SAPELEM - Guides - Vaccum Guide

The advantages of suction cups handling make this gripping technology the solution that should be considered first and foremost.

AVANTAGES

         Reliability
         Simplicity
         No risk of damage to the product
         Gripping by a single surface
         High transfer rates
         Low unit cost
         Quick and easy replacement
         Gripping of all types of products
         Low servicing

LIMITES

         High accuracy positioning
         Limited lifting capacity / gripping surface ratio
         Very porous product

Safety

SAPELEM is very concerned regarding safety matter. Check for the following rules:

         Safety factor
         Material
         Dynamic forces
         Vertical handling
         Altitude

Operating principle of a suction cup

Suction cup is activated by pressure difference between inside (vacuum) and outside (atmospheric). Suction cup is thus able to lift few grams to several tons in accordance with its diameter.

Units:
1 atm = 1,013 bar = 1013 mbar
1daN/cm²
101,3 kPa
760 mmhg

Calculated values:

Tear-out force: F = (Patm - Pv) x S1 Lifting capacity: C max = 1,03 x ΔP x S2 Round suction cup’s lifting capacity: C max = 0,81 . ΔP x D² Calculation of suction cup’s diameter: D = 1,11 x (C/ ΔP)0,5	ABREVIATIONS F : tear-out force Pv : suction cup pressure Patm : atmospheric pressure S : useful surface P : vacuum pressure D : diameter C : theorical lifting capacity
Example: In theory, to lift a 100 kg load, with a vacuum level of 80% D=1,11 x (100/0.8)0,5 = 12,4 cm Nota: 0,81 bar = 80% vacuum = 80 Kpa = 600 mm hg	UNITS U : % vacuum F : Newton Pv : Pascal Patm : Pascal S2 : cm2 S1 : m2 P : bar D : cm C max : kg

True conditions :

Effective suction cup lifting capacities vary significantly from the calculated value, due to:

Product properties:
- Non porous
- Porous
Surface condition:
- Cleanliness
- Roughness
Useful surface of the suction cup
Shape (dimensions) of the product
 Suction cup deformation affected by:
- Vacuum level
- Force applied
- Shape
- Material

    Because of these parameters, a safety factor for vacuum handling is mandatory.

Safety factor :

    SAPELEM represents France at the European Committee for Standardization. The draft code EN 13155 set out by CEN/TC 147 states that:

    « Suction cup lifting systems must be dimensioned so that the adherence strength is always at least equal to 2 the effective component of the nominal load at the lower limit of the vacuum pressure range which may be used (…) »

    This safety factor of 2 (for horizontal handling) takes into account only a part of uncertain parameters (surface condition, etc…). The following points must be specifically considered.

Materials:

    Used materials have a significant effect on the lifting capacity of a suction cup. Performances related to the 4 commonly used materials are indicated on each technical data sheet (see the following section).

Dynamic forces:

    According to the formula F = M × A (Force = Mass × Acceleration), the dynamic forces, induced by movements, must not be neglected. They must be added to the weight of the product. This criterion should be carefully considered especially in the cases of high speeds, high accelerations, quick transfers, fast turning or pivoting. Tear-out force will increase significantly

    When used in vertical applications, a suction cup is subjected to frictional force. A safety factor of 6 should be applied. The values in the force tables of the technical data sheets must therefore be divided by 3. For example, a suction cup rated for 12 kg in horizontal handling becomes 12/3 = 4 kg in vertical handling
.

Altitude :

Higher is the altitude, lower is the atmospheric pressure. If the pressure remains the same in the suction cup, its lifting capacity decreases.

Taking all these parameters into consideration, the example on the previous page with:

a nitrile suction cup
a vacuum of 810 mbar max.
a lower limit of vacuum range at 600 mbar (alarm trip threshold)
a safety factor of K = 2 and with no acceleration

The calculation of the diameter becomes:
D = 1,11 x (KxC/u)0,5 =(2x100/0,6)0,5 = 20,3 cm (and no longer 12.4 cm)

See below for criteria to be taken into account

SAPELEM engineers will help you to determine this data.

Flexible products :

Suction cups quantity must be sufficient to guarantee the product flatness.

Thin or fragile products :

    To prevent the suction cup to deform the product, it is better to use several smaller suction cups or suction cups with stops.

Porous products or uneven surfaces

    Porous materials induce leakage through the products. The vacuum level in the suction cup (and thus its lifting capacity) will be lower (F = k.U).
    Test must be performed to confirm cups and vacuum generator determination.

Sapelem and its retailers network can perform them.

Weight of the product :

The suction cups quantity will also be determined by the weight to be handled and the nominal capacity of each suction cup.
Caution: The lifting capacities are calculated from actual parameters in the above specific conditions. Safety aspects, dynamic forces, altitude …should be taken into account to correct these values

	Nitrile
Ø 10	0,2
Ø 20	0,9
Ø 34	2,7
Ø 53	5,8

Measurement conditions

- lifting capacity kg
- vacuum level 80 %
- on dry sheet metal
- static force, perpendicular to the surface
- sea level
- safety factor 2

Vacuum level effect :

The lifting capacity of a suction cup (thus the suction cups’ quantity to be used to lift a given weight) is directly proportional to the used vacuum level.

