What are suction cups?

A kind of pneumatic elements working through the air pressure difference between inner and outer of the suction cups, which achieved by reducing the air pressure in the temporary sealed room shaped after the suction cups touch the workpiece.


Working principle

A temporary sealed room can be shaped after the suction cup connects the surface of the workpiece. Through the vacuum generating device, we can make the pressure inner much lower than the pressure outside. The inner and outer pressure difference makes the suction cup adhere to the workpiece tightly. The bigger the pressure difference is, the stronger the pressing force will be—the greater the suction cup’s holding force will be. Raise the inner-pressure, the pressure difference will be less, then the suction cup and the workpiece will be separated. Based on the above principle, suction cups are generally used to handle and fix objects.


Materials and catagories

Generally, materials can be divided into rubber, plastic and metal. Most of our common rubber materials are NBR、SI、SE、EPDM、 PUR、FKM、NR and NE.Based on the shapes, suction cups can be divided into flat suction cups, oval suction cups, bellows suction cups and special suction cups. Among these, bellows suction cups can be divided into 1.5 bellows suction cups, 2.5 bellows suction cups and multi bellows suction cups. Based on the methods of reducing the pressure, there are pneumatic suction cups and hand suction cups.


Material sheet


Characters

First, easy to be worn out. Because suction cups are made of common rubber and touch the objects directly, they are worn out fast and often needed to be changed.

Second, easy to use. No matter what material of the workpiece is, rubber suction cups can be used only provided a sealed room. Compared to the electromagnetic suction cups which can only be used to suck common steels, they have extraordinary advantages.

Third, no pollution. Suction cups don’t emit light, heat or electromagnetism, so they will benefit to the environment without pollution.

Fourth, no damage to the workpiece. Due to their working principle and the materials’ characters, suction cups never do any damage to the workpiece, no matter sucking or releasing. In some ranges which are very strict on the demand of the workpiece’s surface, vacuum cups have distinguished advantages compared with the hook or steel-cable style beams.


Calculating formula

First, weight of the workpiece

m=L x W x H x ρ

m=质量 mass (kg)
L=长度 length (m)
W=宽度 width (m)
H=高度 height (m)
ρ=密度 density (kg/m³)

Second, holding force

1.Suction cups horizontal & acting force vertical

Keep suction cups on the workpiece horizontal and moving vertically

Fth = m x (g+a) x s
Fth = theoretical holding force (N)
m = mass (kg)
g = acceleration due to gravity (9.81 m/s2)
a = acceleration of the handling system (m/s2)
      consider the emergency-off situation
S = safety factor – at least 1.5, for critical, inhomogeneous or porous materials or rough surfaces 2.0 or even higher

2.Suction cups horizontal & acting force horizontal

Keep suction cups on the workpiece horizontal and moving horizontally

Fth = mx(g+a/μ)xs = (mg+ma/μ)x s = (mg+Fa/μ)x s
Fth = theoretical holding force (N)
Fa = acceleration force= mxa
m = mass (kg)
g = acceleration due to gravity (9.81 m/s2)
a = acceleration of the handling system (m/s2)
      consider the emergency-off situation
μ = coefficient of friction
   = 0.1 oily surfaces
   = 0.2—0.3 wet surfaces
   = 0.5 wood, metal, glass, stone,surfaces
   = 0.6 rough surface
S = safety factor – at least 1.5, for critical, inhomogeneous or porous materials or rough surfaces 2.0 or even higher

3.Suction cups vertical & acting force vertical

Keep suction cups on the workpiece vertical and moving vertically

Fth = m/μx(g+a)xs/y
Fth = theoretical holding force (N)
Fa = acceleration force = mxa
m = mass (kg)
g = acceleration due to gravity (9.81 m/s2)
a = acceleration of the handling system (m/s2)
      consider the emergency-off situation
μ = coefficient of friction
   = 0.1 oily surfaces
   = 0.2—0.3 wet surfaces
   = 0.5 wood, metal, glass, stone,surfaces
   = 0.6 rough surface
S = safety factor – at least 1.5, for critical, inhomogeneous or porous materials or rough surfaces 2.0 or even higher

Third, each suction cup’s theoretical holding force

F = each suction cup’s theoretical holding force (N)
Fth = theoretical holding force (N)

n = number of suction cups
Cth= each suction cup’s theoretical capacity (kg)
g = acceleration due to gravity (9.81 m/s2)
△p = inner and outer pressure difference (bar)
equals % vacuum in figure
S = suction cup square ( effective sucking area ) (cm2)

Fourth, calculation of suction cups’ diameter

only adapted to round suction cups

d = diameter (mm)
Fth = theoretical holding force (N)
n = number of suction cups
△p =inner and outer pressure difference (bar)
equals % vacuum in figure


Selection of the suction cups

We’ll consider three factors, working environment, surface condition and operation mode. Working environment contains corrosion, ozone, alcohol, temperature and so on. Surface condition means the roughness of the workpiece’s surface, the degree of porosity, oil exists or not etc. Operation mode means the workpiece’s sucking situation, moving direction, frequency of operation and so on. Based on our experience, we’ll do brief explanations on the application of our various suction cups. Hope they are helpful for your selection.

First, flat suction cups

They have a large range of application, especially in the situation that the workpiece needs to be rotated. Compared with bellows suction cups, their volume is smallerr and the inner space is even smaller, so they can be connected to the vacuum generators directly. There’s no permanent distortion while sucking thin workpieces. They are good to resist the radial force while accelerating. It is feasible to use flat suction cups horizontally or vertically.

Second, bellows suction cups

Good buffering, adapt to curve or rough surfaces. Can’t be used vertically except auto suction cups.

Third, foam suction cups

Good flexibility, adapt to very rough workpieces.

Fourth, special suction cups

Adapt to the workpiece with special request. We can offer corresponding solution according to your detailed requirement.

Fifth, hand suction cups

Different from pneumatic suction cups above, external air supply isn’t needed. Their principle is to change the shapes of hand suction cups themselves or use hand pumps to evacuate the air in the suction cups to suck workpieces. There’re flat suction cups and concave suction cups. They are often used to handle and fix surface-smooth workpieces, such as glasses, stainless steel panels, surface-spray-painted objects and so on.

Sixth, disc suction cups

Often shaped in full rings or half rings, mainly made of Silicone. Especially used in CD industry.

Seventh, high temperature suction cups

Can resist temperature 400℃ for a short while, adapt to high temperature steels, Al. sheets and glass plates.

Eighth, sealing rubber

Belong to spare parts of circle-producing suction cups. Adapt to quite rough workpieces, such as concrete objects, fire bricks, rough processed natural stone, rough glass and so on.

Ninth, suction cups especially for vacuum pens

Flat and lip-thin suction cups, mainly made of SE. They are generally used for integrated package to suck some thin and light workpieces such as solar cells and so on.

Tenth, non-touch suction cups

Especially adapt to very thin, porous or surface-sensitive workpieces, such as paper, wafers, solar cells, thin wooden boards, printed circuit boards, film and so on.