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Aa
Absorbers
Absorbers are materials or structures that absorb sound. Porous foams and fibrous materials are often used to absorb airborne sound. Viscoelastic heavy-duty sheets are applied to rigid structures such as thin-walled metal sheets to absorb structure-borne sound.Absorption
Absorption (attenuation) comes from Latin and means to suck in or swallow up. Absorption is the absorption of sound waves by an absorbent material.Absorption classes
Acoustic elements are assigned to one of the absorber classes A, B, C, D or E in accordance with a procedure specified in DIN EN 11654, with this assignment being based on the respective measured sound absorption coefficient. The selection of the class depends on the acoustic requirements of a room, as the materials in the various absorber classes supplement the existing sound absorption in a frequency-dependent manner. The choice of material and the quantity of acoustic elements required therefore depend on the intended application of the space. Since balanced room acoustics also require the reflection of sound waves, sound-reflecting acoustic panels are also produced, which are classified as ‘unclassified’. The absorber classes are divided into highly absorbent (Class A, rated sound absorption coefficient αw: 0.90 to 1.00), highly absorbent (Class B, αw: 0.80 to 0.85), highly absorbent (Class C, αw: 0.60 to 0.75), absorbent (Class D, αw: 0.30 to 0.55) and low-absorbing (Class E, αw: 0.15 to 0.25), whilst acoustic panels with a rated sound absorption coefficient of αw: 0.00 to 0.10 are considered unclassified.Acoustic foam
Acoustic foam is an open-cell foam used for sound absorption in rooms, machinery and vehicles. It converts sound waves into heat by generating frictional losses through the movement of air within the cell pores. Typical materials include PUR foams, melamine foams and reticulated foams. Acoustic foams are used as wall cladding, machine enclosures or vehicle insulation and can reduce both interior noise levels and sound radiation to the outside.Acoustics
The study of sound and mechanical vibrations is known as acoustics.Ageing
Ageing is the gradual degradation of elastomers caused by oxygen, ozone, light, heat, moisture and high-energy radiation, which, individually or in combination, can cause progressive irreversible damage.Airborne sound
Airborne sound is sound that propagates through the air by means of sound waves.Anti-vibration mat
An anti-vibration mat is an elastic underlay placed between a vibrating machine and the ground to reduce the transmission of vibrations and structure-borne noise. Anti-vibration mats are typically crafted from natural or synthetic rubber, frequently featuring a textured surface to enhance the form factor and consequently the load-bearing capacity. They are employed for compressors, pumps, machine tools, domestic appliances and industrial equipment.
Bb
Bitumen sheet
Bitumen sheets are self-adhesive heavy sheets based on bitumen, which are used for structure-borne sound damping of metal components. They are bonded directly to sheet metal, body panels or machine housings and, due to their mass, increase the vibration damping of the substrate. This effectively reduces the so-called rumbling or rattling of these components. Bitumen sheets are particularly common in vehicle manufacturing and mechanical engineering.Building acoustics
Building acoustics deals with the effects of structural conditions on sound propagation between rooms within a building, as well as between the interior of a room and the outside world. The following sub-areas of building acoustics are covered: structure-borne sound, airborne sound insulation, and sound insulation of technical and sanitary installations.
