PTFE (Teflon®) Tubes as Insulators

The benefits of PTFE as an electrical insulator are well known. The high dielectric strength and breakdown voltage of PTFE allows it to be used in applications where standard insulation materials would fail.

In our experience, we have seen PTFE skived tapes used as wrapping around high-voltage junctions and circuits, PTFE components used as transducer covers and high-voltage casings and PTFE pads used to shield metal bodies from one another in electrical and thermal applications.

PTFE (Teflon®) tubes find similar uses as electrical insulators, although one really needs to dig deep to see where exactly they are used. Ever since we started manufacturing PTFE (Teflon®) Tubes, we have begun exploring its application and approaching various clients currently making insulation assemblies to understand whether there is a possibility to use PTFE in their products.

PTFE (Teflon®) Tubes in Cables

The requirement of cables to have a single outer casing that houses a variety of conductors necessitates the use of an insulating medium. PTFE tubes are used to shield each conductor from the next. In this application, it is essential that the tube is both flexible and free of any cracks/inclusions that would affect the insulating properties.

Additionally, since the requirement may be for a cable that is continuous and without joints, the PTFE tube would itself need to be continuous. It is therefore imperative to be able to manufacture a continuous tube that would be free from any defects for a length of at least 150 to 300 meters.

It has taken extensive research and multiple trials to attain a level of extrusion that guarantees a flawless, continuous length of tube.

PTFE Tube forms the insulating medium around the cable core

PTFE (Teflon) Tubes in Short Neutral Sections

While the tubes used inside cables are usually thin-walled tubes (within 1mm wall thickness), there are applications where thick-walled tubes form the outer casing of insulating assemblies.

The Short Neutral Section (SNS), is an insulating assembly used in overhead lines for the railways. Typically, the pantograph will run along a high-voltage wire above the train, allowing current to be supplied to the train. The current is drawn from a sub-station and when switching from one sub-station to the next, the pantograph will pass over the neutral section. The assembly ensures that the wires from two separate sub-stations do not make contact. Hence, it is important for the insulating medium to be effective. Furthermore, since the pantograph runs over the neutral section at high speed, it requires an insulator that is also capable of high wear resistance.

We were approached by the railways to develop this assembly. The core of the product is the thick-walled PTFE tube, which is combined with additives to improve wear resistance, while maintaining the dielectric properties.

PTFE Tube used as an outer sheath for electrical and wear properties

Conductive or Anti-Static PTFE Tube

Because PTFE has such a high resistance to current, there are areas where this becomes a problem. With no way to pass through PTFE, there is the possibility that excess static discharge simply collects on the surface of the material. Once a critical mass of discharge is reached, there is a high possibility of sparking.

In applications involving flammable vapours, such sparking can be very dangerous. To mitigate this issue, fillers such as carbon are added to PTFE to allow for some static discharge to take place through the material. The addition of carbon reduces the insulating properties of PTFE to some extent, but the end properties of the material are still far above any regular insulators.

There are multiple other uses for PTFE (Teflon®) Tubes across industries. As old designs are upgraded, it is important for product designers to keep in mind that PTFE has properties that make many of the older insulating materials obsolete.

Note: Teflon® in the registered trademark of Chemours™

ePTFE Membranes – The Possibilities are Endless

It doesn’t require a scientist or an engineer to take a basic property of a material and extrapolate the possible areas of application.

We have spent the last one year developing ePTFE membranes, as we saw it as a key growth area within the PTFE space. As a technology, it remains obscure. Yet the demand for this product is so vast that it is no wonder that the few companies that have perfected it have been able to command the market (and by extension, the price).

To say that we have perfected ePTFE membranes would still be an overstatement. Being an SME, we have had to focus our R&D in those areas where clients have shown interest, rather than take a broader approach and simultaneously develop multiple variants. However, in our pursuit of client satisfaction, there have been consistent findings that have slowly allowed us to start tapping into the broader demand in the market. In addition to this, what we know about the property of the material gives us insights into other, perhaps less explored areas of application.

