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