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Pneumatics Part‐I Compressed air systems By Amaren P. Das M.Tech (SYSCON) IIT‐B
• General methods of material handling – Clamping , shifting, Positioning , Orienting
• General application – Packing , Filling, Metering, Stacking , stamping etc.
• Machining and working – Drilling , Milling, Forming, Sawing D illi Milli F i S i
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• Availability – Everywhere, unlimited quantity
• Transport – Easily be transported over pipelines over long distance
• Explosion proof – No risk of explosion or Fire
• Cleanliness – Un lubricated exhaust air are clean
• Speed – Fast working medium …. Enables high working speed
– Temperature – Insensitive to temperature fluctuations
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• Preparation – Dust and condensate should not be present Dust and condensate should not be present
• Compression – It is not always possible to achieve uniform and constant piston speed with compressed air
• Force Requirement – Pressure up to 8 bar only p y – Maximum force limited to, 40,000 to 50,000N
• Noise Level – Exhaust air produce noise NFC TS 2009 Pneumatics APDas
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• Pneumatic control circuit – Signal flow – Symbols of hydraulic circuit Symbols of hydraulic circuit
• Actuators • Valves – – – –
Direction control valve Flow control valves Pressure control valves Combination valve Combination valve
• Air preparation (FRL units) • Pumps • Piping & distribution NFC TS 2009 Pneumatics APDas
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• How single acting cylinder works
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• How Double acting cylinder Works
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• A single acting cylinder of 25 mm diameter is to clamp a mm diameter is to clamp a component when a push button is pressed. As long as the push button is pressed the cylinder is to remain in the clamped position . When the push button is released the clamp is retracted l i t t d
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• A piston of a double acting cylinder is to advance when cylinder is to advance when the 3/2 way roller leaver valve 1s2 is actuated and the push button of 3/2 way valve 1S1 is actuated. If either of the two is released, then the cylinder returns to initial position. • How to do it with out using and valve ?
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• A double acting cylinder is to advance if one of the two push buttons are pushed. If either of the push button is released the cylinder should p p y retract. The cylinder should also retract if it has completed its stroke.
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• What does the following circuit do ?
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• The piston of a double acting cylinder is to advance when a 3/2 y way valve is manually pressed. The cylinder is to remain advanced until a second push button is actuated, to move it to initial condition. The signal from the second PB can take effect only when the signal from the 1st PB has been removed. The cylinder is to remain in the initial li d i t i i th i iti l position until a new start signal is given. Speed of cylinder is to be adjusted in both direction
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• A plastic component is embossed using a die driven by a double g y acting cylinder. The die is to advance and emboss the plastic when a push button is operated. The return of the die is effected when a preset pressure is reached. The embossing pressure is to be adjustable. • What changes are required if full extension is also to be sensed ?
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• A double acting cylinder is used press together glued components. Upon operation of a push button, the clamping cylinder extends. • Once fully advanced position is reached, the cylinder is to remain for a time of T=6 sec and then immediately retract to the initial position. Cylinder retraction is to be adjustable. Anew cycle is only possible after the cylinder is fully retracted. NFC TS 2009 Pneumatics APDas
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• An actuator is an output device for conversion of supply energy into useful mechanical work supply energy into useful mechanical work • Pneumatic actuators fall under two groups – Linear motion • Single acting cylinder • Double acting cylinder
– Rotary motion Rotary motion • Air motors • Rotary cylinders
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• Single acting cylinder – – – – –
Si l Single port t Spring return Natural length of spring ‐>limited stroke length Compressed length of spring ‐>extra space Limited stroke 80mm
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• Two ports • Cylinder can do work on both strokes • Forces not equal
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• When moving large mass, sudden stoppage at th endd cause impact the i t on the th cylinder li d cap, andd damages it .
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• Tandem double acting cylinder – Force on the piston is almost doubled Force on the piston is almost doubled
• Through piston rod Cylinder – Guide of cylinder is better, as both side support is there – Same force in both directions
• Multi‐position cylinder – C Consists of two or more double acting i t ft d bl ti cylinder, which are interconnected.
