Material properties and vibration isolation Technical inormation General inormation on Sylomer Sylomer is a special PUR elastomer manuactured by Getzner, which eatures a cellular, compact orm and is used in a wide range o applications in the construction and mechanical engineering industries. In most cases, Sylomer is used as a compression-loaded elastic support element. The characteristics o the elastic support can be adjusted to the structure, construction method and load requirements by selecting the speciic type o Sylomer, the load-bearing area and the thickness. Sylomer materials are available as a continuous roll and are particularly well suited as lat, elastic layers. Above and beyond this, engineered moulder parts made o Sylomer are also available. Quasi-static load delection curve Diagram shows the typical pattern o the load delection curve or Sylomer under compression load. In the lower load ranges, there is a linear relationship between tension and deormation. For elastic bearings, the permanent static load should all in this range. The load range is speciied in the individual product data sheets. Ater the linear load range, the load delection curve moves on a degressive path; the material reacts to additional static and dynamic loads in a particularly sot manner, thus allowing or highly eective vibration isolation. In the product data sheets, the area o the delection curve in which a high degree o eiciency is achieved with a relatively small degree o spring delection, marked with the lighter shading in the diagram. Diagram : Sylomer product series. 8 4 4 8 8.. Speciic load [N/mm ] Speciic load [N/ mm ]..6..8.4. mm mm 37. mm mm. N/ mm Delection [mm] Diagram : Load delection curve, using the example o Sylomer Static range o application Dynamic range For speciic applications, special types can be manuactured with precisely deined stiness. The material s ine cellular structure provides the necessary deormation volume under static and dynamic loads. As a result, elastic bearings with ull-surace load transmission are possible. This oers major engineering and economic advantages, especially in the construction industry. www.getzner.com
For loads and deormations exceeding the degressive range, the delection curve is progressive (the darker shaded area). The material becomes stier. As a result, reduced vibration isolation eiciency can be expected in this load range. Sylomer is not aected by overloading. Ater load removal, the material recovers almost completely even ater very signiicant deormations resulting rom brie, extreme load peaks. No damage is caused to the material. The compression set as per EN ISO 86 or Sylomer is less than %. Behavior under dynamic load Diagram 3 shows the load dependence o the static and dynamic modulus o elasticity (at Hz and 3 Hz). Just like all elastomers, Sylomer reacts to dynamic loads more stily than to static loads. The stiening actor depends on the Sylomer type, the load and the requency, and ranges between.4 and 4. In keeping with the path o the delection curve, the quasi-static and the dynamic moduli o elasticity exhibit minimum levels. Sylomer eatures particularly good vibration isolation properties in this load range. Accordingly, by using Sylomer it has been possible to realize vibratory systems, which result in a high degree o isolation despite relatively small amounts o static subsidence. E-Modulus [N/mm ] 3 Quasi-static Static range o application Dynamic range. N/mm Hz 3 Hz Loss actor When Sylomer materials are subjected to dynamic loads, some o the mechanical work applied is transormed into heat by dampening eects. The dampening behavior o Sylomer materials can be described by the mechanical loss actor, which ranges between.9 and. or Sylomer materials. The speciic values are shown on the product data sheets. Behavior with shearing loads Fundamentally speaking, a Sylomer bearing is soter with regard to shearing loads than with regard to compression loads. The relationship o compression to shearing stiness ranges between actor 4 and, depending on the cellular structure and geometry o the Sylomer bearing. The quasi-static shearing delection curve exhibits relatively linear deormation behavior. Impact o the orm actor Low density, cellular Sylomer materials are volumecompressible. This means that, compared to more compact elastomers, elastic Sylomer elements do not expand very much transverse to the direction o the load. On the other hand, Sylomer bearings with a low orm actor q (deined as the ratio o the load-bearing surace to the periphal surace o the bearing, see Diagram ) exhibit greater subsidence than can be derived rom the delection curves on the product data sheets (pages and 3 show the delection curves or orm actor 3). Page 4 o the product data sheets shows the dependence o the subsidence, the dynamic e-modulus and the natural requencies on the orm actor. These dependencies can be used as correction actors or the delection curves on pages and 3 o the product data sheets or dierent orm actors..4.8..6. Speciic load [N/mm ] Diagram 3: Load dependence o the quasi-static and dynamic e-modulus, using the example o Sylomer Deinition: Form actor = Load area Perimeter surace area