To start with, let us lay out the most fundamental property of this material:

ePTFE membranes allow gases and vapours to pass, while restricting liquids

This ability is what lays the foundation for the myriad applications (and potential applications) of ePTFE membranes. When coupled with the other properties of PTFE – such as temperature resistance, chemical inertness and dielectric strength – it is easy to see why the product is so much in demand.

1. ePTFE Membranes in Automotive Vent Applications
   
   Auto is a well traversed industry for ePTFE usage. We started our development of ePTFE membranes when we were asked to replicate an automotive vent as manufactured by Gore. The vent is a small disk of ePTFE membrane, with an adhesive backing. We were able to develop it in both virgin form and with a carbon filling.The purpose of this vent is to sit on a small opening at the back of the headlamp chamber. Any moisture that could potentially fog the headlights and/or condense within the chamber is released via the vent. However, as the vent is only permeable to gases and not liquids, water is no allowed back into the headlamp chamber, keeping it free from moisture.
   
   
2. ePTFE Membranes in PCB applications
   
   The effect of moisture on PCBs is well known. Apart from rust and corrosion, the presence of excess moisture can cause multiple short circuits, destroying the device within which the PCB is operating.ePTFE membranes are ideal in allowing any moisture built up within the PCB assembly to escape. At the same time, in the event of direct exposure to liquids, the ePTFE membrane shields the PCB, keeping it dry.
   The usefulness of this application is seen in nearly every industry where electronics are used. With mobility becoming more important, the chance of exposing a device to moisture becomes nearly unavoidable (think, dropping your smartphone into water). Having the protection of a breathable ePTFE membrane means the device is less likely to fail in such an event.
   
3. ePTFE Membranes in Cable Wrapping
   
   We have covered this in an earlier post. However, it is useful to reiterate that the high dielectric capabilities of ePTFE drive its use as a cable wrapping medium.ePTFE insulator tape can be made with tightly controlled thicknesses of as little as 0.05mm, with a uniform density, and dielectric constant. Wrapping individual conductors in ePTFE can cut interference, noise, cross-talk, and signal attenuation. In some applications, ePTFE tape helps limit phase shift to 4.3° and signal attenuation to 0.05 dB at 110 GHz.
   
4. ePTFE Membranes in Filtration
   
   Multiple applications within filtration exist for the use of ePTFE. Filtration itself requires different levels of porosity and pore size and the membrane needs to be customised accordingly.
   
   One of the most commonly known filters is used in vacuum pumps. It consists of a single ePTFE layer, moulded into a polypropylene housing (see below).
   
5. ePTFE Membranes in Desalination
   
   We believe this may be a huge growth area going forward. Desalination is an expensive process currently. An ePTFE layer could be used to allow for evaporated vapours from a salt water reservoir to pass through it and into an upper chamber. Consequently, it would prevent the condensed liquid from re-entering the salt water reservoir. In this manner, the water is separated from the salt using only solar energy. Spread over a wide enough area, this could effectively trap evaporating sea water to convert to fresh water.

We expect to continue adding to this list as more uses of ePTFE membrane become apparent. One thing we do know is that is a material of the future and that being able to modify and customise its texture and form would be a key proprietary skill going forward.

PTFE Pricing – Is volatility making a comeback?

An introduction to PTFE Pricing

Being a niche industry, PTFE doesn’t exactly get a lot of press even when large shock waves surge through it, disrupting the operations of manufacturers and end-users alike.

In 2010-11, the price of virgin PTFE began climbing, after having dipped consistently over the preceding 5 years. What started out as an understandable correction soon turned into an all-out crisis, as the price nearly quintupled over the next 8-10 months.

Imagine that scenario in any other industry. If the steel price to see a 5x increase in less than a year, what horrors would that unleash into the broader market? That the PTFE industry survived is a testament to the incredible properties of the material, that make it so difficult to substitute using other polymers.

To make matters worse, since the industry is small, there was no one to really make sense of the economic factors driving the price increases.

We stepped in at that time, partly driven by our own need to analyse the situation, but also because the information we collected seemed like it would be useful to other industry players.

Many articles were released between 2011 and 2013 that charted the various drivers of PTFE pricing and made sense of the driver that would play out going forward.

April 2011 – What’s the matter with PTFE prices?

