PTFE semi-finished products and finished parts

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1 Material characteristics PTFE = Polytetrafluorethylene PTFE is excellently suited as a construction material for the chemicals industry. It temperature resistance ranges from -190 C to +250 C, and it can temporarily sustain temperatures of +300 C. Because of its low friction coefficient, it is used as an anti-friction coating and lubrication material. Because of its particularly high insulation resistance and puncture resistance, it can also be used for insulation purposes. Another specific characteristic of PTFE is its extremely antiadhesive property. As a result of its non-stick effect, no substances adhere to PTFE surfaces. PTFE is non-flammable, does not absorb water and is physically harmless to humans. PTFE is considered to be a member of the thermoplastics group, although it is not suitable for injecting or pouring. PTFE is resistant to nearly all chemicals. It is only susceptible to chlorine trifluoride, elementary fluoride and melted alkali metals. Additionally, PTFE will not swell or dissolve in any common organic and inorganic solvent, even at high temperatures. It belongs to the group of weather-resistant plastics. Material types Standard types Material no Filler material none Coal Glass Bronze Graphite Filler material content [%] Please contact Kempchen to request materials with other filler materials and filler content. PTFE without filler material Pure PTFE is used for applications requiring high chemical resistance, strong anti-adhesive properties or very low friction values. PTFE without filler material may be unsatisfactory for certain areas of application. Unsatisfactory characteristics that may arise include a tendency to cold flow under pressure and relaxation at temperatures, the mechanical resistance and the low capacity for heat conduction. PTFE without filler is used for Bellows O-rings Enveloped gaskets* Steering floaters Spheres Back-up rings Construction parts * see section PTFE-enveloped gaskets PTFE-Compositions By combining pure PTFE with various filler materials, individual physical and mechanical properties can be positively influenced. It is important to consider that other properties may be negatively influenced in the process. The following are the primary results to be attained by using PTFE-types with filler material: Reduction of cold flow Increased regidity at high temperatures greater heat conduction greater abrasion resistance The main filler materials used are glass, coal, graphite and bronze. PTFE Glass Adding glass powder drastically reduces the tendency for cold flow in comparison to pure PTFE. This composition has shown superior performance in all types of applications, but particularly Valve rings Flat gaskets* Sealing cones Bearings V-ring packings * See the section PTFE enveloped gaskets PTFE Coal PTFE coal compound is characterised by a low abrasion and high stability. This composition is commonly used as a material for bearings, particularly at very low temperatures. The PTFE coal composition requires special caution when manufacturing moulding blanks for the machining of piston 223

2 rings, piston guide rings and piston rod packings. The construction of modern dry-running compressors would not be possible without these high-grade rings. Typical applications: Bearing bushings Piston rings Piston guide rings for dry-running compressors Rod packings V-ring packings PTFE Graphite When an exceptionally high level of absrasion resistance is required, PTFE graphite compositions are used. This material also has extremely low initial wear. The PTFE graphite composition is characterised by a very low friction coefficient in comparison with the PTFE coal composition. It must be emphasised that PTFE coal and graphite compositions are show particularly high resistance when used in chemical applications. Examples of applications: Shaft sealing Bearings Sliding plates Construction parts PTFE Bronze The PTFE bronze composition has the lowest tendency for cold flow of all the PTFE compositions. This composition is also characterised by a high capacity for heat conduction and superior abrasion resistance. PTFE bronze is therefore recommended as a bearings material in high-stress applications. This composition has limited suitability in chemical applications, as the bronze particles can be attacked and washed away under certain circumstances. PTFE bronze has been shown to be suitable for: Bearings Piston cuffs Guide rings for hydraulic cylinders Foil bearings Extruded hoses Hoses are manufactured on paste extruders using a special process. The finished lengths depend on the diameter and the thickness of the particular wall. Our product range includes hoses from 2 mm to 200 mm in inner diameter. Applications: Laboratory hoses Filler hoses Cladding for pipelines Steam hoses Hose pipes for adhesive media Electrical cable insulation PTFE foils Foils are cutted with a blade from a compact PTFE cylinders and subsequently turned over heated rollers in to release any existing tension. We supply foils up to 00 mm in width and 6 mm thick. Application areas for PTFE foils: Foil bearings All types of gaskets* Cladding for construction parts Compensators and bellows Cladding for chutes and containers Insulation for the electrical industry * See section PTFE-enveloped gaskets Adhesive PTFE foils Non pre-treated PTFE foils are not adhesive. Foils requiring adhesive properties are therefore prepared after cutting using a chemical finishing treatment for adhesion on one side to steel, plastic, wood, etc. The special adhesive required for pasting is available upon request. Adhesive foils are available at up to 00 mm in width and 3 mm thick. 224