    To get the lifting capacity of a suction cup, at a pressure different to the 0.8 bar indicated in the tables, use the ratio lifting capacities / vacuum level :
                                    (C 0,6/ C 0,8 ) = (ΔP 0,6 / ΔP 0,8)

Example: if at 0.8 bar the lifting capacity of a suction cup is 12 kg, at 0.6 bar it becomes:
                                        C 0,6=(12x(0,6/0,8) = 9 Kg

Bellows’ quantity :

    Bellows’ quantity depends both on the type of the product to be handled and on the type of the used machine. With regard to thin and fragile products likely to have uneven gripping surface it will be better to opt for minimum 1.5 bellow suction cups.

    As regards as stiff products which have a perfectly flat gripping surface we will choose flat suction cups.

    Besides if the manipulator has a low accuracy of position stop it will be advisable to compensate this inaccuracy by bellows’ suction cups.

    For handlings with high accelerations and/or movements with the part in vertical position, it will be advisable to choose stiff enough suction cups (1/2 bellow or flat).

Stop :

Internal stop of suction cup has two main functions :

On thin products: It allows the product to lean on a flat surface so that to limit the deformation and to avoid the breakage of fragile products

o On manipulators with high accelerations: It acts as friction pad between the part and the suction cup. It limits thus the risks of relative skidding

Connector :

There are two technologies of fixing for suction cups :

Grooved connectors for detachable moulded suction cups

Principle:	The suction cup is simply snapped onto the connector
Advantages:	Quick to change (no tool required) Only the suction cup to be changed when worn out
Use:	Light products Horizontal handling
Choice:	Refer to the technical data sheets of the detachable suction cups
Fixing:	Male or female
Size:	From T0 to T4
Fitting:	M5, 1/8, ¼, 3/8

Vulcanized connectors on moulded suction cups

Principle:	The suction cup is vulcanized onto the connector after sticking operation
Advantages:	Perfectly air tight Higher mechanical strenght
Use:	Handling of heavy loads Vertical handling or pivoting Mounting with self regulated vacuum or vacuum safety tank
Choice:	For suction cups Ø>25mm
Fixing:	Male or female
Size:	According to the suction cup
Fitting:	M5, 1/8, ¼, 3/8

The way’s diameter into the connector must be sufficient to allow the passage of the vacuum flow. For your applications on porous products, think about our T3G connector!

Material :

Performance and lifetime optimization of your suction cups depends also on the material.

See the tables below.

Standard and special materials

    For many years, SAPELEM has developed a large choice of materials in order to meet all requirements. All our models are available in standard materials (in stock).

        Some cups can be made in special materials. Please contact us for feasibility.

    When in use, the suction cup is subject to physical, chemical and mechanical stresses. Depending on these parameters, one material will be more suitable than another.

	Standard materials				Special materials
	Silicone	Nitrile	Natural Rubber (parablond)	Polyur éthane	Nitrane	Self-extinguishing Nitrile	EPDM	Viton	Detectable Silicone
Materials abreviations	SI	NBR	NR	PU		NPR	EPDM		SI
Material reference	10	20	30	40	24	29	55	60	12
Temperature range (°C)	-50 to 200	-10 to 80	-10 to 60	0 to 60	-10 to 60	-10 to 60	-30 to 100	-5 to 230	-50 to 200
Colour	White	Black	Beige	Grey	Blue	Brown	Yellow	Black	blue
Shore hardness A (± 5) Din 3555	52	55	42	60	60	60	60	70	52
Physical
Common use
Irregular surface condition
Handling of hot products
Hot products with no contact with Silicone
No mark on the product
Food* or delicate products
Chemical
Sparks, welding projections
Resisting to cleaning process
Nutrient fats
Aqueous products
Hydrocarbons, oils
Acids**
Alcohols**
Mechanical
Gas (e.g.: ozone….)
Abrasion
Flexible or deformable products
Cylindrical products
Sliding, shearing
Mechanical resistance

Legend :

Perfectly suited

Moderately suited

Not very suited

*Specific silicone for food industry: shore hardness from 32 to 50
**Given the diversity of Acids and Alcohols in use, please feel free to contact us for your specific applications

Other materials on request :

For very specific applications, SAPELEM is able to manufacture your suction cups in special materials with the following characteristics :

Material	Reference	Colour	Specific application	Lifting capacity
Silicone containing carbone	15	Black	Conductibilité	Cf. Silicone
High T° Silicone	19	White	Resists up to 250°C steady	Cf. Silicone
Carboxyl Nitrile	25	Black	Resists abrasion	Cf. Nitrile
Nitrile for food industry	27	White	Resists oils and fats	Cf. Nitrile
Butyl	50	Black	Resists acids and alcohols	Cf. Silicone
Epychloridrine	99	Grey	Resists hydrocarbons	Cf. Nitrile

Technical Guide about vacuum gripping

Lifting capacity

Suction cups quantity determination

Suction cups model determination

Restricted access