May 2011 – The mysterious relationship between Fluorspar and PTFE prices

August 2011 – Mapping the PTFE Price Increase

December 2011 – PTFE Pricing Again – is there another price hike in the offing?

March 2012 – PTFE Prices – taking a step back to leap forward?

February 2013 – Mapping the PTFE Price Increase – An Update

Over the past few months, there have been murmurs of a return to the high pricing seen in 2011. Resin suppliers have offered ample warning that a price revision was imminent. So far, this has translated into 2 price corrections to the extent of 10-15% and 8-10% in the months of April and May respectively.

We need to compare this with the escalations seen in 2011-12 and understand that the rise is not quite so sharp. Nonetheless, we also need to compare the cost drivers and ensure that the same pattern is not repeating.

Key Drivers of PTFE Price

Unlike other polymers – such as polythene, polypropylene and polycarbonates, PTFE does not result as a by-product of the oil refining process. This comes as a shock to many, who assume that our fates are tied to oil prices and that we should therefore be benchmarking our final rates accordingly.

PTFE is made from the polymerisation of R22 gas – a refrigerant that finds its use mainly in the air conditioning and refrigerator industries. As a result, PTFE prices are driven by the demand and supply of R22.

When prices started increasing in 2011, the key driver was thought to be Fluorspar – a mineral that is critical to the manufacture of R22. In conjunction with this, a spike in demand from the AC and refrigerator markets in China along with a general crackdown on R22 usage (as it is not an environmentally friendly gas) caused prices to shoot up.

Today, the scenario is slightly different.

For one – we’re over halfway through the summer, so we’re not likely to see any shocks due to AC and refrigerator demand. Furthermore, Fluorspar supply has also regularised. A key effect of the price increase in 2011 was that idle Fluorspar mines in South Africa were reopened, offering an easing of supply to the market that was otherwise dominated by China.

If industry insiders are to be believed, the key driver this time around is environmental. China has been actively seeking to clamp down on R22 usage and has, in the process, shut down two PTFE plants that were not adhering to the standards. It is from here than the supply constraint has originated, driving up PTFE raw material prices within China. Obviously, as the China price is usually the floor price for most goods in the world, this has allowed resin manufacturers around the world to increase rates accordingly.

Where the prices go from here depend on three factors:

1. Whether the shut-down plants will be coming back on line after making the necessary changes
   
   It is yet unclear if the plants have been permanently shut down or are only undergoing an overhaul to make them compliant with the environmental codes. If they do come back online within the next 6-8 months, we would see a return to lower prices
2. Whether the move to phase out R22 will go as scheduled
   
   R22 is being phased out not only in China, but all over the world. India has also committed to stop using the gas completely by 2032. If this phase out continues, it could result in a supply surplus to the PTFE industry, driving down prices. However, if the use of R22 in PTFE is itself restricted, then it would require a shift to alternatives of R22, which would be
   
   expensive.Currently, as there is no talk of restricting R22 in PTFE specifically, it is likely that the former would result
3. Price inelasticity of PTFE
   
   In 2011, one thing that was made clear was that even at 5x multiples, there was still demand for PTFE resins. This allowed the resin manufacturers to continue increasing prices well above the rates that would have resulted from purely economic factors.

Ultimately, it was due to competition from China that forced prices back to normal levels.

In the short term, it is likely that resin suppliers will again try and test the market to see what levels they can sustain at. With the threat of China temporality removed, it remains to be seen how far they will push the market.

We only have snippets of information at this point to make sense of the situation. Clearly, with PTFE being used in so many fields, this poses some concern to many industries. We will be keeping our ears to the ground to see if anything else come up.

End Properties and Characteristics of PTFE (Teflon) Tubing

The development of a new process or product is usually accompanied by a steep learning curve.

Some of the findings are obvious, and may even be accessible in the public domain. Others are less easily understood and might be specific to the manufacturer due to the nature of the set-up, the environment and the materials used.

Our recent installation of a continuous line PTFE Paste Extruder has thrown up many such findings. At each stage, we have needed to evaluate whether the finding impacts the properties of the final product. Given the fact that globally, very few companies manufacture PTFE tubes, our access to external information is limited. Thus, trial and error has been the key to fine tuning the extrusion process and derive a product of consistently good quality.

