Thermoplastic Seals by Synertech
PTFE
What is PFTE?
Polytetrafluoroethylene (PTFE) is a polymer used in a variety of industrial sectors:
- PETROCHEMICAL
- PHARMACEUTICAL
- CHEMICAL
- FOOD
- HYDRAULIC
- AUTOMOTIVE
- ELECTRICAL
- VALVE COMPONENTS
Its main characteristics
- chemical inertness: PTFE is inert to all reagents. It is attacked only by some alkaline metals, fluorine and chlorotrifluorine at high temperatures and pressures. Insoluble in any solvent at temperatures up to 300 °C;
- heat resistance: it is a thermal insulator. It is not flammable and remains stable at temperatures up to 260 °C;
- dielectric characteristics: it has excellent dielectric qualities in a wide range of frequencies and temperatures. It does not absorb water so it can be exposed to atmospheric agents;
- resistant to aging;
- self-lubricating characteristics and minimum friction coefficient.
Fillers and mechanical properties
The virgin PTFE polymer can be filled with “fillers” to increase some of its properties, for example:
- better resistance to compression
- better thermal conductivity
- lower expansion
- reduction of the wear rate
From a mechanical point of view, among the properties of greatest interest are the resistance to compression and deformation, the latter under load and constant temperature.
Sealing profiles
The properties of PTFE described allow it to satisfy the applications in sealing systems. Accompanied by elastomers of different composition (e.g. back-up anti-extrusion rings) or by energized metal springs for dynamic seals (on cylinders, rods and rotating parts), or static (on flanges).
Bearings, valve seats, stuffing boxes, are some of the destinations combined with the suitability for contact with food and pharmaceutical products.
Combinations
GLASS loaded: High wear resistance, high chemical resistance (except alkalis and hydrofluoric acid). Valve seats, seals, bearings that must resist sliding and chemical attack. Suitable for bearings operating at low PV values.
GRAPHITE loaded: Very low friction coefficient, medium resistance to compression. Good resistance to wear. Bearings for applications in high speed conditions and in contact with medium hardness surfaces.
CARBON loaded: Good thermal conductivity. Good resistance to deformation. Bearings for applications in high speed conditions and where the dissipation of electrostatic charges is required. Piston rings for compressors operating in the absence of lubrication.
BRONZE loaded: High resistance to compression. Good resistance to wear and high thermal conductivity. Bearings operating at high speed and without lubrication. Suitable for operating in contact with non-hard counter surfaces.
Other technopolymers
DEVLON
For applications above filled PTFE, Devlon® provides good resistance to oils, greases and solvents. Its low water absorption provides superior dimensional stability.
TFM
It is a chemically modified PTFE, which offers enhanced properties for certain application sectors (electrical, mechanical, chemical, ...). The advantages of conventional PTFE are retained.
- lower deformation under load
- lower permeability.
- high weldability
PCTFE
This material has remarkable mechanical properties in a wide temperature range. Direct contact with water or high humidity does not alter its dimensions, in fact it remains an excellent electrical insulator even in critical conditions of temperature and pressure.
Its properties:
- thermally stable from -240°C to 204°C,
- excellent chemical resistance to all corrosive inorganic liquids,
- it is flammable,
- resists steam and liquids (such as liquid gas),
- has high transparency,
- resistant to ionizing gases.
PEEK
Peek is a polymer (compression molded) used in various industrial sectors and particularly in applications where high performance is required; it has:
- thermal resistance (it maintains its properties unaltered when exposed to a wide thermal range up to 260°C),
- high mechanical properties and sliding stability (even at high temperatures),
- high resistance to abrasion and dimensional stability,
- excellent resistance to chemical aggression (even at high temperatures) and hydrolysis,
- good thermal insulation and resistance to radiation.
Other seals and rings
Spring-energized seals
These seals are mainly made of a PTFE casing (so-called jacket) or other polymers, inside which a metal spring is housed. The spring, compressed against the walls of the casing, remains elastic and compensates for wear and misalignments of the system.
The properties of the technopolymers seen in the previous pages combined with the action of the spring, resistant to corrosion, allows this sealing element to satisfy a wide range of applications, mostly extreme.
- temperatures from -260 °C to +315 °C,
- rotary movements and vertical motion,
- static (3500 Bar) and dynamic (550 Bar) applications,
- resistance to the action of chemical products,
- vacuum applications and HUV applications;
- customization of dimensions and profiles.
Backup anti-extrusion rings
In addition to spring-energized seals, in some situations, the use of back-up anti-extrusion rings is required. The ring profile is functional to a series of variables such as
- the size of the gaps,
- temperature,
- pressure,
- resistance to the action of chemical products.
Spiral wound gaskets
A metal strip with a shaped profile together with a technopolymer strip that acts as a filling, in PTFE or graphite, are wrapped and welded in turn by metal coils. They guarantee a perfect seal in extreme temperature and pressure conditions, recovering the linear excursions resulting from the expansion of the components.
Some applications:
- autoclaves
- heat exchangers
- refining plants
- chemical and petrochemical
- valves
Graphite rings
A graphite tape wound and pressed to the desired density allows to obtain:
- resistance to chemical agents and ageing,
- stable to compression and thermal shock (use as a seal Fire-safe),
- resistant to very low temperatures down to -55 °C,
- in inert and reducing atmospheres up to 300 °C,
- excellent sliding and wear resistance on shafts.