Cc
Causes of vibrations
Moving parts on machines, equipment, apparatus and vehicles generate vibrations and noise. These are caused by irregular or rotating movements of unbalanced masses. Vibrations and shocks have a disruptive effect on the surrounding environment in the form of vibrations and noise.Cell structure of foam
Depending on the type of material or the treatment applied, the cell structure can be open, semi-open or closed. Closed-cell foams include, for example, cellular rubbers or cross-linked PE foams. Open-cell foams are typically PUR foams. During subsequent material treatment, such as reticulation, the cell walls are removed by means of a controlled gas explosion, resulting in open or semi-open cells, for example in filter foams.Cellular rubber
Cellular rubber is a foamed rubber with a closed-cell structure and no outer skin. The closed cells make it permanently water- and air-tight, even when the surface is subjected to mechanical stress. It is manufactured from various types of rubber such as EPDM, CR or NBR and is ideal for seals, insulation and damping applications where protection against moisture is required.Cold foam
Cold foam is the best and most valuable of all foam materials. It can be compared to natural latex foam and is usually produced using the block foam process. Cold foam is a polyether foam which, unlike standard foam, is classified as a highly elastic HR foam (HR = High Resilient). Cold foam offers the following advantages: open-cell structure, high air permeability, breathability, an irregular, coarse pore structure, and high elasticity combined with a supple feel.Compression resistance
Compression hardness, also known as compression resistance, refers to the pressure required to compress a foam material. With a compression hardness of 60, 6.6 kPa (kilopascals) is required to compress the foam to 40% of its original volume. The compression hardness of a foam material is used to describe its strength.Compression set
Compression set (CS) is a measure of how elastomers behave under prolonged, constant compression followed by relaxation. A CS of 0% would mean that the rubber fully regains its original thickness, whilst a CS of 100% indicates that the rubber was completely deformed during the test and shows no recovery.Compression-transfer moulding process (CTM)
In the compression-transfer molding (CTM) process, the rubber compound is injected into the mold cavities through channels as the press closes. CTM molds consist of three parts (upper, middle and lower sections). As friction heat is generated during the CTM process due to the injection into the cavities, the vulcanisation time is reduced. The transfer moulding process is particularly well suited to the production of small rubber moulded parts in moulds with multiple cavities.Compressive stress in rubber
Under compressive stress, the limit of linearity is 15% deformation, relative to the rubber layer thickness. The influence of the shape factor must be taken into account whenever designing a rubber spring for the compression range. The shape factor is defined as the ratio of the active pressure area to the free compression area of the rubber spring. This stems from the prevented transverse elongation and thus the variable modulus of elasticity c of the incompressible material rubber.CR chloroprene rubber
CR chloroprene rubber is also widely known under the trade name Neoprene. CR rubber offers very good resistance to ozone and ageing, but only satisfactory resistance to oil. Thanks to its high chlorine content, CR rubber has good flame-retardant properties. CR chloroprene rubber can be used wherever good flame retardancy, good chemical resistance and good ageing properties are required.Creep and settlement of a spring element
Creep is the time-dependent increase in the elastic deflection of a spring under constant load. It is a consequence of the reduction in the restoring force. The increase in deflection, which reaches half its value after just 24 hours of loading, can usually be disregarded in practice and does not affect the vibration behaviour. The permanent residual deformation, including set, which depends on the number of load cycles and the amplitude and is comparable to creep, is less than 10% of the elastic spring travel for elastomers with good elastic properties.Cross-linked foam
In cross-linked foam, the molecular chains branch out and are chemically and physically bonded together through polymerisation. Cross-linking results in increased mechanical and thermal resistance. Cross-linked foams in our range include, for example, Plastazote PE foam.Cutting processes (waterjet cutting, die cutting, CNC cutting)
Vibraplast AG uses different cutting processes depending on the material, thickness and batch size. Punch cutting uses tools (punching dies) that enable cost-effective production in large quantities. Waterjet cutting is suitable for complex geometries and delicate materials, as it generates no heat input. CNC-controlled knife and oscillating cutting systems enable the production of precise single items and small batches without tooling costs. The choice of the optimal process depends on material properties, geometry, quantity and the required dimensional accuracy.
Dd
Damping ratio / loss factor
The damping ratio describes the extent to which a vibrating system converts vibrational energy into heat. A high damping ratio reduces resonance peaks and ensures that the system returns to rest quickly after excitation. In elastomer applications, the damping ratio is often specified as the loss factor (tan δ). Materials with a high loss factor, such as certain rubber compounds, are particularly suitable for structure-borne sound damping, whilst low-damping materials such as natural rubber are preferred for use in vibration isolators.Decibel (dB)
A decibel (dB) is the unit of sound level.Decoupling
Decoupling refers to the elastic separation of components or machines from their surroundings in order to interrupt the transmission of vibrations and structure-borne noise. In practice, decoupling and vibration isolation are often used interchangeably. Technically speaking, decoupling primarily describes the effect: the vibrating element (e.g. a motor or a pump) is decoupled from the supporting structure in such a way that vibrations can no longer propagate. Decoupling elements made of rubber or foam are simple and cost-effective measures for noise reduction.Density
