in Die ignoranten Massen
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We have spent a significant amount of time looking at liantuo China PTFE Tubing as a material, comparing it to other materials and analyzing its uses based on the various properties it exhibits. However, our focus has been purely on “virgin” PTFE – namely, PTFE in its pure form. In this form, PTFE takes on an opaque-white hue, is best describes as a soft-waxy material and is smooth to the touch.
Compounding PTFE refers to the mixture of PTFE with additives, which would both add and remove certain characteristics from virgin PTFE. It is essentially a mixture of PTFE with other substances – done for the purpose of enhancing one or more of the characteristics of PTFE, so that the compounded material would be a better overall fit to a given application.
Before we delve into the various compounds, let’s look briefly at the process behind PTFE compounds.
In truth – most of the large resin manufacturers (DuPont, Daikin, Solvay etc.) have focused on manufacturing virgin resins and left the compounding to smaller companies – who buy the virgin resin and use it in making their compounds. Although the compounder is very much the owner of the product’s quality – it must be mentioned that the input resin does have a huge impact on the final quality of the compounded grade.
For example – we had procured a large quantity of PTFE+Bronze resin from a Chinese company, only to find that when we moulded large pieces from the resin (in excess of 15-20 Kgs per piece) – the pieces would crack during sintering. When we took it up with the supplier, it became apparent that the base resin was of a poor quality, and unsuitable for large pieces.
The compounding process is usually a proprietary technology of the compounder. However, technical literature will point to one of two ways to compound resin:
1. - Physical blending – a physical process, done in an industrial blender where PTFE and the additives are added in the required proportion. The blended powder is then sifted through a mesh to separate the mixture from ‘lumps’ of PTFE that tend to form during blending. The process is repeated until all lumps are suitable removed.
Blending like this is a tedious process, and requires much iteration. Even when care has been taken, small lumps may still remain which will result in patches of white (assuming the blend is pigmented) on the final product.
- Chemical blending – this is more expensive, but also ensures fewer iterations and more uniformity in the blend. A range of chemicals is available for this process – but the basic principal is to have a liquid aid with a lower surface energy than PTFE. This will allow the pigment to flow in between the PTFE molecules so that even the lumps are suitably coated with the pigment.
However, the finer aspects of compounding are usually learnt only through experience and remain a technology that compounders would not part with easily (understandably!). PTFE Sheet: http://www.liantuoptfe.com/