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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 kPa mbar Torr - kPa - mmHg - inHg % vac
Sea Level 101.3 1013 760 0 0 0 0
90 900 675 10 75 3 10
80 800 600 20 150 6 20
70 700 525 30 225 9 30
60 600 450 40 300 12 40
50 500 375 50 375 15 50
40 400 300 60 450 18 60
30 300 225 70 525 21 70
20 200 150 80 600 24 80
10 100 75 90 675 27 90
Vacío absoluto
0 0 0 101.3 760 30 100
Atmósfera std
Factores de Conversión
1 Torr = 1mm Hg at 00C 1mm H2O = 9.81 Pa 1 Pa = 1 N/m2
Pa Bar kp/cm2 Torr psi (lbf/ in2)
1 1.0 x 10-5 1.020 x 10-5 7.501 x 10-3 1.45 x 10-4
1.0 x 105 1 1.020 7.501 x 102 1.45 x 101
9.807 x 104 9.807 x 10-1 1 7.356 x 102 1.422 x 101
1.333 x 102 1.333 x 10-3 1.36 x 10-3 1 1.934 x 10-2
6.895 x 103 6.895 x 10- 2 7.031 x 10-2 5.172 x 10-1 1
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
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.
Ventajas Bajo costo No emite calor compacto
Desventajas Alto nivel de ruido Flujo alto o vacío alto
Simple etapa
Tipos de generadores de Vacío
Funcionamiento similar al de simple etapa, pero se usan mas difusores para crear mas vaío.
Ventajas Bajo nivel de ruido No genera calor Vajo consumo de
aire (4-1) Diseño compacto Rapida respuesta
Desventajas Alto costo
Multi etapa
Diseno de sistemas
decentralizado
Centralizado
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 Flow Flow
Min. Max.
Norgren(single)
28 55
Norgren (multi) 80 910
SMC 5 135
Festo 11 220
Hoerbiger 13 95
KV 169 680
Copa de Vacio
FUELLE Flat
Materiales de Copas
Material Nitrile Silicon
Tensile Strength r 6
Elongation 4 r
Oil resistant (gasoline) 4 6
Oil resistant (Benzol) 6 6
Solvent resistant (Toluene) 6 6
Solvent resistant (Alcohol) 4 4Weather resistant r 4
Ozone resistant 6 4Heat resistant (+200 deg C) r 4
Cold resistant (-30 deg C) 6 4
Water resistant r r
4 Compatible
r Acceptable
6 Not compatible
Nitrile Silicon
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: 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 vacuum line.
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 Leaking Flowl/s per sq. mm
10% 0.1120% 0.1730% 0.1840% 0.19547% 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 Where : F = lift force (N) p = vacuum (bar) d = suction cup dia. (mm) n = number of suction cups
s = safety factor
F
np
sFd
40
Sizing suction cups
Vertical contact lift Where : F = lift force (N) p = vacuum (bar) d = suction cup dia. (mm) n = number of suction cups s = safety factor m = friction coefficient
F
mnp
sFd
40
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 200kg (2000 N) Horizontal or vertical lift Horizontal Flat or curved surface Flat Porous, yes or no No Operating pressure 6 bar Working vacuum level 60% Centralized or localized system Centralized Number of suction cups 6 (due to size of plate) Suction cup type / material Flat, nitrile Suction cup positioning Evenly distributed around center of
gravity Particle ingress None Non return valve No Pressure switch type None Level compensation None Eject circuit Not required Evacuation time 3 second Tube length / dia. or volume 2.71 liters
Example (calculation)
Suction cup d= 118 mm Nearest standard dia. =
150 mm Part Number - M/58312/01
np
sFd
40
60.6
22000d
40
Example (calculation)
System capacity
Total system capacity (V) is the sum of the internal volume
of the vacuum line (V1) and that of the suction cups (VC).
Thus:
V = V1 + VC
V1 is given as 2.71 litres
VC is obtained from product data sheets.
For M/58312/01 VC = 177cm3 x 6 = 1062 cm3 = 1.06 litres
Therefore: V = 2.71 + 1.06
= 3.77 litres
Example (calculation)
Evacuation timeThe time to evacuate a volume of 1 litre (t1):
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
Flexible connectors
Level compensators
Vacuum products
Cylinders with hollow piston rods
Pneumatic, electronic and electrical pressure switches
Vacuum filters and gauges
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
Removable/replaceable jet modules
End
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