The TexLoc® Library
Technical Terms
 

Annealing
Bar
Burst Strength

Coagulation

Coalescence

Coefficient of Friction

Coefficient of Linear Thermal Expansion
Concentric
Conductivity

Continuous Operating Temperature
Creep
Dielectric Constant
Dielectric Strength
Dissipation Factor

Eccentric

Elongation at Break
Flex Life
Flexural Modulus
Flexural Strength

Heat Treated Tubing

Isotropic

Impact Strength IZOD

Lubricity

Melting Point

Orientation Index (OI)

Paste Extrusion

Permeability
Permitivity
Poission's Ratio (vxy)


Power Factor & Dissipation Factor
Preforming
Reduction Ratio Range
Reground Resin

Reprocessed Resin
Resistivity
Rheology
Shear Damage
Shore Hardness

Sintering
Specific Gravity
Specific Inductive Capacity
Strained Specific Gravity

Stretch Void Index (SVI)

Tensile Elastic Modulus

Tensile Strength
Tensile Strength at Break

Tensile Strength at Yield

Thermal Conductivity

Thermoplastics
Tracking 
Unstrained Specific Gravity
Viscosity

Volts per mil 
Water Absorption
Weep Test
Yield Stress
Young's Modulus of Elasticity

ANNEALING  Back to Top

The process of heating a material, then cooling it slowly.  It is used to reduce the stresses formed during fabrication.   

BAR  Back to Top

A metric unit of measurement used to denote the pressure of gases, vapors and liquids.  

BURST STRENGTH  Back to Top

The pressure at which a tube fails mechanically (i.e. breaks open). 

COAGULATION   Back to Top

The process for separation of PTFE solids from its dispersion.  

COALESCENCE  Back to Top

Refers to the mechanism for melting and consolidation of PTFE parts. After the polymer melts, adjacent particles begin to combine (i.e. coalesce) under the driving force of surface tension.  

COEFFICIENT OF FRICTION  Back to Top

The ratio of the frictional force to the force, usually gravitational, acting perpendicular to the two surfaces in contact. The coefficient is a measure of the difficulty incurred as two materials slide over each other.

COEFFICIENT OF LINEAR THERMAL EXPANSION  Back to Top

The change in unit of length or volume that occurs due to a unit change in temperature.  

CONCENTRIC  Back to Top

Having the same center.  In tubing, this would mean that the wall thickness is the same size all the way around.  i.e.  

 

CONDUCTIVITY  Back to Top

For insulation purposes the high resistivity of plastics is an advantage but, in some cases, it can be a serious disadvantage as it results in high, static charge, build up: this in turn can result in dust pick-up and/or spark generation. The established way of improving conductivity is by adding a conductive filler such as, a high structure, carbon black. The addition of lubricants can minimize the generation of static while the addition of some semi-incompatible liquids can cause static to leak away. 

CONTINUOUS OPERATING TEMPERATURE  Back to Top

Maximum temperature recommended for each grade of plastic to insure no failure occurrence due to material degradation. 

CREEP  Back to Top

Deformation in a part subjected to a continuous load.  Creep is dependent on temperature and the duration and amount of the load. 

DIELECTRIC CONSTANT  Back to Top

This is a measure of how well a material will store an electrical charge. When the material is going to be used as an insulator then a low dielectric constant is needed; when the material is going to be used in condenser applications then a high dielectric constant is needed. It is the ratio of the capacity of a condenser made with a plastic over the capacity of an identical condenser made with air as the dielectric. As this is a ratio it has no dimensions; also known as permitivity and specific inductive capacity.

DIELECTRIC STRENGTH  Back to Top

This term makes more sense if instead of dielectric you use insulation strength as it is a measure of how well a material can withstand a voltage. It is defined as the voltage difference per unit of thickness which will cause catastrophic failure of the dielectric: breakdown occurs when there is a sudden flow of current through the material. It is very dependent upon thickness so that, for example, the dielectric strength for a 0.001 inch film (in volts per mil) is often twice that for a 0.005 inch film of the same material (25.4 volts per mil = 1k volts per mm). For some materials, increasing humidity decreases the results; also decreases rapidly with increasing A.C. frequency. 

ECCENTRIC  Back to Top

Not having the same center.  In tubing, this would mean that the wall thickness is not the same all the way around the tube.eccentric

 

DISSIPATION FACTOR  Back to Top

The ratio of the power dissipated in a dielectric to the product of the effective voltage and the current.  Also called tan delta, permitivity loss factor, dielectric dissipation factor, dielectric loss tangent.  

