Glossary

INDEX
? Asker C

? Coefficient of thermal conductivity
? Complex shear rate
? Compression Set
? Conductivity (dB)
? Cone penetration

? Dielectric breakdown strength
? Dielectric constant
? Dielectric dissipation factor
? Internal damping

? Loss factor (tanδ)
? Low-molecular-weight siloxane

? Magnetic permeability
? Modulus of resilience

? Needle Penetration

? Resonance/
  resonance amplification
? Specific Heat

? Tensile Strength
? Thermal resistance

? Volume Resistance

? Young's modulus
  (Modulus of elasticity in tension)

Asker C

Asker C is a measuring device to measure hardness with a durometer (a spring hardness scale) as stipulated in SRIS0101 (SRIS: Society of Rubber Industry [Japan] Standards) .

When a 20 is listed for Asker C in a physical properties chart, this indicates that the value measured with the Asker C hardness scale is 20. In contrast to a needle penetration test or cone penetration test, larger numbers indicate a harder material.

Similar hardness measurement devices include the JIS K6253 durometer (JIS A durometer) and Asker F.

A JIS A durometer is used to measure the hardness of rubber and is the same as a Shore A durometer. Asker C is a hardness scale used to measure materials that are harder than those measured in a needle penetration test and softer than those for a JIS A durometer.

Coefficient of thermal conductivity

If a temperature difference is present in a substance, then the movement of heat will occur from portions with higher temperatures to those with lower temperatures. Coefficient of thermal conductivity is a coefficient that indicates how easily this movement of heat occurs, so when a temperature difference of 1℃ per unit length (thickness) exists, this is the amount of heat that moves a unit area in a unit time. In other words, when the difference in temperatures for surface A (TA) and surface B (TB) in a 1m³ cube with a volume as indicated in Figure A is 1℃ (TA > TB) , the amount of heat to move 1 m (Aright arrowB) in 1 second is the coefficient of thermal conductivity. Units are indicated in J · m/s · m2 · ℃, W/m · K, or W/m · ℃. The larger the value for coefficient of thermal conductivity, the greater the amount of heat that moves, which means that heat will be easily transferred. Thus, a substance with a large thermal conductivity is preferred as a heat conductor. However, thermal conductivity is given in values for unit length, so even if a substance has a large thermal conductivity, heat-conducting action will decrease if the length (thickness) actually used is greater.
For example, heat-conducting action will be the same for a heat conductor where the thickness is 10 mm with a coefficient of thermal conductivity of 10 W/m · K and a heat conductor where the thickness is 1 mm with a coefficient of thermal conductivity of 1 W/m · K. In addition, coefficient of thermal conductivity is a specific value (physical property) for a substance, and it generally varies according to the temperature. For example, the coefficient of thermal conductivity of air increases with temperature, while the coefficient of thermal conductivity of a metal tends to decrease with a rise in temperature.

Complex shear rate

The complex shear ratio indicates the hardness of a material. It is the elasticity determined when applying (dynamically) sinusoid ally varying force and is a value that will serve as the basis of a vibration insulator design or shock-absorber design.Dynamic elasticity in the direction of compression is indicated by E* (complex compressive elasticity modulus) ; dynamic elasticity in the direction of shearing is indicated by G* (complex shear rate) .

3G*=E*

G* can be broken down into G' (storage shear rate) and G" (loss shear rate) . G' indicates the spring component that a material has (elastic body) ; G" indicates the liquid component (viscous body) .

These values are determined by a dynamic viscosity measurement equipment and will be:

Compression Set

Compression set is the permanent set due to heated compression of a rubber material. A small value indicates that material has a strong ability to recover when compressed for a long period of time. This can be evaluated by tests based on JIS K 6262 standards. A cylinder-shaped test piece is subjected to compressive strain corresponding to 25% of the thickness; after the test piece is kept for a fixed time at high temperatures, it is removed and the thickness is measured after 30 minutes. The compression set rate Cs (%) is indicated by the following equation:

t0: Prior thickness of a test piece (mm)
t1: Spacer thickness (mm)
t2: Thickness (mm) of a test piece 30 min. after removing it from compression equipment

Generally, higher compressibility and test temperatures will mean a greater compression set.At our firm, a given material is compressed at an atmospheric temperature of 100℃ and compression is released after retention for 70 hours; compression set is then calculated after 30 minutes at normal temperatures.

