Transcript Vacuum - PCONTROL
Trecnología de Vacío
Introducción
La tecnología de vacío hace uso del diferencial de presión entre la presión atmosférica y un vacío parcial para realizar el trabajo Si un vacío completo se creara, el diferencial de presión máximo sería 1 atmósfera (alrededor de 1013mbar) The larger the surface area over which this differential is acting the higher is the force
Unidades de medida de Vacío
Vacío absoluto kPa mbar Torr -kPa -mmHg -inHg % vac 101.3 1013 760 90 900 675 80 800 600 0 10 20 0 75 150 0 3 6 0 10 20 70 60 50 40 30 20 10 0 700 525 600 450 500 375 400 300 300 225 200 150 100 75 0 30 40 50 60 70 80 90 0 101.3 225 300 375 450 525 600 675 760 9 12 15 18 21 24 27 30 30 40 50 60 70 80 90 100
Factores de Conversión
Pa 1 1.0 x 10 5 9.807 x 10 4 1.333 x 10 2 6.895 x 10 3 Bar 1.0 x 10 -5 1 9.807 x 10 -1 1.333 x 10 -3 6.895 x 10 -2 kp/cm 2 1.020 x 10 -5 1.020
1 1.36 x 10 -3 7.031 x 10 -2 Torr 7.501 x 10 -3 7.501 x 10 2 7.356 x 10 2 1 5.172 x 10 -1 psi (lbf/in 2 ) 1.45 x 10 -4 1.45 x 10 1 1.422 x 10 1 1.934 x 10 -2 1
1 Torr 1mm H2O 1 Pa = 1mm Hg at 00C = 9.81 Pa = 1 N/m2
Importante
El tamaño físico de un generador del vacío no se rige por la condición de aire inducido, en el nivel de vacío que alcanzará
Tipos de generadores de Vacío
Simple etapa
Ventajas
Bajo costo
No emite calor compacto Desventajas
Alto nivel de ruido Flujo alto o vacío alto
Cuando el aire entra en el difusor y su diámetro aumenta el aire se expande y aumenta su velocidad, el aire que se encuentra en el puerto de vacío es inducido en direccion del flujo y es succionado aumentando así el caudal de salida y creando el vacío.
Tipos de generadores de Vacío
Multi etapa
Ventajas
Bajo nivel de ruido No genera calor
Vajo consumo de aire (4-1) Diseño compacto Rapida respuesta Desventajas
Alto costo
Funcionamiento similar al de simple etapa, pero se usan mas difusores para crear mas vaío.
Diseno de sistemas
Centralizado
decentralizado
Sistema de diseño.
Descentralización
La energía usada es proporcional al volumen de evacuación por lo que se debe considerar la descentralización. Si varios puntos son equipados para vacío, una mayor economía se obtiene si se coloca a cada punto de aplicación un generador de vacío.
Mínimo Volumen de Vacío
Mayor seguridad Maximiza el desempeño del sistema Conclusión – siempre trate en lo posible de obtener le menor cantidad de volumen a evacuar.
Capacidad del generador
Material no poroso
Una vez asegurado el componente, el flujo de vacío es cero.
Requiere bajo caudal Material poroso
Para obtener un adecuado nivel de vacío, el generador debe tener suficiente capacidad de evacuación te aire, que esta en constante fuga dentro del sistema
Alto Flujo General
Copa con sello perfecto = bajo flujo, alto vacío Material poroso = alto flujo, menos vacío
Comparación de flujo.
Comparación de flujo de vació l/min. Manufacturer Norgren (single) Norgren (multi) SMC Festo Hoerbiger KV Flow Min.
28 80 5 11 13 169 Flow
Max.
55 910 135 220 95 680
Copa de Vacio
FUELLE
Flat
Materiales de Copas
Material Tensile Strength Elongation Oil resistant (gasoline) Oil resistant (Benzol) Solvent resistant (Toluene ) Solvent resistant (Alcohol) Weather resistant Ozone resistant Heat resistant (+200 deg C) Cold resistant (-30 deg C ) Water resistant
Nitrile
Nitrile r 4 4 6 6 4 r 6 r 6 r
Silicon
Silicon 6 r 6 6 6 4 4 4 4 4 r 4 r 6 Compatible Acceptable Not compatible
Consideraciones
Velocidad: Considerar los momentos generados por la alta velocidad de transferencia y los movimientos de carga. Cup distortion in certain designs and materials will occur.
Component release: vacuum line.
Ordinarily the workpiece would be released when the air supply is removed and the vacuum level drops. In high speed automation a separate system can be used to eject the workpiece by adding momentary pressure to the Filtration: The ingress of dust, lint or moisture can have a detrimental effect on the efficiency of the venturi. Where ingress is likely fit a vacuum filter.
