The TexLoc Library
Technical Terms |
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.
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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.
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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 | |||
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 | |||
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 | |||
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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 | |||
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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 |
FEP |
PFA |
ETFE |
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. | |||
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UNSTRAINED SPECIFIC GRAVITY Back to Top | |||
| Is measured on a tensile specimen prior to straining it. | |||
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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. | |||
| The relationship between stress and strain in an uniaxial extension. | |||