Conductivity (dB)

When precision machinery is supported by vibration insulators, the proportion of the base frequency transferred to machinery is called the vibration conductivitytau. A dB value is often used to indicate conductivity.

tau  :  Vibration conductivity
a0  :  Forced displacement of the base (or speed and acceleration)
a  :  Mechanical displacement (or speed and acceleration)

When, for example, the vibration conductivity (tau) is 2, it is noted in dB as 6 dB.Every time the conductivity is increased 10-fold, the dB value increases by 20; when it is 1/10, the dB value decreases by 20.

(tau-dB conversion chart)

dB value tau dB value
1 0 dB 0.5 -6 dB
2 6 dB 0.1 -20 dB
10 20 dB 0.01 -40 dB
100 40 dB    

Cone penetration

The complex shear ratio indicates the hardness of a material. It is the elasticity determined when applying (dynamically) sinusoid ally varying force and is a value that will serve as the basis of a vibration insulator design or shock-absorber design.Dynamic elasticity in the direction of compression is indicated by E* (complex compressive elasticity modulus) ; dynamic elasticity in the direction of shearing is indicated by G* (complex shear rate) .

A cone penetration test is a method of measuring the hardness of a material.
Measurement is standardized in JIS K2220; a fixed cone is entered into a test piece to indicate the hardness of a material determined from the length it entered. The cone penetration value is given where 1/10 mm is a cone penetration of 1.
Larger numbers mean that a material is more pliable; this method is used to measure materials that are softer than those subject to a needle penetration test.

Dielectric breakdown strength

Dielectric breakdown is the name of the phenomenon occurring when the voltage applied to an insulator exceeds certain limits; the insulator breaks down electrically and insulating properties are lost so that voltage flows. The voltage at this point is called the dielectric breakdown voltage; the value given by dividing the dielectric breakdown voltage by the material thickness is called the dielectric breakdown strength. Units are indicated in kV/mm; this is a specific value for a substance, but the value can decrease when air bubbles are introduced in the material and when the material absorbs moisture. A substance with a large dielectric breakdown strength is preferred as an insulator.

Dielectric constant

The dielectric constant is the ease of polarization (indicating the size of the quantity of electricity stored) and is a standard used to evaluate its performance as an insulator.

Using an example of a condenser, an insulator is placed between pole plates and voltage is applied, electricity will not flow, though a phenomenon called polarization where positive and negative charges in molecules separate will occur, so electricity will be stored. At this point, the quantity of electricity stored is proportional to the intensity of the magnetic field and area of the pole plates, so it will increase; the rate of change in this event is called the dielectric constant. If the dielectric constant increases, the quantity of electricity stored will increase.

Generally, specific inductive capacity (ratio of the dielectric constant of an insulator and the dielectric constant of a vacuum) is used rather than the dielectric constant. Having a small specific inductive capacity is preferred for an insulator.

In addition, this value is dependent on the frequency and temperature, so care must be taken upon usage.

Dielectric dissipation factor

The dielectric dissipation factor is the degree of electrical energy loss in an insulator and is a standard used to evaluate its performance as an insulator.

Applying alternating voltage to an insulator causes a phenomenon called dielectric loss where a portion of the electrical energy in an insulator is changed to heat energy because particles are vibrating (a type of resistance) , and heat is produced. The dielectric loss tangent (ratio of the charged current and current lost) is used as a standard for the degree of electrical energy loss in this event. With an ideal insulator, the electrical energy loss would be 0, so having a small dielectric dissipation factor is preferred for an insulator.

In addition, this value is dependent on the applied frequency and temperature, so the individual dielectric dissipation factor is given in a test by changing the frequency.

Internal damping

Loss factor (tangent) is used to indicate the size of internal damping (refer to "Loss factor" in Vocabulary)

 : Conductivity during resonance (resonace amplification)

A larger loss factor means that the internal damping of a vibration insulator will be greater. The conductivity (resonance amplification) of a vibration insulator during resonance will decrease.

Loss factor

G"/G'- the ratio of the storage shear rate (G') and loss shear rate (G") is called the loss tangent (loss factor) and is expressed as tangent. It indicates how much energy is absorbed (changed into heat) by a material when it deforms.

