PTFE Properties and Applications of an Exceptional Compound The partially crystalline PTFE compound is derived from the polymerisation of monomer TFE. The macro-molecules generated in this process have a linear structure. The chain structure of PTFE has two interesting peculiarities: The carbon-fluorine compound is one of the strongest compounds found in organic chemistry (dissociation energy 460 KJ/MOL). The carbon chain is nearly completely covered by fluorine atoms, thus being protected against external influences. This results in the exceptionally high chemical resistance of PTFE. Physical and Chemical Properties of Unfilled PTFE The Specialty of Unfilled PTFE is its Combination of Superior Properties which is Unique among Plastic Compounds Exceptionally wide range of thermal appli-cations from minus 260°C to plus 300°C (short-term) Virtually universal chemical resistance Light- and weather-resistant Resistant against hot water vapor Excellent sliding properties Anti-adhesive behavior Non-combustible Good electric and dielectric properties No absorption of water Physiologically harmless (BGA- and FDA-approved for use in food industry applications) Unfilled PTFE has the following, more or less adverse properties: Cold flow behavior Relatively low wear resistance Low resistance to high-energy radiation Poor adhesive behavior PTFE cannot be injected.
Products... Radial shaft seals Seal/guiding elem. for compr. Spring-energized seals Memory packings Metaloseal PTFE-hoses PTFE-foils PTFE-bellows Diaphragms Multi-channel nozzles Rollers for high-tech appl. PTFE bellows complete piston assemblies

PTFE-Compounds PTFE is mixed with fillers for the follow-ing reasons: Significant increase of wear resistance Substantially enhanced resistance against creeping or deformation under load Significant increase of thermal conductivity depending on type of filler used Reduced thermal expansion Possibility of changing electrical properties of PTFE, if needed, by using appropriate fillers Selection of appropriate filler will also impact upon the wear behavior of the contrarotating surface.

Impact of Fillers on Properties and Applications Selection by Compound No. HS 00PRW HS 000RW HS 17022 HS 17019 HS 17020 HS 17027 HS 21027 HS 11018 HS 17034 HS 21054 HS 11031 HS 11035 HS 11041 HS 17100 HS 21029 HS 21037 HS 21059 HS 21060 HS 4080 Select by filler Without filler Graphite Carbon Carbon/Graphite Glass Fibre/ Graphite Glass fibre Bronze/MoS2 Special Compound Compounds,table of the properties

Thermal Properties
Service temperature limits of selected fluoroplastics Melting ranges: PTFE 320-340 °C PFA 300-310 °C FEP 260-290 °C ETFE 265-278 °C PVDF 170-180 °C				Thermal Resistance The thermal resistance of PTFE has a range of minus 260°C to plus 300°C (i.e. no embrittlement in boiling helium at –269°C). No other standard industrial compound can achieve this temperature range. However, continuous operating temperatures depend on the respective stress factors. In practical terms, this means that, under moderate mechanical stress, PTFE may be exposed to temperatures ranging from minus 200°C to plus 260°C. Thermal Expansion When designing components made of PTFE, the relatively high degree of thermal expansion must be taken into consideration: 20-100 °C: = 16 · 10-5 1/K 20-200 °C: = 23 · 10-5 1/K Recordings of the linear expansion coefficient reveal two conspicuous findings: At 19°C there is a conversion within the crystal grid (<19° triclinic, > 19°C heax-agonal) At app. 327°C there is even higher unsteadiness, i.e. the crystal melting point Please note: When performing precision measurements of PTFE components with narrow tolerances, a measurement temperature above 19°C is imperative. As a general rule, PTFE compounds have a lower thermal expansion. The following chart depicts the correlation between temperature and thermal expansion.
Relative length change of PFEF as a function of temperature Coefficient of linear thermal expansion of PFEF as a function of temperature

