Load-bearing capacity of suction cups at sub-zero temperatures - a study by the Kiel University of Applied Sciences (carried out in the first half of 2003) under the direction of Professor Dr Michael Klausner
Experimental setup
The suction cups are placed on a cleaned glass plate and connected to a vacuum of 0.6 bar; a Venturi nozzle with vacuum accumulator serves as the vacuum supply. The entire test set-up is shown in Figure 1. The suction cups are dynamically loaded by a hydraulic cylinder, the tensile force is recorded by a load cell and registered by a measuring bridge. The peak value of the force is read off. For the tensile tests at right angles to the glass, the tensile device was positioned at an angle in the freezer; the resulting measurement error remains less than 0.3%.
When measuring the tensile direction parallel to the glass, the arrangement could be placed vertically. The tensile direction parallel to the glass is the load case when the glass is transported vertically.
Carrying out the experiment
The suction cups and the pulling device are brought to the test temperature, with all suction cups remaining in the chest so that they are not constantly cooled down again.
Six temperatures from - 30.8°C to - 5.5°C were set for the „388-8N“ suction cup (newer rubber compound from Pannkoke). The temperature was controlled by two measuring points:
- Directly on the suction cup
- by a fast-responding Pt100 sensor for the air temperature
A radial fan was sometimes installed in the chest to ensure even temperature distribution. However, this was only able to influence the air temperature; the measuring device and suction cup reacted very slowly. During the tensile test, the chest was closed as shown in the picture.
Results
Suction cup „388-8N“
(new rubber compound used by Pannkoke since the beginning of 2003)
The suction cup was pliable down to -31.6°C and was therefore able to ensure an airtight seal even with clearly perceptible ice patches. When tearing off, it was observed that the lip retracts strongly, the coefficient of friction of the rubber compound on hoar frost or ice is slightly below the value for the combination of suction cup/dry glass.
Almost independent of the temperature, the tensile force was 2800 N when pulling perpendicular to the glass pane.
A drop in tensile force from 3119N at -10.9°C to 1185N at -29.8°C was determined when pulling parallel to the pane. The measured values for parallel pull vary greatly and are dependent on the surface (cleaned, dry, icy, hoarfrost) and pulling speed. A maximum force of 1750 was recorded with light frost. An increased force is observed at low pulling speeds.
Suction cup „388-8N“
(Rubber compound used by Pannkoke until the end of 2002)
The suction cup only functions to a limited extent at -11.4°C and not at all below this temperature. The picture shows that the rubber lip is rigid at -30.8°C. The suction cup works above -5.1°C.
The vertical holding force is 3400N, 3700N was measured for the parallel pull.
Suction cup „388-4N“
(Rubber compound used by Pannkoke until the end of 1999)
The suction cup can be used to a limited extent from -17.4°C, with a vertical pulling force of 2100N. Good usability from -5.4°C, tractive force increases to 3300N. The parallel pull was found to be functional at -10.8°C, the force is 3100N.
Suction cup „540“
The suction cup can be used to a limited extent from -11.5°C, tractive force vertical there 1300N. Good usability from -5.5°C, tractive force remains at 1300N. The parallel pull was found to be functional at -11.5°C, the force is 1200N.
It is noteworthy that the suction cup does not slide but breaks off by rotating over the leading edge. This could be explained by the high starting point of the pulling force in relation to the diameter.
Concluding remark
Overall, there was a clear scattering of the measured values depending on the surface condition.