h l Block w l q= h (w + l) The bulk o the increase in deormation due to creeping occurs ater a relatively short period o time. Subsequent to this short phase, the increase in deormation over a longer period o time is very small. w D Cylinder Getzner s 4 years o experience and numerous reerence projects using Sylomer bearings have repeatedly conirmed this pattern o behavior by the bearings under static long-term load. D d h q= D 4 h Hollow Cylinder D - d q= 4 h Dynamic properties under long-term load A change in the dynamic properties under long-term load conditions can be critical or elastic vibration-isolation bearings in particular. The recommendations or the static application range have seen selected in such a manner that, under the maximum load or the static application range, the natural requency o the system does not change during the load period. Diagram 7 illustrates these relationships: h Diagram : Deinition o the orm actor, block, cylinder, hollow cylinder Static long-term durability As is the case with all elastomers, certain creep eects occur under long-term load. Creep reers to a reversible increase in deormation under unchanging, long-term load conditions. Diagram 6 shows the behavior typical or Sylomer : Spring delection [% o the thickness o the unloaded sample] % % % % Full load Hal load Change in natural requency over times in relation to the data sheet values [%] % 8 % 6 % 4 % % % - % -4 % -6 % -8 % - %. Month Year Years,, Duration o impact [Days] Diagram 7: Dynamic long-term durability o Sylomer % Month Year Years %,, Load duration [Days] Diagram 6: Static long-term durability o Sylomer 3
Poisson s ratio Poisson s ratio can only be stated with adequate precision or materials which are loaded in the linear range. In general, however, Sylomer is also subject to loads in the non-linear range, as a result o which disclosure o the Poisson s ratio as a discrete single value is not realistic. The higher the density and hence the stiness o the Sylomer, the lower the degree o volume compressibility (ideally incompressible Poisson s ratio.). Determination o the Poisson s ratio or Sylomer is subject to corresponding luctuations, depending on the material type (density) and the load (or testing method). The values or Sylomer have been ound to be between.3 and.. Inluence o temperature The working temperature range or Sylomer materials should be between -3 C and +7 C. The glass transition temperature o Sylomer is around - C, and the melting temperature range spans rom + C to +8 C. The maximum temperature to which Sylomer can be briely exposed to without permanent loss o the properties stated in the product sheet depends strongly on the speciic application in question. Please contact the Support department at Getzner Werkstoe or exact inormation. The data listed in the product data sheets is valid or room temperature. The respective dependencies or the individual material types with regard to temperature can be ound in the Details Datasheet. Frequency dependency The e-modulus and the loss actor o Sylomer are dependent on the deormation velocity, and thus on the requency in cases o dynamic load. The dependency o Sylomer on requency can be ound in the Details Datasheet. Amplitude dependence Sylomer shows a low degree o dependency on amplitude, and as a result this can generally be disregarded in the calculations. This is a very important actor, in particular in the ield o mounting systems or buildings and the related amplitudes. Inlammability Sylomer materials are categorized in lammability class B as per DIN 4 (normally combustible). No corrosive gases are generated in the event o combustion. The gases produced are similar in composition to those produced by the combustion o wood or wool. Resistance to environmental conditions and chemicals Sylomer materials are resistant to substances such as water, concrete, oils and ats, diluted acids and bases. A detailed list o resistance to various materials is contained in the data sheet on chemical resistance. Vibration isolation Vibration isolation and isolation o structure-borne noise serve to reduce mechanically transmitted vibrations. This involves the reduction o orces and vibration amplitudes by the use o special visco-elastic construction elements which are aligned in the path o propagation o the vibrations. In the case o structure-borne noise isolation, in addition to the reduction in mechanical vibration, the secondary airborne noise generated by structure-borne noise is also mitigated. For structure-borne noise isolation, the tuning requencies are generally higher than those or vibration isolation. Vibration and structure-borne noise isolation is divided into Emission isolation with the goal reducing the orces transmitted by a machine or other source into the environment. 4