Chemical and Physical Behavior
Absorption of Water Water absorption of PTFE practically equals zero. Even after long submersions in water, according to DIN 53472/8.2, no absorption of water has been noted. Physiological Properties Unfilled PTFE is physiologically neutral. PTFE has frequently been implanted into living tissue without any incompatibility having been noted. FDA- and BGA-approvals can be documented, resulting in permissible application in medical as well as food industry applications. A highly positive factor in this context is the resistance of PTFE against hot vapor, which means that PTFE parts can be sterilized effec-tively in medical, pharmaceutical or food in-dustry operations. Sliding Properties Extremely low intermolecular forces are the reason why PTFE offers the lowest friction coefficient of all solid compounds. PTFE static and dynamic friction coefficients are nearly identical. This means that there is no stick-slip effect. Even at temperatures of below 0°C, these favorable sliding properties are pre-served. Starting at 20°C, the friction coefficient of PTFE shows a slight increase, while modifying PTFE with fillers will only have an insignificant impact on the friction coefficient.		Chemical Resistance Due to the strong fluorine-carbon compound and nearly complete shielding of C-atoms by fluorine, PTFE offers virtually universal chemical resistance. Neither solvents like alcohols, esters, ketones, nor aggressive acids (like fuming sulphuric or nitric acid, hydrofluoric acid, etc.) will change the properties of PTFE. Merely when used in coolants (freons), a reversible weight increase between 4 and 10% has been measured. A minimal chemical reaction (browning) of PTFE will only occur with melted alkali metals. Under higher temperatures and pressures, PTFE will react with elementary fluorine- and chlorine trifluoride. For these reasons, PTFE does not require consultation of extensive charts and/or resis-tance listings. Light and Weather Resistance PTFE has excellent light and weather resistance. For this reason, PTFE offers unlimited suitability for outdoor applications, including extreme weather conditions, without producing any notable changes of its mechanical or electrical properties. Coefficients of friction of PTFE/pearlite iron dry running (p = 0,2 N/mm2, T = 30°C, Rt perlite iron <1,5 µm) . Rubbing speed PTFE-Type v = 0,5m/s v = 1,0 m/s PTFE + unfilled 0,25 0,27 PTFE + 15 % glass fibre 0,15 0,15 PTFE + 25 % glass fibre 0,15 0,15 PTFE + 15 % graphite 0,14 0,14 PTFE + 25 % Carbon 0,22 0,21 PTFE + 60 % bronze 0,20 0,22

Physical properties of PTFE compared to fluorine-containing thermoplastics
Material				PTFE	FEP	PFA	PCTFE	PVDF
Properties		Testing methode	Unit	.
Density	23 °C	DIN 53479	g/cm3	2,15-2,19	2,12-2,17	2,12-2,17	2,10-2,20	1,76-1,78
Tensile strength at break	23 °C	DIN 53455	N/mm2	22-40	18-25	27-29	30-38	38-50
Percent. elong. at break	23 °C	DIN 53455	%	250-500	250-350	300	80-200	30-40
Ball indentation hardness	23 °C	DIN 53456	N/mm2	23-32	23-28	25-30	30	65
Proof-resilience	23 °C	DIN 53455	N/mm2	10	12	14	40	46
Modulus in tension	23 °C	DIN 53457	N/mm2	400-800	350-700	650	1000-2000	800-1800
Modulus in flexure	23 °C	DIN 53457	N/mm2	600-800	660-680	650-700	1200-1500	1200-1400
Flex. stress at conv. deflex.	23 °C	DIN 53452	N/mm2	18-20		15	52-63	55
Shore hardness D	23 °C	DIN 53505		55-72	55-60	60-65	70-80	73-85
Melting temperature	.	ASTM 2116	°C	327	253-282	300-310	185-210	165-178
Cont. service temp. without load	.	.	°C	260	205	260	150	150
Coefficient of thermal exp. 10-5	.	DIN 52328	K-1	10-16	8-14	10-16	4-8	8-12
Thermal conductivity	23 °C	DIN 52612	W/K · m	0,25	0,2	0,22	0,19	0,17
Specific heat	23 °C		KJ/kg · K	1,01	1,17	1,09	0,92	1,38
Oxygen index	.	.	%	>95	>95	>95	>95	>43
Water absorption	.	DIN 53495	%	<0,01	<0,01	<0,03	<0,01	<0,03