Measurement results
Direction of pull: perpendicular to the disc
Pressure: -0.6 bar
Average pulling speed: 3.6 mm/s
| Suction cup: | 388-2003 | Suction cup: | 388-2000 | |||
| Temperature | Power | Temperature | Power | |||
| before pull test | after pull test | before pull test | after pull test | |||
| [°C] | [°C] | [N] | [°C] | [°C] | [N] | |
| -31,6 | 2856,0 | -30,8 | 1851 | |||
| -31,1 | 2773,0 | -30,8 | 1632 | |||
| -30,1 | 2955,0 | -29,9 | 1769 | |||
| -30,6 | 2906,0 | -29,6 | 1750 | |||
| -30,6 | 2781,0 | -30,3 | Medium | 1750,5 | ||
| -30,8 | 2856,0 | Suction cup frozen stiff, only sucks in when pressed hard. | ||||
| -30,8 | Medium | 2854,5 | ||||
| Temperature | Power | Temperature | Power | |||
| before pull test | after pull test | before pull test | after pull test | |||
| [°C] | [°C] | [N] | [°C] | [°C] | [N] | |
| -24,5 | 2735,0 | |||||
| -25,2 | 2798,0 | |||||
| -26,3 | 2867,0 | |||||
| -26,0 | 2783,0 | |||||
| -25,5 | 2708,0 | |||||
| -26,0 | 2957,0 | Suction cup frozen stiff, only sucks in when pressed hard. | ||||
| -25,6 | Medium | 2808,0 | ||||
| Temperature | Power | Temperature | Power | |||
| before pull test | after pull test | before pull test | after pull test | |||
| [°C] | [°C] | [N] | [°C] | [°C] | [N] | |
| -19,9 | -20,2 | 2962,0 | ||||
| -20,2 | -20,6 | 2991,0 | ||||
| -20,2 | -20,6 | 2971,0 | ||||
| -19,8 | -19,6 | 2957,0 | ||||
| -19,2 | -18,6 | 3190,0 | ||||
| -19,8 | -20,7 | 2997,0 | Suction cup frozen stiff, only sucks in when pressed hard. | |||
| -19,9 | Medium | 3011,3 | ||||
Direction of pull: perpendicular to the disc
Pressure: -0.6 bar
Average pulling speed: 3.6 mm/s
| Suction cup: | 388-2003 | Suction cup: | 388-2000 | |||
| Temperature | Power | Temperature | Power | |||
| before pull test | after pull test | before pull test | after pull test | |||
| [°C] | [°C] | [N] | [°C] | [°C] | [N] | |
| -16,8 | -16,8 | 2853,0 | -16,9 | 4057 | ||
| -16,6 | -16,6 | 2804,0 | -16,4 | 3756 | ||
| -16,4 | -16,3 | 2871,0 | -15,3 | 3928 | ||
| -16,2 | -16,0 | 2863,0 | -16,2 | Medium | 3913,7 | |
| -16,2 | -16,4 | 2817,0 | Suction cup stiff, does not suck on its own, must be pressed on strongly by hand. | |||
| -16,5 | -16,5 | 2817,0 | ||||
| -16,5 | Medium | 2837,5 | ||||
| Temperature | Power | Temperature | Power | |||
| before pull test | after pull test | before pull test | after pull test | |||
| [°C] | [°C] | [N] | [°C] | [°C] | [N] | |
| -11,2 | -11,2 | 2967,0 | ||||
| -10,6 | -10,4 | 2699,0 | -11,6 | 3741 | ||
| -11,2 | -13,0 | 2719,0 | -11,2 | 3515 | ||
| -11,9 | -11,4 | 3004,0 | -11,3 | 3524 | ||
| -11,7 | -11,4 | 2961,0 | -11,9 | 3588 | ||
| -11,4 | -11,4 | 2871,0 | -11,2 | 3559 | ||
| -11,3 | Medium | 2870,2 | -11,4 | Medium | 3585,4 | |
| with ice islands > 1 mm, no better results after scraping | Suction cup becomes just flexible, sucks in with light pressure. | |||||
| Temperature | Power | Temperature | Power | |||
| before pull test | after pull test | before pull test | after pull test | |||
| [°C] | [°C] | [N] | [°C] | [°C] | [N] | |
| -6,1 | 2791,0 | -5,9 | 3626 | |||
| -5,4 | 2703,0 | -5,4 | 3486 | |||
| -4,6 | 2756,0 | -4,7 | 3406 | |||
| -5,0 | 2784,0 | -5,3 | 3326 | |||
| -6,3 | 2779,0 | -5,0 | 3405 | |||
| -5,6 | 2748,0 | -4,5 | 3368 | |||
| -5,5 | Medium | 2760,2 | -5,1 | Medium | 3436,2 | |
| wiped | 2802,0 | Suction cup attracts well | ||||
Direction of pull: perpendicular to the disc
Pressure: -0.6 bar
Average pulling speed: 3.6 mm/s
| Suction cup: | 388-1998 | Suction cup: | 540 | |||
| Temperature | Power | Temperature | Power | |||
| before pull test | after pull test | before pull test | after pull test | |||
| [°C] | [°C] | [N] | [°C] | [°C] | [N] | |
| Suction cup frozen stiff, only sucks in when pressed hard. | Suction cup frozen stiff, only sucks in when pressed hard. | |||||
| Temperature | Power | Temperature | Power | |||
| before pull test | after pull test | before pull test | after pull test | |||
| [°C] | [°C] | [N] | [°C] | [°C] | [N] | |
