PTFE for sealing and its variations

PTFE (Polytetrafluoroethylene) - better known by the trade name Teflon®, by Dupont - was accidentally created in 1938 by the chemist Roy Plunkett while experimenting with refrigeration gases. Roy noticed the appearance of a white powder in the cylinder that contained the gas.

Imagine what would have happened if Roy had discarded the substance since his creation was totally outside his research goals?

Since then, PTFE has had several usages, such as coating for household appliances , dental prostheses, artificial bones and in industrial applications for sealing fluids, which is, specifically, what we will address here.

It is important to emphasize that while most elastomers undergo permanent deformation during temperature changes, PTFE has the unique characteristic of resisting degradation and changes in their physical properties, thus allowing a long product life.

They can also be stored indefinitely and can be applied applied in bad weather as the actions of UV rays are inert.

PTFE variations for industrial usage

In the industrial sealing segment, there are three forms of polytetrafluoroethylene: Virgin PTFE, PTFE under applied load and expanded PTFE, which we will cover below.

Virgin PTFE:

Virgin PTFE is how the basic formulation of PTFE without additives and without expansion processes can be called. Because it is the same product, it has high chemical resistance but also high levels of flow and deformation.

Due to the inherent deformation of Virgin PTFE, its gaskets must be applied at temperatures close to the environment, low pressures and in non-critical applications (non-hazardous fluids).

With thinner thicknesses (0,5 mm) it works as an excellent material to be used as an envelope for gaskets and “O” rings, as it creates a chemical protection barrier over the hydraulic or elastomer cardboard gasket.

PTFE under applied load:

The PTFE solution with additives from other substances was introduced in the industry in the 50, 1950s, in order to improve the properties of the virgin PTFE mentioned above. An example of everyday life is Tefal (Teflon + Aluminum) as a non-stick coating.

For the sealing industry, PTFE receives mineral fillers that delay, but do not prevent, the unwanted flow that occurs in virgin PTFE.

Loaded PTFE (microspheres, silica and barium) are formulations that mix mineral additives in the composition of virgin PTFE, making each product suitable for a type of application (acid, alkaline, low torque).

Expanded PTFE:

The PTFE products evolution for sealing has its peak with the expanded PTFE created by the company. Gore on 1969.

The expanded PTFE is manufactured in a process of material traction in one or more directions, increasing its porosity and making it soft.

However, the material has the same composition as a pure PTFE, but with its improved sealing properties and without losing the chemical resistance inherent to the polymer.

The fact that it managed to give the Virgin PTFE a certain softness and porosity ensured that the material was more suitable in relation to the basic sealing characteristics, which are the compressibility and material recovery. Such characteristics ensure that the seal is capable of being compressed and accommodating the flange's imperfections through a crushing pressure.

Not only that, as the expanded PTFE does not have the deformation inherent to other types of PTFE, is able to maintain a resulting pressure (torque of the clamping set) for longer than any other material for similar applications.

PTFE can be expanded unidirectional (image left, below) or multidirectional (image right, below).

In the sealing segment, expanded and modified PTFE is found in blades and gaskets that offer compatibility with almost all chemicals, expanded and modified PTFE is found in blades and sealing gaskets that offer compatibility with almost all chemical products, except fluorine and molten alkali metals .

The high melting point of expanded PTFE, its application at temperatures that can peak up to 315ºC (depending on other factors).

PTFE is also found in compression packings for sealing.

Due to the high chemical resistance of PTFE, the compression packings manufactured with this product , can be used in almost all industry applications and have excellent durability.

We highlight the pure PTFE compression packings used in processes in the pharmaceutical and food industry where there is no product contamination (image above).

With the graphite addition in the compression packings, the resistance to friction is increased and enables use at higher speeds.

As an example, the high-performance GFO compression packing is capable of multiplying the equipment operating time since its graphite amount and braid continuity provide excellent heat dissipation and lubrication for a long length of time, compared to other packing..

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