Wear Behavior

Wear resistance of pure PTFE is relatively low. This is due to the fact that PTFE particles are not compounded in a true melting process but are bonded together in a more or less mechanical manner during a sintering process. Significant improvement of wear resistance is achieved through the addition of fillers like carbon, graphite, glass fibers, bronze or organic fillers. Compared to PTFE filled with mineral or metal substances, the new special compounds, HS 21029, HS 21037 and HS 17100, offer clearly enhanced abrasion resistance even under absolutely dry operating conditions as well as extremely low settling tendency even with unhardened surfaces. The slide-friction coefficient of the respective running mates has no major impact on abrasion behavior. Rather, wear is contingent upon operating conditions (medium, pressure, speed, temperature, lubrication). Because no single PTFE compound can meet all of the respective requirements, the PTFE type optimally suited for the respective application must be investigated.

Abrasion of Unfilled PTFE vs. Various PTFE Compounds test parameters: Test atmosphere: Air T=100°C v=4 m/s p=0,42 N/mm2 Rz= 2 µm Test duration: 100 h

Adhesive Behavior Adhesion of pure PTFE is extremely low (anti-adhesive). This is due to the carbon chain being shielded by fluorine atoms and their low polarization ability. For this reason, PTFE is difficult to moisten (contact angle with water 126°). Principally speaking, the same applies to PTFE compounds. Advantage: No adhesion to media for component linings and/or shrouding. Disadvantage: Due to poor moistening ability, PTFE cannot be bonded to other surfaces in this condition.

Adhesion and Welding Capability Low inter-molecular forces and minimal polarization capability of fluorine atoms are the reasons for the poor adhesion capabilities of PTFE. Therefore, the prerequisites for adhesion must be created by chemically pre-treating the respective surface, i.e. by sodium dissolved in ammonia. Another means of bonding can be achieved by "welding”, using a hotmelt adhesive made of PFA or FEP. Advantage: The PTFE surface requires no etching. Disadvantage: Weld-bonding occurs only at extremely high temperatures of 300-330 °C (= Crystallite melting temperature of PTFE). Electrical Properties The following chart shows some of the electrical parameters of fluorine plastics. Material . . Properties Testing method Unit PTFE Dielectric constant DIN 53483 103 Hz 106 Hz 2,1 2,1 Dielectric dissipation factor DIN 53483 103 Hz·10-4 106 Hz·10-4 0,3 0,7 Resistivity DIN 53482 · cm 1018 Surface resistance DIN 53482 1017 Tracking resistance DIN 53480 . KA 3c Arc resistance DIN 53481 KV/mm 40-80 Dielectric strength ASTM 495 sec. >360 It is a notable aspect that the specific volume resistance of PTFE remains nearly constant up to app. 150°C- Furthermore, the low dielectric constant and the low dielectric loss factor of PTFE are particularly interesting features. With a non-porous PTFE film with a thickness of 0.2 mm, the dielectric strength amounts to app. 60 KV.

PTFE and PTFE Compound Deformation under Load For the most frequently encountered type of load stress, i.e. pressure loads, the chart below provides respective characteristic values. These clearly reveal the lower deformation of PTFE compounds containing 25% of carbon and/or 60% of bronze fillers, as well as the modified types. Deformation under load acc. to ASTM D621 (15N/mm2, 100 h, 23°C, compression-molded specimen: &Mac198; 10 mm, 10 mm high)