G"/G'- the ratio of the storage shear rate (G') and loss shear rate (G") is called the loss tangent (loss factor) and is expressed as tangent. It indicates how much energy is absorbed (changed into heat) by a material when it deforms.

Larger values for tangent mean that more energy is absorbed. In a shock absorption test, the modulus of resilience will decrease; in an agitation test, resonance amplification will decrease.

Low-molecular-weight siloxane

A dimethyl polysiloxane, which is a main component of silicone products, with a low molecular weight and where both ends form a ring is called cyclic polysiloxane. This low-molecular-weight siloxane (cyclic polysiloxane) is, depending on the number of Si atoms, called D3, D4, D5 ・ ・ ・ (the figure is D3) . With a lower D, low-molecular-weight siloxane has smaller molecular weight and therefore more volatile. However, D3 is extremely volatile, so it is not included in silicon products.

Cyclic polysiloxane(D3)

Magnetic permeability

Magnetic permeability is the ease of passing through a material's magnetic flux (the ease of magnetization) . This is one of the standards of evaluating magnetic absorption in applications for electromagnetic wave absorption.

When a substance is placed in space where magnetism is acting (a magnetic field) , it more or less takes on magnetism and becomes a magnet. At this point, increasing the intensity of the magnetic field means that magnetic flux density in a substance (indicating intensity as a magnet) will increase since it is also proportional, though the rate of change in this event is called the magnetic permeability. When magnetic permeability is greater, magnetic flux density will increase. In other words, when the magnetic flux passing though a substance, increases, its intensity as a magnet increase.

Generally, specific magnetic permeability (ratio of the magnetic permeability of a substance and magnetic permeability of a vacuum) is used rather than magnetic permeability. Magnetic flux does not readily pass through a substance with a low specific magnetic permeability like aluminum and, since it penetrates through, magnetic absorption will decrease. In contrast, magnetic flux readily passes through a substance with a high specific magnetic permeability like ferrite, so magnetic absorption will increase.

Modulus of resilience

The modulus of resilience is an indicator of the energy a material absorbs during the impact of an object. It is the ratio of energy an object has during impact and rebound when a test piece is struck by a falling object with a given mass from a given height.

Measurement of the modulus of resilience is standardized in JIS K 6255 and can be a Lupke impact resilience test using a pendulum to calculate the value from the drop and rebound height and a tripso-impact resilience test using a solid disk to calculate the value from drop and rebound angles.

A load W is dropped from a height h1 and strikes a test piece, bouncing to height h2, the energy E absorbed by the rubber material and the modulus of resilience R (%) are indicated in the following equations:

The modulus of resilience can be calculated from these equations if the drop and rebound heights are measured.

At R=0 (%) , a dropped object will stop without bouncing back; at R=100 (%) , it will bounce back to the same position as that from where it was dropped. In addition, (100-R) % will be converted to heat energy by the friction in the rubber. The modulus of resilience for a common rubber material will be markedly affected by the temperature, though our firm's gel is slightly affected by temperature as well as having a higher level of damping.

Needle Penetration

A needle penetration test is a method of measuring the hardness of a material.
Measurement is standardized in JIS K2207; a needle of fixed weight is entered vertically into a test piece to indicate the hardness of a material determined from the length it entered. The needle penetration value is given where 1/10 mm is a needle penetration of 1.
Larger numbers mean that a material is more pliable.

Resonance/resonance amplification

Resonance is the name of a phenomenon occurring when amplitudes in the vicinity of a Specific Heat (refer to "Specific Heat" in Vocabulary) of a vibrating system (a system formed by a vibration insulator and weight resting on the vibration insulator) are amplified when the size of vibrations forcibly applied from the outside is uniform and frequency varies. Conductivity during resonance for a vibration insulator is called the resonance tau.

tau  :  Vibration conductivity
a0  :  Forced displacement of the base (or speed and acceleration)
a  :  Mechanical displacement (or speed and acceleration)

Specific Heat

Specific heat is the amount of heat required to raise the temperature of 1 kg of a substance by 1 ℃. Units are indicated in J/kg ・ ℃ or J/kg ・ K. In other words, having a larger specific heat means that the amount of heat to raise the temperature will be greater, so a substance with a larger specific heat will be harder to heat or cool.