Our journey in developing the product confirms that much of what is learnt needs to be kept proprietary, as it is part of a rich process technology not easily obtained. However, in doing so, we have also studied the final characteristics of PTFE tube and tried to make sense of what properties go in to define a tube of good quality.

Properties of PTFE Tube

When clients approach us with enquiries for PTFE Tubing, they are primarily concerned with 3 factors. Each of these factors plays back into how the PTFE tube is processed and has relevance to the end-application in questions

1. Dimensional stability
   The outer and inner diameters of the tube (OD and ID) are of utmost importance. In almost all cases, the tube will be used in an assembly, where fittings have been designed to accommodate the tube in question. Although minor variations in dimension may be accommodated, the tube needs to adhere to the fitments used with it.
   We have observed that when high quality resins are used, the dimensional stability during extrusion is highly predictable and easily maintained within a tolerance of 50 microns (0.05mm). Certain Chinese resins, when extruded, do not maintain this integrity. So, a tube with a required OD of 6mm may sometimes measure at 5.9mm and at other times measure to 6.2mm, despite all other parameters remaining unchanged.
2. Burst Pressure
   In applications involving high pressures, it is important that the tube does not yield during service.
   An easy formula to calculate the burst pressure is as follows:
   
   There are two critical parameters here that define the effectiveness of the formula.
   The first is the tensile strength – which is denoted by “T”. In most cases, we are told to take a tensile strength of 25Mpa for this value. Our own testing indicates a tensile strength of 28-31Mpa on our tubes, meaning that the value of 25Mpa is safe to use. However, tube that is not properly processed can often have a tensile strength of less than 20Mpa. This means that while a manufacturer may use the value of 25Mpa for calculation, the actual burst pressure is at least 20% lower.
   The other factor – that does not even feature in this formula is the concentricity of the tube. PTFE tube that is non-concentric will show a higher wall thickness on one side as compare to the other side. It will not have the same burst pressure of good quality tubes, even though the ID and OD may be the same. This issue also results in problems when we try and braid the PTFE Tube using stainless steel. The unevenness in wall thickness causes one side of the tube to collapse during braiding due to the pressure applied by the stainless steel.
   
   As a rule, we try and maintain a concentricity exceeding 95%.
   Calculating concentricity is quite simple. It is the ratio of the minimum wall thickness to the maximum wall thickness of the PTFE Tube. So a 6mm x 4mm PTFE tube, which has a wall thickness of 1mm, would need to have a tolerance of +/-0.025 to attain such a degree of concentricity.
   We have observed many tubes where the concentricity varies by up to 0.1mm on the wall thickness (implying a concentricity of only 81% on a 6mm x 4mm tube). While some applications may be fine with this level, it is up to the manufacturer to inform the client regarding the same, as the client may not always be aware of how critical this parameter is in the final application.
   Both concentricity and tensile strength are end properties derived from how the tube is processed during extrusion. Factors such as blending, extrusion pressure and sintering all lend themselves to arriving at a tensile strength acceptable by global standards. Similarly, extrusion speed, alignment and the blending process all play a part in ensuring concentricity exceeds 95%.
3. Visual
   Good quality PTFE tube will have a smooth even surface without any pitting, waviness or discolouration. Visually, concentricity also plays a part, as a tube that is significantly off-centre will usually raise concerns from the client.
   We have already looked at how concentricity is influenced by the extrusion process. Similarly, factors such as quantity of extrusion aid, extrusion speed and pressure, finish on the die and sintering temperatures all weight in on how the tube appears.
   Invariably, visual factors such as pitting, waviness and discolouration will give clues as to the fundamental properties such as tensile strength, elongation and dielectric strength. Hence, these need to be evaluated no just from a cosmetic point of view, but also in terms of what characteristics of the final product are being diminished due to the appearance of visual indicators.

It should be noted that the above characteristics cover only the very basic aspects of PTFE tubing. Products such as anti-static tubing, ePTFE tubing and convoluted tubing will each bring a new set of challenges that will need to be studied from first principles.

For the time being, we are satisfied to have attained global quality standards on characteristics that drive a majority of the demand for PTFE tubes.