Special machine construction in the glass processing industry from Luebeck

Why can a Suction Cup hold something?

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Load capacity of suction cups

The load-bearing capacity of the suction cups is generated solely by the pressure difference between the ambient air pressure and the vacuum in the suction cup. If there is no pressure difference, the suction cup has no holding force.

What forces act on the vacuum cup?
What forces act on the vacuum cup?

The greater this difference, the higher the load capacity of the suction cup.

Dependence on ambient air pressure

At the same time, this means that the load-bearing capacity of the suction cup is reduced when the ambient air pressure is lower. This is important if the appliance is used at higher altitudes, as the holding force decreases. The reason for this is that the ambient air pressure decreases with the height of the terrain and therefore also the force that presses on a surface.

At sea level, the air pressure is 1013 mbar. Every 100 m difference in altitude results in a reduction of approx. 12.5 mbar. In simple terms, if a suction cup carries 100 kg at sea level, this suction cup would only carry 90 kg at an altitude of 1000 m.

Dependence of air pressure on altitude (standard atmosphere)
Height in metresAir pressure in mbar
01013,25
1001001,3
200989,5
400966,1
600943,2
800920,8
1000898,8
1200877,2
1400856,0
1600835,3
1800814,9
2000795,0

Dependence on the area of the suction cup

The holding force of the suction cup depends not only on the pressure difference between the ambient air pressure and the vacuum in the suction cup, but also on the surface area of the suction cup. The contact pressure of the ambient air pressure acts on the surface area: The larger the effective surface area, the greater the total contact pressure.

Dependence on the load direction

In the horizontal direction, the suction cup can only tear off and not slide off (slip off) when overloaded. The suction cup can be subjected to the highest load in this load direction, as it is not possible for it to slide off. Theoretically, the holding force results from the product of surface area x negative pressure. If this value is exceeded, the suction cup tears off; this is referred to as the tear-off force.
In the vertical direction, the suction cup can slide along the surface in the event of overloading before the suction cup detaches from the surface. The coefficient of friction between the suction cup and the transported goods is included in this consideration. In general, the holding force in the vertical direction will be considerably lower than that in the horizontal direction. If this holding force is exceeded, the suction cup will slowly slide off, this is referred to as the sliding force.

Other influencing factors

  • Surface quality of the material
  • Soiling of the material and the suction cup
  • Air permeability of the material
  • Ambient temperature
  • Temperature of the material
  • Bending stiffness of the material

Safety factors

The safety factor 2 is required by the new European standard DIN EN 13155 for both the sliding force and the tear-off force. For the slip-off force, the coefficient of friction µ to be taken into account.

What is the load capacity of the suction cup?

In the diagram below, you can read off the load capacity based on the diameter, taking into account the following points.

  • The load-bearing capacity according to calculations with a safety factor of 2 for the horizontal tear-off force as well as for the vertical sliding force.
  • The coefficient of friction µ was assumed to be 0.5. This is a common value for smooth surfaces such as those found on glass and metals. A different value may have to be used for other materials.
  • Use at a height of 100 metres.
  • Achieved vacuum in the suction cup of -0.6 bar.
The dependence of diameter to load capacity of the vacuum cup.
The dependence of diameter to load capacity of the vacuum cup.

Calculation as follows:

The theoretical calculation of the load capacity of the vacuum cup.
The theoretical calculation of the load capacity of the vacuum cup.

The values for the calculated load-bearing capacity can also be found in the following table.

Depending on the diameter or the available surface area of the suction cup, the calculated load capacity is listed for different vacuum values. Other influencing factors are not taken into account when calculating the load capacity.

Diameter in mmArea in cm²Load capacity in kg
horizontalVertical
0,60,70,80,60,70,8
40133,84,45,01,92,22,5
45164,85,66,42,42,83,2
50205,96,97,92,93,43,9
55247,18,39,53,64,24,8
60288,59,911,34,24,95,7
653310,011,613,35,05,86,6
703811,513,515,45,86,77,7
754413,315,517,76,67,78,8
805015,117,620,17,58,810,1
855717,019,922,78,59,911,3
906419,122,325,49,511,112,7
957121,324,828,410,612,414,2
1007923,627,531,411,813,715,7
1058726,030,334,613,015,217,3
1109528,533,338,014,316,619,0
11510431,236,441,515,618,220,8
12011333,939,645,217,019,822,6
12512336,843,049,118,421,524,5
13013339,846,553,119,923,226,5
13514342,950,157,321,525,028,6
14015446,253,961,623,126,930,8
14516549,557,866,124,828,933,0
15017753,061,970,726,530,935,3
15518956,666,075,528,333,037,7
16020160,370,480,430,235,240,2
16521464,174,885,532,137,442,8
17022768,179,490,834,039,745,4
17524172,284,296,236,142,148,1
18025476,389,1101,838,244,550,9
18526980,694,1107,540,347,053,8
19028485,199,2113,442,549,656,7
19529989,6104,5119,544,852,359,7
20031494,2110,0125,747,155,062,8
20533099,0115,5132,049,557,866,0
210346103,9121,2138,552,060,669,3
215363108,9127,1145,254,563,572,6
220380114,0133,0152,157,066,576,0
225398119,3139,2159,059,669,679,5
230415124,6145,4166,262,372,783,1
235434130,1151,8173,565,175,986,7
240452135,7158,3181,067,979,290,5
245471141,4165,0188,670,782,594,3
250491147,3171,8196,373,685,998,2
255511153,2178,7204,376,689,4102,1
260531159,3185,8212,479,692,9106,2
265552165,5193,0220,682,796,5110,3
270573171,8200,4229,085,9100,2114,5
275594178,2207,9237,689,1103,9118,8
280616184,7215,5246,392,4107,8123,2
285638191,4223,3255,295,7111,6127,6
290661198,2231,2264,299,1115,6132,1
295683205,0239,2273,4102,5119,6136,7
300707212,1247,4282,7106,0123,7141,4
305731219,2255,7292,2109,6127,9146,1
310755226,4264,2301,9113,2132,1151,0
315779233,8272,8311,7116,9136,4155,9
320804241,3281,5321,7120,6140,7160,8
325830248,9290,4331,8124,4145,2165,9
330855256,6299,4342,1128,3149,7171,1
335881264,4308,5352,6132,2154,2176,3
340908272,4317,8363,2136,2158,9181,6
345935280,4327,2373,9140,2163,6187,0
350962288,6336,7384,8144,3168,4192,4
355990296,9346,4395,9148,5173,2198,0
3601018305,4356,3407,2152,7178,1203,6
3651046313,9366,2418,5157,0183,1209,3
3701075322,6376,3430,1161,3188,2215,0
3751104331,3386,6441,8165,7193,3220,9
3801134340,2396,9453,6170,1198,5226,8
3851164349,2407,5465,7174,6203,7232,8
3901195358,4418,1477,8179,2209,1238,9
3951225367,6428,9490,2183,8214,4245,1
4001257377,0439,8502,7188,5219,9251,3
4051288386,5450,9515,3193,2225,4257,6
4101320396,1462,1528,1198,0231,0264,1
4151353405,8473,4541,1202,9236,7270,5
4201385415,6484,9554,2207,8242,5277,1
4251419425,6496,5567,5212,8248,3283,7
4301452435,7508,3580,9217,8254,1290,4
4351486445,9520,2594,5222,9260,1297,2

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