Density describes the weight of the foam in kg/m³ (kilograms per cubic metre). The weight or density of the foam is also an indicator of quality: the higher the density, the more durable the quality. However, density has nothing to do with the perceived firmness. As a rule, lighter foams are cheaper due to the lower amount of material used.DGUV / BGI 5029 (Noise protection in the workplace)
The DGUV (German Social Accident Insurance) and its associated information documents, including BGI 5029, regulate noise protection in the workplace. In Switzerland, the relevant regulations of the SUVA and the Ordinance on the Prevention of Accidents and Occupational Diseases (VUV) apply. Technical noise control measures at source, such as vibration isolation, enclosure and structure-borne sound insulation, are given priority over personal hearing protection under these regulations.Difference between cellular rubber and foam rubber
Cellular rubber and foam rubber are often confused; the difference lies in the material properties, which are determined by the different manufacturing processes. Foam rubber has open cells and a dense outer skin. Thanks to this outer skin, foam rubber is particularly suitable for applications under high mechanical stress and abrasion. However, if the outer skin of the foam rubber is damaged, it can become saturated with water. Cellular rubber lacks an outer skin and features closed cells, making it inherently waterproof and airtight. Both foam rubber and cellular rubber are foamed rubber grades (EPDM, SBR, CR, NBR) that conform well to substrates, which is why they are primarily specified for sealing applications.Difference between structure-borne and airborne sound
Put simply, the difference between structure-borne and airborne sound lies in the medium through which the sound propagates. Airborne sound propagates through the air in the form of sound waves. Structure-borne sound, on the other hand, propagates through solid materials such as steel, concrete, wood, stone, etc. This includes, for example, impact noise or the noise generated by building services systems.Diffuse and direct sound
Diffuse sound is the sound that is present in rooms following reflections off boundary surfaces.Dimensional tolerances in cutting
When processing foam, rubber and plastic sheets, system-related dimensional tolerances arise as a result of the cutting technique. For punching and waterjet cutting, these typically range from ±0.5 to ±1.0 mm, depending on the material, thickness and geometry. CNC-controlled cutting systems are available for more precise requirements. Dimensional tolerance specifications always refer to the finished part in its undeformed state. With soft materials, springback after cutting must also be taken into account.DIN 4109 (Sound insulation in building construction)
DIN 4109 is the authoritative German standard for sound insulation in building construction. It sets out requirements for airborne and impact sound insulation in walls, ceilings, staircases and building services installations. Elastic materials such as rubber, foam and cellular rubber play a key role in meeting these requirements, for example as floating screed underlays, impact sound insulation boards or elastic pipe fixings. In Switzerland, comparable requirements apply in accordance with SIA 181.
Ee
Elastomer/metal bond
Continuous quality checks at all stages of processing ensure a high and consistent standard for the bond. The final inspection involves testing the adhesive strength according to a sampling plan, either by visual inspection of the edge zone at a tensile force of 1.5–3 N/mm² or even by tearing until failure. In general, it can be said that elastomer/metal bonds, following cross-linking of the elastomer and simultaneous curing of the adhesive system, show exclusively a fracture in the elastomer when tested statically.Elastomers
Elastomers are dimensionally stable yet deformable plastics that return to their original shape after being subjected to tensile or compressive stress. In common parlance, elastomers are also referred to as rubber.EN 45545
The rail vehicle standard DIN EN 45545-2 (CEN TS 45545-2) is a European rail vehicle standard. This standard completely replaces national standards, such as DIN 5510. Requirement R1, which is annexed to the standard, is one of the most difficult to meet in terms of test methods. Operational classes 1–4, which are annexed to the standard, govern hazard levels (HL) 1–4.EPDM ethylene-propylene-diene rubber
EPDM rubber offers good resistance to oxygen, ozone and temperature. EPDM is also characterised by above-average chemical resistance. However, its resistance to mineral oils and greases is considered to be rather poor. Thanks to its excellent weather and hot water resistance, EPDM rubber is used in profiles and sealing elements.
Ff
FDA compliance
The FDA (Food and Drug Administration) is an American regulatory authority responsible for monitoring all goods placed on the market in the USA. This also includes all imports into the USA, which is why the FDA’s regulations are also important for European manufacturers. These regulations are binding for exporters to the USA. The FDA imposes extremely strict requirements in the food sector, where a wide range of rubber and plastic products are used and therefore come into contact with food or drinking water. The materials must not release any substances into the food. Consequently, all plastics that come into contact with food must be FDA-compliant.Foam rubber
Foam rubber is an open-cell foam rubber with a characteristic, dense outer skin. The outer skin protects the material from dirt and mechanical abrasion. Thanks to its soft, pliable structure, foam rubber adapts well to uneven surfaces and is particularly suitable for sealing applications. However, if the outer skin is damaged, the material can become saturated with water. Foam rubber is available in various grades such as EPDM, CR or SBR.Foaming processes
Depending on the type of foam production, the following processes are distinguished: In physical foaming, the material is foamed by means of a physical process. In chemical foaming, gases are produced during the manufacture of the plastic, which cause the material to foam. In mechanical foaming, air is stirred into the resin or paste to be foamed; this foam solidifies as the resin cross-links.FPM fluorocarbon rubber
FPM fluororubbers are also known under the brand name Viton. FPM rubber is flame-retardant and, of all elastomers, offers outstanding resistance to high temperatures, ozone, oxygen and chemicals.Frequency
Frequency refers to the number of sound vibrations per second (Hertz, Hz).