Fittings: Conventional design push in fittings are acceptable, although push on fittings are more suitable. Avoid 90 degree bends, preferably swept.
Tube: Conventional nylon or polyurethane
Ejection circuit
Valves can be air or direct acting solenoid 2/2 or 3/2 with a pulse signal to the eject valve
Applications
Packaging machines
Evacuating the vessel of air speeds up liquid filling
Bellows suction cups are ideal for picking up and opening all kinds of bags Labels can be applied quickly and efficiently to particularly soft or uneven products Box and carton forming Electronics
Printed Circuit Board test fixtures Vacuum forceps Automotive
Body panel transfer
Glass component handling And many more…..
Porosity (fixed)
To maintain the desired vacuum level a generator must have the capacity to account for the leaking air. If leakage occurs via a known aperture, flow can be established by using the table Vacuum Level 10% 20% 30% 40% 47% Leaking Flow l/s per sq. mm 0.11
0.17
0.18
0.195
0.2*
Porosity (unknown)
When leakage occurs through a porous material, or in an unknown way, the flow can be established by a test with a vacuum generator. It is connected to the system and the achieved vacuum level read (at least 40%). The flow that occurs at this vacuum level can be seen in the data against each generator. This roughly corresponds to the leaking flow.
Sizing suction cups
When sizing a suction cup it is the required lifting force that is crucial. As the weight of the object being handled is often known and the diameter of the cup is required, a simple equation can be used, dependent on the type of lift taking place.
Horizontal contact lift
Vertical contact lift
Sizing suction cups
Horizontal contact lift F Where :
F = lift force (N)
p = vacuum (bar) d = suction cup dia. (mm)
n = number of suction cups
s = safety factor
d
F
s
40
p
n
Sizing suction cups
Vertical contact lift F Where :
F = lift force (N)
p = vacuum (bar) d = suction cup dia. (mm)
n = number of suction cups
s = safety factor m = friction coefficient
d
F p
s
40
n
m
Suction cup selection
Select the right type of cup for the application Use a safety factor of 2 or 4, depending on type of lift Consider additional dynamic forces Bear in mind positioning accuracy Consider the effect of black rubber on bright surfaces No silicon on pre-painted surfaces Distribution and number of cups in relation to centre of gravity Choose accessories to give the best performance
Example
Task
A glass plate measuring 2500mm x 1250mm is to be lifted from a machine.
The weight of the glass is 200kg. (2000 N)
The internal volume of the vacuum line on the lifting frame is V1 = 2.71 litres.
An evacuation time of t = 3 seconds is required.
The working vacuum level is 60% at 6 bar operating pressure.
Specify
Suction cup type.
Number and size of suction cups.
Total volume to be evacuated.
A suitable vacuum generator.
Example (checklist)
Weight of object to be lifted Horizontal or vertical lift Flat or curved surface Porous, yes or no Operating pressure Working vacuum level 200kg (2000 N) Horizontal Flat No 6 bar 60% Centralized or localized system Centralized Number of suction cups 6 (due to size of plate) Suction cup type / material Suction cup positioning center of gravity Particle ingress Flat, nitrile Evenly distributed around None Non return valve Pressure switch type Level compensation Eject circuit Evacuation time Tube length / dia. or volume No None None Not required 3 second 2.71 liters
Example (calculation)
Suction cup
d
F
p
s n
40
d= 118 mm Nearest standard dia. = 150 mm Part Number - M/58312/01
d
2000 0.6
6 2
40
Example (calculation)
System capacity Total system capacity (V) is the sum of the internal volume of the vacuum line (V 1 ) and that of the suction cups (V C ). Thus: V = V 1 + V C V 1 is given as 2.71 litres V C is obtained from product data sheets.
For M/58312/01 V C = 177cm 3 x 6 = 1062 cm 3 = 1.06 litres Therefore: V = 2.71 + 1.06
= 3.77 litres
Example (calculation)
Evacuation time The time to evacuate a volume of 1 litre (t 1 ): From the vacuum generator technical data refer to the table ‘Time (sec) for evacuation of 1 litre volume to vacuum’ in the column ‘p = -0.6 bar’. Select a generator with a lower figure than that calculated.
We find 0.58 s/l for M/58102/30
Vacuum products
Single stage generator Multi stage generators
Vacuum products
Flat and bellows type suction cups Level compensators Flexible connectors
Vacuum products
Pneumatic, electronic and electrical pressure switches Vacuum filters and gauges Cylinders with hollow piston rods
Modular vacuum management
Sensing, logic and local analogue control
AVAILABLE OCTOBER 2000
Complex integration
Internal silencer High performance jet modules Modular construction Switchable vacuum and blow-off Reduces installation time LED function indicators Reliable check valve design Optional remote control Internal sensor with 4-20 ma output