Cold Flow Behavior When subjected to constant tensile stress or pressure loads, PTFE will already escape, i.e. flow, at room temperatures. This behavior is contingent upon the pressure or tensile stress exerted, the duration of this stress as well as temperature. Due to these properties, PTFE parts subjected to higher levels of mechanical stress are either encapsulated, thus preventing their escape, or PTFE compounds with clearly enhanced pressure resistance properties will be chosen. Combustibility Combustion tests have shown that fluorine polymers are the most difficult of all plastic compounds to ignite. The gaseous decomposition products will only ignite when located within reach of an external flame. As soon as this flame is removed, the combustion process will immediately cease. Ignition temperatures measured with semi-finished PTFE products according to ASTM D 1929 are within the range of 500 to 560°C, the LOI-index (oxygen index) is 95%. Compression-Sintering PTFE powder is fed into a cylindrical tool and then condensed under high pressure. An important requirement of this process is that the air contained inside the tool can almost completely escape. The powder is then compressed on speed-, pressure- and time-controlled hydraulic presses. After the compression process, the pre-molded parts are sintered in electrically heated, circulating-air ovens according to specified programs. For optimum compound properties, compression and sintering parameters must be adapted to the respective PTFE compound.

PTFE and PTFE compounds deformation under load Test temperature: 23 °C Test duration: 100 h High-Energy Radiation PTFE is a plastic compound which is not resistant to radiation. For this reason, PTFE should not be used in rooms exposed to radiation. Extremely high doses of radiation may cause PTFE to decompose, generating gaseous tetrafluoride ethylene. The polymer properties will begin to modify starting at an absorbed radiation dose of 102 J/kg. With a radiation dose of 5 &Mac215; 104 J/kg: reduction of tensile strength by 50-90%. reduction of elongation at break by >90% Processing Processing of PTFE is more difficult than that of standard thermoplastics. At high temperatures (340-380°C) PTFE will merely become highly viscous, which means that injection-molding or regular extrusion is impossible. For this reason, semi-finished products are manufactured by means of compression-sintering or ram-extrusion. Ram-Extrusion Ram-extrusion is a compression process enabling the production of continuous profiles. In this process, a granulate is fed to a cylindrical extrusion pipe via a metering device, condensed by a hydraulically activated ram, and then conveyed through a field inside the pipe heated up to sintering temperature. Inside the sintering area, the individually metered batches "melt together” into a continuous profile.

Elring Products Made of PTFE Guiding elements for pistons and rods Radial shaft seals with PTFE sealing lip Engineering design elements Diaphragms in PTFE-Elastomer-Compounds Elring Spring-Energized Seals Elring Memory Packings PTFE tubes Piston rings for compressors Packings and stepped seals Bellows

Summary Thanks to its exceptional properties, PTFE as well as its compounds provides design engineers with a host of new features for resolving design issues. With its unusual characteristics, PTFE is a special plastic compound suitable for numerous areas of application: Sealing and sliding elements in machinery and automotive manufacturing Corrosion protection in chemical industry applications Insulating compound for electronics and electrical engineering Shrouding and coating of pistons, heating elements, rollers, diaphragms, etc. Medical implants as well as medical equipment and componentry Food industry Tubing/hoses for chemical, pharmaceutical and automotive applications Despite higher compound costs, PTFE parts may offer greater cost benefits than conventional volume plastic compounds. For critical applications, PTFE offers longer service life, higher operating safety and enhanced functions, thus providing customers with an additional competitive edge in a challenging market environment.

Innovations in plastics – for over 40 years we have been one of the technology leaders for seals and engineering design elements. For our customers around the world we develop and produce solutions that stand the test of practical application: from PTFE and PTFE-compounds, thermoset and other high-performance plastics as well as PTFE-composite components including plastics or metals. As single, custom solutions, up to dimensions of 3,000 mm, or from an extensive portfolio of standard series. Our products can be found in virtually any industry as well as in medical technology. Our merger with Venus and the integration of the Venus product portfolio now puts us in a position to offer you PTFE processing capabilities that rank among the most extensive in the world. Benefit from our expanded capacities to deliver complete solutions from the semi-finished product through to the functional solution custom-tailored to your needs. Your previous points of contact are ready to serve you with additional options and greater flexibility. Together, we’ll make the best of plastics for you. PTFE plays a key role in this – a compound with unique properties for engineering applications, even under extreme conditions.