Hh
Hearing range
The human ear can perceive sounds within a frequency range of approximately 16 to 16,000 hertz.Heavy foil
Heavy foils are primarily used for damping metal and plastic components that are subject to strong vibrations. Applying heavy foils increases the mass of these elements, thereby reducing noise. This is known as structure-borne sound damping. Heavy foils made of bitumen or bitumen-free plastic are also suitable for airborne sound insulation.Hertz
Unit of frequency. 1 Hz = one complete oscillation per second.Hysteresis damping
All elastomer materials exhibit hysteresis damping. The damping depends on the rubber grade, temperature, deformation rate, deformation acceleration, shape and type of stress.
Ii
IIR butyl rubber
IIR (isobutene-isoprene rubber), also known as butyl rubber, is characterised by very low gas permeability and good damping properties. It exhibits excellent resistance to oxygen, ozone and weathering and is well suited for vibration damping applications where high damping performance is required. IIR is used, amongst other things, for seals, pressure vessels and vibration isolators.Impact sound
Walking on floors generates structure-borne sound, some of which is radiated as airborne sound. Impact sound insulation can reduce this radiation.Impedance tube
The impedance tube is used to measure the absorption coefficient of a material when sound waves strike it perpendicularly.Indirect transmission
Flank transmission is the transmission of sound through adjacent walls, floors and ceilings.Insertion sound reduction index
The insertion loss describes the actual improvement in sound insulation achieved by installing an insulating material or element in a real-world system. Unlike the theoretical sound insulation index, the insertion loss also takes into account flanking and side-path transmission. It is expressed in decibels and is a key performance indicator for assessing the effectiveness of noise control measures in mechanical engineering and construction.Isolation
Insulation is the containment of airborne or structure-borne noise or vibrations.
Ll
Low-frequency sound / infrasound
Low-frequency sound refers to sound waves in the frequency range below approximately 100 Hz, with infrasound lying below the human hearing threshold of 16 Hz. Low-frequency sound is generated by, amongst other things, wind turbines, compressors, fans and heavy machinery. It travels particularly far and is difficult to dampen. Soft spring elements with a low natural frequency are required to isolate low-frequency vibrations.
Mm
Main excitation frequency
It is essential to accurately identify the dominant natural frequency in every vibration system. The majority of vibration-generating systems requiring elastic mountings are combinations of drive motors and working machines. In most cases, other vibrations at higher frequencies are superimposed on the fundamental vibration of working machines and units; these arise from the unbalanced movements of masses and cause vibrations that may occur either non-uniformly or periodically. Thus, on the one hand, the excitation frequencies can be determined fairly accurately from the rotational speeds, as is the case with motors. In many other cases, such as with textile machinery and machine tools, they are almost impossible to determine by calculation, and vibration measurements should be carried out.Melamine foam / Basotect®
Melamine foam is an open-cell, very lightweight foam based on melamine resin. It is characterised by excellent sound absorption, low thermal conductivity (λ ≈ 0.033 W/mK) and good flame resistance. The best-known product in this category is Basotect® from BASF SE. Melamine foam is used in mechanical engineering, vehicle manufacturing and building services engineering for noise reduction and thermal insulation.MVSS 302
Acoustic foams that meet the FMVSS 302 fire safety standard are primarily used in the automotive and mechanical engineering industries. The addition of flame retardants to the foam reduces the rate of flame spread in the event of a fire (4 inches per minute). The test procedure introduced in the USA as the Federal Motor Vehicle Safety Standard (FMVSS 302) is used by most car manufacturers worldwide.