Tensile Strength

Tensile strength is the mechanical strength as determined with force needed prior to breaking when a rubber material is stretched. Test methods conform to JIS K 6251 and a test piece is stretched by a load at a fixed speed. The force required for it to break is divided by the cross-sectional area, which yields the breaking stress. Test methods are with a dumbbell-shaped test piece or a ring-shaped test piece; our firm uses a test with a dumbbell-shaped test piece. The tensile strength is indicated by the following equation:

TB: (MPa)
FB: Maximum tensile force (N)
A Cross-sectional area of a test piece (mm²)

Thermal resistance

There are various types of thermal resistance, such as heat transfer resistance, thermal resistance due to convection, thermal resistance due to radiation, and contact thermal resistance, though heat transfer resistance is often used for evaluation of a heat conductor and heat conductive tests. This is simply called thermal resistance.

Thermal resistance is the coefficient that indicates the difficulty of heat flowing as part of the movement of heat that occurs when an object is subjected to heat. Units are indicated in K/W or ℃/W. When a heat conductor as in Thermal resistance is the coefficient that indicates the difficulty of heat flowing as part of the movement of heat that occurs when an object is subjected to heat. Units are indicated in K/W or ℃/W. When a heat conductor as in Figure B is sandwiched between a heat-generating object such as a CPU and a heat-dissipating object such as a heat sink, supplying electric power (W) to a heat-generating object, i.e., an amount of heat, means that a temperature difference will be produced at both ends of the heat conductor (the heat-generating object and heat-dissipating object) . The value where this temperature difference is divided by the electric power will be the thermal resistance.Figure B is sandwiched between a heat-generating object such as a CPU and a heat-dissipating object such as a heat sink, supplying electric power (W) to a heat-generating object, i.e., an amount of heat, means that a temperature difference will be produced at both ends of the heat conductor (the heat-generating object and heat-dissipating object) . The value where this temperature difference is divided by the electric power will be the thermal resistance.

In other words, the relationship will be

thermal resistance (℃/W) =temperature difference (℃) ÷ sign amount of heat for a heat source (W)

A smaller temperature difference at both ends of a heat conductor means that heat is more readily transferred, so the level of heat-conducting action is quite high. In other words, a substance with a small thermal resistance is preferred as a heat conductor.

Thermal resistance is not a specific value (physical property) for a substance, so values will differ even with the same material depending on the environment and conditions of usage. In other words, saying thermal resistance means a value indicating heat-conducting characteristics incorporating various conditions such as the state in which a heat-conducting material is placed, the thermal conductivity of the material, material thickness, and the material dimensions.

Volume Resistance

Volume resistance is the name of the electrical resistance value per unit volume. In other words, it is the resistance value between 2 facing surfaces of a 1m³ cube as indicated in Figure C. Units are indicated in Ohm ・ m. In addition, Ohm ・ cm is also used, though this will indicate the resistance value for a 1cm³ cube and not a 1m³ one, so 1 Ohm ・ m =100 Ohm ・ cm.

The resistance value for material as a whole is determined by multiplying the length by the volume resistance and dividing by the cross-sectional area. The volume resistance is a specific value (physical property) for a substance, so when comparing with the same dimensions, a substance with a large volume resistance will also have a large resistance value. In other words, a substance with a large volume resistance is preferred as an insulating material.

Insulators, semiconductors, and conductors can be classified based on the size of resistance. In terms of materials with larger numerical values,

insulators > semiconductors > conductors

Volume resistance is not a specific value for a substance and varies according to temperature. The volume resistance of metal, which is a conductor, increases with a rise in temperature, though it conversely tends to decrease for a semiconductor or insulator with an increase in temperature.

Young's modulus

Young's modulus is an index to indicate hardness. This value indicates how much force can be exerted per unit area when a certain substance is compressed and its thickness is 0 (this is not actually possible). It is also called the compressive elasticity modulus; if this value is large, the substance can be said to be hard

In general, Young's modulus indicates elasticity in a static state (a state where force that changes with time is not exerted) ; the dynamic value is called the complex compressive elasticity modulus (refer to Complex shear rate).

*Taica® , αGEL® , OPTαGEL® , and the visual image of falling eggs are trademarks of Taica Corporation, registered in Japan,the United States and / or other countries.