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PTFE Dichtung

FAQs

Here you can find answers to frequently asked questions about our products, technologies or our company!

How good is the chemical resistance of ePTFE sealing materials?
ePTFE sealings have the same full chemical resistance as usual PTFE. There are only a few exceptions where no full resistance is given, such as molten alkali metals or elemental fluorine.
Are there any resistance lists for KWO ePTFE products?
No. Since all ePTFE sealing materials have the full chemical resistance of conventional PTFE, we refer to the general PTFE literature. A good aid for the chemical resistance of plastics (including PTFE) is the overview of Bürkle GmbH:
Which components contain KWO ePTFE sealings?
There are no other components contained in the ePTFE sealings, apart from the pure PTFE raw material. Only the sealing tapes are equipped with a high-quality adhesive tape for a self-adhesive finishing. The adhesive tape is always smaller than the sealing tape, in order to ensure that the medium to be sealed does not touch the adhesive.
Are the products made of virgin PTFE?
Yes, the raw materials are made of virgin PTFE, that means original and unprocessed PTFE. The special process of expanding requires the use of raw materials with very exactly defined properties. These can only be ensured with a raw material that comes directly from chemical production. The use of recycled PTFE is not suitable for the manufacture of ePTFE products.
Are the self-adhesive sealing tapes suitable for permanent bonding?
No. The adhesive is only used for assembly purposes. Permanent bonding to frames or other components without mechanical clamping, as with flange mounting, is not possible. After installation, the adhesive does not perform any further tasks.
Do wide gaskets seal better than narrow gaskets?
No! In sealing technology, the basic principle is to keep the sealing surface as small as possible in order to achieve the highest possible specific surface pressure (force per surface). This leads to a long-term and higher tightness.
How do I choose the right thickness of ePTFE gaskets?
The thickness of the gasket depends both on the unevenness of the flange surface to be compensated and on the gasket used. Monoaxial gasket tapes can compensate for unevenness of 10 – 15 % of the gasket thickness. A sealing tape of 3 mm thickness thus compensates for gaps of approx. 0.4 mm. Multidirectional gaskets can compensate for unevenness of 15 – 25 % of the gasket thickness. A MultiTex® tape of 3 mm thickness thus compensates for unevenness and gaps up to 0.75 mm. For even steel flanges, 1.5 mm to 2 mm sealing thickness is sufficient. For plastic flanges we recommend a gasket of 3 mm and for glass lined steel flanges a thickness of 6 mm.
What is the main influence to obtain the highest possible tightness?
Surface pressure! The higher the surface pressure on the sealing, the higher the tightness. With high surface pressure, the structure of the gasket is compressed, and the gasket is adapted to the flange surface. This provides perfect conditions for the highest possible tightness.
What is the recommended surface pressure for ePTFE?
A surface pressure of 25 N/mm² or more is the ideal value for all KWO® ePTFE sealing products in order to achieve a technical tightness even in gases with pressure and temperature. For more detailed information and calculation, the sealing characteristics according to DIN EN 13555 are available. The maximum surface pressure should not exceed 150 N/mm².
Are the ePTFE gaskets made of foamed PTFE?
No. The sealing materials are made of expanded PTFE, i.e. stretched PTFE. The process of streching or expanding has nothing to do with foaming. Rather, it is a purely mechanical process in which the tape is stretched by means of temperature and force. This produces the typical fine-fibred fibril structure of expanded PTFE.
Does the embossing of the sheets affect the tightness?
No. The embossing depth of 0.3 mm is very small in relation to the compression of the gasket by at least 0.8 mm. Therefore, there is no influence on the sealing behaviour. The embossing is also an indicator for the correct installation of the gasket: If the embossing is still visible on the gasket after removal, this is a clear indication that the surface pressure was too low.
What is the temperature resistance of ePTFE gaskets?
The material resistance of ePTFE is very high: 270 °C continuous load and short term up to 315 °C. Even under these high temperatures PTFE will not melt, burn, decompose or carbonize. However, the mechanical properties are significantly reduced under high temperatures and the strength is weakened. For this reason, you will find on our data sheets corresponding information on the recommended operating temperatures. These are +150 °C for Universal tapes, +200 °C for CellFlon® tapes and +230 °C for MultiTex® tapes.
Why are ePTFE gaskets used compared to other PTFE gaskets?
An ePTFE gasket has the highest material resistance and high heat resistance. It is a pure material with no other impurities. The creep behaviour of the material is very low or even shows no creep at all. In addition, it offers the best adaptation to uneven surfaces, ensuring a reliable sealing in operation, even if force is lost on the gasket. The material ePTFE is characterized by easy processing and can be used universally for all shapes and sizes.
What's a diffusion leakage?
A leakage through the gasket, which occurs especially when the compression is too low.
What is an interface surface leakage?
This is the leakage between the sealing surface and the gasket. It hardly occurs at all with ePTFE, as the surface adaptation is unequalled.
What is the purpose of fillers at CellFlon® sheets?
The fillers reduce the otherwise very strong creep of pure sintered PTFE.
Can ePTFE be used in nuclear power plants?
Yes, but only in secondary supply areas subject to low radiation, such as cooling water supply. Primary areas are not suitable because of high radiation. However, they are not suitable for PTFE because of the high temperatures and pressures. PTFE is damaged by radioactive radiation over a longer period of time.
How can large unevenness in flanges be compensated?
In case of large unevenness, relining of the tape material is a very good possibility. The procedure can be found in our assembly instructions.
What problems can be caused by pressure peaks? When do pressure peaks occur?
Pressure peaks can occur e.g. with glass lined steel flanges. This can be counteracted with a min. 6 mm MultiTex® gasket.
How much is a gasket compressed?
Universal sealings deform to about 20 %, MultiTex® sealings to about 40 % of the initial height.
What is the durability of PTFE?
PTFE is not subject to ageing and can be stored indefinitely. The adhesive strength of the adhesive strips of self-adhesive tapes is reduced after approx. one year.
What is the difference between monoaxial and multidirectional tapes?
Monoaxial tapes have a typical operating temperature of up to 150 °C and become much wider. Multidirectional sealings are dimensionally stable and therefore have a much wider temperature range.
Are the products food safe?
All KWO® products are made of 100% ePTFE and are therefore typically suitable for use in the food industry.