Nn
Natural frequency
The natural frequency is the frequency at which a system capable of oscillation oscillates freely after a single excitation. It is determined by the mass and stiffness of the system: the greater the mass or the lower the spring stiffness, the lower the natural frequency. The natural frequency is critical when designing vibration isolators: it must be significantly below the excitation frequency in order to achieve effective isolation. If the excitation frequency equals the natural frequency, resonance occurs.Natural or synthetic rubber
To distinguish broadly between natural rubber and synthetic rubber, it should be noted that natural rubber (NR) is a naturally occurring material which, in terms of its structure, serves as a model for all synthetically produced elastomeric materials. NR exhibits very high tensile strength and, particularly in the case of soft elastomer grades, high elasticity, cold flexibility and excellent dynamic properties; this combination is rarely achieved by synthetic elastomers and therefore makes NR indispensable even today for certain applications, particularly for vibration isolation systems. When designing elastomer springs, dynamic hardening must also be taken into account. In low-damping elastomer materials such as NR, this can generally be disregarded. In highly damping compounds, the dynamic spring stiffness can be several times that of the static stiffness. However, if a product faces extreme requirements regarding certain properties, including oxidation resistance and damping characteristics, it is essential to switch to a synthetic rubber.NBR nitrile rubber
NBR acrylonitrile-butadiene rubber (nitrile rubber) stands out for its exceptionally good resistance to mineral oils and fuels, as well as its low compression set. This makes NBR the perfect oil- and fuel-resistant sealing material. On the downside, NBR rubber has very poor ozone resistance.Non-cross-linked foam
Non-cross-linked foam has unbranched molecular chains. This results in lower mechanical and thermal resistance. Non-cross-linked foams are mainly used in logistics packaging.NR natural rubber
Natural rubber is obtained by tapping rubber trees, yielding a white, watery sap (latex) that contains natural rubber. Natural rubber (NR) is an excellent material, exhibiting very high tensile strength, elasticity, cold flexibility and very good dynamic properties. This exceptional combination is only achieved to a limited extent by synthetic elastomers, which is why natural rubber remains irreplaceable for various applications even today. Additional treatment with protective agents is required to enhance resistance to ageing and ozone; furthermore, NR natural rubber is not resistant to mineral oils and fats. NR is available in Shore A hardness ranges of 30–90. Applications include moulded rubber parts, rubber bellows, rubber membranes, flat rubber seals, etc.NR/SBR Natural/Styrene-Butadiene rubber
Natural/SBR rubber is particularly valued in environments where it is exposed to heavy wear caused by friction or constantly abrasive elements. The NR/SBR grade is not resistant to mineral oils and greases.
Oo
Oscillations
Vibrations are movements of masses or particles of mass around a rest position.
Pp
PE foam (polyethylene foam)
PE foam is a closed-cell, cross-linked or non-cross-linked foam based on polyethylene. It is characterised by high moisture resistance, good chemical resistance and excellent shock-absorbing properties. Cross-linked PE foam, such as Plastazote, is dimensionally stable, temperature-resistant and can be cut to precise dimensions. It is frequently used for packaging inserts, transport padding, technical seals and vibration damping.Primer
To enhance adhesion properties, a primer featuring a two-component bonding system is employed. The primer contains no cross-linking agent, meaning that the bond to the substrate is formed exclusively by physical forces (adhesion).PTFE (polytetrafluoroethylene / Teflon®)
PTFE (polytetrafluoroethylene), known by the trade name Teflon®, is an engineering plastic with outstanding chemical resistance to almost all media. PTFE has a very low coefficient of friction, good electrical insulation properties and can be used over a wide temperature range from -200 °C to +260 °C. In the sealing and mechanical engineering sectors, PTFE is used for sliding seals, flat seals and chemically stressed pipes.PU polyurethane rubbers
PU polyurethane rubbers are characterised by excellent wear resistance and exceptionally high tear strength. Their high elasticity and good resistance to high-energy radiation are further advantages. Additionally, they resist oxygen, ozone, mineral oils, and fats, although their hydrolysis resistance is limited in aqueous environments. AU polyurethane rubbers are primarily utilized as scrapers or for rollers and wheels.PUR foam (polyurethane foam)
PUR foam is a versatile polyurethane-based material produced by chemical foaming. Depending on the formulation and manufacturing process, soft, semi-rigid or rigid foams with open or closed cell structures are produced. PUR foams offer good damping properties, high elasticity and can be moulded into almost any shape. Applications include upholstery, acoustic insulation, seals and packaging.