Immission isolation to shield machines, equipment or buildings against vibrations rom the environment. Targeted use o visco-elastic construction elements and the possible deployment o additional masses generally allows or the realization o optimum solutions or vibration isolation or all applications. The amplitude o this vibration ades over time: Delection x A n A n+ One-dimension mass-spring systems Many vibration problems can be approximated with a simple physical model, the so-called mass-spring system (see Diagram 8). I the mass is disturbed rom the equilibrium position by a brie, external orce, the mass oscillates at a natural requency o (see Diagram 9) T=/ Time t ƒ π c m T T = Period duration (s) ƒ = Natural requency (Hz) c = Spring constant (N/m) m = Oscillating mass (kg) F Diagram 9: Fading behavior o a ree vibration displacement x How quickly the amplitude ades depends on the dampening o the spring. For Sylomer materials, dampening is described by the mechanical loss actor. Depending on the product type, the loss actor or Sylomer ranges rom η =.9 to η =.. The relationship between the mechanical loss actor η and the so-called critical dampening ratio D is the ollowing: m η D C D The relationship between dampening and the ratio o two consecutive maximum amplitudes is described by the equation: F e 3 A n+ A n e -Dπ e -ηπ Diagram 8: One-dimensional mass-spring system
Transmission unction The isolation eect o the elastic bearing is described with the transmission unction V(). This reers to the orce transmission unction or the orce excitement (emission isolation), and the amplitude transmission unction or immision isolation. Degree o transmission / isolation actor The isolation eect is oten presented logarithmically in a level orm. In this case, the term used is degree o transmission L() in db. 4 V(ƒ) +η ( ) (-( ) ) +η ( ) L(ƒ) log +η ( ) (-( ) ) +η ( ) The transmission unction describes the mathematical relationship between the system response (amplitude o the vibration) and the impact (amplitude o excitation) and is generally rendered as a unction o the requency ratio /. Transmission unction V() 9 8 7 6 4 3 η =. η =. η =.3 Degree o transmission [db] η =. η =. η =.3 - - - - - -3 3 4 Frequency ratio / Diagram : Degree o transmission Diagram : Transmission unction Frequency ration / Another useul variable is the isolation actor l(), which presents the reduction in the transmitted excitation actor in %: An isolation eect only occurs in the requency range / >. So-called low requency tuning occurs when the natural requency o the system is around a actor o.4 lower than the lowest requency o the mechanical vibrations. 6 I(ƒ) - +η ( ) (-( ) ) +η ( ) In the resonance range / < there is an ampliication o the mechanical vibration in all cases, independent o the dampening. 6
Calculation o natural requency and dampening eect with systems using Sylomer I only one type o Sylomer is used, the natural requency o the ree vibration in line with the static design can be ound in the product data sheets. In this regard, the natural requency o the system depending on the surace pressure or various material thicknesses is presented in Point 3. Calculation o the natural requency occurs in line with (). The dynamic spring constant o the bearing is calculated by: Insertion loss and the isolation actor o the elastic bearing are dependent on the ratio o the excitation requency to the natural requency and the loss actor. They can be calculated using equations () and (6). Moreover, both values are presented in dependence on the natural and excitation requency in the product data sheets under Point 4. Estimation o the natural requency rom the static subsidence as per the ollowing ormula (9) cannot be employed or Sylomer. 7 c E A d E = Dynamic e-modulus (N/mm ) A = Bearing surace (mm ) d = Material thickness (mm) 9 ƒ x x = Static subsidence (cm) As an alternative to (), it is also possible to use the ollowing ormula: 8 ƒ.76 E dσ σ = Surace pressure (N/mm ) The dynamic e-modulus can be ound or the surace pressure under Point in the diagrams in the product data sheets. In all cases the material thickness o the Sylomer bearing in the unloaded state is to be used or calculation o the dynamic spring constant as per (7). I various types o Sylomer are combined, then it is necessary to use the overall stiness o the bearing as a basis or the calculation o natural requency as per (). The overall stiness is derived rom the sum o the individual stinesses as per (7). Modeling Calculation o the real oscillatory system occurs on the basis o a mechanical dummy model For many real vibration problems, it is suicient to use one-dimensional modeling as a mass-spring system. I one wishes to examine the oscillatory system more precisely, then one must allow or urther movement possibilities which are relevant or the real system. Moreover, the oscillating mass can be represented by various discrete individual masses which are linked by springs or dampeners. The number o independent movement possibilities allowed or by the system are reerred to as degrees o reedom. The number o degrees o reedom is identical to the number o possible natural requencies. For measuring vibration isolation, in general the lowest natural requency is relevant. As this requency is approximately the same or all models, a one-dimensional modeling as a mass-spring system is oten suicient. All inormation and data is based on our current knowledge. The data can be applied or calculations and as guidelines, are subject to typical manuacturing tolerances, and are not guaranteed. We reserve the right to amend the data. For bearings which are also subjected to shearing orces, it is necessary to use the dynamic shearing modulus in this regard, instead o the dynamic e-modulus. 7
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