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Three different principles are used for the construction of y rodless cylinders. 1. Band or cable cylinder 2. Sealing band cylinder with slotted cylinder barrel 3. Cylinder with magnetically coupled slide
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1. 2. 3. 4. 5. 6. 7.
Cylinder barrel, seamless drawn tube End cap Bearing Cap Piston rod Seal ring, for leak tightness Bearing bush, to guide the cylinder Scraper ring , to keep dust away NFC TS 2009 Pneumatics APDas
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• Force on the piston Fth =A*P A*P Fth= force on piston A= cross section area of piston P = pressure on the piston face Note: Effective piston force is less than the theoretical force due to presence of friction. Under normal operating condition (4 to 8 bar) friction force can be assumed as 10% of theoretical piston force NFC TS 2009 Pneumatics APDas
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• Area of Piston A=(3.14 * D2 / 4)
– – A’=(D2 ‐ d2 )*3.14/4
• Single acting – Feff= (A*P) ‐ ( FR + FF )
• Double acting – Forward Forward stroke stroke • Feff = A*P – FR – Reverse Stroke • Feff = A’*P – FR
A= Area of piston cap side A’ = Area of piston rod side P = working pressure FR= Friction force FF=Return spring force D= Diameter of Piston d= Dia of rod
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• Length covered by the piston from one end to it f dt other • Stroke length should not be greater the 2mt and 10mt for rodless cylinder Use buckling diagram for • Use buckling diagram for long stroke
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NBR (Nitrile Butadiene Rubber) Max service Temp 95C. Colour :Black. Ideally suited for manufacturing all sealing components used in pneumatic and hydraulic industry hydraulic industry HNBR (Hydrogenated Nitrile rubber) Max service Temp. 150C. Colour: Black. Similar to NBR but provides broader thermal and chemical resistance EPDM Rubber (EPM,EPR), Max Service Temp 150C. Color: Black. Incompatible to mineral oil, but is resistant to many fluids that are incompatible with other elastomers, including steam and break fluid. Viton. Max Service temp 200C, color: Brown. Outstanding chemical compatibility, low compression set and broad temperature range, coupled with its ability to resist extrusion, tearing and wear, makes this a significant compound d k thi i ifi t d
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Silicone Rubber. Max Temp 200C. FDA approved for use in the food industry. Silicones have poor wear, tear and tensile properties.
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Polyurethane . Max Temp 110C , 70C in water. Most popular, low compression set and superior resistance to abrasion and tearing. NFC TS 2009 Pneumatics APDas
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• Converts pneumatic energy into mechanical rotational energy • Types – Piston motors • Clock wise and CCW, max 5000rpm, 1.5 to 20 kW
– Sliding vane motors • Light weight, 3000 to 8500 rpm, 0.1 to 17 kW, used in hand held tools
– Gear motors • Up to 44KW
– Turbine motors • Low power, very high speed 500,000 rpm, Ex. Dentist’s drill NFC TS 2009 Pneumatics APDas
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Direction control valve Non‐Return Valve Pressure control valve Flow control valve Combination valve
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• Direction control valve – The direction control valve controls the Th di i l l l h passage of air signals by generating, canceling or redirecting signals • Input/signaling element : As signaling element the DCV is operated for example , by roller lever to detect the road position • Processing element: P i l t DCV redirects or cancels DCV di l signals depending on the signal input • Control element: DCV must deliver the required quantity of air to match the power component requirement NFC TS 2009 Pneumatics APDas
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– The valve is described by • Number of ports : 2‐way, 3‐way, 4‐way , etc • Number of position : 2 position, 3 position, etc • Method of actuation of valve: mechanically actuate, manually actuated, electrically actuated, • Method of return actuation: Spring return , air Return , etc
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• Working line ISO -5599-3 5599 3
Pilot
Lettering System
Port connection
1
P
Pressure port
2, 4
A, B
Working line
3, 5
R, S
Exhaust port
lines Applied signal stops flow from port 1 to port 2
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P
Applied signal connects Port 1 and 2
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A, B
Connects port 1 & 4
R, S
Auxiliary pilot air
81, 91
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• Different types of actuation – – – – –
Manual Manual Mechanical Pneumatic Electrical Combined
Mechanical
• Manual
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