Rr
REACH and foam
Vibraplast AG uses only REACH-compliant foams.Rebound elasticity
Rebound elasticity is the energy returned as a percentage and is used to assess the elastic behaviour. It indicates the extent to which the material behaves elastically and the extent to which it behaves viscously. The higher the elasticity, the less deformation energy is converted into heat. This test is particularly suitable for providing initial indications of the dynamic behavior of an elastomer using simple methods. Rebound elasticity is highly dependent on temperature.Reflection
Reflection is the bounce-back of sound waves.Resonance
Resonance occurs when a system capable of oscillating is excited at its natural frequency.Reticulation
Reticulation is a post-treatment process applied to foams to achieve permeability to liquids, air or gases. In this process, the cell membranes between the foam cells are removed, whilst the basic structure of the foam remains intact. Only the thin intercellular membranes of the foam are removed, resulting in an open-cell foam that is permeable to air or liquids.Reverberation
Reverberation is the lingering sound heard in rooms and from musical instruments after the sound source has stopped.Reverberation time
Reverberation time is the reverberation of a room. The longer the reverberation time, the longer a sound event remains audible in the room, and the more it echoes and reverberates.RoHS (Restriction of Hazardous Substances)
RoHS is a European directive that restricts the use of certain hazardous substances in electrical and electronic equipment. It covers, amongst other things, heavy metals such as lead, mercury, cadmium and chromium(VI), as well as certain flame retardants. Plastic and elastomer parts used in electronic assemblies must be RoHS-compliant in order to be marketed within the EU.Room acoustics
Room acoustics is a branch of acoustics. This field deals with the distribution of sound levels within rooms. Room acoustics focuses on the acoustic environment in indoor spaces, which helps to improve speech and music intelligibility and reduce sound levels.Room sound absorption
Installing sound absorbers on interior surfaces reduces sound reflection, shortens reverberation time, and enhances room acoustics.Rubber
Rubber is the uncross-linked raw material required for the manufacture of elastomers (rubber). A distinction is made between natural and synthetic rubbers.Rubber processing methods
The required vulcanisation tool or mould contains one or more cavities, depending on the size, sensitivity and output of the rubber/metal part. The mold is first loaded with the prepared metal while open and then, depending on the process, with a precisely metered mixture while the mold is either open or closed. Possible processing methods include compression molding, transfer molding or injection molding.Rubber-metal joints
The most commonly used material for rubber-to-metal bonds is steel, although other metals, such as zinc, aluminium and alloys, can also be used.Rubber-plastic composite
Plastics can also be used in place of metals in rubber-metal bonds. In addition to weight reduction, resistance to corrosion is a further advantage. Complex plastic parts can also be produced efficiently by injection moulding. The plastics are degreased and mechanically prepared in a similar way to metal, and coated with a bonding agent. For the production of rubber-plastic bonds, thermoplastics must be dimensionally stable at vulcanisation temperatures of 160–200 °C; otherwise, deformation of the plastic part may occur during the production of rubber/plastic moulded parts.
Ss
SBR (Styrene-Butadiene Rubber)
SBR (Styrene-Butadiene Rubber) is a widely used synthetic rubber with good mechanical properties and high wear resistance. It is inexpensive to manufacture and is characterized by good abrasion resistance. SBR is not resistant to mineral oils and fats. Typical applications include seals, molded parts, and linings where there is no contact with oil.Self-adhesive / PSA coating
Many technical foam, rubber and sealing products are equipped with a pressure-sensitive adhesive (PSA = Pressure Sensitive Adhesive) layer. This self-adhesive property enables simple, tool-free installation directly onto smooth and slightly roughened substrates. Adhesive strength varies depending on the adhesive system and the substrate material. For demanding applications, e.g. high temperatures or wet environments, special adhesives are available.Shear stress
Under shear stress, the linearity limit is 35% deformation, relative to the rubber layer thickness. The shear modulus G is the sole material constant for elastomers and is fixed for each compound, depending on the Shore hardness.Shielding factor
The reduction in the sound level of sound waves achieved by means of barriers such as noise barriers or partitions is referred to as the shielding factor.Shore A hardness
Hardness is commonly expressed using the Shore A scale. This involves measuring the resistance to penetration by a cone. Finished parts whose test surface deviates from a minimum diameter of 30 mm and a minimum test thickness of 6 mm are to be regarded only as comparative values for measurements taken under the same conditions and not as material constants.Shore hardness
