Standard_Parts_Catalogue

Page 1491 | 3.4 Installing, Lifting, Damping with Leveling Feet, Lifting Gear and Rubber Elements 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 Static load F (machine weight) = 48,000 N, number of feet = 4, ergo: static load per foot = 12,000 N Selected foot: d 1 = 160, static load capacity 20,000 N, R = 9,000 N/mm Resulting in an actual compression s of: = 1.3 mm With an interference frequency of 20 Hz (1,200 rpm), the above graph delivers a degree of insulation of only about 20 %. To optimise, the number of feet may be increased to 5, resulting in a static load per foot of 9,600 N. A leveling foot whose static load capacity is closer to the new result may now be selected. Newly selected foot: d 1 = 120, static load capacity 10,000 N, R = 4,000 N/mm This results in an actual compression s of: = 2.4 mm With the same interference frequency of 20 Hz (1,200 rpm), the above graph now delivers a degree of insulation of approx. 75 %. The first step is to determine the static load F for each leveling foot. With favourably arranged leveling feet and therefore an evenly distributed load F, this value is calculated using the following equation: = static load F [N] / for each leveling foot Use the calculated static load F to select a leveling foot from the table, making sure that the static load F lies as close as pos- sible to the static load capacity without exceeding it. The associated stiffness R of the selected leveling foot is also taken from the table. The actual compression is then calculated using the equation below: = actual compression s [mm] Starting from the calculated actual compression s, the achievable degree of insulation as factor of the interference frequency can now be taken from the graph shown above. To optimise the achievable degree of insulation, the number of leveling feet may be changed such that the static load F for each foot is as close as possible below a load capacity value given in the table. This will increase the compression s which, in turn, results in a higher degree of insulation. In general it can be said that medium to high frequencies can be very well insulated with sufficient compression. GN 248 Leveling Feet continued Definitions Interference frequency [Hz]: is the frequency emanating from a machine, e.g. from the machine main shaft speed [rpm]. Static load F [N]: is the load acting on each vibration-damping element (leveling foot). Degree of insulation [%]: measure for absorbing the interference frequency (damping). Compression s [mm]: is the change in the height of the dampening element (spring excursion). Stiffness R [N/mm]: is the load causing the dampening element to be com- pressed by 1 mm (spring rate). Force due to weight of the machine [N] Number of leveling feet Static load F [N] / per leveling foot Stiffness R [N/mm] Determining the suitable leveling foot and the achievable degree of insulation 12,000 N (static load/foot) 9,000 N/mm (stiffness R) Example 9,600 N (static load/foot) 4,000 N/mm (stiffness R)