Vespel
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Vespel is the trademark of a range of durable high-performance
polyimide Polyimide (sometimes abbreviated PI) is a monomer containing imide groups belonging to the class of high-performance plastics. With their high heat-resistance, polyimides enjoy diverse applications in roles demanding rugged organic materials, suc ...
-based
plastic Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...
s made by
DuPont Dupont, DuPont, Du Pont, duPont, or du Pont may refer to: People * Dupont (surname) Dupont, also spelled as DuPont, duPont, Du Pont, or du Pont is a French surname meaning "of the bridge", historically indicating that the holder of the surname re ...
.


Characteristics and applications

Vespel is mostly used in
aerospace Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial, and military applications. Aerospace engineering consists of aeronautics and astron ...
,
semiconductor A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...
, and transportation technology. It combines heat resistance, lubricity, dimensional stability, chemical resistance, and creep resistance, and can be used in hostile and extreme environmental conditions. Unlike most plastics, it does not produce significant
outgassing Outgassing (sometimes called offgassing, particularly when in reference to indoor air quality) is the release of a gas that was dissolved, trapped, frozen, or absorbed in some material. Outgassing can include sublimation and evaporation (whic ...
even at high temperatures, which makes it useful for lightweight heat shields and
crucible A crucible is a container in which metals or other substances may be melted or subjected to very high temperatures. Although crucibles have historically tended to be made out of clay, they can be made from any material that withstands temperat ...
support. It also performs well in
vacuum A vacuum (: vacuums or vacua) is space devoid of matter. The word is derived from the Latin adjective (neuter ) meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressur ...
applications, down to extremely low
cryogenic In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th International Institute of Refrigeration's (IIR) International Congress of Refrigeration (held in Washington, DC in 1971) endorsed a univers ...
temperatures. However, Vespel tends to absorb a small amount of water, resulting in longer pump time while placed in a vacuum. Although there are polymers surpassing polyimide in each of these properties, the combination of them is the main advantage of Vespel.


Thermophysical properties

Vespel is commonly used as a
thermal conductivity The thermal conductivity of a material is a measure of its ability to heat conduction, conduct heat. It is commonly denoted by k, \lambda, or \kappa and is measured in W·m−1·K−1. Heat transfer occurs at a lower rate in materials of low ...
reference material for testing
thermal insulator Thermal insulation is the reduction of heat transfer (i.e., the transfer of thermal energy between objects of differing temperature) between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with s ...
s, because of high
reproducibility Reproducibility, closely related to replicability and repeatability, is a major principle underpinning the scientific method. For the findings of a study to be reproducible means that results obtained by an experiment or an observational study or ...
and consistency of its thermophysical properties. For example, it can withstand repeated heating up to 300 °C without altering its thermal and mechanical properties. Extensive tables of measured
thermal diffusivity In thermodynamics, thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure. It is a measure of the rate of heat transfer inside a material and has SI, SI units of m2/s. It is an intensive ...
,
specific heat capacity In thermodynamics, the specific heat capacity (symbol ) of a substance is the amount of heat that must be added to one unit of mass of the substance in order to cause an increase of one unit in temperature. It is also referred to as massic heat ...
, and derived
density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...
, all as functions of
temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...
, have been published.


Magnetic properties

Vespel is used in high-resolution probes for
NMR spectroscopy Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique based on re-orientation of atomic nuclei with non-zero nuclear spins in an external magnetic f ...
because its volume magnetic susceptibility (−9.02 ± 0.25×10−6 for Vespel SP-1 at 21.8 °C) is close to that of
water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...
at
room temperature Room temperature, colloquially, denotes the range of air temperatures most people find comfortable indoors while dressed in typical clothing. Comfortable temperatures can be extended beyond this range depending on humidity, air circulation, and ...
(−9.03×10−6 at 20 °C ) Negative values indicate that both substances are
diamagnetic Diamagnetism is the property of materials that are repelled by a magnetic field; an applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force. In contrast, paramagnetic and ferromagn ...
. Matching volume magnetic susceptibilities of materials surrounding NMR sample to that of the
solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...
can reduce susceptibility broadening of magnetic resonance lines.


Processing for manufacturing applications

Vespel can be processed by direct forming (DF) and isostatic molding (basic shapes – plates, rods and tubes). For prototype quantities, basic shapes are typically used for cost efficiency since tooling is quite expensive for DF parts. For large scale CNC production, DF parts are often used to reduce per part costs, at the expense of
material A material is a matter, substance or mixture of substances that constitutes an Physical object, object. Materials can be pure or impure, living or non-living matter. Materials can be classified on the basis of their physical property, physical ...
properties which are inferior to those of isostatically produced basic shapes.


Types

For different applications, special formulations are blended/compounded. Shapes are produced by three standard processes: # compression molding (for plates and rings); # isostatic molding (for rods); and # direct forming (for small size parts produced in large volumes). Direct-formed parts have lower performance characteristics than parts that have been machined from compression-molded or isostatic shapes. Isostatic shapes have isotropic physical properties, whereas direct formed and compression molded shapes exhibit anisotropic physical properties. Some examples of standard polyimide compounds are:
SP-1 virgin polyimide
provides operating temperatures from cryogenic to 300 °C (570 °F), high plasma resistance, as well as a UL rating for minimal electrical and thermal conductivity. This is the unfilled base polyimide resin. It also provides high physical strength and maximal elongation, and the best electrical and thermal insulation values. Example: Vespel SP-1. ; 15% graphite by weight, SP-21: added to the base resin for increased wear resistance and reduced
friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Types of friction include dry, fluid, lubricated, skin, and internal -- an incomplete list. The study of t ...
in applications such as
plain bearing file:NYC 100-driving-axle-friction-bearing.jpg, Plain bearing on a 1906 S-Motor locomotive showing the axle, bearing, oil supply and oiling pad file:Linear-table with detail numbered.png, A sliding table with four cylindrical bearings file:GWR Spo ...
s, thrust washers,
seal Seal may refer to any of the following: Common uses * Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly: ** Earless seal, also called "true seal" ** Fur seal ** Eared seal * Seal ( ...
rings, slide blocks and other wear applications. This compound has the best mechanical properties of the graphite-filled grades, but lower than the virgin grade. Example
Vespel SP-21
; 40% graphite by weight, SP-22: for enhanced wear resistance, lower friction, improved dimensional stability (low coefficient of
thermal expansion Thermal expansion is the tendency of matter to increase in length, area, or volume, changing its size and density, in response to an increase in temperature (usually excluding phase transitions). Substances usually contract with decreasing temp ...
), and stability against
oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...
. Example
Vespel SP-22
; 10% PTFE and 15% graphite by weight, SP-211: added to the base resin for the lowest coefficient of friction over a wide range of operating conditions. It also has excellent wear resistance up to 149 °C (300 °F). Typical applications include sliding or linear bearings as well as many wear and friction uses listed above. Example
Vespel SP-211
; 15% moly-filled (molybdenum disulfide solid lubricant), SP-3: for wear and friction resistance in vacuum and other moisture-free environments where graphite actually becomes abrasive. Typical applications include seals, plain bearings,
gear A gear or gearwheel is a rotating machine part typically used to transmit rotational motion and/or torque by means of a series of teeth that engage with compatible teeth of another gear or other part. The teeth can be integral saliences or ...
s, and other wear surfaces in outer space, ultra-high vacuum or dry gas applications. Example
Vespel SP-3


Material properties data


References

{{DuPont Plastics DuPont products