The most commonly used method for testing the hardness of elastomers is the Shore hardness test in accordance with DIN ISO 7619-1. Shore hardness refers to the resistance of a rubber sample to the penetration of a conical indenter of specific dimensions under a defined compressive force. Depending on the type of indenter used, a distinction is made between Shore A for softer elastomer compounds and Shore D for harder elastomer compounds. To ensure accurate measurement of Shore hardness, the standard specifies a specimen thickness of 6 mm. If measurements are carried out on finished parts with a thinner wall thickness, this usually leads to incorrect results. Standard elastomer compounds for technical rubber moulded parts fall within a hardness range of 20–90 Shore A.SI/MVQ silicone rubber
SI/MVQ is a silicone rubber that offers very high heat resistance and extreme cold resistance, as well as excellent resistance to oxygen, ozone, and UV radiation.Sound
Sound consists of vibrations ranging from 16 to 16,000 Hz in solids (structure-borne sound) and in the air (airborne sound).Sound absorption
Sound waves never propagate without loss; instead, they are always subject to a degree of attenuation—absorption—that varies in magnitude. A high degree of absorption can be achieved using porous materials. Sound absorption is of great importance for the acoustic experience of a room’s occupants. With appropriate sound absorption, the room can be tailored to its specific purpose.Sound absorption coefficient
The sound absorption coefficient α defines the ratio of absorbed to incident sound energy. In the case of total reflection, α = 0; in the case of total absorption, α = 1. Sound absorption refers to the reduction of sound energy, primarily through conversion into heat. The movement of air molecules (= sound) is converted into thermal energy (absorption is synonymous with ‘swallowing’ and ‘soaking up’). The sound absorption coefficient is frequency-dependent; therefore, measurement is carried out in the frequency range from 100 to 5000 Hz.Sound attenuation
Sound attenuation can be understood as the prevention of sound propagation through the absorption of airborne sound. During sound absorption, sound energy is converted into inaudible vibration waves, thereby reducing reflection at an interface. The acoustics within the room are improved and noise is reduced.Sound attenuation
Sound attenuation can be understood as the prevention of sound propagation through the absorption of airborne sound. During sound absorption, sound energy is converted into inaudible vibration waves, thereby reducing reflection at an interface. The acoustics within the room are improved and noise is reduced.Sound bridges
Sound bridges are usually undesirable pathways for sound transmission and can be largely eliminated using a wide variety of noise reduction measures.Sound insulation
Sound insulation focuses on the acoustic separation of rooms from unwanted noise originating from neighbouring rooms or from outside. The transmission of airborne or structure-borne sound is prevented by reflection at the interface between two media.Sound insulation composite systems
To achieve the best possible results, combined materials can also be used as composite systems for structure-borne sound insulation or airborne sound insulation. For example, multi-layer PUR foams, supplemented with a viscoelastic heavy foil.Sound insulation index
The sound insulation index R is a logarithmic quantity that describes airborne sound insulation performance. The sound insulation index is expressed in decibels.Sound insulation index (R)
Indicates the airborne sound insulation of a building component. R = 10 log (incident sound power / transmitted sound power).Sound propagation
Sound waves propagate spherically at the speed of sound and decrease in intensity with increasing distance. This process is strongly influenced by the absorption of sound waves. A distinction is made between two limiting cases: 1. undisturbed sound propagation in a free field and 2. total sound reflection. The nature of sound propagation in a workplace will generally lie between these two idealised extremes. In room acoustics, the structural and technical design of the environment or the surrounding space is described by parameters such as sound absorption coefficient, sound insulation index, sound transmission index and reverberation time. These parameters are important tools in noise reduction technology.Sound reflection
In all noise issues concerning soundproofing or acoustic damping, the reflection of a sound source off an obstacle—such as walls, windows, ceilings, floors, machinery, etc.—is a critical factor. Reflection depends on the frequency and direction of the sound wave relative to the obstacle, as well as on the nature and surface structure of the reflecting obstacle. The returning, reflected wave interferes with the incident wave and, depending on the conditions present, results in the sound wave being cancelled out or amplified in extreme cases. In general, it can be said that hard surfaces produce strong reflections, whilst soft surfaces can achieve high sound absorption.Spring characteristic curve
The spring characteristic curve refers to the relationship between the applied force and the resulting deformation or displacement. The spring properties depend on the modulus of elasticity of the elastomer and the geometric dimensions. Therefore, the definitive identification of a bonded rubber spring is not the measured elastomer hardness in Shore A, but the spring characteristic curve. A spring stiffness of ±12% corresponds to approximately ±3 Shore A. For standard parts without special measures, the spring stiffness tolerance is ±20%.Standard-quality foam
