Charting ePTFE (expanded PTFE) Specifications as per Global Standards
One of the toughest things about being the first in a given field is that there is so little data available for testing against.
As the only Indian company manufacturing ePTFE (expanded PTFE) gasket tapes, we are being met with many questions regarding how the properties of our material hold up against those of competing brands operating in Europe and the USA. However, since the material is so new, there do not exist any established testing standards locally.
Basic Initial Data
To counter this, we initially took up the task of importing tapes from other manufacturers and testing the tensile properties and specific gravity against the same. Initially, we were trying to answer only 2 questions:
- How soft should our tape be?
Since the extent to which we expand the PTFE can be adjusted, it directly impacts the specific gravity of the end product. For a like-to-like comparison, we were hoping to match this with global brands. We eventually found that the standard density of ePTFE Gasket Tapes is 0.6-0.65g/cm3
It should also be mentioned that some clients have specifically come to us asking whether they can get the tapes even softer, as their application is such that not much force can be applied to the tape. We have obliged – getting the density down to as little as 0.3g/cm3 in some cases.
- How strong should our tape be?
ePTFE tape looks great coming out of the machine. It is pure white, soft to touch and very smooth. However, two tapes that look exactly the same, could give completely contrasting values when tested for tensile strength. We found that global brands offered tensile strengths in the range of 5Mpa to 10Mpa.
Once we standardized our production process, our own tapes showed a tensile strength of 12Mpa, so we were satisfied with the result
Looking for global standards
Although we were happy with the results of our testing, there were still gaps in our understanding of our own material. Most notably, what were the other properties we should be testing?
Again, going through competitor data provided very little information on this front. Expanded PTFE is a very niche market and from our own experience of getting the product right, we know that not much information can be divulged with regards to the behavior of the material.
We looked around for global standards and realized that although there are many ASTM standards for regular PTFE, for ePTFE there were none. A few competitors had put up data on compressibility (ASTM F 36) and creep relaxation (ASTM F 38), but these were only comparing values to “leading brands” and not referring to any standard for the values. Others simply quoted the values, but did not elaborate the specifications against which these values would hold up.
We also went through the certifications that competitor brands were providing. These included:
- DVGW VP 403 – The German standard for checking ePTFE Tapes
- TUV MUC-KSP-A066 – The TUV Standard for ePTFE
- BAM – For use in Oxygen rich environments
We contacted each of these organizations and were given estimates on how much the testing would cost. However, at no point are any values discussed. These remain guarded by the certification bodies.
Finally, we came upon the one standard that dealt specifically with ePTFE Tapes and was willing to offer values for us to compare against – the AMS 3255A.
The AMS is globally recognized as a leading authority for aerospace related materials. As such, we felt confident that their values would be stringent and thereby an effective standard to hold ourselves to.
The AMS 3255A prescribes many types of ePTFE Tape. Our basic tape falls under Class 2, Type 1, which requires the following properties to be met:
|Tensile Strength (Fluid/Thermal Stability)||8.27||Mpa|
|Low Temperature Flexibility||No evidence of cracking|
|Liquid Sealability||No fluid leakage or loss of pressurization|
|Reparability||No fluid leakage or loss of pressurization|
Armed with the above data and the testing procedures prescribed by the AMS 3255A, we were able to test our material in-house to confirm that the properties we were observing were as per the requirements of the standards.
In addition to this, we were allkknknso able to test the material with local certification bodies – such as TUV, to confirm the properties.
To the best of our knowledge, the AMS 3255A remains the only globally recognized standard to offer any values and/or testing procedures to verify the properties of ePTFE Gasket Tapes.