ELONGATION AT BREAK  Back to Top

If the strain is converted to a percentage by multiplying by 100, then the result is the elongation. So the elongation at break is defined as:

elongation at break = 100 x increase in gauge length
                                      original gauge length

FLEX LIFE  Back to Top

Plastic tubing's ability to withstand fracture and fatigue when exposed to repeated bending around specified bend radius (generally, performed in old chamber environment) 

FLEXURAL MODULUS  Back to Top

The stiffness in bending is determined by measuring the slope of the initial straight part of the load/deflection curve during a bending test. Assuming this slope is S mm/newton, then the modulus is calculated as below. Note when determining the slope that this is the load divided by the crosshead deflection. Distances on the chart may have to be scaled to give crosshead movement. 

Flexural modulus = L3S
                                 4 b t3 

FLEXURAL STRENGTH  Back to Top

The maximum stress a tube can withstand loaded to failure in bending.  Flexural strength is calculated as a function of load, support span and specimen geometry.  Also called modulus of rupture, bending strength.  

HEAT TREATED TUBING  Back to Top

This tubing has been put through a special heating process to set the dimensions so that if the tubing comes into contact with the elements, such as heat, or other altering processes,  the tubing will hold continue to hold its size.  

IMPACT STRENGTH IZOD  Back to Top

The energy required to break a v-notched sample equal to the difference between the energy in the striking member of the impact apparatus at the instant of impact with the sample and the energy remaining after complete fracture of the sample.  Also called, Izod Impact Energy, notched Izod strength, notched Izod impact strength, Izod v-notch strength, Izod strength, Izod, and IVN.

ISOTROPIC  Back to Top

If isotropic, this means that the tubing has been adequately sintered and the stresses relieved.

LUBRICITY  Back to Top

Lubricity refers to the slipperiness of the tubing,  how little or how much other objects will stick to the tubing.  

MELTING POINT  Back to Top

The temperature at which the solid crystalline and liquid phases of a substance are in thermodynamic equilibrium.  

ORIENTATION INDEX (OI)  Back to Top

A measure of the degree of orientation in the machine direction (longitudinal) versus that of the cross direction (transverse). Zero (0) is the ideal, meaning that the tube is randomly oriented.  In the worst case,  a value of one (1) is present, indicating that all the orientation is in the longitudinal direction. 

PASTE EXTRUSION  Back to Top

Because fine powder PTFE does not melt and flow, the  PTFE powder is blended with a hydrocarbon lubricant to act as an extrusion aid.  It is then formed into a preform and placed inside the barrel of a ram extruder where it is forced through a die.

PERMEABILITY Back to Top


The capacity of material to allow another substance to pass through it. 
 

PERMITIVITY  Back to Top


See Dielectric Constant  
 

PREFORMING  Back to Top

The operation in which PTFE powder is compacted under pressure into a mold.  At TexLoc,  preforms are extruded and each lot of tubing can be traced all the way back to the particular preform it was made from, which in turn can be traced to the actual barrel of resin it was made from.
 

POISSION'S RATIO Back to Top

The ratio of lateral strain to the longitudinal extension caused by uniaxial tensile extension. 

POROSITY  Back to Top

The volume of voids per unit volume of a material. 

POWER FACTOR &DISSIPATION FACTOR   Back to Top

For most dielectrics (insulators) these two factors mean the same and are a measure of how much power is converted to heat; this conversion is obviously undesirable in an insulator and so the power factor should be as low as possible. The term loss factor, or dielectric loss index, is a product of the dissipation factor and the dielectric constant. PVC, which has a high loss factor, can be high frequency welded; PE, which has a low loss factor, cannot be high frequency welded. 

REDUCTION RATIO RANGE  Back to Top

The ratio of the cross section surface areas of the preform and the extrudate in paste extrusion.  Generally, reduction ratio of the resin decreases as molecular weight increases.  The lower the molecular weight, the higher the reduction ratio. 

REGROUND RESIN  Back to Top

Reground resin is produced by grinding PTFE that has been preformed but has never been sintered. 

REPROCESSED RESIN Back to Top

Reprocessed resin is resin that has been produced by grinding preformed and sintered polymers. 

RESISTIVITY  Back to Top

Most plastics are good insulators, that is, they do not conduct electricity very well as they have a high resistivity (a large resistance to the passage of electricity). There may well be a difference between the resistivity of the surface of the plastic and that of the bulk, or body, of the plastic. For this reason both surface and volume resistivity are quoted. In both cases the larger the number quoted, the better is the insulation. A good conductor such as gold has a volume resistivity of 10 -6, carbon is 10 -3, conductive plastic is approximately 10 2; cellulose is 10 6, PVC is 1014 and PS is about 1018.

Insulation resistance is also sometimes quoted; this is a combination of surface resistivity and volume resistivity. It is the ratio of the direct current voltage, applied to the electrodes, to the total current between them. 

RHEOLOGY  Back to Top

A science that studies and characterizes flow of polymers, resins, gums and other materials. 

SHEAR DAMAGE  Back to Top

Damage to the PTFE by removing small particles of crystalline PTFE as the preform is extruded. 

