Every year on Christmas night, Santa Claus secretly brings gifts to the children in the apartments and houses with his sleigh and puts them under the Christmas tree. Unfortunately, in the process, during the landings on the roofs, the load of the sleigh fully loaded with gifts regularly damages the supports of the skids. As a result, they have to be repaired at great expense, and there are delays in delivering the presents. To prevent this from happening again, Santa Claus has decided this year to protect the skids with dampers.
For this purpose, he sent a technical inquiry to RINGFEDER® via our webpage on friction spring dampers. Since he had not sent all the necessary data, he immediately received a questionnaire in which all relevant values were queried. This revealed the following: The maximum mass of the loaded sledge is 957 kg. During a controlled landing, the touchdown speed is 1.3 m/s. The sleigh is equipped with a total of 4 rods. The sleigh is supported on the skids by a total of 4 supports, and a buffer with a RINGFEDER® friction spring is to be installed in each support. Therefore, the touchdown of the sleigh should be damped to a maximum.
As the sleigh is used worldwide, the special lubricating grease F-S3N is used due to the temperatures to be expected and the requirement for maximum possible damping (operating range -73 °C to + 121 °C, damping 66 %).
With
E = ½ x m x v² = 808 J, the energy to be absorbed is 202 J per support.
The static load due to the carriage's own weight is calculated as Fstat = m x g = 957 kg x 9.81m/s² = 9388 N = 9.4 kN → 2.4 kN per support. This must be applied by the spring on the recoil characteristic so that the dead weight of the carriage does not already compress it.
Due to the 66 % damping, the preload force must be three times higher than the static load.
→ Fv = 3 x 2.4 = 7.2 kN per spring
After considering all the data, spring type 05500 with 18 elements was selected. With a preload force of 7.2 kN, the spring has an installation/preload length of 118.2 mm. The energy to be absorbed of 202 J per spring results in an operating force of 27 3 kN; the spring is compressed by 11.7 mm when the sleigh is put on. The resulting utilisation of 68% means that 50,000 landings are possible without any problems. Santa Claus can either have the necessary housing built by the elves in his workshop, or RINGFEDER offers him an adequate complete solution.
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The RINGFEDER team wishes you a Merry Christmas and a Happy New Year 2023.
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