of pneumatic system 84 Homework 3 in A 2 inch diameter piston with a 3 inch stroke, compresses air at atmospheric pressure into a 2 cubic inch space at the top of the cylinder. Use Boyle’s law to determine the pressure after the gas has been compressed ? Compressed Air Air a. 39.9 psig 2 in b. 54.6 psia c. 69.3 psig d. 84 psig e.119.6 psia (choose the right answer and attach the solution) 85 Reference Textbook Peter Croser, Frank Ebel, Pneumatics – Textbook Basic Level, Festo Didactic 1999 (any edition is useful). D. Waller, H. Werner – Pneumatics – Workbook Basic Level, Festo Didactic 2002 (any edition is useful). G. Prede, D. Scholz – Electropneumatics – Textbook Basic Level, Festo Didactic 2002 (any edition is useful). D. Waller, H. Werner – Electropneumatics – Workbook Basic Level, Festo Didactic 2002 (any edition is useful). Michael J.Pinches, John G.Ashby, Power Hydraulics, Prentice-Hall 1989 H. Exner, R. Freitag, Basic Principles and Components of Fluid Technology, Rexroth 1991. http://www.festo-didactic.com/int-en/ http://www.norgren.com/ http://www.pneumatica.be/pneumatics/index.htm http://www.hydraulicspneumatics.com http://pneumatic-source.com 86 HIGHER ENGINEERI NG EDUC ATION ALLI ANCE PROGRAM Contact: thuyptt@hcmute.edu.vn
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