| -24,5 | -24,5 | 1115 | ||||
| -25,5 | -25,3 | 927 | ||||
| -26,3 | -26,1 | 628 | ||||
| -25,4 | ||||||
| Suction cup frozen stiff, only sucks in when pressed hard. | Suction cup stiff, does not suck on its own, must be pressed firmly by hand. | |||||
| Temperature | Power | Temperature | Power | |||
| before pull test | after pull test | before pull test | after pull test | |||
| [°C] | [°C] | [N] | [°C] | [°C] | [N] | |
| -21 | 2830 | -20,9 | -20,2 | 1485 | ||
| -20,9 | 2995 | -19,5 | -19,6 | 1767 | ||
| -21,5 | 3213 | -19,3 | -17,4 | 1889 | ||
| -21,8 | 3516 | -19,4 | -19,5 | 1868 | ||
| -20,1 | 3665 | -19,8 | Medium | 1752,3 | ||
| -21,06 | Medium | 3243,8 | ||||
| Suction cup just barely pliable, becomes increasingly softer when tested. Pressed on by hand | top value on iced disc, then scraped free of ice; suction cup stiff, pressed on by hand. | |||||
Direction of pull: perpendicular to the disc
Pressure: -0.6 bar
Average pulling speed: 3.6 mm/s
| Suction cup: | 388-1998 | Suction cup: | 540 | |||
| Temperature | Power | Temperature | Power | |||
| before pull test | after pull test | before pull test | after pull test | |||
| [°C] | [°C] | [N] | [°C] | [°C] | [N] | |
| -16,8 | 1959 | -16,6 | -16,4 | 1751 | ||
| -17,7 | 2281 | -17,6 | -17,6 | 1853 | ||
| -17,6 | 2282 | -16,4 | -16,1 | 1851 | ||
| -17,4 | Medium | 2174,0 | -16,9 | Medium | 1818,3 | |
| Suction cup becomes just flexible, sucks in with light pressure. | Suction cup stiff, does not suck on its own, must be pressed on by hand. | |||||
| Temperature | Power | Temperature | Power | |||
| before pull test | after pull test | before pull test | after pull test | |||
| [°C] | [°C] | [N] | [°C] | [°C] | [N] | |
| -11,5 | 3172 | -11,2 | 1076 | |||
| -11,3 | -11,1 | 3119 | -11,2 | 1093 | ||
| -11,7 | 2513 | -12,9 | 1583 | |||
| -11,6 | -11,7 | 2103 | -12,0 | 1546 | ||
| -12,6 | 3677 | -11,0 | 1540 | |||
| -11,7 | Medium | 2916,8 | -10,9 | 1540 | ||
| At 3 and 4 disc slightly iced up, suction with strong pressureAt 5 disc wiped and waited 3 min, suction with light pressure | -11,5 | Medium | 1396,3 | |||
| With value 3 suction cup and windscreen wiped light pressure | ||||||
| Temperature | Power | Temperature | Power | |||
| before pull test | after pull test | before pull test | after pull test | |||
| [°C] | [°C] | [N] | [°C] | [°C] | [N] | |
| -6,3 | 3478 | -5,1 | 1449 | |||
| -5,7 | 3441 | -5,8 | 1497 | |||
| -5,1 | 3301 | -5,8 | 1492 | |||
| -4,6 | 3511 | -5,3 | 1489 | |||
| -5,4 | 3259 | -5,3 | 821 | |||
| -5,1 | 3408 | -5,5 | Medium | 1349,6 | ||
| -5,4 | Medium | 3399,7 | At value 4 disc thinly coated with ice Suction cup attracts usably | |||
| Suction cup wiped at value 4 - Suction cup attracts well | ||||||
Direction of pull: parallel to the disc
Pressure: -0.6 bar
Average pulling speed: 3.6 mm/s
| Suction cup: | 388-2003 | Suction cup: | 388-2000 | |||
| Temperature | Power | Temperature | Power | |||
| before pull test | after pull test | before pull test | after pull test | |||
| [°C] | [°C] | [N] | [°C] | [°C] | [N] | |
| -12,3 | 2750,0 | -10,5 | 2830 | |||
| -11,8 | -12,1 | 3016,0 | -10,2 | 3487 | ||
| -11,2 | -11,5 | 3227,0 | -10,2 | 3870 | ||
| -11,0 | 11,2 | 3269,0 | -9,4 | 4048 | ||
| -11,0 | -10,9 | 3208,0 | -9,5 | 4092 | ||
| -9,6 | -10,4 | 3245,0 | -10,8 | 3982 | ||
| -10,9 | Medium | 3119,2 | -10,1 | Medium | 3718,2 | |
| Suction cup frozen stiff, only sucks in when pressed on, becomes supple in the course of the test | ||||||
| Temperature | Power | |||||
| before pull test | after pull test | |||||
| [°C] | [°C] | [N] | slow tension, 0.3 mm/sec, start of creep 1970 N | |||
| -29,9 | 902,0 | |||||
| -29,9 | cleaned | 1284,0 | Thin hoar frost causes an increase in friction coefficient: | |||
| -29,7 | 1271,0 | cleaned: 1067 N, then | ||||
| -29,5 | 1165,0 | max. tensile force after several passes: | ||||
| -29,6 | 1288,0 | |||||
| -30,1 | 1221,0 | Further suction cups at -29.8°C-mean not functional. | ||||
| -29,8 | Medium | 1188,5 | ||||