SHORE HARDNESS  Back to Top

Indentation hardness of a material.  Determined by the depth of an indentation made with a probe of the Shore-type durometer.  

SINTERING  Back to Top

Sintering of PTFE is a thermal treatment during which the polymer is melted, coalesced and rescrystallized during cooling.

SPECIFIC GRAVITY  Back to Top

Due to the properties of fluoroplastic resins, measurement of the molecular weight is virtually impossible.  An indirect property, standard specific gravity, is substituted for molecular weight. A weight test  determines the density and molecular weight of a material. This allows for material characterization such as: density, crystallinity, thermal history, porosity, absorption of other materials, which type of material is best suited for a particular job, etc. 

SPECIFIC INDUCTIVE CAPACITY  Back to Top


See Dielectric Constant
 

STRAINED SPECIFIC GRAVITY  Back to Top

Is measured on a sample of PTFE after it has been strained to break at a strain rate of 5.0 mm/min.

STRETCH VOID INDEX (SVI) Back to Top

A measure of change in the specific gravity of a PTFE specimen as a result of being subjected to tensile strain.  It indicates how well the sintering and the coalescence have eliminated small voids in the PTFE.   Voids directly affect the performance of a tube.

SVI = (Unstrained Specific Gravity - Strained Specific Gravity) x 1000 

TENSILE ELASTIC MODULUS  Back to Top

See Young's Modulus

TENSILE STRENGTH   Back to Top


The maximum load that the sample sustains during a tensile test which continues until the sample breaks is used to calculate the tensile strength. The maximum load may occur as the sample breaks or earlier. To calculate the tensile strength, the maximum load is divided by the test piece cross-sectional area which should be measured before the test is carried out. This area is calculated by multiplying the sample width by sample thickness. These values are measured in the straight central part of the dumb-bell. Normally a number of test pieces (eg five) are measured and tested. The tensile strength should be calculated for each test and then averaged. Disregard results where the test sample was damaged during preparation or the sample broke in the jaws. Tensile strength is thus the maximum stress which the material can sustain in tension. The result for a particular extrudate will depend on the test speed and temperature and also whether the sample was pulled in the machine or the transverse direction.
 

TENSILE STRENGTH AT BREAK  Back to Top

The maximum load per original minimum cross-sectional area of the sample in tension within the gage length when the maximum load corresponds to the break point. 

TENSILE STRENGTH AT YIELD  Back to Top

The maximum load per original minimum cross-sectional area of the sample in tension within hte gage length when the maximum load corresponds to the yield point. 

THERMAL CONDUCTIVITY  Back to Top

Thermal Conductivity Formula per ASTM C177

Equation = (CAL/SEC/CM2, 0C/CM)

PTFE
6 X 10-4

FEP
6 X 10-4

PFA
6.2 X 10-4

ETFE
5.7 X 10-4

OR

BTU-IN./H-FT2-0F

PTFE = 1.7

FEP = 1.4

PFA = 1.8

ETFE = 1.65

THERMOPLASTICS  Back to Top

Polymers that, after final processing, can be repeatedly softened by heating and hardened by cooling by means of physical changes. 

TRACKING  Back to Top


A conductive path may be formed along the surface of a plastic by a spark or arc which means that insulation properties are lost. In general, those plastics which degrade on heating to give volatiles (gases) are more non-tracking and more arc resistant than those plastics which do not.
 

UNSTRAINED SPECIFIC GRAVITY  Back to Top

Is measured on a tensile specimen prior to straining it. 

VISCOSITY  Back to Top

The internal resistance to flow exhibited by a fluid, the ratio of shearing stress to rate of shear. 

VOLTS PER MIL  Back to Top

See Dielectric Strength 

WATER ABSORPTION  Back to Top

Plastics ability or inability to absorb distilled H2O over a given period of time. Generally, a 24 hour time period and the result is expressed in percentage of weight gain. 

WEEP TEST  Back to Top

Used to determine the minimum pressure (WP) at the onset of leak of a military fuel through the tube. 

YIELD STRESS  Back to Top

When testing some resins, the tensile load rises as the sample is pulled but then reaches a value at which there is a marked inflection in the load/extension curve( i.e. there is an increase in deformation without a corresponding increase in load.) The inflection may be a plateau or a marked maximum in the curve and is called the yield point. The stress at this point is called the yield stress and is calculated by dividing the load at the yield point by the original cross-sectional area. In most practical applications, the yield stress represents the highest useable stress that a material can sustain even though the tensile stress may be higher. At the yield point, a neck often forms in the test piece and subsequent deformation occurs by increasing the length of the neck. This process is called cold-drawing of the material. 

YOUNG'S MODULUS OF ELASTICITY  Back to Top

The relationship between stress and strain in an uniaxial extension. 
 
 
 
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