3 PTFE V-ring packings V-ring packings are primarily used for sealing with axial movements. A complete set consists of several V-rings with one pressure and support ring each. Compounds with glass or coal are used at higher pressures due to the tendency for cold flow characteristic of PTFE without filler materials. At particularly high pressures, the packing is reinforced by installing V-rings, and pressure and support rings made from bronze or acid-resistant steel. In this configuration, one metal V-ring is installed in the packing after every or every other PTFE V-ring. PTFE wedge ring packings This robust and reliable packing is suitable for sealing valve shafts at high pressures and with abrasive media. The wedge rings are extruded inwards against the shafts and outward against the housing by the pressure of the stuffing box. The stuffing box follower can only be pre-stressed far enough to reliably seal the packing. It is important to note that PTFE without filler material is not suitable for the manufacture of piston rings. We strongly emphasise the importance of working with the proper PTFE composition in order to guarantee the optimal function of the piston rings. The following are application areas for piston and piston guide rings made from PTFE compositions: Dry-running compressors Cold compressors Pumps for abrasive fluids and fluids with poor lubrication Hydraulic and pneumatic cylinders Piston rings are designed with overlapping, diagonal or straight joints, depending on the application. O-rings For applications where the use of O-rings made from elastomers is not suitable whether as a result of chemical attack or excessive temperatures O-rings made of PTFE are used instead. Because of their low level of elasticity, these O rings are primarily used as static sealings. In order to achieve higher levels of elasticity, a is made around the circumference of the O-ring. The placement of the is aligned with the direction of the pressure. During assembling of the O-ring, the expanding is installed against the direction of pressure. We supply seamless O-rings up to approx. 500 mm in diameter. These are also available in a welded design. Piston rings and piston guide rings Today s industry is increasingly in need of compressors that guarantee lubricant-free gas-tight sealing. In applications requiring the compression of dry gases a compressor at high temperatures and piston speeds, equipping the plant with PTFE piston rings is the design engineer s only option. 225

4 without outer axial inner PTFE-enveloped O-rings PTFE enveloped O-rings unify the superior chemical resistance and low friction of PTFE and the elasticity of O-rings made from elastomers. We cover O-rings made from elastomer with a 0.4 mm thick PTFE envelope. The envelopes can be butted or overlapped The butts/overlaps are to be placed on the side turned away from the pressure. Because only the core, and not the envelope, of these special O-rings is elastic, a PTFE-enveloped O-ring may not be strongly expanded or squeezed. Depending on the application area, a material such as viton, hypalon, silicone, neoprene, perbunan or another elastomer may be selected for the O-ring. PTFE Support rings (Back-up rings) The task of the PTFE support ring is to back-up the constant gap between the pistons and the cylinder. The installation of support rings prevents the extrusion of the rubber O-rings into the sealing gap at axial movements to pressures over approx. 2.5 N/mm 2, leading to the destruction of the O- ring. Diameter Gauge diameter Installation dimension range D d B h , , , , , ,0 The advantages of installing support rings made from materials such as PTFE are as follows: butt inside outer overlapping downwards a) Chemical and thermal resistance butt outside outer overlapping b) Creation of a PTFE film on the bearing surface of the cylinder or piston, reducing the frictional factor of the O- ring c) Easy assembling easy disassembling butt frontal outer overlapping upwards d) Significantly longer life cycle of the O-ring. 226

5 Bellows The following bellow types have proven suitable in practice: Because of the great mechanical demands which may be required in individual cases, and the chemical resistance necessary, PTFE bellows are manufactured from special high-grade semi-finished products with total impermeability. prick pointed, type S: most elongation, low pressures cutting round, type R: moderate elongation, medium pressures cutting angular, type E: least elongation, high pressures Type S Type R Type E The shape of bellows depends on the intended application and is based on the operating pressure, operating temperature, required elongation and radial misalignment. Please provide the following technical information when enquiring: Installation length Elongation, +/- Misalignment, parallel and angular Medium Operating pressure Operating temperature In many cases, the sealing cone from a corresponding PTFE composition is sintered onto bellows for fittings without stuffing boxes. 227

6 PTFE compensators These compensators are manufactured of exceptional nighly compressed PTFE material. The extremely flexible and besides pressure-proofed manufactured from a compact block but in a complex manufacturing procedure without destruction of the existing filamentous structure. The compensators are provided with reinforment rings of stainless steel to increase the pressure-proof. PTFE compensators are suitable to absorption axial and radial movement. Also at applications with critical cinditions no symptoms of fatique occur. A especially long duability distinguish this product from others. Temperature operating pressure diagram Type K-102 Type K-103 n xbolt size Hole - Ø DN a D k l 1 Angel α (Dgree) Movement Installation length A (mm) Elongation + (mm) Movement axial (mm) K-102 K-103 n xbolt size Hole - Ø DN a D k l 1 Angel α (Dgree) Installation length A (mm) Elongation + (mm) Movement axial (mm) x , x , , x 18 19, , , x 18 19, , , x 18 21, , x 18 23, , x 18 23, x x x x x x x , x , , x18 19, , x18 19, , x18 21, , x18 23, , x18 23, , x , x , x , x x x x