Standard-grade foam is characterised by its density and compression hardness, which are the technical indicators of a foam’s quality. Compression hardness describes how foam behaves when compressed under a defined force. The higher this value, the firmer the foam feels. An important quality characteristic of foam is the density, or volume weight, in kilograms per cubic metre (kg/m³). As a rule of thumb, a density of 20–30 kg/m³ represents a standard quality for seat and back cushions as well as budget mattresses, 30–40 kg/m³ describes standard to high-end quality for seat and back cushions, mattresses, boat, camping or garden cushions, and 40–50 kg/m³ represents high-quality to very high-quality, excellent long-lasting elasticity for a wide range of applications.Storage
Elastic mounting using vibration-isolation elements on machinery prevents structure-borne noise from being transmitted into the building structure. This measure minimises the transmission of structure-borne noise right at the source.Structural noise
Installation noise refers to the sounds caused by heating and air-conditioning units, fans, hydraulic systems and lifts.Structure-borne noise isolation
The well-known effects of structure-borne noise create an unavoidable need to provide effective vibration isolation. A relatively simple method of structure-borne noise isolation is achieved by installing an intermediate layer as close as possible to the source of the disturbance, which interrupts the path of the sound vibrations. For example, engines are mounted on specially designed vibration-isolation units, thereby forming a vibration system that is virtually independent of the surrounding environment or support structure. The same applies to building floors, which are periodically subjected to powerful horizontal and vertical impulses simultaneously and are then freed from vibration both horizontally and vertically by means of isolation.Structure-borne sound
Structure-borne sound is sound that propagates through a solid. When sound is transmitted to a solid, it causes the solid to vibrate. For example, sound propagates through thin-walled metal sheets or through masonry.Structure-borne sound insulation
Whilst the construction materials used in machinery and buildings, such as cast iron, steel and concrete, are good sound conductors and are therefore described as ‘sound-hard’ in line with their material consistency, rubber, on the other hand, conducts sound poorly and is very well suited as a ‘sound-soft’ material for structure-borne sound insulation. The insulation effect for structure-borne sound waves is achieved through their partial reflection at the interface between materials, and only a portion of them penetrates the intermediate layer.SVHC substances (Substances of Very High Concern / REACH)
SVHC stands for ‘Substances of Very High Concern’ and refers to substances of very high concern under the European REACH Regulation. These include carcinogenic, mutagenic or reprotoxic substances, as well as persistent and bioaccumulative substances. Manufacturers and distributors are obliged to provide customers, upon request, with information on whether their products contain SVHC substances in a concentration exceeding 0.1% by weight. Vibraplast AG processes only REACH-compliant materials.
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Thermal conductivity
Thermal conductivity is crucial to the thermal insulation properties of an insulating material. Thermal conductivity indicates the amount of thermal energy (W) that flows through a component per metre (m) when there is a temperature difference of 1 Kelvin. The unit of measurement is W/mK and is abbreviated as lambda (λ). The basic rule is: the lower this value, the better the thermal insulation properties of the material. Examples: PUR foam 0.037 / Vibra®fiber polyester fibre mats 0.037 / Basotect® melamine foam 0.033.Thermoplastic elastomers
Thermoplastic elastomers (TPE) are plastics that, at room temperature, are comparable to conventional elastomers. However, TPE plastics can be plastically deformed when heat is applied.Thermosets
Thermosets are hard polymer materials, some of which are glass fibre-reinforced. Once a thermoset has cured, it can no longer be shaped. If high standards are required in terms of chemical resistance, heat resistance and electrical insulation properties, thermosets are the right choice of material.Transmission coefficient
The transmission coefficient τ indicates the proportion of sound energy striking a component that is transmitted to the other side. A transmission coefficient of 0 indicates complete sound insulation, whilst a value of 1 indicates unimpeded sound transmission. It is directly related to the sound insulation index R: the higher the sound insulation index, the lower the transmission coefficient.Types of stress on rubber
When designing bound rubber springs, it is essential to bear in mind that, for the same applied force, the degree of deformation varies depending on the type of stress. The designer can select the direction of the force to subject the rubber to compression, tension, shear or bending. Shear stresses result in the greatest deformations, whilst compressive stresses result in the smallest. Tensile stresses should be avoided due to the non-linear spring characteristic curve, the tendency to flow and the adverse effect of the applied force.
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UL 94 fire safety standard
The UL 94 standard was developed to regulate the fire safety testing of plastics, particularly foams. This standard was originally used in the USA for testing plastics. However, it has since become established worldwide for classifying the flame retardancy and fire safety of plastics and foams.
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